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Neuromonitoring by scalp EEG and Corticography...
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Neuromonitoring by scalp EEG and Corticography recording during Intracranial Vascular Surgery: a Feasibility Study in 20 Patients L. Regli, A.Dehdashti, JG. Villemure,E. Pralong, M. Maeder, D. Debatisse NCH -UNN Neurosurgery CHUV, Lausanne, Switzerland, June 2005 Purpose: Temporary vascular occlusions are frequent during vascular surgery. Real-time detection of cerebral ischemia during surgical repair of intracranial aneurysms can be helpful to the surgeon, especially in determining the duration of temporary vascular occlusion that can be tolerated and the optimal systemic arterial pressure. The most common techniques used clinically for this purpose in anterior circulation aneurysms are somatosensory evoked potentials (SSEPs) ,scalp EEG [and direct cortical EEG recordings. The value of SSEPs has been investigated in a large number of patients and responses were found to change in roughly 20% of surgical procedures, although there is a significant incidence of false negative results [5,6]. Changes in the scalp EEG are less well studied with estimates that 5 to 40% of patients show significant changes. There is insufficient data to form conclusions on the overall sensitivity of cortical strip EEG recordings.The purpose of neurophysiological monitoring is to detect a neuronal threshold of tolerance to ischemia. This preliminary study tested the feasibility of peroperative Corticography (cEEG) and surface EEG during intracranial vascular surgery. Introduction: By definition and classically, neuromonitoring includes all the techniques that allow immediate detection of events liable to cause brain, spinal cord or peripheral-nerve damage, of their current repercussions on nervous function, and of their metabolic correlates. It is mainly used in the operating room (OR) and intensive care unit (ICU). Its primary goals are: (1) the detection of brain dysfunction at a reversible stage in order to prevent irreversible lesions, (2) the indirect evaluation, through brain function, of the importance of some metabolic disturbances or of the level of anaesthesia, and (3) a better knowledge of neurological events occurring intra-operatively, in order to improve subsequent procedures. The EEG was almost immediately considered as a unique tool to evaluate consciousness fluctuations in comatose patients, so that the history of neuromonitoring in the ICU actually dates back the EEG discovery in the late 20ies. ; however; the EEG could hardly be systematically implemented before the advent of computerized signal processing and digital EEG. Evoked potentials (EPs) were progressively introduced, both in the ICU and the OR, at the end of the 70ies. Since then, the number of papers on ICU and OR monitoring almost doubled every 5 years until the beginning of the 1990ies. In the United States, it is currently evident that neuromonitoring should be accessible in any OR or ICU, to the point that some private companies are now created – with support of private insurance companies – to help these hospitals that are not big enough to develop their own neuromonitoring infrastructure. Material and methods Peroperative monitoring with scalp EEG and corticography (cEEG) was performed in 11 patients undergoing craniotomies for intracranial aneuvrysms ,1 patient with ST- MC Bypass and AVM (2 patient). All patients had a preoperative baseline surface recording. At surgery scalp electrodes were positioned in F7-F8 and CP3-CP4, allowing monitoring of anesthesia and intraoperative baseline EEG. Three subdural monopolar electrodes were positioned frontal, temporal, and parietal. Online monitoring was performed with 7 leads: 4 scalp EEG (2 ipsi, 2 contralateral), and 3 ipsilateral Cortico-EEG. Results: In all patients excellent corticographic recordings were obtained. During temporary clipping (5 to 40 minutes) of the middle or anterior cerebral artery, 5 patients presented focal modifications of the corticographic-EEG pattern (slow waves theta & delta or spike and waves pattern), that were not detected on surface EEG. All patients had induced hypertension during temporary clipping. Corticographic changes resolved in all after clip removal. One patient with temporary clipping of the intracranial carotid artery had diffuse slowing seen on corticography, that was moderate on the ipsilateral surface EEG. These changes resolved after clip removal (5minutes). In 3 of 4 patients, very early appearance of “ high frequency waves” ( Beta 3) was observed on corticography just a few seconds after vascular occlusion. These high