Cardiopulmonary arrest in pregnancy is uncommon, occurring only once in every 12,000 obstetrical admissions. Even at the busiest medical centers, this will only total a few obstetrical arrests per year; therefore, few clinicians have had the experience of running many obstetrical codes. There are no published randomized controlled clinical trials of cardiopulmonary resuscitation (CPR) during pregnancy. Most recommendations are supported only by physiological principles and observational studies. The maternal mortality of obstetrical arrest is over 50%.

Advanced cardiac life support (ACLS) guidelines have been developed with a focus on sudden death from ischemic heart disease. Although acute myocardial infarction is increasingly recognized as a cause of maternal arrest during pregnancy, many of the causes of maternal arrest are unique to pregnancy. This and the distinctive physiology of pregnancy necessitate a specific approach to management. The life of the fetus must be highly regarded with the consideration that best outcomes for the baby are likely to be achieved by focusing on resuscitation of the mother. The single most important factor for improving survival is a well-prepared, time-conscious, team approach.

The focus of this chapter will be to help you plan such an approach. We will review (1) pertinent pathophysiology, (2) preparation for ACLS response, (3) how to run an obstetrical code from the perspective of the code leader, (4) the causes of obstetric arrest, and (5) postresuscitative care. It should be noted that the ACLS guidelines published by American College of Cardiologists are the standard in the United States. These are available online at http://circ.ahajournals.org/. Nothing in this chapter should be interpreted as conflicting with these guidelines, but I have taken the liberty of offering simplification in a few areas, while expounding on others.

Current ACLS guidelines have a strong emphasis on minimally interrupted, high-quality CPR.

There are three major specific modifications for the pregnant patient: (1) leftward displacement of the uterus during chest compressions, (2) anticipation of a difficult airway/benefit of early intubation, and (3) consideration of perimortem cesarean delivery within 4 minutes of onset of arrest. These three items are easy to remember and are the most important contents of this chapter.

Fetal and maternal circulation interface at the placenta, driving gas exchange between mother and baby. The maternal cardiopulmonary adaptation to pregnancy provides a balanced delivery of oxygen to maternal and fetal tissues with robust protective mechanisms. Maternal plasma volume and red blood cell mass increase augmenting blood volume by 40% (>1000 mL). The left ventricle dilates and becomes more compliant, increasing stroke volume and cardiac output by 40%. The high oxygen affinity of fetal hemoglobin facilitates oxygen exchange across the placenta and maternal respiratory alkalosis provides a gradient for CO₂ exchange. Uterine contractions during labor result in maternal auto-transfusion, enhancing oxygen delivery when it is needed most. Clinical experience and animal experimentation indicate that during normal pregnancy, maternal systemic and uterine oxygen delivery far exceed the minimal level necessary to sustain maternal and fetal life—with a remarkable reserve to compensate for life-threatening conditions. This can sometimes obscure the lethality of a deteriorating patient’s condition—an obstetrical patient can lose as much as 1500 mL of blood before hemodynamic instability is apparent. During cardiopulmonary arrest, however, oxygen delivery to maternal tissue and the uterus is dramatically reduced or completely eliminated. Maternal or fetal adaptations to catastrophic insult are insufficient to sustain tissue viability. Death begins within minutes.

Pathophysiologic Rationale for CPR Recommendations in Pregnancy

Some normal physiologic changes of late pregnancy have deleterious effects on oxygen delivery. By approximately 20 weeks’ gestation, the gravid uterus begins to compress abdominal and pelvic blood vessels, particularly the inferior vena cava and aorta. This diminishes preload to the heart, decreases maternal stroke volume, and may decrease uteroplacental oxygen delivery. In about 10% of women, these effects are so profound that hypotension is evident in the supine position even in the absence of illness. Therefore, relief of uterine aortocaval compression may profoundly benefit maternal hemodynamics.

