Chapter 14: Amniotic Fluid Embolism

INTRODUCTION

Amniotic fluid embolism (AFE) is a catastrophic syndrome typically occurring during labor and delivery or immediately postpartum. Although presenting symptoms may vary, the most common clinical features include shortness of breath, altered mental status, followed by sudden cardiovascular collapse, disseminated intravascular coagulation (DIC), and often maternal death. The diagnosis remains clinical and involves a triad of sudden hypoxia and hypotension followed by coagulopathy with the exclusion of any other likely cause. The first case report of AFE was published in a 1926 Brazilian medical journal¹ and AFE was recognized as a syndrome in 1941, when two investigators in Chicago described fetal mucin and squamous cells during postmortem examination of the pulmonary vasculature in women who had unexplained obstetric deaths.² Since then, over 1000 studies, case reports, and series have been published in an attempt to elucidate the etiology, risk factors, pathogenesis, and treatment of this mysterious obstetric complication.

The reported incidence of AFE, including both fatal and nonfatal cases, ranges between 1 in 13,000 deliveries in the United States³ to 1 in 50,000 deliveries in the United Kingdom.⁴ Approximate maternal fatality rate and perinatal mortality associated with AFE are 13% to 30% and 9% to 44%, respectively in a study evaluating AFE cases in the United States and Europe (Conde-Agudelo, A 2009). The true incidence and mortality rates of AFE are confounded by several factors: (1) the clinical definition of AFE varies across reports, (2) the signs and symptoms of AFE overlap with other more common obstetrical complications such as hemorrhagic shock due to postpartum hemorrhage, (3) there is not a “gold standard” test for the diagnosis of AFE, (4) the diagnosis of AFE is to a great extent a diagnosis of exclusion, and (5) many of the population-based studies relying on hospital discharge diagnostic codes do not ascertain the clinical diagnosis of AFE from the medical record. In addition, there are several significantly differing international criteria for the diagnosis of AFE compounding the challenges of refining risk factors, diagnosis, pathophysiology, and prognosis. New proposed diagnostic criteria for the case definition of AFE were recently developed by the Society for Maternal Fetal Medicine and the Amniotic Fluid Embolism Foundation in order to improve the identification of true cases for the primary purpose of clinical research. Uniform diagnostic criteria for research reporting of AFE as proposed by the committee are summarized in Table 14-1.