R SLACK1, O YOUDELL1 R WALKER1,2, S WILSON1,2,3
1ALFRED HEALTH, Melbourne, Victoria; 2Monash University, Melbourne, Victoria 3 BAKER IDI, Melbourne, Victoria
Aim: To quantify and describe the effective clearance kinetics of solutes across both a single treatment and one-week of high-flux (HF) HD.
Background: Contemporary understanding of HD solute clearances is drawn from low-flux hollow-fibre dialyser data. HF HD clears solute by both diffusive and convective means, abrogated to some extent by back-filtration. In the era where HF HD is convention, differential clearance dynamics of common solutes is uncharacterised –particularly the degree of variation across 1-week of HD.
Methods: Prospective observational study (n=9) sampling aliquots of post-dialyser effluent at 30-minute intervals across three sequential HD (2.2m2 HF membranes, Qd 500ml/min, mean HD time 4.5hours). Samples were analysed using Abbot Archicentre ci16200 after validation against fluid of known composition. Time-series modelling of solute clearance was undertaken on aggregate and at an intra-individual level.
Results: Cumulative proportion of total dialytic clearance per-hour was similar across each solute with mean (+SEM) of 37 + 2%, 63 + 2.5%, 84+1% across the first three treatment hours respectively. Removal closely followed an exponential decay regression model with median post-log transformation Pearson-coefficients below -0.75 for all solutes (p<0.01). Total estimated clearance strongly correlated with serum level preHD (median Pearson-R 0.73 (p<0.01)) and more modestly with ultrafiltration rates for creatinine, urea and phosphate (median Pearson-R 0.52 (p<0.01)). Effective equilibration fraction from serum into first dialysate sample differed across solutes but did not exceed 45% and did not correlate to ultrafiltration or blood-flow rate. Absolute levels of clearance across the first and third HD of the week were significantly different for urea and phosphate only (p<0.01).
Conclusions: We provide the first detailed time-series analysis of in-vivo HF HD solute clearance dynamics using timed effluent aliquot sampling.