Carotid endarterectomy without shunt: the role of cerebral metabolic protection

Electroencephalographic Burst-Suppression, Perioperative Neuroprotection, Postoperative Cognitive Function, and Mortality: A Focused Narrative Review of the Literature

Burst-suppression is an electroencephalographic pattern that results from a diverse array of pathophysiological causes and/or metabolic neuronal suppression secondary to the administration of anesthetic medications. The purpose of this review is to provide an overview of the physiological mechanisms that underlie the burst-suppression pattern and to present in a comprehensive way the available evidence both supporting and in opposition to the clinical use of this electroencephalographic pattern as a therapeutic measure in various perioperative settings.

Intraoperative Cerebral Monitoring During Carotid Surgery: A Narrative Review

BACKGROUND

Intra-operative neurological monitoring (IONM) during carotid endarterectomy (CEA) aims to reduce neurological morbidity of surgery.

OBJECTIVE

This narrative review analyses the role and results of different methods of IONM.

METHODS

review articles on PUBMED and Cochrane Library, by searching key words related to IONM and CEA, from 2000 up to date.

RESULTS

regional anesthesia in some centers represents the "gold standard". The most often used alternative techniques are: stump pressure, electroencephalogram, somatosensory evoked potentials, transcranical doppler ultrasound, near infrared spectroscopy and routine shunting. Every technique shows limitations. Regional anesthesia can make difficult prompt intubation when needed. Stump pressure shows a wide operative range. Electroencephalogram is unable to detect ischemia in sub-cortical regions of the brain. Somatosensory evoked potentials certainly demonstrate the presence of cerebral ischemia, but are no more specific or sensitive than the electroencephalogram. Transcranical doppler monitoring is undoubtedly operator-dependent and suffers from the limitations that the probe has to be placed relatively near to the surgical site and may impede the operator, especially if it needs constant adjustments; moreover, an acoustic window may not be found in 10% -20% of the subjects. Near infrared spectroscopy appears to have a high negative predictive value for cerebral ischemia, but has a poor positive predictive value and low specificity, because predominantly estimates venous oxygenation as this makes up about 80% of cerebral blood volume. The data on the use of Routine Shunting (RS) from RCTs are limited.

CONCLUSIONS

currently, with no clear consensus on monitoring technique, choice should be guided by local expertise and complication rates. With reflection, best practice may dictate that a standard technique is selected as suggested above and this remains the default position for individual practice. Nevertheless, current techniques for monitoring cerebral perfusion during CEA are associated with false negative and false positive resulting in inappropriate shunt insertion.

[Cerebral protection from ischaemia during carotid endarterectomy]

The purpose of this study was to assess efficacy of cerebral protection during carotid endarterectomy by means of controlled systemic hypertension in patients presenting with various levels of retrograde pressure in the internal carotid artery. The study enrolled a total of 150 patients subjected to carotid endarterectomy. The operation was carried out under general anaesthesia with artificial pulmonary ventilation and was accompanied by haemodynamic monitoring with invasive control of arterial pressure, as well as primary and additional correction of central haemodynamics. Cerebral perfusion was assessed by measuring retrograde pressure in the internal carotid artery. The retrograde pressure index was calculated, according to which the patients were subdivided into three groups: those with values less than 30, with values from 30 to 39, and with values of 40 and more. Controlled systemic arterial hypertension was used as cerebral protection during the period of cross-clamping of the internal carotid artery, with phenylephrine and norepinephrine administered for this purpose. The parameters of central haemodynamics, time intervals of the operation, and the duration of internal carotid artery cross-clamping in the groups did not statistically differ (p>0.05). A statistically significant difference was revealed in the level of systolic arterial pressure necessary for cerebral protection (p<0.05). There were no cerebral circulation impairments, myocardial infarctions, nor lethal outcomes. A conclusion was drawn that individualized correction of central haemodynamics ensured a sufficient level of collateral compensation of the cerebral blood flow, thus making it possible to refuse from using intraluminal shunts.

