The Use of Near-Infrared Cerebral Oximetry in Awake Carotid Endarterectomy

doi:10.1016/S0952-8180(97)00252-3

Journal of Clinical Anesthesia

Volume 10, Issue 2, March 1998, Pages 109-113

https://doi.org/10.1016/S0952-8180(97)00252-3 Get rights and content

Abstract

Study Objective: To determine the utility of cerebral oximetry for monitoring the adequacy of cerebral blood flow (CBF) during carotid cross-clamp.

Design: Prospective study.

Setting: University hospital.

Patients: 16 consecutive ASA physical status III (or higher) patients for awake carotid endarterectomy (CEA).

Interventions: Regional cerebral oxygen saturation (SaO₂) was monitored continuously during CEA, which was performed by the same surgeon, and with standard regional anesthetic, sedation, monitoring, and operative techniques. Data were recorded and analyzed using repeated measures analysis of variance (ANOVA).

Measurements and Main Results: 14 hemodynamically stable patients demonstrated significant decreases in cerebral SaO₂ from baseline: 69 + 1.8% to 64 + 1.2% at carotid cross-clamp (p < 0.001). After 5, 10, and 15-minute cross-clamp time, cerebral SaO₂ was 63 + 1.4%, 64 + 1.5%, and 63 + 1.4%, respectively (p < 0.001, vs. baseline). On cross-clamp removal, cerebral SaO₂ rose significantly: 67 + 1.6% (p < 0.01 vs. 5, 10, and 15 min). Two hypotensive patients (mean arterial pressures of 40 and 43 mmHg) developed signs and symptoms of global cerebral ischemia, with a concomitant decrease in cerebral oximetry (40% and 48%, respectively). These changes resolved with correction of hypotension.

Conclusion: Cerebral SaO₂ decreased significantly on carotid cross-clamp in patients undergoing awake CEA. Hemodynamically stable patients demonstrated no evidence of regional brain failure when SaO₂ decreased to 63% (mean decrease of 7.2%). Two hemodynamically unstable patients had evidence of global brain failure when SaO₂ was less than 48% (mean decrease of 36%). Our findings suggest that cerebral oximetry reflects CBF, and it may be an effective, noninvasive method of monitoring regional cerebral oxygenation changes during CEA. Significant reductions in regional SaO₂ may be tolerated without evidence of brain failure. Further studies are needed to define an SaO₂ threshold that reflects regional brain failure.

Introduction

Near-infrared spectroscopy is a noninvasive technology used to measure cerebral oxygenation. The INVOS 3100 cerebral oximeter (Somanetics, Troy, MI) is a near-infrared spectroscopic device designed for cerebral oximetry, approved by the Food and Drug Administration for investigational use¹. Carotid endarterectomy (CEA) is associated with variable decreases in cerebral perfusion at the time of cross-clamp and, hence, variable decreases in regional cerebral oxygen saturation (SaO₂) would be expected. In an effort to examine the clinical utility of cerebral oximetry, we used the INVOS 3100 cerebral oximeter in patients undergoing CEA during regional anesthesia.

CEA is now established as a prophylactic procedure for the prevention of stroke in patients with symptomatic and asymptomatic internal carotid artery stenosis.1, 2, 3However, the benefit of CEA in both groups of patients requires the occurrence of minimal perioperative morbidity and mortality. One of the most serious complications of CEA is the occurrence, or aggravation, of a neurologic deficit. Two major causes of intraoperative cerebral ischemia are embolic events and decreased cerebral blood flow (CBF). Decreased CBF, secondary to inadequate collateral flow, may be detected by a variety of techniques, including stump pressure monitoring, determination of jugular venous oxyhemoglobin saturation, transcranial Doppler ultrasonography, electroencephalography (EEG), and somatosensory-evoked potentials. However, these techniques may be unreliable because they lack sensitivity and specificity, and the data may be difficult to interpret.4, 5, 6, 7Therefore, neurologic monitoring of the awake patient during carotid cross-clamp has been suggested as the most sensitive indicator of the adequacy of CBF.[8]

