INTRODUCTION — Sudden cardiac arrest (SCA) in pregnancy affects two patients: the mother and the fetus. Depending on availability, management of these patients demands a rapid multidisciplinary approach, including anesthesiology, cardiology, obstetrics, neonatology, and sometimes cardiothoracic surgery [1].

Basic and advanced cardiac life support algorithms should be implemented; however, the physiologic and anatomic changes of pregnancy require some modifications to these protocols (algorithm 1). Randomized trials of approaches to management of pregnant women with SCA are lacking; therefore, recommendations for these modifications are based on expert opinion and data from small case series and small cohort studies involving patients with SCA during cesarean delivery.

This topic will focus on management of SCA during pregnancy. Management of SCA in nonpregnant populations is reviewed separately:

●(See "Overview of sudden cardiac arrest and sudden cardiac death".)

●(See "Supportive data for advanced cardiac life support in adults with sudden cardiac arrest".)

●(See "Advanced cardiac life support (ACLS) in adults".)

●(See "Pathophysiology and etiology of sudden cardiac arrest".)

●(See "Therapies of uncertain benefit in basic and advanced cardiac life support".)

●(See "Approach to sudden cardiac arrest in the absence of apparent structural heart disease".)

TERMINOLOGY — Sudden cardiac arrest (SCA) refers to the sudden cessation of organized cardiac activity with hemodynamic collapse. The event is referred to as SCA if an intervention (eg, defibrillation) or spontaneous reversion restores circulation. The event is called sudden cardiac death if the patient dies. The term "SCA" will be used in this topic to describe both fatal and nonfatal cardiac arrest.

SCA is further subdivided according to cardiac or noncardiac origin. Cardiac origin is assumed if another noncardiac cause is unlikely. Noncardiac causes include hemorrhage, sepsis, anesthetic- and medication-related complications, massive pulmonary embolism, vascular collapse (eg, anaphylaxis, amniotic fluid embolism), and trauma. The obstetric literature generally combines cardiac and noncardiac causes under the umbrella term "sudden cardiac death." This likely results in significant variability in reported cases and in the specific etiologies for sudden death.

The American College of Cardiology/American Heart Association Task Force on Clinical Data Standards published definitions in 2006, which are reviewed separately [2] (see "Overview of sudden cardiac arrest and sudden cardiac death", section on 'Definitions'). The European Society of Cardiology guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death published definitions in 2015 [3].

IDENTIFYING HIGH-RISK WOMEN

Preconception and early pregnancy — Risk assessment to identify those women at increased risk of cardiac complications during pregnancy is advisable, given that cardiac disease is the leading etiology of maternal death. Ideally, risk assessment is performed prior to conception and/or at the time of the initial prenatal evaluation to allow for prepregnancy counseling and for advance multidisciplinary team planning before delivery to optimize outcomes [4,5].

Women with a positive history should be referred to a cardiologist for further evaluation if they are not already under such care. Pregnancy risk indexes (eg, modified World Health Organization classification, Cardiac Disease in Pregnancy study [CARPREG], ZAHARA) have been developed for risk stratification of women with preexisting heart disease. The indexes are described in detail separately. (See "Pregnancy in women with congenital heart disease: General principles", section on 'Maternal cardiovascular risk assessment'.)

Risk assessment involves performing a history/physical examination to identify signs and symptoms of heart disease and medical disorders that may affect cardiac function, obtaining any personal or family history of congenital or acquired cardiovascular disease, and reviewing any available patient-specific data (eg, electrocardiogram, echocardiography, stress testing).

A history of prior arrhythmias, systemic or pulmonary ventricular dysfunction, and prolonged QRS intervals have been identified as risk factors for SCA during pregnancy [3,6]. Risk factors for SCA in the general population should also be considered, and these include hypertension, cigarette smoking, obesity, diabetes mellitus, and a family history of premature coronary heart disease or myocardial infarction. Of note, in a study of the American Heart Association's Get with the Guidelines Resuscitation voluntary registry, which included 462 in-hospital maternal SCAs, approximately one-third had no preexisting conditions or physiologic disorders before the arrest; respiratory insufficiency (36.1 percent) and hypotension/hypoperfusion (33.3 percent) were the most common antecedent conditions [7]. (See "Overview of sudden cardiac arrest and sudden cardiac death", section on 'Risk factors'.)

Late pregnancy — Women who were considered low risk for SCA when presenting for prenatal care and in early pregnancy become high risk if they develop pregnancy-related complications, such as amniotic fluid embolism, cardiomyopathy of pregnancy, postpartum hemorrhage, preeclampsia with severe features, or complications related to anesthesia for delivery. (See 'Etiology' below.)

PREVALENCE — The prevalence of SCA in pregnant women varies from 1 in 20,000 to 1 in 50,000 ongoing pregnancies [8-10]. In the United States, data from the National Inpatient Sample indicated that SCA complicated approximately 1 in 12,000 hospitalizations for delivery between 1998 and 2011, and the frequency remained stable over the interval [11]. Data for Canada between 2002 and 2015 were similar; SCA occurred in 1 in 12,500 deliveries [12].

PATHOPHYSIOLOGY — Arrhythmias due to either cardiomyopathy or a channelopathy are the most common mechanism of SCA in young individuals [13-19]. SCA can occur unpredictably in a predisposed patient or may arise as a result of a combination of a vulnerable substrate (such as preexisting congenital heart disease, valvular disease, cardiomyopathy, or a genetic predisposition to arrhythmias) along with triggers such as hemodynamic shifts, myocardial ischemia, plaque rupture (or coronary dissection), thrombosis, electrolyte abnormalities, and proarrhythmic medications. (See "Pathophysiology and etiology of sudden cardiac arrest".)

