Abstract: Objective To explore the significance of blood pressure at specific time points during dialysis sessions in maintenance hemodialysis (MHD) patients, we compared the body fluid distribution measured by multi-frequency bio-electrical impedance before and after dialysis with the blood pressure at several time points during dialysis sessions. Methods The human body composition analyzer was used to record body fluid distribution before and after dialysis in 74 MHD patients. Blood pressure was measured at several time points including clinic blood pressure, blood pressure after recumbent position for 5 minutes, after 0 minutes, one hour and 2 hours in dialysis sessions, and after completion of dialysis for 30 minutes. The relationship between blood pressure values and body fluid distribution was analyzed by using Spearman correlation method. Results ①Systolic blood pressure (SBP) was the highest before dialysis, and reduced gradually to the lowest after 3 hours in dialysis sessions. SBP then increased after completion of dialysis for 30 minutes, when the blood pressure value ranged between the values after 0 hour and one hour in dialysis sessions. ②Before dialysis, TBW, ECW, ICW, and overhydration (OH) values were significantly correlated with the SBP after 2 hour in dialysis sessions (r=0.248, P= 0.033 for TBW; r=0.251, P=0.031 for ECW; r=0.233, P=0.046 for ICW; r= 0.233, P=0.046 for OH), were significantly correlated with the diastolic pressure after the completion of dialysis for 30 minutes (r=0.305, P=0.008 for TBW; r=0.244, P=0.036 for ECW; r=0.265, P= 0.023 for ICW; r= 0.218, P=0.023 for OH), but had no correlations with the clinic blood pressure, blood pressure after recumbent position for 5 minutes, dialysis for 0 minutes and one hour, and the diastolic pressure after 2 hours in dialysis sessions (P>0.05). ③After dialysis, TBW, ECW, ICW and OH were significantly correlated with the diastolic pressure after the completion of dialysis for 30 minutes (r=0.286, P=0.014 for TBW; r=0.283, P=0.015 for ECW; r=0.239, P=0.040 for ICW; r=0.284, P=0.014 for OH); TBW, ECW and OH were significantly correlated with the SBP after the completion of dialysis for 30 minutes (r=0.230, P=0.049 for TBW; r=0.240, P=0.039 for ECW; r =0.380, P=0.001 for OH); TBW, ECW and ICW were significantly correlated with the SBP after 2 hour in dialysis sessions (r=0.321, P=0.005 for TBW; r=0.287, P=0.013 for ECW; r=0.264, P=0.264 for ICW). Conclusions ①It will be misjudged if only the clinic blood pressure, blood pressure after recumbent position for 5 minutes, and the blood pressure just before dialysis sessions are used to determine the capacity load. ②The blood pressure after 2 hours in dialysis sessions should be closely monitored, and is helpful for timely and accurate adjustment of ultrafiltration volume. ③The blood pressure after completion of dialysis for 30 minutes will be better to reflect the patients' capacity load.

Key words: Multi-frequency bioimpedance analysis, Different time point, Blood pressure, Hemodialysis