Carotid endarterectomy (CEA) is performed to prevent embolic stroke in patients with atheromatous disease at the carotid bifurcation. There is now substantial evidence to support early operation in symptomatic patients, ideally within 2 weeks of the last neurological symptoms. Thus, the anaesthetist may be faced with a high risk patient in whom there has been limited time for preoperative. Hemodynamic instability during carotid endarterectomy (CEA) is often a major. Patients who needed one or the other anesthetic technique for medical reasons.
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CEA requires temporary clamping of the carotid artery being worked on rendering the ipsilateral hemisphere dependent on collateral flow from the vertebral arteries and the contralateral carotid artery through the Circle of Willis. Neurologic monitoring is used to verify adequate perfusion of bilateral regions of the brain and to guide decision making in regards to shunting, BP control, and surgical technique. Also competing needs for increased BP vs. reducing myocardial workload, neurologic monitoring allows for aiming for lowest BP to maintain perfusion while reducing myocardial workload. Monitoring options include an awake patient under local anesthesia, EEG, SSEPs, and less often transcranial doppler(TCD), cerebral oximetry and stump pressures with reliability in that order.
Advantages of an awake patient: The most effective in detecting ischemic episodes, less post-op hypertension when done under field block, easy post-op neurologic exam.
Disadvantages of an awake patient: Requires very cooperative patient. Patient may panic, while draped in sterile field if he/she becomes aphasic or hemiplegic intraoperatively, and could require immediate GA and a secured AW. Anxious patients will have increased sympathetic response increasing risk for myocardial ischemia in patients already prone to cardiac events. And not all surgeons can work quickly enough to make a field block practical or tolerable for older arthritic patients.
EEG records spontaneous electrical activity of cortical surface cells, an area more prone to decreased perfusion. It is a sensitive parameter for ischemia since electrophysiologic activity accounts for 60% of cerebral metabolic demand. EEG changes occur in about 20% of patients during carotid occlusion and are indicative of potentially serious ischemia. Changes lasting more than 10 minutes correlate strongly with post-op neurologic deficits, and thus EEG changes of greater than a mild degree are an indication for shunt placement or induced hypertension. Typical regional cerebral blood flow is 50-55ml/min/100gm brain tissue. Ischemia typically occurs around 18-20 ml/min/100gm and tissue death at 8-10. EEG deterioration begins around 15-20ml/min/100gm, and manifests as frequency slowing or amplitude attenuation, severe ischemia may be isoelectric.
Limitations are that deep structures are not monitored, preexisting deficits or EEG changes reduce predictive value (may not show intraop changes), may miss regional ischemic events, especially if using only 4-channel, and are affected by changes in temperature, BP, PaCO2, and anesthetic depth, however, these are more likely to be b/l. Focal embolic events may also be missed. 16 lead EEG is the gold standard- responds quickly and detects regional changes, but requires a skilled technician and continuous observation, thus processed EEGs with fewer leads, 2-4 channels, are available and widely used. Need electrodes covering bilateral anterior and posterior regions of brain.
SSEPs are based on detection of cortical potentials after electrical stimuli are presented to a peripheral nerve.
Advantages: also evaluates deep brain structures vs. EEG and cortical function only, and may be better for patients with previous CVA and EEG changes.Disadvantages: Not felt to be as sensitive or specific for ischemic injury during CEA. Requires considerable expertise. Also effected by choice of anesthesia and need constant light plane to be maintained to accurately interpret changes in EPs.
Transcranial doppler is not a good sole intraoperative monitor. Measures mean blood flow velocity in MCA and detects emboli. Emboli account for up to 65% of postop deficits. Can detect acute thrombotic occlusion and microemboli and is much more useful in this aspect especially in helping surgeons modify their technique. Does not evaluate functional changes. Also useful for predicting postop hyperperfusion syndrome and help in reducing BP to avoid complications.
Carotid stump pressure estimates hemispheric blood flow by measuring pressure in the carotid stump distal to the clamp. Stump pressure is more often used to determine whether or not a shunt should be placed intraoperatively. The problem with this is that an adquate pressure doesn’t assure perfusion to all regions of the brain. Shunt thresholds vary between surgeons, anesthesiologists, and institutions but a threshold between 40 and 60 mmHg is typical. Nevertheless, in some patients this may not be adequate for compromised areas and in others perfusion is adequate at pressures well below this resulting in unnecessary shunting. On a scientific basis there is no correlation between stump pressure and regional or global blood flow.
None of these have been shown to improve outcome since postoperative emboli and not intraoperative hypoperfusion are most likely cause of periop stroke, but do aid in decision to shunt and BP maintenance.
Keyword history
Anesthesia for Carotid Endarterectomy is of proven benefit to reduce the risk of stroke in patients with high-grade stenosis of the internal carotid artery. Since the disease is atherosclerotic in origin, these patients often are prone to a variety of cerebrovascular and myocardial complications during the perioperative phase.
Anesthesia for Carotid Endarterectomy
Anesthesia for Carotid Endarterectomy demands excellent haemodynamic stability due to the risk of perioperative myocardial damage.
A deep or superficial cervical plexus block is often used to provide regional Anesthesia for Carotid Endarterectomy . Simple local infiltration (field block) has also been widely used as an effective technique. General anaesthetic techniques that have been used include inhalational agent based, narcotic-based or hypnotic-based.
Neurologic assessment of the awake patient is the gold standard for neurologic monitoring during Anesthesia for Carotid Endarterectomy . Regional anaesthesia allows a continuous neurologic assessment.
With general anaesthesia, electroencephalography is the best neurologic monitoring tool. However, EEG may not indicate cerebral ischaemia if barbiturates are administered concurrently.
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Though clinicians differ in their opinion regarding the anaesthetic technique, no clear evidence has yet proven one method to be superior. Perioperative outcome was not influenced by the choice of anaesthetic technique.
Several studies have shown significantly improved haemodynamic stability with regional anaesthesia when compared with patients undergoing Anesthesia for Carotid Endarterectomy under general anaesthesia.
Watts et al recently compared the outcome of Anesthesia for Carotid Endarterectomy performed under local versus general anaesthesia in 548 patients and no difference in postoperatie stroke or death rates was found. However, local anaesthesia was associated with a lower incidence of shunting, less operative time and less postoperative haemodynamic instability, though haemodynamic instability was not defined.
Miller’s Anesthesia 7th edition says about Anesthesia for Carotid Endarterectomy :
“Anesthetic management goals for carotid endarterectomy include protection of the heart and brain from ischemic injury, control of the heart rate and blood pressure, and ablation of the surgical pain and stress responses. These goals must be achieved with another important goal in mind—to have an awake patient at the end of surgery for the purpose of neurologic examination.
The preoperative visit is particularly important in patients undergoing carotid surgery. During this visit, a series of blood pressure and heart rate measurements are obtained from which acceptable ranges for perioperative management can be determined. Patients are instructed to continue all long-term cardiac medications up to and including the morning of surgery.
Unless contraindications exist, aspirin therapy should be continued throughout the perioperative period. As noted earlier, discontinuation of aspirin therapy may be related to an increased rate of MI and transient ischemic events in patients undergoing carotid endarterectomy.
Anesthesia for Carotid Endarterectomy
When patients arrive at the hospital on the day of surgery, they are queried regarding any new cardiovascular or cerebrovascular symptoms. Long-term cardiovascular medications not taken at home should be administered in the preoperative holding area whenever possible.
Patient reassurance is particularly important at this time because anxiety is associated with increases in heart rate, systemic vascular resistance, and myocardial oxygen consumption, which in this patient population could precipitate significant cardiac morbidity. “
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