Intravenous administration of large amounts of fluids (hydration) is a landmark strategy for the prevention of acute kidney injury (CI-AKI) caused by isotonic contrast agents. However, the type of fluid supplementation, the amount, and the timing of administration are unclear. In 2004, it was reported that the use of isotonic sodium bicarbonate solution was associated with a lower incidence of CI-AKI compared to iso-moL sodium chloride solution. A possible mechanism to explain this beneficial effect is the inhibition of the Haber-Weiss reaction by sodium bicarbonate: by alkalinizing the renal parenchyma, administration of sodium bicarbonate or acetazolamide theoretically reduces the production of reactive oxygen radicals caused by the toxic and ischemic effects of the contrast medium. Multiple prospective randomized trials comparing different perfusion regimens of sodium bicarbonate solution in different patient populations followed, yielding inconsistent results. One possible explanation for the conflicting results from the previous trials is the different doses of sodium bicarbonate given. At the time of contrast excretion, sufficient sodium bicarbonate must be given to alkalize the renal medulla to reduce the production of reactive oxygen radicals. However, most trials have not reported changes in urinary PH or serum bicarbonate levels, and larger doses of sodium bicarbonate infusion are needed to further observe the preventive effect on CI-AKI and to look forward to confirming the benefit of sodium bicarbonate. Professor Solomon and colleagues from the University of Vermont College of Medicine, Burlington, USA, designed a prospective double-blind, multicenter, randomized clinical trial (the BOSS study) enrolling patients at high risk of CI-AKI to assess the rate of adverse clinical outcomes with high-dose sodium bicarbonate solution (total dose of approximately 2.0 mEq/kg) infusion. The results were published in a recent issue of Clin J Am Soc Nephrol. The BOSS study was a prospective, double-blind, multicenter (17 centers in the United States) randomized clinical trial. 391 patients with eGFR <45 mL/min/1.73m2 (calculated by the MDRD formula) who underwent elective coronary angiography or peripheral angiography were randomized to a high-dose isotonic sodium bicarbonate solution group (1.3% NaHCO3, 154 mEq /L, target value 2.0 mEq/kg) or similar moL of isotonic sodium chloride solution group (0.9% NaCl, 154 mEq/L). Patients received 5 mL/kg of intravenous 1.3% NaHCO3 solution or 0.9% NaCl solution for more than 60 minutes before imaging. They receive 1.5 mL/kg/h intravenously during and 4 hours after imaging. Since CI-AKI is usually a transient phenomenon, characterized by elevated serum creatinine reflecting a decrease in creatinine clearance. Renal injury is either missed (due to insufficient injury to cause elevated serum creatinine) or overdiagnosed (elevated serum creatinine due to hemodynamic causes, but no injury). Therefore, the primary endpoint of the BOSS study was a composite endpoint consisting of death at 6 months, the rate of need for renal replacement therapy (RRT), or the rate of sustained ≥20% reduction in eGFR. Secondary endpoints included length of hospital stay, mortality, and time to death or receipt of RRT. cKI-AKI was defined as an increase in serum creatinine ≥0.5 mg/dL or 25% from baseline in the first 3 days after imaging. A total of 391 patients were enrolled in the study from March 2010-May 2012. In the intention-to-treat population, the incidence of the primary outcome in the sodium bicarbonate and saline groups was 14.9% and 16.3%, respectively. There was no difference in the incidence of CI-AKI between the two groups (NaHCO3: 14.5%, NaCl: 12.1%). CI-AKI was associated with a higher proportion of persistent loss of renal function at 6 months compared with patients without CI-AKI (21.2% versus 7.7%). The study did not find a difference in mortality, proportion on dialysis or proportion of sustained loss of eGFR at 6 months or CI-AKI in patients undergoing imaging with eGFR <45 mL/min/1.73m2 who were instilled with high-dose sodium bicarbonate solution versus those instilled with saline. The investigators concluded that clinicians can decide whether to use high-dose sodium bicarbonate on a case-by-case basis and that further studies are needed to highlight the effect on mortality.