Carotid Cross-clamping Research Articles

Carotid Endarterectomy Using Regional Anesthesia: A Benchmark for Stenting

Regional block (RB) anesthesia for carotid surgery offers the advantage of continuously monitoring the awake patient's neurologic status during carotid cross-clamping. We retrospectively studied our experience with RB for carotid endarterectomy (CEA) procedures performed during the period January 1, 1995 through December 31, 2001. A total of 388 consecutive CEA procedures were performed; RB was used in 314 and general anesthesia (GA) in 74. Three patients required conversion from RB to GA. GA was used only in patients who could not tolerate a block or needed combined coronary artery bypass grafting (CABG) and carotid surgery. New ipsilateral stroke did not occur in RB patients; one patient extended a previous stroke. Three in-hospital deaths occurred; these were all cardiac-related. In GA patients undergoing CEA without CABG (CEA only, n = 58), one stroke and no deaths occurred. The combined stroke and mortality rate for all CEA-only patients was 1.3 per cent (five of 372). RB allows 90 per cent of procedures to be performed without shunting, thus facilitating endarterectomy and patch angioplasty. CEA performed under RB is similar to carotid stenting because both procedures allow monitoring of the awake patient's neurologic status. The very low procedural complication rate in this study warrants the consideration of carotid surgery under regional block as a benchmark for future carotid angioplasty and stenting studies.

The effectiveness of regional cerebral oxygen saturation monitoring using near-infrared spectroscopy in carotid endarterectomy

Nineteen patients (20 operations) underwent elective carotid endarterectomy without arterial shunt. Carotid cross-clamping caused a significant decrease (from 61.2% to 49.5%, 19.1% decrease from the preclamp baseline) of the ipsilateral cerebral oxygen saturation and it increased to 65.6% after declamping. Cross-clamping also caused a significant decrease (from 2.9 Hz to 1.6 Hz) of the ipsilateral electroencephalogram main frequency and it increased to 3.6 Hz after declamping. Asymmetry of main frequency which was greater than 0.7 Hz was observed when that of oxygen saturation decreased more than 25% during cross-clamping. The reported data indicate that cerebral oxygen saturation less than 54–56.1% and its decrease more than 15.6–18.2% is found to be a predictor of neurologic compromise. In this study, the asymmetry of cerebral oxygen saturation more than 25% was also found to be a risk. Arterial shunt should be used in haemodynamically high risk cases.

The anatomy of the circle of Willis as a predictive factor for intra-operative cerebral ischemia (shunt need) during carotid endarterectomy

The collateral flow to the cerebral hemisphere after carotid cross clamping during carotid endarterectomy is mainly through the circle of Willis, and the circle is incomplete in the majority of cases. A correlation between the status of the circle of Willis and the necessity of shunting was evaluated in 67 carotid endarterectomies with pre-operative four-vessel cerebral angiogram. All carotid endarterectomies were performed with selective shunting, based on the change of consciousness and motor function after carotid test clamping under regional anesthesia. Of the 55 patients with either an anterior or a posterior communicating artery, only four (7.3%) required shunting. Twelve patients had neither anterior nor posterior communicating artery, and 10 (83.3%) showed signs of cerebral ischemia necessitating shunting. Mandatory shunt was significantly higher in patients with absence of collaterals (p = 0.00). The rate of intraoperative cerebral ischemia was significantly higher in patients with poor collateral circulation defined by the anatomy of the circle of Willis. [Neurol Res 2002; 24: 237-240]

Alternative surgery for the kinked internal carotid artery.

Carotid kinking can either be a source of emboli or it may cause cerebral ischemia during head/neck rotation. Surgical techniques to correct the kink usually employ carotid cross-clamping and kink resection. In selected cases the authors used simple kink straightening and fixation. The patients treated by this method were evaluated. Total of 42 operations in 40 patients were performed from 1984 through 1998. Mean age was 56 years, male:female ratio 1:1. Patients presented with either TIAs (n=26), minor stroke (n=13) or were asymptomatic (n=3). There were 2 distinct groups of patients. Group I. were the patients with kinking only (n=28), Group II. the patients in whom the kink was seen at the end of regular carotid stenosis. In all patients the kink was dissected free, straightened and fixed by several stitches. In the Group II. this manoeuvre followed standard carotid micro-endarterectomy. Mean follow-up is 4,8 years (1-15). There was no morbidity, no mortality. Only 1 patient suffered several TIAs in the 6 months period after surgery. All patients are alive and symptom free. In lesser kinks the simple surgical technique without cross-clamping is effective, easy and complication free.

