Objective - To determine effects of epidural administration of morphine and buprenorphine on the minimum alveolar concentration of isoflurane in cats. Animals - 6 healthy adult domestic shorthair cats. Procedures - Cats were anesthetized with isoflurane in oxygen. Morphine (100 μg/kg diluted with saline [0.9% NaCl] solution to a volume of 0.3 mL/kg), buprenorphine (12.5 μg/kg diluted with saline solution to a volume of 0.3 mL/kg), or saline solution (0.3 mL/kg) was administered into the epidural space according to a Latin square design. The minimum alveolar concentration (MAC) of isoflurane was measured in triplicate by use of the tail clamp technique. At least 1 week was allowed between successive experiments. Results - The MAC of isoflurane was 2.00 ± 0.18%, 2.13 ± 0.11%, and 2.03 ± 0.09% in the morphine, buprenorphine, and saline solution groups, respectively. No significant difference in MAC was detected among treatment groups. Conclusions and Clinical Relevance - A significant effect of epidural administration of morphine or buprenorphine on the MAC of isoflurane in cats could not be detected. Further studies are needed to establish whether epidural opioid administration has other benefits when administered as a component of general anesthesia in cats.
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