Amniotic Fluid Embolism (AFE)

Diagnosis & Pathophysiology

• Acute hypoxia
• Cardiovascular collapse
• DIC/coagulopathy

• Phase 1 (minutes): Pulmonary vasospasm → acute RV failure → hypoxia → RV dilation → interventricular septal shift → LV underfilling → systemic hypotension
• Phase 2: LV dysfunction (direct myocardial depression by mediators) + distributive shock

Differential Diagnosis

Key: AFE has no pathognomonic test. Diagnosis is clinical and exclusionary. Fetal squamous cells in maternal pulmonary vasculature are not diagnostic (present in normal pregnancies).

ACLS in the Pregnant Patient — Modified Protocol

Anatomical/Physiological Considerations

• Aortocaval compression by gravid uterus reduces preload
• Cricoid pressure / difficult airway (Mallampati worse in pregnancy)
• Higher O₂ consumption, lower FRC → desaturates faster

Maternal Cardiac Arrest Algorithm (AHA 2020 + ACOG)

CALL FOR HELP IMMEDIATELY
→ Obstetric team + Neonatal team + Anesthesia + Cardiac surgery (ECMO)

1. POSITIONING
   - Manual Left Uterine Displacement (LUD) — DO NOT use tilted board for arrest
   - Supine with LUD (wedge ONLY if no arrest)

2. AIRWAY
   - Early RSI (aspiration risk), smallest ETT (7.0), video laryngoscopy preferred
   - Preoxygenate 100% O₂

3. COMPRESSIONS
   - Standard hand position (slightly higher on sternum if uterus large)
   - Standard 100-120/min, 2-inch depth
   - Full chest recoil

4. DEFIBRILLATION
   - NOT contraindicated; use standard energies (biphasic 200J)
   - Remove fetal monitors before shock
   - Anterior-lateral pad placement

5. DRUGS — Standard ACLS doses
   - Epinephrine 1mg IV q3-5min (safe in pregnancy)
   - Amiodarone for shockable rhythms
   - Magnesium → STOP if already running (can cause arrest)
   - Sodium bicarb for hyperkalemia/TCA only

6. PERIMORTEM CESAREAN DELIVERY (PMCD)
   ★ Begin at 4 MINUTES of arrest if no ROSC
   ★ Target delivery by 5 minutes ("4-minute rule")
   ★ Do NOT transport to OR — deliver at bedside
   ★ Gestational age ≥20 weeks (uterus at umbilicus)
   ★ Purpose: relieve aortocaval compression → improves maternal ROSC
   (fetal benefit is secondary consideration during maternal arrest)

7. POST-ROSC → ICU, ECMO consideration

Management of AFE

Immediate (simultaneous)

Coagulopathy / DIC Management

• Massive transfusion protocol (MTP): pRBC:FFP:Platelets = 1:1:1
• Tranexamic Acid (TXA): 1g IV early (inhibits fibrinolysis)
• Fibrinogen concentrate (target >2 g/L) or cryoprecipitate
• PCC (4-factor) if FFP limited
• rFVIIa as rescue (per retrieved guideline, Management of Severe Peri-Operative Bleeding, p. 49)
• Do NOT give heparin (worsens coagulopathy)
• Thromboelastography (TEG/ROTEM) guided replacement preferred

Advanced Rescue Therapies

• ECMO (VA-ECMO): increasingly used early in refractory AFE arrest; can be bridge to recovery
• IABP or Impella for severe LV failure
• Inhaled prostacyclin (epoprostenol) or iNO for pulmonary hypertension/RV failure
• Steroids (hydrocortisone 500mg): rationale is the anaphylactoid mechanism; not proven but commonly used
• Atropine/Ondansetron: some evidence for vagally-mediated initial phase

Cardiovascular Involvement & Shunts in AFE

Hemodynamic Phases

• Fetal mediators (prostaglandins, leukotrienes, endothelin, serotonin) → pulmonary vasospasm
• Sudden ↑ RV afterload → acute cor pulmonale
• RV dilation → D-shaped septum (interventricular septal bowing into LV)
• ↓ LV preload → low CO → systemic hypotension

• Direct myocardial depression
• Global LV hypokinesis on echo
• Cardiogenic shock

Shunts in AFE

PFO is present in ~25-30% of general population. AFE is one of the triggers that can unmask it acutely. Consider bubble contrast echo (TEE) to evaluate.

Echo Findings in AFE

• RV dilation, hypokinesis
• McConnell's sign (RV free wall akinesis, apex spared) — classically PE but seen in AFE
• D-sign (septal shift)
• TR, elevated RVSP
• LV compression / underfilling
• Global LV dysfunction in phase 2
• Pericardial effusion (rare)

Post-operative / Post-resuscitation Considerations

ICU Management

Neonatal Considerations

• Neonatology team present at delivery
• PMCD neonates may have hypoxic injury; NICU admission standard
• Apgar scoring and cord gas

Psychological/Family

• Debriefing for patient and family (high psychological trauma)
• Multidisciplinary debrief for clinical team
• Long-term: neuropsychological follow-up; PTSD screening

Prognosis

• Maternal mortality: ~20-60% (older series), improving with ECMO and aggressive MTP
• Neurological intact survival: ~15-40%
• Recurrence in future pregnancies: rare but documented; high-risk antenatal care essential

1. Diagnose by exclusion — exclude PE, eclampsia, sepsis, anaphylaxis first
2. DIC is the rule, not the exception — activate MTP early
3. PMCD at 4 minutes is a maternal resuscitative intervention
4. PFO unmasking explains refractory hypoxemia disproportionate to the degree of pulmonary disease
5. VA-ECMO is the ultimate rescue — have a low threshold to activate that team
6. Phase 1 is RV failure; Phase 2 is LV failure — management must track the phase