COMPARATIVE-EVALUATION OF DIFFERENT METHODS TO ESTIMATE UREA DISTRIBUTION VOLUME AND GENERATION RATE

Eight methods to estimate urea distribution volume and generation rate from blood urea samples measured in dialysis patients are reviewed. A n analytical solution has been provided for a double-pool variable vol ume kinetic model to allow for faster and more accurate simulation and identification. The reliable parameter estimates provided by the doub le-pool kinetic model starting from seven samples, were assumed as ref erences for the estimates obtained by the remaining methods. These inc lude three kinetic models and four methods based on urea mass-balance. In particular, the estimation techniques differ in the number of comp artments where urea is assumed distributed (double- and single-pool) o r in the number of blood urea samples. Among the methods based on mass -balance, two techniques neglecting the weight loss or the urea genera tion during dialysis, were also analysed. The results obtained during hemofiltration sessions using three samples, usually available in clin ical practice at the beginning and at the end of dialysis, demonstrate that a new method based on double-pool kinetics provides, on average, the most reliable estimates. Moreover, methods belonging to a single pool view and including both weight loss and urea generation during di alysis seem to underestimate by 1 divided by 2 liters the urea distrib ution volume. However, neglecting the weight loss or the urea generati on can overcompensate this error, resulting in a significant overestim ation of the distribution volume. Finally, it;has been experimentally proved that the single-pool kinetic methods overestimate the urea prod uction rate, while techniques based on mass balance provide more relia ble values.