To the Editor: In their randomized trial comparing sodium bicarbonate vs sodium chloride for prevention of contrast medium–induced nephropathy (CIN), Dr Brar and colleagues1 used a lower dose of bicarbonate than described in other studies2 - 4 and found that this lower dose of bicarbonate was inadequate to significantly reduce CIN. Their study did not document urine pH as was done in other studies.2 - 3 ,5 The bicarbonate concentration in their study was 130 mEq/L compared with 154 mEq/L in the other studies. The administered dose of bicarbonate anion was higher in the studies by Merten et al2 (by 18%), Ozcan et al3 (by 58%), and Recio-Mayoral et al4 (by 202%). The higher doses would likely result in a higher urine pH, although the bicarbonate effect on urine pH is nonlinear.
The hypothesis set forth in the original bicarbonate hydration article2 referred to the establishment of a relatively neutral pH in the medullary portion of the kidney prior to contrast exposure with its subsequent complex cascade of events leading to free radical formation and CIN. A study in children by Assadi5 suggests that even the dose of bicarbonate used by Merten et al may well have been less than optimal, with the urine pH in this pediatric study correlating inversely with CIN. The cohort of 46 children (mean weight, 44 kg; mean serum creatinine level, 1.43 mg/dL) with higher urine pH (7.8) resulting from acetazolamide administration had a 0% incidence of CIN compared with the randomized cohort of 50 children receiving the protocol used by Merten et al (urine pH, 6.4; CIN incidence, 8.7%; P = .049). The study by Merten et al reported a urine pH of 6.5.
Despite the lower bicarbonate dose, the study by Brar et al did show that the majority of outcome measures were improved with bicarbonate, but these results were not statistically significant. The outcome of CIN in 21 patients with the highest risk (estimated glomerular filtration rate ≤30 mL/min per 1.73 m2) was 36% in the bicarbonate group compared with 20% in the saline group (P = .64). A larger sample size may have resulted in a statistically significant difference.
Future studies that use bicarbonate hydration should include an outcome measure of the effectiveness of the bicarbonate dose (urine pH) and use an adequate alkalinizing dose to achieve a neutral urine pH.
Financial Disclosures: Dr Burgess reported that US patent No. 7,019,035 B2 was issued to him on March 28, 2006, and assigned to MD Scientific LLC, in which he has minority ownership. This patent is for a method for sodium bicarbonate prophylaxis to prevent CIN. The other authors reported no disclosures.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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