Fourteen beagles were used to determine the effects of fentanyl and midazolam as a premedicant for mask induction of anaesthesia with sevoflurane. The drugs were administered to each dog in a randomised cross-over design with a seven-day washout period between experiments. After a 15-minute equilibration period, a treatment consisting of fentanyl (10 μg/kg bodyweight) and midazolam (0-2 mg/kg) was given either intravenously or intramuscularly. Anaesthesia was then induced by the use of a facemask with sevoflurane in 100 per cent oxygen at a flow rate of 4 1/minute. Vaporiser settings were increased by 0.8 per cent at 15-second intervals until the value corresponding to 4.8 per cent sevoflurane was achieved. The time to the onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-damp stimulation, and endotracheal intubation and cardiopulmonary variables were measured. Both the treatments with tentanyl and midazolam resulted in a shorter and smoother induction of anaesthesia than treatment with saline, and the cardiopulmonary changes were smaller and milder.
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