Background: Amniotic fluid embolism is a rare obstetric emergency in which amniotic fluid, fetal cells, hair, or other debris enters the maternal circulation, causing cardiorespiratory collapse.

In 1941, Steiner and Luschbaugh described amniotic fluid embolism for the first time after they found fetal debris in the pulmonary circulation of women who died during labor.

Current data from the National Amniotic Fluid Embolus Registry suggests that the process is more similar to anaphylaxis than to embolism, and the name anaphylactoid syndrome of pregnancy has been suggested.

The diagnosis traditionally has been made at autopsy when fetal squamous cells are found in the maternal pulmonary circulation; however, it is known that fetal squamous cells commonly are found in the circulation of laboring patients who do not develop the syndrome. In a patient who is critically ill, aspirate of the distal port of a pulmonary artery catheter that contains fetal squamous cells is considered suspicious for but not diagnostic of amniotic fluid embolism syndrome. Do not neglect other causes of hemodynamic instability.

Pathophysiology: The pathophysiology of amniotic fluid embolism is poorly understood. Amniotic fluid and fetal cells enter the maternal circulation triggering a 2-phase process. In phase I, pulmonary artery vasospasm with pulmonary hypertension and elevated right-ventricle pressure cause hypoxia. Hypoxia causes myocardial and pulmonary capillary damage, the left heart fails, and acute respiratory distress syndrome develops.

Women who survive the above events may enter phase II. This is a hemorrhagic phase characterized by massive hemorrhage with uterine atony and disseminated intravascular coagulation (DIC); however, fatal consumptive coagulopathy may be the initial presentation.

Frequency:
　

• In the US: Incidence of amniotic fluid embolism is estimated at 1:8,000 to 1:30,000 pregnancies.

• Internationally: Incidence is similar to incidence in the US.

Mortality/Morbidity: Maternal mortality approaches 80%. The mortality rate was 61% in the national registry, which contained 46 cases. Between 5-10% of maternal mortality in the US is due to amniotic fluid embolism. Of patients with amniotic fluid embolism, 50% die within the first hour of onset of symptoms. Of survivors of the initial cardiorespiratory phase, 50% develop a coagulopathy.

Survival is rare. Most women who survive have permanent neurologic impairment. Neonatal survival is 70%. No evidence indicates that survivors are at risk for amniotic fluid embolism during future pregnancies.

Race: No racial or ethnic predilection exists.

Sex: Amniotic fluid embolism only occurs in women.

History: Amniotic fluid embolism usually occurs during labor but has been recorded as occurring during abortion, abdominal trauma, and amnioinfusion.

A woman in the late stages of labor becomes acutely dyspneic with hypotension; she may experience seizures quickly followed by cardiac arrest. Massive hemorrhage associated with DIC follows and then death. Most patients die within one hour of onset.

Physical: In case reports, patients are described as developing acute shortness of breath, sometimes with a cough, followed by severe hypotension. Signs and symptoms indicative of possible amniotic fluid embolism include the following:

• Hypotension

  Blood pressure may drop significantly with loss of diastolic measurement.

• Dyspnea

  Labored breathing as well as tachypnea may occur.

• Seizure

  The patient may experience tonic-clonic seizures.

• Cough

  This is usually a manifestation of dyspnea.

• Cyanosis

  As hypoxia/hypoxemia progresses, circumoral and peripheral cyanosis may be evident as well as changes in mucous membranes.

• Fetal bradycardia

  Responding to the hypoxic insult fetal heart rate may drop below 110 beats per minute. If this last for 10 minutes or more it is a bradycardia. A rate of 60 beats per minute or less over 3 to 5 minutes may indicate a terminal bradycardia.

• Pulmonary edema

  Usually identified on chest film.

• Cardiac arrest

• Uterine atony

  Uterine atony usually results in excessive bleeding after delivery. Failure of the uterus to become firm with bimanual massage is diagnostic.

Lab Studies:
　

• Arterial blood gas (ABG)

• Expect changes consistent with hypoxia/hypoxemia

• pH decreased (normal 7.40-7.45)

• P0₂ decreased (normal 104-108 mm Hg)

• PCO₂ increased (normal 27-32 mm Hg)

• Base excess increased

• CBC with platelets

• Hemoglobin and hematocrit should be within normal limits.

• Thrombocytopenia is rare. If platelets are less than 20,000/mm³ or if bleeding occurs with platelets between 20,000-50,000/mm³, transfuse platelets 1-3 units/10 kg/day.

• Prothrombin time and partial thromboplastin

• Prothrombin time (PT) is prolonged because clotting factors are used up. Values are institution specific, but intervention is indicated when the PT is 1.5 times the control value. Administer fresh frozen plasma (FFP) to normalize the PT.

