The development and study of autologous lung oxygenation for cardiac surgery - The double reservoir technique

Cardiopulmonary bypass for closed heart operations has been steadily improving over the last forty years. It is still associated with a significant morbidity and is capable of further design improvement. Autologous lung oxygenation was a technique available in the early days of cardiac surgery but was soon eclipsed by the development of external oxygenators. There are however many inherent advantages associated with the use of the patients own lungs and this study has tried to reevaluate its role. The project started to look at existing levels of knowledge and then to use modern materials and methods to improve the old system. The study has operated at a variety of levels. Firstly, to show that the method could be used safely in a clinical setting; this involved the testing of a variety of cannulae, tubing materials, prime solutions and of perfusion techniques. Secondly, to show that efficient gas exchange was possible using the system. Finally, the study has looked at the effects of using autologous lung oxygenation on the "quality" of the bypass. Measurements of numbers of circulating gaseous microemboli, the platelet function, the level of complement and other humoral cascades have all been looked at. The conclusions are that this technique produces significantly fewer microemboli than conventional bypass, that platelet handling is as good as membrane oxygenators but that complement activation is lower with autologous oxygenation. The study has not been directed to answering the question as to whether this is clinically significant and further, whether its clinical use should be encouraged. The study concludes with a look at the many questions that remain unanswered and attempts to indicate the direction of future investigations