Resuscitation in Pregnancy

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11 Resuscitation in Pregnancy

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

Hemorrhage

During routine vaginal delivery, the average blood loss is 500 mL. Excessive blood loss or postpartum hemorrhage complicates 4% of vaginal deliveries.5 Common causes of hemorrhage around the time of delivery are uterine atony (excessive bleeding with a large relaxed uterus after delivery), vaginal or cervical tears, retained fragments of placenta, placenta previa, placenta accreta, and uterine rupture. Hereditary abnormalities in blood clotting may cause hemorrhage, so inquiries about excessive bleeding, known disorders, and family history are relevant in a patient with excessive bleeding.

Nonhemorrhagic Shock

Causes of nonhemorrhagic obstetric shock—pulmonary embolism, amniotic fluid embolism, acute uterine inversion, and sepsis—are uncommon but are responsible for the majority of maternal deaths in the developed world.6 These conditions must be diagnosed and treated expeditiously. Patients in whom pulmonary embolism is suspected should be administered heparin and then undergo diagnostic imaging. Although fibrinolytic agents are contraindicated in pregnancy, they have been used successfully in patients with life-threatening pulmonary embolism and ischemic stroke. Treatment of amniotic fluid embolism is supportive, the goals being to maintain maternal oxygenation and support blood pressure. Some case reports describe success with the use of cardiopulmonary bypass to treat women suffering from amniotic fluid embolism.

Acute uterine inversion can also cause shock. Cardiovascular collapse complicates approximately half the cases of acute uterine inversion. Classically, the extent of the shock is out of proportion to the blood loss noted. One theory to explain this observation is that a parasympathetic reflex causes neurogenic shock from stretching of the broad ligament or compression of the ovaries (or both) as they are drawn together. Uterine replacement combined with vigorous fluid resuscitation, including blood transfusion as required, should reverse the hypotension.7

Diagnostic Testing

Interventions and Procedures

A fundamental principle in treating pregnant women is that fetal well-being depends on maternal well-being. As with all patients in the emergency department (ED), resuscitation starts with the ABCs (airway, breathing, and circulation). One hundred percent oxygen should be administered to the mother early. Hypoxia should be treated aggressively in this patient population because when the mother is hypoxic, oxygen is shunted away from the fetus. Additionally, preoxygenation is important because apnea results in more rapid hypoxia in the setting of pregnancy. Rapid-sequence induction with precautions for aspiration is essential before intubation. Aggressive volume resuscitation, administration of vasopressors if needed, and close attention to the patient’s body position are all very important in the treatment of hypotension in a pregnant patient. Fetal heart monitoring and, ideally, cardiotocographic monitoring should be initiated as soon as possible for patients in the second or third trimester of pregnancy.8

A commercially produced wedge called a Cardiff wedge is available to aid in the resuscitation of pregnant women. It can be placed under the woman’s right side to support her back while she lies in the preferred left lateral tilt position. In the absence of a wedge, a human wedge can be used, with the patient being tilted on the bent knees of a kneeling rescuer. Pillows, towel rolls, and blanket rolls are readily available in EDs and accomplish the same purpose of angling the woman’s back 30 to 45 degrees from the floor (Fig. 11.1). If for some reason the patient must lie on her back, as in the case for adequate cardiopulmonary resuscitation (CPR), a member of the health care team should manually displace the uterus to the left so that it does not rest on the great vessels.

The American Heart Association (AHA) basic life support guidelines should be followed with two modifications:

The AHA advanced cardiac life support (ACLS) guidelines for medications, intubation, and defibrillation for patients in cardiac arrest should be followed for gravid females with one simple exception—a change in placement of the defibrillation paddles and pads:

Defibrillation energy requirements remain the same (Fig. 11.2).9 Defibrillation will not harm the fetus. ACLS medications should be used as needed. It is reasonable to remove external or internal fetal monitoring devices during electrical shock of the mother because of the possibility of creating an electrical arc to the monitoring equipment, but this is unlikely with the electrical current applied to the maternal thorax. Box 11.2 lists the U.S. Food and Drug Administration categories for the various ACLS drug options during pregnancy.

In pregnant patients with trauma who are in need of a thoracostomy, the chest tube must be placed one or two intercostal spaces higher than normal to avoid diaphragmatic injury. An open supraumbilical approach should be used for diagnostic peritoneal lavage in a pregnant patient, with the gravid uterus palpable on abdominal examination.

