Amniotic fluid embolism

Amniotic fluid embolism

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An amniotic fluid embolism (AFE) is a rare but serious condition with high morbidity and mortality. It is characterized by cardiopulmonary collapse and disseminated intravascular coagulation (DIC). It is the second-leading cause of peripartum maternal death in the US and number one cause of peripartum cardiac arrest.

Risk Factors

Risk factors for the development of AFE are advanced maternal age, multiparity, male fetuses, and trauma. Induction of labor has also been found to increase risk for AFE.

Pathophysiology

AFE is poorly understood. It is thought to originate from a disruption of the placenta-amniotic interface with the subsequent entry of amniotic fluid and fetal elements (such as hair, meconium, squama, and mucin) into the maternal circulation. Upon entering the pulmonary tree, intense pulmonary vasoconstriction occurs. This may be associated with concomitant bronchoconstriction. The hemodynamic result is acute pulmonary arterial obstruction, dilatation of the right ventricle and the right atrium, and significant tricuspid regurgitation. The right ventricular enlargement causes the intraventricular septum to bow into the left ventricle creating obstruction and systolic dysfunction, further raising pulmonary artery pressure and decreasing cardiac output. Hypoxemia and hypotension lead to sudden cardiovascular collapse.

Normally, pregnancies are procoagulant, to begin with, and the introduction of amniotic fluid and fetal elements trigger inflammatory mediators activating the coagulation cascade and fibrinolytic systems resulting in DIC.

Diagnosis

The American Society for Maternal-Fetal Medicine, after a consensus symposium has created its criteria for AFE, which require the following:

1. Sudden cardiopulmonary collapse, or hypotension (systolic blood pressure less than 90 mmHg) with hypoxia (SpO2 less than 90%)
2. DIC, according to the international society on thrombosis and hemostasis (ISTH) definition
3. Symptomatology either during labor or during placental delivery (or up to 30 minutes later)
4. No fever