Abstract: Objective   The amount of liquid remaining in the dialyzer and blood purification pipeline is variable with different drainage methods. This study investigated the evacuation effect of different drainage methods on residual waste volume in the dialyzer and blood purification pipeline after the treatment of hemodialysis patients, and explored the safest and effective drainage method to reduce the risks of environmental pollution and infection.  Methods  The dialyzers and blood purification tubes after hemodialysis of 200 cases were selected. In the experimental group, the dialyzers with the drainage method of negative pressure plus positive pressure (blood pump) guided by the manufacturers were used for 150 cases, who were then divided into 3 subgroups (50/each subgroup); positive pressures were provided by the blood pump of 100ml/min, 200ml/min and 300ml/min for the 3 subgroups respectively. In the control group, the dialyzers with the drainage method of negative pressure plus gravity guided by the manufacturers were used for 50 cases. The transmembrane pressure during drainage, drainage time, and residual waste volume (gram) in dialyzer and blood purification pipeline after drainage were compared between experimental group and control group and among the 3 subgroups in the experimental group.  Results   In the experimental group, the evacuation time was shorter (blood pump speed 200ml/min: 1.48 vs. 2.22 min, Z=6.598, P＜0.001; 300ml/min: 0.49 vs. 2.22 min,            Z=10.920, P＜0.001), and the residual waste volume after drainage was lower (blood pump speed 100ml/min: 90.9 vs. 136.4g, Z=8.202, P＜0.001; 200ml/min: 88.9 vs. 136.4 g, Z=8.888, P＜0.001; 300ml/min: 91.9 vs. 136.4 g, Z=7.894, P＜0.001), as compared with those in the control group. In the control group, the transmembrane pressure during drainage was within the safety range not causing membrane rupture set by the manufacturers, and the transmembrane pressure was lower than that in the experimental group (blood pump speed 100ml/min: 359.5 vs. 457.5 mmHg, Z=-3.965, P＜0.001; 200ml/min: 359.5 vs. 476.0 mmHg, Z=-6.945, P＜0.001; 300ml/min: 359.5 vs. 487.5 mmHg, Z=-9.498, P＜0.001). In the subgroup of blood pump speed 300ml/min in the experimental group, the instant transmembrane pressure exceeded the maximal safety value of 500mmHg set by the manufacturers, leading 10% risk of membrane rupture; in the subgroup of blood pump speed 200ml/min, the transmembrane pressure during drainage was within the safety range, and the evacuation time was shorter than that in the 100m/min subgroup, being the safest and efficient drainage pump speed (1.48 vs. 2.21min, Z=6.359, P＜0.001).  Conclusion  Compared with the dialyzers using negative pressure and gravity as the drainage method, the dialyzers using negative pressure and positive pressure (blood pump) as the drainage method had the advantages of shorter evacuation time and lower residual waste volume when the drainage pump speed was set within the pressure not breaking the membrane.

Key words: Negative pressure and gravity drainage, Negative pressure and positive pressure drainage, Transmembrane pressure