title: Risk factors for severe postoperative nausea and vomiting in a randomized trial of nitrous oxide-based vs nitrous oxide-free anaesthesia.
abstract: BACKGROUND
  Refractory postoperative nausea and vomiting (PONV) requiring repeated treatment with antiemetic drugs is a miserable experience for the patient that may substantially increase the cost of care. As risk stratification may aid in prophylaxis and treatment, we explored risk factors for severe PONV in patients enrolled in a large international, randomized controlled trial (the ENIGMA trial).
  
  
  METHODS
  Two thousand and fifty patients, aged > or =18 yr and undergoing surgery anticipated to exceed 2 h in duration, were recruited. Patients were randomized to nitrous oxide (N(2)O)-based or N(2)O-free anaesthesia. Choice of other anaesthetic, analgesic, and antiemetic drugs was left to the discretion of the anaesthetist. Anaesthetic depth was adjusted according to clinical judgement and, if available, bispectral index (BIS) monitoring. Severe PONV was defined as: (i) two or more episodes of expulsion of gastric contents at least 6 h apart; (ii) received at least three doses of antiemetic medication for treatment of PONV, within 24 h of surgery; or both. We used logistic regression, and classification and regression tree analysis, to define risk factors for severe PONV.
  
  
  RESULTS
  Three hundred and thirty-three (16.6%) patients experienced severe PONV. Age <55 yr, female sex, abdominal surgery, N(2)O administration, absence of BIS monitoring, and longer duration of anaesthesia were predictors of severe PONV [area under receiver operating characteristic curve=0.70 (95% confidence interval: 0.67-0.73)].
  
  
  CONCLUSIONS
  Severe PONV was common and risk factors for it were similar to those reported in other studies that included all patients reporting nausea, vomiting, or both.
authors.affiliation: Department of Anaesthesia and Pain Management, Royal Melbourne Hospital, Grattan St, Parkville, VIC, 3050, Australia. kate.leslie@mh.org.au
authors.forename: K
authors.initials: K
authors.lastname: Leslie
authors.forename: P S
authors.initials: PS
authors.lastname: Myles
authors.forename: M T V
authors.initials: MT
authors.lastname: Chan
authors.forename: M J
authors.initials: MJ
authors.lastname: Paech
authors.forename: P
authors.initials: P
authors.lastname: Peyton
authors.forename: A
authors.initials: A
authors.lastname: Forbes
authors.forename: D
authors.initials: D
authors.lastname: McKenzie
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D018685:Anesthetics, Inhalation / Q000009:adverse effects*; D000932:Antiemetics / Q000008:administration & dosage; D004334:Drug Administration Schedule; D004569:Electroencephalography / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods / Q000706:statistics & numerical data; D009609:Nitrous Oxide / Q000009:adverse effects*; D020250:Postoperative Nausea and Vomiting / Q000188:drug therapy / Q000209:etiology*; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D018685:Anesthetics, Inhalation; D000932:Antiemetics; D009609:Nitrous Oxide