In nonpregnant patients, chest compression is estimated to produce cardiac output approximately 30% of normal. The effectiveness of chest compressions in pregnancy is diminished by aortocaval compression and may be as low as 10% of normal. In healthy late-term pregnancy, the gravid uterus can be shifted off the inferior vena cava if the patient is positioned in left lateral decubitus position, increasing cardiac output by 25%. However, CPR force generation is reduced by left decubitus positioning during arrest. Therefore, when performing CPR on patients with gestational ages more than 20 weeks, manual displacement of the uterus to the left is a better first option (Fig. 17-1). If gestational dates are unknown, palpation of the fundus at or above the umbilicus will identify patients most likely to benefit from manual displacement of the uterus. Fundal height can be misleading in some cases (eg, multiple gestation, intrauterine growth retardation, oligohydramnios, fibroids, etc) but may be the best available data in a dire emergency. Portable ultrasound for determining gestational age should not interfere with resuscitation.

The most recent update to ACLS guidelines (2015 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care) emphasizes the importance of high-quality CPR. Rapid initiation of CPR increases survival to discharge. Even a brief delay between interruption of chest compressions and shock significantly reduces defibrillation success rates. CPR should be started immediately once pulselessness is identified and should not be interrupted—even for intravenous line placement or cesarean delivery—except as briefly as possible (<10 seconds) when indicated by ACLS protocol—to assess cardiac rhythm, administer a shock, or rotate CPR providers. The optimal rate of compression is 100 to 120/min, with a compression depth of 2 in. Complete recoil of the chest should be allowed between compressions. If waveform capnography is used to monitor CPR effectiveness, the partial pressure of end-tidal CO₂ should exceed 10 mm Hg. If an arterial line is present, diastolic pressures should exceed 20 mm Hg.

Pathophysiologic Rationale for Perimortem Cesarean Section—the Four-Minute Rule

See Fig. 17-2.

Although the maneuvers discussed above may partially relieve aortocaval compression, perimortem cesarean delivery is likely to be much more effective. It has been shown that cesarean delivery immediately increases cardiac output by 60% in healthy women. Delivery drastically reduces the perfusion demands of the uterus and placenta, which consume approximately 30% of maternal cardiac output near term; it also provides an approximate 500 mL autotransfusion. Delivery also allows resuscitative access to the infant.

As pregnancy progresses, increasing aortocaval compromise by the enlarging uterus and improving viability of the fetus leads to three clinically important pathophysiologic states, as seen in Table 17-1. At less than 20 weeks, significant aortocaval compression is unlikely, the fetus is not viable, and perimortem cesarean delivery is unlikely to benefit mother or child. From 20 to 24 weeks, maternal hemodynamic benefit and fetal viability are both questionable. At greater than 24 weeks, perimortem cesarean delivery is most likely to benefit mother and infant.

The specific recommended timing of perimortem cesarean delivery is based on observational reports. Katz and colleagues have reviewed all published data on perimortem cesarean deliveries from 1900 through 2004. Their combined analyses show that 71% of babies who survived maternal arrest with good neurologic outcome were delivered in 5 minutes or less (Table 17-2) and that the rate of neurologic injury among survivors increases dramatically if delivery is further delayed. Maternal benefit of perimortem cesarean delivery is less well documented, but many case reports describe dramatic immediate maternal recovery upon perimortem cesarean. Publication bias should be considered when interpreting these reports.

Although we teach the “Four-minute rule,” and find it helps the code team balance priorities in an extremely stressful situation, the decision of when to perform a perimortem cesarean-section (C-section) is complex and dependent on rapidly-changing bedside situation and on the resources of the healthcare delivery system. A great deal of preparation before and during a code is necessary to successfully complete a perimortem cesarean within 5 minutes, and it is likely that few achieve this ideal. The consensus committee on ACLS guidelines concluded that the heterogeneity of patient circumstances and the observational nature of the evidence does not allow for a rigid mandate regarding the timing of perimortem cesarean delivery and therefore recommended only that delivery should be “considered” at 4 minutes. When rapid delivery is impossible to achieve, a delayed procedure might still provide benefit. Maternal survival has been reported after up to a 15-minute delay to perimortem cesarean and infant survival after up to a 30-minute delay. Conversely, it is prudent to proceed immediately to cesarean delivery if there is no hope for maternal survival, CPR is ineffective, or the cause of the arrest is extremely unlikely to be reversed within 4 minutes. A resuscitation algorithm has been recently proposed recommending immediate perimortem cesarean in all maternal arrests after 20 weeks gestation that present with a nonshockable rhythm. We recommend discontinuing fetal monitoring during a code because it does not inform ACLS decisions and has the potential to confound decision-making.

