Spontaneous gas bubbling in microporous oxygenators.

During operation of the microporous membrane oxygenators at some conditions, gas microbubbles penetrate into the blood. This effect, so-called spontaneous bubbling, takes place even when the blood pressure is higher than the gas pressure. This phenomenon was confirmed experimentally both in a model cell with hydrophobic microporous hollow fibers being used in the oxygenators and in in vitro tests on the actual microporous hollow fiber oxygenator. We proposed a mechanism of spontaneous gas bubbling into liquid that contains dissolved gases. Because of a partial pressure gradient, the dissolved gases and water vapors are transported from blood into the gas pore. This causes Stefans gas flow directed from the liquid-gas interface. Because of the high hydraulic resistance of the micropores, gas pressure at the meniscus increases up to gas bubbling. A mishandled priming of the oxygenator as well as the blood pressure pulsation caused by the roller pump operation contribute to spontaneous gas bubbling in the microporous oxygenators. The flow and pressure in the hydrophobic pores were calculated for various gases.