AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Background

Amniotic fluid embolism (AFE) is a rare obstetric emergency in which it is postulated that amniotic fluid, fetal cells, hair, or other debris enter the maternal circulation, causing cardiorespiratory collapse.

In 1941, Steiner and Luschbaugh described AFE 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 suggest that the process is more similar to anaphylaxis than to embolism, and the term anaphylactoid syndrome of pregnancy has been suggested because fetal tissue or amniotic fluid components are not universally found in women who present with signs and symptoms attributable to AFE.¹

The diagnosis of AFE has traditionally been made at autopsy when fetal squamous cells are found in the maternal pulmonary circulation; however, fetal squamous cells are commonly found in the circulation of laboring patients who do not develop the syndrome. In a patient who is critically ill, a sample obtained by aspiration of the distal port of a pulmonary artery catheter that contains fetal squamous cells is considered suggestive of but not diagnostic of AFE syndrome.² The diagnosis is essentially one of exclusion based on clinical presentation. Other causes of hemodynamic instability should not be neglected.

Pathophysiology

The pathophysiology of AFE is poorly understood. Based on the original description, it was theorized that amniotic fluid and fetal cells enter the maternal circulation, possibly triggering an anaphylactic reaction to fetal antigens. However, fetal material is not always found in the maternal circulation in patients with AFE, and material of fetal origin is often found in women who do not develop AFE.

Benson et al³ tested 2 hypotheses concerning the pathophysiology of AFE: (1) Clinical symptoms result from mast cell degranulation with the release of histamine and tryptase, or (2) Clinical symptoms result from activation of the complement pathway. Nine women with AFE were compared with 22 women with normal labors. Serum from patients with AFE was collected within 14 hours of symptom onset and frozen. Urine was collected within 12-24 hours after symptom onset. Control patients had complement levels measured on admission, during labor, and the day after delivery.

Six of the 9 women with AFE died, and all 9 required blood transfusions for disseminated intravascular coagulation (DIC). Seven women had no evidence of mast cell degranulation (ie, either urinary histamine or serum tryptase). Compared with postpartum control patients, complement levels in the AFE group were severely depressed. C3 in the AFE group was 44 compared with 117.2 in the postpartum group. C4 was 10.7 in the AFE group versus 29.4 in the postpartum group. These differences were statistically significant. This suggests that complement activation may play an important role in the pathophysiology of AFE.

Farrar and Gherman⁴ reported the case of a 40-year-old multipara in active labor with acute onset of facial erythema, seizures, hypoxia, cardiac arrest, DIC, and ultimately death. Fetal squames and fibrin thrombi were found in the pulmonary tree at autopsy. Blood drawn 2 hours after symptom onset had a serum tryptase level of 4.7 ng/mL (normal <1 ng/mL).

A case reported by Marcus et al⁵, in which AFE developed after a spontaneous rupture of membranes, demonstrated no increase in mast cells or degranulation in lung tissue as shown by Giemsa staining. Serum tryptase levels were 11.4 ng/mL (normal <11.4 ng/mL).

The initiating event is poorly understood. However, usually during labor or other procedure, amniotic fluid and debris, or some as yet unidentified substance, enters the maternal circulation; this may trigger a massive anaphylactic reaction, activation of the complement cascade, or both. Progression usually occurs in 2 phases. In phase I, pulmonary artery vasospasm with pulmonary hypertension and elevated right ventricular pressure cause hypoxia. Hypoxia causes myocardial capillary damage and pulmonary capillary damage, left heart failure, and acute respiratory distress syndrome. Women who survive these events may enter phase II. This is a hemorrhagic phase characterized by massive hemorrhage with uterine atony and DIC; however, fatal consumptive coagulopathy may be the initial presentation.

Frequency

United States

Incidence of AFE is estimated at 1 case per 8,000-30,000 pregnancies. The true incidence is unknown because of inaccurate diagnoses and inconsistent reporting of nonfatal cases.

International

Incidence is similar to that of the United States.

Mortality/Morbidity

Maternal mortality approaches 80%. Mortality was 61% in the US national registry, which listed 46 cases. Five to 10% of maternal mortality in the United States is due to AFE. Of patients with AFE, 50% die within the first hour of onset of symptoms. Of survivors of the initial cardiorespiratory phase, 50% develop a coagulopathy.
 
