Comparative Trial of Xylazine and Medetomidine as Preanaesthetics Prior to Na Pentobarbital Anaesthesia in Dogs

The effects of medetomidine [20 and 40 micrograms/kg of body weight (BWT) i.m.] followed by sodium pentobarbital were assessed and compared with the effects of xylazine (1 mg/kg of BWT i.m.) in three groups each of 6 dogs. The effects of atipamezole as a specific antidote after anaesthesia were also studied. Medetomidine produced a reliable sedation which was clinically comparable with the xylazine premedication. 40 micrograms/kg medetomidine induced lower induction (non-significantly), total (p less than 0.05), anaesthetic (non-significantly) and anaesthetic per hour (non-significantly) doses of Na pentobarbital compared to the 20 micrograms/kg medetomidine and the xylazine protocols. No significant differences in the total number of re-injections were found between the sedative protocols although a gradual increase in number of re-injections per hour was observed. Significant decreases in heart and respiration rates were noticed during anaesthesia in all groups (p less than 0.01). The heart and respiration rates during anaesthesia in the 40 micrograms/kg medetomidine group were always significantly lower compared to the xylazine group. Body temperature decreased gradually in time during anaesthesia in all groups (p less than 0.05 after 1 hour, p less than 0.01 after 2 and 3 hours) without significant differences between the groups. The extubation time in the medetomidine protocols without antagonisation was significantly greater (p less than 0.01) than the extubation time after antagonisation with atipamezole.