Transcranial cerebral oxymetry during carotid endarterectomy: agreement between frontal and lateral probe measurements as compared with an electroencephalogram

Abstract

Objective: Transcranial cerebral oximetry, which is considered a novel technique, was evaluated during carotid endarterectomy. For practical reasons, the use of a single probe attached to the forehead and overlying the territory of the anterior cerebral artery is recommended. Other monitoring systems (transcranial Doppler, electroencephalograms (EEG)) focus more on the territory of the middle cerebral artery. The aim of this study was to evaluate whether a probe in the frontal area is as representative for monitoring cerebral ischaemia during carotid cross-clamping as a probe in the lateral area. Design: Clinical prospective study. Materials: Sixty patients who underwent carotid endarterectomy were studied with continuous and simultaneous EEG and transcranial cerebral oximetry. Forty-three patients (72%) simultaneously underwent frontal and lateral transcranial cerebral oximetry. The lateral probe was only used in 17 patients. Methods: The percentage decrease of transcranial cerebral oximetry was calculated during cross-clamping. Using the EEG findings as the gold standard in order to detect cerebral ischaemia during carotid cross-clamping, the relationship with transcranial cerebral oximetry was described in terms of sensitivity, specificity and the area under the curve in a receiver operating characteristic curve. Results: The 95% confidence interval of the area under the curve of the receiver operating characteristic of the lateral probe was 0.61–1.00 and that of the frontal probe was 0.65–1.00; therefore there is virtually no difference between the two methods. In 18% of the cases the lateral transcranial cerebral oximetry was hindered by practical failures. Conclusion: Considering the lack of additional information and the practical problems experienced with the lateral probe, it was concluded that transcranial cerebral oximetry with a single frontal probe is a practical non-invasive monitoring system and is at least as representative for monitoring cerebral ischaemia during carotid cross-clamping as a lateral probe.