Continuous intravenous anaesthesia with sufentanil and midazolam in medetomidine premedicated New Zealand White rabbits

Righting and pedal withdrawal reflexes were lost within 3 and 5 min, respectively. Doses of sufentanil and midazolam were 0.48 μg/kg BW and 0.09 mg/kg BW for induction, and 0.72 μg/kg BW/h and 0.13 mg/kg BW/h for maintenance. Apnoea occurred in two rabbits. Induction of anaesthesia caused a significant increase in heart rate, cardiac output and arterial CO2 partial pressure and a decrease in mean arterial pressure, respiratory rate and pH. Mean time from stopping the infusion to endotracheal extubation was 5 min, and to return of the righting reflex 7 min. Anaesthesia was characterized by induction and recovery without excitation, with muscle relaxation, and absence of the pedal withdrawal reflex.TIVA with sufentanil-midazolam provided smooth induction and recovery of anaesthesia in rabbits but with marked hypotension and respiratory depression, requiring mechanical ventilation. Further evaluation is needed to establish if the protocol is useful for rabbits undergoing surgery.The rabbit is the third most commonly used species for experimental research in the European Union, and it is increasing in numbers [1]. It is also the third most common pet species anaesthetised in the United Kingdom [2]. Rabbits are high risk anaesthesia patients, with a mortality risk 14 times higher than in dogs [3]. Possible reasons for this are that rabbits are easily stressed prey animals, they are difficult to intubate endotracheally and react to mask induction with volatile anaesthetics by extended breath-holding [4-6]. Rabbits have a large abdominal cavity in relation to the thoracic cavity, with the results that the pressure from the intestinal mass may interfere with respiration in dorsal recumbency during anaesthesia. Furthermore, obesity is increasing in pet rabbits, which also adds to the problem. Respiratory infection with Pasteurella pneumotropica, which is common in pet rabbits, may cause a reduction of the hydrogen ion driven respiratory drive, adding to the anaesthetic risk