The clinical application of ultrasound for acute kidney injury during sepsis-from macroscopic to microscopic renal perfusion perspectives

Abstract

The aim was to quantify macroscopic renal blood flow and renal cortical microcirculation in patients with septic acute kidney injury (AKI) using ultrasound and contrast-enhanced ultrasound. In this case-control study, patients in the intensive care unit diagnosed with septic AKI were divided into stages 1-3 based on the 2012 KDIGO (Kidney Disease: Improving Global Outcomes) AKI diagnostic criteria. The patients were categorized into mild (stage 1) and severe (stages 2 and 3) groups, while septic patients without AKI served as the control group. Ultrasound parameters such as macrovascular renal blood flow and time-averaged velocity, as well as cardiac function parameters such as cardiac output and cardiac index, were measured. The time-intensity curve in the microcirculation was analyzed through contrast-enhanced ultrasound imaging software to calculate imaging parameters such as peak time, rise time, fall half-time and mean transit time of the interlobar arteries in the renal cortex. In terms of macrocirculation, renal blood flow and time-averaged velocity decreased gradually with the progression of septic acute renal injury (p=0.004, p < 0.001). There was no difference in cardiac output and cardiac index values among the three groups (p=0.17 and p=0.12). In terms of microcirculation, ultrasonic Doppler parameters of the renal cortical interlobular artery, such as peak intensity, risk index and ratio of peak systolic velocity to end-diastolic velocity, gradually increased (all p values <0.05). The temporal contrast-enhanced ultrasound parameters-time to peak, rise time, fall half-time and mean transit time-were prolonged in AKI groups when compared with the control group (p < 0.001, p=0.003, p=0.004 and p=0.009, respectively). In patients with septic AKI, the renal blood flow and time average velocity of macrocirculation in the kidneys are reduced, while the time parameters of microcirculation such as time to peak, rise time, fall half-time and mean transit time are prolonged, especially in patients with severe AKI. These changes are not related to changes in cardiac output or cardiac index.