Intraoperative Use of Electroencephalography as an Assessment of Cerebral Blood Flow

Usefulness and Reliability of the Bispectral Index during Balanced Anesthesia for Neurovascular Surgery in New Zealand White Rabbits

Few data about the electroencephalogram and its calculated indices, such as the bispectral index (BIS), have been reported in rabbits. We aimed to evaluate whether a clinically stable anesthesia was mirrored by consistent and stable BIS values and to investigate the effects of modified cerebral blood supply, due to bilateral carotid clamping and re-opening, on BIS values. We also investigated the effects of fentanyl, as an antinociceptive drug, on the BIS. Sixty-eight rabbits undergoing general anesthesia for surgical creation of carotid bifurcation aneurysms were enrolled. The BIS values were recorded at nine selected time points (TPs) during each procedure and before and after fentanyl administration. The BIS values over time were compared with two-way repeated-measures analysis of variance followed by Tukey test, while the Wilcoxon signed rank test was performed to compare values at clamping and re-opening of the carotids as well as before and after fentanyl administration. The BIS values were significantly lower during anesthesia than at the end of anesthesia and at tracheal extubation; no significant differences were found among other TPs. Adequate depth of anesthesia was mirrored by consistent BIS values among rabbits, and alteration of cerebral blood supply did not modify BIS values, except once. Following fentanyl, BIS values did not change in a clinically relevant way.

Carotid Endarterectomy

Stroke is the second leading cause of death worldwide. One of the main causes of stroke is carotid artery stenosis. Stenosis with atherosclerosis in the carotid artery can cause stroke by hemodynamic ischemia or artery to artery embolism. A most common surgical intervention for carotid artery stenosis is carotid endarterectomy (CEA). Many studies on CEA have been reported and suggested medical indications. For symptomatic carotid stenosis, generally, CEA may be indicated for patients with more than 50% stenosis and is especially beneficial in men, patients aged 75 years or older, and patients who underwent surgery within 2 weeks of their last symptoms. For asymptomatic carotid stenosis, CEA may be indicated for those with more than 60% stenosis, though each guideline has different suggestions in detail. In order to evaluate the indication for CEA in each case, it is important to assess risks for CEA carefully including anatomical factors and comorbidities, and to elaborate each strategy for each operation based on preoperative imaging studies including carotid ultrasonography, magnetic resonance imaging and angiography. In surgery there are many tips on operative position, procedure, shunt usage and monitoring to perform a safe and smooth operation. Now that carotid artery stenting has been rapidly developed, better understanding for CEA is required to treat carotid artery stenosis adequately. This chapter must be a good help to understand CEA well.

Monitoring in carotid endarterectomy

Cerebral ischemia during carotid endarterectomy occurs via several mechanisms: inadequate collateral blood flow during carotid cross-clamping, thromboembolism due to carotid manipulation, and/or rethrombosis at the surgical site. Perioperative strokes increase not only the morbidity of endarterectomy but also its short- and long-term mortality. However, while several predictors of cerebral ischemia have been identified, precise individual risk is hard to assess. Since nonselective shunting during carotid cross-clamping is neither risk-free nor eliminates perioperative stroke, it is advisable to apply intraoperative monitoring techniques for detection and reversal of cerebral ischemia, which may occur at various stages of the procedure. This chapter addresses the methods available for monitoring, with an emphasis on neurophysiologic techniques, which are preferable given their direct assessment of how a decrease in cerebral blood flow impacts brain function. These include electroencephalography, somatosensory evoked potentials, and transcranial motor evoked potentials. Details regarding the methodology, advantages, disadvantages, and interpretation of these tests will be discussed within the anatomic, physiologic, surgical, and anesthetic contexts.

