Somatosensory evoked potentials versus locoregional anaesthesia in the monitoring of cerebral function during carotid artery surgery: preliminary results of a prospective study.

OBJECTIVE: to relate changes in somatosensory-evoked potentials (SEPs) with onset of neurological deficits in patients having carotid endarterectomy (CEA) under locoregional anaesthesia. METHODS: a prospective study of 50 consecutive patients. RESULTS: SEPs yielded an accuracy of 98%, specificity 100%, and sensitivity 89%. In all concordant cases the onset of a neurological deficit in awake patients corresponded to a 30--40% reduction in amplitude of N20-P25 waveforms. After shunting, the N20-P25 took 2--3 min to return to normal. CONCLUSIONS: SEPs are associated with a 2% false negative rate. Their threshold for detecting cerebral ischaemia is lower than the currently reported value for patients under general anaesthesia. The time needed for evoked potentials (2--3 min) to return to normal after shunting limits their usefulness in verifying effective shunting.

Locoregional versus general anesthesia in carotid surgery: is there an impact on perioperative myocardial ischemia? Results of a prospective monocentric randomized trial.

PURPOSE: The incidence of cardiac morbidity and mortality in patients who undergo carotid surgery ranges from 0.7% to 7.1%, but it still represents almost 50% of all perioperative complications. Because no data are available in literature about the impact of the anesthetic technique on such complications, a prospective randomized monocentric study was undertaken to evaluate the role of local anesthesia (LA) and general anesthesia (GA) on cardiac outcome. METHODS: From November 1995 to February 1998, 107 patients were classified by the cardiologist as cardiac patients (IHD; history of myocardial infarction, previous myocardial revascularization procedures, or myocardial ischemia documented by means of positive electrocardiogram [ECG] stress test results) or noncardiac patients (NIHD; no history of chest pain or negative results for an ECG stress test). The patients were operated on after the randomization for the type of anesthesia (general or local). Continuous computerized 12-lead ECG was performed during the operative procedure and 24 hours postoperatively. The end points of the study were ECG modifications (upsloping or downsloping more than 2 mm) of the sinus tachycardia (ST) segment. RESULTS: Fifty-five patients were classified as IHD, and 52 were classified as NIHD. Twenty-seven of the 55 IHD patients (49%) and 24 of 52 NIHD patients (46%) were operated on under GA. Thirty-six episodes of myocardial ischemia occurred in 22 patients (20.5%). Episodes were slightly more frequent (58%) and longer in the postoperative period (intraoperative, 10 +/- 5 min; postoperative, 60 +/- 45 min; P <. 001). As expected, the prevalence of myocardial ischemia was higher in the group of cardiac patients than in noncardiac group (15 of 55 patients [27%] vs 7 of 52 patients [13%]; P <.02). By comparing the two anesthetic techniques in the overall population, we found a similar prevalence of patients who had myocardial ischemia (GA, 12 of 52 [23%]; LA, 10 of 55 [18%]; P = not significant) and a similar number of ischemic episodes per patient (GA, 1.5 +/- 0.4; LA, 1.8 +/- 0.6; P = not significant). Episodes of myocardial ischemia were similarly distributed in intraoperative and postoperative periods in both groups. It is relevant that under GA, IHD patients represent most of the population who suffered myocardial ischemia (83%). On the contrary, in the group of patients operated on under LA, the prevalence was equally distributed in the two subpopulations. CONCLUSION: The results confirm the different hemodynamic impact of the two anesthetic techniques. Patients who received LA had a rate of myocardial ischemia that was half that of patients who had GA. The small number of cardiac complications do not permit us to make any definitive conclusion on the impact of the two anesthetic techniques on early cardiac morbidity, but the relationship between perioperative ischemic burden and major cardiac events suggests that LA can be used safely, even in high-risk patients undergoing carotid endarterectomy.

Intraoperative transcranial Doppler sonography monitoring during carotid surgery under locoregional anaesthesia.

OBJECTIVES: Studies comparing transcranial Doppler ultrasonography (TCD) with other intraoperative monitoring techniques for detecting clamping ischaemia during carotid endarterectomy under general anaesthesia suggest that a reduction of > two-thirds in the mean middle cerebral artery velocity (mMCAv) or a reduction of > 0.4 in the preclamping mMCAv: clamping mMCAv ratio warrants cerebral protection. Our aim was to study the relationship between mMCAvs and clamping ischaemia during carotid endarterectomy in awake patients. MATERIALS AND METHODS: In a consecutive series of 57 patients undergoing carotid endarterectomy under locoregional anaesthesia 51 were monitored by intraoperative TCD, continuous EEG, and neurologic awake testing. RESULTS: Five of the 51 (9.8%) patients had transient clamping ischaemia, which carotid shunting reversed. TCD showed that these five patients had significant lower mean mMCAvs than the other 46 patients, who had no deficits (1.8 +/- 1.1 cm/s vs. 26.2 +/- 8.5, p = 0.0003). Current TCD criteria indicated that four other patients (7.8%) should have been shunted. All four had significantly higher clamping mMCAvs than the five shunted patients (11.5 +/- 1.9 vs. 1.8 +/- 1.1, p = 0.0012). CONCLUSIONS: Intraoperative TCD detected cerebral ischaemia and yielded no false-negative. An mMCAv of 10 cm/s or less may indicate the risk of clamping ischaemia better than the higher threshold currently proposed. This would avoid unnecessary shunting due to false-positives.

The selection for shunting in patients with severe bilateral carotid lesions.

Patients with severe bilateral carotid lesions (stenosis and contralateral internal carotid occlusion) are at high risk of having a stroke, and carotid endarterectomy has been proposed as the best treatment. In spite of improvements in surgical technique, this operation is still associated with significant perioperative complications (5-13%) which are frequently (up to 40%) correlated with intolerance to internal carotid artery clamping. For this reason, intraoperative cerebral monitoring able to accurately detect ischaemia during surgery would be useful. Reviewing our experience from the last 7 years in 74 patients operated on for stenosis and contralateral occlusion of the internal carotid artery, we found a 1.3% neurological morbidity and 1.3% mortality rate. Presenting symptoms included focal transient ischaemia attacks (TIAs) in 57 patients, stroke in 16 patients and two patients were asymptomatic. Half of these patients (37) were operated on under general anaesthesia with electroencephalogram (EEG) monitoring, stump pressure measurement and selective shunting. In this group, two patients (5.4%) sustained a postoperative stroke, one of which was fatal. The remaining 37 patients were operated on under local-regional anaesthesia with selective shunting on the basis of neurological deficit onset or loss of consciousness during the test clamp. There were no postoperative neurological complications in this group but one patient died of acute myocardial infarction on the 6th postoperative day. This experience suggests that it is possible to perform carotid endarterectomy in patients with severe bilateral lesions with a postoperative complication rate similar to that in patients with less complicated obstructive lesions if accurate intraoperative cerebral monitoring is used.