Effect of dexmedetomidine combined with pethidine on minimum alveolar concentration of isoflurane in dogs

The effect of dexmedetomidine alone and when combined with pethidine on a minimum alveolar concentration (MAC) of isoflurane was determined in 24 client- owned adult male dogs before castration. Dogs were assigned to Group 1(n=12; dexmedetomidine, 5 mu g/kg IM) or Group 2 (n=12; dexmedetomidine, 5 mu g/kg and pethidine, 5 mg/kg IM). Sedation and response to noxious stimulation (digit clamping) were evaluated at 15 minutes after drug injection. Then, anaesthesia was induced via a face mask with isoflurane in oxygen and maintained via an endotracheal tube with an end tidal concentration of isoflurane (E'ISO%) of 1%, at the oxygen flow rate of 2 L/min. To determine the isoflurane MAC for each dog, the EISO% was increased once the purposeful movement to the noxious stimulation has been detected or decreased if the movement was not detected. The isoflurane MAC was the mean EISO% between the highest EISO% at which movement was detected and the lowest EISO% at which movement was not detected. Cardiorespiratory variables were measured before drug injection until the isoflurane MAC had been determined. The sedation score of Group 2 was found significantly greater than that of Group 1 (p=0.0001). The isoflurane MAC for Group 2 was 0.98 +/- 0.24% (mean +/- SD) which was significantly lower than 1.31 +/- 0.33% for Group 1 (p = 0.011). Cardiorespiratory variables did not differ significantly between the groups. In conclusion, dexmedetomidine administered with pethidine provided sedative and sparing effects on the isoflurane MAC which were significantly greater than those of dexmedetomidine alone.