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

Abstract

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 µg/kg IM) or Group 2 (n = 12; dexmedetomidine, 5 µg/kgand 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 E´ISO% 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 E´ISO% between the
highest E´ISO% at which movement was detected and the lowest E´ISO% 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).Theisoflurane 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.