The physiologic changes of pregnancy can unmask underlying cardiac disease, increasing the propensity for adverse events. For example, increased progesterone levels can lead to biochemical remodeling in vessel walls that magnify shear forces leading to dissection and rupture. In some otherwise healthy women, SCA occurs as a complication of a pulmonary embolism, severe hemorrhage, or amniotic fluid embolism.

ETIOLOGY

Overview — SCA may be related to conditions unique to pregnancy or etiologies found in the nonpregnant state (table 1). Frequencies by etiology are difficult to summarize because of differences in classification systems.

Two representative large studies are described below:

●A review of the most common causes of SCA in pregnant women in the United States and United Kingdom reported [20]:

•Pulmonary embolism (29 percent)

•Hemorrhage (17 percent)

•Sepsis (13 percent)

•Peripartum cardiomyopathy (8 percent)

•Stroke (5 percent)

•Preeclampsia/eclampsia (2.8 percent)

•Complications related to anesthesia (eg, difficult or failed intubation, local anesthetic toxicity, aspiration, high neuraxial block; 2 percent)

Amniotic fluid embolism, myocardial infarction, preexisting cardiac disease (congenital, acquired, cardiomyopathy), and trauma were additional major causes of cardiac arrest, but the frequencies were not reported.

●The distribution of maternal SCA (n = 4843) from the United States National Inpatient Sample from 1998 to 2011 is shown in the table (table 2) [11].

More recent series have reported high prevalences of overweight/obesity (over 60 percent) and complications of obstetric anesthesia (24 percent) in pregnant women with SCA [21,22].

A through H mnemonic — The following A through H mnemonic was devised by the American Heart Association to help providers remember causes of SCA that should be considered in pregnant women [23]:

●A – Anesthetic complications, accident/trauma

●B – Bleeding

●C – Cardiac

●D – Drugs

●E – Embolic causes

●F – Fever

●G – General including hypoxia, electrolyte disturbances

●H – Hypertension

Role of congenital heart disease — Congenital heart disease is the most common form of heart disease complicating pregnancy in the western world [24,25]. While most women with congenital heart disease tolerate pregnancy well, an increasing number of women have moderate or complex forms of congenital heart disease and are at higher risk of pregnancy complications, including an increased risk of SCA [26]. Those patients at highest risk include those with cyanotic congenital heart disease, severe pulmonary artery hypertension, complex congenital heart disease with sequelae (eg, heart failure or significant valvular disease), congenital heart disease with history of malignant arrhythmia, Marfan syndrome, and prior Fontan procedure. (See "Anesthesia for labor and delivery in high-risk heart disease: General considerations", section on 'Risk stratification'.)

Data on SCA risk in patients with congenital heart disease are limited.

●Data from the Registry Of Pregnancy And Cardiac disease (ROPAC) included 5739 pregnant women of whom 57 percent had congenital heart disease, 29 percent had valvular heart disease, 8 percent had cardiomyopathy (including pregnancy-induced), and 1.6 percent had ischemic heart disease [27]. Maternal death occurred in 34 women (0.6 percent); the underlying cardiac lesions were valvular heart disease (17), congenital heart disease (8), cardiomyopathy (5), and pulmonary hypertension (4). Two deaths were due to SCA, but the underlying cardiac lesion was not stated.

●In a series of 1938 pregnant women of whom 1235 (64 percent) had congenital heart disease, 14 women had a cardiac death or arrest and approximately half of these women had congenital heart disease; most of the remainder had cardiomyopathy [28].

RAPID OVERVIEW OF RESUSCITATION — Resuscitation involves the following maneuvers and interventions, which are performed simultaneously, not sequentially:

●Call a "maternal" code blue, which should include a multidisciplinary team (adult resuscitation, anesthesia, obstetrics, neonatology). Obstetric and neonatal teams do not typically respond to an "adult code blue," so specific and early notification of these teams is critical.

●If the uterus is at or above the umbilicus, manually displace the uterus laterally and to the left (ie, left uterine displacement) to minimize aortocaval compression [29]. (See 'Avoiding aortocaval compression' below.)

●Initiate high-quality chest compression (at least 100 compressions per minute but not more than 120, compressing the chest at least 5 cm [2 inches] but no more than 6 cm [2.5 inches] with each downstroke) and ventilation (two ventilations of approximately 350 to 500 mL after every 30 compressions for patients without an advanced airway and with a uterus above the umbilicus [a larger ventilatory volume, 600 mL, is used if the uterus is below the umbilicus]) using standard hand placement for chest compression [30]. (See "Adult basic life support (BLS) for health care providers", section on 'Performance of excellent chest compressions' and "Adult basic life support (BLS) for health care providers", section on 'Ventilations'.)

●Do not delay usual measures such as defibrillation and administration of medications. (See "Adult basic life support (BLS) for health care providers", section on 'Defibrillation' and "Advanced cardiac life support (ACLS) in adults".)

●Place intravenous access above the diaphragm.

●Assume the patient has a difficult airway. (See "Airway management for the pregnant patient".)

●Estimate the gestational age of the fetus. (See 'Determining gestational age' below.)

