Fundamentals of Hemodynamic Monitoring - Orlando Health
Fundamentals of Hemodynamic Monitoring - Orlando Health
Fundamentals of Hemodynamic Monitoring - Orlando Health
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong><br />
<strong>Monitoring</strong><br />
Self-Learning Packet<br />
* See SWIFT for list <strong>of</strong> qualifying boards for continuing education hours.
Table <strong>of</strong> Contents<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Introduction................................................................................................................... 4<br />
Fundamental Concepts .................................................................................................. 5<br />
Pressure <strong>Monitoring</strong> Systems ........................................................................................ 7<br />
Arterial Blood Pressure <strong>Monitoring</strong> ............................................................................. 17<br />
Central Venous Pressure (CVP) <strong>Monitoring</strong> ................................................................. 28<br />
<strong>Hemodynamic</strong> Case Studies......................................................................................... 40<br />
Conclusion.................................................................................................................... 41<br />
Glossary........................................................................................................................ 42<br />
References ................................................................................................................... 44<br />
Posttest ........................................................................................................................ 45<br />
Appendix 1: Troubleshooting Arterial and CVP <strong>Monitoring</strong> Systems .......................... 50<br />
Appendix 2: Accurate Measurement <strong>of</strong> Noninvasive Blood Pressure.......................... 52<br />
2011 <strong>Orlando</strong> <strong>Health</strong>, Education & Development Page 2
Purpose<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
This packet was designed for healthcare personnel who care for patients with arterial and central<br />
venous catheters in the critical care and intermediate care units. Prerequisites for this packet are a<br />
working knowledge <strong>of</strong> basic cardiovascular anatomy and physiology, cardiovascular<br />
pharmacology, and basic ECG interpretation skills.<br />
Objectives<br />
Upon completion <strong>of</strong> this self-learning packet, the participant should be sufficiently familiar with<br />
hemodynamic principles to:<br />
1. Define cardiac output, stroke volume, preload, afterload and contractility<br />
2. Describe the technical set-up <strong>of</strong> intra-arterial and central venous monitoring equipment<br />
3. Discuss the clinical significance <strong>of</strong> arterial blood pressure and central venous pressure<br />
4. Describe accurate non-invasive arterial blood pressure measurement<br />
5. Discuss clinical indications and contraindications for hemodynamic monitoring using intraarterial<br />
and central venous catheters<br />
6. Identify normal values and waveforms for the hemodynamic values that are obtained from<br />
intra-arterial and central venous catheters<br />
7. Calculate pulse pressure and mean arterial pressure<br />
8. Interpret CVP and arterial pressure and relate them to various normal and abnormal<br />
physiologic states<br />
9. Calculate and evaluate the accuracy <strong>of</strong> invasive hemodynamic monitoring data using the<br />
square wave test and waveform analysis.<br />
10. Identify potential troubleshooting techniques when an inaccurate system is identified.<br />
11. Identify potential complications <strong>of</strong> hemodynamic monitoring with intra-arterial and central<br />
venous catheters<br />
12. Recognize conditions which may alter hemodynamic readings obtained from intra-arterial and<br />
central venous catheters<br />
13. Describe and troubleshoot abnormal assessment findings encountered with intra-arterial and<br />
central venous monitoring<br />
14. Describe correct removal <strong>of</strong> arterial and central venous catheters<br />
2011 <strong>Orlando</strong> <strong>Health</strong>, Education & Development Page 3
Instructions<br />
In order to receive contact hours, you must:<br />
complete the posttest at the end <strong>of</strong> this packet<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
achieve an 84% on the posttest<br />
For Non-<strong>Orlando</strong> <strong>Health</strong> employees: Complete the test using the bubble sheet provided. Be sure<br />
to complete all the information at the top <strong>of</strong> the answer sheet. You will be notified if you do not<br />
pass, and you will be asked to retake the posttest.<br />
Return to: <strong>Orlando</strong> <strong>Health</strong> Education & Development, MP14, 1414 Kuhl Ave, <strong>Orlando</strong>, FL 32806<br />
For <strong>Orlando</strong> <strong>Health</strong> Team Member: Please complete testing via Online Testing Center. Log<br />
on to: SWIFT Departments E-Learning Testing Center. Use your <strong>Orlando</strong> <strong>Health</strong> Network<br />
Login and password. Select “SLP” under type <strong>of</strong> test; choose correct SLP Title. Payroll<br />
authorization is required to download test.<br />
Introduction<br />
<strong>Hemodynamic</strong>s, by definition, is the study <strong>of</strong> the motion <strong>of</strong> blood through the body. In simple<br />
clinical application this may include the assessment <strong>of</strong> a patient’s heart rate, pulse quality, blood<br />
pressure, capillary refill, skin color, skin temperature, and other parameters. As the complexity <strong>of</strong><br />
the patient’s status increases, invasive hemodynamic monitoring may be utilized to provide a more<br />
advanced assessment and to guide therapeutic interventions.<br />
Invasive hemodynamic monitoring is now used routinely in many critical care and intermediate<br />
care units to assist in the assessment <strong>of</strong> single and multi-system disorders and their treatment.<br />
<strong>Hemodynamic</strong> monitoring might include waveform and numeric data derived from the central<br />
veins, right atrium, pulmonary artery, left atrium, or peripheral arteries.<br />
The data provided by invasive hemodynamic monitoring does not take the place <strong>of</strong> careful nursing<br />
assessment. In fact, using hemodynamic data without regard to assessment findings can result in<br />
harm. Thorough nursing assessment provides the framework for interpretation <strong>of</strong> hemodynamic<br />
data and aids in selection <strong>of</strong> interventions that enhance patient outcomes.<br />
This self-learning packet will present information concerning the use <strong>of</strong> intra-arterial and central<br />
venous catheters and introduce techniques to enhance the accuracy <strong>of</strong> data obtained from these<br />
catheters. Physiologic states will be presented that may suggest or contraindicate the use <strong>of</strong> these<br />
devices in the clinical setting. This packet includes a review <strong>of</strong> the essential components <strong>of</strong><br />
arterial and central venous waveforms, and it examines normal and abnormal pressures and their<br />
implications in patient outcomes. It will also examine interventions that may be indicated based<br />
on the patient’s clinical presentation.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 4
Fundamental Concepts<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
The study <strong>of</strong> hemodynamics has its own vocabulary and requires an understanding <strong>of</strong> the<br />
interactions between the heart, blood vessels, and blood. A basic discussion <strong>of</strong> these terms and<br />
concepts is presented here. The cardiac output pushes the blood through<br />
the vascular system. Cardiac output (CO) is calculated by multiplying CO =HR X SV<br />
the heart rate (HR) by the stroke volume (SV).<br />
Stroke volume is the volume <strong>of</strong> blood pumped out <strong>of</strong> the heart with each heartbeat. If the stroke<br />
volume drops, the body will compensate by increasing the heart rate to maintain cardiac output.<br />
This is known as compensatory tachycardia. Tachycardia is an effective compensatory<br />
mechanism up to a point. At heart rates greater than 150 bpm, diastolic filling time becomes so<br />
short that the tachycardia itself produces a drop in stroke volume, and cardiac output can no longer<br />
be maintained. Stroke volume is affected by three factors, preload, afterload, and contractility.<br />
Preload<br />
Preload is defined as the amount <strong>of</strong> stretch on the cardiac my<strong>of</strong>ibril at the end <strong>of</strong> diastole (when<br />
the ventricle is at its fullest). The amount <strong>of</strong> stretch is directly affected by the amount <strong>of</strong> fluid<br />
volume in the ventricle thus preload is most directly related to fluid volume. Starling’s curve<br />
describes the relationship <strong>of</strong> preload to cardiac output.<br />
As preload (fluid volume) increases, cardiac output will also increase until the cardiac output<br />
levels <strong>of</strong>f. If additional fluid is added after this point, cardiac output begins to fall. This reaction<br />
<strong>of</strong> the heart muscle to stretch can be likened to a slingshot. The farther the slingshot is<br />
stretched, the farther it propels a stone. If the slingshot is only slightly stretched, the stone will<br />
travel a very short distance. If the slingshot is repeatedly overstretched, however, it weakens<br />
and eventually loses its ability to launch the stone at all. The slingshot functions best when it is<br />
stretched just the right amount, neither too little nor too much. The same is true <strong>of</strong> the heart.<br />
Too little preload and the cardiac output cannot propel enough blood forward, too much and the<br />
heart will become overwhelmed leading to failure. Just the right amount <strong>of</strong> preload produces<br />
the best possible cardiac output; finding this level <strong>of</strong> preload is called “preload optimization.”<br />
How is preload measured? There is not a practical way to measure my<strong>of</strong>ibril stretch in living<br />
beings, nor is there a widely available method to measure ventricular end-diastolic volume.<br />
Because <strong>of</strong> this, pressures within the cardiovascular system are measured and used as a rough<br />
indicator <strong>of</strong> fluid volume. The theory is that as fluid volume in chamber increases, so too will<br />
the pressures measured in the chamber. This correlation is true only in a limited sense, because<br />
the pressures measured are affected by more than just the fluid volume present. Preload<br />
pressures are also affected by intrathoracic pressure, intra-abdominal pressure, and myocardial<br />
compliance. The key to remember is that pressure is not equal to volume. The pressure is<br />
trended as an indicator <strong>of</strong> volume status, but must be correlated to physical assessment findings<br />
and the patient’s history to come to an accurate clinical impression.<br />
Physical assessment <strong>of</strong> preload includes assessment parameters one would use to evaluate fluid<br />
volume status. Signs <strong>of</strong> inadequate and excess preload are listed below. Note that not all<br />
patients will exhibit all signs, and some symptoms are common to both extremes. Signs <strong>of</strong><br />
inadequate preload include poor skin turgor, dry mucous membranes, low urine output,<br />
tachycardia, thirst, weak pulses and flat neck veins. Signs <strong>of</strong> excess preload in a patient with<br />
adequate cardiac function include distended neck veins, crackles in the lungs, and bounding<br />
pulses. Increased preload in a patient with poor cardiac function presents with crackles in the<br />
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lungs, an S3 heart sound, low urine output, tachycardia, cold clammy skin with weak pulses,<br />
and edema.<br />
CLINICAL APPLICATION<br />
Preload<br />
Insufficient preload is commonly called hypovolemia or dehydration. When insufficient<br />
volume is present in the vascular tree, the sympathetic nervous system is stimulated to<br />
release the catecholamines epinephrine and norepinephrine. These hormones cause<br />
increased heart rate and arterial vasoconstriction. The increased heart rate produces a<br />
compensatory tachycardia while the vasoconstriction helps maintain an adequate blood<br />
pressure. If these patients are treated with catecholamine drugs rather than receiving<br />
volume infusions, the tachycardia becomes very pronounced and the vasoconstriction can<br />
become severe enough that the organs fail and the distal extremities become ischemic.<br />
The first step in treating any form <strong>of</strong> hemodynamic instability is to assess the patient for<br />
signs <strong>of</strong> insufficient preload (e g volume or blood loss)<br />
Afterload<br />
Afterload is defined as the resistance that the ventricle must overcome to eject its volume <strong>of</strong><br />
blood. The focus in this packet is afterload <strong>of</strong> the left ventricle. The most important<br />
determinant <strong>of</strong> afterload is vascular resistance. Other factors affecting afterload include<br />
blood viscosity, aortic compliance and valvular disease. As arterial vessels constrict, the<br />
afterload increases; as they dilate, afterload decreases.<br />
High afterload increases myocardial work and decreases stroke volume. Patients with high<br />
afterload present with signs and symptoms <strong>of</strong> arterial vasoconstriction including cool clammy<br />
skin, capillary refill greater than 5 seconds, and narrow pulse pressure. The pulse pressure is<br />
calculated by subtracting the diastolic blood pressure (DBP) from the systolic blood pressure<br />
(SBP). The normal pulse pressure at the brachial artery is 40 mm Hg. There are not specific<br />
values <strong>of</strong> pulse pressure that are defined as excessively<br />
wide or narrow. Serial measurements <strong>of</strong> pulse pressure Pulse Pressure = SBP - DBP<br />
are compared against one another to detect changes in<br />
vascular resistance.<br />
Low afterload decreases myocardial work and results in increased stroke volume. Patients with<br />
low afterload present with symptoms <strong>of</strong> arterial dilation such as warm flushed skin, bounding<br />
pulses and wide pulse pressure. If the afterload is too low, hypotension may result.<br />
CLINICAL APPLICATION<br />
Afterload<br />
A key component <strong>of</strong> treatment for heart failure is afterload reduction using beta-blockers<br />
and ACE inhibitors. By decreasing the resistance to ventricular ejection the cardiac output<br />
is increased and myocardial workload is decreased. The increase in cardiac output<br />
frequently improves the functional status <strong>of</strong> these patients.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 6
Contractility & Compliance<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
When used in a discussion <strong>of</strong> hemodynamics, the term contractility refers to the inherent ability<br />
<strong>of</strong> the cardiac muscle to contract regardless <strong>of</strong> preload or afterload status. Contractility is<br />
enhanced by exercise, catecholamines, and positive inotropic drugs. It is decreased by<br />
hypothermia, hypoxemia, acidosis, and negative inotropic drugs. Many other factors can affect<br />
afterload, but they are beyond the scope <strong>of</strong> this packet.<br />
