title: Effects of two target-controlled concentrations (1 and 3 ng/ml) of remifentanil on MAC(BAR) of sevoflurane.
abstract: BACKGROUND
  The aim of this prospective, randomized, double-blind study was to determine the effects of two different target-controlled concentrations of remifentanil (1 and 3 ng/ml) on the sevoflurane requirement for blunting sympathetic responses after surgical incision (MACBAR).
  
  
  METHODS
  Seventy-four patients aged 20-50 yr, with American Society of Anesthesiologists physical status I, were anesthetized with propofol, cisatracurium, and sevoflurane with a mixture of 60% nitrous oxide in oxygen. Then, patients were randomly allocated to receive no remifentanil infusion (n = 27) or a target-controlled plasma concentration of 1 ng/ml (n = 27) or 3 ng/ml remifentanil (n = 20). Sympathetic responses to surgical incision (presence or absence of an increase in either heart rate or mean arterial blood pressure of 15% or more above the mean of the values measured during the 2 min before skin incision) were determined after a 20-min period of stable end-tidal sevoflurane and target-controlled remifentanil concentrations. Predetermined end-tidal sevoflurane concentrations and the MACBAR for each group were determined using an up-and-down sequential-allocation technique.
  
  
  RESULTS
  The MACBAR of sevoflurane was higher in the group receiving no remifentanil (2.8% [95% confidence interval: 2.5-3.0%]) as compared with patients of the groups receiving 1 ng/ml (1.1% [0.9-1.3%]; P = 0.012) and 3 ng/ml remifentanil (0.2% [0.1-0.3%]; P = 0.006). When considering a minimum anesthetic concentration (MAC) value in this age population and the contribution of 60% nitrous oxide (0.55 MAC), the combined MACBAR values, expressed as multiples of the MAC, were 1.95 MAC, 1.1 MAC, and 0.68 MAC, in the three groups, respectively.
  
  
  CONCLUSIONS
  A target-controlled concentration of 1 ng/ml remifentanil results in a 60% decrease in the MACBAR of sevoflurane combined with 60% nitrous oxide. Increasing the target concentration of remifentanil to 3 ng/ml produces a further 30% decrease in the MACBAR values of sevoflurane.
authors.affiliation: Department of Anesthesiology, Istituto di Ricovero e Cura a Carattere Scientifico, Ospedale San Raffaele, Via Olgettina 60, 20132 Milan, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Albertin
authors.forename: Andrea
authors.initials: A
authors.lastname: Casati
authors.forename: Piercarlo
authors.initials: P
authors.lastname: Bergonzi
authors.forename: Greta
authors.initials: G
authors.lastname: Fano
authors.forename: Giorgio
authors.initials: G
authors.lastname: Torri
mesh_terms: D000328:Adult; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D018685:Anesthetics, Inhalation; D001794:Blood Pressure / Q000187:drug effects; D016001:Confidence Intervals; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004347:Drug Interactions; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008738:Methyl Ethers; D008875:Middle Aged; D010880:Piperidines / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D000077208:Remifentanil; D000077149:Sevoflurane
chemical_list: D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D010880:Piperidines; D000077149:Sevoflurane; D000077208:Remifentanil