Amniotic Fluid Embolism

This is an anaesthetic crisis. Priority is to:

  • Manage cardiorespiratory collapse
  • Aggressive right ventricular support
  • Prepare for impending DIC

Embolism of amniotic fluid and foetal cells into the maternal circulation, which may precipitate cardiorespiratory collapse via obstructive and distributive shock, occurring in two phases:

Epidemiology and Risk Factors

Epidemiology of AFE:

  • Occurs in ~1:8000-80,000 pregnancies
  • Has high mortality
    • Maternal mortality 37-80%
      ↓ Over time as resuscitation has improved, but remains a leading cause of maternal mortality.
    • Foetal mortality ~20%
  • Has high neurological morbidity
    • Maternal impediment ~7%
    • Foetal impediment 30-50%

Risk factors:

  • Maternal factors
    • Age > 35
  • Pregnancy factors
    • Male foetus
    • Multiple pregnancy
    • Polyhydramnios
    • Eclampsia
    • Placenta praevia
    • Placental abruption
  • Labour and delivery
    • Induction of labour
    • Assisted vaginal delivery
    • Operative deliery

Pathophysiology

AFE requires:

  • Physical rupture of foetal membranes
  • Amniotic fluid pressure to exceed venous pressure
    • Uterus unlikely portal of entry during contractions
    • Likely source is cervical or lower uterine segment tears
    • Late presentation may occur if fluid is compressed into circulation during movement or uterine involution
  • Embolisation of amniotic fluid into maternal circulation
    Two broad theories for mechanism of disease (neither of which independently explains findings):
    • Mechanical
      Obstruction via:
      • Foetal squamous epithelial cells
      • Vernix
      • Mucin
      • Meconium
    • Immunological
      Release of inflammatory and thrombotic mediators:
      • Endothelin
      • Leukotrienes
      • Prostoglandins
      • Thromboplastic
      • Tissue factor

Clinical Manifestations

In general:

  • Timing can be variable
    • 65-70% during active labour
    • 20% during LUSCS
    • 10% following vaginal delivery May occur up to 48 hours post-partum.
  • Presentation may be non-specific
    Hypotension and foetal distress are present in all cases.
  • Classically has a rapid and severe triad of:
    • Hypoxic respiratory failure
      Pulmonary oedema occurs in ~95%.
    • Cardiogenic shock
      Including cardiac arrest.
    • DIC
      Occurs in basically all cases that survive the immediate cardiogenic shock.
  • Cause of sudden and unexplained maternal collapse

May also present with:

  • Bronchospasm
  • Dyspnoea
  • Seizures
  • Dysrhythmias
  • Chest pain
  • Headache

Diagnostic Approach and DDx

Key differentials include other causes of shock, particularly:

  • Obstructive shock
    • Pulmonary embolus
    • Air embolus
  • Distributive shock
    • Sepsis
    • Anaphylaxis
  • Cardiogenic shock
    • Peripartum cardiomyopathy
    • MI
    • LAST
  • Hypovolaemic shock
    • Placental abruption

Investigations

Bedside:

  • Echocardiography
    TTE or TOE if available. Key findings:
    • RV failure
    • Pulmonary hypertension
    • Underfilled LV
    • Intracardiac thrombi/emboli

Laboratory:

AFE is fundamentally a clinical diagnosis, investigations may guide supportive management.

  • Bloods
    • FBE, UEC, CMP Commonly performed but do not aid management. Thrombocytopaenia is rare initially.
    • Cardiac enzymes
    • Coagulation assay
      Classically low (or entirely absent) fibrinogen with prolonged PT and APTT.
    • TEG/ROTEM
      For evaluating DIC.

Imaging:

  • CXR

Other:

  • ECG
    RV strain, tachycardia, ischaemia.

Investigations that have been used for diagnosis include:

  • Maternal PA blood sampling for squamous epithelial cells
    Drawn from a wedged PAC.
  • Histological analysis of cervix
    If a hysterectomy has been performed
  • Autopsy

Management

  • Deliver the foetus
  • Early intubation if required for hypoxia
  • Support circulation with fluid, aggressive vasopressors, and inotropes
  • Early correction hypofibrinogenaemia with cryoprecipitate

Resuscitation:

  • A
    • Generally early intubation
  • B
    • May require bronchodilators
      Note uterine tone; consider avoiding β-agonists.
  • C
    Rapid establishment of:
    • Invasive pressure monitoring
    • Aggressive volume resuscitation
    • Vasopressors
    • Pulmonary vasodilators
    • Mechanical support
      Includes:
      • CPB
      • ECMO
      • IABP
  • H
    • Massive transfusion likely
      Early haematological consultation.

Disposition:

  • ICU admission likely

Complications

Include:

  • ARDS
    Common:
    • 83% of all patients
    • 93% of patients with coagulopathy
    • Rarely may be the sole feature
  • Hysterectomy
    Due to consumptive coagulopathy.
  • Transfusion requirement
    Due to DIC.

Prognosis

  • High mortality
    20-60% in developed nations. Highest in initial periods.
  • Neurological morbidity

References

  1. Metodiev Y, Ramasamy P, Tuffnell D. Amniotic fluid embolism. BJA Education. 2018 Aug;18(8):234–8.