Blood pressure manipulation during awake carotid surgery to reverse neurological deficit after carotid cross‐clamping

We describe the management of three patients undergoing awake carotid surgery who developed signs of cerebral ischaemia after carotid cross-clamping. Drug treatment to increase arterial blood pressure above baseline reversed the neurological deficit and an internal carotid artery shunt was not needed. Shunt insertion is less frequent with regional rather than general anaesthesia, and blood pressure control can reduce this even more. Coincidentally, one of the patients, who gave a history of angina of effort after walking 100 m, complained of chest pain after cross-clamp release. This was treated successfully with sublingual nitroglycerin before ST segment changes became apparent on the ECG. These reports suggest that regional anaesthesia for carotid surgery allows potential complications to be identified earlier than under general anaesthesia using reports from the patient, so that treatment may be modified to prevent morbidity and even mortality.

The Pruitt-Inahara shunt maintains mean middle cerebral artery velocities within 10% of preoperative values during carotid endarterectomy

Objective: The purpose of this study was to assess the ability of the Pruitt-Inahara shunt to maintain adequate middle cerebral artery velocities during carotid endarterectomy. Study Design: Prospectively collected data recorded during 548 carotid endarterectomies performed at a single university hospital were analyzed to look at changes in cerebral blood flow velocities at different stages during the procedure. Parallel data relating to blood pressure and end-tidal carbon dioxide were also examined. Results: During the first carotid artery cross clamp, middle cerebral artery velocity fell by 42%. A total of 169 patients (31%) had velocities that fell below 15 cm/s (electrical activity in the brain becomes altered below this level). After shunt insertion, only 2% of patients had middle cerebral artery velocities less than 15 cm/s. In only one patient was the velocity less than 10 cm/s. Increased systolic or diastolic blood pressure raised flow through the shunt significantly (P =.001). When two criteria used for selective shunt use were compared, only a moderate correlation was found between absolute middle cerebral artery velocity after carotid cross clamping and percentage change in middle cerebral artery velocity relative to preclamp values. Conclusions: The Pruitt-Inahara shunt is able to maintain adequate middle cerebral artery velocity in 98% of patients undergoing carotid endarterectomy. Alterations in blood pressure can significantly affect flow through the shunt. (J Vasc Surg 2000; 32:299-306.)

Maintaining Carotid Flow by Shunting During Carotid Endarterectomy Diminishes the Inflammatory Response Mediating Ischaemic Brain Injury

Objectives: to assess whether shunting during carotid reconstruction affects the release of inflammatory mediators from the ipsilateral hemisphere. Materials and methods: a catheter was placed in the ipsilateral jugular bulb during carotid endarterectomy (CEA) in 20 patients. Eight patients with ICBP (internal carotid backpressure) <40 mmHg received a shunt during CEA and 12 patients with ICBP >40 mmHg were operated upon without a shunt. Four patients with a carotid body tumour were used as controls. Blood was taken from the catheter as well as from the radial artery; before clamping, 5, 15, 30 min after clamping and 5 min after declamping. The oxygen extraction (AVO2) was calculated. Plasma concentrations of interleukin-1β (IL-1β), phospholipase A2(PLA2), thromboxane B2(TXB2), 6-keto-prostaglandin F1α (6-keto-PGF1α) and prostaglandin E2(PGE2) were measured by enzyme-linked immunosorbent assay (ELISA) technique. Results: all patients had a normal postoperative course except for one patient in the no-shunt group, who suffered a stroke 1 h later due to occlusion of the endarterectomy site. The AVO2extraction increased during clamping in patients operated upon without a shunt (p <0.05). This increase was partly recovered to pre-clamp levels 5 min after reperfusion. The extraction remained stable in the non-shunted patients and the control group. The increased extraction in the non-shunted group correlated with increased levels of IL-1β during clamping ( p <0.05) and reperfusion ( p <0.01). PLA2also increased during reperfusion in the non-shunted group ( p<0.05). An increased ratio between TXB2and 6-keto-PGF1α was noted during clamping ( p <0.05) and further increased during reperfusion. The levels of PGE2remained stable in both CEA groups. The PLA2levels, as well as TXB2, 6-keto-PGF1α and PGE2levels, remained unchanged during the procedure in the control group. Conclusions there is a metabolic response to carotid cross-clamping when no shunt is used. However, the clinical significance of this is unclear, since there were no intraoperative strokes.

