INFLUENCE OF VAPORIZER SETTING ON MASK INDUCTION OF DOGS WITH ISOFLURANE USING AN IN-CIRCUIT VAPORIZER

The speed of mask induction using an in-circuit vaporizer may be influ enced by vaporizer setting. To investigate this in clinical patients, 18 dogs were randomly assigned to one of three groups. Each dog was pr emedicated and then mask induced with isoflurane using a Stephen's in- circuit vaporizer set at 1/2, 3/4, Or full ON. We determined inspired isoflurane and oxygen concentrations at the level of the mask, respira tory rate, resistance to mask induction, and time to intubation. No si gnificant differences were found between groups in resistance to induc tion or in time to intubation. At settings of 3/4 and full ON, inspire d isoflurane concentrations at time of intubation ranged from 3.3% to 8.25%, and were significantly higher than those resulting from the 1/2 Setting (range 2.1% to 4.6%). We conclude that it may be preferable t o avoid settings greater than 1/2 when using the Stephen's vaporizer f or mask induction because of the potential adverse effects of high ins pired inhalant anesthetic concentrations. In addition, use of higher v aporizer settings may not significantly speed induction. (C)Copyright 1996 by The American College of Veterinary Surgeons