Arterial Filter Bypass Loop: What Occurs in this Area during Cardiopulmonary Bypass and Are There Potential Patient Implications

The majority of arterial line filters are made from a hydrophilic polyester material, with an effective surface area ranging from 400–800 cm2, enclosed in a polycarbonate housing (1–3). Arterial filters were first reported in the early 1960s and are a standard of care (4). The primary advantage noted with incorporating the filter in the cardiopulmonary bypass circuit is prevention of micro emboli, either being particulate or micro air from reaching the patients circulation (1,5). A landmark study from England in 1994 compared neurological outcome in patients with and without an arterial line filter. Patients without the arterial line filter had more emboli and a poorer outcome (6). During the time of original introduction, manufacturers suggested a bypass loop be incorporated for retrograde priming and de-airing, and as a means for providing uninterrupted blood flow in the event of filter malfunction over the course of bypass (7). If the arterial filter becomes unusable during the course of a bypass case, what is the cause? Also, if the main purpose of the filter was to increase patient safety, how prudent is it to open the bypass loop if the filter has been “filtering out” material with embolic potential, and now it is clogged and rendered useless. More recent filter designs on the market today, such as the Sorin Synthesis® (Mirandola, Italy) integrated oxygenator/arterial filter and the Maquet Quart® (Rastatt, Germany) arterial filter, do not require retrograde filling for priming; neither design incorporates a bypass loop and both are primed in an antegrade fashion (8,9). The Medtronic Affinity® (Minneapolis, MN) arterial filter, which is widely used in conventional cardiopulmonary bypass, is also incorporated in their “resting heart system,” and it does not include a bypass loop in this application. This seriously questions the functional need for the bypass loop, and the patient safety aspect. The purpose of this investigation was to determine what is actually taking place in the stagnant pool of blood proximal to the clamp during bypass.