Carotid artery surgery without a temporary indwelling shunt. 1,917 consecutive procedures

Multicenter retrospective review of results and complications of carotid endarterectomy in 1981

A multicenter retrospective audit of carotid endarterectomies performed during 1981 was completed with 46 institutions contributing 3,328 cases. Overall, there was a 2.5% risk of transient neurological dysfunction following surgery and a 6% risk of stroke or death. The intra-institutional combined major morbidity and mortality varied from 21% to 0. Those institutions with greater than 700 beds had a statistically lower incidence of stroke or death than did other institutions. The incidence of stroke or death postoperatively was significantly lower for patients who were operated on for amaurosis fugax or for unspecified reasons. Those patients who were operated on for a progressing stroke had a higher incidence of stroke but this group was at greatest risk for stroke without surgery. The incidence of postoperative stroke or death was related to the type of arterial repair; vein patch grafting was statistically better than both fabric patch grafting and primary closure. When all patients who were not monitored during surgery were compared to all patients who had electroencephalographic (EEG) monitoring, there was found to be a significant statistical difference in favor of the EEG group. Endarterectomy combined with coronary artery bypass or simultaneous bilateral endarterectomies had a statistically significant higher incidence of stroke or death than did unilateral carotid endarterectomy.

Spectral analysis of EEG during carotid endarterectomy

Spectral analysis of the electroencephalogram (EEG) was monitored during 105 carotid endarterectomies. Seventy-eight percent of the patients showed no significant change in EEG spectral power as a result of clamping of the internal carotid artery. Two patterns of change were observed in the remaining 22% of patients: partial reduction (significant decrease of power in one or two of three frequency bands) and global reduction (significant decrease of power in all three frequency bands). High frequencies (over 10.5 Hz) changed more frequently with clamping than did low frequencies (less than 6 Hz), but reduction of high frequencies alone was tolerated with no postoperative deficits. The only non-shunted patient demonstrating global EEG reduction for the duration of carotid clamping suffered a transient hemiparesis.

The risk-benefit ratio of intraoperative shunting during carotid endarterectomy. Relevancy to operative and postoperative results and complications

The relative risk of shunting versus not shunting during carotid endarterectomy was analyzed retrospectively in 1935 cases undergoing carotid endarterectomy for carotid ulcerative stenosis. The need for shunting was based on a correlation between electroencephalographic changes and a fall in cerebral blood flow below the critical level required for adequate perfusion during the period of carotid occlusion. Patients were divided into four risk categories for surgery, based on medical and neurological risks and angiographic findings. Shunts were required in 30% of the low risk group and 56% of the high risk group. Based on the severity of reductions of cerebral blood flow during the period of carotid occlusion it is concluded that 12% of all patients would have sustained a major deficit, 15% a minor or transient deficit, and 20% a transient deficit without shunting. The risk of shunting 792 cases in this series was 0.5%. Overall minor morbidity, major morbidity, and mortality each approximated 1% in this series.

An assessment of the variability of early scalp-components of the somatosensory evoked response in uncomplicated, unshunted carotid endarterectomy

Although many publications deal with the usefulness of the SER in CEAs, the criteria of calling a SER abnormal during a CEA are largely arbitrary. One way to define the limits of normalcy for SERs during the CEA will be to analyze the SER tracings obtained during unshunted and uncomplicated (intra- and postoperative) CEAs. In 23 such CEAs (10 right, 13 left; clamptime 10-23 mins.), data analysis at the ipsilateral parietal electrode, on stimulation of the contralateral median nerve (square pulse -5.1/sec, 10-30 V, 200 microseconds; bandpass-30-3000 Hz trials-500 stimuli), revealed that (1) latency fluctuations of the N20 (21.4 msec) were narrowest, being less than 1.5 msec different during and after clamping compared to the preclamp latency in all 23 CEAs, whereas those of P25 (27.4 msec) and N35 (38.5 msec) were greater than 2.0 msec different from the preclamp latency in 3 and 8 CEAs respectively, and (2) the amplitudes of N20, P25 and N35 measured from the preceding peak of opposite polarity, fell to less than 75% of the preclamp value on 3, 4 and 7 CEAs respectively. It is concluded that N20 was the most stable of the first three short-latency components in the SER and should perhaps be most relied upon to predict abnormality of the SER during CEAs.

