amniotic fluid embolism

Pathophysiology: AFE is now understood as an anaphylactoid syndrome rather than simple mechanical embolization—fetal antigens entering maternal blood (via placental/uterine vein disruption during labor, C-section, or trauma) trigger a massive inflammatory and complement-mediated response similar to anaphylaxis and sepsis. This causes biphasic hemodynamic collapse: initial pulmonary vasospasm/right heart failure and severe hypoxia, followed by left ventricular failure and cardiogenic shock. Concurrently, amniotic fluid contains tissue factor and procoagulants that activate the coagulation cascade, causing severe DIC with hemorrhage.

Clinical presentation: Classic triad—hypoxia, hypotension, coagulopathy—occurring abruptly during labor, cesarean delivery, or within 30 minutes postpartum. Patients may have acute dyspnea, seizures, cardiac arrest, and profuse bleeding (uterine atony plus DIC). Fetal distress is common if AFE occurs before delivery.

Risk factors: Advanced maternal age, multiparity, placenta previa/abruption, polyhydramnios, cesarean or operative delivery, uterine trauma, and eclampsia—though AFE often occurs without identifiable risk factors and cannot be reliably predicted or prevented.

Diagnosis: Clinical diagnosis of exclusion; no specific confirmatory test. Differentials include pulmonary embolism, eclampsia, anaphylaxis, sepsis, and peripartum cardiomyopathy. Autopsy may show fetal squamous cells/debris in maternal pulmonary vasculature, but this is neither sensitive nor specific.

Management: Immediate resuscitation—ABCs, 100% oxygen, intubation if needed, aggressive hemodynamic support (vasopressors, inotropes), and correction of coagulopathy with blood products (FFP, cryoprecipitate, platelets). Emergent delivery of fetus if not yet delivered. Multidisciplinary team approach (OB, anesthesia, critical care, hematology) is essential. Cardiopulmonary bypass or ECMO may be considered in refractory cases.

Prognosis: High maternal mortality (historically up to 20-60%, more recent estimates lower with early recognition/treatment ~20%); significant risk of neurologic injury in survivors. Fetal mortality/morbidity also significant if AFE occurs antepartum due to hypoxia.

High-yield associations: Think of AFE as a mimic of both anaphylaxis and PE in the peripartum setting; the coexistence of DIC helps distinguish it from a straightforward PE. Often tested with vignette describing a laboring woman who suddenly becomes hypoxic, hypotensive, and starts bleeding uncontrollably.