Background

We aimed to clarify the changes in sevoflurane blood concentrations in cardiovascular surgeries with cardiopulmonary bypass (CPB) under mild to moderate hypothermia.

Methods

In this single-center, prospective observational study, we included patients undergoing elective cardiac surgery with CPB under mild and moderate hypothermia using four types of oxygenators. Radial artery blood samples were collected at repeated time points, both before and during CPB. Simultaneously, bladder temperature was recorded. Sevoflurane blood concentration was measured using gas chromatography.

Results

Sevoflurane blood concentrations gradually increased during general anesthesia induction via native lung ventilation. When using CPB under mild hypothermia, the concentration dropped sharply after switching to an oxygenator but then gradually increased and reached equilibrium. These changes were observed in all four oxygenators, with no significant differences among them. In moderate hypothermic surgeries, the bladder temperature gradually decreased during the pre-circulatory-arrest phase, and the sevoflurane blood concentration increased accordingly. As rewarming began after the distal aortic anastomosis, the bladder temperature gradually increased, and the sevoflurane blood concentration returned to levels observed during native lung ventilation. In total, 85 patients undergoing mild hypothermic cardiac surgery (SE, n = 21; LI, n = 21; TE, n = 22; ME, n = 21) and 25 patients undergoing moderate hypothermic cardiac surgery were analyzed. Using a linear mixed-effects model, bladder temperature was significantly associated with sevoflurane blood concentration in both mild hypothermia (β = − 5.90 μg/mL per °C; n = 73 patients, 1,123 observations; p < 0.001) and moderate hypothermia (β = − 2.11 μg/mL per °C; n = 25 patients, 378 observations; p < 0.001) cardiac surgery. No significant differences in sevoflurane blood concentrations were observed among the four oxygenator types.

Conclusions

We demonstrated chronological changes in sevoflurane blood concentrations during mild and moderate hypothermic cardiac surgery, showing an inverse correlation with bladder temperature.