Amniotic Fluid Embolism

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Chapter 197 Amniotic Fluid Embolism

INTRODUCTION

Description: Amniotic fluid embolism is a rare but frequently fatal complication of labor in which amniotic fluid containing fetal squamous cells and hair enters the maternal vascular system and becomes lodged in the pulmonary vascular bed. Mechanical obstruction and anaphylaxis combine to produce an often-fatal clinical course. The term “anaphylactoid syndrome of pregnancy” has been suggested but has not received wide acceptance.
Prevalence: One of 30,000 deliveries (despite its rarity, one of the most common causes of maternal mortality).
Predominant Age: Reproductive (late labor or immediately postpartum).
Genetics: No genetic pattern.

ETIOLOGY AND PATHOGENESIS

Causes: Anaphylaxis induced by fetal squamous cells and hair. Mechanical obstruction of pulmonary vessels by fetal squamous cells and hair. Diffuse intravascular coagulation resulting in coagulopathy.
Risk Factors: Tumultuous labor, reduced uterine tone, premature separation of the placenta, history of allergy or atopy.

CLINICAL CHARACTERISTICS

Signs and Symptoms (Variable)

• Respiratory distress followed by cyanosis followed by cardiovascular collapse followed by hemorrhage with depletion of fibrinogen; platelets; and factors V, VIII, and XIII) followed by coma

DIAGNOSTIC APPROACH

Differential Diagnosis

• Pulmonary embolism (thrombus)
• Myocardial infarction
• Cardiac arrhythmia

Associated Conditions: Allergy and atopy.

Workup and Evaluation

Laboratory: Coagulation studies, blood gas measurements, renal function studies, all on an ongoing basis.
Imaging: May help in managing pulmonary complications but generally not helpful in establishing the diagnosis.
Special Tests: Continuous monitoring of oxygen saturation and invasive hemodynamic monitoring (pulmonary artery catheter) essential.
Diagnostic Procedures: History and physical examination. Exclusion of other causes.

Pathologic Findings

Fetal squamous cells and lanugo present in the pulmonary vascular space (typical but not sensitive or specific).

MANAGEMENT AND THERAPY

Nonpharmacologic

General Measures: Aggressive airway control and cardiovascular resuscitation (including myocardial support, inotropic agents and fluids, high-concentration oxygen therapy). The use of vasopressors has been reported to be successful. Correction and support for clotting defects (blood and platelets, fresh-frozen plasma, and cryoprecipitate as indicated).
Specific Measures: None. In women who suffer cardiac arrest before delivery, consideration should be given to perimortem cesarean delivery to improve newborn outcome. In those who have not suffered arrest, maternal considerations generally take precedence.
Diet: Nothing by mouth until condition resolved.
Activity: Bed rest until condition resolved.

Drug(s) of Choice

No specific medications. Other medications as needed for cardiovascular, pulmonary, renal, and coagulation support.

FOLLOW-UP

Patient Monitoring: Intensive hemodynamic monitoring required. Laboratory testing in anticipation of coagulopathy.
Prevention/Avoidance: None.
Possible Complications: Acute mortality rates with amniotic fluid embolism approximate 50%. Of women who survive, 50% have a life-threatening bleeding diathesis. Renal failure is common, as are pulmonary edema and adult respiratory distress syndrome. Of women who suffer cardiac arrest during the initial phase, only 8% survive neurologically intact. Overall maternal mortality approaches 80%. More than half of the neonates that survive have neurologic impairment.
Expected Outcome: Prolonged and complicated course for those who survive.

MISCELLANEOUS

Other Notes: The most devastating effects of amniotic fluid embolism appear to be mediated through the anaphylactic reaction induced. Experimental studies indicate that pretreatment with inhibitors of leukotriene synthesis can prevent the development of symptoms in experimental settings.
ICD-9-CM Codes: 673.13 (if diagnosed before delivery), 673.11 (if diagnosed after delivery).

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REFERENCES

Level II

Aguilera LG, Fernandez C, Plaza A, et al. Fatal amniotic fluid embolism diagnosed histologically. Acta Anaesthesiol Scand. 2002;46:334.

Benson MD, Kobayashi H, Silver RK, et al. Immunologic studies in presumed amniotic fluid embolism. Obstet Gynecol. 2001;97:510.

Benson MD, Lindberg RE. Amniotic fluid embolism, anaphylaxis, and tryptase. Am J Obstet Gynecol. 1996;175:737.

Clark SL. New concepts of amniotic fluid embolism: a review. Obstet Gynecol Surv. 1990;45:360.

Clark SL, Hankins GDV, Dudley DA, et al. Amniotic fluid embolism: analysis of the National Registry. Am J Obstet Gynecol. 1995;172:1159.

Martin SR, Foley MR. Intensive care in obstetrics: an evidence-based review. Am J Obstet Gynecol. 2006;195:673.

Level III

Green BT, Umana E. Amniotic fluid embolism. South Med J. 2000;93:721.

Hardin L, Fox LS, O’Quinn AG. Amniotic fluid embolism. South Med J. 1991;84:1046.

Moore J, Baldisseri MR. Amniotic fluid embolism. Crit Care Med. 2005;33:S279.

Morgan M. Amniotic fluid embolism. Anaesthesia. 1979;34:20.

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