Background: The effect of urinary alkalinization in cardiac surgery patients at risk of acute kidney injury (AKI) is controversial and trial findings conflicting. Accordingly, the authors performed a prospectively planned individual patient data meta-analysis of the double-blind randomized trials in this field. Methods: The authors studied 877 patients from three double-blind, randomized controlled trials enrolled to receive either 24h of intravenous infusion of sodium bicarbonate or sodium chloride. The primary outcome measure was a postoperative increase in serum creatinine concentration of greater than 25 or 0.5mg/dl (> 44 ?m/L) within the first five postoperative days. Secondary outcomes included the raw change in serum creatinine, greater than 50 and greater than 100 rises in serum creatinine, developing AKI (Acute Kidney Injury Network criteria), initiation of renal replacement therapy, morbidity, and mortality. Results: Patients were similar in demographics, comorbidities, and cardiac procedures. Sodium bicarbonate increased plasma bicarbonate (P <0.001) and urine pH (P <0.001). There were no differences in the development of the primary outcome (Bicarbonate 45 [39?51 vs. Saline 42 [36?48 , P = 0.29). This result remained unchanged when controlling for study and covariates (odds ratio [OR], 99 confidence interval [CI]: Bicarbonate vs. Control, 1.11 [0.77?1.60], P = 0.45). There was, however, a significant study-adjusted benefit in elective coronary artery bypass surgery patients in terms of renal replacement therapy (Bicarbonate vs. Control, OR: 0.38 [99 CI: 0.25?0.58], P <0.0001) and the development of an Acute Kidney Injury Network grade = 3 (Bicarbonate vs. Control, OR: 0.45 [99 CI: 0.43?0.48], P <0.0001). Conclusions: Urinary alkalinization using sodium bicarbonate infusion is not associated with an overall lower incidence of AKI; however, it reduces severe AKI and need for renal replacement therapy in elective coronary artery bypass patients.