Maternal cardiac arrest (MCA) is a rare but catastrophic event requiring immediate intervention from responders. While the core principles of cardiopulmonary resuscitation (CPR)—circulation, airway, and breathing—remain the same, the pregnant state demands specific modifications to standard procedure. Resuscitation success depends on adapting to the unique anatomical and physiological changes present in a pregnant patient. The primary goal is to save the mother’s life, as her survival provides the best possible outcome for the fetus.
Physiological Changes That Require CPR Modification
Physiological and anatomical changes during pregnancy necessitate modifications to standard CPR techniques, particularly in the later stages. The most immediate concern is aortocaval compression, which occurs when the enlarged uterus presses on the mother’s major blood vessels while she is lying flat. The uterus compresses the inferior vena cava and the aorta, dramatically reducing the blood returning to the heart and overall cardiac output. This reduction in venous return, which can be 30 to 40% in late pregnancy, severely limits the effectiveness of chest compressions.
The body’s respiratory system is also significantly affected, creating a high risk for rapid oxygen deprivation. The growing uterus elevates the diaphragm, decreasing the mother’s functional residual capacity (the volume of air remaining in the lungs after a normal breath). Oxygen consumption is increased by 20% to 33% by the third trimester due to fetal demands and increased metabolism. This combination of reduced lung capacity and higher oxygen demand means that hypoxia can develop much faster than in a non-pregnant patient.
Key Procedural Adjustments During Resuscitation
The most important immediate modification to standard CPR is the manual lateral uterine displacement (LUD), initiated as soon as a pregnant patient over 20 weeks’ gestation collapses. This technique involves manually pushing the uterus to the mother’s left side to shift it off the vena cava and aorta. Relieving this pressure improves venous return to the heart, directly increasing the blood flow generated by chest compressions.
Current guidelines recommend keeping the patient supine on a firm surface to ensure high-quality chest compressions while performing the LUD manually. Chest compressions should be performed at the standard rate of 100 to 120 compressions per minute and at the usual depth of at least two inches. There is no need to adjust the hand placement higher on the sternum, as MRI studies have shown no significant vertical displacement of the heart in late pregnancy.
Airway management requires special attention because pregnant patients have an increased risk of aspiration due to hormonal changes relaxing the esophageal sphincter. Providing supplemental oxygen at 100% compensates for the mother’s higher oxygen demands and lower reserve. The most experienced provider should secure an advanced airway early, as anatomical changes in the throat and mouth can make intubation more difficult.
Addressing the Fetus: The Critical Timeline and Perimortem Delivery
The most aggressive intervention in maternal cardiac arrest is the consideration of an emergency delivery, known as a perimortem cesarean delivery (P-CS). This procedure is performed primarily as a life-saving measure for the mother, not solely for the baby. Removing the fetus and placenta immediately eliminates aortocaval compression, which can suddenly and dramatically improve the mother’s circulation and the effectiveness of CPR.
The decision to proceed with a P-CS is governed by the “4-minute rule.” This rule states that if spontaneous circulation is not restored within four minutes of initiating effective CPR, the delivery must be started. The goal is to have the fetus delivered by the five-minute mark from the time of maternal collapse. This narrow window is based on clinical evidence showing that maternal and fetal outcomes decline significantly if the intervention is delayed.
This rapid timeline requires a well-rehearsed, multidisciplinary team, including obstetric, neonatal, and emergency personnel. The procedure is performed at the site of the resuscitation, without delaying for formal sterile preparation or moving the patient to an operating room. Continuing high-quality chest compressions and manual uterine displacement throughout the preparation and delivery is non-negotiable for maximizing the mother’s chances of survival.