A low priming volume oxygenator for bloodless priming in cardiopulmonary bypass.

The oxygenator described here arose out of the need to dispense with homologous blood in animal perfusions. It was considered that this could best be attained with an oxygenator having a priming volume sufficiently small to allow the use of isotonic solutions without undue dilution and consistent with full gas exchange and adequate temperature control. It was recognized that modifications to existing machines were unlikely to reduce the priming volume sufficiently to allow of total haemodilution without a significant reduction in their performance. As a result the following design was evolved (Figs I and 2). An annular bubble column was devised as the most practical method of attaining efficient gas exchange with a small amount of blood. The annulus increases 'lift' and mixing in the vertical tube and allows of full oxygenation at flows of up to 2 5 1./min. (in the small model shown here) at normal temperature with only 300 ml. of blood in transit through the annular column. Since temperature control is an essential function of cardiopulmonary bypass, both in normothermic and hypothermic perfusions, an appreciable volume of priming blood is usually involved in heat exchange. This volume was eliminated by using the inner surface of the annulus for heat exchange. The efficiency of the bubble type of oxygenator is usually offset by the large volume of blood required for debubbling by settling reservoirs after antifoaming. This volume was considerably reduced by efficient antifoaming, by low-pressure filtration, and by the use of a sump reservoir with an additional filter which together prevent vortex formation in the reservoir.