This study was performed to evaluate anesthetic and cardiovascular effects of xylazine/fentanyl/azaperone and medetomidine/midazolam as preanesthetics and their combinations with antagonists in halothane-anesthetized dogs.
Eight clinically healthy dogs(4.54±2.16㎏) were used at the interval of more than 14 days between experiments in turn for propionyl promazine(PP 0.3㎎/㎏, IM), xylazine/fentanyl/azaperone(XFA 2㎎/㎏, 0.0137㎎/㎏, 0.11㎎/㎏, IM), medetomidine/midazolam(MM 0.02㎎/㎏, 0.3㎎/㎏, IM), combination of XFA and their antagonists (yohimbine 0.05㎎/㎏, naloxon 0.0005㎎/㎏, IV) and combination of MM and their antagonist(atipamezole 0.08㎎/㎏ IM).
The sedation induction times in XFA(2.56±1.01 min) and MM(5.44±2.07 min) groups were significantly better than that of PP group(10.75±2.38 min)(p $lt; 0.05). The thiopental sodium dose required for tracheal intubation in XFA(2.38±3.38㎎/㎏) and MM(3.91±3.47㎎/㎏) groups were significantly less than that of PP group(12.57±2.13㎎/㎏)(p $lt; 0.05).
All time indices expressing the recovery(pedal reflex recurrence time, extubation time, arousal time, standing time and walking time) were significantly shorter in the combination groups of XFA or MM with their antagonists than in PP, XFA and MM groups(p $lt; 0.05).
The suppressions of cardiovascular function of XFA and MM were more than that of PP. Heart rate and cardiac output were recovered by the antagonists of XFA and MM, but mean arterial pressure were not recovered by the antagonists.
PP induced apnea in 4 out of 8 dogs, but XFA in none and MM in one.
The present study suggested that for rapid sedation, prevention of apnea after intubation and rapid recovery after halothane cessation, combinations of xylazine/fentanyl/azaperone or medetomidine/midazolam with their antagonists are recommendable as preanesthetic method in gas anesthetised dogs with normal cardiovascular function.
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