Ann Thorac Surg 2001;72:508
© 2001 The Society of Thoracic Surgeons
Invited commentary
P. Michael McFadden, MDa
a Division of Cardiothoracic Surgery, Ochsner Clinic, 1514 Jefferson Highway, New Orleans, LA 70121, USA
e-mail: mmcfadden{at}ochsner.org
In this article, Dr Yamashita and his colleagues report the results of cerebral oxygenation monitored by near infrared spectroscopy in 13 patients that underwent total arch replacement assisted by selective cerebral perfusion. Changes in intracranial oxyhemoglobin and tissue oxygenation index were compared to values obtained from a control group of 18 patients that underwent either coronary artery bypass (n = 15) or valve replacement (n = 3).
The crux of this article is whether or not near infrared spectroscopy accurately monitors cerebral oxygenation during arch replacement. Existing data on cerebral oxygenation monitoring with near infrared spectroscopy is derived mainly from clinical studies on carotid endarterectomy. Little information is available on its utility in aortic arch repair. Near infrared spectroscopy is simple and noninvasive. The authors accurately point out that its limitations include the inability to detect embolic events and selective monitoring of only a limited region of the brain. In this study, real time near infrared spectroscopy was compared to jugular venous oxygen saturations, a monitoring technique more commonly employed in aortic arch surgery. The study design would have been strengthened had it included a comparison of real time near infrared spectroscopy and simultaneously measured jugular venous oxygen saturations in all patients rather than in only ten patients from each group. The suggestion that a correlation may exist between tissue oxygenation index and jugular venous saturation is not substantiated. The data demonstrates a rather poor correlation (r = 0.44) and suggests that near infrared spectroscopy may have limitations in measuring cerebral oxygen delivery during hypothermic perfusion. The authors’ selection of the alpha-stat method of monitoring oxyhemoglobin is somewhat controversial since recent animal and clinical studies have demonstrated the limitations of this method under conditions of deep hypothermia and hemodilution.
The study, however, does demonstrate a correlation between oxyhemoglobin and tissue oxygenation index in all phases of perfusion. Based on this data and the absence of clinical stroke on postoperative neurological examination and electroencephalography, the authors conclude that near infrared spectroscopy monitoring in aortic arch replacement utilizing selective cerebral perfusion is safe. The mere absence of stroke cannot rule out more subtle forms of neurologic injury such as particulate microembolization, neurologic dysfunction, transient cerebral edema or encephalopathy. Perhaps the application of preoperative and postoperative psychometric testing or intraoperative electroencephalography or magnetic resonance imaging would have better established the absence of neurologic injury.
Despite some inherent weaknesses in design, this study by a recognized and respected surgical group with considerable experience in aortic arch surgery is an important contribution to our understanding of near infrared noninvasive cerebral monitoring in patients undergoing aortic arch replacement. Near infrared spectroscopy, within parameters, has shown considerable promise as an accurate and noninvasive method of monitoring cerebral oxygenation and thus protection. The data provided by this method allows for early intervention and alteration of parameters such as perfusion rate, blood pressure, and transfusion which may be beneficial in the prevention or reversal of cerebral oxygen desaturation.
Related Article
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Cerebral oxygenation monitoring for total arch replacement using selective cerebral perfusion
- Katsushi Yamashita, Teruhisa Kazui, Hitoshi Terada, Naoki Washiyama, Kazuchika Suzuki, and Abul Hasan Muhammad Bashar
Ann. Thorac. Surg. 2001 72: 503-508.
[Abstract]
[Full Text]
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