frequencies preceded the slow wave ( delta) pattern suggesting neuronal ischemia. No patient presented signs or symptoms of cerebral ischemia after surgery. Discussion: The interpretation of intraoperative neurophysiologic results during aneurysm surgery is complex. Two elements involved in interpreting this data were explored in this preliminary study performed on a small patient population. The first was the reliability of the decision of whether a significant change in a monitored modality occurred during vascular occlusion. This study has demonstrated that the reliability varies greatly depending on the recording technique, with good inter-observer reliability for corticography by location in different lobe (temporal, parietal and frontal lobes) but poor reliability for scalp EEG. Secondly, the fraction of modifications in each modality associated with vascular occlusions was determined. We observed that cortical EEG changed more frequently than scalp EEG.The finding that cortical EEG changes more frequently than other modalities with vascular occlusion suggests that cortical EEG would be more sensitive detector of intraoperative ischemia than the other modalities. Indeed these first results indicate that changes will be detected more frequently when corticography by topographical lobe location is employed as part of intraoperative neurophysiologic monitoring during aneurysm and intracranial vascular malformation surgery. It should be noted that this does not guarantee additional sensitivity in the detection of clinically significant ischemia. Corticography is easy to perform and has relatively high reliability of interpretation. We observed different specific corticography EEG pattern during clamping (beta activity before slow waves). Future studies may provide additional information on the true clinical value of this technique in the interpretation and comprehension of vasospasm and level of ischemia during intracranial vascular surgery. Iconography: Typical EEG and Corticography responses: ST-MC bypass Example: intracranial vascular anomalies: Reference list: 1. Emerson RG, Turner CA. Monitoring during supratentorial surgery. J Clin Neurophys 1993;10:404–11. 2. Friedman WA, Chadwick GM, Verhoeven FJS, Mahla M, Day AL. Monitoring of somatosensory evoked potentials during surgery for middle cerebral artery aneurysms. Neurosurgery 1991;29:83–8. 3. Friedman WA, Kaplan BL, Day AL, Sypert GW, Curran MT. Evoked potential monitoring during aneurysm operation: observations after fifty cases. Neurosurgery 1987;20:678–87. 4. Jones T, Chiappa K, Young RR, Ojemann RG, Crowell RM. EEG monitoring for induced hypotension for surgery of intracranial aneurysms. Stroke 1979;292–4. 5. Krieger D, Adams HP, Albert DIMF, Haken MV, Hacke W. Pure motor hemiparesis with stable somatosensory evoked potential monitoring during aneurysm surgery: case Report. Neurosurgery 1992;31:145–50. 6. Little JR, Lesser RP, Luders H. Electrophysiological monitoring during basilar aneurysm operation. Neurosurgery 1987;421–6. 7. Lopez JR, Chang SD, Steinberg GK. The use of electrophysiological monitoring in the intra-operative management of i. c. aneurysms. J Neurol Neurosurg Psych 1999;66:189–96. 8. Mizoi K, Yoshimoto T. Permissible temporary occlusion time in aneurysm surgery as evaluated by evoked potential monitoring. Neurosurgery 1993;33: 434–40. 9. Mooij JJA, Buchthal A, Belopavlovic M. Somatosensory evoked potential monitoring of temporary middle cerebral artery occlusion during aneurysm operation. Neurosurgery 1987;21:492–6. 10. Shinar D, Gross CR, Hier DB, et al. Interobserver reliability in the interpretation of computed tomographic scans of stroke patients. Arch Neurol. 1987;44(2): 149–55. The concept of multimodality monitoring: Multimodality monitoring consists of a tripod: (1) identifying events liable to cause brain damage (“upstream monitoring”), (2) early confirming that these events actually interfere with central or peripheral nervous system function (neurophysiological monitoring), and (3) measuring the metabolic consequences of nervous dysfunction (“downstream monitoring”). Noteworthy, the outcomes of these 3 approaches are not obligatorily correlated with each other and it is even from their convergences or discrepancies that additional useful information can be extracted for optimal patient management. Electrodes positioning: AVM Intracranial Aneurysms Corticography Surface EEG E E G C O R T I C O Delta Waves High Frequencies Burst and alternant EEG pattern Asymetrical burst activity using propofol Surface EEG Surface EEG Surface EEG Corticography Corticography Corticography
Transcript of Neuromonitoring by scalp EEG and Corticography...
