177 Solute Clearance in CRRT: Comparing Measured Effluent Volume to Actual Delivered Dose

Abstract

SOLUTE CLEARANCE IN CRRT: COMPARING MEASURED EFFLUENT VOLUME TO ACTUAL DELIVERED DOSE William Lyndon, Keith Wille, Ashita Tolwani University of Alabama at Birmingham, Birmingham, AL, U.S.A. Substantial efforts have been made towards defining the dose threshold of continuous renal replacement therapy (CRRT) associated with improved survival in critically ill patients with acute kidney injury. Published studies have based dose of CRRT on small solute clearance, expressed as total effluent volume (TEV) per weight and unit time (ml/kg/hr). These studies have not compared CRRT dose based on the measured TEV to the actual delivered dose as determined by direct quantitative measurement of the solute in the effluent. The purpose of this study was to determine whether the measured TEV corrected for pre-dilution replacement fluid (RF) accurately estimates actual delivered small solute clearance. We retrospectively analyzed data that had been prospectively collected for 200 patients enrolled in a randomized controlled trial comparing survival with a prescribed effluent rate of 20 ml/kg/hr (standard dose) to 35 ml/kg/hr (high dose) using pre-dilution continuous venovenous hemodiafiltration (CVVHDF). Filters were changed every 72 hours. Effluent urea nitrogen (EUN) and creatinine (ECr) levels, and TEV were obtained daily. Estimated effluent dose was defined as the TEV corrected for the pre-dilution effect of the RF. Actual delivered dose was calculated as: (EUN/BUN)*TEV for urea and (ECr/SCr)*TEV for creatinine. Complete data were available for 165 patients. The difference in actual delivered dose for the standard dose compared to the high dose group was statistically significant for both measured urea and creatinine clearances (p<0.0001). For the standard dose group, there was no difference between the estimated effluent dose and actual delivered urea and creatinine clearances. For the high dose group, estimated dose based on TEV differed significantly from both the delivered urea clearance by 7.1% (p<0.0001), and the creatinine clearance by 13.9 % (p<0.0001). Direct measurement of solute clearance is indicated if providing predilutional CVVHDF.