This is a randomized, placebo-controlled, prospective, double-blinded. The study will take place at Community Medical Center in Scranton, Pennsylvania. The inclusion criteria are patients undergoing elective, urgent, or emergent cardiac surgery using cardiopulmonary bypass and having a baseline GFR less than 60 ml/min/1.73m2 estimated using the Modification of Diet in Renal Disease equation. Patients will be excluded from the study if they have cardiogenic shock (defined as a cardiac index less 2 L/min/m2 despite high dose inotropes or the need for intra-aortic balloon pump), end-stage kidney disease requiring dialysis, received an infusion of sodium bicarbonate on the same day as cardiac surgery, or if they are enrolled in a separate clinical research trial. This trial will involve two treatment groups. Group one will receive isotonic saline at 3 ml/kg/hr for one hour pre-operatively until the patient is started on cardiopulmonary bypass. Then the infusion will be reduced to 1 ml/kg/hr throughout cardiopulmonary bypass and for six hours following cardiopulmonary bypass. Group two will receive sodium bicarbonate 150mEq in 850ml of a 5% dextrose solution using the same infusion regimen as described above for isotonic saline. The primary efficacy outcome of the study will be the incidence of AKI postoperatively. Acute kidney injury will be defined as an increase in serum creatinine concentration by at least 25% from baseline or an absolute increase of 0.5 mg/dL at any time within the first five postoperative days.