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

Abstract

Purpose: Carbon dioxide (CO₂) increases cerebral perfusion. The effect of CO₂ 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 O₂/Air (95%O₂) to O₂/CO₂ (95%O₂/5%CO₂).

Methods: In this single-center, single-blinded, randomized crossover trial, 30 patients 18-65 years, with body mass index > 35 kg/m², requiring general anesthesia for bariatric surgery, underwent two apneas that were preceded by ventilation with either O₂/Air or O₂/CO₂ in random order. After anesthesia induction, intubation, and ventilation with O₂/Air or O₂/CO₂ 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 (SpO₂) 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 SpO₂ dropped to 80% was similar in the two groups (+ 6 s with O₂/CO₂, 95%CI -7 to 19 s, p = 0.37). Cerebral TOI and PaO₂ were higher after O₂/CO₂ (+ 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: O₂/CO₂ improves cerebral TOI and PaO₂ in anesthetized bariatric patients. Better apnea tolerance could not be confirmed.

Keywords: Hypoxia; apnea tolerance; cerebral oxygenation; tissue oxygenation.