Renal Resistive Index: Response to Shock and its Determinants in Critically Ill Patients.

Introduction: Shock is characterized by micro- and macrovascular flow impairment contributing to acute kidney injury (AKI). Routine monitoring of the circulation regards the macrocirculation but not the renal circulation which can be assessed with Doppler ultrasound as renal resistive index (RRI). RRI reflects resistance to flow. High RRI predicts persistent AKI. Study aims were to determine whether RRI is elevated in shock and to identify determinants of RRI. Materials and Methods: This prospective observational cohort study included two cohorts of patients, with and without shock less than 24-h after intensive care admission. Apart from routine monitoring, three study measurements were performed simultaneously: RRI, sublingual microcirculation, and bioelectral impedance analysis. Results: A total of 92 patients were included (40 shock, 52 nonshock), median age was 69 [60-76] vs. 67 [59-76], P = 0.541; APACHE III was 87 [65-119] vs. 57 [45-69], P<0.001. Shock patients had higherRRI than patientswithout shock (0.751 [0.692-0.788] vs. 0.654 [0.610-0.686], P<0.001). Overall, high age, APACHE III score, lactate, vasopressor support, pulse pressure index (PPI), central venous pressure (CVP), fluid balance, and lowpreadmission estimated glomerular filtration rate, mean arterial pressure (MAP), creatinine clearance, and reactance/m were associated with high RRI at univariable regression (P<0.01). Microcirculatory markers were not. Atmultivariable regression, vasopressor support, CVP, PPI andMAP, reactance/m, and preadmission eGFR were independent determinants of RRI (n = 92, adj.R-2 = 0.587). Conclusions: Patients with shock have a higher RRI than patients without shock. Independent determinants of high RRI were pressure indices of the systemic circulation, low membrane capacitance, and preadmission renal dysfunction. Markers of the sublingual microcirculation were not.