Advanced Trauma Life Support ATLS Student Course Manual 2018
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Advanced Trauma Life Support ATLS Student Course Manual 2018

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ANATOMICAL AND PHYSIOLOGICAL ALTERATIONS OF PREGNANCY 229 n FIGURE 12-2 Full-Term Fetus in Vertex Presentation. The abdominal viscera are displaced and compressed into the upper abdomen. This results in their relative protection from blunt injury, but increased risk for complex intestinal injury from upper abdominal penetrating injury. Elevation of the diaphragm may require placement of chest tubes through a higher intercostal space. elastic tissue results in vulnerability to shear forces at the uteroplacental interface, which may lead to abruptio placentae (n FIGURE 12-2). The placental vasculature is maximally dilated throughout gestation, yet it is exquisitely sensitive to catecholamine stimulation. An abrupt decrease in maternal intravascular volume can result in a profound increase in uterine vascular resistance, reducing fetal oxygenation despite reasonably normal maternal vital signs. Blood Volume and Composition Plasma volume increases steadily throughout pregnancy and plateaus at 34 weeks of gestation. A smaller increase in red blood cell (RBC) volume occurs, resulting in a decreased hematocrit level (i.e., physiological anemia of pregnancy). In late pregnancy, a hematocrit level of 31% to 35% is normal. Healthy pregnant patients can lose 1,200 to 1,500 mL of blood before exhibiting signs and symptoms of hypovolemia. However, this amount of hemorrhage may be reflected by fetal distress, as evidenced by an abnormal fetal heart rate. The white blood cell (WBC) count increases during pregnancy. It is not unusual to see WBC counts of 12,000/mm 3 during pregnancy or as high as 25,000/ mm 3 during labor. Levels of serum fibrinogen and other clotting factors are mildly elevated. Prothrombin and partial thromboplastin times may be shortened, but bleeding and clotting times are unchanged. n TABLE 12-1 compares normal laboratory values during pregnancy with those for nonpregnant patients. (Also see Normal Lab Values during Pregnancy on MyATLS mobile app.) Hemodynamics Important hemodynamic factors to consider in pregnant trauma patients include cardiac output, heart rate, blood pressure, venous pressure, and electrocardiographic changes. Cardiac Output After the 10th week of pregnancy, cardiac output can increase by 1.0 to 1.5 L/min because of the increase in plasma volume and decrease in vascular resistance of the uterus and placenta, which receive 20% of the patient’s cardiac output during the third trimester n BACK TO TABLE OF CONTENTS

230 CHAPTER 12 n Trauma in Pregnancy and Intimate Partner Violence table 12-1 normal laboratory values: pregnant vs. nonpregnant VALUE PREGNANT NONPREGNANT Hematocrit 32%–42% 36%–47% WBC count 5,000–12,000 μL 4,000–10,000 μL Arterial pH 7.40–7.45* 7.35–7.45 Bicarbonate 17–22 mEq/L 22–28 mEq/L PaCO 2 Fibrinogen 25–30 mm Hg (3.3–4.0 kPa) 400-450 mg/dL (3rd trimester) 30–40 mm Hg (4.0–5.33 kPa) 150-400 mg/dL PaO 2 100–108 mm Hg 95–100 mm Hg * Compensated respiratory alkalosis and diminished pulmonary reserve Venous Pressure The resting central venous pressure (CVP) is variable with pregnancy, but the response to volume is the same as in the nonpregnant state. Venous hypertension in the lower extremities is present during the third trimester. Electrocardiographic Changes The axis may shift leftward by approximately 15 degrees. Flattened or inverted T waves in leads III and AVF and the precordial leads may be normal. Ectopic beats are increased during pregnancy. Pitfall Not recognizing the anatomical and physiological changes that occur during pregnancy prevention • Review physiology in pregnancy during the pretrauma team time-out. of pregnancy. This increased output may be greatly influenced by the mother’s position during the second half of pregnancy. In the supine position, vena cava compression can decrease cardiac output by 30% because of decreased venous return from the lower extremities. Heart Rate During pregnancy, the heart rate gradually increases to a maximum of 10–15 beats per minute over baseline by the third trimester. This change in heart rate must be considered when interpreting a tachycardic response to hypovolemia. Respiratory System Minute ventilation increases primarily due to an increase in tidal volume. Hypocapnia (PaCO 2 of 30 mm Hg) is therefore common in late pregnancy. A PaCO 2 of 35 to 40 mm Hg may indicate impending respiratory failure during pregnancy. Anatomical alterations in the thoracic cavity seem to account for the decreased residual volume associated with diaphragmatic elevation, and a chest x-ray reveals increased lung markings and prominence of the pulmonary vessels. Oxygen consumption increases during pregnancy. Thus it is important to maintain and ensure adequate arterial oxygenation when resuscitating injured pregnant patients. Blood Pressure Pregnancy results in a fall of 5 to 15 mm Hg in systolic and diastolic pressures during the second trimester, although blood pressure returns to nearnormal levels at term. Some pregnant women exhibit hypotension when placed in the supine position, due to compression of the inferior vena cava. This condition can be corrected by relieving uterine pressure on the inferior vena cava, as described later in this chapter. Hypertension in the pregnant patient may represent preeclampsia if accompanied by proteinuria. Pitfall Failure to recognize that a normal PaCO 2 may indicate impending respiratory failure during pregnancy prevention • Predict the changes in ventilation that occur during pregnancy. • Monitor ventilation in late pregnancy with arterial blood gas values. • Recognize that pregnant patients should be hypocapneic. n BACK TO TABLE OF CONTENTS