If return of spontaneous circulation (ROSC) is achieved, effort must be directed at further hemodynamic stabilization. Post–cardiac arrest therapeutic hypothermia has been successful in the setting of early pregnancy and is recommended as for nonpregnant patients.10 In a comatose post–cardiac arrest patient with ROSC, the patient should be cooled as soon as possible and within 4 to 6 hours to 32° C to 34.8° C for a 12-to 24-hour duration to gain the best possible neurologic outcome. If a perimortem cesarean section has not been performed because of gestational age less than 24 weeks, fetal monitoring should be performed during hypothermia in anticipation of bradycardia.11

Perimortem Cesarean Section

The two goals of perimortem cesarean section are to improve the unstable hemodynamics of the mother and minimize morbidity and mortality in the child. If resuscitative efforts, including ACLS algorithms and alleviation of aortocaval compression, fail to improve maternal hemodynamics, perimortem cesarean section must be considered. The likelihood that perimortem cesarean section will result in a living and neurologically normal infant is related to the interval between onset of maternal cardiac arrest and delivery of the infant.12,13 The gestational age of the neonate is also critical. If cesarean section is performed in the ED, it should be done rapidly. Time is of the essence. Fetal viability outside the uterus is best beyond 24 weeks’ gestation, but it is not always possible to know the exact gestational age in the ED. On the basis of case reports, it is recommended that cesarean section be performed in the ED if the gestational age is believed to be more than 20 weeks. At this stage of pregnancy, the fundus is likely to be palpable at or above the level of the umbilicus.

The child should be delivered within 5 minutes of maternal cardiac arrest, so the procedure should be initiated within 4 minutes of failed CPR of the mother. The procedure is summarized in Box 11.3. Maternal CPR should be maintained throughout the procedure to optimize blood flow to the uterus and the mother and should be continued after cesarean section. Once delivery is accomplished, ED personnel should be prepared to resuscitate the neonate. It is important to note that published and anecdotal reports describe return of maternal blood pressure and maternal survival after perimortem cesarean section.14 Successful resuscitation of a pregnant woman and her unborn child requires a coordinated team approach.

References

1 Peters CW, Layon AJ, Edwards RK. Cardiac arrest during pregnancy. J Clin Anesth. 2005;17:229–234.

2 Lewis F, editor. The Confidential Enquiry into Maternal and Child Health (CEMACH). Saving mothers’ lives; reviewing maternal deaths to make motherhood safer—2003-2005. The Seventh Report on Confidential Enquiries.

3 Shah AJ, Kilcline BA. Trauma in pregnancy. Emerg Med Clin North Am. 2003;21:615–629.

4 Mallampalli A, Powner DJ, Gardner MO. Cardiopulmonary resuscitation and somatic support of the pregnant patient. Crit Care Clin. 2004;20:748.

5 Miller DA. Obstetric hemorrhage. OBFocus High Risk Pregnancy. Available at http://www.obfocus.com/high-risk/bleeding/hemorrhagepa.htm

6 Thomas AJ, Greer IA. Non-hemorrhagic obstetric shock. Best Pract Res Clin Obstet Gynaecol. 2000;14:19–41.

7 O’Grady JP, Pope CS. Malposition of the uterus. eMedicine [serial online] June 5, 2006. Available at http://www.emedicine.com/med/topic3473.htm

8 Luppo CJ. Cardiopulmonary resuscitation: pregnant women are different. AACN Clin Issues. 1997;8:574–585.

9 Nanson J, Elcock D, Williams M, et al. Do physiologic changes in pregnancy change defibrillation energy requirements? Br J Anaesth. 2001;87:237–239.

10 Rittenberger J, Kelly E, Jang D, et al. Successful outcome utilizing hypothermia after cardiac arrest in pregnancy: a case report. Crit Care Med. 2008;63:1354–1356.

11 Vanden Hoek T, Morrison LJ, Shuster M, et al. Part 12: cardiac arrest in special situations: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122:S829–S861.

12 Weber CE. Postmortem cesarean section: review of the literature and case reports. Am J Obstet Gynecol. 1971;110:158–165.

13 Oates S, Williams GL, Rees GAD. Cardiopulmonary resuscitation in late pregnancy. BMJ. 1988;297:404–405.

14 Katz V, Balderston K, DeFreest M. Perimortem cesarean delivery: were our assumptions correct? Am J Obstet Gynecol. 2005;192:1916–1920.