Increased oxygen pressure to improve the efficiency of membrane oxygenators

Increased O2 pressure was used in a specially constructed oxygenator to test the concept of improved oxygen transfer with hyperbaria. Three membranes were tested: 5-mil Silastic, 1-mil copolymer, and 0.5-mil Teflon. Results are analyzed in terms of pressure, venous saturation, and flow. The 5-mil Silastic proved to be the most reliable and efficient at all levels of saturation and pressure. Oxygen transfers up to 100 cc/m2/min were recorded at lower venous saturations. Normal pCO2 differentials were maintained at atmospheric pressure but decreased as pressure increased. For the Silastic and copolymer membranes, peak efficiency for O2 transfer was at oxygen pressure 3 lb/in2, or 140 mmHg. This usually required a blood pressure of over 300 mmHg using an average blood layer of 0.5 mm. Changes of pressure were more critical than flow, although O2 transfer was found to increase up to flows of 1200 cc/min/m2. Pressure levels of 0-30 lb/in2 were tested. Teflon was most efficient at pressures of 10-15 lb/in2, and did not transfer CO2 in detectable amounts at these pressure levels. Plasma hemoglobin, WBC, and platelets were not seriously altered when studied over 4-hour periods at constant pressures.