Neuromonitoring by scalp EEG and Corticography recording during Intracranial Vascular Surgery: a Feasibility Study in 20 Patients
L. Regli, A.Dehdashti, JG. Villemure,E. Pralong, M. Maeder, D. Debatisse NCH -UNN Neurosurgery CHUV, Lausanne, Switzerland, June 2005
Purpose:Temporary vascular occlusions are frequent during vascular surgery. Real-time detection of cerebral ischemia during surgical repair of intracranial aneurysms can be helpful to the surgeon, especially in determining the duration of temporary vascular occlusion that can be tolerated and the optimal systemic arterial pressure. The most common techniques used clinically for this purpose in anterior circulation aneurysms are somatosensory evoked potentials (SSEPs) ,scalp EEG [and direct cortical EEG recordings. The value of SSEPs has been investigated in a large number of patients and responses were found to change in roughly 20% of surgical procedures, although there is a significant incidence of false negative results [5,6]. Changes in the scalp EEG are less well studied with estimates that 5 to 40% of patients show significant changes. There is insufficient data to form conclusions on the overall sensitivity of cortical strip EEG recordings.The purpose of neurophysiological monitoring is to detect a neuronal threshold of tolerance to ischemia. This preliminary study tested the feasibility of peroperative Corticography (cEEG) and surface EEG during intracranial vascular surgery.
Introduction:By definition and classically, neuromonitoring includes all the techniques that allow immediate detection of events liable to cause brain, spinal cord or peripheral-nerve damage, of their current repercussions on nervous function, and of their metabolic correlates. It is mainly used in the operating room (OR) and intensive care unit (ICU). Its primary goals are: (1) the detection of brain dysfunction at a reversible stage in order to prevent irreversible lesions, (2) the indirect evaluation, through brain function, of the importance of some metabolic disturbances or of the level of anaesthesia, and (3) a better knowledge of neurological events occurring intra-operatively, in order to improve subsequent procedures. The EEG was almost immediately considered as a unique tool to evaluate consciousness fluctuations in comatose patients, so that the history of neuromonitoring in the ICU actually dates back the EEG discovery in the late 20ies. ; however; the EEG could hardly be systematically implemented before the advent of computerized signal processing and digital EEG. Evoked potentials (EPs) were progressively introduced, both in the ICU and the OR, at the end of the 70ies. Since then, the number of papers on ICU and OR monitoring almost doubled every 5 years until the beginning of the 1990ies. In the United States, it is currently evident that neuromonitoring should be accessible in any OR or ICU, to the point that some private companies are now created – with support of private insurance companies – to help these hospitals that are not big enough to develop their own neuromonitoring infrastructure.
Material and methodsPeroperative monitoring with scalp EEG and corticography (cEEG) was performed in 11 patients undergoing craniotomies for intracranial aneuvrysms ,1 patient with ST-MC Bypass and AVM (2 patient). All patients had a preoperative baseline surface recording. At surgery scalp electrodes were positioned in F7-F8 and CP3-CP4, allowing monitoring of anesthesia and intraoperative baseline EEG. Three subdural monopolar electrodes were positioned frontal, temporal, and parietal. Online monitoring was performed with 7 leads: 4 scalp EEG (2 ipsi, 2 contralateral), and 3 ipsilateral Cortico-EEG.
Results:In all patients excellent corticographic recordings were obtained. During temporary clipping (5 to 40 minutes) of the middle or anterior cerebral artery, 5 patients presented focal modifications of the corticographic-EEG pattern (slow waves theta & delta or spike and waves pattern), that were not detected on surface EEG. All patients had induced hypertension during temporary clipping. Corticographic changes resolved in all after clip removal. One patient with temporary clipping of the intracranial carotid artery had diffuse slowing seen on corticography, that was moderate on the ipsilateral surface EEG. These changes resolved after clip removal (5minutes). In 3 of 4 patients, very early appearance of “ high frequency waves” ( Beta 3) was observed on corticography just a few seconds after vascular occlusion. These high frequencies preceded the slow wave ( delta) pattern suggesting neuronal ischemia. No patient presented signs or symptoms of cerebral ischemia after surgery.
