Amniotic Fluid Embolus

The EMS unit you are staffing is dispatched for a patient complaining of respiratory distress. Your response time is 12 minutes to the scene. Upon your arrival at the patient you note an obviously pregnant female who is being held unresponsive in her husband’s arms. The patient’s husband relates to you that she is due to deliver at any time, and she began to have weak contractions this morning. The couple presented to the hospital for the delivery, but was told it was too soon to be admitted. They were to return to the hospital when the patient’s contractions were stronger and closer together. Tonight the patient was at rest in bed where she began to complain of shortness of breath that began very suddenly. The patient’s husband called 9-1-1 immediately.

The patient is pale, cool, diaphoretic, and not responding to any stimuli. Your partner immediately secures an airway utilizing endotracheal intubation and begins to ventilate the patient with 100% oxygen. The patient’s heart rate is a regular sinus rhythm at 130 beats per minute. Despite your best efforts and aggressive ventilation the patient’s heart rate rapidly declines until she has an idioventricular heart rate of 12 beats per minute. The patient and fetus are both pronounced dead on arrival at the hospital. Several days later you find out from the emergency room attending physician that the patient most likely had suffered an amniotic fluid embolism.

Unpreventable and catastrophic to the patient and fetus, amniotic fluid embolism (AFE) is the leading cause of death during labor and during the first few postpartum hours.1 Impacting one of every 8,000–80,000 live births, AFE has a maternal death rate of anywhere from 50%–85%. The fetal death rate is not as great as the maternal rate, though it is still in the area of 21%. However, 50% of the surviving neonates experience permanent neurologic injury secondary to hypoxia.2 Much is still unknown about this devastating illness, with the diagnosis of amniotic fluid embolus still being made largely by clinical suspicion or after a postmortem exam.

Description and Etiology

Normally, amniotic fluid does not enter the maternal circulation because the fluid remains contained within the amniotic sac, safely tucked into the uterus. In amniotic fluid embolus, the barrier that exists between maternal circulation and the amniotic sac becomes breached, which allows amniotic fluid and fetal debris to enter maternal central circulation. The most common routes for this to happen are uterine/placental trauma, the endocervical veins or through the placenta itself.

The amount of amniotic fluid that enters the bloodstream does not appear to influence whether the patient will have a reaction. With some women, the fetal debris and amniotic fluid that enter the blood- stream do not cause any signs or symptoms of distress. With other women, the entry of only minute amounts of amniotic fluid or fetal debris can cause devastating results.

Because of the inconsistent symptoms in patients who are exposed to amniotic fluid and fetal debris, there are several different philosophies regarding amniotic fluid embolus. A recent study has likened the reaction more to an allergic reaction than to an embolic reaction, and has proposed the term “anaphylactoid syndrome of pregnancy” instead of amniotic fluid embolus, because of the close resemblance to anaphylaxis.3 Additional studies have indicated that the embolus may actually be caused by a physical obstruction of the vessels by amniotic fluid and fetal debris, more consistent with the classic presentation of an embolus.

Clinical Presentation

The most common time for the presentation of an AFE is during the third trimester of pregnancy or immediately postpartum. However, the patient can experience an AFE at any time during pregnancy. It remains virtually unknown what factors, if any, predicate AFE. A study examining 46 cases of AFE found that 70% of patients experienced their first symptoms during labor, 11% after vaginal delivery, and 19% during cesarean section (during or without labor).4