Limitation of Near Infrared Spectroscopy Cerebral Oximetry in Predicting Neurologic Intolerance during Carotid Artery Stenting with Proximal Protection

Proximal balloon occlusion prior to carotid artery stenting is considered a relatively safe practice during endovascular treatment of carotid artery stenosis. Transient neurological deterioration affecting the ipsilateral hemisphere is seen soon after balloon inflation, when placed proximal to the stenotic segment. This occurs in cases of bilateral carotid disease due to insufficient collateral blood flow from the contralateral side. Near infrared spectroscopy cerebral oximetry (NIRS) is a valuable tool in detecting hypoperfusion- induced cerebral tissue desaturation (rSO2) during these procedures. This helps the interventional radiologist to deflate the balloon at the earliest to re-establish the cerebral blood flow. The non-invasive nature and continuous real-time interpretation make NIRS an attractive adjunct in the neuroanesthesiolgist's armamentarium for monitoring cerebral ischemia. However, significant contribution from chromophores in the extra-cerebral tissues and external carotid artery circulation can limit its sensitivity during occlusion of the internal carotid artery. In our case, it did not reflect brain ischemia during hypotension and when the neurologic symptoms were obvious. Commonly available cerebral oximetry sensors placed over the frontal region do not cover the parietal lobe where ischemia is likely to occur during occlusion of the carotid artery. In such scenarios, it has been shown that multi-channel NIRS has a better sensitivity in detecting cerebral ischemia. This case report highlights the importance of frequent neurological examination during carotid stenting as rSO2 values might not always suggest cerebral ischemia.