Amniotic fluid embolism syndrome

Abstract

We conducted an evidence-based review of information bout amniotic fluid embolism syndrome (AFES). Amniotic fluid embolism syndrome (AFES), also named “anaphylactoid syndrome of pregnancy”, is a rare but catastrophic pathology that occurs when amniotic fluid, fetal cells, hair, or other debris enters the maternal pulmonary circulation, causing cardiovascular collapse. Although the exact pathophysiology is still unknown, recent studies suggest that the AFES is not a direct consequence of the mechanical respiratory tract obstruction, but complex humoral effect causing anaphylactoid reactions or complement activation. In some women, AFES may lead to a mild degree of organ dysfunction while in others it may lead to coagulopathy, cardiovascular collapse, and death. Maternal mortality due to AFES remains high, although less than in previous years. However, even those who survive generally have a poor outcome, most often neurologic injury due to cerebral hypoxia.

Neonatal outcomes are also poor, although they improve with early delivery. The treatment for AFES is supportive. Since most cases present with sudden cardiorespiratory arrest and hemorrhage, the airway and adequate intravenous access should be secured, and advanced cardiac life support protocols followed so that adequate tissue perfusion for both mother and fetus (if not yet delivered) can be ensured. Previous studies revealed maternal mortality rates as high as 61-86%, but recent estimates suggest a case fatality of 13-26%. This abrupt decrease in risk for maternal mortality from AFES may be the result of early diagnosis and better resuscitative care, in contrast fetal outcome remains poor if AFES occurs before delivery, with a neonatal mortality rate approximately more than 10%.

 

Tablet of Contents:

1. Introduction

2. Materials and methods

3. Results

4. Conclusion

 

1. Introduction

Amniotic fluid embolism syndrome (AFES), also named “anaphylactoid syndrome of pregnancy”, is a rare but catastrophic pathology that occurs when amniotic fluid, fetal cells, hair, or other debris enters the maternal pulmonary circulation, causing cardiovascular collapse. [1]

Meyer first reported it in 1926, and the syndrome was first described at large by Steiner and Lushbaugh in 1941, Lushbaugh reported the clinical and pathological findings of 42 women who died suddenly during or just after labor, the classic triad histopathology of the pulmonary vasculature of these women that included mucin, amorphous eosinophilic material, and squamous cells. [2, 3]

In 1950 AFES becams a published entity, in 1973 Attwood and Rome reported that tears in the uterus permit amniotic fluid entry in the maternal circulation, and in 1976 Resnick published a case report of a well documentated AFES, amniotic fluid was aspirated from a central venous catheter.[3] Although the exact pathophysiology is still unknown, recent studies suggest that the AFES is not a direct consequence of the mechanical respiratory tract obstruction, but complex humoral effect causing anaphylactoid reactions or complement activation. [3] The process is more similar to anaphylaxis than to embolism, giving the term of “anaphylactoid syndrome of pregnancy” because fetal tissue or amniotic fluid components are not universally found in women who present with signs and symptoms attributable to AFE. [4, 5, 6, 7] In some women, AFES may lead to a mild degree of organ dysfunction while in others it may lead to coagulopathy, cardiovascular collapse, and death. [8, 9]

 

2. Materials and methods

We searched several databases including Medline and Uptodate (all from inception to September, 2018) with the terms “amniotic embolism” and “amniotic embolus”. We also searched references in retrieved articles, book chapters, review articles, and reports on maternal mortality from surveillance systems. Inclusion of individual articles was based on scientific merit and clinical relevance. The great majority of studies included were descriptive, mainly case reports and case series.

 

3. Results

Incidence

Incidence of AFES is estimated to occur between 1 in 8000 and 1 in 80,000 deliveries, but true incidence is unknown because of inaccurate diagnosis and inconsistent reporting of nonfatal cases. [10] Previous studies revealed mortality rates as high as 61-86%, but recent estimates suggest a case fatality of 13-26%. This abrupt decrease in risk for maternal mortality from AFES may be the result of early diagnosis and better resuscitative care, in contrast fetal outcome remains poor if AFES occurs before delivery, with a neonatal mortality rate approximately more than 10%. [10]

 

Pathophysiology and Diagnosis

There are two theories regarding the pathogenesis of AFE: the first one reffers to labor related trauma either traumatic, operative delivery, cesarean sectin or abnormal placenta or any other breach of the barrier between maternal blood and amniotic fluid forces the entry of amniotic fluid in the maternal systemic circulation. The debris and amniotic components will reach pulmonary circulation and cause obstruction, hypertension and right ventricular insufficiency.

