title: Optimal propofol-alfentanil combinations for supplementing nitrous oxide for outpatient surgery.
abstract: BACKGROUND
  The combination of propofol and alfentanil with nitrous oxide provides balanced anesthesia with rapid recovery and minimal emetic side effects. The object of this study was to compare recovery parameters at varying proportions of propofol and alfentanil, and to determine the dosing rate and plasma concentration of propofol necessary to supplement nitrous oxide in the presence of varying concentrations of alfentanil
  
  
  METHODS
  Forty-eight patients were anesthetized with nitrous oxide, targeted manual infusions of alfentanil (target plasma concentrations of 0, 50, 100, and 150 ng/ml), and propofol at rates that were varied up or down by 25% depending on the response (movement/no movement) of the preceding patient (at the same alfentanil target concentrations) to ulnar-nerve stimulation. The minimum concentrations of propofol and alfentanil required to prevent movement in 50% of patients (EC50) was determined by logistic regression. Speed of emergence and recovery of cognitive function, time to discharge, and incidence of side effects were compared for four different combinations of propofol and alfentanil with nitrous oxide.
  
  
  RESULTS
  The EC50 for propofol alone with nitrous oxide was 6.1 microg/ml. AlfentaniL at concentrations of 41+/-17 (SD), 113+/-54, and 130+/-61 ng/mL reduced the EC50 of propofol to 3.3, 2.3, and 2.2 microg/ml, respectively, and decreased emergence time (eye opening) to 8.1, 4.9, and 3.4 min, compared with 24.3 min for propofol alone. Side effects did not differ between groups.
  
  
  CONCLUSIONS
  The authors conclude that there is a synergistic effect between propofol and alfentanil, and that combining alfentanil with propofol is associated with faster early recovery.
authors.affiliation: Department of Anesthesiology, University of Washington School of Medicine, Seattle, USA. jpavlin@u.washington.edu
authors.forename: D J
authors.initials: DJ
authors.lastname: Pavlin
authors.forename: R H
authors.initials: RH
authors.lastname: Arends
authors.forename: H C
authors.initials: HC
authors.lastname: Gunn
authors.forename: G
authors.initials: G
authors.lastname: Van Norman
authors.forename: M E
authors.initials: ME
authors.lastname: Koerschgen
authors.forename: D D
authors.initials: DD
authors.lastname: Shen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015760:Alfentanil / Q000008:administration & dosage* / Q000097:blood; D000556:Ambulatory Surgical Procedures; D000777:Anesthetics / Q000008:administration & dosage*; D003071:Cognition / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000008:administration & dosage* / Q000097:blood; D015742:Propofol / Q000008:administration & dosage* / Q000097:blood
chemical_list: D000777:Anesthetics; D015760:Alfentanil; D009609:Nitrous Oxide; D015742:Propofol