To Purge or Not to Purge.

To remove gaseous microemboli (GME) using an oxygenator with an integrated arterial filter, it is recommended by some manufacturers to purge the oxygenator as an additional safety feature while on bypass. In this in vitro study, we evaluated whether purging of oxygenators with an integrated arterial filter is efficient in reducing GME. Five different types of commercially available contemporary oxygenators with an integrated arterial filter based on progressive filter filtration (1), cascade filtration (1), screen filtration (2), or self-venting (1) were tested for their efficiency in removing GME while keeping the purge line open or closed. A bubble counter was used for pre- and post-oxygenator GME signaling, from which the filter efficiency was computed. Freshly drawn heparinized porcine blood was used at blood flow rates of 3 and 5 L/min. Three units of each oxygenator were tested with its specific reservoir at a fixed volume level of 1,500 mL. GME load was introduced into the venous line at 1,000 mL air/min. Measurements started as soon as GME were detected by the pre-oxygenator probe and then continued for 1 minute. There was no statistically significant difference in filter efficiency between the purged and non-purged groups for specific oxygenators. At a blood flow of 3 L/min, the average filter efficiency stayed approximately invariable when comparing the non-purged and purged groups, where 89.1-88.2% indicated the largest difference between the groups. At a blood flow rate of 5 L/min, the filter efficiency changed in one screen filter group from an average of 55.7% in the non-purged group to 42.4% in the purged group. Other filter efficiencies at the blood flow rate of 5 L/min for non-purged compared with purged groups were, respectively, 98.0 vs. 98.0% (screen filtration), 88.6 vs. 85.8% (self-venting filtration), 82.8 vs. 75.5% (progressive filter filtration), and 65.4 vs. 65.1% (cascade filtration). Based on these results, purging while confronted with continuous GME challenge did not result in an increased filter efficiency.