The Renal Resistive Index in Allografts: Is Sonographic Assessment Sufficiently Reproducible in a Routine Clinical Setting? – Reproducibility of the Renal Resistive Index

Abstract

Purpose To assess the reproducibility of the renal resistive index (RRI) in a routine clinical setting. Materials and Methods 22 patients with a kidney allograft and 19 physicians participated in our prospective study. Within 2 hours each patient was examined by 5 different physicians using 2 out of 3 different, randomly allocated ultrasound machines. Each investigator determined the hilar and parenchymal RRI of the allograft. The reproducibility and reproducibility limit of the RRI were assessed as well as Cronbach’s alpha and the intraclass correlation coefficient (ICC). The deviation of the RRI from the mean RRI over the 5 measurements was used as an indicator of reproducibility. The impact of the ultrasound machine, examiner’s level of experience, and kidney function impairment (GFR < 45 ml/min) was assessed with the Kruskal-Wallis test. The bivariate linear correlation of the minimal transplant distance from the body surface with the variance of the parenchymal RRI was analyzed. Results A reproducibility of 0.045 with a reproducibility limit of 0.124 was found for the parenchymal RRI. The ICC between RRIs was good with 0.852 for the parenchymal RRI and 0.868 for the hilar RRI. The type of ultrasound machine used was found to have a significant impact on the deviation of the parenchymal RRI (Kruskal-Wallis-Test, p = 0.003). Variance in serial parenchymal RRI measurements correlated significantly with the depth of the kidney transplant (p = 0.001). Conclusion While the RRI is generally sufficiently reproducible, the type of ultrasound machine used and the depth of the kidney transplant within the recipient’s body have a significant impact on reproducibility. Key Points: Citation Format

POCUS in Intensive Care Nephrology

“…The RRI may also be affected by increased intraabdominal pressure, medications, and the location where it is measured [18,19]. Previous studies have shown reproducibility of RRI among different operators, however most studies involved expert sonographers and intra-observer variability may exist in novice sonographers [20,21]. Lastly, while the RRI evaluates macrovascular perfusion, it is unable to assess slow flow velocities in vessels <2 mm and microcirculatory perfusion plays an important role in AKI due to sepsis [22,23].…”