Pathophysiologic Rationale for Early Endotracheal Intubation

Perimortem cesarean delivery typically requires maternal intubation. The physiologic changes of late pregnancy increase the risk for life-threatening complications during endotracheal intubation roughly 10-fold. Maternal oxygen consumption is significantly increased, lung compression by the gravid uterus reduces functional residual capacity by 20%, and intrapulmonary shunting increases threefold. These factors result in rapid oxygen desaturation, if gas exchange is interrupted. Edema and hyperemia of the upper airway make airway bleeding more common and visualization of the vocal cords more difficult. Furthermore, if preeclampsia is present, airway edema can be further exacerbated with fluid overload. Additionally, progesterone causes decreased gastric motility while simultaneously relaxing esophageal sphincter tone, thereby increasing risk for aspiration.

Thus, the decision to forego prolonged bag-mask ventilation and proceed directly to endotracheal intubation is often indicated in the pregnant patient. Intubation should be performed by the most experienced person available with equipment for difficult airway management available at the bedside. Aspiration risk may be reduced by avoiding prolonged bag-masking which causes gastric distention increasing the risk of passive aspiration. Use of neuromuscular blocking agents to achieve rapid sequence intubation (RSI) can help to prevent vomiting in patients who have intact airway defenses, but are not typically necessary in a code. Proper “sniff position” of the head and neck facilitates direct laryngoscopy. Airway edema may necessitate the use of slightly smaller endotracheal tubes, and the Bougie endotracheal tube introducer can be helpful when laryngoscopic view is difficult.

Nonemergent intubation during pregnancy may actually cause arrest if airway difficulties arise. Therefore, in our practice, the obstetric team and a back-up physician experienced in airway management are notified prior to elective intubation of all pregnant women. The airway anatomy is assessed for potentially difficult endotracheal tube placement and a plan is made for a primary and at least two secondary methods to secure the airway. Equipment necessary to carry out these alternatives, such as a laryngeal mask airway, video laryngoscope, and percutaneous cricothyrotomy kit, are made available at the bedside. Placement of a nasogastric tube is considered to reduce the risk of aspiration pneumonitis (Mendelson syndrome). We often use a high-flow nasal cannula to provide 100% FiO₂ to preoxygenate our pregnant patients and leave the oxygen flowing during the intubation procedure in the attempt to increase the duration of time during RSI before desaturation occurs.

Code Pharmacology and Cardioversion

Little information is available regarding the use of code medications in pregnancy. But there is wide consensus that fetal survival is most dependent on restoring maternal resuscitation. Therefore, concerns regarding teratogenicity or effects of vasopressor agents on uterine blood flow should not restrict the use of any drug recommended to be used in ACLS. The electrical impedance of the chest wall is not altered by pregnancy; therefore, standard defibrillation and cardioversion energies apply in pregnancy. Deleterious effects of maternal defibrillation/cardioversion have not been reported in infants.

Much of the work involved in successfully conducting ACLS for a mother and baby occurs well beforehand. An institution caring for pregnant patients should have a protocol in place to immediately provide the required personnel and equipment to run a successful obstetrical code on a 24/7 basis. The code team should include the adult cardiac arrest team, an obstetrician, labor and delivery nurse, the obstetrical anesthesiologist, and the neonatal and adult intensive care unit (ICU) teams (Fig. 17-3).