Research

Solute removal during continuous renal replacement therapy in critically ill patients: convection versus diffusion

Zaccaria Ricci¹ , Claudio Ronco² , Alessandra Bachetoni³, Giuseppe D'amico⁴, Stefano Rossi⁴, Elisa Alessandri¹, Monica Rocco¹ and Paolo Pietropaoli⁵

¹Department of Intensive Care, Policlinico Umberto I, Rome, Italy

²Department of Nephrology, Dialysis and Transplantation, St Bortolo Hospital, Vicenza, Italy

³Laboratory of Clinical Chemistry, Policlinico Umberto I, Rome, Italy

⁴Department of Intensive Care, Policlinico Umberto I, Rome, Italy

⁵Department of Intensive Care, Policlinico Umberto I, Rome, Italy

author email corresponding author email

Critical Care 2006, 10:R67doi:10.1186/cc4903

Published:	28 April 2006

Abstract

Introduction

The best modality, for continuous renal replacement therapy (CRRT) is currently uncertain and it is poorly understood how transport of different solutes, whether convective or diffusive, changes over time.

Methods

We conducted a prospective cross over study in a cohort of critically ill patients, comparing small (urea and creatinine) and middle (β₂ microglobulin) molecular weight solute clearance, filter lifespan and membrane performance over a period of 72 hours, during 15 continuous veno-venous dialysis (CVVHD) and 15 continuous veno-venous hemofiltration (CVVH)sessions. Both modalities were administered based on a prescription of 35 ml/kg/h and using polyacrylonitrile filters.

Results

Median filter lifespan was significantly longer during CVVHD (37 hours, interquartile range (IQR) 19.5 to 72.5) than CVVH (19 hours, IQR 12.5 to 28) (p = 0.03). Median urea time weighted average (TWA) clearances were not significantly different during CVVH (31.6 ml/minute, IQR 23.2 to 38.9) and CVVHD (35.7 ml/minute, IQR 30.1 to 41.5) (p = 0.213). Similar results were found for creatinine: 38.1 ml/minute, IQR 28.5 to 39, and 35.6 ml/minute, IQR 26 to 43 (p = 0.917), respectively. Median β₂m TWA clearance was higher during convective (16.3 ml/minute, IQR 10.9 to 23) than diffusive (6.27 ml/minute, IQR 1.6 to 14.9) therapy; nonetheless this difference did not reach statistical significance (p = 0.055). Median TWA adsorptive clearance of β₂m appeared to have scarce impact on overall solute removal (0.012 ml/minute, IQR -0.09 to 0.1, during hemofiltration versus -0.016 ml/minute, IQR -0.08 to 0.1 during dialysis; p = 0.79). Analysis of clearance modification over time did not show significant modifications of urea, creatinine and β₂m clearance in the first 48 hours during both treatments. In the CVVHD group, the only significant difference was found for β₂m between 72 hours and baseline clearance.

Conclusion

Polyacrylonitrile filters during continuous hemofiltration and continuous hemodialysis delivered at 35 ml/kg/h are comparable in little and middle size solute removal. CVVHD appears to warrant longer CRRT sessions. The capacity of both modalities for removing such molecules is maintained up to 48 hours.