Interpretation of the four risk factors for postoperative nausea and vomiting in the Apfel simplified risk score: an analysis of published studies.

PURPOSE: The Apfel simplified risk score, developed in 1999, is the most widely used tool for risk stratification of postoperative nausea and vomiting (PONV). It includes four risk factors: female sex, non-smoking status, history of PONV or motion sickness, and use of postoperative opioids. Nevertheless, there is considerable heterogeneity in the definition and application of these risk factors in PONV research. Our aim was to determine how these risk factors are implemented in studies employing the Apfel score.

METHODS: Citations of the index Apfel score paper between 1 September 1999 and 1 September 2019 were identified in the Scopus database. Original full-text reports in English measuring all four risk factors were eligible for inclusion. Data collected included the definition, timing, and collection method of the four risk factors.

RESULTS: Of the identified studies, 255 of the 535 reported all four risk factors, with calculated Apfel risk scores reported in 116 of the 255 (46%) papers. Smoking, PONV, motion sickness, and postoperative opioid use were defined in four (2%), zero (0%), one (0.4%), and seven (3%) papers, respectively. Postoperative opioid use was defined as "anticipated" in 138 (54%) studies and "actual" in 72 (18%) studies and was unclear in 45 (28%) studies.

CONCLUSIONS: Significant variation exists in how the Apfel risk factors are defined and applied in PONV research, particularly with respect to postoperative opioid use. More guidance in the application of this tool may optimize risk estimation and PONV prophylaxis, and potentially improve research quality.