Role of Shunting During Carotid Endarterectomy Steven M. Farley and Wesley S. Moore Temporary clamping of the internal carotid during carotid endarterectomy (CEA) interrupts antegrade blood flow to the brain in the distribution of the ipsilateral middle and anterior cerebral artery. The consequence of clamping the internal carotid artery is of critical importance to the patient and has been the subject of debate for more than 50 years. In a 1998 editorial, Denton Cooley wrote, “No consensus concerning the proper conduct of this procedure exists, or probably ever will.” In describing their first carotid endarterectomy, Cooley and colleagues fabricated a shunt from polyvinyl tubing with large-bore needles at each end. The same patient underwent adjunctive cerebral protection measures including hypercarbia, cooling the head in ice, and barbiturate use. Interestingly, for most of his career, Cooley argued for a no-shunt approach. Few modern surgeons argue that no patients should undergo shunt placement to reestablish antegrade flow during endarterectomy. Therefore, the question is not if to shunt but when to shunt: selectively or routinely? Because little level I evidence exists, a Cochrane report summarized insufficient evidence is available to support the superiority of either method. Therefore, this chapter discusses the techniques and the proposed advantages and disadvantages of both approaches. Selective Shunting The impetus for selective shunting originates from the agreed observation that a majority of patients tolerate carotid clamping, and therefore shunting offers no benefit to most patients. Also, routine carotid shunting has several disadvantages, further weakening the argument for universal shunt placement. A selective approach offers the potential advantages of a shorter operative time and unobstructed inspection of the distal endpoint, and it avoids any risks associated with shunt placement for a majority of patients. Identification of the minority of patients who benefit from shunting remains the challenge. In particular, patients with history of stroke or contralateral carotid occlusion have been reported as high-risk patients. However, the use of preoperative risk factors alone has not proved reliable in identifying patients at risk for ischemic stroke following carotid clamping. The traditional intraoperative techniques for identifying patients for shunt insertion—awake CEA, carotid back pressure measurement, and electroencephalographic (EEG) monitoring are relevant. Transcranial Doppler and cerebral oximetry are newer and less-validated methods to assess the need for shunting. Awake Carotid Endarterectomy Most agree that awake CEA is the gold standard for neurologic monitoring during carotid clamping. The technique involves intraarterial blood pressure monitoring, frequent neurologic checks, and cervical block for analgesia. Patients who develop neurologic changes after test clamping are shunted. Interestingly, many authors report immediate reversal of neurologic symptoms after the establishment of a working shunt, suggesting the value of shunting. Awake CEA has low rates of shunt insertion, with rates around 5%, and reported stroke rates of 1%. An important disadvantage of awake CEA remains: Not all surgeons are trained to perform the operation under cervical block anesthesia. From a metabolic standpoint, awake CEA has been reported to increase the metabolic demands of the brain when compared with general anesthesia. Therefore, patients undergoing an awake CEA may be at greater risk of ischemic injury when compared with those receiving general anesthesia. Another disadvantage is not all patients tolerate the operation for reasons including claustrophobia, pain, cervical arthritis, and redo neck surgery. Without another method for selective shunting, the surgeon may elect to shunt patients routinely. Carotid Back Pressure Measurement During the development of CEA in the 1960s, carotid back pressure was investigated as a surrogate marker of cerebral perfusion after clamping. To measure back pressure, the common and external carotid arteries are clamped. A needle is inserted into the common carotid artery and the pressure is transduced. A patient with a high carotid back pressure should have adequate cerebral collaterals, should tolerate clamping, and, in theory, does not need a shunt. An important advantage of carotid back pressure measurement over other methods for selective shunting is that back pressures do not require advanced training or expensive equipment, making it an option for any surgeon. Studies support equivalent outcomes when compared with routine shunting. The optimal threshold for back pressure has been intensely studied and been reported from 25 to 50 mm Hg. In general, the back pressure cutoff has become more