Pharmacokinetics of isoflurane: Uptake in the body

We investigated the effect of the inspired isoflurane concentration (C _Iiso) on body uptake by comparing the isoflurane concentration in the pulmonary artery blood (PAiso) and that in the arterial blood (Aiso) in 16 patients undergoing coronary artery bypass grafting surgery during the 1st, hour of isoflurane anesthesia. The patients received standardized anesthetics consisting of fentanyl and thiopental and were then allocated to receive either 1% or 2% C_Iiso (n = 8 in each group). C_Iiso and end-tidal isoflurane concentration (C_Eiso) were measured by infrared analysis, and Aiso and PAiso were analyzed by gas chromatography. The cardiac output was measured by thermodilution by use of a pulmonary artery catheter. The body tissue could be represented by the gradient C_Iiso-C_Eiso or Aiso-PAiso over time, respectively. The 2% inspired isoflurane group had twice the gradients (either C_Iiso-C_Eiso or Aiso-PAiso) than the 1% inspired isoflurance group. Additionally, both C _Iiso-C_Eiso and Aiso-PAiso were nearly constant over the hour of the study. The inspired concentration-dependent and near-constant uptake of isoflurane over time has important implications which enable us to apply the uptake pattern of isoflurane to clinical practice.