How should you preoxygenate before rapid sequence intubation (RSI) and why?

• A. Deliver 50% oxygen for 30 seconds.
• B. Use room air during preoxygenation to prevent oxygen toxicity.
• C. Deliver 100% oxygen via a nonrebreather mask or bag-valve mask for 3-5 minutes (or eight deep breaths) to maximize oxygen reserves and delay desaturation.
• D. No preoxygenation is needed before RSI.

Answer: (C)

The main idea is to fill the lungs with oxygen so you have a ready reservoir during the brief pause when the patient is paralyzed for rapid sequence intubation. By delivering 100% oxygen with a mask that seals well (nonrebreather or bag-valve mask) for about 3–5 minutes, or having the patient take eight deep breaths, you wash out nitrogen from the lungs and maximize oxygen stores. This creates a longer safe apnea time, reducing the risk of desaturation while you secure the airway.

Delivering only 50% oxygen for 30 seconds won’t load the lungs with enough oxygen, and using room air won’t increase the reserves at all. Skipping preoxygenation leaves the patient vulnerable to rapid desaturation during the intubation attempt. In some patients, especially those with obesity or lung disease, you may need longer or augmented preoxygenation (for example, with CPAP/NIV), but the core principle remains loading the lungs with 100% oxygen to delay desaturation.