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

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.

Automatic embolus detection compared with human experts. A Doppler ultrasound study.

BACKGROUND AND PURPOSE: Transcranial Doppler ultrasound (TCD) reliably detects the occurrence of microembolic signals (MES). Unfortunately, TCD monitoring is a time-consuming and mentally strenuous procedure. The purpose of this study was to assess whether automatic embolus detection software devices acting as a "stand-alone system" are able to identify MES in patients with solid cerebral microemboli. METHODS: Ten records of TCD monitoring of the middle cerebral artery in patients with symptomatic high-grade carotid artery stenosis were analyzed for the moments at which MES occurred by four observers and three automatic detection software devices (RB11 on TC2000, Pioneer Version 2.10, and Embotec). The results of the three software systems were assessed on the basic assumption that MES were present if at least three of the four observers agreed. RESULTS: The average number of 1-second periods in which MES were detected by the four observers per tape ranged from 5 to 39. The overall kappa values (and SEs) for chance-corrected interobserver agreement between the four observers ranged from .94 (.02) to .99 (.01). The agreement between the software devices and the observers was lower, with kappa values (and SEs) ranging from .18 (.17) to .93 (.07). The RB11 and Embotec systems achieved a kappa value higher than 0.4 in all tapes. The Pioneer system failed to reach a kappa value of 0.4 in three tapes. The RB11 showed a sensitivity of 70% for detecting MES, the Embotec 62%, and the Pioneer 44%. CONCLUSIONS: In patients with symptomatic high-grade carotid artery stenosis, a high degree of agreement in the detection of moments of MES can be achieved between observers. The three automatic detection software devices reached less agreement. Supervision of TCD monitoring and assessment of MES by an experienced observer is still necessary.