Recently, several clinical studies of cerebral oxygenation have been published using several different near-infrared spectroscopic instruments to monitor regional SaO₂ in the brain. Near-infrared spectroscopy allows continuous, noninvasive measurement of cerebral tissue oxygenation, and its use has been advocated in settings of head trauma and acute stroke, and during head and neck surgery.9, 10, 11To date, most studies of cerebral oximetry during CEA have been in patients administered general anesthesia,12, 13while only two reports have been in patients undergoing awake CEA.²[14]

One problem in using cerebral oximetry during CEA is that a critical SaO₂ threshold, below which neurologic dysfunction would develop, remains to be defined. Therefore, we used cerebral oximetry in patients who underwent CEA during regional anesthesia, expanding our original patient population,[4]all of whom were diagnosed and treated by the same surgeon for similar pathology. The purpose of this study was to determine whether changes in cerebral SaO₂ could predict which patients might benefit from insertion of a shunt during CEA with general anesthesia.

Section snippets

Materials and Methods

Following SUNY Health Science Center at Syracuse Institutional Board Review approval, a prospective study was carried out on 16 consecutive ASA physical status III (or higher) patients undergoing elective CEA. Patients were all male, and they ranged in age between 53 and 74 years. Anesthesia was accomplished with deep and superficial cervical plexus block supplemented by local anesthetic infiltration and intravenous (IV) analgesia. CEA was performed by the same surgeon using a standard

Results

All but two patients remained hemodynamically stable systemically before, during, and after the carotid cross-clamp. (The two unstable patients will be considered separately.) Arterial saturation was greater than 95% in the hemodynamically stable patients at all times during the operation. Mean hemoglobin, hematocrit, and ASA scores were 13.6 ± 0 g/dl, 39.7 ± 1.9%, and 3, respectively. Under baseline conditions, and shortly after the hemodynamically stable group entered the operating room (OR),

Discussion

Cerebral protection during CEA is more important than ever, because recent standardized trials demonstrate better outcome in patients with symptomatic and asymptomatic internal carotid artery stenosis treated with CEA rather than medical therapy.1, 2, 3Of the current intraoperative cerebral monitoring techniques, it is generally accepted that neurologic examination in the awake patient is the most sensitive monitor of cerebral function and adequacy of CBF.[8]For this reason, we evaluated

Addendum

The cost of the equipment used in this study, as incurred by our institution, was approximately $50.00 per sensor [we purchased the sensors, and the manufacturer (Somanetics) supplied the cerebral oximeter]. Total cost of this equipment was approximately $800.00.

Acknowledgements

The authors wish to thank Reza Gorji, MD, and Enrico Camporesi, MD, for their support in recording intraoperative oximetric data.

