Updated: Aug 12, 2008
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.
For related information on pregnancy, see Medscape's Pregnancy Resource Center.
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.
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.
Incidence is similar to that of the United States.
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.
No racial or ethnic predilection exists.
AFE only occurs in women.
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.
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
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:
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.
Anaphylaxis
Aortic Dissection
Cholesterol Embolism
Myocardial Infarction
Pulmonary Embolism
Septic Shock
Placental abruption
Aspiration
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 is supportive.
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.
Women who survive AFE will probably require ICU admission. Left heart failure is a common late occurrence. Additionally, survivors will probably have neurologic sequelae.
Drugs are used in amniotic fluid embolism (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.
Used in AFE to maintain blood pressure.
One of several drugs that can be used to maintain perfusion. Dopamine increases myocardial contractility and systolic BP with little increase in diastolic BP. Also dilates the renal vasculature, increasing renal blood flow and GFR.
2-5 mcg/kg/min IV; titrate to BP and cardiac output
Not established
Phenytoin, alpha- and beta-adrenergic blockers, general anesthesia, and MAOIs increase and prolong effects of dopamine
Documented hypersensitivity; pheochromocytoma; ventricular fibrillation, hypovolemia
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Monitor urine flow, cardiac output, pulmonary wedge pressure, and BP during infusion; prior to infusion, correct hypovolemia with either whole blood or plasma, as indicated; monitoring central venous pressure or left ventricular filling pressure may be helpful
Used to improve myocardial contractility in patients with amniotic-fluid embolism.
Cardiac glycoside that acts directly on the cardiac muscle and conduction system. Digoxin causes an increase in force and velocity of systolic contraction, a slowing of the heart rate, and decreased conduction velocity through the AV node.
0.5 mg IV push, then 0.25 mg IV q4h for 2 doses, followed by 0.25 mg PO qd
Not established
Medications that may increase digoxin levels include alprazolam, benzodiazepines, bepridil, captopril, cyclosporine, propafenone, propantheline, quinidine, diltiazem, aminoglycosides, oral amiodarone, anticholinergics, diphenoxylate, erythromycin, felodipine, flecainide, hydroxychloroquine, itraconazole, nifedipine, omeprazole, quinine, ibuprofen, indomethacin, esmolol, tetracycline, tolbutamide, and verapamil; medications that may decrease serum digoxin levels include aminoglutethimide, antihistamines, cholestyramine, neomycin, penicillamine, aminoglycosides, oral colestipol, hydantoins, hypoglycemic agents, antineoplastic treatment combinations (eg, carmustine, bleomycin, methotrexate, cytarabine, doxorubicin, cyclophosphamide, vincristine, procarbazine), aluminum or magnesium antacids, rifampin, sucralfate, sulfasalazine, barbiturates, kaolin/pectin, and aminosalicylic acid
Documented hypersensitivity; ventricular fibrillation; beriberi heart disease; idiopathic hypertropic subaortic stenosis; constrictive pericarditis; carotid sinus syndrome
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Calcium may produce arrhythmias in digitalized patients; hypercalcemia predisposes patient to digitalis toxicity; hypocalcemia can make digoxin ineffective until serum calcium levels are normal; magnesium replacement therapy must be instituted in patients with hypomagnesemia to prevent digitalis toxicity; patients with incomplete AV block may progress to complete block when treated with digoxin; exercise caution in patients with hypothyroidism, hypoxia, and acute myocarditis
Some authorities suggest steroid use may be helpful in AFE because the process may be immune mediated.
Because AFE is more similar to an anaphylactic reaction, steroids that mediate the immune responses are recommended.
500 mg IV q6h
Not established
Corticosteroid clearance may decrease with estrogens; may increase digitalis toxicity secondary to hypokalemia
Documented hypersensitivity; viral, fungal, or tubercular skin infections
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Drug-induced adrenocortical insufficiency; drug-induced psychosis; caution in hyperthyroidism, osteoporosis, peptic ulcer disease, cirrhosis, nonspecific ulcerative colitis, diabetes, and myasthenia gravis
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.
Most commonly used uterotonic. Decreases inflammation by suppressing migration of polymorphonuclear leukocytes and reversing increased capillary permeability.
10 U IM or 10-40 U IV at 250 mL/h in 1000 mL NS
Not established
Pressor effect of sympathomimetics may increase when used concomitantly with oxytocic drugs, causing postpartum hypertension
Documented hypersensitivity; pregnant patients with severe toxemia, unfavorable fetal positions, and a contracting uterus with hypertonic or hyperactive patterns; labor in which vaginal delivery should be avoided such as invasive cervical carcinoma, cord presentation or prolapse, active herpes genitalis, total placenta previa, and vasa previa
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
A uterus that is overstimulated can be hazardous to both mother and fetus; hypertonic contractions can occur in a patient whose uterus is hypersensitive to oxytocin, regardless of whether it was appropriately administered; oxytocin has intrinsic antidiuretic effect that when administered by continuous infusion and patient is receiving fluids by mouth, can cause water intoxication
Acts directly on uterine smooth muscle, causing a sustained tetanic uterotonic effect that reduces uterine bleeding.