The United Kingdom AFE registry reports a mortality of 37%. Of those who survived AFE, 7% were neurologically impaired.⁶

Survival is uncommon, although the prognosis is improved with early recognition and prompt resuscitation. Most women who survive have permanent neurologic impairment. Neonatal survival was 79% in the US registry and 78% in the UK registry.

Race

No racial or ethnic predilection exists.

Sex

AFE only occurs in women.

Age

Previously, advanced maternal age was believed to be a risk factor. No relationship to age has been found in the National Amniotic Fluid Embolus Registry.

CLINICAL

Section 3 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

History

Amniotic fluid embolism (AFE) usually occurs during labor but has occurred during abortion, after abdominal trauma, and during amnioinfusion.

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

Currently no definitive diagnostic test exists. The United States and United Kingdom AFE registries recommend the following 4 criteria, all of which must be present to make the diagnosis of AFE.^{6, 1, 7}

1. Acute hypotension or cardiac arrest
2. Acute hypoxia
3. Coagulopathy or severe hemorrhage in the absence of other explanations
4. All of these occurring during labor, cesarean delivery, dilation and evacuation, or within 30 minutes postpartum with no other explanation of findings

Physical

In case reports, patients are described as developing acute shortness of breath, sometimes with a cough, followed by severe hypotension. The following signs and symptoms are indicative of possible AFE:

• Hypotension: Blood pressure may drop significantly with loss of diastolic measurement.
• Dyspnea: Labored breathing and tachypnea may occur.
• Seizure: Tonic clonic seizures are seen in 50% of patients.
• Cough: This is usually a manifestation of dyspnea.
• Cyanosis: As hypoxia/hypoxemia progresses, circumoral and peripheral cyanosis and changes in mucous membranes may manifest.
• Fetal bradycardia: In response to the hypoxic insult, fetal heart rate may drop to less than 110 beats per minute (bpm). If this drop lasts for 10 minutes or more, it is a bradycardia. A rate of 60 bpm or less over 3-5 minutes may indicate a terminal bradycardia.
• Pulmonary edema: This is usually identified on chest radiograph.
• 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.
• Coagulopathy or severe hemorrhage in absence of other explanation (DIC occurs in 83% of patients.)⁷
• Altered mental status/confusion/agitation

Causes

AFE is considered an unpredictable and unpreventable event with an unknown cause. In the national registry, 41% of patients had a history of allergies. 

Reported risk factors for development of AFE include multiparity, advanced maternal age, male fetus, and trauma. In a retrospective review of a 12-year period encompassing 180 cases of AFE, of which 24 were fatal, medical induction of labor increased the risk of AFE.⁸ In the same study, AFE was positively associated with multiparity, cesarean section or operative vaginal delivery, abruption, placenta previa, and cervical laceration or uterine rupture.

DIFFERENTIALS

Section 4 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Other Problems to be Considered

Placental abruption
Aspiration

WORKUP

Section 5 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Lab Studies

• Arterial blood gas (ABG) levels: Expect changes consistent with hypoxia/hypoxemia.
• • Decreased pH levels (reference range = 7.40-7.45)
  • Decreased PO₂ levels (reference range = 104-108 mm Hg)
  • Increased PCO₂ levels (reference range = 27-32 mm Hg)
  • Base excess increased
• CBC with platelets
• • Hemoglobin and hematocrit levels should be within reference ranges.
  • Thrombocytopenia is rare. If platelets are less than 20,000/µL, or if bleeding occurs and platelets are 20,000-50,000/µL, transfuse platelets at 1-3 U/10 kg/d.
• Prothrombin time and activated partial thromboplastin time
• • 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.
  • Activated partial thromboplastin time (aPTT) may be within reference ranges or shortened.
• If fibrinogen level is less than 100 mg/dL, administer cryoprecipitate. Each unit of cryoprecipitate raises the fibrinogen level 10 mg/dL.
• Blood type and screen in anticipation of the requirement for a transfusion.

Imaging Studies

• Chest radiograph posteroanterior and lateral findings are usually nonspecific, but evidence of pulmonary edema may be observed.

