Non-Invasive Cerebral Autoregulation Monitoring During Awake Carotid Endarterectomy Identifies Clinically Significant Brain Ischaemia

Abstract

Objective: The aim was to evaluate the potential of near infrared spectrometry (NIRS) monitoring enhanced by autoregulation parameters to detect clamp ischaemia during awake carotid endarterectomy (CEA).

Methods: This was a prospective, hypothesis generating, single centre observational study. Fifty-nine consecutive patients with carotid artery stenosis, of whom 15 (25%) were symptomatic, were enrolled. The patients underwent awake CEA with NIRS monitoring. Regional oxygen saturation (rSO₂), relative tissue haemoglobin concentration (rTHb), and mean arterial blood pressure were captured by ICM + software (University of Cambridge Enterprise, Cambridge, UK). The cerebral oxygenation index (COx) and haemoglobin volume index (HVx) were calculated continuously. Two groups were formed depending on neurological symptoms: a symptomatic group with shunt insertion (shunt) and an asymptomatic group (no shunt).

Results: Eight patients (14%) became symptomatic and needed intra-operative shunting. The decrease in ipsilateral rSO₂ was higher in the shunt group (13.5% vs. 5.3%) and rTHB increased on the non-operated side (+0.05 ± 0.01; p = .016). In symptomatic patients no significant change in rTHB was found during clamping, whereas in asymptomatic patients there was a bilateral increase (ipsilateral: + 0.06 [p = .022]; contralateral: + 0.06 [p = .010]). In asymptomatic patients, ipsilateral COx decreased after clamping (-0.06 ± 0.02; p = .024), indicating functional autoregulation. In symptomatic patients, ipsilateral COx increased to 0.32 (+0.19 ± 0.05; p = .048), indicating loss of autoregulation. Accordingly, pooled ipsilateral and contralateral data showed increasing HVx and COx in symptomatic patients (HVx, p < .001; COx, p = .039).

Conclusion: In addition to a drop in rSO₂, the loss of autoregulatory capacity may be useful in identifying clinically significant clamping ischaemia during CEA under general anaesthesia and may allow optimisation of blood pressure management during awake CEA.

Keywords: Carotid endarterectomy; Intraoperative neurophysiological monitoring; Near-infrared spectroscopy; Stroke.