Myocardial compliance refers to the ventricle’s ability to stretch to receive a given volume <strong>of</strong><br />
blood. Normally the ventricle is very compliant so large changes in volume will produce small<br />
changes in pressure. If compliance is low, small changes in volume will result in large changes<br />
in pressure within the ventricle. Refer back to the illustration <strong>of</strong> Starling’s curve on page 5. If<br />
the ventricle cannot stretch, it will be unable to increase cardiac output with increased preload<br />
as described by the curve.<br />
Tissue Perfusion<br />
The whole point <strong>of</strong> assuring adequate cardiac output is to make sure the patient has adequate<br />
tissue perfusion. Tissue perfusion is the transfer <strong>of</strong> oxygen and nutrients from the blood to the<br />
tissues. When performing interventions designed to improve hemodynamics, the bottom-line<br />
for evaluation <strong>of</strong> effectivess is whether or not the intervention was successful in improving<br />
tissue perfusion.<br />
Many <strong>of</strong> the signs <strong>of</strong> inadequate preload, afterload and contractility also reflect poor tissue<br />
perfusion. These signs include: cool clammy skin, cyanosis, low urine output, decreased level<br />
<strong>of</strong> consciousness, metabolic acidosis, tachycardia, tachypnea, and hypoxemia. Labs and<br />
diagnostic testing that are used to evaluate tissue perfusion include arterial blood gases, arterial<br />
lactate levels and pulse oximetry. Poor tissue perfusion is reflected by a low pH, low base<br />
excess and elevated lactate level. Pulse oximetry readings are typically low when tissue<br />
perfusion is compromised to a significant degree.<br />
Pressure <strong>Monitoring</strong> Systems<br />
<strong>Hemodynamic</strong> pressure monitoring systems detect changes in pressure within the vascular system<br />
and convert those changes into digital signals. The digital signals are then displayed on a monitor<br />
as waveforms and numeric data.<br />
The intra-arterial catheter is typically a 20-gauge intravenous-type catheter, inserted via the<br />
radial, brachial or femoral artery. The central venous catheter may be a large or small-bore<br />
catheter with one or more lumens inserted via the subclavian, internal jugular or external jugular<br />
vein.<br />
Semi-rigid pressure tubing attaches the catheter to a transducer set-up. The tubing must be more<br />
rigid than standard IV tubing so that the pressure <strong>of</strong> the fluid within it does not distort the tubing.<br />
If the tubing is distorted in this way, the pressure readings will be inaccurate. The tubing must<br />
also be as short as reasonably possible. Longer tubing will cause distortion <strong>of</strong> the pressure as it<br />
travels over the longer distance.<br />
The transducer is a device that converts the pressure waves generated by vascular blood flow into<br />
electrical signals that can be displayed on electronic monitoring equipment.<br />
The transducer cable attaches the transducer to the monitor, which displays a pressure waveform<br />
and numeric readout.<br />
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The flush system consists <strong>of</strong> a pressurized bag <strong>of</strong> normal saline (which may or may not contain<br />
added heparin, depending on the unit and facility where you work). The pressure must be<br />
maintained at 300 mm Hg to prevent blood from the arterial system from backing up into the<br />
pressure tubing.<br />
An intraflow valve is part <strong>of</strong> the transducer setup and maintains a continuous flow <strong>of</strong> flush<br />
solution (approximately 3-5 ml/hr) into the monitoring system to prevent clotting at the catheter<br />
tip.<br />
A fast flush device allows for general flushing <strong>of</strong> the system and rapid flushing following<br />
withdrawal <strong>of</strong> blood from the system or when performing a square wave test.<br />
Line Setup & Zeroing <strong>of</strong> a Transduced System<br />
The majority <strong>of</strong> hemodynamic monitoring systems are set up in a similar manner. The exact<br />
type <strong>of</strong> transducer system used varies among institutions. Review the policies and guidelines<br />
where you work for more specific information.<br />
Equipment<br />
Assemble all components <strong>of</strong> the system prior to set up (this may be performed by a nurse, a<br />
respiratory therapist or a technician). The components include:<br />
Pressure cuff (pressure pack) for IV bag<br />
One liter bag <strong>of</strong> normal saline<br />
Pre-assembled, disposable pressure tubing with flush device and disposable transducer and<br />
stopcocks<br />
I.V. pole with transducer mount (called a manifold)<br />
Carpenter’s level or other leveling device<br />
Patient monitor, pressure module and monitor cable<br />
Equipment Set-up<br />
1. Obtain a 1000 ml bag <strong>of</strong> 0.9% saline; invert the bag and spike it with IV tubing, then turn it<br />
upright and fill the drip chamber until it is completely full.<br />
2. The tubing comes with stopcock caps with holes in them so one does not have to remove<br />
the caps prior to priming the tubing. Position all stopcocks so the flush solution will flow<br />
through the entire system. Be sure to flush all the stopcock ports. Roll the tubing’s flow<br />
regulator to the OFF position.<br />
3. Activate the fast flush device and flush the saline through the entire setup one more time.<br />
Check to be sure that all air has been purged from the system. Examine the transducer and<br />
each stopcock carefully, as small bubbles tend to cling to these components. Air left in the<br />
tubing can cause inaccurate transmission <strong>of</strong> pressure to the transducer.<br />
4. Replace all vented (the ones with holes) port caps with closed (dead-end) caps, making<br />
sure to maintain the sterility <strong>of</strong> each cap’s insertion end.<br />
5. Place the bag <strong>of</strong> saline into the pressure cuff, and adjust the pressure to at least 300 mm<br />
Hg. This is the pressure that is required to maintain a continuous flow <strong>of</strong> 3-5 ml/minute<br />
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through the intraflow valve. This helps prevent clotting <strong>of</strong> the catheter and backflow <strong>of</strong><br />
blood into the tubing.<br />
6. Before the monitor can measure pressures, the transducer must be zeroed to atmospheric<br />
pressure. The purpose <strong>of</strong> this procedure is to make<br />
sure the transducer reads zero when no pressure is<br />
against it. This procedure is like zeroing a scale<br />
before weighing something to assure accuracy. To<br />
zero the transducer, place the stopcock so it is open<br />
between the transducer and air and press the zero<br />
button on the monitor. Zeroing can be performed<br />
whether or not the patient is attached to the system,<br />
so no particular patient position is required to<br />
complete this step. The transducer should be<br />
rezeroed whenever the reading is in doubt, or<br />
anytime the monitor has been disconnected from the transducer setup.<br />
phlebostatic axis<br />
From Techniques in Bedside<br />
<strong>Hemodynamic</strong> <strong>Monitoring</strong> by E.K. Daily<br />
and J.S. Schroeder, C.V. Mosby, 1981.<br />
Used with permission.<br />
7. Before starting to monitor pressure, the stopcock nearest the transducer must be placed at<br />
the level <strong>of</strong> what is being measured. In most cases (other than intracranial pressure<br />
monitoring) this is at the level <strong>of</strong> the heart. Correct leveling is essential to achieve accurate<br />
pressures and should be checked during routine monitoring and troubleshooting <strong>of</strong> the<br />
monitoring system. To level the transducer, place the transducer at the level <strong>of</strong> the heart.<br />
This location is called the phlebostatic axis, and is located at the 4 th intercostal space,<br />
halfway between the anterior and posterior chest (mid-chest). The midaxillary line is not<br />
accurate for patients with barrel chests or severe chest deformities. To assure that the<br />
stopcock is precisely leveled with this landmark, mark the position <strong>of</strong> the phlebostatic axis<br />
on the patient’s chest with permanent marker. The transducer can be taped directly to this<br />
location, or it may be mounted on a pole and leveled to the phlebostatic axis with a<br />
carpenter’s or laser level. Re-level the transducer anytime the patient changes position or if<br />
the reading is in doubt or outside <strong>of</strong> prescribed parameters. If the transducer to too low,<br />
the reading will be falsely high. Conversely, if the transducer is too high, the reading will<br />
be falsely low.<br />
Technical Aspects <strong>of</strong> Leveling and Zeroing<br />
A number <strong>of</strong> external factors may affect how accurately the hemodynamic monitoring system<br />
reflects the pressures within the patient’s vascular system. There are two important pressures<br />
that can affect hemodynamic readings.<br />
Hydrostatic pressure is the force that is exerted by the fluid within the hemodynamic<br />
monitoring system against the transducer. This pressure is a result <strong>of</strong> a combination <strong>of</strong> factors<br />
that include gravity and the height and weight <strong>of</strong> the fluid column (in other words, the position<br />
or height <strong>of</strong> the IV bag and length <strong>of</strong> tubing, which contains the fluid column), fluid density<br />
and positioning <strong>of</strong> the transducer. Leveling the transducer to the phlebostatic axis eliminates<br />
inaccuracies in pressure readings due to hydrostatic pressure. As long as the stopcock nearest<br />
the transducer is level with the Phlebostatic axis, the patient can be positioned as high as 60<br />
degrees and still have generally accurate pressure measurements. It is essential that pressures be<br />
measured at a consistent head-<strong>of</strong>-bed elevation for trends to be valid.<br />
Atmospheric pressure is the force that is exerted at the earth’s surface by the weight <strong>of</strong> the air<br />
that surrounds the earth. At sea level this pressure is 760 mm Hg, but it varies depending on<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
altitude. Zeroing the monitor eliminates the effect <strong>of</strong> atmospheric pressure on the pressure<br />
readings. Remember, zeroing can be accomplished even before the patient is attached to the<br />
system.<br />
Accurate <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
If invasive hemodynamic monitoring is used, it is essential that it is accurate; otherwise the<br />
patient should not be subjected to the risks associated with this type <strong>of</strong> monitoring.<br />
<strong>Hemodynamic</strong> readings are <strong>of</strong>ten used to titrate therapy, and inaccuracies in measurement can<br />
lead to inappropriate treatment strategies and potential harm to the patient.<br />
System dynamics are tested to assure that the system is accurately reflecting the patient’s<br />
pressures. To accomplish this, the system is subjected to a high, sudden pressure and observed<br />
for its response. The pressure bag attached to the transducer is a convenient source <strong>of</strong> high<br />
pressure. Since the pressure in the pressure bag is kept at 300 mm Hg and most pressure<br />
monitoring systems have a high end <strong>of</strong> 200 mm Hg or so, a fast flush <strong>of</strong> the system appears as a<br />
high flat line during flushing that returns rapidly to baseline when the flush is released. Because<br />
the waveform produced during this maneuver looks like 3 sides <strong>of</strong> a square, this is known as a<br />
square-wave test.<br />
Sharp<br />
rise with<br />
fast flush<br />
Brief flat line<br />
Duration<br />
<strong>of</strong> flush<br />
1-2 sec<br />
Sharp rapid<br />
downstroke that<br />
extends below<br />
The ideal square-wave waveform is depicted above. The initial sharp upstroke is produced<br />
by activation <strong>of</strong> the fast flush system. The flat line is produced for the duration <strong>of</strong> activation <strong>of</strong><br />
the fast flush system, and reflects the high pressure present in the flush bag. The sharp<br />
downstroke represents release <strong>of</strong> the fast flush device.<br />
The square wave should return quickly to baseline after a few rapid sharp waves called<br />
oscillations. If the oscillations are sluggish and far apart, the system is referred to as<br />
“overdamped”. Think <strong>of</strong> the way sound carries in a soundpro<strong>of</strong>ed room; it sounds muffled and<br />
flat. The sound waves in such a room are dampened. An overdamped system muffles pressure<br />
waves, and will underestimate systolic pressures and overestimate diastolic pressures as a<br />
result.<br />
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If the oscillations are too pronounced, the system is referred to as “underdamped”. Other<br />
synonyms for underdamped include “whip” or “fling.” In the sound wave analogy,<br />
underdamping would be like sound in a tiled bathroom. All sounds are magnified, and louder<br />
sounds may ring or echo in the room. Underdamped systems reflect pressure waves in the same<br />
way. All pressures are magnified. An underdamped system will overestimate systolic pressures<br />
and underestimate diastolic pressures.<br />
The first step in performing a square wave test is to activate the fast flush device for 1-2<br />
seconds while recording the resulting waveform on a monitor strip. Perform three or four fast<br />
flushes a few seconds apart each time you record them. Ideally, you should observe a sharp<br />
rapid upstroke with a flat line extending briefly (1-2 seconds) to a sharp rapid downstroke that<br />
extends below the baseline. The behavior <strong>of</strong> this waveform reflects the dynamics <strong>of</strong> the<br />
system and indicates the accuracy with which it is reflecting the patient’s pressures.<br />
To evaluate the system’s response to pressures, determine how fast the oscillations are (the<br />
frequency between them) and how high the waves are (amplitude). Generally, the smaller the<br />
distance between the oscillations the better. The amplitude ratio looks at the size <strong>of</strong> the first<br />
oscillation compared to the second one. The second oscillation should be about 1/3 the height<br />
<strong>of</strong> the first one. This indicates that the system is able to go back to baseline quickly and does<br />
not have distortion when subjected to pressures. The first two oscillations are the primary<br />
focus.<br />
Example <strong>of</strong> a normal square wave test<br />
Baseline<br />
Fast<br />
flush<br />
First oscillation<br />
Second oscillation<br />
Patient’s pressure<br />
waveform<br />
Overdamping<br />
Overdamping will cause reduced waveform magnitude and loss <strong>of</strong> some waveform<br />
components. This can lead to a false low systolic pressure and a false high diastolic<br />
pressure reading. Inaccurate assessment <strong>of</strong> the patient’s hemodynamic status is the end result.<br />
Potential sources <strong>of</strong> overdamping include:<br />
Distensible tubing – use only the semi-rigid tubing that comes with the transducer setup.<br />
Overly long extension tubing – extension tubing should never exceed 3 – 4 feet in length.<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Air bubbles in the circuit – check stopcocks and connections with meticulous care, as air<br />
bubbles tend to cling to these components.<br />
Catheter diameter, length and stiffness - small diameter catheters, long catheters, and s<strong>of</strong>t,<br />
compliant catheters can all cause overdamping.<br />
The nurse must realize that there are some conditions under which the waveform appears<br />
