Amniotic Fluid Embolism

Amniotic fluid embolism is a rare, but potentially fatal condition that may occur during labor or the in early postnatal period. Presumably, entrance of amniotic fluid into the maternal circulation triggers an intense inflammatory response and leads to an abrupt onset of profound hypotension, heart failure, disseminated intravascular coagulation and respiratory failure. The diagnosis is made based on clinical criteria. Ensuring hemodynamic stability and adequate oxygenation of tissues is the mainstay of therapy.

Amniotic Fluid Embolism is the result of anatomic/foreign processes. The incidence of the disease is stipulated as about 0 / 100.000.

Presentation

Symptoms and signs of amniotic fluid embolism appear abruptly during labor or sometimes early postpartum period. Most common findings include sudden onset of dyspnea, acute respiratory distress, marked hypotension, hypoxia, cyanosis and coagulopathy. Severe hemorrhage and DIC are frequent manifestations, as is arrhythmia. Within minutes, cardiogenic shock develops, as a result of pulmonary hypertension and cor pulmonale, followed by pulmonary edema [5]. Convulsions, altered mental status and seizures often develop. It is important to emphasize that these symptoms appear so rapidly that cardiac arrest may occur after just several minutes, which is why attending physicians must act quickly in starting appropriate therapy.

Workup

The diagnosis of amniotic fluid embolism currently rests on clinical grounds. In practice, the nature of the condition mandates a rapid therapeutic approach regardless of laboratory tests. Workup comprises CBC, with emphasis on hemoglobin, hematocrit and platelet count, which are important in assessing the need for blood transfusions, as well as a full coagulation panel, including prothrombin time (PT), activated partial thromboplastin time (aPTT) and fibrinogen should be obtained, to confirm DIC. Additionally, serum electrolytes and arterial blood gas analysis should be obtained. Electrocardiography and plain chest radiography are quick and useful methods to determine the presence of arrhythmia, pulmonary edema and heart failure. At this moment, specific diagnostic markers for amniotic fluid embolism do not exist, but significant attempts toward finding tests that may aid in making the diagnosis are made [10] [11].

Treatment

Managing patients suffering from amniotic fluid embolism can be extremely difficult. Rapid supportive measures should be initiated as early as possible. Severe hemorrhage and anemia are often corrected with blood transfusions, sometimes including both red blood cells and plasma, to replenish coagulation factors that are depleted because of ongoing DIC. Hypotension in these patients requires administration of crystalloid solutions and vasopressor agents such as norepinephrine, dobutamine and dopamine, while correction of electrolytes is also necessary. Oxygen therapy and assisted or mechanical ventilation may be frequently required because of marked hypoxia and heart failure that is unable to compensate for generalized ischemia. Extracorporeal oxygenation, hemodialysis and plasmapheresis are techniques that have shown to life-saving in some studies [12] [13], and their use should be advocated in these patients as frequently as possible. Additionally, uterine artery embolization has shown to be a promising procedure in managing this condition [14].

Prognosis

This condition often leads to fatal outcomes and studies have indicated that death may occur only after a few hours after the onset of symptoms [9]. Mortality rates significantly reduced with advances in intensive care medicine throughout the past decades, but it is still very high, which shows the risk this condition poses to the patient. Variable mortality rates have been reported, but usually range between 20-60% [3], while mortality rates in the last decade have shown to be from 9-44% [2]. Unfortunately, women who do survive amniotic fluid embolism often have neurological sequelae.

Etiology

The exact cause and events that lead to amniotic fluid embolism are still unclear. It is established, however, that the pathogenesis almost always includes interruption of the maternal-fetal barrier and consequent introduction of amniotic fluid into the maternal circulation, which frequently occurs in conditions such as placental rupture, placenta previa, in medically induced labor and in various other conditions [5]. In addition to mechanical factors, immune-mediated reactions to fetal material that is contained in the amniotic fluid is also one of the main theories that attempt to explain the presumed etiology [5].

Epidemiology

Amniotic fluid embolism is rarely encountered in medical practice. Incidence rates have determined that this disorder develops in approximately 1 in 15,200 deliveries in North America. For unknown reasons, the incidence rate in Europe is much lower, with 1 in 59,900 deliveries developing amniotic fluid embolism [2]. After pulmonary embolism and hypertension, this condition is the most common cause of non-abortion-related maternal mortality during labor and is responsible for roughly 10% of all maternal deaths in the United States [6]. Moreover, it is the most common cause of maternal death in Australia and among the top three in the majority of developed countries [2]. Despite its ambiguous etiology, mechanical disruption of the maternal-fetal barrier is almost certain to be one of key events and various risk factors have been established in regard to this factor. Medical induction of labor, advanced maternal age, cesarean section, forceps delivery, placental rupture, placenta previa, uterine rupture, cervical lacerations and multiple-birth deliveries are shown to significantly increase the risk for amniotic fluid embolism [7].

