Amniotic fluid embolism

Did You Know?

• The complication was originally described in 1926 by J. R. Meyer at the University of São Paulo.
• A 1941 case study of eight autopsies by Clarence Lushbaugh and Paul Steiner enabled widespread recognition of the diagnosis.

Signs and symptoms

Amniotic fluid embolism is suspected when a woman giving birth experiences sudden insufficient oxygen to body tissues, low blood pressure, and profuse bleeding due to defects in blood coagulation. Signs and symptoms vary but involve multiple organ systems. A patient may present with a cough due to release of bradykinin, an inflammatory marker causing an anaphylactoid reaction. The cough may progress to dyspnea and shortness of breath from vasoconstriction of pulmonary arterioles, reducing airflow and oxygen delivery. The heart compensates with tachycardia. The fetus, if still in labor, may show tachycardia and decelerations on fetal heart rate tracing. Low pulse oximetry readings confirm hypoxia. Most patients experience hypotension from widespread inflammation and anaphylaxis. As fluid builds in the lungs, pulmonary hypertension develops. The final stage before cardiovascular collapse involves hemorrhaging from overactivation of the coagulation cascade, leading to disseminated intravascular coagulation (DIC).

Causes and pathophysiology

Several mechanisms are posited to cause amniotic fluid embolism. One involves a difficult labor, abnormal placenta, or abdominal trauma (e.g., from caesarean section) disrupting the barrier between maternal and fetal fluid. This disruption causes hydrostatic and oncotic pressure changes, leaking fetal fluid into maternal circulation. The fluid travels through veins to the inferior vena cava, right atrium, right ventricle, and pulmonary artery, disseminating through the pulmonary circuit. Fluid accumulation in alveoli increases pressures, straining the heart and causing pulmonary hypertension, right ventricular heart failure, and cardiovascular collapse. Another school of thought holds that inflammatory markers in amniotic fluid trigger widespread inflammatory activation in maternal blood, causing intense pulmonary vasospasm and dysregulation of pulmonary circulation, leading to systemic failure. This is supported by studies showing amniotic fluid can activate complement, and that C1 esterase inhibitor levels are significantly decreased in AFE patients. Amniotic fluid also contains tissue factor and other clotting factors, producing a hypercoagulable state amplified by decreased C1 esterase inhibitor, which normally inhibits Factor XIa and XIIa. This leads to DIC, often with hyperfibrinolysis due to elevated tissue plasminogen activator and decreased total thrombin-activatable fibrinolysis inhibitor.

Diagnosis

Diagnosis requires the presence of hypoxia, hypotension, and acutely severe hemorrhage occurring during labor or up to 30 minutes after labor. An arterial blood gas (ABG) must be taken immediately to determine acid-base status; it should demonstrate low pH and increased PCO2 consistent with respiratory acidosis. Continuous pulse oximetry readings determine the level of hypoxia and oxygen requirements. Coagulation studies should be collected, with attention to prothrombin time (PT) and partial thromboplastin time (PTT); PT will be prolonged, and PTT may be normal or prolonged. A type and screen should be ordered in case blood products are needed. Biomarkers that may indicate AFE include insulin-like growth-factor-binding protein-1 (ILGFBP-1), which has high sensitivity for detecting a breach in maternal-fetal circulation; significantly low C3 and C4 levels; and high amounts of tumor markers CEA and CA-125 found in amniotic fluid.

Treatment and management

Stabilizing the patient is the first line of action. Oxygen is delivered via a high flow rebreather mask; if the patient is unstable, endotracheal intubation and mechanical ventilation are used. For cardiovascular compromise from late-stage vasodilation, phenylephrine is given to vasoconstrict arteries and raise blood pressure; epinephrine is also administered due to the anaphylaxis-like reaction. If hemorrhage occurs, packed red blood cells are transfused promptly. For DIC, recombinant activated factor VIIa is a quick treatment; serine proteinase inhibitor FOY and Aprotinin have also been used. Heparin may be used, attributable not only to its anticoagulant effect in DIC but also to its ability to enhance C1 esterase inhibitor activity, reducing complement activation and inflammation. A case report documented successful use of C1 esterase inhibitor concentrate. Inhaled milrinone, if used immediately after AFE, may mitigate pulmonary vasoconstriction by causing selective pulmonary vasodilation without significant changes in mean arterial pressure or systemic vascular resistance.