Transcranial Cerebral Oxymetric Monitoring Reduces Brain Hypoxia in Obese and Elderly Patients Undergoing General Anesthesia for Laparoscopic Cholecystectomy

The aims of this prospective, observational study were to evaluate the changes of the regional cerebral saturation (rSO2) measured by near-infrared spectroscopy during elective laparoscopic cholecystectomy under total intravenous anesthesia and the association between patient's characteristics and critical decline of rSO2. Hemodynamics, rSO2, and oxygen saturation were recorded in different time points: before the anesthesia (Tbas), 2 minutes after the induction (supine position) (Tind), 2 minutes after CO2 insufflation (supine) (TCO2), 10 minutes after CO2 insufflation (reverse Trendelenburg) (TrevT), and 2 minutes after deflation (supine) (Tpost). Average age was 53±13 (range: 22 to 79 y). In 12 of a total of 62 patients (19.4%) the rSO2 decreased >20% (20.5% to 28.4%) in TCO2 or TrevT times. Significantly higher decrease of the rSO2 was found in patients older than 65 years and those with body mass index >30 kg/m (P<0.05). Noninvasive monitoring of cerebral oxygenation could be an important part of perioperative care in obese and older patients.

The Relationship of Triphasic Waves with Intracranial Pressure as a Possible Prognostic Marker in Traumatic Brain Injury

Background

Continuous electroencephalography (CEEG) monitoring is used for detection of convulsive and nonconvulsive seizures and assessing the degree of encephalopathy in critically ill patients. A commonly seen encephalopathic pattern on CEEG is generalized periodic discharges with triphasic wave (TW) morphology. The underlying role and prognostic significance of TW in relationship to intracranial pressure (ICP) remain unknown. We present a case highlighting the relationship of TW with ICP in a case with severe traumatic brain injury (TBI).

Method

Case report.

Results

A patient with severe TBI and no underlying metabolic abnormalities was admitted to the neurocritical care unit. TW were seen on CEEG. The TW diminished during episodes of intracranial hypertension but reappeared with reduction of the intracranial pressure.

Conclusion

This study highlights a possible favorable prognostic marker of finding TW in a patient with intracranial hypertension. We have proposed a preliminary understanding of the relationship between TW and intracranial hypertension, which may be helpful in formulating future studies involving larger cohorts.

Intraoperative Neurophysiological Monitoring for Endoscopic Endonasal Approaches to the Skull Base: A Technical Guide

Intraoperative neurophysiological monitoring during endoscopic, endonasal approaches to the skull base is both feasible and safe. Numerous reports have recently emerged from the literature evaluating the efficacy of different neuromonitoring tests during endonasal procedures, making them relatively well-studied. The authors report on a comprehensive, multimodality approach to monitoring the functional integrity of at risk nervous system structures, including the cerebral cortex, brainstem, cranial nerves, corticospinal tract, corticobulbar tract, and the thalamocortical somatosensory system during endonasal surgery of the skull base. The modalities employed include electroencephalography, somatosensory evoked potentials, free-running and electrically triggered electromyography, transcranial electric motor evoked potentials, and auditory evoked potentials. Methodological considerations as well as benefits and limitations are discussed. The authors argue that, while individual modalities have their limitations, multimodality neuromonitoring provides a real-time, comprehensive assessment of nervous system function and allows for safer, more aggressive management of skull base tumors via the endonasal route.

Electroencephalogram monitoring during intracranial surgery for moyamoya disease

We describe our experience with intraoperative electroencephalography in moyamoya surgery, a method to monitor for ischemic changes during the procedure and to minimize the risk of intraoperative and perioperative stroke. Case records and intraoperative electroencephalography recordings of all patients (n=220) treated with surgical revascularization for moyamoya (pial synangiosis) performed for 14 years (1994-2008) were reviewed. Electroencephalographic slowing occurred in 100 cases (45.5%), and was persistent in nine cases (9%). Slowing coincided with specific operative manipulations, most commonly while suturing the donor vessel to the pia, and during closure of the craniotomy. Slowing generally occurred bilaterally, independently of the side of intervention. The presence, length, and severity of slowing were not predictive of perioperative ischemic events. We present additional data on intraoperative electroencephalography with a modified montage to accommodate the craniotomy. Although not predictive of perioperative ischemic events in this series, electroencephalographic changes were correlated with specific operative interventions, and revealed global responses to unilateral manipulation. These findings suggest that prospective analyses of this technique may elucidate additional methods of predicting (and possibly preventing) perioperative ischemic events.