overdamped even though the pressure transmission is accurate. These are discussed later in this<br />
packet. Merely looking at the appearance <strong>of</strong> the waveform and square-wave test is not sufficient<br />
to confirm system accuracy. Use <strong>of</strong> the square-wave test to calculate the dynamic response<br />
is the most accurate way to make decisions about the reliability <strong>of</strong> the monitoring system.<br />
The illustration on this page shows the general appearance <strong>of</strong> a square wave test in an<br />
overdamped system.<br />
2. Brief flat line<br />
1. Initial upstroke (note the<br />
angle <strong>of</strong> upswing, instead <strong>of</strong><br />
a rapid vertical rise)<br />
3. Downstroke (angled down instead<br />
<strong>of</strong> vertical) that does not extend<br />
below the baseline<br />
4. Oscillations following the downstroke are<br />
diminished or absent<br />
5. Patient’s own pressure waveform,<br />
which will show a falsely low reading<br />
for the systolic and falsely high for the<br />
diastolic pressures.<br />
Square wave test configuration: Overdamped. From <strong>Hemodynamic</strong> <strong>Monitoring</strong>: Invasive and Noninvasive Clinical<br />
Application by Gloria Oblouk Darovic, W. B. Saunders. 1995. Used with permission<br />
CLINICAL APPLICATION<br />
Overdamping <strong>of</strong> Arterial Pressure <strong>Monitoring</strong><br />
Overdamping <strong>of</strong> the monitoring system could have disastrous consequences for a patient with<br />
hypertensive crisis, or an intracranial or aortic aneurysm. If these patients are hypertensive, but the<br />
nurse is not aware <strong>of</strong> this due to overdamping <strong>of</strong> the system, the patients may not receive appropriate<br />
interventions to manage their blood pressure and may experience intracranial hemorrhage or<br />
aneurysmal 2011 rupture.<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Underdamping<br />
In an underdamped system, the square wave will be followed by multiple large oscillations, as<br />
noted in the graphic on the next page. Underdamping will cause a false high systolic<br />
pressure reading and a false low diastolic pressure reading, resulting in an inaccurate<br />
assessment <strong>of</strong> the patient’s hemodynamic status.<br />
Underdamping occurs when the natural frequency <strong>of</strong> the system is identical to one frequency <strong>of</strong><br />
the pressure waves being transmitted by the patient. When this happens the tubing vibrates<br />
more intensely, producing overshoot and undershoot spikes. The end result is false high<br />
systolic pressures and false low diastolic pressures. These discrepancies are <strong>of</strong>ten referred to as<br />
artifact or whip. At times, artifact may be so pronounced that accurate waveform interpretation<br />
is impossible.<br />
The illustration below is a depiction <strong>of</strong> a typical square-wave test in an underdamped system.<br />
The presence <strong>of</strong> underdamping may not always be this pronounced.<br />
1. Normal initial<br />
upstroke<br />
2. Flat line<br />
3. Normal downstroke<br />
4. Downstroke followed<br />
by multiple large<br />
oscillations<br />
5. Patient’s own pressure<br />
waveform, which will show a<br />
falsely high systolic pressure<br />
and falsely low diastolic<br />
pressure. This will cause the<br />
pulse pressure to be falsely<br />
wide.<br />
Square wave test configuration: Underdamping. From <strong>Hemodynamic</strong> <strong>Monitoring</strong>: Invasive and Noninvasive Clinical<br />
application, by Gloria Oblouk Darovic. W. B. Saunders, 1995. Used with permission.<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
CLINICAL APPLICATION<br />
Underdamping <strong>of</strong> Arterial Pressure <strong>Monitoring</strong><br />
An underdamped arterial monitoring system can delay identification <strong>of</strong> hypovolemia in patients<br />
recovering from surgery or trauma. The normal hemodynamic response to hypovolemia is<br />
vasoconstriction, identified clinically by a narrowed pulse pressure. Narrowing <strong>of</strong> the pulse<br />
pressure occurs long before hypotension appears. If the patient has an underdamped arterial<br />
monitoring system, the narrowed pulse pressure and early decreases in systolic blood pressure<br />
may go unrecognized by the nurse. This may result in failure to intervene appropriately, and the<br />
patient may experience hypovolemic shock.<br />
Tips for Maintaining an Accurate <strong>Hemodynamic</strong> <strong>Monitoring</strong> System<br />
Use as simple a system as possible. Large numbers <strong>of</strong> stopcocks and extensions decrease<br />
the accuracy <strong>of</strong> the monitoring system, increase the risk <strong>of</strong> fluid leak and line<br />
contamination, and can be a source <strong>of</strong> air bubble collection.<br />
Use short, non-compliant connecting tubing. Standard IV connecting tubing is too<br />
compliant (s<strong>of</strong>t), and absorbs waveform energy, causing overdamping. Shorter tubing<br />
length (less than 3-4 feet) increases the natural frequency <strong>of</strong> the monitoring system and<br />
lessens the chance <strong>of</strong> underdamping.<br />
Maintain tight connections. Inspect connections frequently for fluid leaks. Keep<br />
connections as visible as possible. Luer-lock connections reduce the likelihood <strong>of</strong><br />
accidental disconnection.<br />
Maintain the fast flush system. Pressure bags frequently lose pressure. Check that the<br />
pressure is maintained at 300 mm Hg during routine monitoring <strong>of</strong> the system and any time<br />
the pressure reading is in question. An increase in the frequency <strong>of</strong> fast flushes may be<br />
necessary to maintain system patency in hypercoagulable patients.<br />
Inspect for bubbles. Carefully inspect all fluid-filled components after setup and<br />
periodically thereafter. Dissolved air may come out <strong>of</strong> solution during monitoring. Even<br />
pinpoint air bubbles affect the accuracy <strong>of</strong> the system. These small bubbles tend to cling to<br />
stopcocks and other connections.<br />
Keep tubing away from areas <strong>of</strong> patient movement. Movement <strong>of</strong> the tubing produces<br />
fluid movement in the system and produces external artifact.<br />
2011 <strong>Orlando</strong> <strong>Health</strong>, Education & Development Page 14
Interpreting Pressure Scales<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
In order to verify whether the digital display on the monitor reflects accurate hemodynamic<br />
pressures, the nurse must be able to read a pressure from a printed monitor strip. Because<br />
different hemodynamic waveforms have different sizes, monitors are designed to allow the<br />
clinician to select an appropriate pressure scale. The scale for each printout is displayed at the<br />
beginning <strong>of</strong> the monitor strip, and looks like a stair step. Each step represents an amount <strong>of</strong><br />
pressure identified in parentheses above the pressure waveform. This information is circled in<br />
the monitor strip below.<br />
Steps<br />
0 mm Hg<br />
40 mm Hg<br />
80 mm Hg<br />
120 mm Hg<br />
In order to interpret the pressure displayed on the strip, first identify the correct portion <strong>of</strong> the<br />
waveform to be measured and then determine the pressure based on the scale. On the strip<br />
pictured above, each large box is equal to one step and represents a pressure difference <strong>of</strong> 40<br />
mm Hg. If a different scale were used, the pressure difference represented by the large box<br />
would be different.<br />
On this scale, each small box represents a pressure difference <strong>of</strong> 10 mm Hg. How is this<br />
determined? Each large box is 4 small boxes tall. Each large box represents 40 mm Hg. Divide<br />
the pressure value <strong>of</strong> each large box by its<br />
height in small boxes to find the value <strong>of</strong><br />
each small box. Refer to the picture on the<br />
next page for details.<br />
40 mm Hg = 10 mm Hg/small box<br />
4 small boxes<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 15
0 mm Hg<br />
40 mm Hg<br />
80 mm Hg<br />
120 mm Hg<br />
40 mm Hg<br />
30 mm Hg<br />
20 mm Hg<br />
10 mm Hg<br />
0 mm Hg<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Waveform components will be discussed in the following sections. Interpretation <strong>of</strong> any<br />
pressure waveform depends on an understanding <strong>of</strong> these principles, so use the following<br />
examples to check your work. For the following exercises, assume there are 4 small boxes<br />
contained within each large box.<br />
CHECK YOURSELF<br />
Scale = 0/6/12/18 Each large box = _________ mm Hg<br />
Each small box = _________ mm Hg<br />
Small<br />
box<br />
Scale = 0/60/120/180 Each large box = __________ mm Hg<br />
Each small box = __________ mm Hg<br />
Scale = 0/80/160/240 Each large box = __________ mm Hg<br />
Each small box = __________ mm Hg<br />
2011 <strong>Orlando</strong> <strong>Health</strong>, Education & Development Page 16
CHECK YOURSELF ANSWERS<br />
Scale = 0/6/12/18 Each large box = 6 mm Hg<br />
Each small box = 1.5 mm Hg<br />
Scale = 0/60/120/180 Each large box = 60 mm Hg<br />
Each small box = 15 mm Hg<br />
Scale = 0/80/160/240 Each large box = 80 mm Hg<br />
Each small box = 20 mm Hg<br />
Arterial Blood Pressure <strong>Monitoring</strong><br />
Clinical Significance <strong>of</strong> Arterial Pressure<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Blood pressure has clinical significance because without adequate pressure in the arterial tree,<br />
tissues would not receive oxygen and other vital nutrients, and death would soon follow. Blood<br />
pressure is produced by a combination <strong>of</strong> the pressure generated by each heartbeat and the<br />
resistance to blood flow through the arteries. The resistance to blood flow is part <strong>of</strong> afterload.<br />
Afterload is best described as the resistance the ventricle must overcome to eject its volume <strong>of</strong><br />
blood.<br />
Because blood pressure is partly generated by cardiac contraction, it has a systolic and a<br />
diastolic component. “Normal” blood pressure is 120 mm Hg systolic (SBP) and 60 – 90 mm<br />
Hg diastolic (DBP). Many patients, however, do not have a normal baseline pre-illness blood<br />
pressure. It is therefore essential to know a patient’s pre-illness blood pressure in order to<br />
adequately interpret readings taken during acute illness.<br />
Blood pressure is not uniform throughout the arterial tree. The systolic blood pressure is lowest<br />
in the aorta, and increases as the arteries become smaller. In acutely ill patients the aortic<br />
pressure is most significant because it determines the force with which blood is pumped<br />
through the cerebral and coronary arteries. There is no simple method for determining aortic<br />
pressure. Because <strong>of</strong> this, mean arterial pressure is <strong>of</strong>ten used.<br />
The mean arterial pressure (MAP) is the average driving force in the arterial system and is<br />
essentially the same in all parts <strong>of</strong> the body. The adjective “normal” used to describe mean<br />
arterial pressure has little meaning. A minimal MAP <strong>of</strong> 60 mm Hg is required to perfuse the<br />
heart, brain and kidneys. A MAP <strong>of</strong> 70 to 90 is desirable to reduce left ventricular workload in<br />
a cardiac patient, but a MAP <strong>of</strong> 90 to 110 may be required to maintain cerebral perfusion in a<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
neurosurgical patient. The best MAP depends on the physiologic circumstances <strong>of</strong> each<br />
individual patient.<br />
To calculate mean arterial pressure, use the following formula and round to the nearest whole<br />
number:<br />
MAP = SBP + (2 x DBP)<br />
3<br />
Example: MAP for a patient with a blood pressure <strong>of</strong><br />
120/60 is:<br />
MAP= 120+ (2 x 60) = 120 + 120 = 240 =80<br />
3 3 3<br />
CHECK YOURSELF<br />
Calculation <strong>of</strong> Mean Arterial Pressure (MAP)<br />
Blood Pressure = 100/60 MAP = _________________<br />
Blood Pressure = 180/98 MAP = _________________<br />
Blood Pressure = 150/70 MAP = _________________<br />
CHECK YOURSELF ANSWERS<br />
Calculation <strong>of</strong> Mean Arterial Pressure (MAP)<br />
Blood Pressure = 100/60 MAP = 73<br />
Blood Pressure = 180/98 MAP = 125<br />
Blood Pressure = 150/70 MAP = 97<br />
Comparison <strong>of</strong> Invasive and Noninvasive Blood Pressure<br />
Measurements<br />
Invasive and noninvasive (cuff) measurement <strong>of</strong> blood pressure <strong>of</strong>ten yield markedly different<br />
measurements. It is important to realize that there is no direct relationship between the<br />
results obtained from the two methods. Invasive arterial monitoring measures pressure<br />
whereas non-invasive blood pressure measurement reflects blood flow. Blood pressure and<br />
blood flow are two distinct phenomena that follow different rules <strong>of</strong> physics and physiology.<br />
In addition, there are many potential sources <strong>of</strong> error when taking a blood pressure (see<br />
Appendix 2 for accurate blood pressure measurement).<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Non-invasive measurements will yield lower readings than the invasive system in low-flow<br />
states such as hypotension or vasoconstriction. Conversely, non-invasive readings are higher<br />
than invasive ones when arterial vasodilation is pronounced, as in sepsis.<br />
Which measurement should be trusted? Direct monitoring <strong>of</strong> arterial blood pressure is the<br />
only scientifically and clinically validated method for real-time continuous monitoring <strong>of</strong><br />
blood pressure. Good correlation <strong>of</strong> invasive and non-invasive blood pressure measurement is<br />
not a valid gauge for the accuracy <strong>of</strong> the invasive monitoring system. The take-home message<br />
is that the invasive monitoring system provides the most accurate measurement <strong>of</strong> blood<br />
pressure when the following criteria have been met:<br />
The transducer is leveled to the phlebostatic axis<br />
The system is zeroed appropriately<br />
All system components are in working order<br />
The system dynamics have been analyzed and determined to be optimal or acceptable<br />
Indications for Invasive Arterial <strong>Monitoring</strong><br />
Intra-arterial catheters are routinely used in the critical care environment to provide continuous<br />
blood pressure measurements or access for frequent blood collection. Specific indications may<br />
include patients:<br />
experiencing prolonged shock <strong>of</strong> any type<br />
with hemodynamic instability<br />
undergoing any major vascular, thoracic, abdominal or neurologic procedures or surgery.<br />
with acute hypotension or hemorrhage<br />
receiving vasoactive infusions<br />
in hypertensive crisis, including those with dissecting aortic aneurysm or CVA<br />
receiving intra-aortic balloon counterpulsation<br />
with significant pulmonary system compromise requiring mechanical ventilation, or those<br />
who may have severe acid-base imbalance requiring frequent monitoring <strong>of</strong> arterial blood<br />
gases<br />
undergoing thrombolytic therapy for coronary, cerebral or vascular occlusions (must be<br />
inserted prior to initiation <strong>of</strong> thrombolytic therapy) to allow for continuous blood pressure<br />
monitoring and to permit blood collection for diagnostic laboratory studies without the need<br />
for venipuncture<br />
requiring frequent venipunctures for diagnostic blood testing<br />
