Sodium Bicarbonate Reduces the Incidence of Contrast-induced Nephropathy

Abstract & Commentary

Source: Merten GJ et al. Prevention of contrast-induced nephropathy with sodium bicarbonate: A randomized controlled trial. JAMA 2004;291:2328-2334.

The objective of this prospective, single-center, randomized trial was to compare the efficacy of sodium bicarbonate with sodium chloride as the hydration fluid to prevent contrast-induced nephropathy. A total of 119 patients with stable creatinine levels of at least 1.1 mg/dL, who were scheduled for cardiac catheterization, computed tomography or other imaging procedures, completed the study. Patients received 154 mEq/L of either sodium bicarbonate or sodium chloride as a bolus of 3 mL/kg per hour for 1 hour before exposure to the nonionic, low-osmotic radiographic contrast agent iopamidol, followed by an infusion of 1 mL/kg per hour for 6 hours after the procedure. Serum creatinine levels were measured at baseline and one and two days after contrast. Contrast-induced nephropathy was defined as an increase in 25% or more in serum creatinine within two days of contrast use.

There were no significant differences between the two groups in age, sex, incidence of diabetes, ethnicity, or contrast volume. Baseline serum creatinine was slightly higher, but not statistically different, in patients receiving sodium bicarbonate treatment with a mean (SD) of 1.89 (0.69) mg/dL compared with 1.71 (0.42) mg/dL for sodium chloride. The primary outcome measure of contrast- induced nephropathy occurred in 13.6% (8 of 59 patients) who received sodium chloride but in only 1.7% (1 of 60 patients) who received sodium bicarbonate, for a mean difference of 11.9% (95% CI, 2.6%-21.2%; P = 0.02). A follow-up registry of 191 patients meeting the study criteria and treated with sodium bicarbonate was included and resulted in three cases of contrast-induced nephropathy (1.6%, 95% CI 0-3.4%).

Commentary by Stephanie Abbuhl, MD, FACEP

It is an exciting finding that an easily administered and inexpensive treatment apparently can reduce the incidence of contrast-induced renal failure. Despite less than perfect methodology, the results of this study are impressive and should lead to consideration of implementing a standard protocol in every emergency department (ED) for the administration of sodium bicarbonate hydration fluid in patients with renal insufficiency who are to undergo either a procedure or an imaging study requiring intravenous contrast. The simplified solution used in the registry patients was prepared by adding 3 ampules (150 mEq) of sodium bicarbonate to 1 L of D5W and infusing a bolus of 3.5 mL/kg for 1 hour immediately before the contrast injection, followed by 1.18 mL/kg per hour thereafter for 6 hours.

The success of sodium bicarbonate is consistent with the theory that contrast injury is caused by free radicals generated within the acid environment of the renal medulla. Sodium bicarbonate may interrupt oxidant injury by either slowing free radical production and/or by acting as a scavenger for potent oxidants.1 Urine pH measurements after the initial bolus of fluid showed that a small but significant increase in urinary alkalinization occurred in patients who received sodium bicarbonate when compared with those who received sodium chloride (mean pH 6.5 vs 5.6; P = 0.002).

Practically speaking, the most difficult part of implementing a protocol for preventing contrast-induced renal failure is determining what creatinine level cutoff to use when deciding which patients should receive sodium bicarbonate prophylaxis. We tend to forget that creatinine levels can be amazingly deceptive and are only a crude reflection of a patient’s glomerular filtration rate (GFR), the best overall measure of kidney function. A creatinine level of 1.0 mg/dL can indicate excellent renal function in a young male and reflect significant renal insufficiency in an older female. Serum creatinine levels should be interpreted with respect to age, sex, body mass, and race. An estimated GFR of less than or equal to 60 mL/min/1.73 m2 defines chronic kidney disease and is the most important risk factor for the development of contrast-induced nephropathy.1 A handy calculator for GFR, which requires only the creatinine value, age, race, and sex of the patient, can be found at www.kidney.org/kls/professionals/gfr_calculator.cfm and is also found on many personal digital assistants.

Dr. Abbuhl, Medical Director, Department of Emergency Medicine, The Hospital of the University of Pennsylvania; Associate Professor of Emergency Medicine, University of Pennsylvania School of Medicine, Philadelphia, is on the Editorial Board of Emergency Medicine Alert.

Reference

1. McCullough PA, Sandberg KR. Epidemiology of contrast-induced nephropathy. Rev Cardiovasc Med 2003; 4:S3-S9.