J Thorac Cardiovasc Surg 2005;129:1194-1195
© 2005 The American Association for Thoracic Surgery
Reply to the Editor
Yasir Abu-Omar, MRCSa,
Paul M. Matthews, MD, DPhil, FRCPb,
David P. Taggart, MD, PhD, FRCSa
a Department of Cardiothoracic Surgery John Radcliffe Hospital, Oxford, United Kingdom
b Centre for Functional MRI of the Brain, John Radcliffe Hospital, Oxford, United Kingdom
We thank Motallebzadeh and Jahangiri for their interest in our article.
The advantages of multirange, multifrequency transcranial Doppler technique are, respectively, rejection of artifacts and differentiation between gaseous and solid microemboli. This is of particular relevance because automatic rejection of artifacts significantly reduces bias in the interpretation of high-intensity transient signals and avoids interobserver variability, whereas discrimination between solid and gaseous microemboli may have important pathophysiologic, therapeutic, and prognostic implications.
The limitation of undercounting showers of microemboli (such as during removal of crossclamps and side clamps) was, in fact, discussed in our article. Although Motallebzadeh and Jahangiri suggest that this limitation may be responsible for a large difference in embolic count relative to previous reports, a review of the literature reveals that there is already wide variability among different studies (Table 1) because of differences in detection characteristics among various transcranial Doppler systems. Furthermore, the phenomenon of "undercounting" may actually serve to underestimate the benefits of off-pump surgery with a "no touch" aortic technique, where such showers are not seen.
At the time of our study, it was not our routine practice in Oxford to use arterial line filters. We now do so, although evidence for this is still not compelling. Others have reported an abundance of microemboli during cardiopulmonary bypass despite the use of 40-µm arterial filtration,1 and leukocyte-depleting arterial line filters have reportedly failed to improve neurocognitive outcome.2 On the other hand, the use of a cell saver in place of cardiotomy suction can potentially reduce the number of lipid microemboli. Although a combination of these techniques is likely to reduce microembolization during cardiopulmonary bypass, it is still unlikely to reach the levels seen in off-pump surgery with a "no touch" aortic technique.
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