ANATOMICAL AND PHYSIOLOGICAL ALTERATIONS OF PREGNANCY 229<br />

n FIGURE 12-2 Full-Term Fetus in Vertex Presentation. The abdominal viscera are displaced and compressed into the upper abdomen. This<br />

results in their relative protection from blunt injury, but increased risk for complex intestinal injury from upper abdominal penetrating injury.<br />

Elevation of the diaphragm may require placement of chest tubes through a higher intercostal space.<br />

elastic tissue results in vulnerability to shear forces at<br />

the uteroplacental interface, which may lead to abruptio<br />

placentae (n FIGURE 12-2).<br />

The placental vasculature is maximally dilated<br />

throughout gestation, yet it is exquisitely sensitive<br />

to catecholamine stimulation. An abrupt decrease in<br />

maternal intravascular volume can result in a profound<br />

increase in uterine vascular resistance, reducing fetal<br />

oxygenation despite reasonably normal maternal<br />

vital signs.<br />

Blood Volume and Composition<br />

Plasma volume increases steadily throughout pregnancy<br />

and plateaus at 34 weeks of gestation. A smaller<br />

increase in red blood cell (RBC) volume occurs, resulting<br />

in a decreased hematocrit level (i.e., physiological<br />

anemia of pregnancy). In late pregnancy, a hematocrit<br />

level of 31% to 35% is normal. Healthy pregnant patients<br />

can lose 1,200 to 1,500 mL of blood before exhibiting<br />

signs and symptoms of hypovolemia. However, this<br />

amount of hemorrhage may be reflected by fetal distress,<br />

as evidenced by an abnormal fetal heart rate.<br />

The white blood cell (WBC) count increases during<br />

pregnancy. It is not unusual to see WBC counts of<br />

12,000/mm 3 during pregnancy or as high as 25,000/<br />

mm 3 during labor. Levels of serum fibrinogen and<br />

other clotting factors are mildly elevated. Prothrombin<br />

and partial thromboplastin times may be shortened,<br />

but bleeding and clotting times are unchanged.<br />

n TABLE 12-1 compares normal laboratory values during<br />

pregnancy with those for nonpregnant patients. (Also<br />

see Normal Lab Values during Pregnancy on My<strong>ATLS</strong><br />

mobile app.)<br />

Hemodynamics<br />

Important hemodynamic factors to consider in pregnant<br />

trauma patients include cardiac output,<br />

heart rate, blood pressure, venous pressure, and<br />

electrocardiographic changes.<br />

Cardiac Output<br />

After the 10th week of pregnancy, cardiac output can<br />

increase by 1.0 to 1.5 L/min because of the increase in<br />

plasma volume and decrease in vascular resistance<br />

of the uterus and placenta, which receive 20% of the<br />

patient’s cardiac output during the third trimester<br />

n BACK TO TABLE OF CONTENTS

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