Surgery to remove plaque from the carotid artery in the neck requires the artery to be clamped for a period of time. In some patients this reduces blood flow to the brain enough to cause temporary symptoms, and a temporary plastic tube called a shunt has to be inserted to restore flow. When the operation is performed with the patient awake under a local anaesthetic block, doctors decide whether a shunt is needed by talking to the patient and testing the strength of the hand on the opposite side during clamping. This is called the awake neurological test.
A device called a cerebral oximeter can measure the oxygen level in the front part of the brain continuously and without needles, using light shone through the forehead. It has been suggested as a way of detecting reduced brain blood flow during this operation, and would be particularly useful for patients who are asleep under general anaesthesia and cannot be tested. However, previous studies have often chosen their alarm level after looking at their own results, and have often allowed the operating team to see the oximeter readings, which makes the results appear better than they really are.
In this study, 150 adults having planned carotid surgery under a local anaesthetic block will have a cerebral oximeter attached to the forehead throughout the operation. The screen will be covered so that neither the anaesthetist nor the surgeon can see the readings, and the decision to insert a shunt will be based only on the awake neurological test, exactly as it is now. The oxygen readings will be stored inside the device and examined only after the operation.
The main question is how accurately a fall of 20% or more in brain oxygen level, a level chosen in advance from previous published research, identifies the patients whose awake test becomes abnormal during clamping. The second question is whether the total amount of low brain oxygen during clamping is related to confusion or stroke in the first three days after surgery, and to memory change one month later. Participants complete a short memory test before the operation and again at one month, using different versions of the test on each occasion.
Age 18 years or older.
Internal carotid artery stenosis of at least 50% if symptomatic, or at least 70% if asymptomatic, measured by NASCET criteria, with an indication for carotid endarterectomy.
Elective surgery planned under regional anaesthesia using combined superficial cervical plexus and carotid sheath block.
Able to cooperate with awake neurological testing and with cognitive assessment.
Emergency or urgent surgery within 48 hours of an acute stroke.
Inability to cooperate with testing, including aphasia, dementia, a baseline Montreal Cognitive Assessment score below 18, or severe visual or hearing impairment.
Redo ipsilateral endarterectomy, simultaneous bilateral endarterectomy, or a combined procedure such as concomitant coronary artery bypass grafting.
Bilateral forehead skin lesions preventing sensor placement.
Consecutive adults with carotid artery stenosis scheduled for elective carotid endarterectomy under regional anaesthesia at a single tertiary referral centre in Hanoi, Vietnam.
Cohort
Prospective
Masked continuous cerebral oximetry
Diagnostic testContinuous bilateral frontal near-infrared spectroscopy recorded at a minimum of one value every 5 seconds throughout surgery using a single oximeter model, with the display covered and alarms disabled so that no value is visible to the anaesthetic or surgical team. Readings contribute to no clinical decision.
Standardised awake neurological test
Diagnostic testSerial structured assessment of verbal responsiveness, naming, contralateral hand grip strength and level of consciousness at fixed intervals during carotid cross-clamping, performed by an anaesthetist masked to rSO2 and serving as the sole basis for shunt placement.
Serial cognitive assessment
Diagnostic testMontreal Cognitive Assessment administered using alternate versions at baseline and at one month by an assessor masked to all oximetry data.
1. Sensitivity and specificity of a 20% or greater relative decline in ipsilateral rSO2 for a positive awake neurological test
The pre-specified primary index test threshold is compared with the awake neurological test as reference standard in a two-by-two table. Sensitivity and specificity are reported as percentages with 95% Wilson confidence intervals, together with positive and negative predictive values, positive and negative likelihood ratios and overall accuracy.
Incidence of new neurological deterioration within 72 hours
Composite outcome defined as the occurrence of either a new focal neurological deficit or stroke, assessed using the National Institutes of Health Stroke Scale with imaging confirmation, or postoperative delirium, assessed twice daily using the Confusion Assessment Method for the Intensive Care Unit or the 3-Minute Diagnostic Confusion Assessment Method. Reported as the number and percentage of participants with the composite outcome, and analysed in relation to cumulative intraoperative cerebral desaturation burden.
Area under the receiver operating characteristic curve of the relative decline in ipsilateral rSO2
Discrimination of the continuous relative decline in ipsilateral rSO2 for a positive awake neurological test, expressed as the area under the curve with a 95% confidence interval.
Sensitivity and specificity at additional pre-specified rSO2 thresholds
Accuracy against the awake neurological test at a relative decline of 12% or more, a relative decline of 10% or more, an absolute decline of 10 percentage points or more, and an absolute value below 50%. Each reported as sensitivity and specificity in percent with 95% Wilson confidence intervals.
Cumulative cerebral desaturation burden
Area under the ipsilateral rSO2 curve below the line corresponding to a 20% relative decline from the pre-clamp awake baseline, computed from raw trend data and expressed in percentage-minutes.
Device-reported area under the curve index
The area under the curve index generated by the oximeter, quantifying depth and duration below a low alarm limit fixed at 50% for all participants, expressed in percentage-minutes and calculated as the difference between the values recorded at declamping and at clamping. Agreement with the raw-data measure is reported.
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Nguyen Toan Thang
Lead sponsor
Bach Mai Hospital
Sponsor institution
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