• Partial thromboplastin time (PTT) may be normal or shortened.

• If fibrinogen is less than 100 mg/dL, administer cryoprecipitate. Each unit of cryoprecipitate will raise the fibrinogen 10 mg/dL.

• Blood type and screen in anticipation of the requirement for a transfusion.

Imaging Studies:
　

• Chest x-ray, posterior-anterior (PA), and lateral (LAT) findings usually are nonspecific, but evidence of pulmonary edema may be seen.

Other Tests:
　

• A 12-lead ECG may show tachycardia, ST segment, T-wave changes, and findings consistent with right-ventricle strain.

Procedures:
　

• Arterial line to accurately measure blood pressure and to obtain ABG readings

• Pulmonary artery catheter to monitor wedge pressure, cardiac output, oxygenation, and systemic pressures

Histologic Findings: On autopsy, blood vessels in the lungs may show evidence of fetal debris (ie, squamous cells, vernix, and mucin).

Kobayashi et al used antibody TKH-2, which reacts with meconium and the mucin derived from amniotic fluid, glycoprotein, to stain the lung tissue of women who were diagnosed with amniotic fluid embolism. TKH-2 immunostaining appears to be a sensitive method of detecting mucin in the lungs of women suspected of having an amniotic fluid embolus.

Medical Care: Treatment is supportive.

• Administer oxygen to maintain normal saturation. Intubate if necessary.

• Initiate cardiopulmonary resuscitation (CPR) if the patient arrests. If she does not respond to resuscitation, perform perimortem cesarean section.

• Treat hypotension with crystalloid and blood products. Use pressors as necessary.

• Consider pulmonary artery catheterization in hemodynamically unstable patients.

• Continuously monitor the fetus.

• Treat coagulopathy with fresh frozen plasma for a prolonged PTT, cryoprecipitate for fibrinogen lower than 100 mg/dL, and platelets for platelet counts less than 20,000.

Surgical Care: Perform emergent cesarean section in cases of maternal arrest that are unresponsive to resuscitation.

Consultations: Women who survive amniotic fluid embolism most likely will require admission to the ICU. Left heart failure is a common late occurrence. Additionally, survivors most likely will have neurologic sequelae.

• Consult the intensive care service in anticipation of transfer to that unit.

• Consult neurology as needed if patient shows signs of neurologic deficits.

Drugs are used in amniotic fluid embolism to stabilize the patient. Pressors are used to maintain blood pressure, and inotropes are used to improve contractility. Use of steroids has been suggested because the process may be immune mediated. Uterotonics may be used to limit postpartum bleeding.
　

Drug Category: Sympathomimetic/vasopressor agents -- Used in amniotic fluid embolism to maintain blood pressure.

Drug Category: Inotropes/inotropic agents -- Used to improve myocardial contractility in patients with amniotic-fluid embolism.

Drug Category: Steroids -- Some authorities suggest steroid use may be helpful in amniotic fluid embolism, because the process may be immune mediated.

Drug Category: Uterotonics -- Uterine Atony (failure of the uterus to contract and involute thus closing off the bleeding spiral arteries after delivery of the placenta) may be a source of significant postpartum bleeding. These drugs cause the uterus to contract.

Further Inpatient Care:
　

• Admit patient into the ICU.

Transfer:
　

• Transfer to a level 3 hospital may be required once the patient is stable.

Deterrence/Prevention:
　

• Amniotic fluid embolism is an unpredictable event.

Complications:
　

• Pulmonary edema is a common occurrence in survivors. Pay close attention to fluid input and output.

• Left heart failure may occur. Some sources recommend inotropic support.

• DIC treat with blood components.

Prognosis:
　

• Maternal mortality is 61%.

• Most survivors have neurologic deficits.

• Infant intact survival is 70%. Neurologic status of the infant is directly related to the time elapsed between maternal arrest and delivery.

Patient Education:
　

• Risk of recurrence is unknown. The recommendation for elective cesarean section during future pregnancies in an attempt to avoid labor is controversial.

Medical/Legal Pitfalls:
　

• Failure to respond emergently is a pitfall. Amniotic fluid embolism is a clinical diagnosis. Steps must be taken to stabilize the patient as soon as symptoms manifest.

• Failure to perform perimortem cesarean delivery in a timely fashion is a pitfall. After 5 minutes of unsuccessful CPR, abdominal delivery is recommended.

• Failure to consider the diagnosis during legal abortion is a pitfall. A review of the literature indicates that most case reports of amniotic fluid embolism have occurred during late second-trimester abortions.