Effect of morphine and flunixin meglumine on isoflurane minimum alveolar concentration in goats

To determine the effect of morphine and flunixin meglumine on isoflurane (ISO) minimum alveolar concentration (MAC) in goats.

Prospective, randomized experimental study.

Five adult, wether goats from 1 to 3 years in age, and weighing 24-65 kg.

Anesthesia was induced using ISO, which was delivered via a mask. Goats were intubated and ventilated to maintain an end-tidal carbon dioxide concentration between 25 and 30 mm Hg (3.3-4 kPa). End-tidal ISO concentration was measured using an infrared analyzer. The baseline ISO MAC that prevented purposeful movement in response to clamping a claw was determined. Following baseline MAC determination, each goat received one of the following four treatments intravenously (IV): morphine (2 mg kg(-1)), flunixin (1.5 mg kg(-1)), flunixin (1.5 mg kg(-1)) plus morphine (2 mg kg(-1)) or saline, and the MAC was re-determined. Goats were studied at weekly intervals, and each goat received each treatment in a randomized fashion.

The baseline ISO MAC for the control treatment was 1.43%. Morphine reduced the MAC by 29.7%. Flunixin did not significantly decrease the MAC nor did it potentiate the effect of morphine on MAC. The quality of recovery was good in all cases.

Morphine (2 mg kg(-1), IV) significantly reduced the ISO MAC in goats and did not adversely affect the quality of recovery.

The use of morphine, at the dose studied, in association with ISO anesthesia, will allow a clinically significant reduction in the concentration of ISO required to maintain general anesthesia in goats.