Other Tests

• A 12-lead ECG may show tachycardia, ST segment and 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 (eg, squamous cells, vernix, mucin).

Aguilera et al⁹ reported fetal epithelial squamous cells obstructing 80% of pulmonary capillaries and fetal epithelial squamous cells in the alveoli on autopsy. A blood sample from a central venous catheter also showed fetal squames.

Marcus et al⁵ found focal interstitial hemorrhages in the kidneys, the left ventricle, and the interventricular septum. Alcian blue periodic acid-Schiff (PAS) stain was positive for mucin in the vasculature and oil red O stain for lipid was positive in the lungs.

Hankins and colleagues¹⁰ reported on goats injected with fresh amniotic fluid (n=8), filtered amniotic fluid (n=14), and meconium-stained fluid with solid debris (n=7). The animals were euthanized 3 hours after the procedure and samples of the lungs were taken. Amniotic fluid debris was found in 7 out of 7 of the meconium-stained group, 2 out of 8 of the fresh fluid group, and 1 out of 14 of the filtered group. Hankins et al concluded that, in this model, histopathologic confirmation of AFE was unreliable except in cases involving meconium-stained fluid.

Kobayashi et al¹¹ used antibody TKH-2, which reacts with meconium and the mucin derived from amniotic fluid (glycoprotein) to stain the lung tissue of women with AFE. TKH-2 immunostaining appears to be a sensitive method of detecting mucin in the lungs of women suspected of having an amniotic fluid embolus.

TREATMENT

Section 6 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

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 a perimortem cesarean delivery.
• Treat hypotension with crystalloid and blood products. Use pressors as necessary.
• Consider pulmonary artery catheterization in patients who are hemodynamically unstable.
• Continuously monitor the fetus.
• Treat coagulopathy with FFP for a prolonged aPTT, cryoprecipitate for a fibrinogen level less than 100 mg/dL, and transfuse platelets for platelet counts less than 20,000/µL.
• Lim and colleagues¹² reported a case of AFE in which the coagulopathy was treated with activated recombinant factor VIIa. The range of doses to treat serious bleeding is from 20-120 mcg/kg.
• Hemodialysis with plasmapheresis¹³ and extracorporeal membrane oxygenation with intra-aortic balloon counterpulsation¹⁴ have been described in case reports with successful outcomes in treating AFE patients with cardiovascular collapse.

Surgical Care

Perform emergent cesarean delivery in arrested mothers who are unresponsive to resuscitation.

Goldszmidt and Davies¹⁵ reported 2 cases of AFE in which the hemorrhage was controlled with bilateral uterine artery embolization. In both cases, bleeding was arrested with the procedure and both patients survived.

Consultations

Women who survive AFE will probably require ICU admission. Left heart failure is a common late occurrence. Additionally, survivors will probably have neurologic sequelae.

• Consult the intensive care service in anticipation of transfer to that unit.
• Consult neurologists as needed if a patient shows signs of neurologic deficits.

MEDICATION

Section 7 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Drugs are used in AFE 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 AFE to maintain blood pressure.

Drug Category: Inotropes/inotropic agents

Used to improve myocardial contractility in patients with amniotic-fluid embolism.

Drug Category: Corticosteroids

Some authorities suggest steroid use may be helpful in AFE because the process may be immune mediated.

Drug Category: Uterotonics

Cause the uterus to contract. 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.

FOLLOW-UP

Section 8 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Further Inpatient Care

Admit the patient into the ICU.

Transfer

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

Deterrence/Prevention

AFE 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.
• Treat DIC with blood components. Consider activated factor VIIa for severe hemorrhage. Bilateral uterine artery embolization has been successful in controlling blood loss in 2 reported cases.

Prognosis

• Maternal mortality is 61%.
• Most survivors have neurologic deficits.
• The intact infant survival rate is 70%. Neurologic status of the infant is directly related to the time elapsed between maternal arrest and delivery.
• Risk of recurrence is unknown. Successful subsequent pregnancies have been reported. The recommendation for elective cesarean delivery during future pregnancies in an attempt to avoid labor is controversial.

