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Ann Thorac Surg 2003;75:1361
© 2003 The Society of Thoracic Surgeons

Correspondence

Cerebral perfusion and cognitive function

R. Peter Alston, MD, FRCA

Department of Anaesthesia, Critical Care and Pain Medicine, Royal Infirmary of Edinburgh, 1 Lauriston Place, Edinburgh EH10 5AU, United Kingdom

e-mail: p.alston{at}ed.ac.uk

To the Editor:

An important limitation of transcranial near-infrared spectroscopy is that it can only measure one small area of the brain. Although oxygenation in the areas being examined may have been adequate, the rest of the brain could have been hypoperfused, which may account for Reents and colleagues [1] being unable to relate regional cerebral oxygen saturation (ScO2) to cognitive outcome. A limitation of their study design is that they have not reported the levels of arterial carbon dioxide tension (PaCO2). Paco2 is the fundamental determinant of cerebral perfusion in this setting, and correction for its level would have reduced much of the between-group variation in SCO2 [2]. An important limitation of their analysis is that they have dichotomized the results of the cognitive tests. We have argued against dichotomization as arbitrary and unjustified [3]. This view is supported by a recent, extensive review of the subject by McCallum and colleagues [4], who conclude that it has substantial negative consequences including spurious statistical findings. Cognition tests and ScO2 are continua and should be handled statistically as such.

However, our own work would support Reents and colleagues’ conclusion that regional cerebral perfusion has no influence on short-term cognitive outcome after coronary artery bypass grafting surgery. Using it as a measure of global cerebral perfusion, we have been unable to relate jugular bulb desaturation to long-term cognitive or neurologic outcome [3, 5].

References

  1. Reents W., Muellges W., Franke D., Babin-Ebell J., Elert O. Cerebral oxygen saturation assessed by near-infrared spectroscopy during coronary artery bypass grafting and early postoperative cognitive function. Ann Thorac Surg 2002;74:109-114.[Abstract/Free Full Text]
  2. Millar S.A., Alston R.P., Andrews P.J., Souter M.J. Cerebral hypoperfusion in the immediate postoperative period following coronary artery bypass grafting, heart valve and abdominal aortic surgery. Br J Anaesth 2001;87:229-236.[Abstract/Free Full Text]
  3. Robson M.J., Alston R.P., Deary I.J., Andrews P.J.D., Souter M.J., Yates S. Cognition after coronary artery surgery is not related to postoperative jugular bulb oxyhemoglobin desaturation. Anesth Analg 2000;91:1317-1326.[Abstract/Free Full Text]
  4. MacCallum R.C., Zhang S., Preacher K.J., Rucker D.D. On the practice of dichotomization of quantitative variables. Psychol Methods 2002;7:19-40.[Medline]
  5. Robson M.J.A., Alston R.P., Deary I.J., Andrews P.J.D., Souter M.J. Jugular bulb oxyhaemoglobin desaturation, S100B and neurologic and cognitive outcome after coronary artery surgery. Anesth Analg 2001;93:839-845.[Abstract/Free Full Text]




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