Feasibility of in vivo contrast-enhanced imaging of the renal cortex during hemorrhagic shock

A direct and non-invasive measurement of kidney function could aid in early recognition of acute kidney injury (AKI) at bedside and may prevent severe kidney damage. This study investigates the feasibility of contrast-enhanced ultrasound (CEUS) imaging of the renal cortex in an in vivo pig model of hemorrhagic shock. We hypothesize that the inflow-slope (SL) of the time-intensity curves (TICs) is lower as a result of decreased renal blood flow (RBF) in shock, caused by severe hemorrhage. Sixteen pigs underwent surgery to expose the right kidney and hemorrhagic shock was induced. Hemodynamics were measured at baseline (t0), 15 min after blood withdrawal (t1: early shock), and 60 min later (t2: late shock). RBF was measured using an ultrasonic flow probe, which was considered as the golden standard for measuring flow. For the CEUS measurements a bolus of microbubbles was injected in the jugular vein and imaged using the Vevo2100 (VisualSonics) transmitting at 18 MHz and recording 10 frames per second. Regions of interest were drawn in the cortex and TICs were analyzed. We showed that changes in the renal cortical inflow slope could be measured using CEUS. However, our results indicate a disparity in the kidney in response to hemorrhagic shock: a decrease in RBF results in an increase of microbubble-inflow in the renal cortex. As the flow probe placed around the renal artery measured flow of red blood cells, we can conclude that the inflow-slope of the TIC does not directly reflect the flow of red blood cells.