Middle Cerebral Artery Circulation During Carotid Surgery: A Transcranial Doppler Study

Objective - Perioperative carotid cross-clamping might induce low stump pressures as well as hypoperfusion of the middle cerebral artery. In this study blood flow velocities in the middle cerebral artery were compared with intraoperative measurements of the poststenotic carotid blood pressure. Design - Forty-one patients with internal carotid artery stenosis were operated on without shunting, under general anesthesia. Poststenotic carotid pressures and middle cerebral artery flow velocities were measured before and during cross-clamping. The hemodynamic responses to preoperative carotid compressions and intraoperative cross-clamping were evaluated. Results - In seven patients the poststenotic carotid blood pressure decreased on clamping despite unchanged or even increased middle cerebral artery blood flow velocities. In all other patients, pressure changes were significantly correlated to the decrease in middle cerebral artery blood flow velocities. Autoregulatory blood flow velocity responses after preoperative common carotid artery compression were not reproducible by cross-clamping. Conclusions - Stump blood pressure measurements may not reflect middle cerebral artery perfusion in about 20% of thrombendarterectomies performed under general anesthesia. A possible explanation might be dimished cerebral autoregulation and changes in collateral flow distributions.

Systemic blood pressure and cerebral blood flow velocity during carotid surgery.

To evaluate the effect of mean arterial blood pressure (MAP) on cerebral perfusion during carotid surgery, we investigated blood flow velocity in the middle cerebral (Vs,mca) using transcranial Doppler ultrasonography (TCD). During carotid crossclamping, treatment included either phenylephrine-induced hypertension without shunting (Group XC; n = 11) or insertion of a shunt (Group S; n = 12). Increasing MAP in Group XC before crossclamping (81 + /-13 mmHg to 107 +/- 12 mmHg) caused an increase of Vs,mca (59 +/- 17 cm/s to 75 +/- 20 cm/s; p < 0.001). During crossclamping without a shunt, Vs,mca was not dependent on MAP, and was reduced (mean 47 +/- 24 cm/s) in relation to preclamp values. In Group S, Vs,mca was always dependent on MAP and the preclamp velocity was maintained (before shunt: 75 +/- 26 cm/sec; during shunt: 79 +/- 30 cm/sec). Although we found an impaired cerebral autoregulation, Vs,mca was independent of MAP during carotid crossclamping. Thus, TCD measurements have to be interpreted with caution during crossclamping, and the effect of induced hypertension has to be confirmed with more invasive measures of cerebral blood flow.

Brain-specific protein C activation during carotid artery occlusion in humans.

Activation of plasma protein C (PC) zymogen by thrombin-thrombomodulin at the endothelial surface is an important endogenous antithrombotic mechanism. It is unknown whether activated protein C (APC) is generated in vivo in the cerebrovasculature, because there is only limited thrombomodulin expression in human brain vascular endothelium. Therefore, we tested the hypothesis that carotid occlusion produces brain-specific PC activation. Blood samples were simultaneously collected from the ipsilateral internal jugular vein and radial artery before and during carotid cross-clamping and on "de-occlusion" in 8 awake patients undergoing routine carotid endarterectomy. Plasma PC zymogen and circulating APC levels were measured using enzyme immunocapture assay and expressed as percent of pooled plasma controls. Internal jugular vein APC levels increased 28% exclusively during carotid occlusion and then decreased 32% with de-occlusion (F=8.1, P<0.005). PC zymogen increased only 5.9% with occlusion (F=6.3, P<0.02), consistent with hemoconcentration. There were no changes in radial artery PC or APC levels. These findings demonstrate brain-specific protein C activation in humans during carotid occlusion and suggest a protective role for endogenous APC generation during cerebrovascular occlusion.

