Abstract: Objective  Through online clearance monitoring (OCM), the quantitative relationship among the changes of urea clearance (K), its influencing factors and dialysis adequacy during dialysis processes are discussed.  Methods   A total of 152 maintenance hemodialysis patients were investigated. The K value during a hemodialysis session was recorded by OCM every hour. ANOVA of repeated measurements was used to explore the rule of K change during hemodialysis. Multivariate linear regression was used to explore the influencing factors for average K value. Results  The K value decreased linearly with time during a hemodialysis session (F=447.552, P＜0.001 ). The K value was positively correlated with blood flow rate (BFR) (β=0.706, 95% CI：0.403～0.526, P＜0.001) and ultrafiltrate coefficient (β=0.183, 95% CI：0.074～0.223, P＜0.001), and was negatively correlated with haematocrit (HCT) (β=-0.242, 95% CI：-0.877～-0.405, P＜0.001) and age (β=-0.106, 95% CI：-0.209～-0.011, P=0.030). We also found that there was a significant correlation between the difference of K value and three times of dry body weight and the dialysis adequacy of Kt/V (Pearson correlation analysis, r=0.808, P＜0.001).  Conclusion   The K value decreases linearly and slowly during a hemodialysis session. The ways to increase K value include the increase of BFR, the use of high-flux dialyzer, and the maintenance of HCT within 33～36%. We infer that the K value should be more than three times of the dry body weight to obtain a standard level of dialysis adequacy.

Key words: Urea clearance, Dialysis sufficiency, Online clearance monitoring, Dialysis session length, Dry body weight