Anaphylactoid Syndrome/Amniotic Fluid Embolism
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- Amniotic fluid embolism (AFE) is a syndrome associated with cardiorespiratory collapse during pregnancy or shortly after delivery.
- Classically includes a triad of hypoxia, hypotension, and coagulopathy surrounding labor and delivery
- Varies widely because of lack of diagnostic criteria
- 1.2 to 7.7 per 100,000 deliveries in the United Kingdom, Canada, and United States
Difficult to assess, as this is a rare event
Etiology and Pathophysiology
- Incompletely understood
- Amniotic fluid enters maternal circulation through disruption of uterine vessels.
- Causes an abnormal activation of proinflammatory mediators in susceptible patients, leading to cardiopulmonary arrest similar to anaphylaxis or systemic inflammatory response syndrome
- However, fetal cells can also be found in pulmonary artery samples following normal delivery.
- Hemodynamic response not caused by pulmonary vasculature obstruction. Instead, an initial period of pulmonary and systemic hypertension is followed by:
- Pulmonary vasoconstriction, resulting in severe pulmonary HTN, VQ mismatch, and hypoxia
- Acute cor pulmonale: right ventricular failure with ventricular dilation and deviation of the interventricular septum
- Impaired left ventricular filling and myocardial ischemia causing left ventricular failure as the dominant hemodynamic alteration
- Coagulopathy present in 83% of patients (1)[B], but incompletely understood
- Amniotic fluid can induce platelet aggregation, lead to release of platelet factor III, activate factor X, and the complement cascade.
- Tissue factor in amniotic fluid can induce thrombocytopenia in animal models, but it is unclear if any of these factors are present in large enough quantities to induce such a significant coagulopathy.
- Disseminated intravascular coagulation (DIC) results with potential for massive hemorrhage.
A genetic component has not been identified.
Large population based studies have identified several risk factors:
- Medical induction of labor
- Maternal age ≥35 years old
- Multiple gestation
- Cesarean section prior to development of symptoms
- Cervical laceration or uterine rupture
- Causality of association with operative vaginal delivery or cesarean section is not always clear.
- Placental abruption
No identified measure known to reduce the risk of AFE
Commonly Associated Conditions
- Cesarean section: Strong association with AFE as emergent cesarean may be required for delivery given fetal distress; may be causative in some cases
- DIC: consumptive coagulopathy that is often a component of the initial presentation of AFE