Renal Resistive Index (RRI) Measured in Critically Ill Patients on Mechanical Ventilation Admitted to Intensive Care: Is It a Marker of Tissue Perfusion?

Monitoring tissue hypoperfusion improves early recognition of organ dysfunction and clinical outcome. This study aimed to evaluate the association between RRI and tissue hypoperfusion indices in critically ill patients on mechanical ventilation admitted to the intensive care unit (ICU). A prospective observational study was conducted between 1 October and 31 March 2023 in the 51-bed ICU of a tertiary hospital. The correlation of renal resistive index (RRI) with tissue hypoperfusion indices and its association with shock and 28-day ICU mortality was analysed. Of the 575 patients who were admitted to the ICU during the study period, 128 were included in the study. When the entire cohort was evaluated, RRI showed positive correlations with P(cv–a) CO2 (r=0.476, p <0.001),P(cv–a) CO2/C(a–cv) O2 (r=0.687, p<0.001), and lactate (r=0.389, p <0.001). In the multivariate analysis, RRI >0.7(OR: 5.95; 95% CI: 2.09–16.96; p<0.001) and lactate ≥2 mmol (OR:3.50; 95% CI:1.39–8.82; p=0.008 were independently associated with shock. In the multivariable analysis, only RRI >0.7 was independently associated with 28-day ICU mortality (OR: 7.42; 95% CI: 2.66–20.69; p<0.001).The combination of RRI + lactate yielded the highest AUC (0.743; 95% CI:0.655–0.831), followed by RRI + P(cv–a) CO2/C(a–cv) O2 (AUC:0.685; 95% CI:0.591–0.779). RRI may provide additional information regarding systemic circulatory disturbances and tissue perfusion. RRI and lactate levels may be independently associated with shock, while RRI may also be independently associated with 28-day ICU mortality.