title: Propofol sparing effect of remifentanil using closed-loop anaesthesia.
abstract: BACKGROUND
  General anaesthesia is a balance between hypnosis and analgesia. We investigated whether an increase in remifentanil blood concentration would reduce the amount of propofol required to maintain a comparable level of anaesthesia in 60 patients undergoing ambulatory surgery.
  
  
  METHODS
  Patients were allocated randomly to receive remifentanil to a target blood concentration of 2 ng ml(-1) (low), 4 ng ml(-1) (medium), or 8 ng ml(-1) (high), administered by target-controlled infusion (TCI). After equilibration, propofol TCI was commenced in closed-loop control, with auditory evoked potentials (AEPex) as the input signal, aiming for an AEPex of 35. This was to ensure a comparable and unbiased level of anaesthesia in all patients.
  
  
  RESULTS
  We found a dose-dependent decrease in propofol requirements with increasing remifentanil concentrations. The mean (95% CI) propofol target blood concentration during adequate anaesthesia was 4.96 (3.85-6.01) micro g ml(-1) in the low, 3.46 (2.96-3.96) micro g ml(-1) in the medium, and 3.01 (2.20-3.38) micro g ml(-1) in the high group. There was no significant difference when recovery end points were achieved between the groups. Cardiovascular changes were moderate, but most pronounced in the high concentration group, with a decrease in heart rate of 21% compared with baseline. The mean calculated effect site propofol concentration at loss of consciousness was 2.08 (1.85-2.32) micro g ml(-1), and at recovery of consciousness was 1.85 (1.68-2.00) micro g ml(-1).
  
  
  CONCLUSIONS
  This study confirms a synergistic interaction between remifentanil and propofol during surgery, whereas the contribution of remifentanil in the absence of stimulation seems limited. In addition, our results suggest that the propofol effect site concentration provides a guide to the value at which the patient recovers consciousness.
authors.affiliation: University of Glasgow, Department of Anaesthesia, Glasgow Royal Infirmary, UK.
authors.forename: S E
authors.initials: SE
authors.lastname: Milne
authors.forename: G N C
authors.initials: GN
authors.lastname: Kenny
authors.forename: S
authors.initials: S
authors.lastname: Schraag
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000556:Ambulatory Surgical Procedures; D000771:Anesthesia, Intravenous / Q000379:methods; D019162:Anesthetics, Combined / Q000008:administration & dosage* / Q000097:blood; D018686:Anesthetics, Intravenous / Q000008:administration & dosage* / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005072:Evoked Potentials, Auditory / Q000187:drug effects; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006552:Hernia, Inguinal / Q000601:surgery; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D010880:Piperidines / Q000008:administration & dosage* / Q000097:blood; D015742:Propofol / Q000008:administration & dosage* / Q000097:blood; D011446:Prospective Studies; D000077208:Remifentanil; D014648:Varicose Veins / Q000601:surgery
chemical_list: D019162:Anesthetics, Combined; D018686:Anesthetics, Intravenous; D010880:Piperidines; D000077208:Remifentanil; D015742:Propofol