Relative Contraindications for Intra-Arterial <strong>Monitoring</strong><br />
There are few, if any, absolute contraindications to the use <strong>of</strong> arterial lines; however, there are<br />
some relative contraindications. This means that the conditions listed below will increase the<br />
risk <strong>of</strong> complications when using an intra-arterial catheter. This increased risk must be<br />
examined relative to the benefit that the patient will receive in the form <strong>of</strong> more accurate<br />
assessments and interventions. Relative contraindications include the following:<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Peripheral vascular disease due to increased risk <strong>of</strong> limb ischemia<br />
Coagulopathies or bleeding disorders due to increased risk <strong>of</strong> hemorrhage at the insertion<br />
site<br />
Current or recent use <strong>of</strong> fibrinolytics or anticoagulants causing an increased risk <strong>of</strong> bleeding<br />
at the insertion site. (However, as noted above under “Indications,” an arterial line is<br />
generally inserted prior to initiation <strong>of</strong> fibrinolytic therapy for continuous blood<br />
pressure monitoring and to allow for blood collection for diagnostic laboratory<br />
studies)<br />
Insertion sites that are infected or burned<br />
Insertion sites where previous vascular surgery has been performed, or that would involve<br />
catheter placement through vascular grafts<br />
Catheter Site Determination<br />
A physician, nurse, or respiratory therapist, depending on the policies <strong>of</strong> the facility or unit<br />
where you work, may perform the actual insertion <strong>of</strong> the intra-arterial catheter. The most<br />
preferred insertion site is the radial artery. Alternate insertion sites include the femoral and<br />
brachial arteries. The femoral artery is not a preferred site due to its anatomic location. If the<br />
femoral artery is used, the monitoring catheter must be a minimum <strong>of</strong> two inches in length.<br />
If the radial artery is used, the modified Allen test must be performed prior to cannulation to<br />
ensure that the ulnar artery provides adequate circulation to the hand to prevent tissue ischemia<br />
or necrosis.<br />
Compression <strong>of</strong> ulnar artery<br />
Compression <strong>of</strong> radial artery<br />
To perform the modified Allen test, pressure is applied to both the radial and ulnar arteries.<br />
The patient opens and closes their fist several times until the hand blanches. Pressure is then<br />
maintained on the radial artery while releasing pressure from the ulnar artery. The hand is<br />
observed for the return <strong>of</strong> blood flow or flushing. If color does not return to the hand within 5<br />
to 10 seconds, the radial artery should not be used.<br />
Care and Maintenance <strong>of</strong> Arterial Catheters<br />
Proper assessment and care <strong>of</strong> arterial catheters helps prevent complications, ensure accuracy <strong>of</strong><br />
intra-arterial pressure readings, and promote patient comfort. Arterial line care may be<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 20
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
performed by nurses or respiratory therapists. Specific points involved in care and maintenance<br />
<strong>of</strong> an intra-arterial pressure monitoring system include the following:<br />
Frequently monitoring distal pulses, skin temperature, nail blanching and capillary refill<br />
<strong>Monitoring</strong> and limiting motion <strong>of</strong> an underlying joint closest to insertion site.<br />
Observing insertion site for redness, drainage, bruising and discoloration<br />
Assessing skin integrity at the insertion site and around any devices applied to limit joint<br />
mobility<br />
Changing the dressing using sterile technique any time the dressing is soiled or disrupted,<br />
or when required by hospital policy<br />
Using proper technique when obtaining blood from an intra-arterial catheter:<br />
- Maintain aseptic technique for any line access and use standard precautions<br />
- Withdraw blood gently and slowly from the line<br />
- Flush the collection port to prevent clot formation and bacterial colonization<br />
- Maintain sterility <strong>of</strong> the system; place a new sterile cap over the sample port.<br />
- Fast-flush the system to the patient for no more than 3 seconds at a time<br />
- Do not use a syringe to manually flush arterial catheters. Manual flushing with a<br />
syringe generates enough pressure that the injected fluid can invade the cerebral<br />
circulation.<br />
- Maintain any blood conservation devices placed in the monitoring system according to<br />
manufacturer’s guidelines and your hospital’s policies<br />
Hazards and Complications <strong>of</strong> Arterial Catheters<br />
Any invasive procedure involves a degree <strong>of</strong> risk for complications. When properly inserted<br />
and monitored, the risk <strong>of</strong> complications from an indwelling intra-arterial catheter can be<br />
minimized by frequent assessment <strong>of</strong> the patient. Specific complications may include the<br />
following:<br />
Failure to analyze system dynamics, which may result in over- or under-estimation <strong>of</strong> the<br />
patient's true blood pressure<br />
Infection, which may be local or systemic. The risk <strong>of</strong> infection becomes greater the longer<br />
the catheter remains in place.<br />
Embolization from fibrin, particulate matter, flush solution or air, which may result in<br />
embolic infarctions <strong>of</strong> distal tissue and digital necrosis<br />
Vascular insufficiency, caused by the catheter, arterial spasm or plaque<br />
Bleeding, which may include minor surface bleeding from the site, hematoma and vascular<br />
compression under the insertion site, or massive occult bleeding (the femoral artery may<br />
leak up to 1,500 ml <strong>of</strong> blood into the retroperitoneal space)<br />
Accidental disconnection or opening <strong>of</strong> the system, which may result in rapid external<br />
blood loss<br />
Excessive blood loss and decreased hemoglobin/hematocrit due to multiple blood draws for<br />
diagnostic laboratory studies<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Arterial spasm due to catheter irritation or trauma to the vessel during insertion, which may<br />
decrease blood flow distal to the insertion site<br />
Inadvertent removal due to excessive patient movement or the pressure exerted on the site<br />
by limb restraints<br />
Skin breakdown and arterial erosion related to indwelling catheters and tubing.<br />
Intra-Arterial Waveforms<br />
A normal arterial pressure waveform has five main components. See diagram below.<br />
1. The anacrotic limb, or anacrotic rise, is a rapid upstroke that begins at the opening <strong>of</strong><br />
the aortic valve in early systole. The steepness, rate <strong>of</strong> ascent, and height <strong>of</strong> this initial<br />
upswing is related to the contractility and stroke volume <strong>of</strong> the left ventricle.<br />
2. The systolic peak represents the highest pressure generated by the left ventricle during<br />
myocardial contraction. This point marks the patient’s actual systolic blood<br />
pressure.<br />
3. The dicrotic limb begins during late systole as the flow <strong>of</strong> blood out <strong>of</strong> the left ventricle<br />
starts to decrease.<br />
4. The dicrotic notch marks the closure <strong>of</strong> the aortic valve and the beginning <strong>of</strong> diastole.<br />
5. The end diastole landmark is the location at which the patient’s actual diastolic blood<br />
pressure is measured.<br />
In the following examples, note the effect <strong>of</strong> hypertension and hypotension on the arterial line<br />
waveform. Hypertension generally results in a very steep anacrotic limb and a shortened early<br />
systolic phase <strong>of</strong> contraction. On the dicrotic limb, this rapid ejection <strong>of</strong> blood from the left<br />
ventricle early in systole may result in changes to the waveform prior to the dicrotic notch. On<br />
the tracing below, note the variations from one waveform to another while the appearance <strong>of</strong><br />
the dicrotic notch remains very consistent.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 22
Note the variability in<br />
the waveform near the<br />
systolic peak.<br />
Note the scale<br />
printed on the<br />
paper by the<br />
monitor showing<br />
the pressure<br />
levels. The blood<br />
pressure is<br />
180/100.<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
In the example below, hypotension has resulted in an overdamped appearance <strong>of</strong> the waveform<br />
with a decrease in the steepness <strong>of</strong> the anacrotic limb. When the blood is ejected from the left<br />
ventricle with decreased force, there may not be a pronounced dicrotic notch since there is less<br />
<strong>of</strong> a difference between the systolic and diastolic pressures.<br />
Decreased rise<br />
and slope <strong>of</strong><br />
anacrotic limb<br />
Systolic pressure, here about 75<br />
Note the scale printed on the paper by the monitor allowing the determination <strong>of</strong> pressure<br />
levels from the waveforms. In this case, it appears that the diastolic is about 75 and the<br />
systolic is about 50.<br />
Dicrotic notch<br />
showing aortic<br />
valve closure (note<br />
consistent<br />
configuration)<br />
Diminished or<br />
absent dicrotic<br />
notch<br />
Diastolic pressure, here about 50<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 23
0<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Arterial Waveform Examples<br />
The following are some examples <strong>of</strong> arterial line waveforms for practice and determination <strong>of</strong><br />
actual pressures.<br />
Example 1<br />
In the example below, the top waveform is the cardiac rhythm reflected in lead II. The bottom<br />
waveform reflects the arterial pressure tracing. Note the scale displayed at the beginning <strong>of</strong> the<br />
strip, and the notation as to what that scale is.<br />
Locate the dicrotic notch in this example. Based on this waveform, what is the arterial line<br />
blood pressure? Measure the systolic blood pressure at the peak <strong>of</strong> systole and the diastolic<br />
pressure just prior to the anacrotic rise. The correct locations for measurement <strong>of</strong> systolic and<br />
diastolic pressure are marked with bold horizontal lines on the strip.<br />
40<br />
80<br />
120<br />
SBP = 120<br />
mm Hg<br />
DBP = 55<br />
mm Hg<br />
The dicrotic notch is not clearly visible on this waveform. Lack <strong>of</strong> a distinct dicrotic notch<br />
indicates this waveform may be overdamped. The nurse should perform a square wave test and<br />
analyze the system dynamics to determine if this system is reflecting accurate pressures. What is<br />
the estimated arterial blood pressure in this case? The pressure here was documented at 120/55,<br />
but cannot be considered reliable until system dynamics have been assessed.<br />
Example 2<br />
The top waveform is the ECG tracing <strong>of</strong> lead II. The bottom waveform represents the arterial<br />
pressure tracing. Look at the stairstep scale at the beginning <strong>of</strong> the bottom waveform. In this<br />
case, the initial flat line represents a pressure <strong>of</strong> 40 mm Hg, the second is at 58 mm Hg, the<br />
third is at 76 mm Hg, and the top one is at 94 mm Hg. Most scales begin at zero, but this one<br />
does not. Why? Some monitors have a setting called “optimize” that will automatically select a<br />
scale to fit the waveform displayed. This strip was obtained using an “optimized” scale. This<br />
type <strong>of</strong> scale can help show increased detail, but the scale must be reset any time the patient’s<br />
pressures change significantly.<br />
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The dicrotic notch is identified with an arrow. Recall that the dicrotic notch on the arterial<br />
waveform represents closure <strong>of</strong> the aortic valve and the onset <strong>of</strong> diastole.<br />
What is this patient’s arterial blood pressure? In this case, the pressure is 90/49 with a mean<br />
arterial pressure <strong>of</strong> 63. This pressure was obtained by calculating the value <strong>of</strong> each small box<br />
using the scale on the strip. In this case, each step is equal to 18 mm Hg, and each small box is<br />
equal to 4.5 mm Hg. Refer back to the section on interpreting pressure scales for more<br />
information.<br />
Note that the pressure obtained would be slightly different if the first waveform had been<br />
analyzed. There will always be beat-to-beat variations in pressure waveforms.<br />
58<br />
76<br />
94<br />
Dicrotic<br />
Notch<br />
SBP = 90<br />
DBP = 49<br />
Example 3<br />
Once again, the top waveform is the ECG tracing. The bottom waveform is the arterial<br />
pressure tracing. Cover the waveform at the bottom <strong>of</strong> the page and check your skills. Label<br />
the pressure scale, locate the dicrotic notch, and determine this patient’s arterial blood pressure.<br />
Are any interventions or troubleshooting called for?<br />
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Waveform Analysis Answer: Example 3<br />
In this case, the pressure waveform is <strong>of</strong>f the scale the majority <strong>of</strong> the time, so the pressure<br />
cannot be accurately calculated. The scale and dicrotic notch are marked on the strip. The<br />
appropriate intervention in this case is to assess the level <strong>of</strong> the transducer and re-level if<br />
needed. If the transducer is level with the phlebostatic axis, the scale should be increased.<br />
0 mm Hg<br />
40 mm Hg<br />
80 mm Hg<br />
120 mm Hg<br />
Dicrotic Notch<br />
Example 4<br />
Cover the waveform analysis at the bottom <strong>of</strong> the page before completing this skill. What is the<br />
scale on this waveform? What is the arterial blood pressure? Where is the dicrotic notch? Is any<br />
intervention or troubleshooting necessary?<br />
Waveform Analysis Answer: Example 4<br />
This waveform appears dampened; the dicrotic notch is not visible. This may be due to<br />
hypotension, poor system dynamics (overdamping) or a scale that is too large for the<br />
waveform. Note the marked scale. The patient’s pressure according to the strip is 105/45, but<br />
this is not accurate if the waveform is overdamped. The appropriate interventions (in order)<br />
would be to check the patient, correct the level <strong>of</strong> the transducer if needed, aspirate and flush<br />
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the line, and select a smaller scale. If these interventions failed to improve the waveform,<br />
system dynamics should be assessed using a square-wave test.<br />
0<br />
60<br />
120<br />
180<br />
SBP = 105 mm Hg<br />
DBP = 45 mm Hg<br />
Troubleshooting<br />
Whenever a change occurs in the waveform appearance or numeric readings always check the<br />
patient first. If the patient’s assessment is unchanged and there is reason to believe that the<br />
waveform appearance or numeric values are not an accurate reflection <strong>of</strong> the patient’s status,<br />
zero and level the transducer again. If this does not resolve the problem, assess the system<br />
dynamics using the square wave test. To further troubleshoot the system, refer to Appendix 1:<br />
Troubleshooting Arterial and CVP <strong>Monitoring</strong> Systems.<br />
Removal <strong>of</strong> Arterial Catheters<br />
The arterial catheter should be removed as soon as it is no longer needed, the site appears<br />
infected, or the tissues distal to the catheter become ischemic. In any case, it should not remain<br />