●Use end-tidal carbon dioxide monitoring to determine the presence of return of spontaneous circulation, which reduces interruptions in cardiopulmonary resuscitation (CPR) by obviating the need for pulse checks. Although an end-tidal CO₂ level >10 mmHg may correlate with return of spontaneous circulation, it is not predictive of survival or long-term outcome [23]. (See "Adult basic life support (BLS) for health care providers", section on 'Pulse checks and rhythm analysis'.)

●A dedicated timer should alert the entire resuscitative team when four minutes have elapsed after the onset of a maternal cardiac arrest. If there is no return of spontaneous circulation with the usual resuscitation measures and the uterine fundus is at or above the umbilicus, at four minutes begin perimortem cesarean (also called resuscitative hysterotomy [31]), and complete delivery of the newborn by five minutes following SCA. In pregnant women, delivery early in the resuscitation process is a key intervention for improving success rates. (Perimortem cesarean delivery can be defined as a cesarean delivery after CPR has been initiated [9].) (See 'Delivery as part of the resuscitation process' below.)

●After 15 minutes of unsuccessful resuscitation, initiate direct cardiac massage if appropriate resources and personnel are available [32,33]. Thoracotomy and open chest massage are particularly effective for patients with chest trauma, tension pneumothorax, massive pulmonary embolism, pericardial tamponade, and chest or spine deformities. Thoracotomy may also facilitate treatment of the underlying cause of the arrest (eg, removal of pericardial fluid/thrombus in cardiac arrest due to pericardial tamponade). (See 'Imaging' below.)

●Evaluate need to institute cardiopulmonary bypass [32]. (See 'Imaging' below.)

●Continue resuscitation measures until all resources and attempts have been exhausted. This will vary depending on the clinical circumstances and resources of the facility. (See "Advanced cardiac life support (ACLS) in adults", section on 'Termination of resuscitative efforts'.)

Simultaneously, factors causing or contributing to cardiac arrest should be treated promptly (eg, bleeding/disseminated intravascular coagulation, electrolyte abnormalities, tamponade, hypothermia, hypovolemia, hypoxia, hypermagnesemia, myocardial infarction, poisoning, embolism [pulmonary, amniotic fluid, coronary], anaphylaxis, tension pneumothorax, anesthesia complications, aortic dissection). Treatment of these disorders is reviewed in separate topic reviews.

RESUSCITATION PROCEDURES — The sequence for resuscitation in adults is well-described separately. (See "Advanced cardiac life support (ACLS) in adults".)

Specific issues in pregnant women are described below and in the algorithm (algorithm 1). Resuscitation in pregnancy is characterized by concurrent interventions.

Airway management — Active airway management is the initial consideration. Intubation by an expert provider is recommended due to the risk of aspiration and difficulty in providing adequate ventilation without securing the airway. Both intubation and bag mask ventilation can be more difficult in the late stages of pregnancy due to narrowing of upper airways (particularly in the third trimester) and decreased thoracic compliance. Back-up airway procedures, including supraglottic airway devices (eg, laryngeal mask airway) and cricothyrotomy, may be required in some cases.

●Pregnant women are at increased risk of rapidly developing hypoxemia because of decreased functional residual capacity and increased oxygen consumption as well as increased intrapulmonary shunting [34-38]. Bag-mask ventilation (8 to 10 breaths/minute) with 100 percent oxygen (two-handed, >15 L/minute) and suctioning the airway are critical before intubation in a pregnant woman to avoid desaturation. (See "Airway management for the pregnant patient".)

●Intubation via direct or video laryngoscopy and 100 percent oxygen is performed using a smaller sized endotracheal tube (0.5 to 1.0 mm less in internal diameter compared with that used for nonpregnant women). Endotracheal tube placement should be verified using capnography.

●Cricoid pressure during laryngoscopy, once universally recommended, is now controversial because of lack of evidence of benefit and its ability to make both intubation and placement of a supraglottic airway more difficult. If used, pressure must be applied correctly over the cricoid cartilage, and the operator should discontinue it in cases where laryngoscopic view of the glottis is inadequate. (See "Carbon dioxide monitoring (capnography)".)

●Supraglottic airway devices, such as the laryngeal mask airway, should be considered if unable to intubate [39]. No more than two attempts with either direct laryngoscopy or videolaryngoscopy before insertion of a supraglottic device are recommended [23].

●A large uterus (fundus above the umbilicus) that elevates the diaphragm may increase resistance to ventilation. In these patients, lower ventilation volumes (350 to 500 mL) are used compared with nonpregnant women (600 mL). Ventilation during cardiopulmonary resuscitation (CPR) should allow the chest to rise but not cause overinflation, which will further decrease thoracic compliance and increase intrathoracic pressure, impending venous return to the heart.

●Hyperventilation has adverse effects and should be avoided in any patient undergoing resuscitation. In pregnancy, nonphysiologic respiratory alkalosis (normal pregnancy is associated with mild respiratory alkalosis) can cause uterine vasoconstriction, which can lead to fetal hypoxia and acidosis [40]. (See "Advanced cardiac life support (ACLS) in adults", section on 'Airway management'.)

Chest compressions — High-quality chest compressions (at least 100 compressions per minute but not more than 120, compressing the chest at least 5 cm [2 inches] but no more than 6 cm [2.5 inches] with each downstroke) are the cornerstone of the resuscitation process. The 2015 American Heart Association (AHA) guideline on SCA in pregnancy recommends the same hand position for and performance of chest compressions in pregnant women and nonpregnant adults because of an absence of data supporting a different approach in pregnancy [23]. This position is the center of the chest over the lower (caudad) portion of the sternum.