Bispectral index changes in carotid surgery

BACKGROUND

Intraoperative monitoring of cerebral ischemia with shunting during carotid endarterectomy (CEA) remains controversial. Our objective was to evaluate the sensitivity and specificity of BIS changes during carotid clamping in relation to shunted patients in awake CEA.

METHODS

Eighty CEAs under cervical block were included. There were two patient groups: with clinical signs of cerebral ischemia (shunted patients) and without signs of cerebral ischemia (nonshunted patients). Data were based on bispectral index (BIS) values and neurological monitoring at different surgery time points, with special attention paid during carotid clamping. BIS values were compared between shunted and nonshunted patients. Sensitivity and specificity, along with positive and negative predictive values of a percentage BIS value decrease during carotid clamping from baseline BIS values, were calculated in both patient groups.

RESULTS

Shunting was performed in 11 patients with cerebral ischemia at carotid clamping. Mean BIS values were 82.82+/-11.98 in shunted patients and 92.31+/-5.42 in nonshunted patients at carotid clamping (p<0.001). Relative decreased BIS values in relation to basal BIS values were 13.57% in shunted patients and 3.68% in nonshunted patients (p<0.05). The percentage decrease in BIS was 14%, sensitivity was 81.8% (95% CI 49.9-96.8), and specificity was 89.7% (95% CI 79.3-95.4).

CONCLUSION

BIS monitoring during carotid clamping is an easy, noninvasive method which correlates with cerebral ischemia in patients undergoing CEA. A decrease>or=14% from the basal BIS value presents a high negative predictive value, and ischemia is unlikely without a decrease. Nonetheless, a decrease may not always indicate cerebral ischemia with a low positive predictive value.

DY-9760e, a Calmodulin Antagonist, Reduces Brain Damage after Permanent Focal Cerebral Ischemia in Cats

DY-9760e (3-[2-[4-(3-chloro-2-methylphenyl)-1-piperazinyl]ethyl]-5,6-dimethoxy-1-(4-imidazolylmethyl)-1H-indazole dihydrochloride 3.5 hydrate), a calmodulin antagonist, provides protection against Ca(2+) overload-associated cytotoxicity and brain injury after cerebral ischemia in rats. In this study, we assessed the effect of DY-9760e on ischemic infarct volume in cats subjected to permanent focal cerebral ischemia. DY-9760e was infused for 6 h, beginning 5 min after occlusion of the middle cerebral artery. The infarct volume was measured at the end of drug infusion. DY-9760e, at the dose of 0.25 but not 0.1 mg/kg/h, significantly reduced cerebral infarct volume without affecting any physiological parameters, and its protective effect was mainly evident in the cerebral cortex, where the penumbra, a salvageable zone, exists. The present study demonstrates that DY-9760e protects against brain injury after focal ischemia in a gyrencephalic animal as well as in the rodents reported previously and suggests its therapeutic value for the treatment of acute stroke.

Electroencephalography (EEG) and somatosensory evoked potentials (SEP) to prevent cerebral ischaemia in the operating room

We review the principal aspects of EEG and SEP to detect and prevent cerebral ischaemia in the operating room during interventions at risk. EEG and SEP are variables that indirectly reflect cerebral blood flow (CBF) provided that anaesthetic regimen, body temperature, and arterial blood pressure of the patient are stable. When CBF decreases and reaches the functional threshold, slowing and/or attenuation of EEG occurs while the amplitude and the latency of cortical SEP are, respectively decreased and lengthened. Based on these changes, numerous criteria corresponding to critical thresholds have been defined. A decrease in EEG amplitude greater than 30% or EEG changes lasting more than 30 s have been considered as significant by clinicians. The main criteria resulting from computerized EEG analysis were a reduction in total power and/or in spectral edge frequency. Regarding SEP, a more than 50% decrease in N20 amplitude and/or a more than 1 ms increase in central conduction time were the most frequently used criteria. According to the bulk of literature, it may be concluded that processed EEG analysis is more sensitive than visual EEG analysis to detect cerebral ischaemia, and that SEP are not less sensitive than conventional EEG. Moreover, literature shows that SEP are as specific as computerized EEG analysis to disclose ischaemia during carotid endarterectomy.

