Pharmacokinetics of desflurane elimination from respiratory gas and blood during the 20 minutes after cardiac surgery.

Background/purpose: Desflurane, with a low blood-gas partition coefficient, is an ideal anesthetic to achieve rapid offset and recovery from general anesthesia. Investigation of desflurane elimination from blood and respiratory gas should provide useful information with respect to a patient's recovery from anesthesia. Therefore, this study is designed to characterize the pharmacokinetics of desflurane elimination after cardiac surgery.

Methods: Sixteen patients undergoing coronary artery bypass graft surgery were enrolled. At the end of surgery, multiple gas and blood samples were taken in the 20 minutes before and after stopping desflurane administration, with prior maintenance of a fixed 7% inspired desflurane in 6 L/minute oxygen flow for 60 minutes before the cessation. The blood desflurane concentrations, including internal jugular-bulb blood (Jdes), arterial blood (Ades) and pulmonary arterial blood (PAdes) were analyzed using gas chromatography. The inspiratory desflurane concentration (CIdes) and end-tidal desflurane (CEdes) were measured with an infrared analyzer, and cardiac output was measured using an Opti-Q pulmonary artery catheter.

Results: Before cessation of desflurane administration, the inspiratory desflurane concentration (CIdes) was relatively higher than end-tidal (CEdes), arterial (Ades), internal jugular-bulb blood (Jdes), and pulmonary (PAdes) concentrations in sequence (CIdes > CEdes > Ades≈ Jdes > PAdes). During the elimination phase, rapid decay occurred in CEdes, followed by Jdes, Ades and PAdes. Twenty minutes after stopping desflurane administration, the desflurane concentrations were: PAdes > Ades≈ Jdes > CEdes. The decay curves of desflurane concentrations demonstrated two distinct elimination components: an initial, fast 5-minute component followed by a slow 15-minute component.

Conclusion: Desflurane is eliminated fastest from the lungs, as indicated by CEdes, compared to elimination from circulating blood. The initial, rapid 5-minute desflurane washout reflected the diluting effect of functional residual capacity of the lungs.