Carotid endarterectomy with patch closure versus carotid eversion endarterectomy and reimplantation: A prospective randomized study

Background: Although carotid eversion endarterectomy (CEE) has obtained consensus providing excellent early and late results, conventional carotid endarterectomy (CEA) with or without patching continues to be considered the gold standard surgical procedure. The few studies published to date comparing CEE with CEA in a small series of patients have failed to show substantial advantages of one technique over the other, and further randomized comparative studies are still required. The purpose of this study was to compare the outcome of CEA with routine patch closure (CEAP) with that of CEE and reimplantation (CEER) of the internal carotid artery in the common carotid artery. Methods: Three hundred thirty-six primary CEAs performed in 310 patients were randomized into 2 groups, 167 CEAPs and 169 CEERs. Surviving patients underwent duplex ultrasound scan control at 30 days, 6 months, 12 months, and every postoperative year thereafter. The mean follow-up was 34 months (range, 1 to 69 months). Demographic characteristics, risk factors, associated diseases, and indications for surgery were comparable in the 2 groups. Results: Although the rate of intraoperative electroencephalogram changes was comparable in the 2 groups, the incidence of shunting was statistically higher in the CEAP group (28.1% vs 1.2%, P < .00001). The carotid cross-clamping time was significantly lower in the CEER group ( P = .01). Although all deaths were in the CEAP group, the overall perioperative death and stroke-related death rates were comparable in the 2 groups. The perioperative stroke rate was statistically higher in the CEAP group (2.9% vs 0%, P = .03). Although the recurrent stenosis rate was comparable in the 2 groups (1.2% vs 0%), the CEAP group had a statistically higher rate of combined recurrent stenoses and occlusions (4.9% vs 0%, P = .003). The late mortality rate was similar in both groups. Conclusions: Although the outcome of CEAP in this series is consistent with that of the main reported trials, the CEER procedure is less likely than CEAP to cause perioperative stroke and death and seems superior in reducing the incidence of recurrent stenosis and late occlusive events. (Surgery 1999;125:271-9.)

Preoperative Volume Expansion Improves Tolerance to Carotid Artery Cross-Clamping during Endarterectomy

The benefit of carotid endarterectomy for carotid artery stenosis relates to both appropriate patient selection and careful surgical technique. Critical to the latter is the ability to afford intraoperative neuroprotection during carotid cross-clamping, although the optimal strategy to assure this protection remains debated. This report describes the impact of adding preoperative colloid volume expansion to a surgical algorithm that includes electroencephalographic (EEG) monitoring and barbiturate-induced burst suppression for EEG lateralization refractory to hypertension. The incidence of ischemic EEG change during carotid cross-clamping was observed. The results of an initial series of patients (n = 45) reported before incorporation of volume expansion were compared with the results of the current series (n = 155) of carotid endarterectomies, which included preoperative volume expansion with 6% hetastarch (500 or 1000 cc). With preoperative volume expansion, there was a 40% decrease in the incidence of EEG lateralization during carotid cross-clamping (17.4 versus 28.9%, P < 0.05) and a 63% decrease in the EEG lateralization refractory to induced hypertension (5.8 versus 15.6%, P < 0.05). The combined perioperative stroke and death rate was 1.3%. These results support the use of preoperative colloid volume expansion in carotid endarterectomy as a means of increasing the cerebral tolerance to carotid cross-clamping.

Transcranial cerebral oxymetry during carotid endarterectomy: agreement between frontal and lateral probe measurements as compared with an electroencephalogram

Objective: Transcranial cerebral oximetry, which is considered a novel technique, was evaluated during carotid endarterectomy. For practical reasons, the use of a single probe attached to the forehead and overlying the territory of the anterior cerebral artery is recommended. Other monitoring systems (transcranial Doppler, electroencephalograms (EEG)) focus more on the territory of the middle cerebral artery. The aim of this study was to evaluate whether a probe in the frontal area is as representative for monitoring cerebral ischaemia during carotid cross-clamping as a probe in the lateral area. Design: Clinical prospective study. Materials: Sixty patients who underwent carotid endarterectomy were studied with continuous and simultaneous EEG and transcranial cerebral oximetry. Forty-three patients (72%) simultaneously underwent frontal and lateral transcranial cerebral oximetry. The lateral probe was only used in 17 patients. Methods: The percentage decrease of transcranial cerebral oximetry was calculated during cross-clamping. Using the EEG findings as the gold standard in order to detect cerebral ischaemia during carotid cross-clamping, the relationship with transcranial cerebral oximetry was described in terms of sensitivity, specificity and the area under the curve in a receiver operating characteristic curve. Results: The 95% confidence interval of the area under the curve of the receiver operating characteristic of the lateral probe was 0.61–1.00 and that of the frontal probe was 0.65–1.00; therefore there is virtually no difference between the two methods. In 18% of the cases the lateral transcranial cerebral oximetry was hindered by practical failures. Conclusion: Considering the lack of additional information and the practical problems experienced with the lateral probe, it was concluded that transcranial cerebral oximetry with a single frontal probe is a practical non-invasive monitoring system and is at least as representative for monitoring cerebral ischaemia during carotid cross-clamping as a lateral probe.

