Ann Thorac Surg 2002;73:1178-1179
© 2002 The Society of Thoracic Surgeons
Invited commentary
R. Alan Hall, MDa
a Virginia Mason Medical Center, Cardiothoracic Surgery, X3-CAR, 1100 Ninth Ave, Seattle, WA 98111, USA
e-mail: ctsrah{at}vmmc.org
I commend the authors for obtaining control groups for this study. The authors choose healthy age matched controls for single photon emission computed tomography (SPECT) scanning, and this is certainly reasonable. We found that at any age, better-educated subjects tended to have better baseline cerebral perfusion as measured by SPECT. I wonder if the test subjects and control group individuals were similar in terms of education level, activity level, and measures of independence, all of which influence global and regional cerebral blood flow (CBF). Regardless, the finding that patients in need of coronary revascularization have diminished cerebral perfusion as compared to healthy volunteers is probably accurate and implies these patients are at risk for cerebral injury. We believe that SPECT may identify a subset of patients with "diminished cortical reserve" and accordingly are vulnerable to cognitive injury from any insult, surgery included.
The authors found cerebral blood flow to be significantly reduced postoperatively as compared to preoperatively. What to account for this? Emboli, ischemic injury, cerebral edema or perhaps altered test environments. Carbon dioxide was lower at time of postoperative SPECT. Was respiratory rate comparable? Were patients compensating for smaller tidal volumes with a relative tachypnea? Similarly, hemodilution with a lower hematocrit postoperatively affects CBF and while a correction factor was applied to global CBF, none exists for regional blood flow evaluations. With significant differences in hematocrit and partial pressure of carbon dioxide before and after surgery, it is difficult to say that cerebral perfusion has indeed changed relative to baseline. It would be fascinating to restudy these patients months down the road, presumably when hematocrit and carbon dioxide levels had normalized, to see if these changes in cerebral perfusion persisted and as this is an important finding, the authors should be encouraged to consider a third SPECT scan in these patients.
While the authors did not find cognitive dysfunction correlated with perfusion drop off, there was a trend in that direction and they may have been hampered by the small study population. A larger group may be warranted. Finally, I wish the authors had statistically studied the relationship between preoperative SPECT and postoperative cognitive dysfunction. While many investigators have documented cognitive injury as a consequence of cardiac surgery, screening tests to predict who will be injured are lacking. We believe that preoperative SPECT, a relatively inexpensive and safe test, will identify a subset of patients at risk for cognitive injury and such patients may benefit from alternative treatments. We are excited to see SPECT utilized by researchers in cardiovascular medicine and congratulate the authors on completing this complex study.
Related Article
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Cerebral blood flow and cognitive dysfunction after coronary surgery
- Hanne Abildstrom, Peter Høgh, Bjørn Sperling, Jakob T. Moller, Stig Yndgaard, and Lars S. Rasmussen
Ann. Thorac. Surg. 2002 73: 1174-1178.
[Abstract]
[Full Text]
[PDF]
