[Optimization of the dosage of volatile anesthetics based on pharmacokinetic and dynamic models]

The quantitative aspects of dosing of volatile anaesthetics to establish and maintain constant alveolar concentrations are in general only discussed in the framework of closed circuit anaesthesia. A systematic approach to determine the appropriate dosage for arbitrary flows on the basis of pharmacokinetic models and to adjust the parameters of the model to the individual patient is described. A pharmacodynamic model of the volatile agents isoflurane, enflurane and halothane based on the electroencephalogram is worked out and added to the kinetic model. The median of the EEG power spectrum serves as a monoparametric correlate of depth of anaesthesia. A system theoretic consideration of the coupled subsystems, anaesthesia machine and patient, enables the establishment of interactive dosing strategies, thus offering the possibility of adapting dosage to the different painful phases of surgery. The implications of these dosing strategies for feed back control of anaesthesia by electroencephalographic means are discussed.