in place for longer than five days. A physician’s order is required for removal.<br />
To remove the arterial catheter, obtain clean gloves, sterile gauze squares, and materials for a<br />
pressure dressing. Tell the patient what you are doing and instruct him/her to remain still. Don<br />
gloves. Remove the dressing carefully and cleanse the site with sterile saline if needed. If<br />
sutures are in place, remove them carefully. Palpate the pulse proximal to the insertion site and<br />
lightly place the fingers <strong>of</strong> one hand directly over the pulse and keep them there. With the other<br />
hand, gently remove the catheter. Allow the artery to bleed briefly (it should spurt) before<br />
firmly compressing the artery with the first hand. Allowing the artery to bleed helps ensure that<br />
any particulate matter present on the catheter is expelled. Hold firm pressure on the artery for at<br />
least five minutes for a radial site, longer for a femoral or brachial site. Gently release the<br />
pressure, keeping the fingers over the pulse. If there is no bleeding or swelling, apply a pressure<br />
dressing to the site. If bleeding or swelling is noted upon release <strong>of</strong> pressure, immediately<br />
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reapply pressure proximal to the insertion site and hold for five minutes longer. Longer<br />
pressure holds may be required for patients with low platelet counts or elevated PT/PTT.<br />
Monitor the site after removal according to your hospital’s policies. Document the appearance<br />
<strong>of</strong> the site, the length <strong>of</strong> time required to achieve hemostasis, and the patient’s tolerance <strong>of</strong> the<br />
procedure in addition to vital signs. Also document the appearance <strong>of</strong> the catheter after<br />
removal. Instruct the patient to notify the nurse if any bleeding, pain, or numbness occurs at or<br />
distal to the site. If any bleeding or swelling is noted after removal, apply pressure again as<br />
previously described and notify the physician.<br />
Central Venous Pressure (CVP) <strong>Monitoring</strong><br />
Clinical Significance <strong>of</strong> CVP <strong>Monitoring</strong><br />
The CVP is the pressure <strong>of</strong> the blood emptying into the right ventricle during diastole (the right<br />
ventricular end-diastolic pressure, or RVEDP). This pressure reflects what is known as right<br />
ventricular preload. Thus, measuring CVP is one method <strong>of</strong> assessing right ventricular<br />
preload in the absence <strong>of</strong> a pulmonary artery catheter. The normal CVP ranges from 0 to 8<br />
mm Hg.<br />
There are many factors that may alter the CVP, resulting in a pressure that is not an accurate<br />
indication <strong>of</strong> right ventricular end-diastolic volume. Any condition that causes increased<br />
intrathoracic pressure, such as pneumothorax or some types <strong>of</strong> mechanical ventilation will<br />
cause the CVP to be quite high, while end-diastolic volume is acutely low. Conditions that<br />
diminish elasticity or contractility and cause the right ventricle to become stiff, such as<br />
pericardial tamponade and myocardial ischemia or infarction, can also result in a high pressure<br />
with a low blood volume. Because <strong>of</strong> this, the CVP is not extremely helpful in patients with<br />
increased intrathoracic pressure or abnormal myocardial contractility. In clinical practice, the<br />
CVP is most appropriately used to help monitor fluid status or guide fluid resuscitation in<br />
dehydrated or hypovolemic patients in the absence <strong>of</strong> cardiac dysfunction. As with any<br />
hemodynamic pressure, the trend <strong>of</strong> values is more significant than any one reading.<br />
A decreased CVP generally indicates that there is a diminished volume <strong>of</strong> blood returning from<br />
the venous system to the right side <strong>of</strong> the heart. This may be due to absolute hypovolemic<br />
states caused by dehydration, hemorrhage, vomiting or diarrhea. It may also be caused by<br />
relative hypovolemic states caused by fluid losses from the intravascular space due to an<br />
alteration in capillary membrane permeability, caused by conditions such as peritonitis, bowel<br />
obstruction or the systemic inflammatory response syndrome (SIRS). In addition, vasodilation<br />
may allow blood to pool within the blood<br />
vessels and decrease venous return and<br />
CVP; vasodilatation may be a result <strong>of</strong><br />
medications, anaphylaxis, sepsis or<br />
neurogenic shock.<br />
What do absolute hypovolemia, relative<br />
hypovolemia and vasodilatation have in<br />
common? In each case the overall<br />
intravascular capacity is greater than the<br />
volume <strong>of</strong> blood contained within the<br />
intravascular space. A decreased CVP<br />
Conditions other than Hypervolemia that<br />
Elevate CVP<br />
Pneumothorax<br />
Hemothorax<br />
Intra-abdominal hypertension<br />
Pericardial tamponade<br />
Mechanical Ventilation with positive<br />
end-expiratory pressure (PEEP)<br />
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reading should thus be considered in combination with a patient’s diagnosis, history and<br />
assessment findings in order to determine the best way to equalize the intravascular capacity<br />
with the intravascular volume and restore a normal CVP. Fluids and/or vasopressors may be<br />
indicated depending on the cause <strong>of</strong> a decreased CVP to reverse hypovolemia or vasodilatation.<br />
In any case, the numeric CVP value alone is meaningless without correlation with the patient’s<br />
diagnosis, history and thorough physical assessment.<br />
An elevated CVP indicates that the pressure within the right ventricle is increased above<br />
normal when the ventricle is full just prior to systole. This can be due to many factors,<br />
including fluid overload, myocardial infarction, cardiogenic shock, heart failure, pulmonary<br />
CLINICAL APPLICATION<br />
Elevated CVP with Hypovolemia<br />
The CVP can be elevated even when fluid volume status is normal or depleted if the<br />
intrathoracic pressure is high. Sources <strong>of</strong> increased intrathoracic pressure include<br />
mechanical ventilation with PEEP, pneumothorax, hemothorax, and high intraabdominal<br />
pressure. Remember that pressure is not equal to volume.<br />
As with any hemodynamic findings, an elevation in the CVP must be examined in light<br />
<strong>of</strong> other assessment findings to determine the cause for the elevation. Interventions<br />
must be based on the pathophysiologic basis for the pressure increase. Patients with<br />
heart failure, volume overload and pulmonary edema may require diuresis and positive<br />
inotropes, but these interventions would not help the patient with an elevated CVP due<br />
to a tension pneumothorax<br />
edema, COPD, pulmonary embolus, pneumothorax, pulmonary hypertension, pericardial<br />
effusion, or tamponade. Right-sided valvular disorders such as tricuspid regurgitation and<br />
pulmonic stenosis may also elevate the CVP reading.<br />
Description and Function <strong>of</strong> CVP Lines<br />
Central venous catheters may be small or large-bore, and single or multi-lumen. They can be<br />
inserted peripherally (PICC) or via the jugular or subclavian veins. Any catheter that is inserted<br />
centrally and has its tip in the superior vena cava can be used to monitor central venous<br />
pressure. This includes Hickman<br />
catheters, Groshong catheters, dual-lumen<br />
dialysis catheters as well as the more<br />
common dual or triple lumen central<br />
venous catheters. If a multi-lumen catheter<br />
is used, the CVP is measured via the<br />
distal port. Other ports are too far away<br />
from the right atrium to accurately<br />
reproduce the CVP waveform.<br />
CVP monitoring cannot be performed<br />
through PICC lines. These long, pliable<br />
catheters do not produce accurate<br />
waveforms. Other types <strong>of</strong> catheters<br />
unsuitable for CVP monitoring include<br />
Placement <strong>of</strong> a central venous catheter, from Techniques in<br />
Bedside <strong>Hemodynamic</strong> <strong>Monitoring</strong> by E.K. Daily and J.S.<br />
Schroeder C V Mosby 1981 Used with permission<br />
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Port-A-Caths and introducers. The Port-A-Cath has a one-way valve that interferes with<br />
monitoring and the tip <strong>of</strong> the introducer is too far away from the right atrium to be suitable.<br />
Central venous catheters are placed so that the catheter tip (distal end) is located in the superior<br />
vena cava as it opens into the right atrium. This allows measurement <strong>of</strong> the pressure within the<br />
venous system at the point at which it empties into the right atrium. The catheter tip should not<br />
enter the right atrium. A catheter inside the atrium can induce atrial dysrhythmias and could<br />
perforate the myocardium.<br />
Indications for the Use <strong>of</strong> Central Venous Catheters<br />
Central venous catheters are commonly used in the clinical setting for monitoring and<br />
therapeutic purposes. Primary indications include the following:<br />
Rapid administration <strong>of</strong> fluids and blood products in patients with any form <strong>of</strong> shock<br />
Administration <strong>of</strong> vasoactive and caustic drugs<br />
Administration <strong>of</strong> parenteral nutrition, electrolytes or hypertonic solutions<br />
Venous access for monitoring CVP and assessing the response to fluid or vasoactive drug<br />
therapy<br />
Insertion <strong>of</strong> transvenous pacemaker<br />
Lack <strong>of</strong> accessible peripheral veins<br />
<strong>Hemodynamic</strong> instability<br />
Relative Contraindications<br />
There are few absolute contraindications to the use <strong>of</strong> central venous catheters. The relative<br />
contraindications listed below will increase the risk <strong>of</strong> complications when using a central<br />
venous catheter. However, this increased risk must be considered relative to the benefit that<br />
the patient will receive in the form <strong>of</strong> more advanced assessments and interventions. Relative<br />
contraindications include the presence <strong>of</strong> the following:<br />
Coagulopathies or bleeding disorders (monitor platelet count, PT, PTT)<br />
Current or recent use <strong>of</strong> fibrinolytics or anticoagulants<br />
Insertion sites that are infected or burned, or where previous vascular surgery has been<br />
performed, or involve catheter placement through vascular grafts<br />
Patients with a high risk <strong>of</strong> pneumothorax (such as those with COPD, or those on<br />
mechanical ventilation with PEEP or CPAP)<br />
Patients with suspected or confirmed vena cava injury<br />
Selection <strong>of</strong> Catheter and Insertion Site<br />
Various types <strong>of</strong> central venous catheters exist. The choice <strong>of</strong> catheter is made by the physician<br />
and based on the clinical indication. For the purposes <strong>of</strong> this self-learning packet, discussion<br />
will be limited to those catheters that are centrally inserted, most commonly through the<br />
subclavian, internal jugular or external jugular veins.<br />
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Large gauge single-lumen catheters may be used for rapid fluid administration in patients in<br />
shock or following major trauma, or in patients receiving only maintenance fluid administration<br />
and intermittent monitoring <strong>of</strong> the central venous pressure using a water manometer. The most<br />
common practice is to use multi-lumen catheters, especially the triple-lumen central venous<br />
catheter. Multi-lumen catheters allow for simultaneous administration <strong>of</strong> fluids and multiple<br />
drugs that may not be compatible when administered through a single line. These catheters<br />
also allow for continuous monitoring <strong>of</strong> the central venous pressure through the distal port<br />
while drugs and fluids are being administered through the proximal ports. Do not monitor and<br />
infuse through the same port; the CVP will not be accurate.<br />
The choice <strong>of</strong> insertion site is generally determined by the physician, based on his or her<br />
experience, and patient-related factors, such as anatomy, burn, surgical or trauma sites, and<br />
pulmonary hyperinflation due to chronic lung disease or mechanical ventilation.<br />
Insertion <strong>of</strong> a Central Venous Catheter<br />
Physicians generally insert the types <strong>of</strong> central venous catheters (CVC) discussed in this selflearning<br />
packet. In some institutions, physicians’ assistants or nurse practitioners may be<br />
credentialed to perform the procedure. Unless an emergency situation exists, the physician<br />
obtains informed consent from the patient or healthcare surrogate before the catheter is placed.<br />
Check your hospital’s policies for specific information.<br />
Nursing personnel <strong>of</strong>ten assist with catheter insertion. It is preferable to have two nurses<br />
assisting; one to assist with the technical procedure and another to monitor and comfort the<br />
patient. While assisting a physician with a CVC insertion, the following steps should be used as<br />
general guidelines:<br />
The physician explains the procedure to the patient to obtain informed consent<br />
Prepare IV solution, and set up the monitoring system as previously described<br />
Obtain medication for pain or sedation as ordered by physician<br />
Position the patient as needed using pillows or rolled towels, or place the patient in the<br />
Trendelenberg position; this prevents air from being passively drawn into the venous<br />
system during the negative intrathoracic pressure generated by inspiration<br />
Wear surgical cap, face mask, sterile gown and gloves and provide these items for the<br />
physician and others in the immediate area<br />
Assist with cleansing and draping <strong>of</strong> the insertion site (using sterile towels) as needed<br />
Provide patient comfort and emotional support during procedure<br />
Monitor respiratory rate and status, heart rate and rhythm, and patient response to the<br />
procedure. Observe the cardiac monitor, if available, during the procedure and inform the<br />
physician immediately if a dysrhythmia occurs.<br />
Assist with keeping the patient’s head and hands away from the insertion site and<br />
maintaining a sterile field<br />
Assist with connection <strong>of</strong> the hemodynamic monitoring setup to the catheter hub as<br />
requested, and apply a sterile occlusive dressing to the insertion site<br />
If using a multi-lumen catheter, aspirate air from each lumen and flush with appropriate<br />
solution or initiate IV fluids as ordered<br />
Obtain a CVP reading as previously described<br />
Immediately obtain a chest x-ray. Unless an emergency situation exists, medications are not<br />
administered via the CVC until placement is confirmed with a chest x-ray.<br />
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Document the insertion, the patient’s response and the results <strong>of</strong> the chest x-ray. Also<br />
document the length marking at the skin on the catheter. Length is marked in 10 cm<br />
increments using black rings. One black ring equals 10 cm, two black rings equals 20 cm,<br />
etc.<br />
Obtain orders from the physician for CVP monitoring, the desired CVP, and high and low<br />
CVP values requiring notification.<br />
Hazards and Complications<br />
The insertion and maintenance <strong>of</strong> a central venous catheter involves some significant risks to<br />
the patient. The CVC is a flexible tube that is placed through a puncture in a large blood vessel<br />
