Scope

Resuscitation of a pregnant woman is an infrequent event. Cardiac arrest statistics are difficult to quantify, but cardiac arrest reportedly occurs in roughly 1 in 30,000 near-term pregnancies.¹ More recent data suggest an increase in maternal mortality from cardiac arrest, with frequency rates of 1 in 20,000.² In the event of cardiac arrest in a pregnant woman, two lives must be resuscitated. Quick, decisive management is paramount for the livelihood of the mother and her unborn child. Knowing exactly what to do and acting quickly ensure the best possible outcome for the mother and her unborn child.

Anatomy and Physiology

What are generally considered abnormal vital signs in nonpregnant people may actually be within the normal range for a pregnant woman. In gravid females, the heart rate and respiratory rate are increased. In the second trimester, blood pressure is decreased by 5 to 15 mm Hg, but it returns to normal near term. Hypoxemia occurs earlier in pregnant patients because of diminished reserve and buffering capacity. Pregnant patients have a slight respiratory alkalosis—PCO₂ of 30 mm Hg and pH of 7.43—that must be taken into account when interpreting arterial blood gas values. Central venous pressure decreases in pregnancy to a third-trimester value of 4 mm Hg.³

A pregnant woman has less respiratory reserve and greater oxygen requirements. The gravid uterus pushes up on the diaphragm, which results in reduced functional residual capacity. Minute ventilation and tidal volume rise, as does maternal oxygen consumption. The basal metabolic rate increases during pregnancy. The greater oxygen demands of the unborn child significantly alter the mother’s respiratory physiology, and the mother hyperventilates to meet the demands of the fetus. A pregnant patient at baseline is in a state of compensatory respiratory alkalosis because of excessive secretion of bicarbonate. A pregnant woman’s ability to compensate for acidosis is impaired. Other physiologic changes that may affect resuscitation are airway edema and friability, reduced chest compliance, and higher risk for regurgitation and aspiration.

As the uterus grows, it moves from the pelvis into the abdominal cavity, which pushes the contents of the abdominal cavity up toward the chest. In late pregnancy, the gravid uterus compresses the aorta and inferior vena cava and limits venous return to the heart. Stroke volume is decreased when a near-term pregnant woman is lying on her back and increased when the uterus is moved away from the great vessels. A woman in the second or third trimester of pregnancy should be placed in the left lateral tilt position, or the uterus should be manually displaced to the left to optimize cardiac output and venous return. During late pregnancy, cardiac output is increased. Pulmonary capillary wedge pressure remains unchanged, as does the ejection fraction.

Electrocardiographic changes, including left axis deviation secondary to the diaphragm moving cephalad and changing the position of the heart, are also present during pregnancy. Q waves are present in leads III and aVF, and flattened or inverted T waves are seen in lead III.

During pregnancy blood volume increases, which causes a dilution anemia. The average hematocrit value is 32% to 34%. White blood cell counts are higher than normal and platelet counts are lower in pregnancy. Blood urea nitrogen and serum creatinine values are lower than normal, as are cortisol values. The erythrocyte sedimentation rate is increased. Albumin and total protein levels are decreased. Fibrinogen levels double in pregnancy, so a patient with disseminated intravascular coagulation could have a normal fibrinogen level.

Pregnancy-related changes can be seen on radiographic studies. A chest radiograph of a pregnant woman shows an increased anteroposterior diameter, mild cephalization of the pulmonary vasculature, cardiomegaly, and a slightly widened mediastinum. Widening of the sacroiliac joints and pubic symphysis are apparent on imaging of the pelvis. Radiography should not be avoided in a pregnant woman because of concerns about radiation exposure of the fetus, which can simply be shielded. Ultrasonography can be used at the bedside to identify fluid in the abdomen, pelvis, and pericardium and to evaluate fetal activity and heart rate. Fetal well-being is closely linked to the well-being of the mother, so all studies indicated for diagnosis and treatment of the mother should be performed.

Differential Diagnosis

Pregnant women are generally young and healthy. The rare cardiac arrest in a gravid female may be due to venous thromboembolism, severe pregnancy-induced hypertension, amniotic fluid embolism, or hemorrhage. In addition to such pregnancy-related problems, pregnant women are not exempt from common conditions that affect the general population. Trauma and sepsis may lead to cardiopulmonary failure and the need for maternal resuscitation. Box 11.1 lists key etiologic factors leading to cardiac arrest in pregnant patients.⁴