Discussion:The interpretation of intraoperative neurophysiologic results during aneurysm surgery is complex. Two elements involved in interpreting this data were explored in this preliminary study performed on a small patient population. The first was the reliability of the decision of whether a significant change in a monitored modality occurred during vascular occlusion. This study has demonstrated that the reliability varies greatly depending on the recording technique, with good inter-observer reliability for corticography by location in different lobe (temporal, parietal and frontal lobes) but poor reliability for scalp EEG. Secondly, the fraction of modifications in each modality associated with vascular occlusions was determined. We observed that cortical EEG changed more frequently than scalp EEG.The finding that cortical EEG changes more frequently than other modalities with vascular occlusion suggests that cortical EEG would be more sensitive detector of intraoperative ischemia than the other modalities.
Indeed these first results indicate that changes will be detected more frequently when corticography by topographical lobe location is employed as part of intraoperative neurophysiologic monitoring during aneurysm and intracranial vascular malformation surgery. It should be noted that this does not guarantee additional sensitivity in the detection of clinically significant ischemia. Corticography is easy to perform and has relatively high reliability of interpretation. We observed different specific corticography EEG pattern during clamping (beta activity before slow waves). Future studies may provide additional information on the true clinical value of this technique in the interpretation and comprehension of vasospasm and level of ischemia during intracranial vascular surgery.
Iconography:
Typical EEG and Corticography responses:
ST-MC bypass
Example: intracranial vascular anomalies:
Reference list:1. Emerson RG, Turner CA. Monitoring during supratentorial surgery. J Clin Neurophys 1993;10:404–11.2. Friedman WA, Chadwick GM, Verhoeven FJS, Mahla M, Day AL. Monitoring of somatosensory evoked potentials during surgery for middle cerebral artery aneurysms. Neurosurgery 1991;29:83–8.3. Friedman WA, Kaplan BL, Day AL, Sypert GW, Curran MT. Evoked potential monitoring during aneurysm operation: observations after fifty cases. Neurosurgery 1987;20:678–87.4. Jones T, Chiappa K, Young RR, Ojemann RG, Crowell RM. EEG monitoring for induced hypotension for surgery of intracranial aneurysms. Stroke 1979;292–4.5. Krieger D, Adams HP, Albert DIMF, Haken MV, Hacke W. Pure motor hemiparesis with stable somatosensory evoked potential monitoring during aneurysm surgery: case Report. Neurosurgery 1992;31:145–50.6. Little JR, Lesser RP, Luders H. Electrophysiological monitoring during basilar aneurysm operation. Neurosurgery 1987;421–6.7. Lopez JR, Chang SD, Steinberg GK. The use of electrophysiological monitoring in the intra-operative management of i. c. aneurysms. J Neurol Neurosurg Psych 1999;66:189–96.8. Mizoi K, Yoshimoto T. Permissible temporary occlusion time in aneurysm surgery as evaluated by evoked potential monitoring. Neurosurgery 1993;33: 434–40.9. Mooij JJA, Buchthal A, Belopavlovic M. Somatosensory evoked potential monitoring of temporary middle cerebral artery occlusion during aneurysm operation. Neurosurgery 1987;21:492–6.10. Shinar D, Gross CR, Hier DB, et al. Interobserver reliability in the interpretation of computed tomographic scans of stroke patients. Arch Neurol. 1987;44(2): 149–55.
The concept of multimodality monitoring: Multimodality monitoring consists of a tripod: (1) identifying events liable to cause brain damage (“upstream monitoring”), (2) early confirming that these events actually interfere with central or peripheral nervous system function (neurophysiological monitoring), and (3) measuring the metabolic consequences of nervous dysfunction (“downstream monitoring”). Noteworthy, the outcomes of these 3 approaches are not obligatorily correlated with each other and it is even from their convergences or discrepancies that additional useful information can be extracted for optimal patient management.
Electrodes positioning:
AVM
Intracranial Aneurysms
Corticography
Surface EEG
EEG
CORTICO
Delta Waves
High Frequencies
Burst and alternant EEG pattern
Asymetrical burst activity using propofol
Surface EEG
Surface EEG
Surface EEG
Corticography
Corticography
Corticography
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