Monitoring Renal Blood Flow With Contrast Enhanced Ultrasound During Coronary Angiogram

Contrast induced nephropathy (CN) is a common cause of acute kidney injury and is associated with increased morbidity and mortality and healthcare cost. Iodinated contrast media (ICM) induce kidney injury through vasoconstriction and ischemia as well as direct tubular toxicity. Older subjects, individuals with preexisting kidney disease, diabetes, hypotension, and those exposed to higher volumes of ICM are at higher risks for CN. Within the last several years, multiple strategies have been used in clinical studies to reduce the risk of CN in high risk individuals with inconsistent results. In general, it is agreed that volume expansion is effective in reducing the risk. However, no study has looked at changes in renal blood flow (RBF) in response to volume expansion or after exposure to ICM to investigate its relationship with occurrence of CN. In this proposal, up to 125 individuals with preexisting kidney disease as evidenced by an estimated glomerular filtration rate (eGFR) between 30 - 60 ml/min/1.73 m2 and up to 25 individuals with normal renal function (total of up to 150 individuals) who are scheduled for coronary angiography will be studied. Each individual will have serial measurements of RBF; at baseline, after volume expansion with normal saline, and after exposure to ICM, using the novel technique of contrast enhanced ultrasound (CEU). The investigators will investigate the utility of monitoring RBF with CEU in predicting the occurrence of CN (a rise of \> 0.3 mg/dL or 25% in baseline serum creatinine 48 hours after exposure to ICM) after adjusting for other known risk factors in the group of subjects with reduced GFR. The investigators will also examine the correlation between RBF changes and other urinary and serum biomarkers of kidney injury in this group. Up to 25 individuals with a normal kidney function will be studied in a separate part of the study in which the accuracy of CEU based measurements of RBF will be compared to the RBF and blood flow