Cardiac arrest in a pregnant patient is a rare medical emergency where the heart abruptly stops pumping blood effectively. With an incidence of about 1 in 30,000 pregnancies, understanding its causes is crucial for improving outcomes for both the mother and the baby. This event can arise from physiological changes, pregnancy-related complications, and underlying medical conditions. Identifying these factors allows for better risk assessment and prompt intervention.
How Pregnancy Changes the Body
Pregnancy brings about profound physiological adaptations across multiple bodily systems to support the developing fetus. The cardiovascular system undergoes substantial changes, including a significant increase in blood volume, often by 40-45%, and a rise in cardiac output by 30-50% due to increased heart rate and stroke volume. Systemic vascular resistance typically decreases, leading to a drop in blood pressure during the first and second trimesters. These adjustments place an increased workload on the heart.
The respiratory system also adapts to meet the heightened oxygen demands of pregnancy. Tidal volume, the amount of air inhaled or exhaled with each breath, increases by 30-50%. While the respiratory rate generally remains unchanged, the diaphragm’s resting position shifts upward, reducing lung volumes like functional residual capacity. This can make pregnant individuals more susceptible to hypoxemia, a state of low oxygen in the blood.
Changes in the hematologic system include an increase in both plasma and red blood cell volume, though plasma increases more, leading to a physiological dilutional anemia. Pregnancy also induces a hypercoagulable state, meaning the blood clots more easily due to increased clotting factors. This adaptation helps prevent excessive bleeding during childbirth but elevates the risk of blood clot formation.
Causes Directly Related to Pregnancy
Certain conditions are unique to pregnancy or are significantly exacerbated by gestation’s physiological changes, contributing to cardiac arrest.
Severe hemorrhage is a leading cause, often resulting from complications like postpartum hemorrhage, placental abruption, or placenta previa. Profound blood loss can lead to hypovolemic shock, where the body does not have enough blood volume to adequately pump to organs, culminating in cardiac arrest.
Amniotic fluid embolism (AFE) is a rare condition where amniotic fluid, fetal cells, or other debris enter the mother’s bloodstream. This triggers an acute inflammatory reaction, leading to sudden cardiorespiratory collapse and often disseminated intravascular coagulation (DIC). AFE can rapidly progress to cardiac arrest.
Preeclampsia and eclampsia, characterized by high blood pressure during pregnancy, can lead to cardiac arrest. Preeclampsia involves widespread organ damage, and if it progresses to eclampsia, seizures can occur. These conditions can cause heart failure, pulmonary edema (fluid in the lungs), or stroke.
Peripartum cardiomyopathy (PPCM) is a form of heart muscle weakness that develops in the last month of pregnancy or within five months after delivery. This condition impairs the heart’s ability to pump blood effectively, leading to symptoms of heart failure such as shortness of breath and fatigue. PPCM can cause arrhythmias, cardiogenic shock, or sudden cardiac death.
Other Significant Medical Causes
Cardiac arrest in pregnant patients can stem from medical conditions not exclusive to pregnancy but whose risk or impact is altered by the pregnant state.
Pulmonary embolism (PE), a blockage in the lung arteries, is a significant cause due to the increased risk of blood clots during pregnancy. Blood clots, often originating in the legs or pelvis, can travel to the lungs, leading to sudden cardiovascular collapse.
Sepsis, a severe response to infection, can lead to cardiac arrest. Infections such as chorioamnionitis (infection of the amniotic sac) or pyelonephritis (kidney infection) can progress to widespread inflammation and organ dysfunction, resulting in septic shock. The body’s immune system changes during pregnancy, potentially influencing the response to severe infections.
Complications related to anesthesia administered during labor or delivery can contribute to cardiac arrest. These can include adverse drug reactions, severe drops in blood pressure from regional anesthesia, or difficulties with airway management and intubation. Physiological changes in pregnancy affect how anesthetic agents are processed and increase the risk of aspiration.
Pre-existing cardiac disease places additional strain on the heart during pregnancy. Conditions such as congenital heart disease, valvular disease, or coronary artery disease can be exacerbated by the increased blood volume and cardiac output of pregnancy. This added workload can lead to heart failure, arrhythmias, or myocardial infarction.
Trauma, such as that sustained in a motor vehicle accident or from falls, can cause cardiac arrest in pregnant patients. While trauma can affect anyone, specific considerations apply to pregnant individuals, including potential for direct injury to the uterus and modifications to resuscitation efforts. The gravid uterus can compress major blood vessels when a pregnant patient lies on her back, complicating resuscitation.