Sex distribution
Age distribution

Pathophysiology

It is postulated that mechanical and immunological factors are the most important contributors to the development of this disorder. For amniotic fluid to reach maternal circulation, it is thought that some form for breach of the maternal-fetal barrier is necessary, leading to changes in pressure gradients that force amniotic fluid to pool into maternal vessels [2]. But invasion of amniotic fluid alone is determined to be insufficient for the pathogenesis of this disorder, which bring into question the immune-mediated mechanisms that are presumed to be involved [6]. From one hand, various contents of the amniotic fluid (meconium, particulate matter, but also various inflammatory molecules including prostaglandins and leukotrienes) are shown to be important mediators of vasoconstriction and it is assumed that some form of anaphylaxis occurs when these substances interact with the immune system of the mother; and from the other, activation of the complement system in response to these contents are shown to be of key elements in the development of severe inflammation, DIC and shock [5] [8]. Once the amniotic fluid reaches the pulmonary artery, marked vasoconstriction and pulmonary hypertension develops within a few hours, leading to cor pulmonale, right heart failure and severe hypoxia, and eventually left-heart failure and shock.

Prevention

Despite the fact that this life-threatening condition was described almost 100 years ago, the exact factors that lead to this condition remain unknown, hence prevention strategies currently do not exist.

Summary

Amniotic fluid embolism is a life-threatening obstetric complication that results in rapid patient deterioration, usually occurring either during labor or in the early postpartum period [1]. Although this medical phenomenon was initially described almost 100 years ago [2], the exact reasons for the appearance of this disorder remain unclear. It is thought that the entry of amniotic fluid into maternal circulation stems from disruption of the maternal-fetal barrier during labor and subsequent changes in pressure gradients that force amniotic fluid out of the fetal compartment. This theory is supported by the fact that a significantly increased risk for amniotic fluid embolism is established in women who present with placenta previa, polyhydramnios, abruption of the placenta and in those in whom operative deliveries were necessary [3]. This condition is seen in approximately 1 in 15,200 women in North America, while incidence in rates in Europe indicate that 1 in 59,900 deliveries are complicated by an amniotic fluid embolism [1]. The pathogenesis model, apart from amniotic fluid entry into the systemic circulation of the mother, is thought to involve a systemic inflammatory response due to the contents of the fluid. As the amniotic fluid reaches the circulation, extensive vasoconstriction occurs, especially in the pulmonary artery and results in cor pulmonale and severe right heart failure, eventually leading to severe hemodynamic instability. It is shown that amniotic fluid directly reduces coagulation time, activates the complement cascade and induces severe coagulopathy by interfering with various factors involved in this process [4]. Disseminated intravascular coagulation (DIC), initially right and followed by left heart failure, respiratory failure and shock ensue rapidly. Since this condition is known to be fatal within the first few hours in approximately 20-60% of women, early and aggressive therapy may significantly improve survival rates [3]. The diagnosis is made based on clinical criteria, the most common symptoms being abrupt development of hypotension, arrhythmia, respiratory distress, convulsions and hemorrhage. Guided by laboratory studies comprising of a complete blood count (CBC), coagulation panel, serum electrolytes and arterial blood gasses, treatment aims to stabilize blood pressure and tissue oxygenation that often calls for blood transfusions, assisted ventilation, fluid administration, use of vasopressors and various other strategies that are required to restore hemodynamic stability.

Patient Information

Amniotic fluid embolism is a rare but often life-threatening condition that develops during birth or shortly after birth. It is established to occur approximately once in every 15,000-60,000 deliveries and despite that almost a century has passed since this condition was described in literature, the exact cause remains unknown. Several conditions have shown to increase the risk for developing this condition, including rupture of the placenta, multiple-birth pregnancies, placenta previa, advanced age of the mother, but also medical induction of labor and cesarean delivery. It is hypothesized that the barrier that separates the fetus and the mother is disrupted during labor, which leads to passage of amniotic fluid into maternal blood vessels. More importantly, various components of the amniotic fluid supposedly cause a marked inflammatory reaction in the mother, leading to abrupt and profound changes in the circulatory system. Rapid development of severe symptoms such as hypotension, arrhythmia, heart failure, respiratory arrest and shock is observed. Severe bleeding and marked disturbances in blood coagulation are frequent, together with convulsions and seizures. The diagnosis is made based on clinical grounds, as the rapid onset and profound deterioration of the condition of the patient during labor are hallmarks of amniotic fluid embolism. Treatment aims to restore blood pressure and establish adequate oxygenation of tissues through administering both blood and plasma transfusions and intravenous fluids together with drugs that increase tension of blood vessels. Because cessation of breathing may occur within minutes after onset, oxygen therapy and either assisted or mechanical ventilation are indicated to prevent lung failure. Recently, various techniques that can more efficiently reach adequate blood pressure control have been recommended in these patients, such as hemodialyis and extracorporeal oxygenation, which includes the use of machines for inserting oxygen into the circulation. Amniotic fluid embolism is often a fatal condition, with maternal mortality rates reaching up to 60%, which is why early and aggressive treatment within the first few minutes after the onset of symptoms can save the patient. Unfortunately, prevention strategies of this condition remain to be created ad women who survive this condition often have long-term neurological sequelae, which illustrates the danger this condition poses.

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References

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