Sufentanil and medetomidine anaesthesia in the rat and its reversal with atipamezole and butorphanol

Injectable anaesthetics are widely used to anaesthetize rats, but recovery times are often prolonged. Reversible anaesthetic regimens have the advanta ge that animals may be recovered quickly, thus reducing the incidence of po stoperative complications such as hypothermia, and also providing a means o f treating inadvertent anaesthetic overdose. This study assessed and compar ed the characteristics of anaesthesia induced with combinations of sufentan il and medetomidine administered as a single subcutaneous or intraperitonea l dose, and reversal with butorphanol and atipamezole. Combinations of sufe ntanil/medetomidine at 40 mu g/150 mu g and 50 mu g/150 mu g/kg administere d subcutaneously, and 80 mu g/300 mu g/kg by intraperitoneal injection were found to produce surgical anaesthesia for 101 +/- 49, 124 +/- 45 and 76 +/ - 23 min (means +/- SD) respectively. All three combinations produced marke d respiratory depression 30 min after injection (<50% of resting respirator y rate). Oxygen saturation measured by pulse oximetry, was <50% in all grou ps 30 min following drug administration. Subcutaneous administration is rec ommended since it resulted in a more reliable and more rapid induction of a naesthesia than intraperitoneal administration. The administration of butor phanol and atipamezole (0.2/0.5 mg/kg s.c.) resulted in a rapid (<7 min) re versal of anaesthesia and an associated respiratory depression. The inducti on of anaesthesia with sufentanil/medetomidine and its reversal with a comb ination of atipamezole and butorphanol is an effective technique for anaest hetizing rats. However, due to the marked respiratory depression and the re sulting hypoxia, we recommend that this regimen should only be used in anim als which are free from respiratory disease and that oxygen should be provi ded during anaesthesia.