Amniotic Fluid Embolism

Epidemiology

  • Timing: amniotic fluid embolism occurs anywhere between 20 wks of pregnancy and 48 hrs postpartum (but most cases occur during labor)
  • Incidence: 1 in 8,000-80,000 births
  • Mortality: amniotic fluid embolism accounts for 10-15% of all maternal deaths (it is the 3rd leading cause of maternal mortality)
  • Type of Delivery: amniotic fluid embolism can occur in both spontaneous and C-section deliveries, as well as with therapeutic abortions

Risk Factors for Amniotic Fluid Embolism

  • Intrauterine pressure catheters
  • Abruptio placenta (occurs in 50% of cases)
  • Prior fetal demise (occurs in 40% of cases)
  • Tumultuous labor:
  • Uterine stimulants:
  • Meconium staining:
  • Fetal distress/death:
  • Advanced maternal age:
  • Multiparity:

Etiology

  • Post-delivery or C-section: most occur within 1 hr after delivery (may occur up to 48 hrs post-partum)
  • Post-abortion: AFE occurs in 1:400,000 abortions
  • Post-amniocentesis:

Physiology

  • Amniotic fluid entry into maternal venous blood through uterine venous channels (possibly occurring when membranes rupture or uterus is instrumented)
  • May involve thromboplastic activity of amniotic fluid with intravascular activation of inflammation and coagulation (subsequent hyperfibrinolysis occurs after the acute event), pulmonary vessel obstruction from amniotic fluid emboli, alveolar capillary leak, anaphylaxis to fetal antigens, and LV dysfunction with pulmonary edema
  • Pulmonary HTN may occur due to pulmonary vascular occlusion by amniotic fluid

Pathology

  • Autopsy findings: mucin, fetal squamous cells, lanugo, vernix caseosa, bile-containing meconium in pulmonary vasculature

Diagnosis

  • CBC: thrombocytopenia may be seen
  • PFT’s: decreased DLCO
  • ECHO: CO is usually normal
    • Pulmonary HTN may occur, but major hemodynamic impairment is related to LV dysfunction
  • CXR/Chest CT Patterns:
    • Normal CXR:
    • Pulmonary edema: may be seen in some cases
  • Swan: PA blood can be sent to look for squames, hair, and mucin (but detection of fetal squames is common even in normal post-partum females)
  • V/Q scan: normal (necessary to rule out acute PE)
  • Pulmonary Angiogram:
  • PT/PTT/Fibrinogen
    • DIC parameters are positive in 40% of cases
    • Hypofibrinogenemia

Clinical

(abrupt symptom onset)

Pulmonary Manifestations

  • Acute Lung Injury-ARDS (see [[Acute Lung Injury-ARDS]])
    • Epidemiology: occurs in 75% of cases
    • Clinical: dyspnea
  • Pulmonary Hypertension (see Pulmonary Hypertension, [[Pulmonary Hypertension]])

Cardiac Manifestations

  • Hypotension
  • LV failure
  • Shock
  • Cardiac arrest

Neuro Manifestations

  • Altered mental status
  • Agitation
  • Tonic-clonic seizures (10-20%)

Other Manifestations

  • Nausea
  • Chills
  • Hemorrhage (50%)
  • Disseminated Intravascular Coagulation

Prognosis

  • <75% of patients survive the first hour of event (overall mortality rate is >85%)
  • Many survivors have long-term neurologic disability

Treatment

  • Supportive care: blood products, volume resuscitation, Swan, etc.
  • Anti-fibrinolytic agents (aminocaproic acid, cryoprecipitate): unclear role

References

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