Elective Carotid Artery Stenting in the Presence of Contralateral Occlusion

Significant carotid stenosis in the presence of an occluded contralateral artery has a poor prognosis with medical therapy alone. Carotid cross clamping during surgical endarterectomy results in critical flow reductions in patients with inadequate collateral flow, and represents a significant risk for procedural strokes. Carotid stenting is being evaluated as an alternative to endarterectomy. We describe the immediate and late outcome of a series of 26 patients treated with carotid stenting in the presence of contralateral carotid occlusion. The mean age of the patients in this group was 65 ± 9 years, 23 (89%) were men and 10 (39%) were symptomatic from the vessel treated. The procedural success of carotid stenting in this group of patients was 96%. The mean diameter stenosis was reduced from 76 ± 15% to 2.8 ± 5%. There was 1 (3.8%) minor stroke in a patient who developed air embolism during baseline angiography. At late follow-up there was no neurologic event in any patient at a mean of 16 ± 9.5 months after the procedure. Thus, carotid stenting of lesions with contralateral occlusion can be performed successfully with a low incidence of procedural neurologic complications and late stroke.

USE OF NEAR-INFRARED SPECTROSCOPY (NIRS) DURING CAROTID ENDARTERECTOMY (CEA)

Patients undergoing combined CABG and CEA are at increased risk for the development of perioperative embolic strokes. Contributory to this risk is the use of shunting during CEA. Selective shunting is associated with the lowest operative stroke rate, [1] therefore patient selection is critical. We used a new dual-probe NIRS system to quantitate the adequacy of cerebral collateral circulation during carotid cross-clamping & to develop a criterion for shunt placement. Methods. Following IRB approval, we studied 20 patients undergoing elective CEA. Two separate NIRS probes (B & C Medical, Inc.) were secured to the R & L forehead. Each probe consists of 4 laser diodes (750, 780, 810, 840 nm) and 2 photodectors which monitor regional cerebral oxygenation via continuous measurements of oxyhemoglobin (Delta HbO2), deoxyhemoglobin (Delta Hb) and total hemoglobin (Delta THb). Values are expressed in [micro sign]mol/L change from baseline. Results. Following carotid clamping, 2 types of response were observed, 1) most patients (n=13) showed minimal changes in measured parameters under both probes, indicating an adequate collateral circulation and no need for shunt, 2) other patients (n=7) showed a rapid decrease in Delta HbO2 and THb with a reciprocal increase in Hb on the ipsilateral side. Figure 1. This corresponds to the Cerebral Ischemic Threshold [2] of decreased Delta HbO2 >or=to 5 [micro sign]mol/L and reflects impaired cerebral blood flow and need for shunt placement. Following insertion of shunt, HbO2 remains below baseline and Hb above baseline indicating improved but incomplete restoration of carotid flow. Postoperatively, no patients sustained neurological deficits.Figure 1Discussion. NIRS appears useful in detecting changes in cerebral oxygenation and assessing adequacy of collateral circulation and necessity for shunt placement during CEA. In this study, 35% of patients were intolerant to carotid artery clamping and were at risk for developing cerebral ischemia had a shunt not been employed. Others [3,4] have shown good correlations between NIRS measurements during CEA and changes in TCD, SEP and SPECT. Additional clinical studies correlating the use of NIRS with surgical outcome are indicated.

