Importance of Body Water in the Efficacy of Convective Solute Transport in Online Hemodiafiltration

High‐volume online hemodiafiltration (OL‐HDF) has been associated with improved patient survival compared to conventional hemodialysis in recent trials, where the importance of convective volume (CV) in this benefit is noted. The purpose of this study was to determine the corporal composition parameters influencing the efficacy of CV in the removal of different molecular weight (MW) molecules. Demographic data, corporal composition parameters with bioimpedance spectroscopy, dialysis features and the reduction rates of different MW molecules in a four‐hour OL‐HDF session were collected in 61 patients. We observed a significant negative correlation of β2‐microglobulin, cystatin‐C, myoglobin and prolactin reduction rates with body surface area, weight, total body extracellular (ECW) and intracellular water (ICW), lean tissue mass and body cellular mass. The multivariable regression analysis identified ECW and ICW as the only corporal composition factors independently associated to the relative elimination of β2‐microglobulin (Beta: –0.801, P = 0.002 for ECW and Beta: –1.710, P = 0.001 for ICW), cystatin‐C (Beta: –0.656, P = 0.010 for ECW and Beta: –1.511, P = 0.004 for ICW) and myoglobin (Beta: –0.745, P = 0.014 for ECW and Beta: –2.103, P = 0.001 for ICW), in addition to CV. Prolactin reduction was only associated with ICW (Beta: –1.540, P = 0.028). When adjusting CV with ECW and ICW, only the ratio CV/ECW was an independent predictor for higher elimination of β2‐microglobulin, cystatin‐C and myoglobin. The corporal composition parameters independently associated to the reduction of medium‐sized molecules are the extracellular and intracellular water. The ratio “convective volume/extracellular water” predicts higher efficacy of convective transport. Adjusting the convective volume to patient features could be useful to monitor the efficacy of OL‐HDF and to prescribe individualized therapies.