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J Thorac Cardiovasc Surg 1997;114:871-872
© 1997 Mosby, Inc.

LETTERS TO THE EDITOR

Cerebral oxygenation during cardiopulmonary bypass in children

Clinic of Cardiac Surgery
The Children's Hospital Boston
Harvard Medical School
300 Longwood Ave.
Boston, MA 02115

To the Editor:

We read with great interest the study of Kurth and coworkers ¹ on cerebral oxygenation during cardiopulmonary bypass in children. Our understanding of this very important subject has been improved by the introduction of near-infrared devices. In Kurth's study, cerebral saturation was obtained during cardiac operations with various degrees of pump flow, hematocrit values, and temperatures. The purpose of the study was to determine the factors influencing oxygen extraction of the brain during cardiopulmonary bypass, which others have also studied experimentally and clinically. ^2-5 Kurth and associates concluded that hypothermia is the factor that decreases cerebral oxygen extraction, with hematocrit value and pump flow as cofactors. We believe that this statement is debatable and unproved by this study.

The authors used alpha-stat management during the operation, meaning that they did not correct blood gas values for temperature. Therefore other important operative parameters in the study, especially pH and carbon dioxide tension (PCO ₂), were by no means constant, as stated by the authors. These changes are simply neglected. In a recent study, we ⁴ also showed a similar correlation between oxygenated hemoglobin in brain tissue measured by near-infrared spectroscopy and jugular bulb oxygen saturation on the one hand and the temperature during cardiac surgery on the other hand. However, this relation became insignificant if controlled for pH and PCO ₂. In fact, pH and PCO ₂ were the only significant parameters influencing oxygen saturation in the jugular bulb and oxygenated hemoglobin in brain tissue. Other clinical and experimental studies have confirmed the importance of pH and PCO ₂ management for cerebral oxygenation and postoperative brain function. ⁶

Kurth and associates suggest that a decrease in temperature might increase cerebral oxygenation during cardiac operations. This statement should be accepted cautiously. In fact, using multivariate analysis, we found that hypothermia had a slight but significant adverse affect on the redox status of cytochrome aa3, which could be explained by the shift of the hemoglobin binding curve with hypothermia. Furthermore, the redox status of cytochrome aa3 was the only intraoperative parameter correlated with postoperative neuropsychologic dysfunction. ⁵ Therefore one might argue that decreasing blood temperature during a period of high cerebral oxygen demand is not beneficial but rather detrimental.

In conclusion, we appreciate the honest attempt of the authors to increase our knowledge of cerebral oxygenation during cardiac surgery. However, the conclusions of this study may be misleading, because important variables influencing cerebral oxygenation were not controlled. In addition, as Jonas ⁷ stressed in his commentary, brain tissue saturation measured by near-infrared spectroscopy does not reflect the true oxygen demand of the brain during hypothermia.

12/8/84298

References

1. Kurth CD, Steven JM, Nicolson SC, Jacobs ML. Cerebral oxygenation during cardiopulmonary bypass in children. J Thorac Cardiovasc Surg 1997;113:71-9.
   
2. Shinoka T, Shum-Tim D, Jonas RA, et al. Higher hematocrit improves cerebral outcome after deep hypothermic circulatory arrest. J Thorac Cardiovasc Surg 1996;112:1610-21.
   
3. Hiramatsu T, Miura T, Forbess JM, et al. pH strategies and cerebral energetics before and after circulatory arrest. J Thorac Cardiovasc Surg 1995;109:948-57.
   
4. Nollert G, Möhnle P, Tassani-Prell P, Reichart B. Determinants of cerebral oxygenation during cardiac surgery. Circulation 1995;92(Suppl):II327-33.
   
5. Nollert G, Möhnle P, Tassani-Prell P, et al. Postoperative neuropsychological dysfunction and cerebral oxygenation during cardiac surgery. Thorac Cardiovasc Surg 1995;43:260-4.
   
6. Schell RM, Kern FH, Greeley WJ, et al. Cerebral blood flow and metabolism during cardiopulmonary bypass. Anesth Analg 1993;76:849-65.
   
7. Jonas RA. Commentary on Kurth et al. ¹
   

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This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Georg Nollert Dominique Shum-Tim Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nollert, G. Articles by Shum-Tim, D. Search for Related Content PubMed Articles by Nollert, G. Articles by Shum-Tim, D.