Critically Ill COVID-19 Patients With Acute Kidney Injury Have Reduced Renal Blood Flow and Perfusion Despite Preserved Cardiac Function: A Case-Control Study Using Contrast-Enhanced Ultrasound

Background Acute Kidney Injury (AKI) is a common complication of COVID-19 critical illness but the pathophysiology is uncertain. Some evidence has indicated that a vascular aetiology may be implicated. We used contrast enhanced ultrasound (CEUS) and echocardiography to study renal perfusion and global blood flow and compared our findings with measurements taken in a group of septic shock patients and healthy volunteers. Methods Prospective case-control study. Renal perfusion variables were assessed with contrast enhanced ultrasound (CEUS); macrovascular blood flow was assessed using Doppler analysis of large renal vessels; echocardiography was used to assess right and left heart function and cardiac output. Results CEUS derived parameters were reduced in in COVID-19 associated AKI compared to healthy controls (perfusion index 3415 v 548 a.u., p = 0·001; renal blood volume 7794 v 3338 a.u., p = 0·04). Renal arterial flow quantified using time averaged peak velocity (TAPV) was also reduced compared to healthy controls (36·6 v 20·9 cm/s, p = 0.004) despite cardiac index being similar between groups (2.8 v 3.7 L/min/m2, p = 0.07). There were no differences in CEUS derived or cardiac parameters between COVID-19 and septic shock patients but patients with septic shock had more heterogeneous perfusion variables. Conclusion Both large and small vessel blood flow is reduced in patients with COVID-19 associated AKI compared to healthy controls, which does not appear to be a consequence of right or left heart dysfunction. A reno-vascular pathogenesis of COVID-19 AKI seems likely.