Previous AHA guidelines suggested a more cephalad hand position in pregnancy to adjust for elevation of the diaphragm by the gravid uterus. The updated guideline was based, in part, on a magnetic resonance imaging study that showed no significant vertical displacement of the heart in the third trimester of pregnancy relative to the nonpregnant state [30]. (See "Adult basic life support (BLS) for health care providers", section on 'Performance of excellent chest compressions'.)

The maternal position during chest compression is supine, with manual uterine displacement. (See 'Avoiding aortocaval compression' below.)

Intravenous access — Intravenous access should be established above the diaphragm since drugs administered via the femoral vein may not reach the maternal heart until the fetus is delivered. Access to an antecubital vein with two 14-gauge catheters can be as effective as central line catheters for volume replacement but these do not allow hemodynamic monitoring [32].

In the absence of intravenous access, rapid intraosseous access can be achieved in a few seconds using commercially available kits.

If neither intravenous nor intraosseous access is possible, the endotracheal tube can be used to administer certain medications including lidocaine, atropine, naloxone, and epinephrine. (See "Advanced cardiac life support (ACLS) in adults", section on 'Management of specific arrhythmias'.)

Avoiding aortocaval compression — We suggest manual uterine displacement to avoid aortocaval compression and to preserve supine positioning of the upper torso for optimal chest compression vector forces. A hand is used to apply maximal leftward push to the right upper border of the uterus to achieve displacement of approximately 1.5 inches from the midline [41].

Left lateral uterine displacement is necessary in the pregnant patient with fundal height at, or above, the umbilicus to minimize aortocaval compression (supine hypotensive syndrome), optimize venous return (preload), and generate adequate stroke volume during CPR. Our preference for manual uterine displacement is based on a randomized trial that compared manual uterine displacement versus operating room table tilt during cesarean delivery and demonstrated significantly fewer episodes of hypotension and a lower ephedrine requirement in the manual displacement group [41]. In addition, manual displacement of the uterus allows the patient's upper torso to remain supine, which enables application of maximum resuscitative force for effective chest compressions, improves airway and intravenous access, and improves access for defibrillation.

The inferiority of maternal tilt compared with the supine position plus manual displacement was shown in a study that used a calibrated force transducer to assess the maximum chest compression force generated at various angles of inclination in late pregnancy [42]. The maximum resuscitative force (expressed as percent body weight) was 67 percent in the supine position and decreased to 36 percent in the full lateral position. An angle of 27 degrees appeared to be the optimal angle in late pregnancy but achieved only 80 percent of the force generated in the supine position. However, if manual uterine displacement is not possible, the operating room table can be tilted or pillows, a wood or foam resuscitation wedge (eg, Cardiff wedge), or rolled up towels or blankets can be placed under the patient to achieve a tilt of no more than 30 degrees [42].

Defibrillation — Management of ventricular arrhythmias may require defibrillation. The physiologic changes of pregnancy, including increases in blood volume and decreases in functional residual capacity, do not appear to alter transthoracic impedance or transmyocardial current [43]. Therefore, current energy requirements for adult defibrillation are appropriate for use in pregnant women (biphasic shock 120 to 200 joules with subsequent increase in energy output if the first shock is ineffective) [23].

Before delivering the countershock, remove fetal monitoring equipment to prevent electrocution injury to the patient or rescuers. This risk is theoretical and of greatest concern when the fetus has scalp electrodes. Fetal monitors also detract from the resuscitation priorities determined by maternal status and maternal responses to resuscitative interventions. (See "Basic principles and technique of external electrical cardioversion and defibrillation".)

If a pacemaker or implantable cardioverter defibrillator is present, defibrillation is still appropriate. Defibrillation pads are placed in an anterior/posterior position that is not over these devices.

In a study of AHA's Get with the Guidelines Resuscitation voluntary registry, which included 462 in-hospital maternal SCAs, 76.4 percent of women had a nonshockable first documented pulseless rhythm (pulseless electrical activity: 50.8 percent; asystole: 25.6 percent) [7]. The remainder had a shockable rhythm (11.7 percent: 6.5 percent ventricular fibrillation and 5.2 percent pulseless ventricular tachycardia) or unknown rhythm (11.9 percent). Return of spontaneous circulation occurred in 73.6 percent of patients. In this cohort, the presenting rhythms are suggestive of potentially reversible clinical etiologies, such as hemorrhage, hypoxemia, thromboembolism, exposure to toxins, and electrolyte/acid/base disturbances.

Determining gestational age — In pregnant women, determining gestational age is critical as the likelihood of neonatal viability is a factor in decision making. If the prenatal record or a corroborating family member is not available, physical examination can aid in estimating the gestational age.

Uterine size correlates with gestational age but can be misleading in some situations, such as when there is a multiple gestation, large fibroids, severe oligohydramnios (decreased amniotic fluid volume), polyhydramnios (increased amniotic fluid volume), or maternal obesity.

The formula for estimating gestational age by physical examination is:

The top of the uterine fundus is generally at the level of the umbilicus by 20 weeks of gestation in a singleton pregnancy. Ultrasound is a reliable method for gestational age assessment but may not be possible due to time and logistical constraints during maternal assessment and resuscitation. (See "Prenatal assessment of gestational age, date of delivery, and fetal weight" and "Preterm birth: Definitions of prematurity, epidemiology, and risk factors for infant mortality" and "Periviable birth (limit of viability)".)

Fetal heart rate monitoring — In general, the status of the mother should guide management during the resuscitation process; if the status of the mother is poor and deteriorating, the status of the fetus will be further compromised. Therefore, fetal heart rate monitoring is not recommended during the resuscitation process.