conservative in an attempt to yield a high sensitivity and not miss patients who might benefit from shunting. Comparing back pressure with EEG, a back pressure of less than 50 mm Hg is sensitive in identifying 97% of patients with EEG changes. AbuRahma and colleagues randomized routine shunting versus selective shunting using a threshold of less than 40 mm Hg. In the selective shunting group, 38% of patients were shunted, and there was no statistically significant difference in the stroke rate. The lower specificity of carotid back pressure results in shunt insertion rates of around 40%. When compared with the shunt insertion rate of 4% to 7% for awake patients, the use of back pressure with a higher threshold of 50 mm Hg likely results in unnecessary shunting in many patients. The potential benefit of shunting may be lost by unnecessarily exposing some patients to the risks of shunting. Also, back pressure accuracy can be questioned. In series of awake patients or with EEG monitoring, patients with back pressures greater than 50 mm Hg can demonstrate signs of cerebral ischemia. Another concern regarding back pressures is that unlike EEG or neurologic examination, it does not directly monitor the perfusion of the brain. Back pressures likely do not identify possible intracranial arterial lesions that can make areas of the brain dependent on antegrade flow at risk. Also, poststroke patients have areas of relative hypoperfusion in the healed, collateralized postischemic penumbra. These areas are sensitive to hypoperfusion, and back pressures do not identify these areas. Similarly, back pressures represent a snapshot of cerebral pressure and do not continuously monitor brain function. If physiologic changes occur after clamping, the perfusion status of the brain remains unknown. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Embolic Protection Devices to Prevent Stroke during Percutaneous Angioplasty and Stenting Management of Acute Limb Ischemia Complicating Aortic Reconstruction Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join Tags: Current Therapy in Vascular and Endovascular Surgery Aug 25, 2016 | Posted by admin in CARDIOLOGY | Comments Off on Role of Shunting during Carotid Endarterectomy Full access? Get Clinical Tree
Role of Shunting During Carotid Endarterectomy Steven M. Farley and Wesley S. Moore Temporary clamping of the internal carotid during carotid endarterectomy (CEA) interrupts antegrade blood flow to the brain in the distribution of the ipsilateral middle and anterior cerebral artery. The consequence of clamping the internal carotid artery is of critical importance to the patient and has been the subject of debate for more than 50 years. In a 1998 editorial, Denton Cooley wrote, “No consensus concerning the proper conduct of this procedure exists, or probably ever will.” In describing their first carotid endarterectomy, Cooley and colleagues fabricated a shunt from polyvinyl tubing with large-bore needles at each end. The same patient underwent adjunctive cerebral protection measures including hypercarbia, cooling the head in ice, and barbiturate use. Interestingly, for most of his career, Cooley argued for a no-shunt approach. Few modern surgeons argue that no patients should undergo shunt placement to reestablish antegrade flow during endarterectomy. Therefore, the question is not if to shunt but when to shunt: selectively or routinely? Because little level I evidence exists, a Cochrane report summarized insufficient evidence is available to support the superiority of either method. Therefore, this chapter discusses the techniques and the proposed advantages and disadvantages of both approaches. Selective Shunting The impetus for selective shunting originates from the agreed observation that a majority of patients tolerate carotid clamping, and therefore shunting offers no benefit to most patients. Also, routine carotid shunting has several disadvantages, further weakening the argument for universal shunt placement. A selective approach offers the potential advantages of a shorter operative time and unobstructed inspection of the distal endpoint, and it avoids any risks associated with shunt placement for a majority of patients. Identification of the minority of patients who benefit from shunting remains the challenge. In particular, patients with history of stroke or contralateral carotid occlusion have been reported as high-risk patients. However, the use of preoperative risk factors alone has not proved reliable in identifying patients at risk for ischemic stroke following carotid clamping. The traditional intraoperative techniques for identifying patients for shunt insertion—awake CEA, carotid back pressure measurement, and electroencephalographic (EEG) monitoring are relevant. Transcranial Doppler and