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4/1/2013

Amniotic Fluid Embolism

Amniotic Fluid Embolism (AFE) is an uncommon, catastrophic obstetric emergency. The frequency of AFE is 2-7 cases per 100,000 births with a mortality rate as high as 60%. It is responsible for approximately 10-15% of maternal deaths in developed countries. If AFE occurs prior to delivery, the neonatal mortality rate is estimated to be 10-50%. Many surviving neonates suffer neurologic impairment. Neurologic impairment is also common in maternal survivors, particularly those who suffer associated cardiac arrest. Although the pathophysiology of AFE is not known, it has been suggested that entry of amniotic fluid into the maternal circulation activates inflammatory mediators causing an anaphylactoid response.

Although AFE occurs most commonly during labor and delivery or the immediate postpartum period, it has been reported to occur as late as 48 hours postpartum. AFE should be considered in the differential diagnosis of sudden cardiorespiratory collapse in the laboring or recently delivered woman. Patients may also present with acute severe consumptive coagulopathy without cardiorespiratory symptoms. Risk factors for AFE include advanced maternal age, multiparity, pre-eclampsia, eclampsia, diabetes mellitus, and polyhydramnios or other uterine over-distention. Labor abnormalities associated with an increased risk of AFE include precipitous labor, induction of labor, placental abruption, cervical laceration, and uterine rupture.

Three phases have been described during the clinical course of AFE. The first phase involves pulmonary and systemic hypertension with resultant severe pulmonary vasoconstriction, characterized by respiratory distress and hypoxemia, leading to altered mental status followed by hemodynamic collapse. The second phase involves decreased systemic vascular resistance and left ventricular stroke work index. The third phase is characterized by lung injury and coagulopathy, which may include disseminated intravascular coagulation (DIC). The tissue injury and end organ system failure seen in AFE with pulmonary vascular constriction often lead to pulmonary hypertension, right-sided heart failure, and global myocardial depression.

The management of AFE includes early recognition and prompt multidisciplinary management including anesthesia, respiratory therapy, critical care, and MFM. Massive blood transfusion protocols should be activated. An operating room, interventional radiology team, and the Intensive Care Unit should be made available. Laboratory assessment is not necessary to make the diagnosis, but arterial blood gas analysis, serial blood counts, and coagulation studies may help guide resuscitation. An arterial catheter to monitor blood pressure can be helpful. The management should focus on oxygenation and circulatory support with CPR and debrillation as needed, blood products, judicious use of intravenous fluids to avoid right heart overload, vasopressors, and if necessary, cardiopulmonary bypass. If AFE occurs prior to delivery, maternal resuscitation is aided by expeditious delivery.

Control of hemorrhage and correction of coagulopathy should be the goal of replacement therapy of blood products, with the possible use of recombinant factor VII if needed. Hysterectomy may be required to control hemorrhage. Support of maternal oxygenation often requires high oxygen flow rate and invasive mechanical ventilation with increasing levels of oxygen and increased positive end-expiratory pressures. The goal of therapy is to limit hypoxemia and hypotension to prevent ischemic consequences such as brain injury, acute renal damage, and myocardial ischemia.

Further Reading:

Cunningham F, Leveno KJ, Bloom SL, et al, Obstetrical Hemorrhage. Williams Obstetrics, 25e New York, NY: McGraw-Hill; 2018. Chapter 41.

Pacheco LD, Clark SL, Klassen M, Hankins GDV. Amniotic fluid embolism: principles of early clinical management. Am J Obstet Gynecol. 2020 Jan;222(1):48-52. doi: 10.1016/j.ajog.2019.07.036. Epub 2019 Jul 31. PMID: 31376394.

Society for Maternal-Fetal Medicine (SMFM), Amniotic fluid embolism: diagnosis and management. Am J Obstet Gynecol. 2016 Aug;215(2):B16-24. doi: 10.1016/j.ajog.2016.03.012. Epub 2016 Mar 14.

Initial Approval:  April 2013; Revised: September 2015, Reaffirmed March 2018, Revised November 2018, Reaffirmed July 2020, Revised January 2022, Minor revisions September 2023

 

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