The Use of Near-Infrared Cerebral Oximetry in Awake Carotid Endarterectomy

Study Objective: To determine the utility of cerebral oximetry for monitoring the adequacy of cerebral blood flow (CBF) during carotid cross-clamp. Design: Prospective study. Setting: University hospital. Patients: 16 consecutive ASA physical status III (or higher) patients for awake carotid endarterectomy (CEA). Interventions: Regional cerebral oxygen saturation (SaO 2) was monitored continuously during CEA, which was performed by the same surgeon, and with standard regional anesthetic, sedation, monitoring, and operative techniques. Data were recorded and analyzed using repeated measures analysis of variance (ANOVA). Measurements and Main Results: 14 hemodynamically stable patients demonstrated significant decreases in cerebral SaO 2 from baseline: 69 + 1.8% to 64 + 1.2% at carotid cross-clamp (p < 0.001). After 5, 10, and 15-minute cross-clamp time, cerebral SaO 2 was 63 + 1.4%, 64 + 1.5%, and 63 + 1.4%, respectively (p < 0.001, vs. baseline). On cross-clamp removal, cerebral SaO 2 rose significantly: 67 + 1.6% (p < 0.01 vs. 5, 10, and 15 min). Two hypotensive patients (mean arterial pressures of 40 and 43 mmHg) developed signs and symptoms of global cerebral ischemia, with a concomitant decrease in cerebral oximetry (40% and 48%, respectively). These changes resolved with correction of hypotension. Conclusion: Cerebral SaO 2 decreased significantly on carotid cross-clamp in patients undergoing awake CEA. Hemodynamically stable patients demonstrated no evidence of regional brain failure when SaO 2 decreased to 63% (mean decrease of 7.2%). Two hemodynamically unstable patients had evidence of global brain failure when SaO 2 was less than 48% (mean decrease of 36%). Our findings suggest that cerebral oximetry reflects CBF, and it may be an effective, noninvasive method of monitoring regional cerebral oxygenation changes during CEA. Significant reductions in regional SaO 2 may be tolerated without evidence of brain failure. Further studies are needed to define an SaO 2 threshold that reflects regional brain failure.

Incidence, timing, and causes of cerebral ischemia during carotid endarterectomy with regional anesthesia

Purpose: Controversy exists regarding the best technique to identify cerebral ischemia during carotid endarterectomy (CEA). Regional anesthesia allows continuous evaluation of neurologic function and therefore can help determine the incidence, timing, and causes of cerebral ischemia. Methods: The timing and clinical manifestations of any neurologic event during CEA and as long as 30 days afterward was determined by review of operative reports, hospital charts, and outpatient records of consecutive patients who underwent CEA under regional anesthesia over a 68-month period. Results: Two hundred patients underwent CEA; indications were asymptomatic stenosis >60% in 25%, transient ischemic attack with stenosis >50% in 52%, and prior stroke with stenosis >50% in 23%. Eight patients (4%) were converted to general anesthesia for nonischemic reasons. Of the remaining 192 patients, 183 (95.5%) underwent the procedure with regional anesthesia and no shunt, 2% had cerebral ischemia and underwent shunt placement, and 2.5% had cerebral ischemia, were converted to general anesthesia, and underwent shunt placement. Cerebral ischemia developed in nine patients after carotid cross-clamping, manifested by loss of consciousness in four, confusion in two, dysarthria and confusion in one, and decreased contralateral motor strength in two. Immediate cerebral ischemia developed in four of the nine patients within 1 minute of cross-clamping; all four underwent shunt placement. In five of the nine patients, cerebral ischemia occurred between 20 and 30 minutes after cross-clamping; all occurred during relative intraoperative hypotension (average reduction of 35 mm Hg in the systolic pressure). All awake patients in whom ischemic symptoms developed immediately regained and maintained normal neurologic function with shunt placement. Five of 26 patients (19%) with contralateral occlusion required a shunt; none had postoperative ischemia. The mean carotid cross-clamp time was 27 minutes. Postoperative (30 day) complications included a 0.5% stroke rate, a 0.5% rate of postoperative transient ischemic attack, a 0.5% rate of worsening of preexisting acute stroke, and a 0.5% rate of myocardial infarction (no deaths). Of the nine patients who had intraoperative ischemic changes, none had a postoperative neurologic deficit; the three patients who had postoperative neurologic changes had no intraoperative ischemic symptoms. Conclusions: CEA with regional anesthesia allows continuous neurologic monitoring and can be performed safely even when contralateral occlusion coexists; intraoperative shunting for ischemia is necessary in 4.5% of all cases and in 19% of patients with contralateral occlusion. Intraoperative ischemia was flow-related in our patients; it occurred early from ipsilateral carotid clamping and late from reduced collateral flow as a result of hypotension. Monitoring should be continued throughout cross-clamping to identify late cerebral ischemia. Postoperative cerebral ischemia is not associated with intraoperative ischemia, if corrected. (J Vasc Surg 1998;27:329-37.)

