Association Between the Time of Surgery and the Incidence of Postoperative Nausea-Vomiting: A Propensity Score Matched Analysis.

Background The probability of postoperative nausea and vomiting (PONV) may be influenced by the time of day. Since there has been no recent study published exploring this association, we conducted a study to determine the effect of surgical time of day on PONV. Methods With ethics approval, data of all patients undergoing elective non-cardiac non-neurosurgery, with a high risk of PONV, and which had a 24-hour assessment of PONV between October 2017 and December 2020 were extracted. Surgical sessions were classified as either morning surgery (defined as start-time and end-time before noon) or afternoon surgery (defined as surgery start-time at or after 12 noon). Those patients who had surgical sessions extending from morning sessions to afternoon sessions were excluded. A propensity-score-matching (PSM) based on 1:1 matching was performed to potential biases. For the entire study population before matching, we used Pearson's chi-square test or Fisher's exact test for categorical variables, and Student's t-test or Mann-Whitney U-test for normally or non-normally distributed continuous variables, respectively. For the matched study population, we used conditional logistic regression to test for differences. A p-value of <0.05 was considered statistically significant. Results Of the 3808 surgical sessions, 1439 surgical sessions were excluded from the analysis because they extended between morning and afternoon surgery. After 1:1 PSM, 1043 matched pairs were obtained. The incidence of PONV, prior to matching, remained statistically insignificant even after PSM. Conclusion We found that the time of surgery (morning or afternoon) did not affect both the overall incidence and severity of PONV. The association between PONV and time of day remained statistically insignificant prior to and after propensity matching for a number of covariates.