Original contribution
A clinical evaluation of near-infrared cerebral oximetry in the awake patient to monitor cerebral perfusion during carotid endarterectomy

https://doi.org/10.1016/j.jclinane.2004.09.007Get rights and content

Abstract

Study Objective

To evaluate the relationship between continuous noninvasive monitoring of cerebral saturation (regional cerebral oxygen saturation [rSo2]) and occurrence of clinical and electroencephalographic (EEG) signs of cerebral ischemia during carotid cross-clamping.

Design

Prospective clinical study.

Setting

University hospital.

Patients

Fifty ASA physical status II and III inpatients undergoing elective carotid endarterectomy with a cervical plexus block.

Interventions

rSo2 was continuously monitored throughout surgery, while an independent neurologist evaluated the occurrence of both clinical and EEG signs of cerebral ischemia induced during carotid cross-clamping.

Measurements and Main Results

rSo2 was recorded 1 and 3 minutes after clamping the carotid artery during a 3-minute clamping test. In 5 patients (10%), the carotid clamping test was associated with the occurrence of clinical and EEG signs of cerebral ischemia. All these patients were treated with the placement of a Javid shunt, which completely resolved the symptoms. In no patient was permanent neurological injury reported at hospital discharge. In 4 of these patients, EEG signs of cerebral ischemia were present at both observation times, and in one of them, the duration of cerebral ischemia was less than 2 minutes. The percentage rSo2 reduction from baseline during the carotid clamping test was 17% ± 4% in patients requiring shunt placement and only 8% ± 6% in those who did not require it (P = .01). A decrease in rSo2 15% or greater during the carotid clamping test was associated with a 20-fold increase in the odd for developing severe cerebral ischemia (odds ratio, 20; 95% confidence interval, 6.7-59.2) (P = .001); however, this threshold had a 44% sensitivity and 82% specificity, with only 94% negative predictive value.

Conclusions

Continuous rSo2 monitoring is a simple and noninvasive method that correlates with the development of clinical and EEG signs of cerebral ischemia during carotid cross-clamping; however, we could not identify an rSo2 threshold that can be used alone to predict the need for shunt placement because of the low sensitivity and specificity.

Introduction

It is well documented that carotid endarterectomy (CEA) improves neurological outcome in patients with high-grade stenosis of the carotid artery [1], [2]. However, the need for cross-clamping the carotid artery may result in serious brain damage during surgery because of insufficient collateral blood flow, a situation that makes intraoperative monitoring of cerebral perfusion a necessity in the prevention of severe neurological complications [3].

Real-time clinical evaluation of neurological function still remains unsurpassed by any currently available alternative measure of brain perfusion but can be applied only when regional anesthesia is used. If the patient is not awake, electroencephalography (EEG) is the standard monitoring system routinely used to detect alterations in cerebral perfusion during CEA [4], [5]; however, this monitoring system requires a dedicated technician and EEG machine. Near-infrared spectroscopy (NIRS) is a noninvasive technique that allows continuous monitoring of cerebral oxygenation through the scalp and skull [6] and has been demonstrated to accurately recognize cerebral hemoglobin oxygen desaturation produced by systemic hypoxemia [7]. This technology has been demonstrated to be clinically useful during open-heart surgery, neurosurgical procedures, and management of patients with head injury [8], [9], but it might also identify a critical level of regional cerebral oxygen saturation (rSo2) predicting cerebral ischemia during CEA sufficient to dictate the need for temporary shunting.

The aim of this prospective study was to evaluate the relationship between rSo2 monitoring and occurrence of both clinical and EEG signs of cerebral ischemia in awake patients receiving carotid cross-clamping during carotid CEA performed with regional anesthesia.

Section snippets

Materials and methods

After San Raffaele Hospital Ethical Committee Approval and written informed consent were obtained, 50 ASA physical status II and III adults, aged 51 to 90 years and undergoing elective CEA with regional anesthesia, were prospectively studied. Patients with contralateral carotid occlusion, evidence of cortical ischemic lesion on computed tomography scan, or neurological deficit of the contralateral side were excluded from the study.

Oral premedication with diazepam (0.07 mg/kg) was given 90

Results

All surgical procedures were successfully completed, and none of the study patients reported permanent neurological deficit at hospital discharge. Fifty consecutive patients (aged 51-90 years, ASA physical status II-III) were included in the study. In 1 patient, who did not show any clinical sign of cerebral ischemia, the EEG recording was not reliable as a result of technical problems, and the patient was thus excluded from the final analysis.

In 5 patients (10%), the carotid clamping test was

Discussion

Monitoring rSo2 provides information on the balance between cerebral oxygen supply and consumption and has been reported to be clinically useful during open-heart surgery, neurosurgical procedures, management of patients with head injury, and monitoring of cerebral perfusion in patients undergoing CEA [16], [17], [18]. The results of this prospective investigation confirm previous findings that changes in regional rSo2 during the first 3 minutes after carotid clamping correlate with the

Acknowledgments

The authors thank Mrs Carla Fornara (Department of Neurophysiology, Vita-Salute University of Milan, San Raffaele Hospital) for her valuable help with EEG monitoring.

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