Hemodynamics in Critical Care Module 2: Central Monitoring

Hemodynamics Beyond the Basics
Hemodynamics in
Critical Care Module 2:
Central Monitoring
This module will review
– Right arterial pressures / central venous pressures
– Pulmonary artery pressures
– Systemic vascular resistance
– Pulmonary vascular resistance
UOHI Clinical Services 2009
Central Venous Pressure
• Indication of Right Ventricular End Diastolic Volume
– Preload of RV
– Indication of fluid volume
state
CVP / RAP
• The pressure in the right atrium, commonly
referred to as the central venous pressure,
measures how much pressure the blood returning
to the heart is under.
• The venous system has a high capacitance that
means it can adapt to various volume states.
• Veins, by virtue of thinner walls that lack muscles,
stretch when the pressure increases.
• This stretch allows the veins to hold more, but
increases the venous pressure.

RAP
• This can lead to swollen ankles and increased
jugular venous distention.
• When more blood tries to enter the right atrium
than the right atrium can hold, the result is an
increase in the CVP.
• Thus CVP can be an indicator of fluid status.
• More blood volume causes the veins to stretch
and increases the intravenous pressure; less
blood volume causes the veins to constrict and
decreases the intravenous pressure.
RAP
• Though the CVP pressure can inform about fluid
balance, it can be a later indicator.
• Excessive fluid takes awhile to increase the CVP
and frequently there are other indicators such as
rales or pulmonary edema first.
• The CVP also represent the preload of the right
ventricle. Preload is the amount of stretch in a
chamber just before contraction.
CVP/RAP
• The more the stretch, the better the next
contraction (up to a point of course).
• Thus, if the CVP is elevated then the pressure in
the right ventricle, just before contraction is
elevated.
• Conversely, if the CVP is low, then the preload of
the right ventricle is low and the next contraction
will be less efficient
CVP/RAP
• Remember what is going on inside the heart just
before the right ventricle contracts.
• The tricuspid valve is open allowing blood to
move freely between the right atrium and right
ventricle.
• Therefore, the pressure in the right atrium and
right ventricle should be identical, since they are
openly connected.

CVP/RAP
• The CVP is reported as a mean pressure
measurement, not a systolic and diastolic as other
pressures we discuss.
• Normal range for the CVP varies from textbook to
textbook, but a good range is 2 to 6 mmHg.
CVP/RAP
There are many potential causes of CVP elevation;
• fluid overload,
• right heart failure,
• (late) left heart failure
• tricuspid stenosis. which reduces the output of the
right ventricle leaving it too full to receive all the
blood from the right atrium resulting in increased
CVP.
CVP/RAP
• Pulmonary embolism, which also reduces the
output of the right ventricle as above causing
increased CVP.
• Pericardial tamponade –
– the entire heart is under increased pressure
due to the constriction of the pericardium.
– This allows less blood to be pumped forward,
not because of the cardiac dysfunction, but
simply because of the constriction.
CVP/RAP
• Differentiating between each of these causes
relies on interpreting all the hemodynamic
information at our disposal and a careful
assessment of the patient.

CVP/RAP
Waveform - CVP
• Actually 3 separate waves
– a wave – atrial systole
– c wave – peak at opening of tricuspid valve
– v wave – ventricular systole
a wave
x descent
c wave
v wave
y descent
Rise in pressure due to atrial contraction.
a waves are larger in the presence of any resistance to
RV filling, (tricuspid stenosis, RV failure, cardiac
tamponade) because resistance will increase pressure
as the atrium attempts to contract and eject blood.
Fall in pressure due to atrial relaxation.
Rise in pressure due to ventricular contraction and
bulging of the closed tricuspid valve.
Rise in pressure during atrial filling.
Fall in pressure due to the opening of the tricuspid
valve and the beginning of ventricular filling.
CVP/RAP Waveform
CVP/RAP Waveform

Measuring CVP
Measuring CVP
Measuring CVP
Moving from CVP to PA Measurements…
• CVP can be measured via a central line such as a
introducer or the distal port of a triple lumen
catheter
• It can also be obtained via a PA catheter
• Pressures measurements further forward from the
CVP are usually obtained via a PA catheter
(sometimes called a Swan-Ganz catheter)

Pulmonary Artery Pressures
Why insert a PA catheter
• Means to evaluate fluid status
– Indicator of preload
• Means to evaluate LV function
– PAOP, PCWP, wedge
• Means to evaluate CO measurement
– Thermodilution technique
– Intermittent or continuous
PA Catheter
• Multi-lumen, polyvinylchloride catheters with balloon
at the tip
• Flow directed catheter
• Inflation of balloon ensures that blood flow will move
the catheter forward in the direction of blood flow
• Typically bonded with heparin
• Lumens from 2-7
• Length from 60-110 cm
• Size from 4-8 French
PA Catheter
PA Catheter Insertion
• Most PA catheters have 4 lumens
• Prior to insertion
– Balloon lumen for inflation
– Flush all lumens with solution
– Distal lumen in PA
– Check integrity of balloon
– Proximal lumen in RA – drug infusion, CVP
– Always deflate passively!
monitoring
– Prepare fluid filled system that has been
– Thermistor to measure blood temperature
leveled and zeroed
• Other lumens may be used for
– Connect to appropriate lumens
– Temporary transvenous pacing
• PA distal – PA pressures
– Measurement of RVEDV and RVEF
• Proximal infusion – CVP
– Continuous measurement of CO and SvO 2 • Proximal injectate – CO device

