Dialysis and Patient Factors Which Determine Convective Volume Exchange in Patients Treated by Postdilution Online Hemodiafiltration.

Recent reports suggest a survival advantage for dialysis patients treated by postdilutional online hemodiafiltration (OL-HDF) who achieve higher volume convective exchanges. As such, the factors associated with achieving higher convective volume exchange were determined. The convective exchange volumes during the midweek OL-HDF session in a cohort of 653 patients with corresponding bio-impedance measurements of volume status and sessional electronic records were audited. Mean patient age was 64.9 ± 14.9 years, 65.3% male, 47.7% diabetes, with 81.6% dialyzing using fistula access. Sessional substitution volume exchanged was 17.0 ± 3.5 L (83.8 ± 13.9 mL/min), with a filtration fraction of 23.3 ± 4.6%, sessional time of 3.8 ± 0.5 h, and blood flow 321 ± 28 mL/min. As expected, convection exchange volume achieved was associated with sessional time (β 3.24, P < 0.001), blood flow (β 0.03, P < 0.001), dialysate flow (β 0.03, P < 0.001), but also patient factors: postsessional intracellular water (ICW) (β 0.07, P = 0.002), and serum albumin (β 0.71, P = 0.011). In addition convective exchange was lower for diabetics (16.6 ± 3.0 vs. 17.3 ± 3.8 L, P < 0.01), and for patients with higher Davies co-morbidity grades (16.6 ± 2.8 vs. 17.0 ± 3.6 vs. 17.9 ± 4.0 L), P = 0.01 respectively. As expected the convective volume exchanged with OL-HDF was associated with sessional time and blood and dialysate flows. However, the convective volume exchange achieved was also associated with patient factors, including ICW, which is related to body cell mass and also co-morbidity. Although some center practices can be modified to increase convective exchange, patient factors are not so readily remediable. As such, highly comorbid patients may not be able to achieve the higher volume convective exchanges reported to be associated with improved patient survival.