There is no evidence that carbon dioxide-enriched oxygen before apnea affects the time to arterial desaturation, but it might improve cerebral oxygenation in anesthetized obese patients: a single-blinded randomized crossover trial

Purpose Carbon dioxide (CO 2 ) increases cerebral perfusion. The effect of CO 2 on apnea tolerance, such as after anesthesia induction, is unknown. This study aimed to assess if cerebral apnea tolerance can be improved in obese patients under general anesthesia when comparing O 2 /Air (95%O 2 ) to O 2 /CO 2 (95%O 2 /5%CO 2 ). Methods In this single-center, single-blinded, randomized crossover trial, 30 patients 18–65 years, with body mass index > 35 kg/m 2 , requiring general anesthesia for bariatric surgery, underwent two apneas that were preceded by ventilation with either O 2 /Air or O 2 /CO 2 in random order. After anesthesia induction, intubation, and ventilation with O 2 /Air or O 2 /CO 2 for 10 min, apnea was performed until the cerebral tissue oxygenation index (TOI) dropped by a relative 20% from baseline (primary endpoint) or oxygen saturation (SpO 2 ) reached 80% (safety abortion criterion). The intervention was then repeated with the second substance. Results The safety criterion was reached in all patients before cerebral TOI decreased by 20%. The time until SpO 2 dropped to 80% was similar in the two groups (+ 6 s with O 2 /CO 2 , 95%CI -7 to 19 s, p = 0.37). Cerebral TOI and PaO 2 were higher after O 2 /CO 2 (+ 1.5%; 95%CI: from 0.3 to 2.6; p = 0.02 and + 0.6 kPa; 95%CI: 0.1 to 1.1; p = 0.02). Conclusion O 2 /CO 2 improves cerebral TOI and PaO 2 in anesthetized bariatric patients. Better apnea tolerance could not be confirmed.