Urea kinetic modelling: new hemodialysis prescription procedure

The National Cooperative Dialysis Study (NCDS) showed the viability of the single-pool urea kinetic model (spUKM) to maintain the blood urea nitrogen (BUN) level of the renal patient in an adequate target interval, defining the single-pool normalized clearance of urea spKt/V as an index of the hemodialysis dose. However, the urea distribution is a nonuniform problem, due to the barriers between pools in the body distribution volume. The urea rebound induced by the hemodialysis is a consequence of this nonuniform distribution and limits the applicability of the NCDS. The viability of a more recent index, the equilibrated Kt/V (eKt/V), is being studied, because it is not affected by the urea rebound. This index is defined substituting the postdialysis BUN by equilibrated BUN (measured about an hour from the end of hemodialysis). In spite of its good results to calculate the hemodialysis dose in the presence of urea rebound, the eKt/V is unable to prescribe a hemodialysis, because the equilibrated clearance is different to the dialyzer clearance. We present a new hemodialysis prescribing procedure which calculates the adequate dialyzer clearance to obtain a target time averaged concentration of urea. This procedure is supported by a new model that we have developed: the normalized single-pool urea kinetic model (spUKM/sup norm/), which is able to calculate a good approximation to the real Kt/V based in dialyzer clearance. The eKt/V and spKt/V are used in intermediate steps of our procedure, and so the actual advances in these indexes can be taken into account.