A Pilot Randomized Controlled Study of Mild Hypercapnia During Cardiac Surgery With Cardiopulmonary Bypass

To test whether targeted therapeutic mild hypercapnia (TTMH) would attenuate cerebral oxygen desaturation detected using near-infrared spectroscopy during cardiac surgery requiring cardiopulmonary bypass (CPB).

Randomized controlled trials.

Operating rooms and intensive care unit of tertiary hospital.

The study comprised 30 patients undergoing cardiac surgery with CPB.

Patients were randomly assigned to receive either standard carbon dioxide management (normocapnia) or TTMH (target arterial carbon dioxide partial pressure between 50 and 55 mmHg) throughout the intraoperative period and postoperatively until the onset of spontaneous ventilation.

Relevant biochemical and hemodynamic variables were measured, and cerebral tissue oxygen saturation (SctO₂) was monitored with near-infrared spectroscopy. Patients were followed-up with neuropsychological testing. Patient demographics between groups were compared using the Fisher exact and Mann-Whitney tests, and SctO₂ between groups was compared using repeated measures analysis of variance. The median patient age was 67 years (interquartile range [IQR] 62-72 y), and the median EuroSCORE II was 1.1. The median CPB time was 106 minutes. The mean intraoperative arterial carbon dioxide partial pressure for each patient was significantly higher with TTMH (52.1 mmHg [IQR 49.9-53.9 mmHg] v 40.8 mmHg [IQR 38.7-41.7 mmHg]; p < 0.001) as was pulmonary artery pressure (23.9 mmHg [IQR 22.4-25.3 mmHg] v 18.5 mmHg [IQR 14.8-20.7 mmHg]; p = 0.004). There was no difference in mean percentage change in SctO₂ during CPB in the control group for both hemispheres (left: -6.7% v -2.3%; p = 0.110; right: -7.9% v -1.0%; p = 0.120). Compliance with neuropsychological test protocols was poor. However, the proportion of patients with drops in test score >20% was similar between groups in all tests.

TTMH did not increase SctO₂ appreciably during CPB but increased pulmonary artery pressures before and after CPB. These findings do not support further investigation of TTMH as a means of improving SctO₂ during and after cardiac surgery requiring CPB.