Renal effects of bicarbonate versus saline infusion for iso- and lowosmolar contrast media in rats

Hydration is widely accepted as an effective measure to prevent contrast media (CM)-induced acute kidney injury (AKI). Whether bicarbonate (NaHCO₃) infusion has a greater effect than saline is disputed. Effective prevention of CM-induced AKI by NaHCO₃ has been found by several clinical trials. However, others found either no effect or an enhanced incidence of CM-induced AKI after giving NaHCO₃. Because of their different tubular resorption, NaHCO₃ and saline may have a different capacity to flush the nephron. In this study, we compare the magnitudes by which NaHCO₃ and saline can enhance urinary flow, prevent a decline in glomerular filtration rate (GFR), and limit an increase in urine viscosity, as caused by CM administration.

Prewarmed (37°C) CM were administered as 1.5 mL bolus into the thoracic aorta of anesthetized rats. Following 2 CM were studied: iso-osmolar iodixanol (320 mg I/mL) and low-osmolar iopromide (370 mg I/mL). Four protocols (n = 7 rats per protocol) were followed: (1) saline + iodixanol, (2) saline + iopromide, (3) NaHCO₃ + iodixanol, and (4) NaHCO₃ + iopromide. Isotonic saline or NaHCO₃ were infused at a rate of 4 mL/h per kg BM, initiated 60 minutes before CM administration and continued throughout the observation period of 100 minutes. Urine volume was measured gravimetrically, urine viscosity was measured by a microviscometer, and GFR was determined by creatinine clearance.

As compared with saline infusions, NaHCO₃ infusions did not significantly alter the effects that iodixanol and iopromide exerted on urine flow rate, urine viscosity, and GFR. In the iopromide protocols, CM-induced increase in urine flow was about 50% greater than in the respective iodixanol protocols. Conversely, in the iodixanol protocols, urine viscosity was up to 10-fold greater than in the respective iopromide protocol. In the iodixanol protocols, GFR decreased transiently (10-30 min post-CM) by up to 50%, whereas GFR did not decrease in the iopromide protocols.

Infusing either saline or NaHCO₃ seems to make little difference with regard to urine flow, urine viscosity, and GFR. However, the CM used has a significant effect on these measures. Iopromide enhances urine flow by a greater magnitude than iodixanol, whereas the latter increases urine viscosity to a larger degree than iopromide and transiently decreases GFR.