Hypercapnia prevents jugular bulb desaturation during rewarming from hypothermic cardiopulmonary bypass

BACKGROUND. The rewarming period of hypothermic cardiopulmonary bypass (CPB) is associated with reduced jugular bulb venous oxygen saturation (SjO2). This study investigates the effects of normocapnia vs. hypercapnia on changes in SjO2 during rewarming from hypothermic CPB for coronary artery bypass graft in patients classified as American Society of Anesthesiologists physical status 111.

Anesthesia was induced and maintained with fentanyl, midazolam, and continuous infusion of etomidate. Hypothermic CPB (27 degrees C) was managed according to alpha-stat conditions. The SjO2 percentage was measured using a fiberoptic catheter placed in the right jugular bulb via the right internal jugular vein. Data were recorded before and during the rewarming period. Patients were assigned to a normocapnic (PaCO2: 36-40 mmHg, n = 10) or hypercapnic (PaCO2: 45-50 mmHg, n = 10) PaCO2 regimen during rewarming.

The maximum reduction of SjO2 occurred during rewarming with the jugular bulb temperature at 35-36 degrees C. In contrast, SjO2 did not change during rewarming from hypothermia in hypercapnic patients.

These results show that mild hypercapnia prevents the desaturation of SjO2 seen with the normocapnic group during the rewarming period from hypothermic CPB. These data suggest that mild hypercapnia during rewarming from CPB is associated with a better balance between cerebral oxygen supply and demand.