Best Method for Preoxygenation During RSI
For standard RSI in critically ill patients, use 100% oxygen via tight-fitting face mask for 3 minutes with the patient positioned head-up at 25-30°, targeting an end-tidal oxygen concentration >90%. 1
Standard Preoxygenation Technique
Positioning (Critical First Step)
- Position ALL patients with head elevation of 25-30° before starting preoxygenation 1
- This increases functional residual capacity and extends safe apnea time by approximately 30% (from 2.5 to 3.5 minutes in obese patients) 1
- Even moderate head elevation of 20° significantly prolongs desaturation time in the general population 1
- For obese patients specifically, use ramping position (external auditory meatus level with sternal notch) 1
Oxygen Delivery Method
- Use tight-fitting face mask with 100% oxygen at 10-15 L/min for 3 minutes 1
- Ensure mask seal is adequate—absence of capnograph trace indicates significant leak 1
- Use two-handed mask technique if needed to minimize leak 1
- Do NOT use Hudson-type face masks with or without reservoir 1
Target Endpoint
- Achieve end-tidal oxygen concentration (FeO₂) >90% 1
- This is the accepted standard for effective preoxygenation 1
Alternative Techniques Based on Clinical Scenario
For Hypoxemic Patients (SpO₂ <93%)
Use non-invasive positive pressure ventilation (NIPPV) with CPAP 5-10 cmH₂O and pressure support 1
- NIPPV has the strongest evidence for decreasing critical desaturation during RSI in severely hypoxemic patients 1
- Target tidal volume 7-10 mL/kg with CPAP to reduce absorption atelectasis 1
- Keep airway pressure <20 cmH₂O to minimize gastric distension 1
- Continue NIPPV until immediately before laryngoscopy 1
High-flow nasal oxygen (HFNO) is an acceptable alternative but evidence shows it may be slightly inferior to NIPPV for preventing desaturation 1
- HFNO provides the advantage of continued oxygen flow during laryngoscopy 1
- Recent trial showed desaturation rates of 27% with HFNO versus 23% with NIPPV in all patients, and 35% versus 24% respectively in patients with PaO₂/FiO₂ <200 1
For Agitated/Uncooperative Patients
Use medication-assisted preoxygenation (delayed sequence intubation) with ketamine 1
- Administer ketamine 1-1.5 mg/kg IV to achieve dissociative state 1
- This allows patient to tolerate face mask, NIPPV, or HFNO 1
- Wait until adequate preoxygenation achieved (FeO₂ >90%), then administer neuromuscular blocking agent 1
- Observational data shows mean oxygen saturation increase of 8.9% after ketamine administration 1
For Obstetric Emergencies
Shorten preoxygenation time to 2 minutes due to decreased FRC 1
- Vital capacity maneuvers are NOT recommended in pregnant patients 1
- Consider NIV with PEEP to achieve FeO₂ >90% more rapidly 1
- Head-up positioning increases FRC by approximately 188 mL but benefit on desaturation time not definitively proven 1
Techniques to AVOID
Vital Capacity Maneuvers
- Do NOT use 4 vital capacity breaths in 30 seconds—this is inferior to 3-minute spontaneous ventilation 1
- 8 vital capacity breaths in 60 seconds is equivalent to 3-minute technique but requires excellent patient cooperation 1
- Increasing oxygen flow to 20 L/min does NOT improve 4-breath technique 1
Positive Pressure Ventilation in Normoxemic Patients
- Avoid PPV during preoxygenation in patients with SpO₂ ≥93%—associated with lower intubation success and increased aspiration risk 2
- Reserve PPV for hypoxemic patients only 2
Critical Pitfalls to Avoid
- Never remove oxygen source before complete apnea—preoxygenation is lost after just 5 breaths (20 seconds) if all devices removed 3
- Leave nasal cannula in place during laryngoscopy for apneic oxygenation—extends time to 8 breaths (39 seconds) 3
- Failure to position patient head-up is the most common error—this single intervention extends safe apnea time by 30% 1
- Inadequate mask seal negates preoxygenation efforts—check for capnograph waveform 1
- Preoxygenating flat supine in obese patients reduces tolerance to apnea to as little as 2.5 minutes 1