ObstetricsTier 2Disease (DEADMAN)

Amniotic fluid embolism

Description

Rare, catastrophic obstetric emergency - amniotic fluid/fetal material enters maternal circulation, triggering an anaphylactoid-like systemic reaction rather than simple mechanical embolism
Classic triad: sudden hypoxia, hypotension/cardiac arrest, coagulopathy (DIC)

Rare (in the order of 1-in-several thousand to tens of thousands of deliveries) but a leading cause of direct maternal mortality where it occurs
Typically during labour, delivery, or immediately postpartum; can also occur after caesarean or uterine trauma

Amniotic fluid components (fetal squames, lanugo, mucin, tissue factor) enter the maternal circulation via breaks in the utero-placental interface -> trigger an anaphylactoid/inflammatory cascade -> profound pulmonary vasospasm and right heart failure, then left heart failure, and massive DIC from tissue factor exposure

Clinical diagnosis of exclusion - no confirmatory test; made in the correct clinical context after excluding other causes of sudden collapse (PE, eclampsia, anaphylaxis, sepsis, haemorrhage)
Biphasic course: acute cardiorespiratory collapse, followed (if the mother survives the first phase) by severe coagulopathy/DIC

Resuscitation is entirely supportive - airway/breathing/circulation, high-flow oxygen/intubation, aggressive haemodynamic support (vasopressors, inotropes)
Immediate perimortem/emergency caesarean if arrest occurs undelivered - improves both maternal and fetal outcomes
Massive transfusion protocol for DIC, guided by coagulation studies rather than crystalloid-heavy resuscitation
Multidisciplinary team (obstetrics, anaesthetics, ICU, haematology) mobilised immediately

Weakly associated risk factors: induction of labour, advanced maternal age, multiple pregnancy, polyhydramnios, placenta praevia/abruption, instrumental/caesarean delivery - but AFE can occur with no risk factors and is largely unpredictable

High mortality (historically quoted up to 20-40%, improving with rapid resuscitation and blood product availability); a significant proportion of survivors have neurological injury from the hypoxic insult
Fetal outcome is closely tied to time-to-delivery if arrest occurs before birth

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