title: Comparison of the anesthetic requirement for tolerance of laryngeal mask airway and endotracheal tube.
abstract: We tested the hypothesis that the laryngeal mask airway (LMA) is tolerated at lighter levels of anesthesia than an endotracheal tube (ET). We studied 20 unpremedicated, nonsmoking ASA physical status I or II patients aged 18-40 yr whose surgery lasted > 1 h. Subjects were randomly assigned to receive either an ET or LMA. Anesthesia was induced with intravenous propofol and the LMA or ET was inserted. The ET-group patients received 1.5 mg/kg of succinylcholine, preceded by vecuronium (0.015 mg/kg IV). Maintenance of anesthesia was with only isoflurane and approximately 66% N2O in O2 by spontaneous ventilation. All gas concentrations were measured by a Raman spectrometer sampling from the breathing circuit end of the LMA or ET. Toward the end of the procedure, the end-tidal N2O and isoflurane concentrations were allowed to decrease to < 3 vol% and 0.8 +/- 0.05 vol%, respectively. The end-tidal isoflurane concentration was then decreased in 0.1% +/- 0.05% decrements, each stable value being held for 5 min. The patient was observed for signs of reaction to the presence of the LMA or ET. The mean (range) end-tidal isoflurane concentrations for reaction to ET and LMA were 0.55% (0.4-0.7) and 0.35% (0.2-0.51), respectively (P < 0.001). These data confirm the original hypothesis of the study.
authors.affiliation: Department of Anesthesiology, Oregon Health Sciences University, Portland 97201-3098.
authors.forename: C J
authors.initials: CJ
authors.lastname: Wilkins
authors.forename: P G
authors.initials: PG
authors.lastname: Cramp
authors.forename: J
authors.initials: J
authors.lastname: Staples
authors.forename: W C
authors.initials: WC
authors.lastname: Stevens
mesh_terms: D000293:Adolescent; D000328:Adult; D000758:Anesthesia; D005260:Female; D006801:Humans; D007442:Intubation, Intratracheal; D007530:Isoflurane / Q000494:pharmacology; D017214:Laryngeal Masks; D008297:Male; D015742:Propofol / Q000494:pharmacology
chemical_list: D007530:Isoflurane; D015742:Propofol