Minimum Alveolar Concentration of 1–653 and Isoflurane in Pigs: Definition of a Supramaximal Stimulus

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We determined the anesthetic potencies of a new fluorinated anesthetic, 1–653, and isoflurane in pigs as a preliminary to a study of the relative cardiovascular and electroencephalographic effects of these agents. Clamps were sequentially applied to the dew claw and/or tail of each animal to determine the minimum alveolar concentration (MAC) that suppressed movement in response to each of these stimuli. MAC obtained by clamping the tail (8.28 ± 1.34% [mean ± standard deviation] for 1–653 and 1.653 ± 0.36% for isoflurane) was more variable and lower than MAC obtained by clamping the dew claw (10.00 ± 0.94% for 1–653 and 2.04 ± 0.19% for isoflurane). We conclude that the type of stimulus applied affects the MAC value obtained for 1–653 and isoflurane. Clamping the tail is not a supramaximal stimulus in pigs; a greater stimulus is provided by clamping the dew claw.

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