Neuroprotection assessment by topographic electroencephalographic analysis: effects of a sodium channel blocker to reduce polymorphic delta activity following ischaemic brain injury in rats

The spatiotemporal electroencephalogram (EEG) pathology associated with brain injury was studied using high-resolution, 10-electrode cortical EEG mapping in a rat model of middle cerebral artery occlusion (MCAo). Using this model we evaluated the ability of the novel sodium channel blocker and neuroprotective agent RS100642 to resolve injury-induced EEG abnormalities as a measure of neurophysiological recovery from brain injury. The middle cerebral artery (MCA) was occluded for 1 h during which a dramatic loss of EEG power was measured over the injured cortex with near complete recovery upon reperfusion of blood to the MCA region in all rats. The resultant progression of the MCAo/reperfusion injury (6-72 h) included the appearance of diffuse polymorphic delta activity (PDA), as visually indicated by the presence of high-amplitude slow-waves recorded from both brain hemispheres. PDA was associated with large increases in EEG power, particularly evident in outer 'peri-infarct' regions of the ipsilateral parietal cortex as visualized using topographic EEG mapping. Post-injury treatment with RS100642 (1.0 mg/kg, i.v.) significantly reduced the PDA activity and attenuated the increase in EEG power throughout the course of the injury. These effects were associated with a reduction in brain infarct volume and improved neurological function. These methods of EEG analysis may be helpful tools to evaluate the physiological recovery of the brain from injury in humans following treatment with an experimental neuroprotective compound.

Carotid endarterectomy with routine electroencephalography and selective shunting: Influence of contralateral internal carotid artery occlusion and utility in prevention of perioperative strokes

OBJECTIVE

Carotid endarterectomy (CEA) is associated with a risk of cerebral ischemia during carotid clamping, particularly in the face of contralateral internal carotid artery (ICA) occlusion. We examined the results of CEA with continuous electroencephalography in patients without and with contralateral ICA occlusion.

DESIGN AND SETTING

We reviewed 564 primary CEAs with routine electroencephalography and general anesthesia performed between April 1, 1989, and March 31, 1999, in a community teaching medical center. Main outcome measures were perioperative stroke, temporary lateralizing neurologic deficit, and death. Shunts were placed primarily for significant electroencephalographic changes after carotid clamping but also selectively for contralateral ICA occlusion, prior stroke, or surgeon choice. CEA was performed for asymptomatic disease in 35% of cases.

RESULTS

Significant electroencephalographic changes occurred in 16% versus 39% (P <.001) and shunts were placed in 13% versus 55% (P <.001) of patients with patent (n = 507) versus occluded contralateral ICA (n = 57), respectively. The fraction of CEAs with significant electroencephalographic changes during clamping was stable, but shunt use declined slightly over time as our confidence in electroencephalography increased. Patches were placed more often (86% versus 65%; P =.002), but other operative details were similar when the contralateral ICA was occluded. Five early (30 days) strokes (0.9%) and eight early temporary postoperative neurologic events (1.4%) occurred, all ipsilateral to CEA and all after the patient left the operating room with none in patients with contralateral ICA occlusion. Two perioperative deaths occurred, one in a patient without and one in a patient with contralateral ICA occlusion. Neither of these deaths was related to ipsilateral stroke. No increase in stroke rate with decreased shunt use over time was seen.