Benefits, shortcomings, and costs of EEG monitoring

A 5-year experience with 562 carotid endarterectomies, using electroencephalogram (EEG) monitoring and selective shunting, was reviewed. EEG changes occurred in 102 patients (18%). The frequency of EEG changes, as related to cerebral vascular symptoms, was as follows: transient ischemic attacks, seven per cent (19/259); completed strokes, 37% (36/98); vertebral basilar insufficiency, 24% (32/135); asymptomatic, 21% (15/71). Patients with contralateral carotid occlusion exhibited EEG changes in 37% (28/76) of operations. Fifteen patients suffered perioperative strokes (2.6%). Nine of the 15 were associated with a technical problem of either thrombosis of the internal carotid artery (five) or emboli (four). Technical problems were more common when shunts were used (five per cent) than when they were not (0.9%). Patients who suffered strokes prior to surgery were more at risk to develop a perioperative stroke (three per cent) than those not suffering prior strokes (0.3%). The EEG did not change in three patients who had lacunar infarcts prior to surgery and who awoke with a worsened deficit. Our series does not clearly establish the advantages of EEG monitoring, which is expensive (+375/patient) and may not detect ischemia in all areas of the brain. However, the use of shunts may introduce a risk of stroke due to technical error that is equal or greater than the risk of stroke due to hemodynamic ischemia. Since the need for protection is unpredictable by angiographic or clinical criteria, the benefit of EEG monitoring may be in reducing the incidence of shunting in those patients whose tracing remains normal after clamping. The decision to shunt, however, when there is electrical dysfunction after carotid clamping should be based not only on the EEG but also on the clinical signs and computed tomography (CT) scan. Our data does not show a net benefit in selective shunting unless the patient has sustained a stroke prior to surgery.

Local anaesthesia in carotid surgery. A prospective study of 111 endarterectomies in 100 patients

A prospective study was carried out on 100 patients consecutively undergoing carotid endarterectomy in local anaesthesia, in order to evaluate the usefulness of clinical signs in awake patients for monitoring of cerebral function and to determine the need for internal shunt in carotid surgery. The indications for operations were transient ischemic attacks in 67 patients and major or minor stroke in 24 (16 with persistent neurologic deficit). In nine asymptomatic patients the endarterectomy was prophylactic, following detection of bruit and angiographic stenosis. Bilateral stenosis was present in 47 patients, including 13 with total occlusion of the contralateral vessel, and 60 patients had significant vertebral artery stenosis. The carotid artery was first tentatively occluded and, if this was well tolerated for 5 min, endarterectomy was done without an internal shunt. Neurologic deficit signs during the trial occlusion necessitated such shunt in 16 patients with pressure in the internal carotid stump ranging from 0 to 40 (mean 22.4) mmHg. On the other hand, 11 additional patients with stump pressure less than 35 mmHg tolerated the trial occlusion well, underwent carotid endarterectomy without internal shunt and had no deficit symptoms during or after operation. One patient died postoperatively. Hemiparesis appeared in two more patients, but resolved completely in one and gave only minor sequelae in the other. These complications were related to the preoperative condition (stroke) and the postoperative residual pressure gradient. It is concluded that trial occlusion of the carotid artery and observation of the awake patient provide reliable information on the need for an internal shunt during carotid endarterectomy.

Determining criteria for shunt placement during carotid endarterectomy. EEG versus back pressure

EEG monitoring and carotid back pressure were performed on 100 patients undergoing elective carotid endarterectomy. Shunts were inserted selectively in those patients who showed change in EEG after a trial period of carotid clamping (15%). No patient in the series awoke with a neurologic deficit. Back pressures were significantly lower in the shunted group and these pressures roughly correlated with EEG changes. Only one patient with a back pressure of greater than 40 mmHg had EEG changes and this patient had a recent mild stroke. EEG changes were most frequent in patients with contralateral carotid occlusions and in asymptomatic significant stenoses. EEG is a more discriminating indicator for shunt insertion than back pressure, although a pressure greater than 40 mmHg is safe in patients without recent stroke.

