An obese 39-year-old female undergoing abdominal hysterectomy with Trendelenburg positioning develops desaturation when the head is flexed. What is the most likely explanation for this desaturation?

An obese 39-year-old female undergoing abdominal hysterectomy with Trendelenburg positioning develops desaturation when the head is flexed. What is the most likely explanation for this desaturation?

• A. Diffusion hypoxia
• B. Decreased functional residual capacity
• C. Mainstem intubation
• D. Decreased cardiac output

Answer: (C)

Desaturation occurring when the head is flexed in an intubated patient points to endotracheal tube migration into the right mainstem bronchus. Neck flexion tends to push the tube deeper, and the right mainstem bronchus is more vertical and in line with the trachea, making it a common site for accidental advancement. Ventilation then predominantly supports the right lung while the left lung becomes underventilated, leading to a drop in oxygen saturation. In obese patients and with Trendelenburg positioning, this risk is heightened because repositioning can readily alter tube position. Diffusion hypoxia would not be tied to a head position and typically relates to emergence events, while decreased FRC or cardiac output explains other mechanisms or baseline risks rather than a position-triggered single-event desaturation. If this happens, listen for bilateral breath sounds, verify with capnography, and withdraw the tube a few centimeters until both lungs are ventilated and breath sounds are equal, then re-secure and reassess.

Desaturation occurring when the head is flexed in an intubated patient points to endotracheal tube migration into the right mainstem bronchus. Neck flexion tends to push the tube deeper, and the right mainstem bronchus is more vertical and in line with the trachea, making it a common site for accidental advancement. Ventilation then predominantly supports the right lung while the left lung becomes underventilated, leading to a drop in oxygen saturation. In obese patients and with Trendelenburg positioning, this risk is heightened because repositioning can readily alter tube position. Diffusion hypoxia would not be tied to a head position and typically relates to emergence events, while decreased FRC or cardiac output explains other mechanisms or baseline risks rather than a position-triggered single-event desaturation. If this happens, listen for bilateral breath sounds, verify with capnography, and withdraw the tube a few centimeters until both lungs are ventilated and breath sounds are equal, then re-secure and reassess.