AFE remains poorly understood. There are 2 main theories:
Mechanical: thought to be related to direct obstruction of the maternal circulation by fetal squamous cells in amniotic fluid.
Immune mediated: activation of the immune system caused by exposure of fetal antigens leading to a series of cellular events not dissimilar to SIRS and anaphylaxis.
A biphasic response has been described and point of care transthoracic echocardiography may be helpful:
- Phase 1: (lasts about 30 min): the pulmonary artery pressure increases, and causes right ventricular failure with subsequent microvascular damage and hypotension.
- Phase 2: occurs in patients who survive the initial insult, and is characterised by left ventricular failure, endothelial activation and leakage, and DIC.
