K & T covariate with V in hemodialysis. As K increases and T decreases, V also decreases.

The authors varied urea clearance (K), dialysis time (T), and ultrafiltration (UF) in 294 hemodialyses on 23 patients and studied changes in urea space (V), determined by total dialysate urea removal. As K increased and UF and T decreased, V also decreased. K, T, and V, thus, covariate and dialysis adequacy, as studied by KT/V is not a simple function of three independent variables. Patients dialyzed quickly with little UF will need a higher KT/V than those dialyzed slowly with much UF.