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September 22/29, 2004

Prevention of Contrast-Induced Nephropathy With Sodium Bicarbonate

Author Affiliations

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2004;292(12):1428-1429. doi:10.1001/jama.292.12.1428-a

To the Editor: We found some of the results in the study by Dr Merten and colleagues1 surprising. The change in serum creatinine level after radiographic contrast (mean difference, 0.11 mg/dL; 95% confidence interval [CI], −1.10 to 0.30) was not significant while the change in estimated glomerular filtration rate (GFR) (mean difference, −8.6%; 95% CI, −17.0 to −0.2) was significant. Since in using the Levey formula, serum creatinine is the major determinant in calculating GFR, one might expect the change in creatinine and GFR to be of similar magnitude. We wonder if changes other than in creatinine could explain the calculated GFR change. The Levey formula uses age and sex, which would not change over 2 days, but also uses blood urea nitrogen (BUN) and serum albumin levels. While these values are stable over the long-term, it is possible that the infusion of sodium bicarbonate (NaHCO3) expanded extracellular fluid volume to a greater amount and for a longer time than the control solution of sodium chloride (NaCl). This might occur since the volume of distribution of NaHCO3, in the absence of acidosis, is limited to extracellular space while some chloride does enter cells. If this were the case, the BUN and albumin values might show a change from the preinfusion values. We are interested in knowing if the authors have these data. If it were the case that NaHCO3led to greater and longer lasting extracellular fluid volume expansion than NaCl, it might comprise a partial explanation for the apparent protection against acute renal failure in this study. The relative lack of a steady state of extracellular space would be a reason not to use formulas such as that of Levey et al2 during acute clinical changes.

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