Assessment of the effect of prior noxious stimulation on minimum alveolar concentration determinations in the dog and rabbit




Gianotti, Giacomo

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University of Guelph


This thesis determines and compares the sparing effect of ketamine on the minimum alveolar concentration (MAC) of isoflurane in rabbits and dogs using two methods in a crossover random design. One method determined the MAC of isoflurane and ketamine combined after previous determination of the MAC of isoflurane during the same day. The second method determined the MAC for the combination without prior determination of the MAC of isoflurane. The concentration of ketamine and norketamine in plasma were also determined in dogs. For the first method, the MAC of isoflurane in rabbits was 2.15 ± 0.09% (mean ± SD) and decreased to 1.63 ± 0.07% during ketamine administration (1 mg/kg bolus and a constant rate infusion [CRI] of 40 µg/kg/min). In dogs, the same ketamine dose decreased the MAC of isoflurane from 1.18 ± 0.14% to 0.88 ± 0.14%. Re-determination of MAC of isoflurane performed after stopping the CRI yielded a MAC value of 2.04 ± 0.11% in rabbits and of 1.09 ± 0.16% in dogs. MAC values of the isoflurane and ketamine combination determined for the second method were 1.53 ± 0.22% in rabbits and 0.79 ± 0.11% in dogs. MAC values of isoflurane after stopping the CRI of ketamine were 1.94 ± 0.25% in rabbits and 1.10 ± 0.17% in dogs. The MAC value obtained in dogs for the isoflurane and ketamine combination with the first method was significantly higher with respect to the MAC value obtained with the second method (0.88 ± 0.14 versus 0.79 ± 0.11%); whereas in rabbits, MAC values were similar. During ketamine administration in dogs, plasma concentrations of ketamine at MAC values were similar for the first and second method (824 ± 195.7 ng/mL and 729 ± 133.4 ng/mL, respectively). After stopping the CRI, plasma concentrations during isoflurane MAC were also similar for the two methods (407 ± 176.2 ng/mL and 347 ± 81.2 ng/mL, respectively). MAC values for the isoflurane and ketamine combination obtained with both methods were statistically different in dogs but not in rabbits, however these findings may be the result of the design of the study and tolerable experimental error derived from MAC studies rather than true species differences.



MAC, Anesthesia, ketamine, isoflurane, dog, rabbit