Personal viewpoint: Limiting maximum ultrafiltration rate as a potential new measure of dialysis adequacy

While the solute clearance marker (Kt/Vurea ) is widely used, no effective marker for volume management exists. Two principles apply to acute volume change in hemodialysis: (1) the plasma refill rate, the maximum rate the extracellular fluid can replace a contracting intravascular volume (±5 mL/kg/hour) and (2) the rate of intravascular volume contraction where coronary hypoperfusion, myocardial stun, and vascular risk escalates (observed at ≥10 mL/kg/hour). In extended hour and higher frequency hemodialysis, intravascular contraction rates are usually equilibrated by the plasma refill rate, but in "conventional" in-center hemodialysis, volume contraction rates commonly exceed the capabilities of the plasma refill rate, resulting in inevitable hypovolemia. To minimize cardiovascular risk, fluid removal rates should ideally be ≤10 mL/kg/hour, acknowledging that this may be challenging in the in-center setting. Two options exist to limit volume removal to >10 mL/kg/hour: restricting interdialytic weight gain (always conflict-fraught, often unachievable) or extending sessional duration to allow additional removal time. Just as Kt/Vurea quantifies solute removal, a simple-to-apply rate variable should also apply for volume removal. As predialysis and target postdialysis weights are both known, a simple measure--a maximum rate for ultrafiltration (UFRmax )--would advise the sessional duration (T) required to minimize organ stun by removing the required fluid load (V) from any patient of predialysis weight (W). This would ensure a removal rate no greater than 10 mL/kg/hour-T (hours) = V (mL)/10 × W (kg). Used together, Kt/Vurea and UFRmax would form a solute and volume composite, each dialysis treatment continuing until both solute and volume requirements are fulfilled.