(usually the subclavian, femoral or jugular) and threaded through the venous system towards<br />
the right atrium. These catheters are frequently used for infusing high volumes <strong>of</strong> fluids, or for<br />
infusing fluids that may be irritating to blood vessels. Specific complications may include the<br />
following:<br />
Infection, either local or systemic<br />
Bleeding, either on the surface or below it, which may lead to hematoma, vascular<br />
compromise and hypovolemia<br />
Air or fluid (IV fluid or blood) in the mediastinum, thoracic cavity, pleural or pericardial<br />
space, leading to a pneumothorax, hemothorax, pleural effusion, pericardial tamponade or<br />
widened mediastinum<br />
Vascular erosion due to catheter or irritating fluids<br />
Cardiac dysrhythmias resulting from irritation by catheter tip or electrical microshock<br />
(electricity transmitted by the catheter to the heart)<br />
Embolism caused by air, particulate matter, catheter tip, or clot formation<br />
The most significant risk to the patient is infection. To minimize the risk to your patients, use<br />
meticulous sterile technique when caring for the CVC. Follow your hospital’s policies for<br />
dressing changes and CVC access. Most hospitals require the dressing be changed whenever it<br />
is soiled, but discourage routine daily dressing changes. The more the site is exposed to the<br />
environment, the greater the risk <strong>of</strong> infection. A sterile occlusive dressing is used for all CVC<br />
sites. If there is no drainage at the site, a transparent dressing is preferred so the site can be<br />
assessed visually. If drainage is present at the site, a sterile absorbent dressing must be used and<br />
changed as needed. Document the insertion site as outlined by the policies and guidelines in<br />
your hospital.<br />
In most cases, the CVC will remain in place a maximum <strong>of</strong> 5 days. After 5 days, the catheter<br />
site is changed or the catheter is replaced using an over-the-wire technique at the current site.<br />
The decision on whether to change the site is made by the physician and is based on the<br />
condition <strong>of</strong> the current site, culture results, and availability <strong>of</strong> other access sites.<br />
CVP Line Setup<br />
Central venous catheters are used in a variety <strong>of</strong> units and settings. In critical care units, they<br />
may be attached to a transducer and monitored by a hardwire system in a manner similar to<br />
intra-arterial lines. Guidelines on transducing this system are covered in the Pressure<br />
<strong>Monitoring</strong> section <strong>of</strong> this self-learning packet. In general care and step-down units, a central<br />
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venous catheter may also be connected to a water manometer to measure the CVP. However,<br />
water manometer systems do not allow for waveform interpretation or square-wave testing,<br />
making them more prone to error than transduced systems. Because <strong>of</strong> this, water manometer<br />
systems are becoming less common and will not be discussed in this packet.<br />
CVP Waveforms<br />
When a properly placed central venous catheter is attached to an electronic monitor, a classic<br />
waveform that reflects the pressure within the right atrium is produced. The components <strong>of</strong> a<br />
normal CVP waveform reflect pressure changes in the right atrium resulting from the<br />
movement <strong>of</strong> blood in and out <strong>of</strong> the atrium during the cardiac cycle. They are shown below,<br />
along with their relationship to a normal ECG rhythm tracing.<br />
Normal ECG<br />
rhythm tracing<br />
CVP<br />
waveform<br />
CVP value recorded at the midpoint <strong>of</strong> the X descent.<br />
Components <strong>of</strong> the CVP Waveform. From Thelan’s Critical Care Nursing: Diagnosis and Management by Linda<br />
Urden, Kathleen Stacy and Mary Lough, C.V. Mosby, 2002. Used with permission.<br />
Components <strong>of</strong> the CVP waveform include:<br />
The A wave occurs after the P wave <strong>of</strong> the ECG complex during the PR interval. It reflects<br />
the increased atrial pressure that occurs with atrial contraction. Note that the A wave will<br />
be absent in patients who do not have a distinct atrial contraction, such as those with atrial<br />
fibrillation. Since the CVP value should be a reflection <strong>of</strong> the Right Ventricular End-<br />
Diastolic Pressure, the CVP reading is taken at the last half <strong>of</strong> the A wave at the midpoint<br />
<strong>of</strong> the X descent. Calculate the CVP by averaging the pressure measured at the peak<br />
<strong>of</strong> the A wave and at the subsequent trough.<br />
The X descent reflects atrial relaxation.<br />
The C wave occurs at the end <strong>of</strong> the QRS complex at the beginning <strong>of</strong> the ST segment on<br />
the ECG tracing. It reflects closure <strong>of</strong> the tricuspid valve between the right atrium and right<br />
ventricle and the slight bulging <strong>of</strong> the tricuspid valve during ventricular contraction. The C<br />
wave is not always visualized.<br />
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The V wave occurs at the end <strong>of</strong> the T wave on the ECG tracing. It reflects the increased<br />
pressure during passive atrial filling.<br />
The Y descent occurs prior to the P wave on the ECG tracing. It reflects the opening <strong>of</strong> the<br />
tricuspid valve and the passive flow <strong>of</strong> blood from the right atrium into the right ventricle<br />
prior to atrial contraction.<br />
Obtaining a CVP Reading<br />
A CVP waveform consists <strong>of</strong> a number <strong>of</strong> components that may generate constantly changing<br />
numeric values on the monitor. Which number is recorded as the actual CVP? It is important<br />
not to take the reading from the digital display on the monitor, since this value represents the<br />
average pressure throughout the entire cardiac and respiratory cycles.<br />
The CVP may vary considerably from inspiration to expiration due to changes in intrathoracic<br />
pressure. To eliminate this variation in readings, all hemodynamic measurements are taken<br />
at end-expiration. The most accurate method is to obtain an actual printout <strong>of</strong> the CVP<br />
waveform and ECG tracing and average the A wave at end-expiration. The CVP value is<br />
recorded at the midpoint in the X descent. The waveform below demonstrates how to determine<br />
where end-expiration occurs on the monitor strip. In spontaneously breathing patients the CVP<br />
baseline will fall during inspiration and rise during expiration. Take the measurement just prior<br />
to the baseline fall <strong>of</strong> inspiration.<br />
Inspiration<br />
Expiration<br />
Measure CVP here<br />
Patients receiving positive-pressure ventilation exhibit baseline rise during inspiration with<br />
baseline fall during expiration. In these patients, take the reading just prior to the rise <strong>of</strong><br />
inspiration. When in doubt as to which part <strong>of</strong> the patient’s waveform represents expiration, try<br />
this; place a hand on the patient’s chest while watching the CVP waveform on the monitor.<br />
Note whether the baseline rise is occurring on inspiration or expiration then take the<br />
measurement.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 34
CVP from a patient on mechanical ventilation:<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
The CVP will also change significantly with changes in patient position. <strong>Hemodynamic</strong><br />
measurements are ideally recorded when the patient is laying flat in the supine position. This is<br />
<strong>of</strong>ten impractical, as many patients cannot tolerate lying flat for even a few moments. In such a<br />
case the CVP can be measured with the patient in the supine position with the head <strong>of</strong> bed<br />
elevated anywhere between 0 and 60 degrees. It is essential that all measurements be taken<br />
from the same patient position for trends to be valid. When taking the initial CVP<br />
measurement, record the head <strong>of</strong> bed position along with the reading. Make sure the patient is<br />
in the same position with each subsequent measurement. Document the head <strong>of</strong> bed elevation<br />
with each CVP measurement.<br />
As mentioned before, the A wave will be absent in patients without distinct atrial contractions,<br />
such as those in atrial fibrillation or those with ventricular pacemakers and no atrial activity.<br />
How is a CVP obtained in patients without an A wave? In these cases, a reading may be taken<br />
on the CVP waveform where it aligns with the end <strong>of</strong> the QRS complex on the ECG tracing. As<br />
always, take the reading at end-expiration.<br />
22 mm Hg<br />
Read CVP here<br />
Inspiration Expiration Inspiration<br />
Take CVP reading here<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 35
CVP Waveform Examples<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Example 1<br />
The following are examples <strong>of</strong> CVP waveforms for practicing determination <strong>of</strong> actual<br />
pressures. In the first example below, the top tracing represents the ECG lead V1, and the<br />
bottom tracing represents the CVP waveform. Note that the scale is 0-10-20-30, and that the<br />
monitor always measures pressures in mm Hg. On the CVP waveform below; the A wave, the<br />
C wave, and the V wave have been labeled. Which component <strong>of</strong> the cardiac cycle does each<br />
<strong>of</strong> these waves signify? Refer to the beginning <strong>of</strong> this section to review. Take particular note <strong>of</strong><br />
where each <strong>of</strong> these waves occurs in relation to the ECG tracing. If necessary, take a ruler or<br />
the edge <strong>of</strong> a sheet <strong>of</strong> paper and line up the different pressure waves with their components on<br />
the ECG tracing. Note that this tracing has been expanded to better allow identification <strong>of</strong> the<br />
components <strong>of</strong> the CVP waveform.<br />
A Wave<br />
P Wave<br />
C Wave V Wave<br />
The CVP is calculated by averaging the peak and trough <strong>of</strong> the A wave. In this case the peak is at<br />
7.5 mm Hg and the subsequent trough is at 5 mm Hg. To find the average, add the numerical value<br />
<strong>of</strong> the peak and trough and divide the sum by 2. In this case, 7.5 + 5 = 12.5 and 12.5/2 = 6.25.<br />
Pressures are not expressed in fractions, so round to the nearest whole number. In this case the<br />
CVP reading is 6 mm Hg.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 36
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Example 2<br />
In this example, the strip has been greatly enlarged to show greater detail. Locate the A wave,<br />
the C wave, and the V wave on the CVP tracing <strong>of</strong> this spontaneously breathing patient. Note<br />
once again that the A wave occurs immediately after the P wave on the ECG tracing above it,<br />
reflecting atrial contraction. Measure the CVP by averaging the peak and trough <strong>of</strong> the A<br />
wave. What pressure reading should be documented on this waveform? Check your answers<br />
against the waveform analysis on the following page.<br />
Waveform Analysis Answer: Example 2<br />
0<br />
10<br />
20<br />
30<br />
P wave<br />
A<br />
C<br />
V<br />
15 mm Hg 10 mm Hg<br />
Expiration Inspiration<br />
In this example, the A wave is identified by lining up the P wave from the ECG tracing above.<br />
Note that it would be impossible to identify the A wave correctly without the ECG tracing. In<br />
this strip the C wave is not always present; this is a normal variation.<br />
Respiratory variation is slight, but present on this strip. Note that the pressure was read from<br />
the circled A wave. This A wave was selected because it is the last complete A wave before the<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 37
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
baseline falls. Recall that in spontaneously breathing patients the baseline drops during<br />
inspiration. In this case the peak <strong>of</strong> the A wave is at 15 mm Hg and the trough is at 10 mm Hg.<br />
The average <strong>of</strong> these two numbers is (15+10)/2 = 25/2 = 12.5. The CVP is rounded to 13 mm<br />
Hg.<br />
Example 3<br />
This waveform was taken from a patient on a mechanical ventilator. Identify the scale, the A<br />
wave, C wave (if present) and V wave, and calculate the CVP. Remember to make your<br />
measurement at end-expiration. In the mechanically ventilated patient the baseline falls during<br />
expiration. Compare your answers with the waveform analysis below.<br />
Waveform Analysis Answer: Example 3<br />
Note the difference in the appearance <strong>of</strong> the baseline change with mechanical ventilation. The<br />
A wave has been marked with a broken line and is followed by a C wave and a V wave. The<br />
scale was obtained using the optimize setting on the monitor and includes positive and negative<br />
pressures. The peak <strong>of</strong> the A wave is at 2 mm Hg and the trough is at -4 mm Hg. This gives a<br />
mean pressure <strong>of</strong> -1 mm Hg. There should not be a negative pressure generated by passive<br />
exhalation on mechanical ventilation. The correct intervention is to check the patient, then<br />
check the level <strong>of</strong> the transducer and re-level if needed.<br />
-10<br />
Mechanical<br />
-4<br />
+2<br />
+8 A V<br />
Insp. Exp. Insp. Exp.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 38
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Troubleshooting<br />
Whenever a change occurs in the waveform appearance or numeric readings always check the<br />
patient first. If the CVP is high, auscultate heart and lung sounds to assess for the development<br />
<strong>of</strong> murmurs, rales and an S3 or S4. If the CVP reading is low, examine other indices <strong>of</strong> fluid<br />
status, such as skin turgor, jugular vein distension, condition <strong>of</strong> mucous membranes, skin<br />
temperature and color, and pulse quality. If the patient’s assessment is unchanged and there is<br />
reason to believe that the waveform appearance or numeric values are not an accurate reflection<br />
<strong>of</strong> the patient’s status, begin by re-zeroing and re-leveling the transducer. If this does not<br />
resolve the issue, assess the system dynamics using a square wave test. For other common<br />
problems and possible solutions refer to Appendix 1 at the end <strong>of</strong> the packet.<br />
Removal <strong>of</strong> Central Venous Catheters<br />
The central venous catheter should be removed as soon as it is no longer needed or if the site<br />
appears infected. In any case, it should not remain in place for longer than five days. A<br />
physician’s order is required for removal.<br />
To remove the central venous catheter, obtain clean gloves and sterile gloves, sterile gauze<br />
squares, and materials for a dressing. Explain the procedure to the patient and instruct them to<br />
remain still. Place the patient flat to minimize the risk <strong>of</strong> air aspiration. Don clean gloves.<br />
Remove the dressing carefully and cleanse the site with sterile saline if needed. If sutures are in<br />
place, remove them carefully.<br />
Instruct the patient to take a deep breath and hold it. If the patient is unable to perform a breath<br />
hold, time the removal <strong>of</strong> the catheter to coincide with a period <strong>of</strong> positive intrathoracic<br />
pressure. In spontaneously breathing patients this will occur during exhalation. In mechanically<br />
ventilated patients positive intrathoracic pressure occurs when the ventilator delivers a breath.<br />
