Intradialytic hypotension occurred in about 20 to 30% of treatments. Therefore, it is important to observe the variation of intravascular volume and blood pressure to prevent intradialytic hypotension during hemodialysis (HD). In this study, we constructed a mathematical model to understand the variation of intravascular volume in HD patients. Then, we examined the validity of the model. By applying this model, we proposed a method for identifying patients in need of pharmacotherapy to prevent intradialytic hypotension during HD. In 14 patients with end-stage renal disease (ESRD), we measured the variation of intravascular volume through blood volume monitoring (BVM) during HD. Then, we estimated the water movement rate, r, and the maximum excess volume in extravascular, VO. max, using nonlinear least-squares method. The relation of the mathematical model and the BVM value showed a high correlation. The correlation coefficient R (=0.95) could be used to detect patients in need of observation. Further, the relation of the maximum excess volume in extravascular, VO. max, and difference between body weight and dry weight showed also a high correlation. The model expressed correctly the variation of the intravascular volume. The correlation coefficient R of the mathematical model and the BVM value and the maximum excess volume in extravascular, VO. max were important parameters to manage HD. We proposed the mathematical model and new index to control HD efficiently.