The more modern theory reffers to AFE as an anaphylactoid reaction in response to the systemic inflamatory mediators produced as a reaction to the AF componentes (fetal cells, scuamas, lanugo etc.) and vasoactive components. The maternal circulation activates inflammatory mediators, causing a humoral or immunologic response. [10] Those products include platelet-activating factor, leukotriens, cytokines, bradykinin, thromboxane snd arachidonic acid.

Tissue factor and tissue factor pathway inhibitor, which trigger intravascular coagulation, are higher in amniotic fluid than in maternal serum. [10]. The most active mediator increased by the AF components in the maternal circulation is endothelin that has potent vaso and bronchocosntriction actions producing bronchospasm and coronary vasoconstriction with myocardial ischemia that may contribute to respiratory and cardiovascular collapse. [10] There are studies that claim an unmediated procoagulant action of AF explaining the disseminated intravascular clotting as the final step of the AFE pathophysiology (DIC).

Literatture examination reaveals two clinical forms of AFE typical and atypical. Uszynski also documented that symptoms vary in both forms of AFES:

•    Typical, (classic) has three phases: Phase 1-respiratory and circulatory disorders, Phase 2-coagulation disturbances of maternal hemostasis, Phase 3-acute renal failure and acute respiratory distress syndrome (ARDS), and leading to cardiopulmonary collapse.

•    Atypical: there can be many atypical forms from DIC as primar manifestation to in contrast to typical embolism, cardiopulmonary collapse does not occur in atypical embolism but the first symptom is life threatening hemorrhage due to DIC. Atypical embolism was observed during caesarean section or immediately after it, in cases of profound rupture of uterine cervix, as well as in the course of placenta abruption and in association with induced midtrimester abortion. [10]

AFES may be more likely in situations when exchange of fluids between the maternal and fetal circulation occurs. However, the data to support these risk factors are flawed and none sufficient to alter standard obstetric care [11]:

•    Cesarean or instrumental vaginal delivery

•    Precipitous or tumultuous labor

•    Advanced maternal age (e.g., ≥35 years)

•    Placenta previa, placenta accrete/percreta/increta, or placental abruption

•    Grand multiparity (≥5 live births or stillbirths)

•    Cervical lacerations

•    Fetal distress

•    Eclampsia

•    Pharmacologic induction of labor

•    Uterine rupture

•    Polyhydramnios

•    Miscarriage, abortion, amniocentesis

Duration or stage of labor does not appear to be a risk factor.

AFES should be suspected in a pregnant or postpartum woman who develops abrupt onset hypotension, hypoxemia, cardiovascular compromise, hemorrhage in association with disseminated intravascular coagulation, and/or acute neurologic changes. AFES is a clinical diagnosis of exclusion that is based upon the constellation of classic clinical findings and the exclusion of other causes of the presenting symptoms. [11]

Investigational diagnostic tests include:

•    Levels of zinc coproporphyrin-1 and sialyl Tn antigen have been shown to be increased in some patients with AFES that presented with cardiopulmonary collapse. [11]

•    Measuring TKH-2 (a fetal antigen that can also be observed in maternal lung samples), insulin-like growth factor binding protein-1, or squamous cell carcinoma antigen have been detected in some patients with AFES but are of uncertain diagnostic significance. [11]

The differential diagnosis of AFE includes obstetric, nonobstetric, and anesthetic etiologies. [11]

•      Anaphylaxis.

•      Aortic dissection.

•      Cholesterol embolism.

•      Myocardial infarction.

•      Pulmonary embolism.

•      Eclampsia and coma

•      Septic shock.

•      Toxic reaction to local anesthetic drugs

•      Gastric content aspiration

•      Air embolism.

•      Hemorrhagic shock in an obstetric patient.

 

Management

A  multidisciplinary,  team-based  approach  (critical  care,  maternal-fetal  medicine, respiratory  care,  nursing,  and  anesthesia  specialists)  is  preferred  because  it  allows simultaneous diagnostic evaluation and administration of therapy. [11]

1.  Therapeutic – The treatment for AFES is supportive. Since most cases present with sudden cardiorespiratory failure/arrest and hemorrhage, the airway and adequate intravenous access should be secured, and advanced cardiac life support protocols followed so that adequate tissue perfusion for both mother and fetus (if not yet delivered) can be ensured.

