What is the ideal preoxygenation method for Difficult Sequence Intubation (DSI)?

Ideal Preoxygenation Method for Delayed Sequence Intubation (DSI)

For DSI, use medication-assisted preoxygenation with ketamine to achieve a dissociative state, then apply non-invasive positive pressure ventilation (NIPPV) with CPAP 5-10 cmH₂O in a 25-30° head-up position for 3 minutes, targeting end-tidal oxygen >90%. 1

Understanding DSI Context

DSI specifically addresses the agitated or uncooperative patient who cannot tolerate standard preoxygenation techniques. The core principle is administering dissociative-dose ketamine first to allow the patient to tolerate effective preoxygenation before proceeding with paralysis and intubation. 1

Step-by-Step DSI Preoxygenation Protocol

1. Patient Positioning (Before Ketamine)

• Position patient at 25-30° head-up immediately, as this increases functional residual capacity and extends safe apnea time by approximately 30% compared to supine positioning. 2, 3, 1
• This positioning benefit applies to all patients, not just obese patients, with even a 20° angle significantly prolonging desaturation time. 2

2. Administer Dissociative-Dose Ketamine

• Give ketamine to achieve dissociative state that allows patient to tolerate face mask, NIPPV, or high-flow nasal oxygen. 1
• This is the defining step of DSI that differentiates it from standard rapid sequence intubation. 1

3. Apply NIPPV for Preoxygenation

• Once patient is dissociated, apply tight-fitting face mask with NIPPV using CPAP 5-10 cmH₂O and pressure support. 1
• Use 100% oxygen at 10-15 L/min flow rate for effective denitrogenation. 3, 1
• Continue for 3 minutes to achieve end-tidal oxygen concentration (FeO₂) >90%. 2, 3, 1

4. Monitor Effectiveness

• Continuously monitor end-tidal oxygen concentration, targeting >85%, ideally >90%. 1
• Use waveform capnography to confirm adequate mask seal—absence of capnograph trace indicates significant leak and inadequate preoxygenation. 3, 1
• Monitor SpO₂, blood pressure, heart rate, and ECG throughout. 1

Why NIPPV Over Other Methods for DSI

NIPPV is superior to standard face mask or high-flow nasal oxygen in hypoxemic patients requiring DSI. 1 Evidence shows:

• NIPPV with CPAP 5-10 cmH₂O decreases critical desaturation during rapid sequence intubation in hypoxemic patients. 1
• High-flow nasal oxygen is acceptable but slightly inferior to NIPPV for preventing desaturation. 1
• Standard face mask alone (without positive pressure) shows poor response in critically ill patients, with only 20% demonstrating significant benefit. 2

Apneic Oxygenation During Intubation Attempt

After administering neuromuscular blockade and beginning laryngoscopy:

• Continue nasal oxygen at 5-15 L/min via nasal cannula throughout the intubation attempt to provide apneic oxygenation. 2
• In obese patients, nasopharyngeal insufflation at 5 L/min doubles the arterial oxygen desaturation time compared to no apneic oxygenation. 2
• High-flow nasal oxygen during apnea can extend safe apnea time to a median of 14 minutes in difficult airway patients. 2

Critical Pitfalls to Avoid in DSI

• Never skip head-up positioning—this is the most common error and dramatically reduces apnea tolerance, especially in obese patients where supine positioning reduces tolerance to as little as 2.5 minutes. 3, 1
• Do not use vital capacity maneuvers—they are inferior to 3-minute tidal volume breathing and require excessive patient cooperation that defeats the purpose of DSI. 2, 1
• Avoid positive pressure ventilation in normoxemic patients—it is associated with lower intubation success and increased aspiration risk. 1
• Ensure adequate mask seal—inadequate seal negates all preoxygenation efforts, particularly problematic in edentulous or bearded patients. 3

Special Considerations for High-Risk Populations

Obese Patients

• Head-up positioning is absolutely essential, extending safe apnea time from 2.5 minutes supine to 3.5+ minutes at 25° elevation. 2, 3
• NIPPV provides additional benefit in preventing desaturation during intubation compared to conventional 5-minute preoxygenation. 2

Pregnant Patients

• Shorten preoxygenation time expectation to 2 minutes due to decreased functional residual capacity. 2, 1
• Consider NIV with PEEP to achieve FeO₂ >90% more rapidly. 2, 1
• During labor, desaturation occurs at 98 seconds versus 292 seconds in pregnancy due to increased oxygen consumption. 2

Critically Ill/Hypoxemic Patients

• NIPPV is the preferred method as these patients show poor response to standard bag-valve mask preoxygenation. 2, 1
• High-flow nasal oxygen at low flow (15 L/min) did not demonstrate benefit in preventing desaturation in critically ill patients. 2