CONCLUSION

Routine use of electroencephalography was associated with apparent complete elimination of intraoperative strokes and less than 1% risk of perioperative strokes. These observations appear to be true even in the face of contralateral ICA occlusion. Electroencephalography is a sensitive detector of cerebral ischemia and a valuable tool for determination of need for shunting during CEA. Surgeons should consider routine use of electroencephalography and selective shunting for significant electroencephalographic changes with clamping.

Persistent posttraumatic cerebrospinal fluid leakage

OBJECT

Persistent posttraumatic cerebrospinal fluid (CSF) leakage frequently complicates skull base fractures. Although many CSF leaks will cease without treatment, patients with CSF leaks that persist greater than 24 hours may be at increased risk for meningitis, and many will require surgical intervention. The authors reviewed their 15-year experience with posttraumatic CSF leaks that persisted longer than 24 hours.

METHODS

The authors reviewed the medical records of 51 patients treated between 1984 and 1998 with CSF leaks that persisted for 24 hours or longer after traumatic head injury. In 27 patients (55%) spontaneous resolution of CSF leakage occurred at an average of 5 days posttrauma. In 23 patients (45%) surgery was required to resolve the leakage. Eight patients (16%) with occult CSF leaks presented with recurrent meningitis at an average of 6.5 years posttrauma. Forty-three (84%) patients with CSF leaks sustained a skull fracture, most commonly involving the frontal sinus, whereas parenchymal brain injury or extraaxial hematoma was demonstrated in only 18 patients (35%). Delayed CSF leaks, with an average onset of 13 days posttrauma, were observed in eight patients (16%). Among patients with clinically evident CSF leakage, the frequency of meningitis was 10% with antibiotic prophylaxis, and 21% without antibiotic prophylaxis. Thus, prophylactic antibiotic administration halved the risk of meningitis. A variety of surgical approaches was used, and no significant neurological morbidity occurred. Three (13%) of 23 surgically treated patients required additional surgery to treat continued CSF leakage.

CONCLUSIONS

A significant proportion of patients with CSF leaks that persist greater than 24 hours will require surgical intervention. Prophylactic antibiotic therapy may be effective in this group of patients. Patients with skull base or frontal sinus fractures should be followed to detect the occurrence of delayed leakage. Surgery-related outcome is excellent.

Comparison of simultaneous electroencephalographic and mental status monitoring during carotid endarterectomy with regional anesthesia

PURPOSE

This study examines the accuracy of intraoperative electroencephalographic (EEG) monitoring for the detection of cerebral ischemia by comparing EEG with simultaneous mental status evaluation (MSE) during carotid endarterectomy in awake patients.

METHODS

Between 1994 and 1997, 208 consecutive carotid endarterectomies were prospectively evaluated for cerebral function during surgery with simultaneous MSE and EEG monitoring. Regional anesthesia (RA), which consisted of superficial cervical block, was chosen preferentially in 75% of the cases, with general anesthesia (GA) reserved for the patients who did not fulfill the criteria for RA. When available, 8-channel EEG monitoring was performed (59% with RA and 55% with GA).

RESULTS

The EEG was a reliable predictor in comparison with MSE in most but not all cases of cerebral ischemia. Significant neurologic changes were noted using MSE in 4 of 89 patients (4.5%) that were not detected using EEG (false negative results). Conversely, 6 of 89 cases (6.7%) showed unilateral slowing without associated changes in MSE (false positive results). For the awake patients, 21 of 150 cases (14%) showed MSE changes that required a shunt. By contrast, 9 of 32 GA cases (28%) showed EEG changes that would have led to shunting (P = NS). In the RA group, there were no strokes versus 3 of 58 cases (5.2%) with strokes in the GA group. Two of 150 cases (0.1%) had transient ischemic attacks in the RA group. There was 1 myocardial infarction in the GA group; no deaths occurred in this series.

CONCLUSION

EEG monitoring yielded a significant number of false positive (6.7%) and false negative (4.5%) results in the detection of neurologic deficits when compared with MSE in the awake patients. In this series, the preferential use of RA resulted in less shunt use and was possibly associated with a lower stroke rate.