Renal Doppler to assess renal perfusion in the critically ill: a reappraisal

To describe the method and significance of Doppler-based resistive index (RI) and to provide an updated description of its interest with a special focus on the critically ill. Review of selected studies on RI found in the PubMed, Ovid and Cochrane databases. Additional references were retrieved from the selected studies. An increasing body of evidence suggests that renal Doppler may help to assess perfusion of native or transplanted kidneys. In addition, recent studies suggest that it may be useful in critically ill patients. The RI is a parameter derived from Doppler examination that is calculated as follows: . Renal Doppler has proven to be valuable for assessing large arterial or venous abnormalities and has been suggested to assess renal perfusion and to predict acute kidney injury (AKI) in critically ill patients. However, numerous factors have been shown to influence renal Doppler and may constitute potential confounding factors. Moreover, experience with critically ill patients is scant and our understanding of factors influencing RI in this setting is limited. Doppler-based RI seems to be a promising tool in the critically ill to assess the risk of AKI, help in differentiating persistent from transient AKI, or assess changes in renal perfusion as consequences of therapeutic intervention. However, we still lack large, adequately powered studies in non-selected populations of patients before implementing this technique in clinical practice. In addition, the impact of several factors that may influence this parameter remains to be evaluated.