Effects of repeated anaesthesia with ketamine/medetomidine and of pre-anaesthetic administration of buprenorphine in rats

Two groups of rats were anaesthetized at weekly intervals for 6 weeks with either ketamine/medetomidine alone (60 mg/0.4 mg/kg i.p.) or ketamine/medet omidine (45 mg/0.3 mg/kg i.p.) one hour following buprenorphine (0.05 mg/kg s.c.). Animals that received buprenorphine had longer periods of surgical anaesthesia (P = 0.04) and a greater depression of both mean pedal withdraw al score (P < 0.01) and mean respiratory rate (P = 0.014). Mean total durat ion of anaesthesia was also greater in the buprenorphine group on day I. Sl eep times reduced with successive doses of anaesthetic in the buprenorphine group (P = 0.024). Two animals in the buprenorphine group died. Repeated a naesthesia with ketamine/medetomidine alone was not associated with anaesth etic mortality. These results indicate that although buprenorphine has a cl ear anaesthetic-sparing effect, its use with ketamine/medetomidine may be a ssociated with an increased risk of anaesthetic-related mortality.