【Abstract】 Objective To investigate the related factors for blood pressure changes in hemodialysis patients, and to measure central blood volume (CBV) by ultrasound dilution method for the prevention of hypotension and the adjustment of dry body weight during dialysis. Methods Sixty patients were assigned in 3 groups based on their previous blood pressure in patients’ dialysis records: high blood pressure (HBP) group, low blood pressure (LBP) group and normal blood pressure (NBP) group. CBV, cardiac output (CO), cardiac index (CI), and peripheral vascular resistance (PVR) were examined by ultrasound dilution method during the dialysis at one hour and 3 hours. Results In the 60 patients, CO (-12.3±15.8%), CI (-18.2±21.0%) and CBV (-0.12±0.16%) were significantly decreased (p＜0.01), but without significant changes in blood pressure and PVR. However, the decreases of CO, CI and CBV were only detected in LBP group but not in HBP and NBP groups. In a dialysis session, change of CBV was positively correlated with that of CO (r=0.648, P＜0.001), and was negatively correlated with changes of PVR (r = -0.487, P＜0.001) and ultrafiltration volume (r = -0.524, P＜0.005). By using CBV to monitor patient’s dry body weight in 101 dialysis sessions for 10 hypertension patients and 10 hypotension patients, we observed normal blood pressure during and after dialysis sessions. Conclusions CBV is a useful marker for circulating blood volume. During a dialysis session, the decrease of CBV reflects the decrease of extracellular fluid, and is also related to hypotension. CBV correlates positively with CO, and negatively with PVR and ultrafiltration volume. Blood pressure change positively correlates with the change of heart rate. In the 3 groups, factors relating to PVR change are uncertain. By measuring CBV, CO and CI using ultrasound dilution method before and after a dialysis session, we can estimate the appropriate ultrafiltration volume and dry body weight, and perform the dialysis under a normal and stable blood pressure condition.