cerebral oximetry are newer and less-validated methods to assess the need for shunting. Awake Carotid Endarterectomy Most agree that awake CEA is the gold standard for neurologic monitoring during carotid clamping. The technique involves intraarterial blood pressure monitoring, frequent neurologic checks, and cervical block for analgesia. Patients who develop neurologic changes after test clamping are shunted. Interestingly, many authors report immediate reversal of neurologic symptoms after the establishment of a working shunt, suggesting the value of shunting. Awake CEA has low rates of shunt insertion, with rates around 5%, and reported stroke rates of 1%. An important disadvantage of awake CEA remains: Not all surgeons are trained to perform the operation under cervical block anesthesia. From a metabolic standpoint, awake CEA has been reported to increase the metabolic demands of the brain when compared with general anesthesia. Therefore, patients undergoing an awake CEA may be at greater risk of ischemic injury when compared with those receiving general anesthesia. Another disadvantage is not all patients tolerate the operation for reasons including claustrophobia, pain, cervical arthritis, and redo neck surgery. Without another method for selective shunting, the surgeon may elect to shunt patients routinely. Carotid Back Pressure Measurement During the development of CEA in the 1960s, carotid back pressure was investigated as a surrogate marker of cerebral perfusion after clamping. To measure back pressure, the common and external carotid arteries are clamped. A needle is inserted into the common carotid artery and the pressure is transduced. A patient with a high carotid back pressure should have adequate cerebral collaterals, should tolerate clamping, and, in theory, does not need a shunt. An important advantage of carotid back pressure measurement over other methods for selective shunting is that back pressures do not require advanced training or expensive equipment, making it an option for any surgeon. Studies support equivalent outcomes when compared with routine shunting. The optimal threshold for back pressure has been intensely studied and been reported from 25 to 50 mm Hg. In general, the back pressure cutoff has become more conservative in an attempt to yield a high sensitivity and not miss patients who might benefit from shunting. Comparing back pressure with EEG, a back pressure of less than 50 mm Hg is sensitive in identifying 97% of patients with EEG changes. AbuRahma and colleagues randomized routine shunting versus selective shunting using a threshold of less than 40 mm Hg. In the selective shunting group, 38% of patients were shunted, and there was no statistically significant difference in the stroke rate. The lower specificity of carotid back pressure results in shunt insertion rates of around 40%. When compared with the shunt insertion rate of 4% to 7% for awake patients, the use of back pressure with a higher threshold of 50 mm Hg likely results in unnecessary shunting in many patients. The potential benefit of shunting may be lost by unnecessarily exposing some patients to the risks of shunting. Also, back pressure accuracy can be questioned. In series of awake patients or with EEG monitoring, patients with back pressures greater than 50 mm Hg can demonstrate signs of cerebral ischemia. Another concern regarding back pressures is that unlike EEG or neurologic examination, it does not directly monitor the perfusion of the brain. Back pressures likely do not identify possible intracranial arterial lesions that can make areas of the brain dependent on antegrade flow at risk. Also, poststroke patients have areas of relative hypoperfusion in the healed, collateralized postischemic penumbra. These areas are sensitive to hypoperfusion, and back pressures do not identify these areas. Similarly, back pressures represent a snapshot of cerebral pressure and do not continuously monitor brain function. If physiologic changes occur after clamping, the perfusion status of the brain remains unknown. Only gold members can continue reading. Log In or Register to continue Share this:Click to share on Twitter (Opens in new window)Click to share on Facebook (Opens in new window) Related Related posts: Embolic Protection Devices to Prevent Stroke during Percutaneous Angioplasty and Stenting Management of Acute Limb Ischemia Complicating Aortic Reconstruction Treatment of Dyslipidemia and Hypertriglyceridemia Intraoperative Assessment of the Technical Adequacy of Carotid Endarterectomy Stay updated, free articles. Join our Telegram channel Join Tags: Current Therapy in Vascular and Endovascular Surgery Aug 25, 2016 | Posted by admin in CARDIOLOGY | Comments Off on Role of Shunting during Carotid Endarterectomy Full access? Get Clinical Tree
