Sequential Blood Filtration for Extracorporeal Circulation: Initial Results from a Proof-of-Concept Prototype

Abstract

Micropore filters are used during extracorporeal circulation to prevent gaseous and solid particles from entering the patient's systemic circulation. Although these devices improve patient safety, limitations in current designs have prompted the development of a new concept in micropore filtration. A prototype of the new design was made using 40-μm filter screens and compared against four commercially available filters for performance in pressure loss and gross air handling. Pre- and postfilter bubble counts for 5- and 10-mL bolus injections in an ex vivo test circuit were recorded using a Doppler ultrasound bubble counter. Statistical analysis of results for bubble volume reduction between test filters was performed with one-way repeated-measures analysis of variance using Bonferroni post hoc tests. Changes in filter performance with changes in microbubble load were also assessed with dependent t tests using the 5- and 10-mL bolus injections as the paired sample for each filter. Significance was set at p < .05. All filters in the test group were comparable in pressure loss performance, showing a range of 26-33 mmHg at a flow rate of 6 L/min. In gross air-handling studies, the prototype showed improved bubble volume reduction, reaching statistical significance with three of the four commercial filters. All test filters showed decreased performance in bubble volume reduction when the microbubble load was increased. Findings from this research support the underpinning theories of a sequential arterial-line filter design and suggest that improvements in microbubble filtration may be possible using this technique.

Figure 1.

Inset graphic showing exterior view of the prototype filter. Cutaway showing interior view with sequential filter placement.

Figure 2.

Circuit design showing flow direction and test filter placement.

Figure 3.

Means plot for percent bubble volume reduction (BVR) (5-mL test).

Figure 4.

Means plot for percent bubble volume reduction (BVR) (10-mL test).

Figure 5.

Affinity filter showing pre- and postfilter mean bubble counts for 5-mL and 10-mL bolus injection tests.

Figure 6.

D734 filter showing pre- and postfilter mean bubble counts for 5-mL and 10-mL bolus injection tests.

Figure 7.

AL8 filter showing pre- and postfilter mean bubble counts for 5-mL and 10-mL bolus injection tests.

Figure 8.

Prototype filter showing pre- and postfilter mean bubble counts for 5-mL and 10-mL bolus injection tests.

Figure 9.

Quart filter showing pre- and postfilter mean bubble counts for 5-mL and 10-mL bolus injection tests.

Figure 10.

Scaled comparison of filter-housing shape and size between the Dideco D734 and PALL AL8 filters.

Figure 11.

Nonscaled comparison of the blood flow path between the Maquet Quart and prototype filters showing approximate angle and direction of flow in relation to the rising inner wall or guide plate found in each design.