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Ann Thorac Surg 1996;62:103-104
© 1996 The Society of Thoracic Surgeons
Department of Cardiothoracic Surgery, Mount Sinai Medical Center, One Gustave Levy Place, New York, NY 10029.
In this article, Usui and colleagues have reviewed a large series of patients undergoing aortic arch operations with retrograde cerebral perfusion (RCP) at a number of different institutions in Japan. As pointed out by Usui and colleagues themselves, their results do not show any improvement in overall mortality or in neurologic morbidity when compared with several series of patients undergoing aortic arch operations with hypothermic circulatory arrest without retrograde perfusion. Usui and colleagues believe that the future of RCP is nevertheless bright. Because a number of surgeons have adopted this technique for more-or-less routine clinical use, some observations regarding the patients who fared especially poorly with RCP in this series deserve comment.
Usui and colleagues cite their experimental studies, which suggest that retrograde perfusion can provide as much as half the nutritive flow to the brain provided by antegrade perfusion, but their optimistic views of the efficacy of RCP have not been confirmed by others. Our experimental studies have shown that only 5% to 6% of blood infused into the superior vena cava returns to the aortic arch after retrograde perfusion, and that preservation of cerebral function by RCP, as measured by behavioral evaluation, cerebral histology, and quantitative electroencephalography, although somewhat superior to that produced by simple circulatory arrest, is still considerably inferior to the protection afforded by antegrade cerebral perfusion. The idea that the rate of flow during RCP is inadequate to meet the metabolic needs of the brain even at hypothermic temperatures is consistent with the observation in this study that patients with long intervals of RCP (>60 minutes) fared poorly. An additional factor that may have contributed to the high morbidity and mortality in patients with long intervals of RCP, not mentioned by Usui and colleagues, is cerebral edema. Cerebral edema has been shown experimentally to be an inevitable accompaniment of prolonged RCP, especially at higher perfusion pressures.
As pointed out by Usui and colleagues, the way in which RCP is implemented may have a significant impact on its efficacy, and therefore on clinical outcome, but unfortunately these influences could not be cleanly separated in this study. Retrograde perfusion pressures less than 15 mm Hg and greater than 35 mm Hg were associated with higher rates of neurologic dysfunction, but the significance of the impact of perfusion pressure on outcome was confused by grouping all perfusion methods together. The multivariate analysis of the impact of different perfusion methods on outcome showed that their influence was confounded by the greater impact of duration of RCP. In our experience and that of others, if the superior vena cava is perfused with the inferior vena cava unclamped, the vast majority of the infused blood shunts through venous collaterals to the inferior vena cava and thence to the right atrium: my colleagues and I therefore believe that total body retrograde perfusion is much more likely to result in effective flow to the brain.
Although RCP may not prove to be a safe way of prolonging the interval of hypothermic circulatory arrest during aortic arch operations, it may still be useful as a way of preventing or reducing particulate embolism, which is a major cause of permanent neurologic dysfunction in these patients: we have some experimental evidence to bolster this claim. In clinical practice, we use short intervals of RCP only in those patients with an especially high risk of embolization. Although we have the impression that RCP used in this way has been helpful in reducing the incidence of strokes, we do not have a strictly comparable control group, and use of RCP has certainly not eliminated strokes altogether.
In summary, although the results reported by Usui and colleagues do not demonstrate the superiority of RCP over simple hypothermic circulatory arrest in aortic arch operations, they do represent a useful summary of clinical experience with the technique, and should lead to future more rigorous studies, which may define a context in which RCP can help reduce morbidity and mortality during these high-risk operations. At present, the results of this study suggest that prolonged RCP, especially at high perfusion pressures, should be avoided.
Related Article
Ann. Thorac. Surg. 1996 62: 94-104.
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