2. Diagnostic – Bedside clinical evaluation and diagnostic investigations should be undertaken while initial resuscitative therapies are ongoing. This involves a thorough history and examination including vaginal/pelvic examination, particularly in those who present with vaginal hemorrhage. Typical investigations include complete blood count, chemistries, renal and liver function tests, cardiac enzymes, brain natriuretic peptide levels, chest radiography, arterial blood gases, electrocardiography, and/or bedside ultrasonography (if available). The primary purpose of initial investigations is to narrow the differential since AFES is a diagnosis of exclusion. Once stabilized, a more thorough investigation can be undertaken.

Management of shock and cardiac arrest – Initial strategies should focus on standard basic and advanced cardiac life support maneuvers to treat shock and cardiac arrest. [8]

Hemodynamic support – The approach to hypotensive patients with AFES is the same as among those without AFES with the exception that excessive fluid administration should be avoided since hypotension in AFES is almost always due to cardiogenic shock and coexisting intravascular hypovolemia is rare. [8]

Management of respiratory failure – The management of respiratory failure is supportive and includes the administration of supplemental oxygen, and in most cases mechanical ventilation. [8]

Management of hemorrhage and disseminated intravascular coagulopathy – Blood product transfusion may be required for some patients with bleeding due to disseminated intravascular coagulopathy (DIC). Importantly, in those with vaginal hemorrhage, a detailed examination and investigation should be undertaken to locate and treat the source of bleeding including excluding uterine atony (ie, the most common cause of postpartum hemorrhage). [8] Delivery of the fetus – When AFES presents intrapartum, the need for immediate delivery must be determined. The decision is made on a case-by-case basis, but factors that favor urgent delivery include a nonreassuring fetal heart rate tracing, rapid and progressive deterioration of the mother’s condition, or the opinion that delivery of the fetus may facilitate maternal resuscitative efforts. Operative vaginal delivery is reasonable if the cervix is fully dilated and the fetal head has descended to a station of at least +2/5. Otherwise, an emergency cesarean delivery is indicated. [8]

 

4. Conclusion

•    Amniotic fluid embolism syndrome (AFES) is a catastrophic condition that typically occurs during labor and delivery or postpartum. It is unpredictable, unpreventable, and rare (1 to 12 cases per 100,000 deliveries) and its pathophysiology is poorly understood. [8], [10]

•    AFES is characterized by the abrupt and fulminant onset of hypotension due to cardiogenic shock/arrest, hypoxemic respiratory failure, and hemorrhage from disseminated intravascular coagulation. [8], [10]

•    A multidisciplinary, team-based approach (critical care, maternofetal, respiratory care, nursing, and anesthesia specialists) is preferred because it allows simultaneous diagnostic evaluation and administration of therapy [8], [10]:

➢    The treatment for AFES is supportive. The airway and adequate intravenous access should be secured and advanced cardiac life support protocols followed so that adequate tissue perfusion for both mother and fetus (if not yet delivered) can be ensured. Importantly, for patients who have not delivered, prompt delivery of the fetus is critical, provided that the fetus is viable.

➢    Bedside clinical evaluation and diagnostic investigations involve a thorough history and examination as well as a gynecological examination. Typical investigations include complete blood count, chemistries, renal and liver function tests, cardiac enzymes, brain natriuretic peptide levels, chest radiography, arterial blood gases, electrocardiography, and/or bedside ultrasonography (if available). Once stabilized, a more thorough investigation can be undertaken.

➢    Maternal mortality due to AFES remains high, although less than in previous years. However, even those who survive generally have a poor outcome, mostoften neurologic injury due to cerebral hypoxia. Neonatal outcomes are also poor, although they improve with early delivery. [8], [10]

 

The authors:

PLES Liana [1],[2]

LESNIC Anca [1]

SIMA Romina [1],[2]

STĂNESCU Anca Daniela [1],[2]

[1] Clinical Hospital “Sf. John”, “Bucur” Maternity, Bucharest, (ROMANIA).

[2] UMF “Carol Davila”, Bucharest, Bucur Clinic, Bucharest, (ROMANIA).

 

Contributo selezionato da Filodiritto tra quelli pubblicati nei Proceedings “SOGR 2018 – 17th National Congress of the Romanian Society of Obstetrics and Gynecology & First Advanced Colposcopy Course - 2018”

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Contribution selected by Filodiritto among those published in the Proceedings “SOGR 2018 – 17th National Congress of the Romanian Society of Obstetrics and Gynecology & First Advanced Colposcopy Course - 2018”

To buy the Proceedings click her.