This step is extremely important. If the catheter is removed during a period <strong>of</strong> negative<br />
intrathoracic pressure, an air embolus could be drawn in through the open tract.<br />
While the patient holds his/her breath, remove the catheter smoothly. Once the catheter has<br />
been removed, apply moderate pressure with sterile gauze and tell the patient to resume<br />
breathing. Obtain any catheter cultures that have been ordered now. Usually the intercutaneous<br />
portion <strong>of</strong> the catheter is cultured. This is the portion <strong>of</strong> the catheter that tunneled through the<br />
skin. Sometimes a catheter tip culture is also requested.<br />
After a minute or two, gently release the pressure. If there is no bleeding or swelling, apply a<br />
sterile dressing to the site according to the policies <strong>of</strong> your hospital. If bleeding or swelling is<br />
noted on release <strong>of</strong> pressure, immediately reapply the pressure and hold again. Longer pressure<br />
holds may be required for patients with low platelet counts or elevated PT/PTT. Apply a sterile<br />
dressing to the site. At this point the patient’s head may be elevated to a position <strong>of</strong> comfort.<br />
Monitor the site after removal according to your hospital’s policies. Document the appearance<br />
<strong>of</strong> the site, the length <strong>of</strong> time required to achieve hemostasis, and the patient’s tolerance <strong>of</strong> the<br />
procedure in addition to vital signs. Also document the appearance <strong>of</strong> the catheter upon<br />
removal. Instruct the patient to notify the nurse if bleeding or pain occurs at the site. If bleeding<br />
or swelling is noted after removal, apply pressure again as previously described and notify the<br />
physician.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 39
<strong>Hemodynamic</strong> Case Studies<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
These cases will provide the opportunity to see how hemodynamic monitoring may assist in<br />
determining appropriate interventions for differing situations.<br />
Case 1<br />
You are caring for a 29-year old male patient with a BP <strong>of</strong> 74/30. What should you do about<br />
his hypotension? You can’t be sure without knowing the reason for it. In addition, the CVP<br />
reading is 1 mm Hg. This additional information indicates that the patient has a diminished<br />
blood volume returning to the right heart, but still doesn’t tell you what interventions should<br />
receive the highest priority. Further assessment reveals that the patient received approximately<br />
10-12 bee stings approximately 15 minutes ago and has a pre-existing allergy to bee stings.<br />
You now correctly determine that the patient is in anaphylactic shock, and that he is<br />
hypotensive not because he has lost blood volume, but because anaphylaxis results in massive<br />
vasodilation and decreased blood return to the right atrium. Note the patient’s pulse pressure; it<br />
is wide, indicating arterial vasodilation. Taking all the data into consideration allows you to<br />
intervene appropriately with epinephrine, antihistamines, and IV fluids to fill the vascular<br />
space.<br />
Case 2<br />
You are caring for a 79-year old male patient with a BP <strong>of</strong> 74/50. Should you treat him in the<br />
same manner as the patient in case 1 because he is hypotensive? Note that the pulse pressure is<br />
much narrower in this case, indicating vasoconstriction and increased left ventricular afterload.<br />
Additional information includes a CVP reading <strong>of</strong> 15 mm Hg. What does this tell us? Only<br />
that we have an increased right ventricular end diastolic pressure. We don’t yet know if this is<br />
due to MI, fluid overload, valvular disease, COPD, pericardial tamponade or a pneumothorax,<br />
since all <strong>of</strong> these can cause the combination <strong>of</strong> an elevated CVP with hypotension. However,<br />
as we continue our patient assessment we will assess heart and lung sounds, peripheral pulses,<br />
skin condition, etc. Our assessment reveals heart sounds to be S1-S2-S3-S4; lung sounds include<br />
bilateral rales approximately ½ up. Upon examining peripheral pulses, we note them to be<br />
weak but find that our patient has 2+ bilateral pedal pitting edema. This patient has symptoms<br />
<strong>of</strong> heart failure and elevated right ventricular preload and will likely benefit from positive<br />
inotropic agents and diuretic therapy. Vasodilators might also be used to diminish the venous<br />
return to the heart, but their use will require caution due to his hypotension.<br />
Case 3<br />
You are caring for a 63-year old female with a BP <strong>of</strong> 84/70 and a CVP <strong>of</strong> 24 mm Hg. Should<br />
we diurese this patient because she has an elevated CVP? History reveals that she was<br />
admitted last night with a diagnosis <strong>of</strong> acute inferior wall MI. Your assessment reveals that her<br />
lungs are clear, and heart sounds reveal S1-S2 with a pansystolic murmur over the left lower<br />
sternal border. So what do we do? The CVP alone would seem to indicate fluid overload and<br />
the need for diuretics. However, based on your assessment findings, the physician orders an<br />
echocardiogram that reveals tricuspid regurgitation due to papillary muscle dysfunction caused<br />
by the MI. In this case, diuretics would greatly diminish the amount <strong>of</strong> blood reaching the left<br />
ventricle and would then result in a significant decrease in cardiac output, shock and possibly<br />
death. The results <strong>of</strong> the echocardiogram lead the physician to consult a cardiac surgeon for an<br />
immediate valve replacement.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 40
Conclusion<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
In addition to the guidelines contained in this packet, there are many other considerations in the<br />
insertion, management and removal <strong>of</strong> invasive lines. Check your hospital’s guidelines, policies,<br />
and procedures for other essential information regarding central lines, such as the manner in which<br />
fluids or drugs are administered through a central line, which nursing personnel may access a<br />
central line and how to perform dressing changes.<br />
<strong>Hemodynamic</strong> monitoring does not take the place <strong>of</strong> careful nursing assessment. Using<br />
hemodynamic data without regard to patient assessment findings can result in harm. Thorough<br />
nursing assessment provides the framework for interpretation <strong>of</strong> hemodynamic data and aids in<br />
selection <strong>of</strong> interventions that enhance patient outcomes.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 41
Glossary<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
“A” wave: The portion <strong>of</strong> the CVP waveform caused by atrial contraction; located just after the P<br />
wave on the ECG tracing. The “A” wave is averaged to obtain the CVP.<br />
“C” wave: The portion <strong>of</strong> the CVP waveform caused by closure <strong>of</strong> the tricuspid valve; located<br />
between the “A” and “V” waves. It may not always be present.<br />
“V” wave: The portion <strong>of</strong> the CVP waveform caused by passive atrial filling. The “V” wave<br />
occurs during ventricular systole and appears just after the QRS complex on the ECG waveform.<br />
Afterload: The resistance the ventricle must overcome to eject its volume <strong>of</strong> blood. Afterload is<br />
most strongly affected by vascular resistance.<br />
Allen’s test: A clinical assessment <strong>of</strong> ulnar arterial blood flow<br />
Amplitude: Height <strong>of</strong> a waveform<br />
Amplitude ratio: Comparison <strong>of</strong> the height <strong>of</strong> the first and second oscillations after a squarewave<br />
test. It is used in analysis <strong>of</strong> system dynamics.<br />
Anacrotic limb: The portion <strong>of</strong> the arterial waveform that coincides with ventricular ejection<br />
Atmospheric pressure: The pressure exerted on all objects by the weight <strong>of</strong> the earth’s<br />
atmosphere. The atmospheric pressure varies with altitude.<br />
Cardiac Output: The amount <strong>of</strong> blood pumped out <strong>of</strong> the heart in one minute. The cardiac output<br />
is the product <strong>of</strong> the heart rate times the stroke volume.<br />
Central venous pressure (CVP): The pressure <strong>of</strong> blood in the superior or inferior vena cava just<br />
before it enters the right atrium.<br />
Compliance: The ability <strong>of</strong> a tissue to stretch<br />
Contractility: The inherent ability <strong>of</strong> a muscle fiber to forcefully contract.<br />
Dicrotic notch: The portion <strong>of</strong> the arterial waveform caused by closure <strong>of</strong> the aortic valve<br />
Distal port: The port on a catheter that is farthest away from the catheter hub, usually at the tip <strong>of</strong><br />
the catheter.<br />
Fling: See Underdamped<br />
Hydrostatic pressure: The pressure exerted by the weight <strong>of</strong> a fluid. In hemodynamics, it is the<br />
pressure exerted by the column <strong>of</strong> fluid between the patient and the transducer.<br />
Inotropic: Affecting contractility; a positive inotropic effect increases contractility and a<br />
negative inotropic effect decreases it.<br />
Manometer: Pressure gauge<br />
Mean arterial pressure: The average pressure throughout the arterial tree during systole and<br />
diastole. Mean arterial pressure is fairly uniform throughout the arterial tree, and is a better marker<br />
<strong>of</strong> perfusion than systolic blood pressure.<br />
Natural frequency: The frequency with which a system responds to a stimulus.<br />
Oscillations: Rapid up-and-down changes in a waveform. In hemodynamics, refers to the<br />
waveform immediately following the square-wave test.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 42
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Overdamped: Sluggish, under-responsive. An overdamped hemodynamic monitoring system will<br />
yield false low systolic pressures and false high diastolic pressures; normal waveform components<br />
may appear slurred or be absent.<br />
Phlebostatic axis: The approximate anatomic location <strong>of</strong> the heart, located at the fourth<br />
intercostal space, halfway between the anterior and posterior chest wall.<br />
Preload: The amount <strong>of</strong> stretch on the cardiac my<strong>of</strong>ibril at the end <strong>of</strong> diastole. Preload is most<br />
closely related to fluid volume present in the ventricle but is commonly measured as pressure. The<br />
CVP reflects the preload <strong>of</strong> the right ventricle.<br />
Pulse pressure: The difference between the systolic and diastolic blood pressure. Pulse pressure<br />
is wide (high) in vasodilated states and narrow (low) in vasoconstricted states.<br />
Square-wave test: A series <strong>of</strong> rapid fast-flushes <strong>of</strong> the hemodynamic monitoring system used to<br />
assess the system’s response to sudden large changes in pressure.<br />
Stroke volume: The amount <strong>of</strong> blood pumped with each heartbeat<br />
System dynamics: The response <strong>of</strong> a system to an extreme stimulus. In hemodynamics, system<br />
dynamics are evaluated using the square-wave test.<br />
Titrate: Adjust therapy in response to a prescribed parameter. This term is generally used in<br />
reference to IV drugs that are adjusted frequently based on a prescribed parameter such as blood<br />
pressure.<br />
Transducer: A device that converts pressure waves or pulses into a digital signal that can be<br />
displayed as a waveform on a monitor.<br />
Underdamped: also described as hyperdynamic, hyper-responsive. An underdamped<br />
hemodynamic monitoring system will yield false high systolic pressures and false low diastolic<br />
pressures. This phenomenon is also called catheter “whip” or “fling”.<br />
Whip: See Underdamped<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 43
References<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Alspach, J., et. al. (2006). AACN Core Curriculum for Critical Care Nursing. Philadelphia, PA:<br />
W.B. Saunders.<br />
McGhee, B. H. & Bridges, E. J. (2002). <strong>Monitoring</strong> arterial blood pressure: What you may not<br />
know. Critical Care Nurse, 22(2), 60-79.<br />
Diehl, T. S. (Ed) (2011) <strong>Hemodynamic</strong> <strong>Monitoring</strong> Made Easy (2 nd ed). Ambler, PA: Lippincott,<br />
Williams, & Wilkins<br />
Lynn-McHale Wiegand, D., (2011) AACN Procedure Manual for Critical Care. Philadelphia,<br />
PA: Elsevier Saunders.<br />
Sole, Mary Lou, et. al. (2008). Introduction to Critical Care Nursing (5 th ed). Philadelphia, PA:<br />
W.B. Saunders.<br />
Lough, M. E., Stacy, K. M., & Urden, L. D. (2010). Critical Care Nursing: Diagnosis and<br />
Management (6th ed.). St. Louis: Mosby.<br />
Puntillo, K. A., & Schell, H. M. (2006). Critical Care Nursing Secrets (2 nd ed). Philadelphia, PA:<br />
Hanley & Belfus.<br />
Carlson, K.K, et. al. (2009). AACN Advanced Critical Care Nursing. St. Louis, MO: Saunders<br />
Elsevier.<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 44
Posttest<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Please submit your answers via the online testing center found on the E-Learning page in<br />
Swift.<br />
1. The pressure bag around the flush solution for a transduced hemodynamic monitoring<br />
system is correctly maintained at what pressure?<br />
A. 3-5 mm Hg<br />
B. 150 mm Hg<br />
C. 180 mm Hg<br />
D. 300 mm Hg<br />
2. Which <strong>of</strong> the following solutions is most commonly used as the continuous flush for<br />
transduced hemodynamic monitoring systems?<br />
A. Normal saline<br />
B. Lactated ringers<br />
C. D51/4 Normal saline<br />
D. D51/2 Normal saline<br />
3. When setting up pressure monitoring system, it is important to use pressure (semi-rigid)<br />
tubing because:<br />
A. Use <strong>of</strong> standard IV tubing may result in an overdamped waveform<br />
B. Standard IV tubing will not connect properly to the transducer hub<br />
C. Use <strong>of</strong> standard IV tubing may result in catheter whip and overestimation <strong>of</strong> the<br />
patient’s systolic blood pressure<br />
D. Standard IV tubing may allow leaking <strong>of</strong> blood from the system<br />
4. The transducer from a hemodynamic monitoring system should be leveled at which <strong>of</strong> the<br />
following locations?<br />
A. 2 nd intercostal space at the midclavicular line<br />
B. 2 nd intercostal space at the mid-chest<br />
C. 4 th intercostal space at the mid-chest<br />
D. 4 th intercostal space at the midaxillary line<br />
5. The square-wave test is a method <strong>of</strong> assessing which <strong>of</strong> the following about a transduced<br />
hemodynamic monitoring system?<br />
A. Zeroing <strong>of</strong> the system<br />
B. Dynamic response <strong>of</strong> the system<br />
C. Harmonic response <strong>of</strong> the system<br />
D. Compensation for atmospheric pressure within the system<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 45
6. Overdamping <strong>of</strong> the hemodynamic monitoring system may result in:<br />
A. A false low systolic and false high diastolic pressure reading<br />
B. A falsely high systolic and falsely low diastolic pressure reading<br />
C. A falsely low systolic pressure reading<br />
D. A falsely low diastolic pressure reading<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
7. What could potentially occur when underdamping <strong>of</strong> a patient’s intra-arterial line setup is<br />
present?<br />
A. Overestimation <strong>of</strong> the patient’s blood pressure and a false widened pulse pressure<br />
