Pre-oxygenation with tidal-volume breathing of 100% O2 for 3 minutes extends safe apnoea time. In a morbidly obese patient (BMI 48 kg/m2), what modification to pre-oxygenation technique is recommended to further extend this safe apnoea window?

• A Increasing FiO2 to 100% by increasing flow rate only
• B Rapid hyperventilation for 2 minutes immediately before induction
• C 25–30 degree head-up position with high-flow oxygen; applying CPAP or PEEP during pre-oxygenation to recruit atelectatic alveoli ✓
• D Bilateral TPVB to improve chest wall compliance

Explanation

Morbidly obese patients have markedly reduced FRC due to cephalad diaphragm displacement and increased chest wall mass, predisposing to rapid atelectasis and oxygen desaturation during apnoea. The modified position (reverse Trendelenburg/ramped position — 25–30 degrees head-up) reduces diaphragmatic compression and improves FRC. Applying CPAP (10 cmH2O) during pre-oxygenation recruits atelectatic alveoli and increases oxygen stores. Apneic oxygenation (insufflating oxygen via nasal cannula at 15 L/min during laryngoscopy) also significantly extends safe apnoea time by delivering oxygen via diffusion. Obesity markedly shortens desaturation time from the standard 8–10 minutes to as little as 1–2 minutes.

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.