Outflow Obstruction of Soft-Shell Venous Reservoir Bags: A Preliminary Investigation

Potential problems have occurred during cardiopulmonary bypass where the area directly above the outlet port of the soft-shell venous reservoir containing a screen has collapsed similar to when the bag is empty, although there are still several hundred milliliters in the bag. A preliminary investigation was conducted to rule out the possibility of this outflow obstruction being attributable to poor flow design through the reservoirs. The test circuit consisted of a cardiotomy reservoir, a centrifugal pump, 3/8 and 1/2 in PVC tubing, and one of the test venous reservoirs (BARD S-2116, Medtronic 1385 and MVR-1600, Sarns 4858). The circuit was primed with outdated packed red blood cells, platelets, human albumin, normal saline, and 10,000 units of sodium heparin in concentrations to simulate routine bypass. Each reservoir was tested at 6.5–7.0 L/min flows for a least 20 min each. None of the reservoirs tested demonstrated the phenomenon that had been observed clinically. This dismisses flow design flaws as a possible cause. Further clinical investigation must be performed to identify the possible cause or causes of this problem.