B. Improper administration <strong>of</strong> diuretics to reduce volume overload<br />
C. Underestimation <strong>of</strong> the patient’s blood pressure<br />
D. Clotting <strong>of</strong> the catheter tip<br />
8. Air bubbles in the transducer or connecting tubing may cause :<br />
A. Clotting at the catheter tip<br />
B. Overdamping <strong>of</strong> the pressure waveform<br />
C. Underdamping <strong>of</strong> the pressure waveform<br />
D. Overestimation <strong>of</strong> the patient’s systolic pressure<br />
9. Which <strong>of</strong> the following represents a relative contraindication for the use <strong>of</strong> invasive<br />
arterial monitoring?<br />
A. Presence <strong>of</strong> an intra-aortic balloon pump<br />
B. Current or recent or use <strong>of</strong> fibrinolytics and anticoagulants<br />
C. <strong>Hemodynamic</strong> instability<br />
D. Recent CVA or head trauma<br />
10. A narrow pulse pressure is associated with:<br />
A. Low afterload states<br />
B. Arterial vasodilation<br />
C. Low heart rates<br />
D. High afterload states<br />
11. You suspect that a clot has formed at the tip <strong>of</strong> your patient’s intra-arterial catheter. Which<br />
<strong>of</strong> the following interventions should receive the highest priority at this time?<br />
A. “Fast flush” using the intraflow valve for 2-3 seconds<br />
B. Inflate the pressure bag to at least 300 mm Hg<br />
C. Attempt to manually aspirate the clot with a syringe<br />
D. Attempt to manually flush the line with a syringe using no more than 5-10 cc <strong>of</strong><br />
flush solution<br />
2011 <strong>Orlando</strong> Regional <strong>Health</strong>care, Education & Development Page 46
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
12. When using the rapid continuous flush <strong>of</strong> an arterial line, how long should you<br />
continuously flush at any given time?<br />
A. No more than 3 seconds<br />
B. 3-5 seconds<br />
C. 15 seconds<br />
D. 30 seconds<br />
13. You are preparing to remove a central venous catheter. You place the patient flat and<br />
instruct him to hold his breath during removal <strong>of</strong> the catheter to prevent:<br />
A. Pneumothorax<br />
B. Atrial dysrhythmias<br />
C. Air embolization<br />
D. Bleeding<br />
14. You are caring for a patient with a right radial arterial line. Upon assessment, you note<br />
the patient’s right hand to be cool and dusky. The fingernails blanch poorly, and capillary<br />
filling is extremely prolonged. Which complication <strong>of</strong> intra-arterial lines is the most<br />
likely explanation?<br />
A. Local infection at the insertion site<br />
B. Vascular insufficiency caused by the catheter, arterial spasm or plaque<br />
C. Hypovolemia due to bleeding at the puncture site<br />
D. Air bubbles in the transducer<br />
15. You are caring for a patient with a left radial arterial line. Based on the pressure tracing<br />
below, which has a scale <strong>of</strong> 0/40/80/120, what value should you document for this<br />
patient’s blood pressure?<br />
A. 180/82<br />
B. 120/55<br />
C. 110/55<br />
D. 86/42<br />
16. Invasive monitoring <strong>of</strong> central venous pressure is indicated for:<br />
A. <strong>Monitoring</strong> <strong>of</strong> right ventricular afterload<br />
B. Administration <strong>of</strong> fibrinolytic medications<br />
C. <strong>Monitoring</strong> <strong>of</strong> vena cava injuries<br />
D. <strong>Monitoring</strong> <strong>of</strong> right ventricular preload<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
17. The CVP <strong>of</strong> a patient in normal sinus rhythm is calculated by averaging the:<br />
A. Peak and trough <strong>of</strong> the A wave<br />
B. Peak and trough <strong>of</strong> the V wave<br />
C. Top <strong>of</strong> the V waves during inspiration<br />
D. Midpoint <strong>of</strong> the Y descent<br />
18. The central venous pressure (CVP) most closely reflects:<br />
A. Volume within the right ventricle just before ventricular contraction<br />
B. Pressure within the right ventricle just before ventricular contraction<br />
C. The volume <strong>of</strong> blood ejected from the right ventricle during systole<br />
D. The resistance to ejection <strong>of</strong> blood from the right ventricle during systole<br />
19. Which <strong>of</strong> the following conditions can cause an increase in the CVP?<br />
A. Arterial vasoconstriction, tachycardia and decreased preload<br />
B. Arterial vasoconstriction, decreased contractility, and elevated preload<br />
C. Arterial vasodilation, tachycardia and bronchospasm<br />
D. Arterial vasodilation, venous vasodilation and third spacing<br />
20. Which <strong>of</strong> the following conditions can cause a decrease in the CVP?<br />
A. Pneumothorax<br />
B. Tricuspid regurgitation<br />
C. Pulmonary hypertension<br />
D. Severe sepsis<br />
21. You are caring for a 71-year old female patient who was admitted with a diagnosis <strong>of</strong><br />
COPD and respiratory failure. Her cardiac monitor shows atrial fibrillation with a<br />
ventricular response <strong>of</strong> 90-100. In this case, the CVP is read by drawing a vertical line to<br />
the CVP waveform from the<br />
A. Beginning <strong>of</strong> the P wave on the ECG<br />
B. End <strong>of</strong> the P wave on the ECG<br />
C. End <strong>of</strong> the QRS on the ECG<br />
D. Beginning <strong>of</strong> the T wave on the ECG<br />
22. Numeric values should be taken from the hemodynamic waveform:<br />
A. While the patient holds his breath<br />
B. With the patient flat<br />
C. At end-inspiration<br />
D. At end-expiration<br />
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23. According to the waveform below, the CVP is:<br />
Spontaneous Ventilation<br />
A. 6 mm Hg<br />
B. 8 mm Hg<br />
C. 12 mm Hg<br />
D. 17 mm Hg<br />
<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
24. You are caring for a patient in normal sinus rhythm with a central venous catheter who is<br />
on a mechanical ventilator. The CVP waveform rises and falls with the patient’s<br />
respiratory cycle. The monitor gives a digital CVP reading <strong>of</strong> 32. How can you most<br />
accurately determine the correct CVP reading?<br />
A. Take the CVP reading immediately following the QRS complex<br />
B. Take the CVP reading by averaging the peak and trough <strong>of</strong> the A wave closest to<br />
the end <strong>of</strong> expiration<br />
C. Determine the average <strong>of</strong> the CVP reading throughout the respiratory cycle<br />
D. Report the value <strong>of</strong> the lowest point on the CVP tracing<br />
25. You are caring for a post-operative patient following vascular surgery who has a right<br />
radial intra-arterial line. The monitor has been displaying an intra-arterial blood pressure<br />
<strong>of</strong> approximately 128/70 for the past two hours since the patient returned from PACU.<br />
Unexpectedly, the monitor alarms and displays an intra-arterial blood pressure <strong>of</strong> 64/40.<br />
Which <strong>of</strong> the following actions should receive the highest priority at this time?<br />
A. Pull back, rotate, or reposition the catheter<br />
B. Place the patient flat in bed and level the transducer at the phlebostatic axis<br />
C. Assess the patient for signs <strong>of</strong> low blood pressure, then check the system<br />
D. Open the patient’s IV wide to provide intravascular volume and restore fluid<br />
balance<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Appendix 1: Troubleshooting Arterial and CVP <strong>Monitoring</strong> Systems<br />
Overdamping or absent pressure wave form<br />
Causes Prevention Intervention<br />
Catheter tip against<br />
vessel wall<br />
Partial occlusion <strong>of</strong><br />
catheter due to clot<br />
formation<br />
Secure catheter after insertion to<br />
prevent movement<br />
Eliminate kinks from tubing<br />
Use continuous flush device under 300<br />
mm Hg pressure<br />
Consider heparinized flush solution<br />
Positional catheter Immobilize area <strong>of</strong> catheter insertion<br />
Securely tape catheter at insertion site<br />
Air bubbles in<br />
transducer or<br />
connector tubing<br />
Pressure bag not at<br />
300 mm Hg<br />
Carefully flush transducer and tubing<br />
during set-up<br />
Maintain tight connections<br />
Do not allow flush solution bag to<br />
completely empty<br />
Keep flush solution drip chamber<br />
completely full<br />
Pull back, rotate, or reposition<br />
catheter<br />
Aspirate clot with a syringe. Then<br />
flush line for 2-3 seconds using the<br />
intraflow valve<br />
Reposition external portion <strong>of</strong><br />
catheter (CVP)<br />
Reposition patient to eliminate<br />
kinks in the monitoring catheter<br />
Check system, aspirate air, close<br />
system to patient, disconnect<br />
transducer and flush out air<br />
bubbles, reconnect system<br />
maintaining sterility, inspect for<br />
any bubbles and aspirate if needed,<br />
fast flush<br />
Maintain pressure bag at 300 mm Hg Inflate pressure bag to 300 mm Hg<br />
Stopcock turned <strong>of</strong>f Maintain stopcocks in proper position<br />
Keep stopcocks visible and out <strong>of</strong><br />
reach <strong>of</strong> patient<br />
Transducer placed<br />
too high<br />
Maintain transducer at the level <strong>of</strong> the<br />
4 th intercostal space at mid-chest<br />
(phlebostatic axis)<br />
Improper scale Maintain scale to approximate<br />
expected pressures. Scales that are<br />
much higher than the pressure<br />
displayed will cause waveform<br />
components to disappear.<br />
Tubing or<br />
connections<br />
loosened<br />
Prevent tubing from kinking; maintain<br />
tight connections<br />
Turn stopcock to proper position<br />
Return transducer to proper level<br />
Adjust scale to approximate<br />
pressure to obtain adequate<br />
waveform<br />
Tighten all connections; straighten<br />
any kinks in tubing<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Excessively high pressure waveform (including catheter whip or fling)<br />
Causes Prevention Intervention<br />
Excessive catheter<br />
movement in vessel,<br />
excessive tubing<br />
length, catheter too<br />
small for vessel<br />
Transducer placed<br />
too low<br />
Use optimal size catheter for artery,<br />
and correct semi-rigid tubing; Do not<br />
use excess extension tubing<br />
Maintain transducer at the level <strong>of</strong> the<br />
4 th intercostal space at mid-chest<br />
(known as the phlebostatic axis)<br />
Inability to flush line or to withdraw blood<br />
Causes Prevention Intervention<br />
Clot on catheter tip,<br />
kinked tubing,<br />
incorrect stopcock<br />
positioning, catheter<br />
bent or positional,<br />
inadequate pressure<br />
in pressure bag<br />
Maintain<br />
pressure bag at 300 mm Hg<br />
stopcock and tubing in proper<br />
position<br />
joint at insertion site in straight<br />
line position<br />
Reduce tubing length by removing<br />
any extensions and stopcocks that<br />
are not necessary, observe for and<br />
remove micro-bubbles from tubing<br />
Return transducer to proper level<br />
Check position <strong>of</strong> stopcocks, tubing<br />
and joint underlying insertion site;<br />
use immobilization device if<br />
necessary; check pressure in<br />
pressure bag and inflate to 300 mm<br />
Hg if necessary.<br />
If problem cannot be resolved,<br />
notify physician and prepare for<br />
possible removal <strong>of</strong> catheter; label<br />
affected ports “do not use”<br />
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<strong>Fundamentals</strong> <strong>of</strong> <strong>Hemodynamic</strong> <strong>Monitoring</strong><br />
Appendix 2: Accurate Measurement <strong>of</strong> Noninvasive Blood Pressure<br />
In order to obtain an accurate blood pressure measurement the equipment must be functioning<br />
correctly. If a mercury manometer is used, check that there is no cloudiness in the chamber, the<br />
meniscus is exactly at zero and the meniscus can be viewed at eye level. If an aneroid<br />
manometer is used, check that the needle is at zero at the start and end <strong>of</strong> the pressure<br />
measurement, and position the manometer in your direct line <strong>of</strong> vision. Suspect a cuff leak if<br />
the pressure on the manometer does not rise steadily as the cuff is inflated. Also, check to see<br />
that the screw valve on the bulb is functioning well.<br />
Follow these steps to take accurate blood pressure measurements:<br />
1. Select the appropriate size cuff. Compare the length <strong>of</strong> the bladder inside the cuff with the<br />
circumference <strong>of</strong> the patient’s arm. If the bladder is at least 80% <strong>of</strong> arm circumference and<br />
does not overlap itself, the size is correct. A cuff that is too small will cause a false high<br />
reading and a cuff that is too large will result in a false low reading.<br />
2. Palpate the brachial artery along the inner arm. Avoid measuring blood pressures in an arm<br />
that has an I.V., shunt, edema, injury or paralysis.<br />
3. Wrap the cuff smoothly and snugly around the upper arm, centering the bladder over the<br />
brachial artery. Don’t place the cuff over clothing or let a rolled-up sleeve constrict the arm.<br />
The lower cuff edge should be one inch above the antecubital space. Instruct the patient not<br />
to talk during the measurement. Support the patient’s arm at the level <strong>of</strong> his heart, and flex<br />
the elbow slightly.<br />
4. Determine the level <strong>of</strong> maximum inflation by rapidly inflating the cuff until you can no<br />
longer feel the brachial pulse, and add 30 mm Hg to that reading.<br />
5. Deflate the cuff rapidly and and steadily, then wait 15 – 30 seconds before reinflating.<br />
6. Insert the earpieces <strong>of</strong> the stethoscope, making sure they point forward and apply the bell <strong>of</strong><br />
the stethoscope lightly but with complete contact over the brachial pulse. Korotk<strong>of</strong>f’s<br />
sounds are low frequency and may be missed when listening with the diaphragm <strong>of</strong> the<br />
stethoscope.<br />
7. Inflate the cuff rapidly and steadily to the level <strong>of</strong> maximum inflation determined in step 4.<br />
8. Release the air slowly so the pressure falls at a rate <strong>of</strong> 2 – 3 mm Hg per second, listening<br />
for the onset <strong>of</strong> at least two consecutive beats. Note the closest mark on the manometer, this<br />
is the systolic pressure.<br />
9. Listen for the cessation <strong>of</strong> sound (or a muffling <strong>of</strong> sound in children), this is the diastolic<br />
pressure. Continue listening for 10 – 20 mm Hg below the last sound to confirm the<br />
reading, then make sure to deflate the cuff rapidly and completely.<br />
10. If you need to repeat the measurement, wait 1 – 2 minutes so the blood trapped in the arm<br />
veins can be released.<br />
If an automatic blood pressure cuff is used, follow the same procedure for finding the correct<br />
size and placing the cuff on the arm. Automatic cuff measurements are frequently inaccurate. If<br />
an automatic cuff is used, an initial pressure reading must be compared to a blood pressure<br />
obtained using a manual cuff. If there is more than 10 mm Hg difference between the automatic<br />
and manual cuff measurements, the automatic cuff should not be used. When using an<br />
automatic cuff, remove the cuff from the arm after each measurement to prevent skin<br />
breakdown. If frequent automatic cuff measurements must be taken, remove the cuff as soon as<br />
clinically feasible. If frequent blood pressure measurements are required for a period longer<br />
than a few hours, consider whether invasive measurement <strong>of</strong> blood pressure is warranted.<br />
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