Abstract
BACKGROUND: The Doppler-derived renal resistive index (RRI) is emerging as a promising bedside tool for assessing renal perfusion and risk of developing acute kidney injury in critically ill patients. It is not known what level of ultrasonography competence is needed to obtain reliable RRI values. OBJECTIVE: The aim of this study was to evaluate the feasibility of RRI measurements by an intermediate and novice sonographer in a volunteer population. METHODS: After a focused teaching session, an intermediate (resident), novice (medical student) and expert sonographer performed RRI measurements in 23 volunteers consecutively and blinded to the results of one another. Intraclass correlation coefficients and Bland-Altman plots were used to evaluate interobserver reliability, bias and precision. RESULTS: Both non-experts were able to obtain RRI values in all volunteers. Median RRI in the population measured by the expert was 0.58 (interquartile range 0.52-0.62). The intraclass correlation coefficient was 0.96 (95% confidence interval 0.90-0.98) for the intermediate and expert, and 0.85 (95% confidence interval 0.69-0.94) for the novice and expert. In relation to the measurements of the expert, both non-experts showed negligible bias (mean difference 0.002 [95% confidence interval - 0.005 to 0.009, p = 0.597] between intermediate and expert, mean difference 0.002 [95% confidence interval - 0.011 to 0.015, p = 0.752] between novice and expert) and clinically acceptable precision (95% limits of agreement - 0.031 to 0.035 for the intermediate, 95% limits of agreement - 0.056 to 0.060 for the novice). CONCLUSIONS: RRI measurements by both an intermediate and novice sonographer in a volunteer population were reliable, accurate and precise after a brief course. RRI is easy to learn and feasible within the scope of point-of-care ultrasound.