Impact of Residual Kidney Function on Convection Volume Targets in Hemodiafiltration.

BACKGROUND: Adoption of Haemodiafiltration is increasing as the preferred modality of haemodialysis. Current haemodiafiltration practice relies on achieving 'High Convection Volume' (HiCV) (≥23 Litres or ≥21L/1.73m2 Body surface area) without individualisation. Enhanced clearance of middle molecules such as β2Microglobulin (β2M) may be a driver of the benefits attributed to haemodiafiltration. Understanding the relationship of convection volume with β2M removal and the impact of residual kidney function on this relationship could allow individualisation of haemodiafiltration based on residual kidney function. METHODS: We examined the relationships of delivered convection volume, pre-dialysis and post-dialysis β2M levels and β2M reduction ratio (β2M-RR) in 274 adults receiving maintenance hemodiafiltration in relation to a single dialysis session. We also evaluated the impact of residual kidney function on these relationships. Residual kidney function was estimated as glomerular filtration rate (GFR) - the average of urea and creatinine clearances obtained from interdialytic urine collections. RESULTS: Pre-dialysis β2M had no relationship with convection volume and was determined largely by GFR. Post-dialysis β2M and β2M-RR were closely related to delivered convection volume (Adjusted R2 0.545 and 0.561 respectively, p < 0.001). Body surface area adjusted HiCV related better to β2M removal parameters than unadjusted HiCV. The strength of association between HiCV and post-dialysis β2M and β2MRR was higher at lower GFR and was maximum in anuric patients. At GFR >2ml/min the relationship between HiCV and β2M removal parameters was not statistically significant. β2MRR level corresponding to HiCV was ≥75%, for post-dialysis β2M it was ≤7.5 mg/L in anuric and ≤5.5 mg/L in uric patients. Achieving HiCV or equivalent β2M levels ensured achieving minimum target urea clearance (spKt/Vurea >1.2). CONCLUSIONS: Achieving HiCV was most impactful in removing β2M in anuric patients. Impact was less at GFR > 2ml/min. This suggests the prospect of individualising convection volume based on residual kidney function.