Differences in chamber structure contribute to the incidence of venous air trap chamber coagulation during AN69ST-CHF: clinical and in vitro evaluation

Background: During continuous kidney replacement therapy (CKRT) in patients with sepsis and critical conditions, circuit coagulation can occur, often for unclear reasons. In this study, we investigate how the structure of the venous air trap chamber may contribute to venous air trap chamber coagulation. Clinical data were evaluated and experiments were performed. Methods: The clinical evaluation involved patients who underwent continuous hemofiltration (CHF) using an acrylonitrile-co-methallyl sulfonate surface-treated (AN69ST) hemofilter (AN69ST-CHF) and either an ACH-Σ or Prismaflex CKRT machine in our ICU from April to July 2019. The patient data were divided into two groups based on CKRT machine and the percentage of CHF procedures that could continuously be performed for 22 h (CHF target achievement rate), and coagulation sites were evaluated. Statistical analysis was performed by the Mann–Whitney U test and Pearson’s chi-square test. For in vitro experiments, a system was constructed to circulate a 33% glycerol solution at a flow rate of 150 ml/min. In a venous air trap chamber, fluid dye disappearance times and fluid movements were visually evaluated. Results: The clinical evaluation included 22 procedures (8 patients) in the ACH-Σ group and 22 procedures (11 patients) in the Prismaflex group, without significant differences in patient backgrounds between the groups. The CHF target achievement rate was 72.7% (16/22) in the ACH-Σ group and 77.3% (17/22) in the Prismaflex group, revealing no significant difference (p = 0.73). However, significantly fewer venous air trap chamber coagulations were observed in the Prismaflex group (1/5) than in the ACH-Σ group (5/6) (p < 0.01). In vitro evaluation found that the dye disappearance time was significantly shorter when using the Prismaflex device (17.5 s ± 0.7 s) than the ACH-Σ device (51.2 s ± 0.7 s; p < 0.05). Visual evaluation revealed that in the ACH-Σ venous air trap chamber the upper layer of the accumulated fluid was quite stagnant, whereas fluid flowed with uniform agitation through the Prismaflex venous air trap chamber. Hence, differences were observed in fluid flow and retention in the vein air trap chambers, depending on the chamber structure. Conclusion: Chamber structure may contribute to the occurrence of venous air trap chamber coagulation during CKRT.