How dialysis frequency and duration impact uremic toxin and fluid removal: a pediatric perspective

Three-weekly 4-h hemodialysis/hemodiafiltration (HD/HDF) per week has become the "standard HD/HDF" regimen in children across the globe, although increasingly criticized, since crucial determinants such as residual kidney function and patient preferences are not considered. As a consequence, several children fail to achieve adequate dialysis while on a "standard HD/HDF." In these circumstances, an extended dialysis prescription such as short daily (2-3 h/session, 5-7 days a week) or nocturnal HD/HDF (6-9 h/session, 3-5 days a week), either at home or in a dialysis center, may be considered. The purpose of this educational review is to summarize the impact of dialysis duration and frequency on uremic toxin and fluid removal. Moreover, we aim to summarize the existing literature on HD/HDF strategies with extended dialysis duration and/or increased frequency (> 12 h dialysis time per week) in pediatrics. Dialysis duration and frequency plays a crucial role in uremic toxin removal, in particular for uremic toxins with retarded transport in patients, such as phosphate, β₂-microglobulin (β₂m), and protein-bound uremic toxins. Also, increasing dialysis duration and/or frequency decreases the gap between plasma refilling and ultrafiltration volume), thereby decreasing the need for a high ultrafiltration rate. Observational studies in children demonstrate a beneficial effect of extended dialysis regimens (i.e., more frequent or longer duration) on blood pressure control, left ventricular hypertrophy, growth, and quality of life. PTH levels tend to decrease in the majority of studies, while hypocalcemia or suppressed PTH levels were also reported. Dietary restrictions were decreased or stopped, along with tapering of phosphate binders and potassium chelators. Extended HD/HDF regimens are beneficial in a particular group of children. Pediatric-specific international guidelines are needed to support pediatric nephrologists in determining for which children extended HD regimens are beneficial, along with increasing efforts to decrease the financial, organizational, and psychosocial barriers that are present in extended HD/HDF.