Selective Patch Angioplasty and Intraoperative Shunting in Carotid Endarterectomy: A Single-Center Review of 141 Procedures

Objective: Open surgical treatment of carotid artery stenosis, namely, carotid endarterectomy (CEA), has evolved since its inception in 1953. Despite improvements in the treatment of carotid occlusive disease through technological and surgical innovations, the use of patch grafting in CEA’s remains controversial. We evaluate the durability of the primary closure and the safety of selective shunting during carotid endarterectomy (CEA) as determined by intraoperative EEG and postoperative outcomes.

Methods: A consecutive series of CEA’s performed by the senior author at a single academic medical center from 2001 to 2012 were reviewed. All cases were performed under continuous intraoperative electroencephalography (EEG). Patch angioplasty was used in cases where there was tortuosity of the vessel within the region of the endarterectomy and narrow vessel diameter at the distal end of the arteriotomy. Shunting was used when intraoperative EEG showed a > 50% reduction in a waveform in any lead. Patients were evaluated for restenosis via imaging or ultrasound at six months and subsequently annual follow-up.

Results: One hundred and forty-one CEA’s were performed on 132 (76 male, 56 female) patients with an average age of 71 years (range: 40–95 years). Four (3%) cases required patch angioplasty and three (2%) required intraoperative shunts. The cross-clamp time ranged from 22 to 74 minutes, and the duration increased with the use of shunts and patches. Complications were rare and included recurrent stenosis (n=2), postoperative transient ischemic attack (n=1), ischemic stroke in (n=1), temporary hypoglossal nerve weakness (n=2), temporary marginal mandibular nerve weakness (n=6), and neck hematoma (n=1).

Conclusion: Intraoperative EEG data suggests that primary closure and selective shunting in CEA can result in outcomes comparable with routine patch angioplasty and shunting.

Intentional Hypertension During Dissection of Carotid Arteries in Endarterectomy Prevents Postoperative Development of New Cerebral Ischemic Lesions Caused by Intraoperative Microemboli

BACKGROUND:

Low blood flow velocity in the middle cerebral artery (MCA) correlates with the development of postoperative cerebral ischemic lesions related to generation of microemboli during dissection of carotid arteries in carotid endarterectomy (CEA).

OBJECTIVE:

The purpose of this prospectively controlled trial was to determine whether increased mean blood flow velocity in the MCA by intentional hypertension during carotid dissection in CEA prevented postoperative development of new cerebral ischemic lesions caused by intraoperative microemboli.

METHODS:

Patients with ipsilateral internal carotid artery stenosis (&gt;70%) underwent CEA under transcranial Doppler monitoring of mean blood flow velocity and microembolic signals in the ipsilateral MCA. Attempts were made to keep systolic blood pressure during carotid dissection between −10% and +10% of the preoperative value (controls, n = 65) or above a +10% increase (intentional hypertension group, n = 65).

RESULTS:

Incidence of new ischemic lesions on postoperative diffusion-weighted magnetic resonance imaging was significantly lower in the intentional hypertension group both for all patients (controls, 15.4%; intentional hypertension group, 3.1%; P = .03) and in a subgroup of 37 patients showing microembolic signals during carotid dissection (controls, 52.6%; intentional hypertension group, 11.1%; P = .013). Logistic regression analysis demonstrated the absence of intentional hyperperfusion (95% confidence interval: 1.77-100.00; P = .012) and high number of microembolic signals (95% confidence interval: 1.00-1.62; P = .05) during carotid dissection were significant independent predictors of the postoperative development of new ischemic lesions on diffusion-weighted magnetic resonance imaging.

CONCLUSION:

Increased MCA mean blood flow velocity by intentional hypertension during dissection of the carotid artery in CEA prevents the postoperative development of new cerebral ischemic lesions caused by intraoperative microemboli.

