Comparison of surgical site and patient's history with a simplified risk score for the prediction of postoperative nausea and vomiting

Although site of surgery and previous occurrence of postoperative nausea and vomiting are often used to decide whether prophylactic anti-emetic drugs are indicated, the value of these predictors is unclear. We compared these two risk factors against a simplified four-factor risk score. We analysed data from 1566 adult inpatients who received balanced anaesthesia without prophylactic anti-emetics. Sensitivity, specificity, predictive value and area under the receiver operating characteristic curve were used to quantify predictive properties. Nausea and vomiting occurred in 600 (38.3%) patients within 24 h. Sensitivity and specificity were, respectively, 47% and 59% for surgical site; 47% and 70% for history of postoperative nausea and vomiting; and 58% and 70% for risk score with three or more factors. The area under the curve for surgical site was 0.53 (95% CI 0.50-0.56); that for patient's history was 0.58 (95% CI 0.56-0.61) while for risk score it was 0.68 (95% CI 0.66-0.71; P < 0.001). Prediction using surgical site or patient's history alone was poor while the simplified risk score provided clinically useful sensitivity and specificity.