What are the common causes of cardiac arrest during delivery?

Common Causes of Cardiac Arrest During Delivery

The most common causes of maternal cardiac arrest during delivery are hemorrhage, cardiovascular diseases (including myocardial infarction, aortic dissection, and myocarditis), amniotic fluid embolism, sepsis, aspiration pneumonitis, pulmonary embolism, and eclampsia. 1

Primary Causes of Maternal Cardiac Arrest

Obstetric Causes

• Hemorrhage: Leading cause of maternal cardiac arrest

  • Placenta previa
  • Placental abruption
  • Uterine rupture
  • Postpartum hemorrhage

• Amniotic Fluid Embolism: Rare but catastrophic complication

  • Presents with sudden hypoxemia, hypotension, and coagulopathy
  • Often occurs during delivery or immediately postpartum

• Preeclampsia/Eclampsia: Develops after 20th week of gestation

  • Can produce severe hypertension and ultimately diffuse organ-system failure
  • If untreated, can lead to maternal and fetal mortality 1

Medical Causes

• Cardiovascular Diseases:

  • Myocardial infarction
  • Aortic dissection
  • Cardiomyopathy
  • Congenital heart disease (third most common cause of maternal cardiac deaths) 1

• Pulmonary Embolism:

  • Risk increases during pregnancy due to hypercoagulable state
  • Can be massive and life-threatening 1

• Sepsis:

  • Can rapidly progress to septic shock and cardiac arrest

Iatrogenic Causes

• Magnesium Sulfate Toxicity:

  • Can cause ECG changes at levels of 2.5-5 mmol/L
  • AV nodal conduction block, bradycardia, hypotension, and cardiac arrest at levels of 6-10 mmol/L
  • Particularly dangerous if the woman becomes oliguric 1

• Anesthetic Complications:

  • Spinal shock from regional anesthesia
  • Loss of airway control or pulmonary aspiration during general anesthesia induction
  • Hypoventilation or airway obstruction during emergence from anesthesia 1
  • Bezold-Jarisch reflex (vasovagal syncope) during spinal anesthesia 2

Physiological Considerations

Pregnancy causes significant physiological changes that can complicate resuscitation efforts:

• Aortocaval Compression: When the uterus is large enough (typically ≥20 weeks), it can compress the inferior vena cava and aorta when the mother is supine, reducing venous return and cardiac output 1

• Respiratory Changes: Decreased functional residual capacity and increased oxygen consumption lead to rapid desaturation during apnea 1

• Cardiovascular Changes: Increased blood volume, cardiac output, and heart rate with decreased systemic vascular resistance 3

Management Considerations

When cardiac arrest occurs during delivery, immediate actions should include:

1. High-quality CPR with left uterine displacement to relieve aortocaval compression 1

2. Consider perimortem cesarean delivery (PMCD) if return of spontaneous circulation (ROSC) is not achieved quickly:

   • Should be considered for women in the second half of pregnancy (≥20 weeks)
   • Ideally performed within 4 minutes of cardiac arrest if ROSC is not achieved 1
   • Improves maternal resuscitation by relieving aortocaval compression 4

3. Address the underlying cause based on the most likely etiology:

   • For hemorrhage: Blood products, uterotonic agents (with caution)
   • For magnesium toxicity: Empirical calcium administration may be lifesaving 1
   • For amniotic fluid embolism: Supportive care, possibly extracorporeal life support 1, 4

Prevention and Preparation

Given the rarity but severity of maternal cardiac arrest (approximately 1:12,000 admissions for delivery in the United States) 1, preparation is essential:

• Team planning should involve obstetric, neonatal, emergency, anesthesiology, intensive care, and cardiac arrest services 1
• Protocols for management of out-of-hospital cardiac arrest in pregnancy should facilitate timely transport to centers capable of performing perimortem cesarean delivery 1

Understanding these causes and being prepared for immediate intervention is crucial for improving outcomes for both mother and baby during this rare but critical emergency.