What are the advantages of pre-oxygenation before the induction of anesthesia?

Advantages of Pre-oxygenation Before Induction of Anaesthesia

Pre-oxygenation before induction of anaesthesia is strongly recommended to prevent arterial oxygen desaturation during intubation attempts, which significantly reduces morbidity and mortality by extending the safe apnoea time. 1

Primary Benefits of Pre-oxygenation

• Increased oxygen reserves: Pre-oxygenation replaces nitrogen in the lungs with oxygen, creating an oxygen reservoir that delays arterial desaturation during apnoea
• Extended safe apnoea time:
  • Without pre-oxygenation: 1-2 minutes before desaturation to SpO₂ <90%
  • With proper pre-oxygenation: 6-8 minutes before desaturation 1
• Prevention of hypoxemia: Absence of pre-oxygenation can lead to arterial oxygen desaturation (SpO₂ <90%) in 30-60% of cases, even in ASA I patients 1

Clinical Impact on Patient Safety

• Reduced morbidity and mortality: The fourth national audit (NAP4) in the UK revealed difficult or failed intubation represented 39% of airway control incidents, frequently associated with arterial oxygen desaturation 1
• Increased time for airway management: Provides additional time for laryngoscopy, tracheal intubation, and airway rescue maneuvers 1
• Essential for rapid sequence induction: Pre-oxygenation is a critical component of rapid sequence induction and intubation techniques 1

Effective Pre-oxygenation Techniques

Several methods have proven effective:

1. Tidal volume breathing: 100% oxygen for 3 minutes via tight-fitting facemask 1, 2
2. Deep breathing techniques: 8 vital capacity breaths over 60 seconds 2
3. Enhanced techniques for high-risk patients:
   • CPAP (5-10 cm H₂O) if oxygenation is impaired 1
   • Non-invasive ventilation with or without PEEP 2
   • Head-up positioning (25-30° elevation) - increases safe apnoea time by approximately 30% 2

Special Considerations for High-Risk Populations

Pre-oxygenation is particularly crucial for patients at risk of rapid desaturation:

• Obese patients: Reduced functional residual capacity (FRC) leads to faster desaturation 1, 2
• Pregnant women: Experience more rapid desaturation (SpO₂ <90% on average at 98 seconds) due to decreased FRC and increased oxygen consumption 2
• Critically ill patients: Higher risk of rapid desaturation; may benefit from non-invasive ventilation for pre-oxygenation 2
• Children: Require modified techniques due to higher risk of rapid hypoxemia 2

Optimizing Pre-oxygenation Effectiveness

The effectiveness of pre-oxygenation depends on:

• Proper mask seal: Leaks significantly impair pre-oxygenation 1, 2
• Adequate fresh gas flow: Minimum 5 L/min, preferably 8 L/min or higher 3
• End-tidal oxygen fraction (FeO₂): Pre-oxygenation is considered effective when FeO₂ is greater than 90% 1
• Patient positioning: Proper positioning improves pre-oxygenation efficacy 2

Peroxygenation During Intubation

• Nasal oxygen: Applying nasal oxygen at 15 L/min during intubation attempts maintains high oxygen levels in the hypopharynx 1
• High-flow nasal oxygen (HFNO): Can be used at 30-70 L/min to further extend safe apnoea time 1

Potential Limitations and Risks

While minimal compared to benefits, potential concerns include:

• Absorption atelectasis: A consequence of pre-oxygenation, but benefits outweigh this risk 4
• Delayed detection of esophageal intubation: Rare but possible 4
• Hemodynamic effects: Minimal due to short duration of pre-oxygenation 4

Conclusion

Pre-oxygenation is a simple, effective technique that significantly improves patient safety during anaesthesia induction by extending the safe apnoea time. It should be performed in all patients undergoing general anaesthesia, with particular attention to optimizing technique in high-risk populations.