PA Catheter
PA Catheter Insertion
PA Catheter Insertion
PA Catheter Insertion
• Waveform at distal tip visualized continuously
(make sure the stopcocks are turned the right way!)
• Balloon fully inflated when CVP wave is visualized
• Catheter advanced with balloon inflated – blood
flow will carry or “float” the catheter through RA, RV
and into PA
• Be sure to use your
handout to become
familiar with how the
tracing appear as the
catheter moves thru the
heart

Pulmonary
Wedge Pressure
Pulmonary
Wedge Pressure
Tracing from RA
Tracing as catheter moves from RA TO RV
Pulmonary
Wedge Pressure
Pulmonary
Wedge Pressure
Tracing as balloon is inflated for PWP

Pulmonary Right Pulmonary Ventricle Atrium Artery
Wedge Pressure
Waveforms - PA
• Changes in waveform as PA catheter is advanced
from the right atrium, rt ventricle into pulmonary
artery
If there is no lung or
mitral valve disease, the
PAD and PWP are
looking forward into the
left ventricle and can tell
us the LVEDP
Tracing as balloon is inflated for PWP
Waveforms - PA
Waveforms - PA
• The PAP is constantly monitored by the distal port
of the PA catheter.
• The pulmonary artery systolic pressure (PAS)
approximates the systolic pressure in the RV, but
the pulmonary diastolic pressure (PAD) is higher,
and the waveform less steep.
• The PA waveform includes a diastolic notch which
represents closure of the pulmonic valve.
• In the absence of lung or mitral valve disease, the
PAD approximates the pulmonary artery wedge
pressure (PAWP) and can, therefore, aid in
evaluation of preload without wedging the
catheter.

PA Pressures
• The pulmonary artery pressure is reported as a
systolic and a diastolic number.
• The normal range for the systolic PAP is 12 - 25
mmHg.
• There is variation in the normal range in various
textbooks
• The diastolic PAP normal range is 7 to 15 mmHg..
• The mean PAP pressure has a normal range of
10 to 15 mmHg.
• A typical reading for the PA pressure is 20/12 with
a mean of 13.
PA Pressures
• The pulmonary artery pressures measure the
resistance of blood flow through the lungs.
• Again fluid overload, left heart failure, constrictive
pericarditis, and pulmonary embolism can all
cause the PAP to increase, but tricuspid and
pulmonic valve stenosis will decrease the PAP
because less blood can be ejected from the right
ventricle.
• The same effect occurs with right ventricular
failure, the lack of blood being pushed into the
pulmonary artery will decrease the PAP readings.
PA Pressures
• Anything that increases the PA pressures will also
lead to elevated CVP pressures, because the
pressure will be transmitted back to the right
ventricle when the pulmonic valve is open.
• And, once the right ventricular pressures are
increased the pressure will be transmitted back to
the right atrium when the tricuspid valve is open.
• But, anything that increases the right atrial or right
ventricular pressures will not necessarily increase
the PA pressures.
• This is helpful in diagnosing the cause of the
pressure problems
PWP or PAD
• The PAOP, colloquially referred to as "the wedge",
gives valuable information about fluid status with
respect to the left side of the heart.
• When this is documented, compare it to the
pulmonary artery diastolic (PAD) pressure.
• They should differ by only a few points, with the
PAD being about 2 to 4 mmHg higher than the
PAD.
• If the PAD is less than 25 mmHg and in the
absence of lung or valvular problems, it is a
adequate reflection of the POAP and can be
used in calculations and indication of LVEDP.

PWP or PAD
• When the PAC balloon is inflated, the pressures
from the right side of the heart can no longer
reach the tip of the catheter.
• The tip of the catheter now measures the
pressures in front of the catheter in the pulmonary
artery.
• But, the pressure in the pulmonary artery in front
of the catheter is really the pressure from the
pulmonary veins pushing back on the blood in the
pulmonary artery.
PWP or PAD
• The pressure pushing back into the pulmonary
veins, comes from the left atrium.
• Therefore, a catheter in the right side of the heart,
can measure pressures in the left side of the
heart.
• There are some caveats however….. If the patient
has pulmonary hypertension or pulmonary
embolism, conditions that specifically alter blood
flow from the right side of the heart to the left side,
then the PAOP does not accurately reflect left
sided pressures
PWP or PAD
• That said, if the PAOP accurately reflects the left
atrial pressure, then we can actually measure the
pressure in the left ventricle - if the mitral valve is
open.
• Remember, if two areas of the heart are openly
connected, the pressure will quickly equalize in
the two chambers.
• If the pressure in the left atrium was higher then
the pressure in the left ventricle when the mitral
valve is open, then blood would move from the
higher pressure area into the lower pressure area
and vice versa.
PWP or PAD
• Therefore, we can measure the pressure in the
left ventricle as long as the mitral valve is open.
And, when is the mitral valve open? - during
diastole, as the left ventricle is filling with blood.
• Therefore, the pressure the PAD/PAOP is
measuring is actually the left ventricular pressure
during diastole, or Left Ventricular End Diastolic
Pressure (LVEDP)!!!
• This pressure actually gives us preload for the left
ventricle, which is directly related to the amount of
stretch the left ventricle has just before it contracts

