Temperature dependence of thermodynamic activity in volatile anesthetics: Correlation between anesthetic potency and activity

Temperature dependence of the saturated concentration and the activity coefficient of anesthetics (1-propanol, diethyl ether, chloroform, and halothane) in water were evaluated using vapor pressure and H NMR measurement. We found that these physical values (quantities) correlate with anesthetic potencies estimated according to the thermodynamic equilibrium model. The anesthetic potency for hydrophilic anesthetic (diethyl ether) decreased with decreasing temperature because of the temperature specificity of this saturated concentration. In contrast, potencies of hydrophobic anesthetics (chloroform and halothane) increased with decreasing temperature because of the temperature specificity of those activity coefficients. By assuming that anesthetics interact with hydrated water of cell membranes, the temperature dependence of anesthetic potencies in vivo is qualitatively explicable.

Temperature dependence of the activity coefficient γwγw of anesthetics in water in the vicinity of clinical concentration. The relative temperature on the horizontal axis indicates the ratio of the solution temperature and the boiling point of anesthetics. The asterisk indicates γwγw at the relative temperature corresponding to a body temperature of 37 °C. Circles: 1-propanol (278 mM); triangles: diethyl ether (28 mM); diamonds: chloroform (2.8 mM); squares: halothane (2.8 mM). Each concentration without 1-propanol is much smaller than each saturated concentration.Figure optionsDownload as PowerPoint slide