0.2 mg IM; may repeat q10-15min for 3 doses
Not established
Concurrent administration of methylergonovine with vasoconstrictors or other ergot alkaloids may produce additive effect
Documented hypersensitivity; glaucoma, Tourette syndrome; anxiety
D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Caution in sepsis, obliterative vascular disease, or hepatic or renal insufficiency
Prostaglandin similar to F2-alpha (dinoprost), but has longer duration and produces myometrial contractions that induce hemostasis at placentation site, which reduces postpartum bleeding.
0.25 mg IM q10-15min; not to exceed 3 doses
Not established
Increases toxicity of oxytocic agents
Documented hypersensitivity; pelvic inflammatory disease
X - Contraindicated; benefit does not outweigh risk
Caution in cardiovascular disease, asthma, hypotension or hypertension, adrenal disease, diabetes, renal or hepatic disease, a compromised uteri, and jaundice; do not inject IV (may induce hypertension and bronchospasm)
Admit the patient with amniotic fluid embolism (AFE) into the ICU.
Transfer to a level 3 hospital may be required once the patient is stable.
AFE is an unpredictable event.
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].
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].
Benson MD, Kobayashi H, Silver RK, et al. Immunologic studies in presumed amniotic fluid embolism. Obstet Gynecol. Apr 2001;97(4):510-4. [Medline].
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].
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].
Tuffnell DJ. United kingdom amniotic fluid embolism register. BJOG. Dec 2005;112(12):1625-9. [Medline].
O'Shea A, Eappen S. Amniotic fluid embolism. Int Anesthesiol Clin. 2007;45(1):17-28. [Medline].
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].
Aguilera LG, Fernandez C, Plaza A, et al. Fatal amniotic fluid embolism diagnosed histologically. Acta Anaesthesiol Scand. Mar 2002;46(3):334-7. [Medline].
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].
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].
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].
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].
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].
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].
amniotic fluid embolism, anaphylactoid syndrome of pregnancy, obstetric emergency, fetal debris in pulmonary circulation, amniotic fluid embolization, AFE, fetal squamous cells. anaphylactic reaction to fetal antigens, hypoxia, myocardial capillary damage, pulmonary capillary damage, left heart failure, acute respiratory distress syndrome, disseminated intravascular coagulation, DIC
Lisa E Moore, MD, FACOG, Assistant Professor, Department of Obstetrics and Gynecology, Division of Maternal Fetal Medicine, University of New Mexico Health Sciences Center
Lisa E Moore, MD, FACOG is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association, and Society for Maternal-Fetal Medicine
Disclosure: Nothing to disclose.
John J Kavanagh Jr, MD, Chief, Professor, Department of Internal Medicine, Section of Gynecological and Medical Therapeutics, MD Anderson Cancer Center, University of Texas College of Medicine
John J Kavanagh Jr, MD is a member of the following medical societies: American Association for Cancer Research, American Association for the Advancement of Science, American Association for the History of Medicine, American College of Physicians, American Federation for Medical Research, American Medical Association, Society of Gynecologist Oncologists, Southern Medical Association, and Texas Medical Association
Disclosure: Nothing to disclose.
Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.
A David Barnes, MD, PhD, MPH, FACOG, Consulting Staff, Department of Obstetrics and Gynecology, Mammoth Hospital, Mammoth Lakes, California, Pioneer Valley Hospital, Salt Lake City, Utah, Warren General Hospital, Warren, Pennsylvania and Mountain West Hospital, Tooele, Utah
A David Barnes, MD, PhD, MPH, FACOG is a member of the following medical societies: American College of Forensic Examiners, American College of Obstetricians and Gynecologists, American Medical Association, Association of Military Surgeons of the US, and Utah Medical Association
Disclosure: Nothing to disclose.
Frederick B Gaupp, MD, Consulting Staff, Department of Family Practice, Hancock Medical Center
Frederick B Gaupp, MD is a member of the following medical societies: American Academy of Family Physicians
Disclosure: Nothing to disclose.
Carl V Smith, MD, The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, University of Nebraska Medical Center
Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, American Medical Association, Arkansas Medical Society, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association, and Society for Maternal-Fetal Medicine
Disclosure: Nothing to disclose.
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 ]
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