Advancements in Removing Small Bubbles

The benefits of self-venting technology as a continuous gaseous microemboli purge

Most oxygenator manufacturers integrate arterial filters and oxygenators — offering better technology to improve patient care.

The new integrated arterial filters offer the same functionality of a traditional filter — trap particulate and purge gaseous microemboli (GME). But some, like the CAPIOX® FX Oxygenator, accomplish these functions in simple but innovative ways.

Methods of GME Removal

In a 2008 published study that ranked gaseous microemboli separation performance, Riley wrote, "Arterial line filters are arguably the most important component in the cardiopulmonary bypass circuit to protect the patient from gaseous macro- and microemboli originating in the perfusion circuit." ¹

Methods to remove GME from the circuit with integrated arterial filters varies. First-generation designs simply attach the arterial filter to the oxygenator. These first-generation designs use the traditional vent to purge air to the venous reservoir.

The CAPIOX FX Oxygenator is unique because of its self-venting function which removes GME through the microporous hollow fibers — it does not require purging through a vent port.

How self-venting technology works

"The self-venting method of GME elimination separates the emboli from the blood in the circuit rather than returning them to the venous reservoir for removal."

A 32 micron screen filter surrounds the fiber layer of the CAPIOX FX Oxygenator. Particulate microemboli in the blood are trapped in the filter mesh while gaseous emboli remain inside the oxygenator and in contact with the hollow fibers.

During bypass, the blood-side pressure is higher than that of the gas-side pressure of the inner lumen of the hollow fiber. Driven by the pressure differential, gaseous emboli enter the inner lumen of the microporous hollow fibers. Once the emboli enter the inner lumen, they are eliminated via the gas outlet.

The self-venting method of GME elimination separates the emboli from the blood in the circuit rather than returning them to the venous reservoir for removal.

Concerns with purging GME to the venous reservoir

As De Somer wrote in a published study, "Since the advent of cardiopulmonary bypass, the generation and elimination of gaseous and solid microemboli have been a concern." ²

First-generation integrated arterial filters use a vent (or purge) port to remove the GME. If microemboli enter the perfusion circuit, they are trapped by the arterial filter, and then exit from the vent (purge) port with blood flow shunted to the venous reservoir.

Clinical concerns of purging through a vent port:

• Difficult to determine the actual blood flow to the patient due to shunting
• Continuous blood flow to the venous reservoir increases the dynamic hold-up volume of blood
• Need to close the vent port when blood circulation is stopped to prevent back flow to the patient
• Recirculation of the GME may break them into smaller emboli — making them easier to pass through the venous reservoir filter and more difficult to eliminate from the circuit

Self-venting microemboli removal is a 'simple bubble movement' through the hollow fiber's micro-pores

"The design of the Terumo CAPIOX FX Oxygenator with its integrated filter optimizes the performance of the hollow fibers to self-vent gaseous microemboli," says Carl Freytag, Senior Clinical Specialist, Terumo Cardiovascular.

Figure 1 shows a concept of the self-vent function.

"The integrated screen filter efficiently traps the gaseous microemboli, maintaining them in close proximity to the large surface area of micro-pores of the hollow fibers," Carl adds. "The blood-side to gaseous-side positive pressure gradient effectively drives the emboli through the micro-pores to the gas-side of the hollow fibers for immediate removal from the cardiopulmonary bypass circuit.

“It is a simple bubble movement through the hollow fiber's micro-pores," he adds.

Although the self-venting method of microemboli removal in the CAPIOX FX Oxygenator is different than a traditional purge, clinical studies have shown it to be just as effective. ^{3, 4} More important, removing GME via the gas phase helps eliminate GME from the circuit rather than recirculating them to the venous reservoir.

Figure 1: Illustration of self-venting purge through the oxygenator hollow fiber.