After informed consent and assent is obtained, urine and serum samples will be collected for the study protocol. Urine specimens for creatinine, NGAL, and IL-18 will be collected pre-operatively for baseline measurement in addition to post-operatively at 6, 12, 24, and 72 hours. Cystatin C will be measured pre-operatively to assess chronic renal function. Serum creatinine will be measured pre-operatively and post-operatively at 12 hours and daily as part of usual clinical care.