skip to main content

Cerebral Oximetry Carotid Surgery — FRCA Final MCQ

Instant feedback + full explanation. One question, done properly.

HardGeneral AnaesthesiaCerebral Oximetry Carotid SurgeryFRCA Final

A 60-year-old man (ASA III) is undergoing right carotid endarterectomy under general anaesthesia using selective shunting. Immediately after internal carotid artery cross-clamping, correctly positioned bilateral NIRS monitoring shows a persistent 25% reduction in right-sided regional cerebral oxygen saturation from the stable pre-clamp value; the contralateral value is unchanged. The mean arterial pressure has been increased to 20% above the patient's awake baseline, arterial oxygen saturation is 99%, normocapnia is confirmed and haemoglobin concentration is unchanged. What is the most appropriate next intervention?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: D — Request insertion of a temporary carotid shunt

The correct answer is D. The abrupt, ipsilateral and persistent 25% fall in rSO2 after cross-clamping indicates clamp-related cerebral hypoperfusion. Because sensor position, oxygenation, carbon dioxide, haemoglobin and perfusion pressure have already been addressed, a temporary intraluminal shunt is required to restore flow across the clamp. Published NIRS thresholds vary, but reductions of approximately 15–20% have been used to direct selective shunting; NIRS should therefore be interpreted as a trend within a physiological algorithm rather than as an infallible absolute threshold. FiO2 1.0 provides little benefit when arterial saturation is already 99%. Hypothermia and thiopental are not substitutes for restoring cerebral blood flow. Deepening anaesthesia may lower cerebral metabolic demand but can worsen haemodynamics and does not correct the perfusion deficit.

Reference: Pennekamp CWA et al. Near-infrared spectroscopy to indicate selective shunt use during carotid endarterectomy. European Journal of Vascular and Endovascular Surgery. 2013;46:397–403. https://pubmed.ncbi.nlm.nih.gov/23973277/