Case scenario: amniotic fluid embolism.

A MNIOTIC fluid embolism (AFE) is a rare but potentially catastrophic obstetric emergency. Despite earlier recognition and aggressive treatment, morbidity and mortality rates remain high. An estimated 5–15% of all maternal deaths in Western countries are due to AFE. Recent retrospective reviews of population-based hospital databases in Canada and the United States found AFE incidences of 6.1–7.7 cases per 100,000 births. The United States cohort used data from the Healthcare Cost and Utilization ProjectNationwide Inpatient Sample from 1998 to 2003, which included all hospital admissions in the United States. The Canadian database included three million hospital deliveries from 1991 to 2002. The only prospective study also included data from three million deliveries in the United Kingdom and reported an incidence of 2.0 per 100,000 births. This cohort used the United Kingdom Obstetric Surveillance System to identify women with AFE from 2005 to 2009. Early studies revealed mortality rates as high as 61–86%, but more recent estimates suggest a case fatality of 13– 26%. This decrease in risk for maternal mortality from AFE may be the result of previous diagnosis and better resuscitative care as well as changes to case inclusion criteria. Fetal outcome remains poor if AFE occurs before delivery, with a neonatal mortality rate approximately 10%. First reported by Meyer in 1926, and then later identified as a syndrome in 1941 by Steiner and Lushbaugh, AFE has historically been a postmortem diagnosis; confirmed only at autopsy revealing epithelial squamous cells, lanugo hair, and fat from vernix or infantile mucin in the maternal pulmonary vasculature. More recent incidence data results from national registries in the United States and the United Kingdom, which used clinical entry criteria in laboring women or parturients undergoing cesarean section or dilation and evacuation of an intrauterine fetal demise. These criteria included acute maternal cardiovascular collapse with evidence of respiratory compromise and/or coagulopathy. The pathophysiology of AFE is not completely understood. AFE most commonly occurs during labor, delivery, or the immediate postpartum period. However, it has been reported to occur up to 48 h postpartum. Once thought to be the result of an actual embolic obstruction of the pulmonary vasculature by components of amniotic fluid, AFE might result from immune activation and present as an anaphylactoid process. AFE likely involves a spectrum of severity from a subclinical process to a catastrophic event. Early recognition and prompt and aggressive resuscitative efforts enhance the probability of maternal and neonatal survival.