Maturation Decreases Ethanol Minimum Alveolar Anesthetic Concentration (MAC) More than Desflurane MAC in Rats

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Abstract
The potency of conventional inhaled anesthetics increases with increasing age:the 50% effective dose (minimum alveolar anesthetic concentration [MAC]) for anesthesia in the neonatal animal or human exceeds MAC in the young adult by approximately 30% to 60%. We tested whether this relationship also applies to the alkanols, using ethanol as a representative alkanol. We found that the MAC of ethanol in neonatal rats was 1.86 times (86% greater than) the MAC for adult rats, based on ethanol partial pressures determined from brain specimens. In contrast, the MAC of desflurane in neonatal rats was 1.19 times (19% greater than) the MAC for adult rats, less than one-fourth the 86% found for ethanol. These differences must be explained by any unitary theory of narcosis. Alternatively, the mechanistic basis for alkanol versus conventional inhaled anesthetics may differ in part or whole. (Anesth Analg 1997;84:852-8)