Anaesthetist prediction of postoperative opioid use: a multicentre prospective cohort study

Background: The Apfel simplified risk score includes four risk factors: female sex, non-smoking status, postoperative nausea and vomiting or motion sickness history, and postoperative opioid use. The score is calculated preoperatively, so postoperative opioid use must be predicted. We aimed to determine whether anaesthetists can predict patients' postoperative opioid use and dose. Methods: Specialist anaesthetists from eight hospitals preoperatively predicted opioid use and dose in the post-anaesthesia care unit (PACU) and for the first 24 h postoperatively, which was compared with actual opioid use and dose. Opioid doses were converted to oral morphine equivalents (MEQ). Correlations between predicted and actual opioid use and dose were analysed with Spearman's rho and linear regression. Results: A total of 487 anaesthetist–patient pairs were included. Anaesthetists overpredicted opioid use (398 [82%] predicted vs 251 [52%] actual patients requiring opioids in the PACU; 396 [81%] predicted vs 291 [60%] actual in the first 24 h) (Spearman's rho [95% confidence interval] 0.24 [0.16–0.33], P<0.001 in the PACU; 0.36 [0.28–0.44], P<0.001 in the first 24 h). Anaesthetists also overpredicted opioid dose (median [inter-quartile range] 12 [8–20] mg predicted MEQ vs 4 [0–18] mg actual MEQ in the PACU; 32 [18–60] mg vs 24 [0–65] mg MEQ in the first 24 h) (Spearman's rho 0.21 [0.13–0.29], P<0.001 in the PACU; 0.53 [0.40–0.60], P<0.001 in the first 24 h). Conclusions: Specialist anaesthetists cannot accurately predict opioid use or dose in the PACU or the first 24 postoperative hours. The Apfel risk criterion for postoperative opioid use may be inaccurate in clinical practice.