If CPR is successful and the mother becomes hemodynamically stable, fetal heart rate monitors can be applied to assess the status of a fetus who is at a potentially viable gestational age. Intervention (in utero resuscitation measures, delivery) for an abnormal fetal heart rate pattern depends on maternal- and fetal-specific factors. (See "Intrapartum fetal heart rate monitoring: Overview".)

Delivery as part of the resuscitation process — The AHA and others recommend cesarean delivery if spontaneous circulation has not returned within four minutes of maternal cardiorespiratory collapse [23,44,45]. Ideally, perimortem cesarean (resuscitative hysterotomy) should be initiated within four minutes, and delivery of the newborn should be completed within five minutes (known as the "four-minute rule" or the "five-minute rule"). Perimortem instrumental vaginal delivery (forceps, vacuum) is appropriate if it can be achieved within this time frame [23]. To achieve this time frame, delivery needs to be performed at the location of the SCA, which is often not an operating room [9,46].

The rationale for this approach is based on case reports, small case series, and experimental data showing [29,47-53]:

●Irreversible brain damage can occur in nonpregnant individuals after four to six minutes of anoxia.

●Pregnant women become anoxic sooner than nonpregnant women because of decreased functional residual capacity.

●If the uterine fundus is at or above the umbilicus, ineffective resuscitation efforts may become effective when the uterus is no longer gravid and potentially causing aortocaval compression. Sudden substantial improvement in hemodynamics with a return of pulse and blood pressure immediately after perimortem cesarean delivery has been observed [9,54-57]. (See 'Minimum gestational age' below.)

●Intact fetal survival diminishes as the time between maternal death and delivery lengthens. (See 'Evidence for the five-minute rule' below.)

Despite implementation of maneuvers to ameliorate aortocaval compression, CPR may not restore spontaneous circulation or provide adequate cardiac output. Blood flow during CPR is produced by mechanical compression of the heart between the sternum and the spine and phasic fluctuations in intrathoracic pressure. Despite appropriate use of leftward uterine displacement, the mechanical effects of the gravid uterus can decrease venous return from the inferior vena cava, obstruct blood flow through the abdominal aorta, and diminish thoracic compliance, all of which contribute to unsuccessful CPR [58]. Without restoration of cardiac output, both mother and fetus are at risk for hypoxia and eventually anoxia, especially when interruption of normal cardiac and respiratory function persists beyond four minutes [59]. Although it may be counterintuitive to operate on a hemodynamically unstable patient, cesarean delivery may be lifesaving for both mother and fetus in this situation. Cardiac output peaks immediately after delivery as the evacuated uterus contracts and blood from myometrial veins is autotransfused into the systemic venous system [60]. Also, the contracted uterus lifts off the vena cava, resulting in greater venous blood return to the heart, which increases stroke volume. However, unusual or ongoing blood loss during and immediately after delivery can counteract these effects.

Practically, the goal of delivering the infant within five minutes has been difficult to achieve [10,61]. In a literature review including 57 perimortem cesarean deliveries with time to delivery information, the time was <5 minutes in 4 cases, <10 minutes in 18 cases, and <15 minutes in 32 cases [61]. Only perimortem cesarean delivery within 10 minutes and in-hospital arrest were predictive of maternal survival. The reviewers believed perimortem cesarean delivery was beneficial for one-third of mothers and was not harmful in any case. Overall neonatal survival was 64 percent (42/66) in singleton pregnancies with a potentially viable fetus delivered by perimortem cesarean delivery; neonatal survival was attributed to perimortem cesarean delivery in half of these cases. Only in-hospital arrest was predictive of neonatal survival. The mean time from arrest to delivery for newborn survivors was 14±11 minutes versus 22±13 minutes for newborn nonsurvivors.

While acknowledging that both maternal and neonatal injury-free survival rates diminish steadily as the time interval from maternal arrest to birth increases, the American College of Obstetricians and Gynecologists has opined that, even if delivery does not occur within four to five minutes, perimortem cesarean (resuscitative hysterotomy) still may be beneficial and should be considered [62].

Evidence for the five-minute rule — Although there have been no controlled clinical trials in this area, a review of case reports of perimortem cesarean delivery from 1900 to 1985 suggested that normal neonatal neurologic outcome was most likely when delivery was completed within five minutes of maternal SCA. In this review, 42 of 42 infants delivered within 5 minutes had a normal neurologic outcome compared with 7 of 8 infants delivered within 6 to 10 minutes, 6 of 7 infants delivered within 11 to 15 minutes, 0 of 1 infant delivered between 16 and 20 minutes, and 1 of 3 infants delivered within 21 to 25 minutes [51].

The authors' subsequent evaluation of perimortem cesarean cases reported from 1985 to 2004 noted the procedure was associated with spontaneous return of maternal circulation or improvement in maternal hemodynamic status in 12 of 20 cases, particularly when the delivery was completed within five minutes of maternal SCA [50]. No case of perimortem cesarean delivery resulted in deterioration of the maternal condition, although these case reports were highly subject to reporting bias. Similarly, neonatal outcomes were best when delivery was completed within 5 minutes; 9 of 12 infants delivered within this time frame had a normal neurologic outcome (neonatal outcome was not reported for 3 infants), 2 of 6 infants born from 6 to 15 minutes after maternal cardiac arrest had normal outcomes (1 infant outcome was not reported), and 4 of 7 infants delivered after 15 minutes of maternal arrest had normal outcomes.

