Predictive value of carotid artery stump pressures during carotid endarterectomy

The ideal method of monitoring cerebral perfusion during carotid endarterectomy remains controversial. This article reviews many of the larger studies in the literature that have attempted to evaluate the usefulness of carotid artery stump pressure. Topics discussed include stump pressure alone, regional anesthesia, stump pressure and EEG, and stump pressures and transcranial Doppler ultrasonography.     

Correlation of neurologic complications and pressure measurements during carotid endarterectomy

There was no significant difference between the mean occluded internal carotid artery pressure in asymptomatic, transient ischemic attack or prior stroke patients. The stump pressure was not consistently elevated at the second operation in those having undergone bilateral procedures. Estimate of back bleeding from the internal carotid artery operation did not necessarily correlate with the stump pressure. Adequate back bleeding was recorded in patients with a low stump pressure, and reduced bleeding was noted in individuals with a high stump pressure. The pressure gradient across the stenosis of the bifurcation of the carotid artery was helpful in assessing the degree of stenosis present. The occluded internal carotid artery pressure seemed to be a helpful aid in indicating those patients with poor collateral flow and, therefore, at high risk of ischemic brain damage. The use of an inlying shunt in those individuals having a low stump pressure may be expected to reduce the over-all neurologic complication rate in patients undergoing carotid endarterectomy.     

Prevention of postoperative thrombotic stroke after carotid endarterectomy: the role of transcranial Doppler ultrasound

PURPOSE: To determine the incidence of particulate embolization after carotid endarterectomy (CEA), the effect of dextran-40 infusion in patients with sustained postoperative embolization, and the impact of transcranial Doppler (TCD) monitoring plus adjuvant dextran therapy on the rate of postoperative carotid thrombosis. METHODS: Prospective study in 100 patients who underwent CEA with 6-hour postoperative monitoring using a TCD that was modified to allow automatic, intermittent recording from the ipsilateral middle cerebral artery waveform (10 minute sample every 30 minutes). An incremental dextran-40 infusion was commenced if 25 or more emboli were detected in any 10-minute period. RESULTS: Overall, 48% of patients had one or more emboli detected in the postoperative period, particularly in the first 2 hours. However, sustained embolization that required Dextran therapy developed in only five patients. In each case, the rate of embolization rapidly diminished. CONCLUSIONS: A small proportion of patients have sustained embolization after CEA, which in previous studies has been shown to be highly predictive of thrombotic stroke. Intervention with dextran reduced and subsequently stopped all the emboli in those in whom it was used and contributed to a 0% perioperative morbidity and mortality rate in this series.     

Predicting the effect of carotid artery occlusion during carotid endarterectomy: comparing transcranial doppler measurements and cerebral angiography

BACKGROUND and PURPOSE: We correlated the mean transcranial Doppler blood flow velocity (FVm) during carotid endarterectomy with the functional collateral pathway(s) documented by angiography. METHODS: Three patient groups were established: group 1 was dependent on the anterior communicating artery, group 2 on the anterior communicating artery and ipsilateral posterior communicating artery, and group 3 on the ipsilateral posterior communicating artery. Continuous middle cerebral artery FVm and electroencephalographic monitoring were performed in 45 patients during carotid endarterectomy. RESULTS: Clamped FVm was lowest in group 3 at 17+/-9 cm/s versus 36+/-16 and 33+/-11 cm/s for groups 1 and 2 (P<0.01). FVm values in groups 1 and 2 were similar. There was significant cerebral arterial vasodilation in group 3 patients on the basis of a pulsatility index of 0.38+/-0.15. The maximum FVm after clamp release was similar among the 3 groups. Normalized blood flow velocity 1 minute before release of the clamp was increased from the minimum flow velocity after clamping only in group 1 and 2 patients. CONCLUSIONS: The ipsilateral posterior communicating artery is a minor collateral pathway during acute carotid occlusion that contributes little to the collateral flow if there is a functional anterior communicating artery. Collateral flow through the middle cerebral artery is not recruited during occlusion in group 3 patients. The reperfusion FVm transient is independent of the primary collateral pathway. Documentation of functional collateral pathways on the basis of Doppler or angiographic examination may be advantageous in future studies since it can provide the basis for comparison among studies.     

