title: Nitrous oxide (N(2)O) reduces postoperative opioid-induced hyperalgesia after remifentanil-propofol anaesthesia in humans.
abstract: BACKGROUND
  The aim of this study was to test if intraoperative administration of N(2)O during propofol-remifentanil anaesthesia prevented the onset of postoperative opioid-induced hyperalgesia (OIH).
  
  
  METHODS
  Fifty adult ASA I-II patients undergoing elective open septorhinoplasty under general anaesthesia were studied. Anaesthesia was with propofol, adjusted to bispectral index (40-50), and remifentanil (0.30 μg kg(-1) min(-1)). Patients were assigned to one of the two groups: with N(2)O (70%) and without N(2)O (100% oxygen). Mechanical pain thresholds were measured before surgery and 2 and 12-18 h after surgery. Pain measurements were performed on the arm using hand-held von Frey filaments. A non-parametric analysis of variance was used in the von Frey data analysis. P<0.05 was considered statistically significant.
  
  
  RESULTS
  Baseline pain thresholds to mechanical stimuli were similar in both groups, with mean values of 69 [95% confidence interval (CI): 50.2, 95.1] g in the group without N(2)O and 71 (95% CI: 45.7, 112.1) g in the group with N(2)O. Postoperative pain scores and cumulative morphine consumption were similar between the groups. The analysis revealed a decrease in the threshold value in both groups. However, post hoc comparisons showed that at 12-18 h after surgery, the decrease in mechanical threshold was greater in the group without N(2)O than the group with N(2)O (post hoc analysis with Bonferroni's correction, P<0.05).
  
  
  CONCLUSIONS
  Intraoperative 70% N(2)O administration significantly reduced postoperative OIH in patients receiving propofol-remifentanil anaesthesia.
authors.affiliation: Departamento de Anestesiología, Pontificia Universidad Católica de Chile, Hospital Clínico U.C., Marcoleta 367, PO Box: 114-D, Santiago, Chile.
authors.forename: G
authors.initials: G
authors.lastname: Echevarría
authors.forename: F
authors.initials: F
authors.lastname: Elgueta
authors.forename: C
authors.initials: C
authors.lastname: Fierro
authors.forename: D
authors.initials: D
authors.lastname: Bugedo
authors.forename: G
authors.initials: G
authors.lastname: Faba
authors.forename: R
authors.initials: R
authors.lastname: Iñiguez-Cuadra
authors.forename: H R
authors.initials: HR
authors.lastname: Muñoz
authors.forename: L I
authors.initials: LI
authors.lastname: Cortínez
mesh_terms: D000293:Adolescent; D000328:Adult; D000701:Analgesics, Opioid / Q000009:adverse effects*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D005260:Female; D006801:Humans; D006930:Hyperalgesia / Q000517:prevention & control*; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009609:Nitrous Oxide / Q000494:pharmacology*; D010149:Postoperative Pain / Q000517:prevention & control*; D010880:Piperidines / Q000494:pharmacology*; D015742:Propofol / Q000494:pharmacology*; D011446:Prospective Studies; D000077208:Remifentanil
chemical_list: D000701:Analgesics, Opioid; D018686:Anesthetics, Intravenous; D010880:Piperidines; D008012:Lidocaine; D009609:Nitrous Oxide; D000077208:Remifentanil; D015742:Propofol