MISCELLANEOUS

Section 9 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

Medical/Legal Pitfalls

• Failure to respond emergently is a pitfall. AFE 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 AFE have occurred during late second-trimester abortions.

FURTHER READING

Section 10 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

In 1993, Benson suggested a broader clinical definition of amniotic fluid embolism (AFE). Type 1 AFE was associated with DIC and type 2 AFE was not associated with DIC. The onset of symptoms as late as 48 hours postpartum were included in the definition. These criteria were not used in the AFE registries and have not been widely accepted. The article nonetheless provides interesting reading about possible nonfatal AFE.

Benson MD. Nonfatal amniotic fluid embolism. Three possible cases and a new clinical definition.
Arch Fam Med. 1993 Sep;2(9):989-94. [Medline] 

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Further Reading
• References

1. Clark SL, Hankins GD, Dudley DA, et al. Amniotic fluid embolism: analysis of the national registry. Am J Obstet Gynecol. Apr 1995;172(4 Pt 1):1158-67; discussion 1167-9. [Medline].
2. Clark SL, Pavlova Z, Greenspoon J, et al. Squamous cells in the maternal pulmonary circulation. Am J Obstet Gynecol. Jan 1986;154(1):104-6. [Medline].
3. Benson MD, Kobayashi H, Silver RK, et al. Immunologic studies in presumed amniotic fluid embolism. Obstet Gynecol. Apr 2001;97(4):510-4. [Medline].
4. Farrar SC, Gherman RB. Serum tryptase analysis in a woman with amniotic fluid embolism. A case report. J Reprod Med. Oct 2001;46(10):926-8. [Medline].
5. Marcus BJ, Collins KA, Harley RA. Ancillary studies in amniotic fluid embolism: a case report and review of the literature. Am J Forensic Med Pathol. Mar 2005;26(1):92-5. [Medline].
6. Tuffnell DJ. United kingdom amniotic fluid embolism register. BJOG. Dec 2005;112(12):1625-9. [Medline].
7. O'Shea A, Eappen S. Amniotic fluid embolism. Int Anesthesiol Clin. 2007;45(1):17-28. [Medline].
8. Kramer MS, Rouleau J, Baskett TF, Joseph KS,. Amniotic-fluid embolism and medical induction of labour: a retrospective, population-based cohort study. Lancet. Oct 21 2006;368(9545):1444-8. [Medline].
9. Aguilera LG, Fernandez C, Plaza A, et al. Fatal amniotic fluid embolism diagnosed histologically. Acta Anaesthesiol Scand. Mar 2002;46(3):334-7. [Medline].
10. Hankins GD, Snyder R, Dinh T, et al. Documentation of amniotic fluid embolism via lung histopathology. Fact or fiction?. J Reprod Med. Dec 2002;47(12):1021-4. [Medline].
11. Kobayashi H, Ohi H, Terao T. A simple, noninvasive, sensitive method for diagnosis of amniotic fluid embolism by monoclonal antibody TKH-2 that recognizes NeuAc alpha 2-6GalNAc. Am J Obstet Gynecol. Mar 1993;168(3 Pt 1):848-53. [Medline].
12. Lim Y, Loo CC, Chia V, Fun W. Recombinant factor VIIa after amniotic fluid embolism and disseminated intravascular coagulopathy. Int J Gynaecol Obstet. Nov 2004;87(2):178-9. [Medline].
13. Kaneko Y, Ogihara T, Tajima H, Mochimaru F. Continuous hemodiafiltration for disseminated intravascular coagulation and shock due to amniotic fluid embolism: report of a dramatic response. Intern Med. Sep 2001;40(9):945-7. [Medline].
14. Hsieh YY, Chang CC, Li PC, Tsai HD, Tsai CH. Successful application of extracorporeal membrane oxygenation and intra-aortic balloon counterpulsation as lifesaving therapy for a patient with amniotic fluid embolism. Am J Obstet Gynecol. Aug 2000;183(2):496-7. [Medline].
15. Goldszmidt E, Davies S. Two cases of hemorrhage secondary to amniotic fluid embolus managed with uterine artery embolization. Can J Anaesth. Nov 2003;50(9):917-21. [Medline].

Article Last Updated: Dec 5, 2007