Protocol for electrophysiological monitoring of carotid endarterectomies

Near zero stroke rates can be achieved in carotid endarterectomy (CEA) surgery with selective shunting and electrophysiological neuromonitoring. though false negative rates as high as 40% have been reported. We sought to determine if improved training for interpretation of the monitoring signals can advance the efficacy of selective shunting with electrophysiological monitoring across multiple centers, and determine if other factors could contribute to the differences in reports. Processed and raw beta band (12.5-30 Hz) electroencephalogram (EEG) and median and tibial nerve somatosensory evoked potentials (SSEP) were monitored in 668 CEA cases at six surgical centers. A decrease in amplitude of 50% or more in any EEG or SSEP channel was the criteria for shunting or initiating a neuroprotective protocol. A reduction of 50% or greater in the beta band of the EEG or amplitude of the SSEP was observed in 150 cases. No patient showed signs of a cerebral infarct after surgery. Selective shunting based on EEG and SSEP monitoring can reduce CEA intraoperative stroke rate to a near zero level if trained personnel adopted standardized protocols. We also found that the rapid administration of a protective stroke protocol by attending anesthesiologists was an important aspect of this success rate.

A case of traumatic internal carotid artery aneurysm secondary to carotid shunting

The use of a carotid shunt is a well-accepted method for the prevention of cerebral ischemia during carotid surgery. Although carotid surgeons are familiar with the risks associated with shunt use, few reports have been published detailing the nature, incidence, or severity of shunt-related complications. We report on a patient with dilatation of the distal cervical internal carotid artery at the site of Pruitt-Inahara (LeMaitre Vascular, Inc. Burlington, Mass) shunt balloon inflation. To our knowledge, this complication of shunting during carotid endarterectomy has not been previously described.

The mechanisms of the direct action of etomidate on vascular reactivity in rat mesenteric resistance arteries

BACKGROUND

Etomidate minimally influences hemodynamics at a standard induction dose in young healthy patients, but can cause significant systemic hypotension at higher doses for induction or electroencephalographic burst suppression (i.e., cerebral protection) in patients with advanced age or heart disease, and during cardiopulmonary bypass. However, less is known about its action on systemic resistance arteries.

METHODS

Using an isometric force recording method and fura-2-fluorometry, we investigated the action of etomidate on vascular reactivity in small mesenteric arteries from young (7-8 wk old, n = 179) and aged (96-98 wk old, n = 10) rats.

RESULTS

In the endothelium-intact strips from young rats, etomidate enhanced the contractile response to norepinephrine or KCl (40 mM) at 3 microM but inhibited it at higher concentrations (>or=10 microM). The enhancement was still observed after treatment with N(G)-nitro l-arginine, tetraethylammonium, diclofenac, nordihydroguaiaretic acid, losartan, ketanserin, BQ-123, or BQ-788, but was not observed in aged rats. In the endothelium-denuded strips from young rats, etomidate (>or=10 microM) consistently inhibited the contractile response to norepinephrine or KCl without enhancement at 3 microM. In the fura-2-loaded, endothelium-denuded strips from young rats, etomidate inhibited norepinephrine- or KCl-induced increases in both intracellular Ca(2+) concentration ([Ca(2+)]i) and force. Etomidate still inhibited the norepinephrine-induced increase in [Ca(2+)]i after depletion of the intracellular Ca(2+) stores by ryanodine, which was sensitive to nifedipine. Etomidate had little effect on norepinephrine- or caffeine-induced Ca(2+) release from the intracellular stores or Ca(2+) uptake into the intracellular stores. During stimulation with norepinephrine or KCl, etomidate had little effect on the [Ca(2+)]i-force relation at low concentrations (<or=30 microM) but caused its downward shift at 100 microM.

CONCLUSIONS

In small mesenteric arteries, etomidate influences the contractile response to norepinephrine or membrane depolarization through endothelium-dependent enhancing and endothelium-independent inhibitory actions. The enhancement is at least in part independent of nitric oxide, endothelium-derived hyperpolarizing factor, cyclooxygenase products, lipoxygenase products, angiotensin II, serotonin, or endothelin-1, but may involve some signaling pathway that is impaired by aging. The endothelium-independent inhibition is due to decreases in both the [Ca(2+)]i and myofilament Ca(2+) sensitivity in vascular smooth muscle cells. The decrease in [Ca(2+)]i would be due mainly to inhibition of voltage-gated Ca(2+) influx. The observed inability of lower concentrations (1-3 microM) of etomidate to cause significant vasodilation is consistent with minimal changes in hemodynamics during induction of anesthesia with etomidate in young subjects, whereas the observed vasodilator action of higher concentrations of etomidate might underlie systemic hypotension caused by higher doses of etomidate in the clinical setting.

