Objective: Monitoring the central nervous system during carotid endarterectomy plays an important role in detection of cerebral ischemia. With optical spectroscopy in the near-infrared light range it is now possible to measure regional cerebral oxygen saturation (rSO2) noninvasively. Numerous studies emphasize the importance of cerebral oxygen balance rather than absolute values of cerebral blood flow or metabolic rate. In this study data from oxygen saturation measured in the jugular bulb (SJO2) were compared to rSO2.
Methods: 10 patients undergoing elective carotid end-arterectomy were enrolled after written informed consent and approval by the local ethics committee. rSO2 data were measured by cerebral spectroscopy (INVOS 3100, Somanetics, Michigan/USA). To avoid lesions of the internal carotid artery, a 4-F oxymetry catheter (OPTICATH, Abbot GmbH, Wiesbaden) was placed in the jugular bulb by retrograde approach after preparation by the surgeon. Anaesthesia and mechanical ventilation were standardised.
Results: After cross-clamping of the internal carotid artery rSO2 significantly decreased (60.5 +/- 3.5%) compared to baseline (66.0 +/- 1.4%). After declamping rSO2 increased significantly (63.0 +/- 4.2%) and was close to baseline at the end of operation (65.0 +/- 2.8%). The SJO2 time course showed good correlation compared to rSO2 data (r = 0.85). After cross-clamping SJO2 decreased significantly (51.5 +/- 6.3%) in comparison to baseline (59.5 +/- 4.9%). Declamping increased SJO2 to 59.5 +/- 6.3%. No changes in latencies or amplitudes of SEP were observed throughout the operation.
Conclusions: Noninvasive cerebral optical spectroscopy is a useful tool to determine the brain tissue oxygenation. The positive correlation to jugular bulb oxygen saturation is somewhat unexpected as rSO2 evaluates regional while SJO2 measures global oxygen content. However our results suggests that both methods are able to detect episodes of cerebral ischemia during carotid endarterectomy. The interpretation of the changes of cerebral oxygen saturation with respect to neurological outcome warrants further studies.