Comparison of sevoflurane with isoflurane for rapid mask induction in midazolam and butorphanol-sedated dogs

Rapid mask induction can be a useful induction technique for veterinary pat ients, although it is often accompanied by exaggerated excitement responses in unpremedicated animals (Mutoh et al.: Jpn. J. Vet. Anesth. Surg. 26, 10 9-116; J. Vet. Med. Sci. 57, 1007-1013; J. Vet. Med. Sci. 57, 1121-1124; 19 95). The aim of this study was to compare sevoflurane with isoflurane for r apid mask induction in six dogs sedated by a combination of midazolam (0.1 mg/kg) and butorphanol (0.2 mg/kg). Induction with sevoflurane (5 %, 2.4 mi nimum alveolar concentration [MAC]) in O-2 resulted in shorter time to loss of the palpebral reflex, negative tail clamp response, and successful intu bation than with isoflurane (3 %, 2.4 MAC) in O-2. There were no changes in heart rate or mean arterial blood pressure during induction with sevoflura ne, whereas an increase in heart rate was observed in dugs induced with iso flurane. A decrease in respiratory rate compared with the pre-induction rat e was observed during induction, and associated mild respiratory acidosis, characterized by an increase in arterial PCO2, was measured at the end of t he induction period in both induction groups. None of the animals had episo des of induction-related complications. These results suggest that both sev oflurane and isoflurane produce a smooth onset of induction in midazolam an d butorphanol-sedated dogs. Sevoflurane is a more suitable for rapid mask i nduction than isoflurane since it provides faster induction associated with a lower blood/gas partition coefficient.