Evaluation of Changes of Systemic Blood Pressure and Shunt Incidence in CEA

BACKGROUND

Induced hypertension is widely recommended as a protective measure in carotid endarterectomy (CEA) to prevent shunt insertion. In this study changes of systemic blood pressure were evaluated in relation to the shunt rate when CEA was performed under local anaesthesia.

MATERIALS AND METHODS

In 930 CEAs performed for a high-grade (>70%) ICA stenosis under local anaesthesia the mean systemic blood pressure was measured preoperatively (RR1) and directly before carotid cross-clamping (RR2). A ratio was calculated from these values (RRR=RR2/RR1). A shunt was only inserted for clinical signs of cerebral ischemia. If that became necessary later after cross-clamping had been tolerated primarily, the blood pressure during this period was also recorded (RR3). Also the presence of a contralateral ICA occlusion and baseline blood pressure levels were considered as factors with potential impact on shunt necessity.

RESULTS

Among the 638 male (69%) and 292 female (31%) patients with a median age of 70 years (ranging from 52 to 91 years) 82 (9%) had a contralateral ICA occlusion. A shunt was used in 177 operations (19%) and significantly more frequent in patients with a contralateral ICA occlusion (39/82=48% vs. 138/848=16%, p<0,001). RRR was significantly reduced in patients who needed a shunt (0.95 (0.41-1.53) vs. 1.0 (0.54-1.9), p=0.002) which was only true for patients with a patent contralateral ICA. The shunt rate did not differ when contrasting RRR thresholds (<0.7 vs. >1.3) or preoperative blood pressure levels (<100 mmHg vs. >120 mmHg) were compared. RRR did not differ between directly or delayed shunted patients. RR3 did not differ significantly from RR2. A regression analysis identified the presence of a contralateral ICA occlusion as the only independent parameter influencing shunt insertion.

CONCLUSIONS

Changes in systemic blood pressure during CEA under local anaesthesia seem to influence shunting rather marginally. The value of induced hypertension to prevent cerebral ischemia should be newly discussed.

Electrophysiology and neuronal integrity following systemic arterial hypotension in a rat model of unilateral carotid artery occlusion

Patients with carotid artery stenosis may be particularly susceptible to hypotension-associated cerebral ischemia and subsequent neurological sequelae. Measuring somatosensory evoked potentials (SEP), electroencephalogram (EEG), direct current (DC) potential, and histology, we compared the temporal evolution of cortical functional perturbations as well as neuronal integrity in a model of unilateral carotid artery occlusion and systemic hypobaric hypotension (HH) at the lower limit of cerebral blood flow autoregulation (50 mm Hg). Serial measurements of EEG power spectra as well as SEP-amplitudes and latencies of N10.3 were performed before, during, and up to 60 min after 30 min-HH (n=7) or the control condition (n=7) in male Wistar rats. In two additional groups (with [n=7] or without [n=7] HH), cortical spreading depressions (CSD) were elicited to ascertain their contribution to brain injury. Hematoxilin-Eosin (H&E) staining was used to assess neuronal cell death at 5 days after surgery. Relative to baseline, HH attenuated ipsilateral EEG power spectrum (by maximally 62%), increased SEP-latencies (by approximately 6-10%) and amplitudes (by approximately 57-70%), and induced selective neuronal cell death in the cerebral cortex and hippocampus (P<0.05 vs. contralateral). Spontaneous CSD occurred in approximately 30% of HH-animals. Repolarization of the DC-potential during HH was significantly prolonged relative to normotensive conditions (10.3+/-11.5 min, P<0.001). Our model may help to understand underlying pathophysiology and improve outcome in a clinical subset of patients with carotid artery stenosis and transient systemic hypotension.