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

While the solute clearance marker ( Kt / V urea ) 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 m L /kg/hour) and (2) the rate of intravascular volume contraction where coronary hypoperfusion, myocardial stun, and vascular risk escalates (observed at ≥10 m L /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 m L /kg/hour, acknowledging that this may be challenging in the in‐center setting. Two options exist to limit volume removal to >10 m L /kg/hour: restricting interdialytic weight gain (always conflict‐fraught, often unachievable) or extending sessional duration to allow additional removal time. Just as Kt / V urea 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 ( UFR max )—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 m L /kg/hour— T (hours) =  V (mL)/10 ×  W (kg). Used together, Kt / V urea and UFR max would form a solute and volume composite, each dialysis treatment continuing until both solute and volume requirements are fulfilled.