Stump pressure: an unreliable guide for shunting during carotid endarterectomy

A correlative analysis was made between the neurological status of the awake patient and the internal carotid artery stump pressure in 125 consecutive patients undergoing carotid endarterectomy. There was no mortality in this series. Twenty-four patients lost consciousness immediately after carotid cross-clamping, even though stump pressures were above 50 mm Hg in more than one third of the cases. The majority (80.8%) of the patients tolerated cross-clamping (stump pressures were between 20 and 90 mm Hg). This study demonstrated the variability of cerebral tolerance relative to absolute stump pressure guidelines, such as 25 or 50 mm Hg; reliance on these values to determine the need for intraoperative shunting could lead to stroke at operation. Our experience also showed that assessment of the awake but tranquil patient continues to be the safest and most reliable guide to selective shunting during carotid endarterectomy.     

Transcranial Doppler monitoring and causes of stroke from carotid endarterectomy

A dysfunction in the intracellular signal transduction pathways may be implicated in the pathophysiology of bipolar disorder. In particular, the phosphatidylinositol (PI) signal transduction pathway may be a possible site of dysfunction. Platelets, peripheral cells, and post-mortem brain samples have been used as models in preliminary studies aimed at investigating this hypothesis. Emerging findings from clinical studies are consistent with a hyperfunction in the PI pathway in the manic state, which could be state-related. Findings of increased protein kinase C (PKC) activity in the manic state, and increased intracellular Ca2+ responsiveness in the manic and possibly depressed states, are also consistent with a hyperactive PI pathway in this disorder. Future research should attempt to replicate and extend these preliminary findings further.     

Interpretation of embolic phenomena during carotid endarterectomy

BACKGROUND AND PURPOSE: Air and particulate emboli are a major source of morbidity during carotid endarterectomy (CEA); however, amplitude overload and poor time resolution have restricted the ability of transcranial Doppler ultrasound to differentiate between the two. METHODS: We have now overcome these two limitations by (1) rerouting embolic signals away from the audio frequency amplifier to avoid amplitude overload and (2) substituting the Wigner distribution function for the fast Fourier transform to improve time and frequency resolution. Thus, we can now accurately determine embolic duration and embolic velocity, the product of which is the sample volume length (SVL). This measurement represents the physical distance over which an embolic signal can be detected. The underlying hypothesis was that air reflected more ultrasound and would therefore be detected over a greater SVL. RESULTS: The median SVL (interquartile range) for 75 in vitro air emboli was 1.97 cm (range, 1.70 to 2.35) compared with 0.27 cm (range, 0.16 to 0.43) for 185 particulate emboli detected during the dissection phase of CEA. Off-line analysis on an additional 560 embolic signals detected during different phases of CEA suggested that 46 of 143 (32%) of emboli immediately after shunt insertion were particulate, as were 19 of 33 (58%) occurring during shunting, 28 of 78 (36%) after restoration of flow in the external carotid artery, 23 of 251 (9%) after restoration of flow in the internal carotid artery, and 55 of 55 (100%) of those emboli detected during the early recovery phase. CONCLUSIONS: This development provides objective physical criteria upon which embolus characterization (particulate/air) can be based. This could have major implications for future patient monitoring with respect to modification of surgical technique and pharmacological intervention.     

