The Effects of Pressure on Gases in Solution: Possible Insights to Improve Microbubble Filtration for Extracorporeal Circulation

Abstract

Improvements in micropore arterial line filter designs used for extracorporeal circulation are still needed because microbubbles larger than the rated pore sizes are being detected beyond the filter outlet. Linked to principles governing the function of micropore filters, fluid pressures contained in extracorporeal circuits also influence the behavior of gas bubbles and the extent to which they are carried in a fluid flow. To better understand the relationship between pressure and microbubble behavior, two ex vivo test circuits with and without inline resistance were designed to assess changes in microbubble load with changes in pressure. Ultrasound Doppler probes were used to measure and compare the quality and quantity of microbubbles generated in each test circuit. Analysis of microbubble load was separated into two distinct phases, the time periods during and immediately after bubble generation. Although microbubble number decreased similarly in both test circuits, changes in microbubble volume were significant only in the test circuit with inline resistance. The test circuit with inline resistance also showed a decrease in the rate of volume transferred across each ultrasound Doppler probe and the microbubble number and size range measured in the postbubble generation period. The present research proposes that fluid pressures contained in extracorporeal circuits may be used to affect gases in solution as a possible method to improve microbubble filtration during extracorporeal circulation.

Air Transmission Comparison of the Affinity Fusion Oxygenator with an Integrated Arterial Filter to the Affinity NT Oxygenator with a Separate Arterial Filter

“…Furthermore, both oxygenator-arterial filter systems allowed the transmission of bubbles larger than their rated filter pore size. For bubbles larger than the pore size to transit through the filter requires the bubble to distort through the pore under conditions of higher prescreen pressures or coalesce postfilter under conditions of higher pressure drops (12,13).…”

“…Indeed, as more bubbles larger than the pore size accumulate on the filter screen and partially obstruct fluid flow, there would be increasing prescreen pressure contributing more force to exceed the bubble point pressure. Furthermore, the elevated pressure drop across the filter would facilitate dissolved gases to come out of the solution postfilter (12,13).…”

Can the Oxygenator Screen Filter Reduce Gaseous Microemboli?

“…Preoxygenator pressure was adjusted to 300 mmHg at the targeted pump flow rate by stepwise occlusion of the venous line (9). The HCU water temperature was set to 38 C to reach the target temperature at 37 C, the sweep gas flow to 1.0 L per minute, and FiO 2 to 0.21.…”

Working toward Best Practice: Microbubble Filtration and Patient Safety During Extracorporeal Circulation

“…Moreover, because it is implied that the Fusion system generates a higher-pressure drop as a feature of normal operation, it is presumed that the line pressure had to be artificially raised during testing with the Affinity NT system to reproduce the bolus volume delivered between trials. This could open an unwanted potential for complicating the study with bias against the affinity NT oxygenator as the net effect would be to compress microbubbles more than they would naturally occur when using this system in a clinical setting (2). Although the Fusion oxygenator is designed to benefit from its integrated system with tighter fiber-bundle, imposing the same line pressure on the looser fiber-bundle of the Affinity NT oxygenator would appear to be counterproductive in achieving a balanced outcome.…”

“…In line with this would be a review of the bolus delivery system used, whether passive or active, and how this might impact outcomes of these critical studies. When considering the complexities that can arise from the variable nature that gas in solution can assume (2), it is easy to reason that there is probably…”