Additional features favoring infant survival include absence of sustained prearrest maternal hypoxia, minimal or no signs of fetal distress before maternal cardiac arrest, aggressive and effective resuscitative efforts for the mother, and neonatal intensive care unit on site of the emergency cesarean delivery.

Minimum gestational age — The minimum gestational age for perimortem cesarean delivery is controversial. Although physiologically aortocaval compression begins as early as 20 weeks, there is some imprecision within the range of 20 to 24 weeks [29]. Neonatal viability is also an imprecise assessment as it is uncertain which extremely preterm infants, particularly those born at 23 and 24 weeks of gestation, have a reasonable chance of survival without severe deficits. Most centers would provide full neonatal support to infants at least 24 weeks of gestation, and some centers provide this level of care to infants greater than 22^0/7ths weeks of gestation [63]. (See "Periviable birth (limit of viability)".)

Given these variables, perimortem hysterotomy is a reasonable option for pregnancies ≥20 weeks of gestation/uterine size at or above the umbilicus to relieve aortocaval compression and facilitate return of spontaneous circulation regardless of fetal status (alive or demised) [32,50]. If the fetus is alive, there may be a neonatal benefit from perimortem hysterotomy at >22 to 24 weeks of gestation.

Delivery issues

●High-quality chest compressions should be continued without interruption until return of spontaneous circulation.

●Assisted vaginal delivery is appropriate if the cervix is fully dilated, the fetus is at a low station, and delivery can be accomplished within five minutes of maternal cardiorespiratory collapse.

●Cesarean delivery is performed if the fetus cannot be delivered within five minutes vaginally.

•Location – Transporting the patient to an operating room is not a priority [46]. An emergency cesarean delivery kit (eg, preloaded scalpel, sutures, needle holders, towel clips, retractors, forceps, scissors, suction tube, sponges, Kelly clamps, uterine pack, equipment for neonatal care/resuscitation) should be part of the resuscitation cart in patient care areas that commonly serve pregnant women or such carts should be transported to the location of the pregnant patient who has arrested.

•Consent – In the United States, there are no published reports of physician liability for performing perimortem cesarean delivery without consent following maternal cardiac arrest [20].

•Broad spectrum antibiotics are administered to decrease the risk of postpartum infection. (See "Cesarean birth: Preoperative planning and patient preparation", section on 'Antibiotic prophylaxis'.)

•Technical points – We suggest a vertical skin incision to provide fast entry, adequate uterine exposure, and access to the diaphragm, which may be useful for further resuscitative interventions. (See 'Selected clinical scenarios' below.)

Bleeding may be minimal during the procedure due to hypoperfusion. Extraction of the placenta and closure of the hysterotomy are important steps to prevent subsequent hemorrhage when hemodynamic stability is eventually restored. (See "Cesarean birth: Surgical technique and wound care".)

●Oxytocin is given routinely after vaginal or cesarean delivery to reduce maternal blood loss and the risk of postpartum hemorrhage. We suggest a continuous intravenous infusion of a dilute oxytocin solution (eg, 20 milliunits/minute). Intramyometrial administration of 10 units oxytocin is an effective alternative to intravenous infusion.

Intravenous bolus injection of oxytocin should be avoided because of the risk for significant hypotension, cardiovascular collapse, and death. (See "Management of the third stage of labor: Prophylactic drug therapy to minimize hemorrhage", section on 'Oxytocin'.)

Use of medications for resuscitation during pregnancy — All medications (including amiodarone) used for treatment of SCA in the nonpregnant patient are used for the pregnant patient and at the same doses. Given the lethality of SCA, the benefits from use of potentially lifesaving drugs outweigh any known or possible fetal risks.

●Epinephrine (1 mg intravenous push every three to five minutes) is recommended in patients with asystole. (See "Supportive data for advanced cardiac life support in adults with sudden cardiac arrest", section on 'Epinephrine'.)

●Magnesium sulfate is commonly used in obstetrics for a variety of indications (prevention of eclamptic seizures, fetal neuroprotection before preterm delivery, tocolysis). If magnesium toxicity is suspected, magnesium sulfate infusion should be discontinued, and calcium chloride (10 mL of a 10 percent solution) or calcium gluconate (10 to 30 mL of a 10 percent solution) should be given intravenously or intraosseously early in the resuscitation process. (See "Preeclampsia: Management and prognosis", section on 'Antidote'.)

●Advanced cardiac life support (ACLS) guidelines do not recommend routine use of sodium bicarbonate during CPR, but it may be useful in life-threatening hyperkalemia or tricyclic antidepressant overdose. (See "Therapies of uncertain benefit in basic and advanced cardiac life support".)

However, if neither of these conditions is known or strongly suspected to be present, bicarbonate is not indicated and may worsen fetal acidosis. Since bicarbonate crosses the placenta very slowly, overcorrection of maternal acidosis will lead to pooling of carbon dioxide in the fetal compartment [33].

●Arrhythmias are difficult to control, especially those resulting from bupivacaine toxicity. Amiodarone, a primary drug in the ACLS arrhythmia treatment algorithm, is the favored treatment for severe bupivacaine-induced arrhythmias; administration of the local anesthetic lidocaine to treat local anesthetic toxicity is not indicated as it has had equivocal success [64]. The arrhythmias are often refractory to therapy; emergency cardiopulmonary bypass may be lifesaving until the drug dissociates from cardiac tissue [65].