Resolving extra- and intracranial signal changes during adult near infrared spectroscopy

Extracranial tissues have a significant effect on cerebral near infrared spectroscopy (NIRS) measurements in adults. Carotid surgery provides the opportunity to determine the relative contributions from the intra- and extracranial vascular territories. To assist/ a specifically gated Laser Doppler flowmetry probe can be inserted between the NIRS optodes to co-monitor cutaneous blood flow associated with external carotid artery (ECA) clamping, whilst transcranial Doppler can ge employed to monitor relative c;hahges in the intracranial blood flow seen during internal carotid artery (ICA) clamping. Established criteria for severe cerebral ischemia (SCI) following carotid cross clamping was applied to 703 consecutive patients undergoing carotid surgery for high grade stenosis. Ipsilateral frontal NIRS recorded the difference (Total-ΔHbdiff) in concentrations of oxy- and deoxy-hemoglobin. Interrupted time series analysis following clamping of the ECA and ICA allowed the different vascular components of Total-ΔHbdiff(ECA-ΔHbdiff and ICA-ΔHbdiff) to be identified. Data from 76 patients was suitable. Sixteen (27 %) patien.ts fulfilled the criteria for SCI. Patients who demonstrated an ICA-ΔHbdiff of > 6.8 μmol l-1 all showed SCI. No patient with an ICA-ΔHbdiff < 5.0 μmol l-1 showed SCI. Thus an ICA-t1Hbdiff threshold of 6.8μmol l-1 provided a 700%.specificity for SCI, whereas an ICA-tΔHbdiff < 5.0 Ilmoll-7 was 700% sensitive for excluding SCI. When Total-ΔHbdiff was used without removing the ECA component; thresholds for SCI could not be resolved. NIRS can provide quantified thresholds for severe ischemia in the adult. brain provided the extracranial component is removed. [Neural Res 1998; 20 (Suppl 1): 519–522]

Carotid endarterectomy under regional anesthesia.

Regional anesthesia for carotid endarterectomy is a simple, reliable, and virtually complication-free technique. We began to perform a series of carotid endarterectomy under regional anesthesia at our institution in May 1990. This report describes our experience with 180 operated patients from May 1990 till December 1995, with regional anesthesia. All patients were operated with microsurgery and we utilized the deeply cervical plexus block at the C-4 level associated with superficial block, along the posterior border of the externocleidomastoid muscle. The main advantage of this technique of anesthesia is that it is the only exact method of assessing the need of a shunt by using the neurological status of the awaken patient during trial carotid cross-clamping. The regional anesthesia allows carotid endarterectomy to be safely performed on patients with advanced cardiac disease or severe chronic obstructive pulmonary disease who were not good candidates for general anesthesia. In this 180 patients we performed 198 consecutive endarterectomies (10% bilateral) with a total morbidity-mortality rate of 2.0%.

Somatosensory evoked potential monitoring in carotid surgery. I. Relationships between qualitative SEP alterations and intraoperative events

This paper presents the results of intraoperative median nerve SEP monitoring in 205 successive patients undergoing isolated carotid endarterectomy (CE) ( N=172) or CE followed by coronary bypass (CBP) and/or vascular replacement (VR) ( N=33). The left and right median nerves were alternately stimulated and recordings performed on 4 channels: cervical, ipsi- and contralateral parietal, and frontal. SEPs were qualitatively rated in terms of mild, moderate, or severe ipsilateral, contralateral, or bilateral abnormalities. The SEP abnormalities were subdivided into 5 categories as a function of their relationships with intraoperative events: no alterations (67.3%), early or late SEP alterations after carotid cross-clamping (15.6%), SEP alterations after a drop in blood pressure (occurring outside of or within the cross-clamping period) (15.1%), SEP alterations of a most likely embolic origin (2.4%), SEP changes after head positioning (1%), and SEP changes after a modification of the anesthetic regimen (1.5%). Only moderate to severe SEP alterations occurring soon after carotid cross-clamping justified shunt installation in 16% of the cases. SEP alterations after a drop in blood pressure were reversed merely by restoring blood pressure. The neurological outcome was uneventful in 94.2% of cases. Of the 12 patients who developed neurological sequellae, only one case presented transient sequellae after isolated CE without SEP changes while most cases either had undergone combined CE and CBP and/or VR (6 cases) or had presented SEP alterations of embolic origin (3 cases). We conclude that our system of qualitative rating of SEPs proved very sensitive to intraoperative hemodynamic disturbances or macroembolisms.