title: Survival analysis of postoperative nausea and vomiting in patients receiving patient-controlled epidural analgesia.
abstract: BACKGROUND
  Postoperative nausea and vomiting as well as postoperative pain are two major concerns when patients undergo surgery and receive anesthetics. Various models and predictive methods have been developed to investigate the risk factors of postoperative nausea and vomiting, and different types of preventive managements have subsequently been developed. However, there continues to be a wide variation in the previously reported incidence rates of postoperative nausea and vomiting. This may have occurred because patients were assessed at different time points, coupled with the overall limitation of the statistical methods used. However, using survival analysis with Cox regression, and thus factoring in these time effects, may solve this statistical limitation and reveal risk factors related to the occurrence of postoperative nausea and vomiting in the following period.
  
  
  METHODS
  In this retrospective, observational, uni-institutional study, we analyzed the results of 229 patients who received patient-controlled epidural analgesia following surgery from June 2007 to December 2007. We investigated the risk factors for the occurrence of postoperative nausea and vomiting, and also assessed the effect of evaluating patients at different time points using the Cox proportional hazards model. Furthermore, the results of this inquiry were compared with those results using logistic regression.
  
  
  RESULTS
  The overall incidence of postoperative nausea and vomiting in our study was 35.4%. Using logistic regression, we found that only sex, but not the total doses and the average dose of opioids, had significant effects on the occurrence of postoperative nausea and vomiting at some time points. Cox regression showed that, when patients consumed a higher average dose of opioids, this correlated with a higher incidence of postoperative nausea and vomiting with a hazard ratio of 1.286.
  
  
  CONCLUSIONS
  Survival analysis using Cox regression showed that the average consumption of opioids played an important role in postoperative nausea and vomiting, a result not found by logistic regression. Therefore, the incidence of postoperative nausea and vomiting in patients cannot be reliably determined on the basis of a single visit at one point in time.
authors.affiliation: Department of Anesthesiology, Taichung Veterans General Hospital, Taichung, Taiwan, ROC.
authors.forename: Shang-Yi
authors.initials: SY
authors.lastname: Lee
authors.affiliation: Department of Anesthesiology, Taichung Veterans General Hospital, Taichung, Taiwan, ROC; Department of Nursing, Hung Kuang University, Taichung, Taiwan, ROC.
authors.forename: Chih-Jen
authors.initials: CJ
authors.lastname: Hung
authors.affiliation: Department of Anesthesiology, Taichung Veterans General Hospital, Taichung, Taiwan, ROC.
authors.forename: Chih-Chieh
authors.initials: CC
authors.lastname: Chen
authors.affiliation: Department of Anesthesiology, Taichung Veterans General Hospital, Taichung, Taiwan, ROC; Department of Financial and Computational Mathematics, Providence University, Taichung, Taiwan, ROC. Electronic address: chihcheng.wu@gmail.com.
authors.forename: Chih-Cheng
authors.initials: CC
authors.lastname: Wu
mesh_terms: D015360:Analgesia, Epidural / Q000009:adverse effects; D016058:Analgesia, Patient-Controlled / Q000009:adverse effects; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D020250:Postoperative Nausea and Vomiting / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors
keywords: epidural analgesia; logistic models; patient-controlled analgesia; postoperative nausea and vomiting; survival analysis