title: Hypothermia decreases ethanol MAC in rats.
abstract: Despite the known capacity of hypothermia to increase anesthetic potency (decrease the partial pressure required to produce anesthesia), many in vitro studies examine the effects of ethanol and other anesthetics in oocytes or isolated neurons at room temperature. We tested whether, as predicted for potent inhaled anesthetics, a proportionate increase in solubility with hypothermia matched a decrease in ethanol minimum alveolar concentration (MAC), and thereby made the use of a single anesthetic concentration appropriate regardless of temperature. We determined ethanol MAC in normothermic (37.3 degrees C) and hypothermic (28.5 degrees C) rats, and, at the two temperatures, also determined ethanol solubilities in olive oil and saline. Ethanol MAC decreased, while olive oil/gas and saline/gas partition coefficients increased. However, the increase in the saline/gas partition coefficient did not match the decrease in MAC, and thus the aqueous-phase partial pressure producing absence of movement in 50% of rats (EC50) values for ethanol decreased by 17%. Although this decrease is not large, it may be important for comparative estimates of the in vitro effects of ethanol at different temperatures.
authors.affiliation: Department of Anesthesia and Perioperative Care, S-455, University of California, San Francisco, CA 94143-0464, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Won
authors.forename: Irene
authors.initials: I
authors.lastname: Oh
authors.forename: Robert
authors.initials: R
authors.lastname: Brosnan
authors.forename: Edmond I
authors.initials: EI
authors.lastname: Eger
authors.forename: James M
authors.initials: JM
authors.lastname: Sonner
mesh_terms: D000818:Animals; D002492:Central Nervous System Depressants / Q000493:pharmacokinetics*; D000431:Ethanol / Q000493:pharmacokinetics*; D007035:Hypothermia / Q000378:metabolism*; D008297:Male; D000069463:Olive Oil; D010313:Partial Pressure; D010938:Plant Oils; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride; D012995:Solubility; D013696:Temperature
chemical_list: D002492:Central Nervous System Depressants; D000069463:Olive Oil; D010938:Plant Oils; D000431:Ethanol; D012965:Sodium Chloride