PWP or PAD
• This is the first indicator of fluid imbalances.
• If the PAD / PAOP is too high, then the pressure
in the left ventricle during diastole is too high.
• This means that the heart is having difficulty
pumping the blood it receives forward.
• In general, this occurs due to fluid overload, or
heart failure of the left ventricle.
• This change occurs as soon as the fluid level
starts to rise and, therefore, is a better indicator
than the CVP.
PWP or PAD
• If the PAD / PAOP is too low, this usually means that
dehydration or volume loss is present.
• The fluid loss can be relative or actual.
• In sepsis fluid leaks from the blood vessels and
enters the interstitial spaces.
• This will cause the PAD / PAOP to decrease as less
blood returns to the heart, specifically the left
ventricle, causing left ventricular preload to
decrease.
• If the fluid loss is actual, as in dehydration or
significant bleeding, then the result to the PAOP is
the same - a decrease.
Cardiac Output
• Cardiac output can be measured with the
pulmonary artery catheter using a method known
as thermodilution.
• Thermodilution refers to injecting fluid, of a known
temperature, and measuring the effect on the
blood as it travels past the pulmonary artery
catheter tip.
• All PACs have a thermistor, which is basically a
temperature measuring device
Cardiac Outputs
• If you inject room temperature D5W into the
injectate port of the pulmonary artery catheter,
then the temperature of the blood will decrease by
an amount related to the relative volumes of the
injected fluid to the amount of blood in the heart.
• The amount of time for the temperature of the
blood to return to normal is directly related tot he
cardiac output.
• When the cool D5W is injected in the heart, the
temperature of the blood is decreased.

Cardiac Outputs
• Then the heart contracts and ejects a certain
percentage of the cooler blood, say 50%.
• Now an equal amount of new, body temperature
blood, mixes with the cooled blood that is left.
• Then the heart contracts again and ejects 50% of
this slightly warmer blood.
• This cycle happens over and over again,
contraction ejects cooled blood and then adds
warmer blood to the mix.
Cardiac Outputs
• How long the process takes to increase the blood
temperature back to pre-injection levels tells us
how fast the heart is pumping blood out of the
heart - the cardiac output
• This temperature change can be represented as a
graph of the temperature difference between the
pre-injection blood and the post-injection blood
Cardiac Outputs
• On this strip, you will see three examples of this
graph.
Cardiac Outputs
• The curves first grow taller as the injected blood
gets ejected and passes the thermistor.
• Then the curves begin to grow smaller slowly as
progressively warmer blood begins to pass by the
temperature sensor.
• The height of the curve represents the change in
temperature and the length of the curve
represents how much time has passed.

SVR
• Systemic vascular resistance, SVR for short,
measures the resistance to ejecting blood from
the left ventricle. It is a calculated value that is
given by the formula
• We can calculate cardiac output and can measure
CVP and MAP (mean arterial pressure).
SVR
• This value is effected by total blood volume and
artery size.
• Dilated arteries decrease the resistance to
ejecting blood and therefore lower SVR.
• Conversely, constricted arteries cause the SVR to
rise.
• This is one way the body regulates cardiac output
and blood pressure.
SVR
• Small changes in the diameter of a blood vessel
has dramatic effects on the pressure needed to
push blood through that artery.
• If you double the size of the artery, you need
1/16th of the pressure to push blood through it.
• If you cut the artery size in half, then you need 16
times as much pressure to get the blood through
that artery.
PVR
• Pulmonary Vascular Resistance
– Tells us how hard the right heart has to work to
get blood through the lungs and back to the left
heart
Mean pulmonary arterial Pressure -PWP
Pulmonary Vascular Resistance = x 80
Cardiac Output
• Normal values range from 20-120 dynes/sec/cm -5
• Issues that may increase pulmonary vascular
resistance and in turn right ventricular afterload
include pulmonary emboli, pulmonary edema,
sepsis, acidosis, hypoxemia, pulmonary
hypertension and some congenital or valvular heart
diseases.

PVR
• Factors that may decrease PVR include the use
of pulmonary vasodilator drugs or gases and the
correction of hypoxemia or acidemia.
You’re done !!
• Take a moment to go to Classmarker and
challenge yourself with a quiz