Renal Artery Resistance Index: Missing Biomarker in the Multiparametric Evaluation of Patients with Cardiorenal Syndrome?

Background: RARI has been studied in relation to AKI, in critically ill patients, kidney transplant recipients, and in CDK, with values ranging between 0.65 and 0.8. It is associated with systemic circulation and vascular distensibility, reflects the interaction between systemic and renal circulation, and could serve as a marker of AKI in cardiorenal syndrome. The objective is to determine the association between RARI and VExUS in patients with cardiorenal syndrome. Methods: This observational study included hospitalized patients with chronic kidney disease exacerbated by cardiorenal syndrome. VExUS was used, a renal scintigraphy was performed, and renal changes along with bilateral RARI were confirmed through three measurements. The Shapiro-Wilk test was conducted, along with analysis of frequencies, means, and medians. Spearman's correlation was used. Results: In 22 patients: 9 (40.9%) had VExUS 0 but presented with tissue congestion and 13 (59%) had intravascular congestion. The RARI was 0.62 (range: 0.52–0.73), showing an association with creatinine with p = 0.001 (95% CI: 0.1–0.127). In patients with VExUS 0, the RARI was 0.63, and in those with VExUS 1–3 it was 0.61, with no statistical difference (ρ = -0.12, p = 0.22, 95% CI: -0.5 to 0.3). For the degree of AKI, ρ = -0.07 (p = 0.37, 95% CI: -0.47 to 0.3). Conclusion: RARI is correlated with pulse pressure and arterial stiffness. In cardiorenal syndrome, the measurement of both venous and arterial parameters could provide information on renal prognosis. There is no difference in RARI between intravascular and tissue congestion. A lower cutoff value than previously reported in the literature was found—0.58—with a sensitivity of 75% and a specificity of 83% for AKI.