Effects of carotid endarterectomy on blood flow in the internal carotid artery

A retrospective study of patients operated upon for carotid stenosis was undertaken with special emphasis on the internal carotid artery (ICA) blood flow. A total of 212 endarterectomies were performed in 198 patients. The overall operative mortality was 1.4%, and the cerebral morbidity was 2.8%. A temporary inlying shunt was used routinely during endarterectomy. In two of 198 endarterectomies the shunt itself could not be excluded as a possible cause of postoperative neurological deficits. The ICA blood flow before and after endarterectomy was determined by electromagnetic flowmetry in 160 operations. Flow measurements were compared in TIA and stroke patients, in patients with high and low degrees of luminal constriction, and in patients with occluded or "open" (minimal stenosis) contralateral ICA. The results indicate that the preoperative blood flow, as well as the increase in blood flow after removal of the stenosis, is determined not only by the degree of luminal constriction, but also by the magnitude of blood flow from all precerebral feeding arteries and their intracranial collateral circulation. In treatment of carotid stenosis critical evaluation of symptoms, angiography, and haemodynamics are essential. Endarterectomy is beneficial because an embolic source is removed, and probably because perfusion is improved to areas of the brain with marginal circulation. The main factors regulating the normal cerebral perfusion are cardiac output (mean perfusion pressure), arterial pCO2 and PO2, haematocrit, and the arterial and venous blood pressures. Comparatively few investigations have been published on the effect of endarterectomy upon internal carotid artery (ICA) blood flow 4, 12, 14, 27. Since 1970 we have routinely measured the ICA blood flow before and after endarterectomy. This paper reviews the clinical and haemodynamic results of our patients operated on for carotid stenosis.

Routine electroencephalographic (EEG) monitoring during carotid endarterectomy

Controversy continues concerning the advisability of routine shunting, no shunting, or selective shunting during carotid endarterectomy. Because of its reflection of the physiologic state of the end organ, the authors chose routine 18 lead EEG monitoring as a guide to selective shunting and as an indication of adequate shunt function during all carotid endarterectomies performed from December 1977 through July 1982. In that period, 200 patients underwent 219 endarterectomies under general anesthesia and EEG monitoring. Ischemic EEG changes at the time of carotid cross clamping suggested the need for intraluminal shunts in 16% of patients. Insertion of shunts restored the EEG pattern to normal in all instances, although in two patients, adjustment of the shunt was required to maintain this results. EEG changes requiring shunting occurred in 10% of patients with unilateral disease, in 27% of patients with bilateral disease, and in 42% of patients with unilateral stenosis and contralateral occlusion. Twenty-seven patients had small fixed neurologic deficits before operation. Surgery was not delayed in these individuals who demonstrated no increased requirement for shunts and no new postoperative neurologic deficits. In the group of 150 endarterectomies performed as separate procedures, there was one (0.7%) fixed neurologic deficit after operation, one transient deficit (0.7%), and one death (0.7%). Sixty-nine endarterectomies were performed simultaneously with open heart surgery and were associated with one fixed neurologic deficit (1.4%) and two transient deficits (2.9%). All four deaths in this group were attributable to the cardiac surgical procedures. These results indicate that selective shunting based on EEG monitoring permits the safe performance of carotid endarterectomy, even in patients considered to be at high risk for postoperative neurologic deficit.

Routine use of a shunt for carotid endarterectomy

A temporary inlying shunt used during carotid endarterectomy is the ideal method of cerebral protection. The data presented suggest that if meticulous technique is used, the potential complications of a shunt may be avoided and excellent clinical results expected. When a shunt is used properly, carotid endarterectomy may be performed in a teaching situation with a high degree of safety.