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 advantage that animals may be recovered quickly, thus reducing the incidence of postoperative complications such as hypothermia, and also providing a means of treating inadvertent anaesthetic overdose. This study assessed and compared the characteristics of anaesthesia induced with combinations of sufentanil and medetomidine administered as a single subcutaneous or intraperitoneal dose, and reversal with butorphanol and atipamezole. Combinations of sufentanil/medetomidine at 40 mu g/150 mu g and 50 mu g/150 mu g/kg administered 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 marked respiratory depression 30 min after injection (<50% of resting respiratory rate). Oxygen saturation measured by pulse oximetry, was <50% in all groups 30 min following drug administration. Subcutaneous administration is recommended since it resulted in a more reliable and more rapid induction of anaesthesia than intraperitoneal administration. The administration of butorphanol and atipamezole (0.2/0.5 mg/kg s.c.) resulted in a rapid (<7 min) reversal of anaesthesia and an associated respiratory depression. The induction of anaesthesia with sufentanil/medetomidine and its reversal with a combination of atipamezole and butorphanol is an effective technique for anaesthetizing rats. However, due to the marked respiratory depression and the resulting hypoxia, we recommend that this regimen should only be used in animals which are free from respiratory disease and that oxygen should be provided during anaesthesia.