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Comparison of solute clearance in three modes of continuous renal replacement therapy

Parakininkas, Daiva MD; Greenbaum, Larry A. MD, PhD

Pediatric Critical Care Medicine: May 2004 - Volume 5 - Issue 3 - p 269-274
doi: 10.1097/01.PCC.0000123554.12555.20
Laboratory Investigation

Objectives: To compare the clearances of low molecular weight molecules using three modalities of continuous renal replacement therapy (CRRT) at the low blood flow rates typically used in pediatric patients.

Design: A controlled, in vitro laboratory study.

Setting: Research laboratory of a health sciences university.

Subjects: AN69 dialysis hemofilter.

Interventions: CRRT was performed using a 0.6 m2 AN69 hemofilter. Human whole blood and plasma were combined to achieve a hematocrit of approximately 30%. Urea and creatinine were added to obtain concentrations of approximately 54 mmol/L of blood urea nitrogen and 1770 μmol/L of creatinine. Clearance data for urea and creatinine at a blood flow rate of 60 mL/min were generated using predilution continuous venovenous hemofiltration (CVVH), postdilution CVVH, and continuous venovenous hemodialysis (CVVHD).

Measurements and Main Results: Clearance of all three modalities was compared at a replacement solution (CVVH) or dialysate (CVVHD) flow rate of 16.7% of the blood flow rate. Both postdilution CVVH and CVVHD had a urea clearance of 11.3 mL/min, which was 15% greater than the 9.8 mL/min urea clearance of predilution CVVH (p < .005). Creatinine clearance with postdilution CVVH (10.7 mL/min) was 15% greater than the 9.0 mL/min clearance produced by predilution CVVH (p < 0.01). Predilution CVVH and CVVHD were compared at a flow rate of either replacement solution (CVVH) or dialysate (CVVHD) of 33% and 50% of the blood flow rate. Postdilution CVVH was not performed at high ultrafiltration rates due to the potential problem of hemoconcentration. CVVHD clearances of urea and creatinine were statistically superior to predilution CVVH at both flow rates.

Conclusions: CVVHD was superior to predilution CVVH for clearance of urea and creatinine. Postdilution CVVH and CVVHD gave nearly equivalent clearances. At the low blood flow rates used in pediatric patients, which raise concerns about high ultrafiltration during postdilution CVVH causing excessive hemoconcentration and filter clotting, CVVHD appears to be the optimal modality for maximizing clearance of small solutes during CRRT.

From the Division of Pediatric Critical Care (DP) and Division of Pediatric Nephrology (LAG), Medical College of Wisconsin, Milwaukee, WI.

Supported, in part, by grants from the Children’s Hospital of Wisconsin Foundation, the Elaine C. Kohler Fund for Healing, and the Steigleder Fund.

Address requests for reprints to: Larry A. Greenbaum, MD, PhD, Medical College of Wisconsin, Department of Pediatrics, 8701 Watertown Plank Rd., Milwaukee, WI 53226. E-mail:

©2004The Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies