An Experimental Evaluation of the Capiox 1.6 and 5.4M2 Membrane Oxygenators for Air Removal Efficiency in the Conventional and Inverted Positions

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Abstract
Membrane oxygenators do not create bubbles but most will transmit the bubbles which are common in venous reservoir bags. We previously reported the elimination of arterial micro-air in the 0.8m2 Capiox when operated in the inverted position with an open purge line. This same lung failed to eliminate micro-air when operated in the conventional orientation.The purpose of this study was to test the effectiveness of the Capiox as a bubble trap in lungs with a larger surface area (subgroup a-1.6m2) (subgroup b-5.4m2) and at higher flows.Two test circuits were constructed for each size lung (Group 1—conventional orientation) (Group 11—inverted). The circuits were primed with dilute, outdated human blood (Hct. 20 ± 2%). Ten injections of air (5ml) were done for each lung in both test positions. A bubble counter on the outlet side of the lung was used to count bubbles passed through the membrane oxygenator following the air challenge.Thirty second counts were significantly higher (p<.001) in Group I than in Group II for both size lungs. The counts for both groups were: Group I(alb) Group II-inverted (alb) Size 39.4 ± 20.2/30.7 ± 7.8 0.6 ± 0.96/2.0 ± 1.3 (21-30μ), 23.6 ± 11.6/19.6 ± 7.93 0.22 ± 0.6/0.2 ± 0.6 (31-40μ), 18.8 ± 9.13/13.4 ± 4.03 0/0.1 ± 0.3 (41-50μ), 14.5 ± 7.53/21.1 ± 2.99 0/0 (51-60μ), 10.7 ± 6.38/10.1 ± 3.18 0/0 (61-70μ), 8.6 ± 3.47/7.5 ± 3.5 0/0 (71-80μ), 7.9 ± 3.51/5.7 ± 2.91 0/0 (81-90μ) 17.7± 14.67/50.0 ± 4.52 0/0 (>90μ). The inverted orientation of both the Capiox 1.6 and 5.4 m2 lungs with an open purge line was superior to the conventional orientation for micro-air removal. As a bubble trap, both lungs compare favorably to an arterial filter in air handling characteristics.(All data reported as mean ± S.D.).

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