Predicting hemodynamic ischemia by transcranial Doppler monitoring during therapeutic balloon occlusion of the internal carotid artery

PURPOSE: Our objective was to evaluate the sensitivity of transcranial Doppler (TCD) sonographic monitoring during permanent balloon occlusion of the internal carotid artery (ICA) in predicting hemodynamic ischemia. METHODS: Thirty-two consecutive patients underwent controlled therapeutic balloon occlusion of the ICA. Selection criteria included assessment of the circle of Willis by compression angiography, clinical tolerance during a 20-minute test occlusion, and TCD monitoring of the ipsilateral middle cerebral artery. The mean blood flow velocity (MBFV) (n = 32) and pulsatility index (PI) (n = 28) were recorded. In 25 patients, MBFV changes upon motor stimulation were recorded before and after ICA occlusion. RESULTS: Twenty-eight (88%) of the patients had no complications. Three patients suffered delayed symptoms 30 minutes to 20 hours after balloon detachment. Two of these patients recovered spontaneously within 1 day, the other improved after extracranial/intracranial (EC/IC) bypass surgery. One patient, who did not tolerate the test occlusion, suffered a hemodynamic stroke despite EC/IC bypass before permanent balloon occlusion. No embolic complications occurred. The mean MBFV reduction was 20% (range, 0% to 55%); the mean PI reduction was 20% (range, 0% to 56%). No complications occurred in patients who had mild MBFV and PI reduction (30% or less, n = 21). All three patients with severe MBFV or PI reduction (> 50%) had neurologic symptoms. Among those with moderate MBFV or PI reduction (30% to 50%, n = 8), symptoms developed in only one patient who had moderate reduction of both MBFV (33%) and PI (38%). Motor vasoreactivity showed wide variation and was markedly reduced in two symptomatic patients. CONCLUSION: TCD monitoring reflects changes in cerebral hemodynamics after therapeutic balloon occlusion of the ICA. MBFV and PI reductions under 30% are highly predictive of clinical tolerance. A reduction of more than 50% may be a critical threshold for the occurrence of symptoms; in such cases, EC/IC bypass should be considered before proceeding with permanent balloon occlusion.     

Noninvasive prediction of intracranial pressure curves using transcranial Doppler ultrasonography and blood pressure curves

BACKGROUND AND PURPOSE: Until now the assessment of intracranial pressure (ICP) required invasive methods. The objective of this study was to introduce an approach to a noninvasive assessment of continuous ICP curves. METHODS: The intracranial compartment was considered a "black box" system with an input signal, the arterial blood pressure (ABP), and an output signal, the ICP. A so-called weight function described the relationship between ABP and ICP curves. Certain parameters, called transcranial Doppler (TCD) characteristics, were calculated from the cerebral blood flow velocity (FV) and the ABP curves and were used to estimate this weight function. From simultaneously sampled FV, ABP, and (invasively measured) ICP curves of a defined group of patients with severe head injuries, the TCD characteristics and the weight function were computed. Multiple regression analysis revealed a mathematical formula for calculating the weight function from TCD characteristics. This formula was used to generate the ICP simulation. FV, ABP, and ICP recordings from 11 patients (mean age, 46 +/- 14 years) with severe head injury were studied. In each patient, ICP was computed by a simulation procedure, generated from the data of the remaining 10 patients. The simulation period was 100 seconds. RESULTS: Corresponding pressure trends with a mean absolute difference of 4.0 +/- 1.8 mm Hg between computed and measured ICP were observed. Shapes of pulse and respiratory ICP modulations were clearly predicted. CONCLUSIONS: These results demonstrate that this method constitutes a promising step toward a noninvasive ICP prediction that may be clinically applicable under well-defined conditions.     

Intraabdominal hemorrhage during combined coronary artery bypass and carotid endarterectomy

Intraabdominal complications during cardiopulmonary bypass are extremely rare, with an incidence of less than 1% in multiple retrospective studies. These complications are associated with a high mortality, and their rapid diagnosis is critical to the outcome of the patient. We present a case of spontaneous intraabdominal hemorrhage after combined carotid endarterectomy and four-vessel coronary artery bypass grafting, which was diagnosed through a diaphragmatic window.     

