Effect of Hypothermia in Dogs on Anesthetizing and Apneic Doses of Inhalation Agents

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Abstract
Moderate hypo-thermia in dogs rectilinearly decreased anesthetic requirements for cyclopropane, diethyl ether, fluroxene, halothane and methoxy-flurane. The greatest reductions (52 and 53%) occurred with the most lipid-soluble agents, halothane and methoxyflurane, and the smallest (20%) with the least soluble, cyclopropane. Reductions with ether and fluoroxene were 42 and 37%. More profound hypothermia to 22-24C. led to further reductions, suggesting that between 18-21[degree]C. cold itself would be sufficient for anesthesia. Moderate hypothermia also decreased the concentration of anesthetic required to produce apnea, so that the anesthetic index (apneic concentration/anesthetic concentration) did not change significantly with decrease in temperature except for diethyl ether, whose index rose significantly over 10[degree]C. At normothermia there was a significant difference between the index for cyclopropane (2.4) and that for methoxyflurane (3.4), but no significant difference existed among the other agents.