What is the most common cause of mortality for general anesthesia in pregnancy?

Aspiration of Gastric Contents is the Most Common Cause of Mortality for General Anesthesia in Pregnancy

The aspiration of gastric contents is the single most common cause of death in anesthesia events during pregnancy, accounting for the highest mortality in general anesthesia for obstetric patients 1.

Understanding the Risk of Aspiration in Pregnancy

Pregnant women are at particularly high risk for aspiration during general anesthesia due to several physiological changes:

• Delayed gastric emptying
• Increased intra-abdominal pressure from the gravid uterus
• Reduced lower esophageal sphincter tone
• Higher risk of regurgitation and vomiting

Incidence and Mortality Data

The 4th National Audit Project (NAP4) identified that aspiration of gastric contents was responsible for:

• Eight deaths, making it the single most common cause of death in anesthesia events 1
• 36 cases of aspiration of gastric contents out of 42 total aspiration cases in 2,872,600 general anesthetics 1
• 29 of these patients required ICU admission with half needing prolonged stays 1

While historical data from Mendelson's 1946 paper showed an aspiration incidence of 1:667 in obstetric patients with a mortality rate of 1:22,000, more recent studies show improved but still concerning rates:

• Modern aspiration incidence: approximately 1:1,547 general anesthesias for cesarean sections (0.064%) 2
• Aspiration represents 61.5% of all anesthetic complications in obstetric patients 2

Risk Factors for Aspiration During Pregnancy

Key risk factors that increase aspiration risk include:

• Emergency procedures (identified in all 8 cases in one study) 2
• Difficult tracheal intubation (50% of cases) 2
• Obesity (particularly vulnerable to aorto-caval compression) 1
• Inadequate depth of anesthesia 1
• Inappropriate airway management 1
• Failure to use rapid sequence induction with cricoid pressure 1

Prevention Strategies

To reduce the risk of aspiration and associated mortality:

1. Use rapid sequence induction with cricoid pressure

   • NAP4 identified cases where omission of rapid sequence induction led to patient harm or death 1
   • While not providing 100% protection, it remains the standard for at-risk patients 1

2. Proper cricoid pressure technique

   • Apply 10 N (1 kg) force initially to the awake patient
   • Increase to 30 N (3 kg) after loss of consciousness 1
   • Release immediately if active vomiting occurs 1

3. Pharmacological prophylaxis

   • Antacids (reduce risk of intragastric pH < 2.5 by 83%) 3
   • H2 antagonists (reduce risk by 91%) 3
   • Combined antacids plus H2 antagonists (reduce risk by 98%) 3

4. Prefer regional over general anesthesia when possible 4

Management of Aspiration When It Occurs

If aspiration occurs:

• Immediate recognition is critical
• Prompt treatment including suctioning (used in 54% of cases)
• May require bronchodilators (30%), intubation/prolonged intubation (9.3%), antibiotics (4.7%), or CPAP (2.3%) 1

Common Pitfalls to Avoid

1. Improper cricoid pressure technique

   • Too much force can cause retching and increase aspiration risk 1
   • Improper positioning may not effectively compress the hypopharynx 1

2. Failure to recognize high-risk patients

   • All pregnant women should be considered to have a full stomach 4
   • Emergency cases have 10x higher aspiration risk 1

3. Inadequate preparation

   • NAP4 found cases where rapid sequence induction was omitted despite clear indications 1
   • Only 3.1% of cases in one study received preventive measures 2

4. Focusing only on induction

   • NAP4 found most aspiration events occurred during maintenance or extubation, not just during induction 1

Remember that while aspiration is a relatively rare event in modern anesthesia practice, it remains the most significant cause of mortality in obstetric general anesthesia and requires vigilant prevention strategies.