INDUCTION OF ANESTHESIA AND TRACHEAL INTUBATION WITH SEVOFLURANE IN ADULTS

Background: The speed, quality, and cost of mask induction of anesthes ia and laryngeal mask airway insertion or tracheal intubation mere stu died in young non-premedicated volunteers given high inspired concentr ations of sevoflurane (6 to 7%). Methods: Twenty healthy persons who w ere 19 to 32 years old participated three times, received 6 1/min fres h gas flow, and were randomized to receive 6 to 7% sevoflurane in 66% nitrous oxide/28% oxygen by face mask until tracheal intubation (treat ment 1) or until laryngeal mask airway insertion (treatment 3), or 6 t o 7% sevoflurane without nitrous oxide to tracheal intubation (treatme nt 2). Participants exhaled to residual volume and took three vital ca pacity breaths of the gas mixture; thereafter ventilation was manually assisted. The time of exposure to the inhaled gas was varied for cons ecutive participants. It was either increased or decreased by 30-sec i ncrements based on the failure or success of the preceding volunteer's response to laryngoscopy and intubation after a preselected exposure time. Failure was defined as poor jaw relaxation, coughing or bucking, or inadequate vocal cord relaxation. Results: Loss of the lid-lash re flex in unpremedicated young volunteers was achieved in 1 min and did not differ among groups. Average time (and 95% confidence interval) fo r acceptable conditions for LMA insertion was achieved in 1.7 (0.7 to 2.7) min, and all participants had an immediate return of spontaneous ventilation. The time for acceptable tracheal intubating conditions af ter manual hyperventilation by mask was 4.7 (3.7 to 5.7) min and 6.4 ( 5.1 to 7.7) min in treatments 1 and 2, respectively. There were no cas es of increased secretions or laryngospasm. The incidence of breath ho lding and expiratory strider (''crowing'') was 7.5% and 25%, respectiv ely, during treatment 1 and 15% and 40%, respectively, during treatmen t 2. Conclusions: The induction of anesthesia to loss of lid reflex in young non-premedicated adults approaches the speed of intravenous ind uction techniques. No untoward airway responses were noted during mask induction of anesthesia with a three-breath technique. In response to intubation, no adverse airway responses, including jaw tightness, lar yngospasm, and excessive coughing or bucking, occurred in participants whose duration of mask administration of sevoflurane met the appropri ate times (as determined in this study).