title: Intraoperative nitrous oxide as a preventive analgesic.
abstract: Preventive analgesia is defined as the persistence of the analgesic effects of a drug beyond the clinical activity of the drug. The N-methyl D-aspartate receptor plays a critical role in the sensitisation of pain pathways induced by injury. Nitrous oxide inhibits excitatory N-methyl D-aspartate sensitive glutamate receptors. The objective of our study was to test the efficacy of nitrous oxide as a preventive analgesic. We conducted a retrospective analysis of data from a subset of patients (n = 100) randomly selected from a previous major multicentre randomised controlled trial on nitrous oxide (ENIGMA trial). Data analysed included postoperative analgesic requirements, pain scores and duration of patient-controlled analgesia during the first 72 postoperative hours. There was no significant difference in postoperative oral morphine equivalent usage (nitrous group 248 mg, no nitrous group 289 mg, mean difference -43 mg, 95% confidence interval 141 to 54 mg). However, patients who received nitrous oxide had a shorter duration of patient-controlled analgesia use (nitrous group 35 hours, no nitrous group 51 hours, mean difference -16 hours, 95% confidence interval -29 to -2 hours, P = 0.022). There was no difference in pain scores between the groups. The shorter patient-controlled analgesia duration in the nitrous oxide group suggests that intraoperative nitrous oxide may have a preventive analgesic effect.
authors.affiliation: Department of Anaesthesia and Perioperative Medicine, The Alfred Hospital, Melbourne, Victoria, Australia.
authors.forename: D K
authors.initials: DK
authors.lastname: Stiglitz
authors.forename: L N
authors.initials: LN
authors.lastname: Amaratunge
authors.forename: A H
authors.initials: AH
authors.lastname: Konstantatos
authors.forename: D E
authors.initials: DE
authors.lastname: Lindholm
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016058:Analgesia, Patient-Controlled / Q000379:methods; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000627:therapeutic use; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007430:Intraoperative Care / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009020:Morphine / Q000008:administration & dosage / Q000627:therapeutic use; D009609:Nitrous Oxide / Q000494:pharmacology*; D010147:Pain Measurement; D010149:Postoperative Pain / Q000517:prevention & control*; D016032:Randomized Controlled Trials as Topic; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D009020:Morphine; D009609:Nitrous Oxide