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. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12871-023-01982-9.