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Cerebral ischemia during carotid endarterectomy occurs via several mechanisms: inadequate collateral blood flow during carotid cross-clamping, thromboembolism due to carotid manipulation, and/or rethrombosis at the surgical site. Perioperative strokes increase not only the morbidity of endarterectomy but also its short- and long-term mortality. However, while several predictors of cerebral ischemia have been identified, precise individual risk is hard to assess. Since nonselective shunting during carotid cross-clamping is neither risk-free nor eliminates perioperative stroke, it is advisable to apply intraoperative monitoring techniques for detection and reversal of cerebral ischemia, which may occur at various stages of the procedure. This chapter addresses the methods available for monitoring, with an emphasis on neurophysiologic techniques, which are preferable given their direct assessment of how a decrease in cerebral blood flow impacts brain function. These include electroencephalography, somatosensory evoked potentials, and transcranial motor evoked potentials. Details regarding the methodology, advantages, disadvantages, and interpretation of these tests will be discussed within the anatomic, physiologic, surgical, and anesthetic contexts.
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To remedy carotid artery stenosis and prevent stroke surgical intervention is commonly used, and the gold standard being carotid endarterectomy (CEA). During CEA cerebrovascular hemoglobin oxygen saturation decreases and when this decrease reaches critical levels it leads to cerebral hypoxia that causes neuronal damage. One of the proposed mechanism that affects changes during CEA and contribute to acute brain ischemia (ABI) is oxidative stress. The increased production of reactive oxygen species and reactive nitrogen species during ABI may cause an unregulated inflammatory response and further lead to structural and functional injury of neurons. Antioxidant activity are involved in the protection against neuronal damage after cerebral ischemia. We hypothesized that neuronal injury and poor outcomes in patients undergoing CEA may be results of oxidative stress that disturbed function of antioxidant enzymes and contributed to the DNA damage in lymphocytes.
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The beach chair position is commonly used when performing shoulder arthroplasty. However, this position has been associated with hypotension, potentially leading to cerebral hypoperfusion, which may cause neurologic injury. In addition, shoulder arthroplasty cases are associated with longer operative times, posing a potentially greater risk of cerebral hypoperfusion. We aim to evaluate the risk of cerebral desaturation events (CDEs) during the course of total shoulder arthroplasty.
Twenty-six patients undergoing shoulder arthroplasties were monitored for changes in cerebral perfusion. Seven specific time-points during the procedure were labeled for comparison of events: baseline, beach chair, incision, humeral broaching, glenoid reaming, glenoid component implantation, and humeral component implantation. Cerebral oxygen perfusion was measured using near-infrared spectroscopy. A CDE was described as a decrease of oxygen saturation greater than 20%.
Nineteeen of 25 subjects experienced a CDE. 42% of these patients experienced CDEs during semi–beach chair positioning. Patients experienced the largest oxygen saturation drop during semi–beach chair positioning. Transition from baseline to semi–beach chair was the only event to have a statistically significant decrease in cerebral perfusion (8%, P < .05). There was a statistically significant percentage change in mean oxygen saturation in the semi–beach chair interval (10%, P < .01) and the semi–beach chair to incision interval (7%, P < .01).
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Neurologic Derangement and Regional Cerebral Oxygen Desaturation Associated with Patency of the Circle of Willis during Carotid Endarterectomy
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To explore the relationship between the maximal fractional decrease of regional cerebral oxygen saturation (rSO₂) in neurologic derangement and the patency of the circle of Willis and contralateral carotid artery stenosis.
A prospective observational study.
A tertiary-care university hospital
This study enrolled 307 patients undergoing carotid endarterectomy under regional anesthesia.
No interventions.
Magnetic resonance angiography and carotid color-duplex ultrasound were performed, and the rSO₂ was recorded. The relationship between the maximal fractional decrease of rSO₂ from preclamp baseline against shunt insertion and patency of the circle of Willis was analyzed by a 2-way analysis of variance. Receiver operating characteristic analysis of the maximal fractional decrease of rSO₂ also was performed to calculate the cut-off value for detecting neurologic derangement. In addition, probability of shunt insertion was estimated by logistic regression. Patency of the circle of Willis did not influence the maximal fractional decrease of rSO₂. When both anterior and posterior circulations were nonpatent, the degree of contralateral carotid artery stenosis (Contra) was 54.7%±29.0% versus 40.7%±26.0% in patients with versus without shunting, respectively (p<0.05). The cut-off value of rSO₂ for predicting shunt insertion was 25.8%, regardless of the patency of the circle of Willis. Probability of shunt insertion for nonpatent anterior circulation = exp(–2.02+0.02×Contra)/[1+exp(–2.02+0.02×Contra)].
The rSO₂ can be used to predict shunt insertion, regardless of the patency of the circle of Willis. The probability of shunt insertion increased with increasing degree of contralateral carotid artery stenosis in the absence of anterior circulation in the circle of Willis.
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Citation Excerpt :
A noninvasive technique, NIRS allows continuous monitoring and has been demonstrated to accurately recognize cerebral oxygen desaturation.25,26 This technique is used extensively to monitor cerebral perfusion during cardiovascular surgery, neurosurgical procedures and carotid endarterectomy (CEA).3,35 In awake subjects undergoing CEA, cerebral oxygen desaturation, detected using NIRS, correlated with development of clinical and EEG signs of cerebral ischemia during carotid cross-clamping.30
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Original ContributionsThe Use of Near-Infrared Cerebral Oximetry in Awake Carotid Endarterectomy

Abstract

Introduction

Section snippets

Materials and Methods

Results

Discussion

Addendum

Acknowledgements

J Vasc Surg

J Vasc Surg

Lancet

Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade stenosis

N Engl J Med

Jugular venous oxygen saturation as an index of adequacy of cerebral oxygenation

Surgery

Intraoperative assessment of cerebral ischemia during carotid surgery

J Cardiovascular Surg

Benefits, shortcomings, and costs of EEG monitoring

Ann Surg

Original Contributions
The Use of Near-Infrared Cerebral Oximetry in Awake Carotid Endarterectomy