The Rhodes index of nausea, vomiting and retching (RINVR) is a patient self-report instrument to assess the objective and subjective factors of nausea and vomiting. The aim of this study is to evaluate the reliability and validity of the RINVR in postoperative nausea and vomiting (PONV).

The RINVR, VAS for nausea and incidence of emetic episodes were administered to 150 patients approximately 30 minutes apart at 6 hours and 24 hours after surgery. The validity was evaluated by Spearman's correlation and internal consistency of reliability was determined using Cronbach's alpha. To determine test-retest reliability, second administration of the RINVR was done 2 hours after the first. The test-retest reliability was evaluated by Spearman's correlation and agreement.

Cronbach's alpha of nausea, vomiting, retching and total experience scores of the RINVR ranged from 0.912 to 0.968. Test-retest scores of all items were strongly correlated (Spearman's coefficients: 0.962-1.000, P < 0.0001) and highly agreed (weighted kappa: 0.932-1.000). Coefficients of construct validity for nausea components (vs VAS for nausea) and emetic components (vs incidence of emetic episodes) of the RINVR were 0.860-0.928 and 0.724-0.811, respectively (P < 0.0001). The overall weighted kappa between the incidences of PONV assessed by the RINVR and by patient self-assessment of VAS for nausea and incidence of emetic episodes was 0.917-0.945. The number of patients in "great" total experience category was 1.33% or less. There was no significant difference of VAS for nausea between "severe" and "great" nausea experience categories.

The RINVR was a reliable and valid instrument to assess PONV.