A 62-year-old man has undergone a right carotid endarterectomy (CEA). Immediately following surgery, in the recovery room, he is noted to be weak on the contralateral side.
How is a patient undergoing CEA evaluated preoperatively?
Patients with cerebrovascular disease, and, in particular, carotid stenosis are at very high risk of coronary artery and peripheral arterial disease. It would be unusual for a patient to have carotid stenosis who did not have evidence of atherosclerosis elsewhere. Patients undergoing CEA, therefore, require a preoperative cardiac evaluation, according to American College of Cardiology/American Heart Association guidelines.
With respect to patient risk factors, the guidelines provide algorithms for how patients should be evaluated and managed intraoperatively. As part of this patient’s preoperative evaluation, a thorough neurological examination should have been performed with special attention paid to motor function. This patient may well have been weak on the left side prior to surgery, in which case the hemiparesis might be due to a preexisting condition. If this is a new finding, it requires aggressive management.
Is general or regional anesthesia the optimal anesthetic technique for managing patients undergoing CEA?
For the past several decades, the majority of patients undergoing CEAs in the United States have had general anesthesia. General anesthesia was chosen because many surgeons operating in the neck area felt more comfortable if the airway was controlled, and the patient was completely anesthetized should evidence of cerebral ischemia develop.
More recently, regional anesthesia has been advocated as providing an adequate surgical field, a comfortable and relaxed patient (if done with monitored anesthesia care), stable hemodynamics, and ideal monitoring of cerebral function during crossclamping because an awake patient provides the best evidence of adequate cerebral perfusion. The patient can indicate or be observed for evidence of aphasia, facial droop, or hemiparesis. Regional anesthesia is usually performed with superficial cervical plexus blocks.
How should cerebral function be monitored intraoperatively in this patient?
When the carotid is crossclamped, the ability to identify inadequate cerebral circulation in the ipsilateral hemisphere is critical, as there is a window of opportunity for immediate intervention and correction of any deficit.
Global and focal neurological status can continuously be assessed in awake patients, if the patient is mildly sedated when undergoing regional anesthesia. In such a situation, practical assessment consists of frequent (every 2-5 min) examination of strength using the contralateral handgrip and maintenance of constant verbal contact with the patient to assess level of consciousness.
In patients undergoing general anesthesia, indirect cerebral monitoring techniques have been used to assess the adequacy of the cerebral circulation. These techniques include stump bleeding, stump pressure, jugular venous oxygen saturation, EEG, a processed EEG (such as the bispectral index or evoked potentials), TCD, arteriography, and measurement of blood flow using xenon. Back bleeding of the distal carotid artery following crossclamp and incision of the artery suggests reasonable collateral circulation above the clamp. It is very subjective and nonquantitative.
To better qualify and quantify the adequacy of collateral perfusion (Figure 26-9), stump pressure measurements can be used. Some surgeons believe that a shunt should be used in all patients with a previous cerebrovascular accident, independent of stump pressure, and for any patient whose stump pressure is less than 25 mm Hg. However, this is controversial, as many neurosurgeons and vascular surgeons use 50 mm Hg as a cutoff.
The cerebral circulation.
The EEG is sometimes used for monitoring patients undergoing CEA under general anesthesia. In such a circumstance, inhalation or intravenous anesthesia can influence the EEG, but gross changes associated with carotid clamping can be detected. However, analyzing the EEG is labor and technology intensive and requires interpretation of the data.
For this reason, techniques that employ a processed EEG (eg, the bispectral index monitor) are being explored as a monitor for cerebral ischemia. Evoked potentials, such as auditory and visual evoked potentials, have also been examined, but do not seem to have significant clinical application.
Jugular venous oxygen saturation has been studied in an attempt to identify the acute onset of cerebral ischemia. Because it is a global measure, it does not reflect regional, or, in particular, focal cerebral ischemia and therefore is not used for routine clinical practice. TCD ultrasonography provides noninvasive assessment of blood flow in the middle cerebral artery.
How should hemodynamics be controlled intraoperatively?
During carotid clamping and immediately afterward in the recovery room, patients are often hemodynamically labile. Bradycardia can develop during surgical manipulation of the carotid sinus because of the direct stimulation of the vagus nerve. Tachycardia may develop as a result of stress or pain or as a direct result of manipulation of the carotid sinus with release of catecholamines into the circulation.
Hypotension is also observed because of the direct vasodilating and negative ionotropic effects of anesthetic agents. Hypotension following carotid unclamping is common, particularly in patients with more severe carotid stenosis. This could be due to a cerebral protective process. Cerebral autoregulation protects the brain from reperfusion by reducing cerebral production of renin, vasopressin, and norepinephrine, which results in hypotension. Hypertension is also a frequent finding in patients undergoing CEA. Many patients have hypertension as a comorbid condition, which is often further exacerbated by the surgical stress and manipulation of the carotid body, which causes release of catecholamines and sympathetic stimulation.
Invasive arterial pressure monitoring and suitable venous access to infuse vasoactive medications are necessary during carotid surgery.
What is the most likely etiology of this patient’s findings?
This patient most likely has had a cerebrovascular accident due to an arterio-to-arterial embolus; more than 95% of patients will fit into this category. Weakness can also develop as a result of a hyperperfusion syndrome, which occurs in patients with severe carotid stenosis who have now reestablished flow to the affected cerebral hemisphere. Such patients usually have a greater than 95% carotid stenosis with a less than 1-mm channel in the affected carotid artery. Typically, the syndrome does not develop in the postoperative anesthesia care unit (PACU), but several hours afterward when the patient begins complaining of a headache, and, in severe cases, develops hemiparesis.
Because a cerebrovascular accident is most likely, when the anesthesiologist is called to see such a patient in the PACU, a thorough neurological examination quantifying any cranial nerve involvement and the degree of weakness on the contralateral side should be performed. Any hemodynamic changes need to be treated immediately, with assurance of adequate hemoglobin and oxygenation levels. Ultrasonic evaluation of the carotid artery is frequently required. The surgeon needs to be notified at once, as it may be necessary to return to the operating room to explore the carotid artery.