Use of Fluoride as a Marker Solute to Quantify the Current Effective Delivered Dose in Continuous Renal Replacement Therapy: An "in vitro" Study

Abstract

Background: The current effective delivered dose is a quality indicator for continuous renal replacement therapy. Its periodic assessment might enable physicians to deliver personalised treatments. Yet, its quantification as by extracorporeal urea clearance (Cl) is cumbersome and thus often neglected in routine practice. The aim of this in vitro study is to demonstrate the non-inferior effectiveness of assessing the current effective delivered dose using a simpler, cheaper and faster approach based on measurement of fluoride rather than urea extracorporeal Cl.

Methods: We compared urea and fluoride removal in 3 post-dilution continuous veno-venous haemofiltration (CVVH) and 3 continuous veno-venous haemodialysis (CVVHD) in vitro experimental models. Experiments ran for 180 min, using 3 L of human blood, heparin anticoagulation and a machine dose of 30 mL/kg/h. Urea and fluoride were measured in the inflow, outflow and effluent lines to compare sieving coefficients (SC), saturation coefficients (SA) and transmembrane Cls.

Results: In CVVH, the median SC values were 1.06 (1.02-1.07) and 1.02 (1.01-1.04) for fluoride and urea, respectively (discrepancy of 4.3%), while transmembrane convective Cls were 31.28 (30.01-31.31) mL/kg/h and 30.30 (29-31.85) mL/kg/h (discrepancy of 3.13%), respectively. In CVVHD, the median SA values were 1.01 (0.96-1.02) and 1 (0.95-1.01) for fluoride and urea, respectively (discrepancy of 1.6%), while transmembrane dialytic Cls were 30.26 (29.52-31.32) mL/kg/h and 31.16 (30-31.75) mL/kg/h (discrepancy of -2.97%), respectively.

Conclusion: Fluoride transmembrane removal was close to that observed with urea, in terms of SC, SA and transmembrane Cl. Fluoride seems as much accurate as urea in assessing the current effective delivered dose during both CVVH and CVVHD and might therefore be adopted for dose measurement. Besides accuracy, fluoride bedside assessment could present many advantages over urea, particularly in terms of availability, costs, time requirement and rapidity of assessment.

Keywords: Haemodialysis; Haemofiltration; Mass balance error; Saturation coefficient; Sieving coefficient; Urea.