RecruitingDevice studyA Comparison of Renal vs Limb NIRS for Predicting Cardiac Surgery Associated Acute Kidney InjuryAcute kidney injury (AKI) is a complication of cardiac surgery that can affect outcome. Near Infrared Spectroscopy (NIRS) is a technology that uses light to determine how well oxygenated tissues are. This technology is routinely used in cardiac surgery to measure the oxygen level in the brain by placing a sensor sticker on the forehead. The purpose of the study is to determine whether NIRS sensor stickers placed on the skin over the kidney can predict AKI better than when sensors are placed on the skin over the participant's limbs. This study is being conducted by investigators from the department of anesthesiology at the University of Utah.