gynecology and obstetrics
Amniotic Fluid Embolism
Pathophysiology of Amniotic Fluid Embolism
The long-standing term amniotic fluid "embolism" implies a primarily mechanical, obstructive disorder, as occurs in thromboembolism or air embolism. However, because amniotic fluid is completely soluble in blood, it cannot cause obstruction. Furthermore, the minor amounts of fetal cells and tissue debris that may accompany the amniotic fluid into the maternal circulation are too small to mechanically obstruct enough of the pulmonary vascular tree to cause the marked hemodynamic changes that occur in this syndrome. ) similar to the systemic inflammatory response syndrome (SIRS) that occurs in Sepsis and Septic Shock . The inflammatory response causes organ damage, particularly to the lungs and heart, and triggers the coagulation cascade, resulting in Disseminated Intravascular Coagulation (DIC) (DIC). The resulting maternal hypoxia and hypotension have profound adverse effects on the fetus. Because maternal exposure to fetal antigens is likely fairly common during labor and delivery, it is not clear why only a few women develop amniotic fluid embolism. It is thought that different fetal antigens in varying amounts probably interact with unknown maternal susceptibility factors. Many factors are associated with increased risk of amniotic fluid embolism, but evidence is inconsistent. As with exposure to fetal antigens, many of the risk factors are commonplace or at least much more likely than amniotic fluid embolism, and there is no good pathophysiologic understanding of why only a few women with risk factors develop the syndrome. Nonetheless, risk is generally thought to be increased by the following: Advanced maternal age Multifetal Pregnancy None Polyhydramnios None Placenta Previa None Placenta Accreta None Placental Abruption (Abruptio Placentae) None Abdominal trauma Eclampsia Induction of Labor None Cervical lacerations Operative Vaginal Delivery None Uterine Rupture None Cesarean Delivery None 