Comparison of hemodynamic cerebral ischemia and microembolic signals detected during carotid endarterectomy and carotid angioplasty

BACKGROUND AND PURPOSE: There has been concern about carotid percutaneous transluminal angioplasty (PTA) carrying a greater risk of cerebral ischemia than carotid endarterectomy. We set out to compare cerebral hemodynamics and microembolization during carotid PTA and CEA. METHODS: We used transcranial Doppler to monitor the middle cerebral artery of 28 patients undergoing carotid PTA (n = 14) or carotid endarterectomy (CEA) with a shunt (n = 14). Each period during which the internal carotid artery was occluded by PTA balloon or by clamp when the shunt was not in place was timed. Individual periods were summated to give a total occlusion time. Ischemic time was defined as the period for which mean middle cerebral artery velocity fell to a third or less of baseline. Microembolic signals were counted during each procedure. RESULTS: CEA resulted in significantly longer individual and total occlusion time than PTA (mean individual occlusion time, seconds), CEA, 168 +/- 51; PTA, 20 +/- 7; P < .001; mean total occlusion time; CEA, 337 +/- 70; PTA, 26 +/- 10; P < .001. Ischemic time was also significantly longer during CEA than during PTA (CEA, 165 +/- 40; PTA, 17 +/- 5; P = .001). There were significantly more microembolic signals during PTA than during CEA (mean number of microembolic signals during CEA, 52 +/- 64; during PTA, 202 +/- 119; P = .001). There was no correlation between any of the parameters measured and periprocedural stroke, which occurred in one patient in each group. CONCLUSION: PTA results in less hemodynamic ischemia but more cerebral microembolism than CEA. In this small series, however, it is not possible to comment on the relations between ischemic time, microembolism, and stroke.     

Prospective study of carotid endarterectomy and contralateral carotid occlusion

A total of 700 patients who had carotid endarterectomy (CEA) in the UK and Ireland during a 6-month interval between March and August 1994 were studied prospectively. Some 108 patients (15.4 per cent) had a contralateral internal carotid artery occlusion. Previous reports have shown an associated stroke rate of about 10 per cent in these patients. This study assessed complications and outcome for patients undergoing CEA with contralateral internal carotid artery occlusion compared with those without. The indications for surgery were comparable between the two groups although the patients with occlusion had a slightly higher incidence of arrhythmia and stroke. Intraoperative shunts were used in a significantly higher proportion of those with occlusion (83.3 versus 64.7 per cent, P = 0.0001). The combined death and stroke rate for patients with occlusion was 5.6 per cent compared with 2.4 per cent for the remainder (P not significant). On the basis of the present data, CEA with a contralateral carotid artery occlusion carries only a slight increase in the rate of postoperative stroke and death. This increase was not statistically significant and is lower than that reported previously.     

Cerebral Ischemia during carotid endarterectomy with severe but reversible changes

Electroencephalographic monitoring of a patient during carotid endarterectomy demonstrated severe ipsilateral voltage suppression with preservation of rhythms when the common carotid artery was clamped. Because the atheromatous plaque extended almost to the base of the skull, it was impossible to insert a shunt. Occlusion time was 19 minutes. After carotid flow was re-established, there was a rapid recovery of voltage. The patient awoke with a profound hemiparesis, but this cleared almost completely within a week. The EEG changes indicated severe ischemia, but, though function was transiently impaired, there was no apparent cerebral necrosis. This case represents the most severe yet reversible episode of ischemia during carotid clamping reported to date. Preservation of EEG rhythms, even in the face of voltage suppression, may have been a favorable sign.     

