A nomogram approach to hemodialysis urea modeling.

Two sets of nomograms were developed for modeling hemodialysis urea kinetics. The first set is designed to arrive at an initial dialysis prescription. One nomogram estimates the mass transfer area coefficient (KoA) based on urea clearances of a dialyzer, based on urea clearances provided in the manufacturer's product literature. A second nomogram uses the dialyzer KoA value to estimate the expected in vivo urea clearance (K) based on the nominal blood flow rate. The computations include corrections for blood flow-related errors in urea clearance, blood water content, and cardiopulmonary recirculation. Mean urea clearance measured in a series of patients was 226 +/- 22 mL/min and did not differ significantly from mean clearance estimated using this nomogram (232 +/- 8 mL/min). Another pair of nomograms, based on an anthropometric formula, can be used to estimate urea distribution volume (V) from patient sex, height, and weight. The first set of nomograms is designed to estimate an initial dialysis prescription because the nomograms propose an estimated K and an estimated V. Once the target Kt/V is chosen, the appropriate initial treatment time (t) is computed algebraically. The second set of nomograms was developed to verify delivery of the dialysis prescription and to estimate the normalized protein catabolic rate (PCRn). Kt/V is estimated from the postdialysis to predialysis blood urea nitrogen ratio and the ratio of ultrafiltrate volume to postdialysis weight (UF/W). The PCRn is estimated from the predialysis blood urea nitrogen and Kt/V. In a series of 115 patients, Kt/V and PCRn determined from the nomograms correlated highly with corresponding values determined from formal urea modeling (r = 0.99).(ABSTRACT TRUNCATED AT 250 WORDS)