EFFICIENT INSPIRED CONCENTRATION OF SEVOFLURANE FOR VITAL CAPACITY RAPID INHALATION INDUCTION (VCRII) TECHNIQUE

Study Objectives: To evaluate the efficient inspired concentration of sevoflurane for a vital capacity rapid inhalation induction (VCRII) technique with respect to induction time, characteristics, and acceptability. Design: Prospective study. Setting: Medical college hospital. Patients: 68 unpremedicated healthy adult volunteers were assigned to one of four groups in order of sequential entry of informed consent. Interventions: 3%, 4.5%, 6%, or 7.5% concentrations of sevoflurane were administered for 5 minutes (3% and 4.5%) or 3 minutes (6% and 7.5%) using a single breath technique. Measurements and Main Results: The mean induction time required with 3%, 4.5%, 6%, or 7.5% sevoflurane was 120 +/- 26 sec, 79 +/- 18 sec, 52 +/- 15 sec, or 47 +/- 17 seconds, respectively. Each induction time was significantly different from the others (p < 0.05) except for that between 6% and 7.5%. There appeared to be a direct inverse relationship between the mean induction time and the logarithm of inspired concentration of sevoflurane, but this relationship did not extend beyond concentrations above 6%. Blood pressure decreased by approximately 18% from baseline at the end of inhalation of the drug, and heart rate remained constant in all groups. Except of one subject in the 7.5% group, no coughing war observed and laryngospasm, breath-holding, and secretions were not seen in any subjects. Slight limb movement was observed in a few subjects in each group. All subjects except one in the 3% group would accept undergoing a similar procedure again. Conclusion: Sevoflurane 6% can be recommended for VCRII, but increasing the concentration higher than this does not markedly shorten the induction time and thus seems to add little benefit.