title: The relationship between calculated effect-site sevoflurane levels and awakening from anaesthesia.
abstract: We have previously described a system that displays real-time estimates of effect-site sevoflurane concentrations. Estimates of effect-site levels should be similar to minimum alveolar concentration (MAC) values, which are determined after allowing time for equilibrium. This study aimed to determine estimated effect-site sevoflurane concentrations at awakening from routine anaesthesia and to compare this with published estimates of MAC-awake. If these values were similar; this would validate our approach to the calculation of effect-site concentration. Sixty-five patients undergoing a variety of surgical procedures were observed. Prior to disconnection from the breathing circuit, forward estimates of effect-site sevoflurane were recorded. Patients were observed in the post-anaesthesia care unit and the time at which they responded to command was recorded.Age-adjusted effect-site sevoflurane at the time of awakening was determined. Correlation with patient, surgical and anaesthetic factors including age, gender; ASA status and intraoperative opioid usage were explored. Mean age-adjusted calculated effect-site concentration at awakening was 0.59 (SD 0.27) vol%. This value is within the range of values determined for MAC-awake of sevoflurane. There was no correlation with any of the demographic or anaesthetic factors, but patients undergoing major surgery woke at a significantly lower mean sevoflurane level. These results support the use of effect-site sevoflurane concentration to guide administration of anaesthesia.
authors.affiliation: Department of Anaesthesia, Christchurch Hospital, Christchurch School of Medicine and Health Sciences, Christchurch, New Zealand.
authors.forename: R R
authors.initials: RR
authors.lastname: Kennedy
authors.forename: M M
authors.initials: MM
authors.lastname: Sakowska
mesh_terms: D000367:Age Factors; D000762:Anesthesia Recovery Period; D000769:Anesthesia, Inhalation / Q000379:methods; D018685:Anesthetics, Inhalation / Q000008:administration & dosage* / Q000494:pharmacology; D001143:Arousal / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005260:Female; D005283:Fentanyl / Q000494:pharmacology; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage* / Q000494:pharmacology; D008874:Midazolam / Q000494:pharmacology; D008875:Middle Aged; D000077149:Sevoflurane; D018709:Statistics, Nonparametric; D013514:Surgical Procedures, Operative
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D008874:Midazolam; D005283:Fentanyl