A simplified risk score for predicting postoperative nausea and vomiting -Conclusions from cross-validations between two centers

Background: Recently, two centers have independently developed a risk score for predicting postoperative nausea and vomiting (PONV). This study invest igated (1) whether risk scores are valid across centers and (2) whether ris k scores based on logistic regression coefficients can be simplified withou t loss of discriminating power. Methods: Adult patients from two centers (Oulu, Finland: n = 520, and Wuerz burg, Germany: n = 2202) received inhalational anesthesia (without antiemet ic prophylaxis) for various types of surgery. PONV was defined as nausea or vomiting within 24 h of surgery. Risk scores to estimate the probability o f PONV were obtained by fitting logistic regression models. Simplified risk scores were constructed based on the number of risk factors that were foun d significant in the logistic regression analyses. Original and simplified scores were cross-validated. A com bined data set was created to estimate a potential center effect and to construct a final risk score. The discrimin ating power of each score was assessed using the area under the receiver op erating characteristic curves. Results: Risk scores derived from one center were able to predict PONV from the other center (area under the curve = 0.65-0.75). Simplification did no t essentially weaken the discriminating power (area under the curve = 0.63- 0.73). No center effect could be detected in a combined data set (odds rati o = 1.06, 95% confidence interval = 0.71-1.59). The final score consisted o f four predictors: female gender, history of motion sickness (MS) or PONV, nonsmoking, and the use of postoperative opioids. If none, one, two, three, or four of these risk factors were present, the incidences of PONV were 10 %, 21%, 39%, 61% and 79%. Conclusions: The risk scores derived from one center proved valid in the ot her and could be simplified without significant loss of discriminating powe r. Therefore, it appears that this risk score has broad applicability in pr edicting PONV in adult patients undergoing inhalational anesthesia for vari ous types of surgery. For patients with at least two out of these four iden tified predictors a prophylactic antiemetic strategy should be considered.