Nitrous oxide (N2O) reduces postoperative opioid-induced hyperalgesia after remifentanilpropofol anaesthesia in humans

Abstract

Background. The aim of this study was to test if intraoperative administration of N2O during propofolremifentanil anaesthesia prevented the onset of postoperative opioid-induced hyperalgesia (OIH). Methods. Fifty adult ASA III 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 2O (70) and without N2O (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 2O and 71 (95% CI: 45.7, 112.1) g in the group with N2O. 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 2O than the group with N2O (post hoc analysis with Bonferronis correction, P<0.05). Conclusions. Intraoperative 70 N2O administration significantly reduced postoperative OIH in patients receiving propofolremifentanil anaesthesia. © The Author [2011]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved.