J Thorac Cardiovasc Surg 2000;120:1013-1014
© 2000 The American Association for Thoracic Surgery
Cardiopulmonary bypass temperature and extension of intraoperative brain damage: Controversies persist
Mario Gaudino, MD,
Gianfederico Possati, MD
Department of Cardiac Surgery
Catholic University
Divisione di Cardiochirurgia
Policlinico Universitario A. Gemelli
Largo A. Gemelli 8 Rome 00168, Italy
To the Editor:
We applaud Engelman and colleagues
1 for their effort to further clarify the relationship between systemic perfusion temperature and the extent of intraoperative brain damage, and we are persuaded that our observations 2 suggest further investigation on the neurologic safety of normothermia. However, for insights into this controversial issue to be useful, these investigations should be rigorous in their study design and provided with sufficient statistical power, neither of which seem to be fully applicable to the study by Engelman's group. The following points support this statement:
- As even a moderate degree of brain hypothermia can confer substantial benefit in terms of brain protection, 3 the inclusion of patients operated on with tepid (32°C) and warm (37°C) systemic perfusion in the same study group is methodologically incorrect, putting together patients with different degrees of neurologic risk.
- No rigorous definition of intraoperative stroke is given by the authors. As cardiopulmonary bypass temperature can obviously influence the extent of intraoperative but not postoperative strokes, the exclusion of the latter from data analysis must be rigorous. Our data demonstrate that the difference between normothermic and hypothermic patients tends to disappear when intraoperative and postoperative events are considered together, testifying the strong confounding effect of this methodologic mistake.
- Thus, despite the prospective design of the study, computed tomographic (CT) data analysis (which represents the real core of the investigation) was in fact retrospective. By contrast, in our series CT scans were prospectively evaluated.
- The number of strokes in the three temperature groups is low: 4 in the warm perfusion series, 5 in the cold perfusion series, and 3 in the tepid systemic perfusion series. If one excludes the 3 patients in the tepid group, on the basis of point 1 (above), a total of 9 patients remain, greatly limiting the statistical power of the analysis. From this viewpoint, the similarity of the hypothermic and normothermic series appears more a consequence of the limited amount of data analyzed than the result of a true absence of difference. Our own investigation analyzed almost 3-fold more cases and (although not randomized) can obviously provide statistically more sound data.
- We agree that, different from the anesthesiology examination used in our article, the sophisticated neurologic evaluation used by Engelman and colleagues allowed the authors to detect even minimal cerebral events. However, this method led to the inclusion in the study of a considerable number of small ischemic cerebral events (and indeed only 6 strokes had a spatial extension > 300 mm3). This fact further limits the statistical power of the CT analysis and, coupled with the small number of cases, reduces to a minimum the possibility of detecting a difference between the two series.
On the basis of these considerations, the report by Engelman and associates is certainly worthy of consideration, but it does not allow any definitive conclusion on the neurologic safety of normothermia. Only further large scale, carefully designed, prospective randomized investigations on this subject will clarify this controversial issue. For this reason, we strongly ask for the worldwide cooperation of teams involved in this field of clinical research to establish such a study.
For the moment, the evidence in the literature does not allow the liberal adoption of normothermic systemic perfusion in all patients subjected to coronary artery bypass operations.
12/8/109246
doi:10.1067/mtc.2000.109246
References
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Engelman RM, Pleet AB, Hicks R, Rousou JA, Flack JE ed, Deaton DW, et al. Is there a relationship between systemic perfusion temperature during coronary artery bypass grafting and extent of intraoperative ischemic central nervous system injury? J Thorac Cardiovasc Surg 2000;119:230-2.[Abstract/Free Full Text]
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Gaudino M, Martinelli L, Di Lella G, Glieca F, Marano P, Schiavello R, et al. Superior extension of intraoperative brain damage in case of normothermic systemic perfusion during coronary artery bypass operations. J Thorac Cardiovasc Surg 1999;118:432-7.[Abstract/Free Full Text]
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Busto R, Dietrich WD, Globus MY-T, Valdes I, Scheinberg P, Ginsberg MD. Small differences in intraischemic brain temperature critically determine the extent of ischemic neuronal injury. J Cereb Blood Flow Metab 1987;7:729-38.[Medline]
