Continuous Blood Volume Monitoring and Ultrafiltration Control.

Continuous blood volume monitoring (CBVM) is believed to be a promising method for making the determination of patients' "dry weight" more objective, and ultrafiltration (UF) control more appropriate. Although blood volume response to UF and the interrelation between blood volume changes and changes in hemodynamic parameters are highly individual, certain principles of this response and interrelation can be identified and exploited for effective use of CBVM. The present work summarizes the authors' findings from practical CBVM application over the past 5 years and their opinions on the future development of this method. Four distinct types of blood volume response to constant UF rate were identified: Type 1, flat line throughout the whole session; Type 2, flat line during the first part of dialysis, followed by a linear decrease during the remaining time; Type 3, linear decrease right from dialysis start; and Type 4, linear decrease first, followed by a flat line during the remaining time. The possibility of a shift from one type to the other was verified. Blood volume reduction due to UF was found to have a static and a dynamic component. The most important factors affecting both components were found to be, by sensitivity analysis of a three-pool kinetic model, degree of overhydration, vascular system compliance, and UF volume (for the static component); and UF coefficient of the capillary wall and UF rate (for the dynamic component). Type 3 response, induced by more vigorous UF, was found to significantly decrease the volume of residual daily diuresis on the first postdialysis day. If confirmed, this finding may serve as a basis for the response type choice in patients with still significant residual renal function. Exploitation of the existence of dynamic blood volume reduction component for the first generation of automated biofeedback UF controllers may be complemented by automated identification of patient's plasma refilling capacity and/or position of his/her point on the Guytonian pressure/volume characteristics curves, and thus may more advanced "intelligent" UF controllers be constructed in the future.