A Simplified In Vitro System for Evaluating Gas Transfer Characteristics of Oxygenators

Despite the excellent performance of membrane oxygenators, bubble oxygenators continue to dominate routine open heart surgery. Newer versions with reduced gas:blood flow ratios continue to appear for clinical application 1•2. The new models generally provide data on partial pressure of oxygen (p02) of oxygenated blood at given blood and oxygen flow rates from clinical perfusions37. Clinical data has admitted drawbacks in evaluating the candidate oxygenator. Thus there would seem to be a need for a simple in vitro system for evaluating the performance of an oxygenator. Such a system should offer close control over such parameters as hemoglobin content, temperature pH, pCo2, p02 and percentage oxygen saturation. Control of such functional parameters is difficult, if not impossible in ex vivo experiments, thanks to the variable hemodynamic responses of the experimental animals. This paper describes a simple in vitro test setup which offers easier and more accurate control of blood gas parameters than the conventional ex vivo and in vitro systems. Figure I illustrates a conventional circuit used for the evaluation of an oxygenator810• 14. The blood circuit incorporates a deoxygenator system consisting of two bubble oxygenators and venous and arterial reservoirs. A calibrated pump gives controlled blood flow into the test oxygenator. About 4-6 liters of blood are used to