This study evaluated the quality of anaesthesia and the cardiorespiratory effects induced by the combination of
medetomidine with either
ketamine,
propofol or
fentanyl.
Medetomidine premedication (1000 or 1500 micrograms/m2 body surface area) was followed by intravenous induction of anaesthesia with
ketamine (3.0 mg/kg),
propofol (2.0 mg/kg) or
fentanyl (2.0 micrograms/kg) in bitches undergoing elective ovariohysterectomy. Anaesthesia was prolonged by incremental doses of the induction agents as necessary. The mean (sem) overall doses (including induction) were 0.09 (0.01) mg/kg/min for
ketamine, 0.06 (0.01) mg/kg/min for
propofol and 0.07 (0.005) microgram/kg/min for
fentanyl during procedures which lasted 88 (6) minutes, 72 (3) minutes and 79 (7) minutes, respectively. At the end of the procedure,
medetomidine was antagonised with
atipamezole. The quality of anaesthesia, heart rate and arterial blood pressure were recorded continuously and arterial blood
gases were measured at intervals. At the end of the procedure, the animals received 10 micrograms/kg
buprenorphine intramuscularly for postoperative
analgesia. From the adequacy of anaesthesia, the lack of significant adverse side effects and the reliable and rapid recovery it is concluded that, in healthy dogs anaesthetised with
ketamine or
propofol,
medetomidine is a satisfactory
sedative-
analgesic premedicant. The differences in haemodynamics and the quality of recovery suggest that the combination of
medetomidine with
propofol provided the better quality anaesthesia. The combination of
medetomidine with
fentanyl was unsuitable for obtaining surgical anaesthesia in spontaneously breathing animals owing to the severity of the
respiratory depression at dosages needed for general anaesthesia.