TEMPERATURE-DEPENDENCE OF THE POTENCY OF VOLATILE GENERAL-ANESTHETICS- IMPLICATIONS FOR IN-VITRO EXPERIMENTS

Background: When performing experiments at room temperature with volat ile general anesthetics and in vitro mammalian preparations (such as i solated neurons), the question arises as to which concentrations of an esthetics are ''clinically relevant.'' Different choices can lead to d ifferent interpretations of the anesthetic sensitivities of putative t arget sites. Methods: Published data on the temperature dependence of minimum alveolar concentration were analyzed. Results: Although gas-ph ase potencies of volatile anesthetics increase markedly with decreasin g temperature, the corresponding aqueous-phase potencies are relativel y constant. Changes in minimum alveolar concentration with temperature can be accounted for, on physical grounds, in terms of the temperatur e dependencies of anesthetics binding to their central nervous system target sites. Conclusions: When performing room-temperature in vitro e xperiments on simple mammalian preparations with a volatile anesthetic , the aqueous-phase (but not the gas-phase) minimum alveolar concentra tion calculated at normal body temperature is, to a first approximatio n, the appropriate choice for a clinically relevant anesthetic concent ration. Recommended aqueous-phase minimum alveolar concentration value s (in mM) for desflurane, enflurane, halothane, isoflurane, and sevofl urane have been calculated.