Oxygenation of Blood for Clinical Applications

Abstract

The analytical description of blood oxygenation is of both practical and theoretical importance. The design of clinical oxygenators in the past has been based on experimental trials, whereas the newer generation of such devices rely upon theoretical analysis or implications. Initial clinical use of oxygenators was for short-term open heart surgery, and direct contact of blood with the gas phase was allowed (1). Longer term lung prosthesis or assistance would be possible if the trauma associated with this direct contact could be avoided (2). For this reason, membrane oxygenators have been proposed where the flowing blood and gas phases are separated by a permeable membrane. The interposing of such a membrane results in several problems associated with the additional resistance to the transfer of O₂ and CO₂ compared with the direct contact oxygenators. Not only Is there a resistance associated with the membrane itself, but the blood adjacent to the membrane approaches stagnant conditions. The zero flow membrane region results in diffusion controlled mass transfer which is generally more significant in dictating oxygenator size (and complexity) than is the membrane resistance. A recent proliferation of membrane oxygenator design innovations reflect attempts to augment diffusion with convection in the direction perpendicular to the flow (3,4,5). Whereas diffusion is an extremely efficient method of transfer over short distances (10⁻⁴ cm.) (6), it is ineffective in practical channel dimensions (0.1 cm.). Therefore, an understanding of diffusional processes in a flowing blood stream is of immediate practical importance.