Construction and evaluation of a simple membrane oxygenator for small organ perfusion

A simple membrane oxygenator for isolated organ perfusion is described. The membrane employed consisted of an ordinary silicone rubber tubing, 2 mm internal diameter, 0.3 mm wall thickness, the length of the tubing varying according to the required gas transfer. When describing the capacity of the oxygenator, it was found that the maximum gas transfer rate per unit membrane surface was an inadequate measure, since this would vary with both flow rate through the oxygenator and the gas binding capacity of the perfusate. The following formula for the function describing the relation between maximally possible change in gas concentration in the perfusate (C), flow rate (F) and actual change in gas concentration in the perfusate (U) was proposed: U=C-e(-bF), b being a constant specific for the gas and the membrane. This formula was tested by a series of in vitro experiments and proved to give a valid description of the capacity of the oxygenator. It was also found that carbon dioxide was always more easily transferred than oxygen, so that oxygen transfer capcity was the limiting factor in the use of the oxygenator. To facilitate the construction of the right size membrane, a nomogram was constructed for oxygen transfer.