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Ann Thorac Surg 2001;71:2085-2086
© 2001 The Society of Thoracic Surgeons
a Department of Cardiovascular Surgery, General Hospital Klagenfurt, St. Veiter Straße 47, A-9020 Klagenfurt, Austria
To the Editor
I thank Dr Whitaker very much for his detailed comments to our paper. However, I cannot agree with all his statements: S100-protein is a long-known specific marker for cerebral injury and is widely used in neurology and traumatology [1].
Doctor Whitaker is right in stating that thymic cells also contain S100 protein. As the mean age in our patient groups was 65 years it is unlikely that any vital thymic tissue was encountered in the mediastinum; secondly, in both patient group mediastinal fat was divided in the same fashion to expose the ascending aorta, therefore thymic tissue cannot account for the difference in S100 levels we found.
Another mechanism for elevated S100 levels could be microemboli caused by cardiotomy suction or sternotomy itself as suggested by Anderson and colleagues [2]. In our study a cellsaver device was used in both groups and only when the patient was put on bypass the cardiotomy suction was activated in group A. It is long known that extracorporeal circulation impairs biological membranes [3], such as the blood-brain barrier or pulmonary endothelium. Whether this is by microembolism, reduced local circulation, activation of the complement system or other mechanisms is not yet entirely clear; we can, however, not see any contradiction to our conclusion that "off-pump" surgery seems to be more physiologic.
With regard to neurologic or neuropsychologic impairment we were not able to find any difference between the two surgical methods used in our study. In accordance with Whitaker we also believe that "studies must be differently designed to test one or the other," as we already stated in our conclusion. Permanent neurologic deficits are fortunately very rare in coronary artery surgery (none occurred in our patient group) and neuropsychological impairment is hard to evaluate and dependent on a variety of factors, most of them not associated with the surgical technique used (such as age, preoperative neurobehavioral status, preoperative cerebral circulation, lifestyle, drinking habits and so on). This is why we think that the clinical impact of reduced S100 levels in the perioperative period in "off-pump" patients can only be addressed in specifically designed, large-scale studies. In our conclusion we were therefore very careful not to over-interpret our findings.
Again I would like to thank Dr Whitaker for his interesting remarks and the Editor for giving us the opportunity to participate in the discussion.
References
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