What is the evidence for rapid sequence induction (RSI) in preventing aspiration in high-risk patients?

Evidence for Rapid Sequence Induction in Preventing Aspiration

Rapid sequence induction (RSI) is recommended for patients at high risk of aspiration, though there is moderate-quality evidence supporting its use rather than direct evidence of efficacy in preventing aspiration. 1

Risk Factors for Aspiration

RSI should be performed in patients with:

• Inadequate fasting (less than 2 hours for liquids, less than 6 hours for food)
• Active vomiting
• Ileus or sub-ileus
• Impaired protective reflexes
• Gastrointestinal motility disorders
• Pregnancy (third trimester and during birth)
• Bowel and stomach obstruction and distension
• Sepsis
• Patients receiving opioids 1, 2

Components of Rapid Sequence Induction

Patient Positioning

• Head and torso inclined (semi-Fowler) position is suggested during RSI (conditional recommendation, very low-quality evidence) 1
• This position may improve first-pass intubation success through:
  • Enhanced preoxygenation via increased functional residual capacity
  • Improved laryngeal view
  • Reduced risk of clinically significant aspiration 1

Preoxygenation

• Consistent pre-oxygenation with FiO2 of 1.0 (FetO2 > 0.9)
• Oxygen flow > 10 L/min using a completely sealing respiratory mask with capnography
• Duration: 3-5 minutes 2, 3
• High-flow nasal oxygen (HFNO) is suggested when laryngoscopy is expected to be challenging 1

Medication Administration

1. Neuromuscular Blocking Agents (NMBAs):

   • Strong recommendation to administer an NMBA when using a sedative-hypnotic induction agent (low-quality evidence) 1, 3
   • Options:
     • Succinylcholine (1.5 mg/kg IV) - first-line with rapid onset and short duration
     • Rocuronium (0.9-1.2 mg/kg IV) - alternative when succinylcholine is contraindicated 3, 4

2. Induction Agents:

   • A sedative-hypnotic induction agent must be used when an NMBA is administered (best practice statement) 1
   • Options include etomidate (0.2-0.3 mg/kg IV), propofol, ketamine (1-2 mg/kg IV), or thiopental 3, 2
   • The European Society of Anaesthesiology and Intensive Care recommends a fast-acting muscle relaxant such as succinylcholine 1-2 mg/kg or rocuronium 0.9-1.2 mg/kg for RSI (strong recommendation, moderate evidence) 1

3. Opioids:

   • Consider pre-treatment with fentanyl (1-3 mcg/kg) to blunt sympathetic response 3

Cricoid Pressure

• Practice varies internationally
• Some evidence suggests cricoid pressure can make intubation more difficult and may not prevent aspiration of gastric contents 1
• If direct laryngoscopy is difficult, cricoid pressure should be released 1
• Use should align with current standard practice in the practitioner's country 1

Ventilation Strategies

• Traditional RSI avoids positive pressure ventilation before securing the airway
• Modified or "controlled" RSI includes gentle bag-mask ventilation before laryngoscopy 1
• In children, experts suggest ventilating with FiO2 0.8 and small peak inspiratory pressure (ideally <15 cmH2O) if SpO2 falls below 95% 1

Gastric Decompression

• Nasogastric tube decompression is advised when benefits outweigh risks in patients at high risk of regurgitation (best practice statement) 1
• Before surgery, gastric emptying with a nasogastric tube is mandatory in patients with ileus and passage or defecation disorders 4

Special Considerations

Pediatric Patients

• "Controlled" or "modified" RSI is often preferred in children to decrease risks of hypoxemia, hemodynamic complications, and difficult intubation 1
• This includes preoxygenation, deep anesthesia with an opiate and hypnotic agent, non-depolarizing muscle relaxant, and gentle bag-mask ventilation before laryngoscopy 1

Difficult Airway Management

• If unexpected difficult airway occurs, a 2nd generation extraglottic airway device should be used 2
• Equipment for difficult airway management should be immediately available 3

Limitations and Caveats

• Despite widespread use, there is limited high-quality evidence specifically demonstrating RSI's efficacy in preventing aspiration
• The incidence of aspiration is rare, but consequences can be severe (death or brain injury) 1
• Three factors reduce aspiration risk: expertise, support from an experienced anesthesiologist, and close monitoring 2
• RSI techniques should be individualized based on patient factors and clinical scenario while maintaining core principles 2

RSI remains the standard of care for patients at high risk of aspiration despite limited direct evidence of efficacy, as the potential benefits in preventing aspiration-related morbidity and mortality outweigh the risks when performed correctly.