●Early administration of a 20 percent lipid emulsion (conventional soybean oil-based, such as Intralipid) is an important component in resuscitation of local anesthetic-induced cardiotoxicity. This therapy, which theoretically acts as a lipid sink that binds lipid-soluble local anesthetics (eg, bupivacaine), has rapidly gained acceptance [66] since the first case reports documenting its efficacy were published in 2006 [67,68].

Lipid rescue should be initiated at the first signs of severe systemic local anesthetic toxicity while the airway is being secured. An intravenous bolus of 1.5 mL/kg lean body mass of 20 percent lipid emulsion is given over one minute, followed by an infusion of 0.25 mL/kg/minute until at least 10 minutes following successful achievement of circulatory stability. If circulatory stability is not obtained within five minutes, a second 1.5 mL/kg bolus may be administered, followed by an infusion of 0.5 mL/kg/minute. The maximum total cumulative dose of lipid is 10 mL/kg over 30 minutes [69]. (See "Local anesthetic systemic toxicity", section on 'Lipid rescue'.)

Although the anesthetic propofol is formulated as a 10 percent lipid emulsion, it should not be used for lipid rescue since the dose needed to treat local anesthetic toxicity would result in massive hypotension that may counteract any positive effect.

Checklists — The American Society of Regional Anesthesia and Pain Medicine has published a checklist for treatment of local anesthetic systemic toxicity [70]. A consensus statement by the Society for Obstetric Anesthesia and Perinatology on the management of SCA during pregnancy encouraged the use of checklists to improve team performance [39]. Maternal resuscitation guidelines from the AHA also encourage institutions to create and utilize checklists during obstetric crises and to institute mock code drills of maternal SCA.

IMAGING — Transesophageal echocardiography (TEE) and cardiopulmonary limited ultrasound examination (CLUE) are quick, portable, and reliable means of identifying potential causes of hemodynamic collapse during labor and delivery, such as pericardial effusion/tamponade and ventricular failure [71-77]. CLUE is more convenient and does not require interruption of ventilation if the patient has not yet been intubated.

TEE requires getting a probe and machine and stopping respiratory support during intubation of the esophagus with the TEE probe. After the patient has been intubated, the TEE probe can be inserted without interrupting ventilation. TEE can detect previously unrecognized cardiac conditions and is helpful for placement of venous and arterial cannulae for extracorporeal membrane oxygenation and placement of intraaortic balloon counterpulsation. TEE can also be utilized to assess the effects of intraaortic balloon counterpulsation and inotropic agents [78].

SELECTED CLINICAL SCENARIOS

Failure to respond to initial procedures — The following interventions may be appropriate for patients with SCA who fail to respond to standard resuscitative measures:

●Direct cardiac massage – After 15 minutes of unsuccessful closed chest cardiopulmonary resuscitation (CPR), direct cardiac massage via thoracotomy or through the diaphragm (if the abdomen is open) can be implemented [79]. Direct cardiac massage results in near normal systemic perfusion throughout the compression cycle and with higher cranial and myocardial flow than achieved with external chest compressions of conventional CPR [80].

●Intraaortic balloon pump, cardiopulmonary bypass, and extracorporeal membrane oxygenation – Intraaortic balloon pump, cardiopulmonary bypass, and extracorporeal membrane oxygenation have been used to treat patients with cardiovascular collapse, including those with pulmonary embolism, local anesthetic toxicity, illicit drug use such as cocaine, amniotic fluid embolism, and pulseless electrical activity. Case reports have described successful resuscitation using cardiopulmonary bypass intraoperatively during cesarean delivery and postpartum in women with amniotic fluid embolism and pulmonary embolism [71,81]. However, use of this technology is hampered by the preparation time required to institute the intervention. (See "Extracorporeal membrane oxygenation (ECMO) in adults" and "Amniotic fluid embolism".)

ST elevation myocardial infarction — For pregnant women with ST elevation myocardial infarction, percutaneous coronary intervention is the preferred reperfusion strategy since fibrinolytics are relatively contraindicated in pregnancy [82]. ST elevation myocardial infarction in pregnant women may be secondary to coronary artery dissection; coronary artery catheterization is required for diagnosis and management. (See "Acute myocardial infarction and pregnancy" and "Spontaneous coronary artery dissection".)

Massive pulmonary embolism and ischemic stroke — Successful systemic thrombolysis has been reported for massive pulmonary embolism and for ischemic stroke during pregnancy [83]. If systemic thrombolysis is utilized, excessive bleeding may complicate imminent cesarean delivery or the postoperative course of patients who were recently delivered. Transfusion of blood products should be anticipated: In one review of postpartum systemic thrombolytic therapy, blood transfusion was necessary in 12 of 13 cases, a large amount of blood was required for transfusion in 7 of these 12 cases, and laparotomy was eventually required to control bleeding in 5 of the 12 cases (including 3 hysterectomies) [84]. Severe bleeding was most common in patients who had a cesarean delivery, and laparotomy was only necessary in patients who had a cesarean delivery. Management of pulmonary embolism and ischemic stroke, including thrombolysis, is discussed separately. (See "Treatment, prognosis, and follow-up of acute pulmonary embolism in adults" and "Approach to thrombolytic (fibrinolytic) therapy in acute pulmonary embolism: Patient selection and administration" and "Initial assessment and management of acute stroke" and "Approach to reperfusion therapy for acute ischemic stroke".)

POSTARREST CARE — In the absence of the need for chest compression, the patient should be placed at 90 degrees left lateral tilt to avoid aortocaval compression, which can also occur postpartum since the uterus remains enlarged [23].

