Supplementary Material for: Venous Chamber Design: A Comparative Analysis of Retention Characteristics

Introduction
The air trap chamber used in continuous renal replacement therapy (CRRT) often causes clot formation due to gas interface, blood stasis and turbulent flow. The designs of this chamber vary widely. Few studies have quantitatively evaluated ex-vivo quasi blood stasis for different chamber types.

Methods
Flow retention characteristics at 20, 30, 40, 50, and 60 s in a top-feed chamber (where blood flow enters vertically from the top and passes through a mesh within the air trap chamber with a chamber 12 mL in volume) and a side-feed chamber (where blood flow enters from the side and bottom, without a mesh filter, with a flow deviator and 6mL chamber volume) were evaluated using a 30% glycerin and iodine povidone-solution. Still images of the chambers at each time point were converted to 8-bit grayscale using Image J software (ver.1.54, Maryland, U.S.), with a brightness threshold in the range of 1–80 to compare the two chamber designs.

Results
Both chambers showed a decrease in the values of the highlighted areas over time; however, from 20 s, the side-feed chamber showed significantly lower values of the highlighted areas compared with the top-feed chamber. Similar to the findings at 20 s, significant differences in the values of the highlighted areas, favored the side-feed chamber and persisted at 30, 40, 50, and 60 s. Furthermore, pseudo-blood remained superficially in the top-feed chamber, while the side-feed chamber exhibited vortex flow, less stasis, turbulence and stagnation.

Conclusion
The two chambers tested emptied of pseudo blood at different rates, with varying retention characteristics, with the side-feed chamber showed less pseudo-blood retention at all time points assessed.