Renal Doppler resistive index : applications in perioperative and critical care

Abstract

Doppler-derived renal resistive index (RRI) has emerged as a promising bedside tool for assessing renal hemodynamics, and elevated values ≥0.70 have been associated with adverse outcomes in various clinical settings. This thesis explored new aspects of RRI within perioperative and critical care, as well as the epidemiology of long-term renal outcomes after surgery in Sweden.

In study I, we assessed the feasibility of RRI as a point-of-care ultrasound (POCUS) method. After a focused teaching session, an intermediate (resident) and a novice sonographer (medical student) performed RRI measurements in 23 volunteers, and the results were compared to measurements by an expert. Measurements by both nonexperts were reliable, accurate and showed clinically acceptable precision. In study II, RRI was measured in 51 patients with Coronavirus disease 2019 during the first wave of the pandemic in six intensive care units at two sites of the Karolinska University Hospital. In these patients, RRI was generally elevated, associated with acute kidney injury, and seemed to decrease dynamically with renal recovery. In study III, perioperative data from 23 Swedish hospitals were matched with extensive national public authority and quality registries. Among 237 124 patients without preoperative renal dysfunction undergoing non-cardiac surgery, 0.67% developed advanced chronic kidney disease, and 7.1% developed major adverse kidney events (advanced chronic kidney disease, kidney failure, or all-cause death) within the first postoperative year. We identified several perioperative risk factors for these outcomes, including advanced acute kidney disease within 90 days after surgery. In study IV, associations of preoperative RRI with long-term renal and cardiovascular outcomes were investigated in 96 patients who had undergone on-pump cardiac surgery at the Karolinska University Hospital. RRI ≥0.70 was associated with persistent renal dysfunction, major adverse kidney events (persistent renal dysfunction, renal replacement therapy, or all-cause death), and major adverse cardiovascular events (myocardial infarction, unstable angina, decompensated heart failure, stroke, or cardiovascular death) within 5 years after surgery.

In conclusion, this thesis suggests that RRI can be used as a POCUS method with implications for assessing renal outcomes in perioperative and critical care, both in the short and long term. Further, this thesis sheds light on the epidemiology and important risk factors for postoperative long-term renal outcomes. RRI may have a role as a bedside measure to identify patients with an elevated risk for such outcomes.