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CPAP Preoxygenation Obesity — FRCA Final MCQ

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ModerateAirway ManagementCPAP Preoxygenation ObesityFRCA Final

A 50-year-old man (ASA III) with a BMI of 48 is undergoing bariatric surgery. During preoxygenation, you achieve an end-tidal O2 of only 72% after 3 minutes of tidal breathing with 100% O2 via a tight-fitting face mask. What is the most effective technique to improve preoxygenation in this patient?

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Correct answer: D — Extend preoxygenation to 10 minutes with tidal breathing

In morbidly obese patients, standard preoxygenation is less effective due to reduced FRC and increased oxygen consumption. CPAP (5-10 cmH2O) during preoxygenation combined with head-up/ramped positioning significantly improves end-tidal O2 and extends safe apnoea time. CPAP recruits atelectatic lung, increases FRC, and improves V/Q matching. The head-up/ramped position elevates the FRC further by reducing abdominal compression on the diaphragm. Adding THRIVE (apnoeic oxygenation via HFNC during laryngoscopy) further extends safe apnoea time. The target end-tidal O2 should be >90%.

Reference: DAS – 2025 – Difficult intubation guidelines; AAGBI – 2015 – Obesity perioperative management