Desflurane pharmacokinetics during cardiopulmonary bypass

Objective: To describe the washin and washout of desflurane when first administered during cardiopulmonary bypass (CPB) for cardiac surgery. Design: A single-arm prospective study. Setting: University-affiliated hospital operating room. Participants: Ten adult patients presenting for cardiac surgery. Interventions: Consenting patients presenting for cardiac surgery received anesthesia with midazolam and fentanyl. Patients were cooled to 32°C on CPB, then desflurane 6% was administered and blood samples drawn repeatedly from the arterial and venous bypass cannulae as well as from the membrane oxygenator inlet and exhaust from 2 to 32 minutes of desflurane administration. Just before rewarming, final (maximum) washin samples were taken. On rewarming, desflurane was discontinued, and blood and gas samples were taken 2 to 24 minutes thereafter. Measurements and Main Results: CPB time was 116 ± 10 minutes, and ischemic time was 81 ± 6 minutes. Mean pump flow was 4.49 ± 0.03 L/min, and mean arterial pressure was 70.1 ± 1 mmHg during the study period. Arterial washin of desflurane was initially rapid; arterial concentrations reached 50% of administered concentrations within 4 minutes, but then slowed, reaching 68% of inspired concentrations at 32 minutes (desflurane concentration 4.0% ± 0.3%). Arterial washout of desflurane was more rapid; arterial concentrations fell to 18% of the maximum concentration reached within 4 minutes, and only 8% of the maximum arterial concentration was present in blood 20 minutes later. Conclusion: Desflurane showed rapid initial washin and washout on CPB when administration was started at 32°C and stopped at time of rewarming.