Evaluation of hyperoxia-induced hypercapnia in obese patients after cardiac surgery: a randomized crossover comparison of conservative and liberal oxygen administration.

Recent studies on patients with stable obesity-hypoventilation syndrome have raised concerns about hyperoxia-induced hypercapnia in this population. This study aimed to evaluate whether a higher oxygen saturation target would increase arterial partial pressure of carbon dioxide (PaCO₂₎ in obese patients after coronary artery bypass grafting surgery (CABG).

Obese patients having CABG were recruited. With a randomized crossover design, we compared two oxygenation strategies for 30 min each, immediately after extubation: a peripheral oxygen saturation (SpO₂) target of ≥ 95% achieved with manual oxygen titration (liberal) and a SpO₂ target of 90% achieved with FreeO₂, an automated oxygen titration device (conservative). The main outcome was end-of-period arterial PaCO₂.

Thirty patients were included. Mean (standard deviation [SD]) body mass index (BMI) was 34 (3) kg·m^-2 and mean (SD) baseline partial pressure of carbon dioxide (PCO₂) was 40.7 (3.1) mmHg. Mean (SD) end-of-period PaCO₂ was 42.0 (5.4) mmHg in the conservative period, compared with 42.6 (4.6) mmHg in the liberal period [mean difference - 0.6 (95% confidence interval - 2.2 to 0.9) mmHg; P = 0.4]. Adjusted analysis for age, BMI, narcotics, and preoperative PaCO₂ did not substantively change the results. Fourteen patients were retainers, showing an elevation in mean (SD) PaCO₂ in the liberal period of 3.3 (4.1) mmHg. Eleven patients had the opposite response, with a mean (SD) end-of-period PaCO₂ decrease of 1.8 (2.2) mmHg in the liberal period. Five patients had a neutral response.

This study did not show a clinically important increase in PaCO₂ associated with higher SpO₂ values in this specific population of obese patients after CABG. Partial pressure of carbon dioxide increased with liberal oxygen administration in almost half of the patients, but no predictive factor was identified.

www.clinicaltrials.gov (NCT02917668); registered 25 September, 2016.