Improved gas exchange performance of the intravascular oxygenator by active blood mixing

The intravascular oxygenator and carbon dioxide removal device (IVOX; CardioPulmonics, Salt Lake City, UT) has been shown to perform 30% of the gas exchange in animals and patients with acute respiratory failure. Among the factors that limit gas exchange is the mass transfer resistance in the blood phase. To determine if a reduction in mass transfer resistance by mixing venous blood can enhance the O₂ transfer and CO₂ removal by IVOX, a right atrium-pulmonary artery venovenous bypass circuit was used in sheep to model the adult vena cava. A size 9 IVOX (894 fibers with 0.41 m² surface area, n = 5) was incorporated in the bypass circuit and the blood flow controlled by a roller pump ranging from 1 to 4 l/min. An intra-aortic balloon was placed near the shaft of the IVOX and pulsated at the rate adjusted to best improve CO₂ removal (100-120 bpm). O₂ transfer and CO₂ removal were measured with balloon pulsation on and off at different flow rates. Results showed that blood mixing by pulsation of the balloon caused a 25-49% increase in O₂ transfer by IVOX, and this increase remained relatively constant throughout the full flow range. CO₂ removal was also increased by up to 35%, but at flows between 3.5 and 4 l/min, the effect of mixing was diminished. It is concluded that reduction in the mass transfer resistance by blood mixing improves gas exchange. Because O₂ is more diffusion limited, it is more dependent upon mixing of blood for gas exchange than CO₂. More design improvements to incorporate active mixing may further enhance the gas exchange performance of IVOX.