Complete MR angiography and Doppler ultrasound as the sole imaging modalities prior to carotid endarterectomy

OBJECTIVE: To assess the combination of duplex Doppler ultrasound (DUS) and complete carotid magnetic resonance angiography (MRA) for the non-invasive imaging of carotid disease and their effect on outcomes. Determine inter-reader agreement of carotid MRA. MATERIALS AND METHODS: One-hundred and ten carotid bifurcations were evaluated using DUS, 2D and 3D time-of-flight MRA from the aortic arch to the Circle of Willis in 55 patients. Percentage stenoses were determined by two blinded readers using standardized criteria. Clinical follow-up was by chart review. RESULTS: Correlation of Doppler and MRA was excellent (r=0.903, P<0.001). Inter-reader agreement (K) for MRA was good: internal carotid artery (ICA) (0.750), external carotid artery (ECA) (0.674) and common carotid artery (CCA) (0.410). Differences in CCA readings were due to minor differences in categorizing lesions as CCA versus ICA or ECA. MRA and Doppler detected nine occluded ICAs. Two DUS occlusions had ICA flow by MRA; one due to a reconstituted precavernous ICA, one a near occluded vessel. Five patients (9%) had surgical management modified by MRA with four not having surgery: three distal ICA/Siphon occlusions and one less severe stenosis by MRA. One tandem lesion not visualized by DUS was surgically significant. Nine aortic arch abnormalities had no surgical impact, possibly due to small sample size. Of 41 endarterectomies, there were no complications from errors of diagnosis. CONCLUSION: Carotid MRA correlates well with DUS with good inter-reader agreement. MRA confirms Doppler findings, expands anatomical information and identifies tandem lesions from the aortic arch to the Circle of Willis which can affect surgical management. This approach to carotid artery imaging appears to have no negative effect on surgical outcome.     

Neuropsychologic effects of carotid endarterectomy

This study assessed neuropsychologic changes after internal carotid endarterectomy using a design that limited the confounding effects of surgical and anesthesiological stress. Twenty-eight patients (mean age = 65.9 years, SD = 8.4, range 45-79), underwent extensive neuropsychological assessment before and on the seventh day after carotid endarterectomy for symptomatic carotid stenosis greater than 75%. A similarly assessed control group of 30 patients underwent elective orthopaedic surgery. A third cognitive assessment was performed 4 months postoperatively on a subgroup of the study patients. No significant cognitive change occurred in the control group. The study patients showed significant improvement in verbal memory, constructive abilities, verbal attainment, and visual attention; a trend towards further improvement of verbal functions was evident at the late postoperative assessment. No side-specific cognitive change was observed. In conclusion, carotid endarterectomy performed for currently accepted indications significantly improves several cognitive functions.     

Transcranial Doppler sonography in the pre- intra- and post-operative evaluation of 85 patients undergoing carotid endarterectomy

Porcine somatotropin (pST) administration reduces the sensitivity of pigs to insulin, and after several days of treatment, it alters baseline circulating concentrations of pST, insulin, glucose, and other metabolites. The length of time required to develop this reduction in whole-body insulin sensitivity has not been established. To investigate this, eight castrate pigs received daily injections of either recombinant pST (120 micrograms/kg BW) or exicipient. Intravenous insulin tolerance tests (1.0 microgram/kg BW) were done before the first pST injection (Day 0) and on Day 1, 3, 5, and 8 of pST treatment. Control animals had insulin tolerance tests on Day 0 and again on Day 8 of treatment. By Day 8, the glucose response to the insulin tolerance tests in pST-treated pigs was 45% of the response of the control group (P < 0.01). Glucose response areas between Day 1, 3, 5, and 8 of pST treatment were not different (P > 0.10). The maximum effect of pST on glucose response to insulin was achieved by Day 1. Therefore, factors responsible for the development of reduced whole-body insulin sensitivity in pST-treated pigs are fully expressed within 21 hr of the initial pST treatment.     

Plastic repair of the carotid artery in carotid endarterectomy

The work is based on an analysis of results of 70 carotid endarterectomies performed on 68 patients aged from 43 to 67 years. 53% of the patients were operated upon at the stage of a relative compensation of brain blood circulation. Multiple character of injuries of the brachiocephalic arteries took place in 70.5% of the cases. Plasty of the internal carotid artery is thought by the authors to be necessary by means of using a flap of lyophylized allopericardium, with the diameter of its orifice less than 8 mm.