Core temperature lability is associated with increased mortality after in-hospital cardiac arrest. Hyperthermia should be avoided [85]. It is unclear whether therapeutic hypothermia is beneficial. The American Heart Association recommends avoiding routine use of therapeutic hypothermia because in undelivered patients it may not be safe for the fetus (pregnant women have been excluded from trials on therapeutic hypothermia) and in postpartum patients it may impair coagulation and contribute to bleeding complications [23]. However, the induction of mild to moderate hypothermia (target temperature 32 to 34°C for 24 hours) may be beneficial in comatose pregnant women and has been used successfully in this setting [86,87]. It should also be considered in women not following commands or showing purposeful movements following resuscitation from cardiac arrest. Temperature issues are discussed in more detail separately. (See "Initial assessment and management of the adult post-cardiac arrest patient", section on 'Temperature management'.)

In the hypothermic undelivered woman, the fetal heart rate may have a low baseline (90 to 100 beats per minute) with diminished variability [88]. Absent variability and fetal heart decelerations suggest deterioration in the fetal status; delivery should be considered if the fetus is at a viable gestational age.

OUTCOME — SCA in pregnant women is associated with high maternal and neonatal fatality rates (30 to 80 percent and ≥60 percent, respectively, in large studies) [7,9-12,61]. Approximately 12 percent of maternal survivors and 21 percent of neonatal survivors had poor neurologic outcomes (cerebral performance category 3/4) in one such study [61]. Although there is a high risk of maternal mortality after cardiac arrest, in-hospital survival appears to be higher than that for nonpregnant, reproductive-age women [89,90]. This may be due to differences between the two groups in clinical risk factors and/or differences in intensity of patient monitoring among various hospital units.

Maternal and neonatal survival depends on several factors, including the underlying etiology for the arrest, maternal location at the time of the arrest (out-of-hospital versus in-hospital), speed of resuscitative efforts, and the skills and resources of the health care providers [91]. A high survival rate in series with a high proportion of anesthetic complications may be due to the opportunity for immediate resuscitation in the operating room or labor and delivery room by skilled personnel with appropriate resources [12] and the possibility of better prearrest maternal condition.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Basic and advanced cardiac life support in adults".)

SUMMARY AND RECOMMENDATIONS

●The A through H mnemonic is useful as a reminder of the causes of sudden cardiac arrest (SCA) in pregnant women (see 'Etiology' above):

•A – Anesthetic complications, accident/trauma

•B – Bleeding

•C – Cardiac

•D – Drugs

•E – Embolic causes

•F – Fever

•G – General including hypoxia, electrolyte disturbances

•H – Hypertension

●Key principles for resuscitation of pregnant women are (algorithm 1) (see 'Rapid overview of resuscitation' above):

•Call a maternal code blue, which should include a multidisciplinary team.

•If the uterus is above the umbilicus, displace it off aortocaval vessels. We suggest manually displacing the uterus laterally to the patient's left rather than tilting the entire patient (Grade 2C). A hand is used to apply maximal leftward push to the right upper border of the uterus to achieve displacement of approximately 1.5 inches from the midline. Leave the upper torso supine. (See 'Avoiding aortocaval compression' above.)

•Assume a difficult airway. Bag-mask ventilation with 100 percent oxygen and suctioning of the airway are critical before intubation in a pregnant woman. Oxygenate well to avoid desaturation and avoid respiratory alkalosis; ventilation volumes may need to be lower than in nonpregnant women if the uterus is very large. (See 'Airway management' above.)

•Place hands for chest compression at the same location, and perform compressions in the same way as in nonpregnant adults. (See 'Chest compressions' above.)

•Do not delay usual measures such as defibrillation and the administration of medications. Energy requirements for adult defibrillation are the same as in nonpregnant women. All medications at the same doses for treatment of cardiopulmonary arrest in the nonpregnant patient are used for the pregnant patient. (See 'Defibrillation' above and 'Use of medications for resuscitation during pregnancy' above.)

•Designate a dedicated timer to notify the resuscitation team when four minutes have elapsed after the onset of a maternal cardiac arrest. (See 'Delivery as part of the resuscitation process' above.)

•If there is no return of spontaneous circulation with the usual resuscitation measures and the uterine fundus is at or beyond the umbilicus, we agree with the American Heart Association guidelines that recommend expeditious perimortem cesarean delivery (resuscitative hysterotomy) (Grade 1C). Ideally, the cesarean should be started at four minutes following cardiac arrest and delivery of the newborn completed by five minutes following the arrest. In pregnant women, delivery early in the resuscitation process is a key intervention for improving success rates. Assisted vaginal delivery is appropriate if the neonate can be delivered within five minutes of maternal cardiorespiratory collapse (eg, if the head is on the perineum). (See 'Delivery as part of the resuscitation process' above.)

•Perform delivery at the site of resuscitation. (See 'Delivery issues' above.)

●Postarrest, induction of mild to moderate hypothermia (target temperature 32 to 34°C for 24 hours) is reasonable in women who are comatose or not following commands or showing purposeful movements following resuscitation. It is not used routinely because in undelivered patients it may not be safe for the fetus and in postpartum patients it may impair coagulation and contribute to bleeding complications. (See 'Postarrest care' above.)

●Cardiac arrest in pregnant women is associated with high maternal and neonatal fatality rates. Survival of the mother and neonate depends on several factors, including the underlying etiology for the arrest, maternal location at the time of the arrest (out-of-hospital versus in-hospital), speed of resuscitative efforts, and the skills and resources of the health care providers. (See 'Outcome' above.)