Renal Resistive Index is Associated With Acute Kidney Injury in COVID-19 Patients Treated in the ICU

Abstract Background: Renal resistive index (RRI) is a promising tool for prediction of acute kidney injury (AKI) in critically ill patients but is not described among patients with Coronavirus disease 2019 (COVID-19). The aim of this study was to describe the pattern of RRI in relation to AKI in patients with COVID-19 treated in the intensive care unit.Methods: In this observational cohort study, RRI was measured in COVID-19 patients in six ICUs at two sites of a Swedish University Hospital. AKI was defined by the creatinine criteria in the Kidney Disease Improving Global Outcome classification. We investigated the association between RRI and AKI diagnosis, different AKI stages and urine output.Results: RRI was measured in 51 patients, of which 23 patients (45%) had AKI at the time of measurement. Median RRI in patients with AKI was 0.80 (IQR 0.71-0.85) compared to 0.72 (IQR 0.67-0.78) in patients without AKI (p=0.004). Compared to patients without AKI, RRI was higher in patients with AKI stage 3 (median 0.83, IQR 0.71-0.85, p=0.006) but not in patients with AKI stage 1 (median 0.76, IQR 0.71-0.83, p=0.347) or AKI stage 2 (median 0.79, min/max 0.79/0.80, n=2, p=0.134). RRI was higher in patients with an ongoing AKI episode compared to patients who never developed AKI (median 0.72, IQR 0.69-0.78, p=0.015) or patients who developed AKI but had recovered at the time of measurement (median 0.68, IQR 0.67-0.81, p=0.021). Oliguric patients had higher RRI (median 0.84, IQR 0.83-0.85) compared to non-oliguric patients (median 0.74, IQR 0.69-0.81) (p=0.009).Conclusions: Critically ill COVID-19 patients with AKI have higher RRI compared to those without AKI, and elevated RRI may have a role in identifying severe and oliguric AKI in these patients.