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, common clinical features include shortness of breath, altered mental status, followed by sudden cardiovascular collapse, disseminated intravascular coagulation (DIC), and maternal death. The first case report of AFE was published in a 1926 Brazilian medical journal¹ and AFE was recognized as a syndrome in 1941, when 2 investigators 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, and pathogenesis of this mysterious obstetric complication.

The incidence of AFE, including both fatal and nonfatal cases, ranges between 1 in 12,953 deliveries in the United States³ to 1 in 50,000 deliveries in the United Kingdom.⁴ 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. Diagnostic criteria for AFE as proposed in the US national registry⁵ are summarized in Table 14-1.

There have also been wide variances in the published maternal mortality rates associated with AFE. In the US national registry examining 46 cases of AFE, the maternal mortality rate was 61%, with a neurologically intact maternal survival rate of 15% in cases which occurred in the late 1980s and early 1990s. More recent population-based studies have reported a decreased case fatality rate from AFE (Table 14-2).^{3,4,5,6,7,8,9,10,11,12,13, 14} These improving survival statistics may in part reflect improvement in general and specialized medical ...