Monitoring Of Evoked Potentials Research Articles

The expression of c-fos and transmitter calcitonin gene-related peptide in the chronic compressive injury of the nerve root

To investigate the significance of c-fos oncogene morphogenetic protein's locational expression, and the correlativity between nerve transmitters calcitonin gene-related peptide (CGRP) expression and nerve root's functional change using the animal model of the chronic compressive injury in the nerve root. The animal model of chronic compressive injury of the nerve root was established by transplanting autogenous cancellous bone into the intervertebral foramen. During different injury phase (1, 2, 4, 8, 12, 24 weeks after operation), the functional status of the nerve root was determined under the monitoring of evoked potential, and the expression changes of c-fos oncogene morphogenetic protein and nerve transmitter CGRP were detected using in situ hybridization technique and their expression intensity was determined using automatic image analytic instrument respectively. One week after operation, the c-fos expression strengthened in both anterior and posterior root fiber obviously. Two to four weeks after operation, the expression of the posterior root fiber weakened than the anterior root fiber. After 12 weeks, the anterior root fiber expression turned down obviously, however the posterior root fiber expression backed up slightly compared with that of the 8 weeks. By the time of 24 weeks after operation, the expression enhancement in all roots disappeared. CGRP expression increased obviously at the site of compressive axon of both anterior and posterior root. The expression of the posterior root axon and ganglion cell was higher than that of the anterior root axon. CGRP expression was diminished in the second week than the first week, and that was especially obvious in the posterior root and ganglion cell. But 4 weeks after operation, the expression enhanced once more, and that was more obvious inside the anterior root axon. Eight weeks after operation, the expression intensity attained the high peak. Twelve weeks after operation, the expression started the slow-moving descent. The expression of c-fos gene protein is beneficial to localize the damaged part of certain nerve. During chronic injury, the degeneration of posterior root sensory fiber is earlier than the anterior root motor fiber. The expression of CGRP strengthened when the nerve fiber degenerated by the harmful stimulation, and the expression intensity is positively related with pain. That suggests when the nervous tissue is hurt, the information of warning and regulation should be sent out to our body.

Role of Intraoperative Electromyography (EMG) in Addition to Somatosensory Evoked Potential (SSEP) Monitoring during Cervical Spine Surgery: Our Preliminary Results

s: 32nd Annual Meeting of the Society of Neurosurgical Anesthesia and Critical Care, Las Vegas, Nevada, October 22, 2004: MONITORING/SPINAL CORD

Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery.

The aims of this study were to compare the efficiency of motor evoked potentials (MEPs), somatosensory evoked potentials (SSEPs), and microvascular Doppler ultrasonography (MDU) in the detection of impending motor impairment from subcortical ischemia in aneurysm surgery; to determine their sensitivity for specific intraoperative events; and to compare their impact on the surgical strategy used. Motor evoked potentials, SSEPs, and MDU were monitored during 100 operations for 129 aneurysms in 95 patients. Intraoperative events, monitoring results, and clinical outcome were correlated in a prospective observational design. Motor evoked potentials indicated inadequate temporary clipping, inadvertent occlusion, inadequate retraction, vasospasm, or compromise to perforating vessels in 21 of 33 instances and deteriorated despite stable SSEPs in 18 cases. Microvascular Doppler ultrasonography revealed inadvertent vessel occlusion in eight of 10 cases and insufficient clipping in four of four cases. Stable evoked potentials (EPs) allowed safe, permanent vessel occlusion or narrowing despite reduced flow on MDU in five cases. Two patients sustained permanent and 10 showed transient new weakness, which had been detected by SSEPs in two of 12 patients and MEPs in 10 of 11 monitored cases. The surgical strategy was directly altered in 33 instances: by MEPs in 16, SSEPs in four, and MDU in 13. Monitoring of MEPs is superior to SSEP monitoring and MDU in detecting motor impairment, particularly that from subcortical ischemia. Microvascular Doppler ultrasonography is superior to EP monitoring in detecting inadvertent vessel occlusion, but cannot assess remote collateral flow. Motor evoked potentials are most sensitive to all other intraoperative conditions and have a direct influence on the course of surgery in the majority of events. A controlled study design is required to confirm the positive effect of monitoring on clinical outcome in aneurysm surgery.

FEATURE EXTRACTION FROM MLAER SIGNALS AND VALIDATION DURING PROPOFOL ANAESTHRSIA

The depth of anaesthesia (DOA) is generally considered adequate if the patient neither moves in response to surgical stimulus nor shows any signs of autonomic reflexes. So the measuring of depth of anaesthesia is very important because it helps the anesthetist to monitor the anesthetic state of the patient from the start of giving the anaesthetic drugs up to the patient awakeness and helps him to control the required amounts of the anaesthetic drugs during the surgery. There is no direct method to judge the DOA. It seems logical that, since the brain is the primary site of action of anaesthetic agents, there should be some measure of anaesthetic effects on the brain. The brain electrical activity (Electroencephalogram (EEG) and evoked potentials (EP)) have been studied to develop quantitative monitors of DOA. Due to the large problems with the EEG monitoring, EP monitoring has been suggested as an alternative indicator of anaesthetic depth. The mid latency auditory evoked response (MLAER) was seemed to be the most promising measure of DOA, which is independent of the agent being used. The aim of this paper is to propose an approach to explore a reliable index reflecting the changes in amplitudes and latencies of MLAER waves, which are related to depth of anaesthesia

Effect of Sevoflurane/Nitrous Oxide Versus Propofol Anaesthesia on Somatosensory Evoked Potential Monitoring of the Spinal Cord During Surgery to Correct Scoliosis

Effect of Sevoflurane/Nitrous Oxide Versus Propofol Anaesthesia on Somatosensory Evoked Potential Monitoring of the Spinal Cord During Surgery to Correct Scoliosis

Mechanisms of signal change during intraoperative somatosensory evoked potential monitoring of the spinal cord.

In scoliosis surgery, intraoperative somatosensory evoked potential (SSEP) monitoring has reduced the incidence of postoperative neurologic deficits. Many factors affect the amplitude and latency of SSEP waveforms during surgery. Somatosensory evoked potential amplitude decreases with ischemia and anoxia because of temporal dispersion of the afferent volley and conduction block in damaged axons. In conjunction with surgical manipulations, minor drops in blood pressure may result in substantial SSEP changes that reverse when perfusion pressure is increased. Irreversible anoxic injury to central nervous system white matter with loss of SSEP waveforms is dependent on calcium influx into the intracellular space. Somatosensory evoked potential monitoring may be less sensitive for detecting acute insults in the presence of preexisting white matter lesions. Increased extracellular potassium from acute baro-trauma can block axonal conduction transiently even when there is no axonal disruption. Marked temperature-related drops in SSEP amplitude may occur after exposure of the spine but before instrumentation and deformity correction. Hypothermia may increase false-negative outcomes. Short-interval double-pulse stimulation may improve the sensitivity of the SSEP in detecting early ischemic changes. For neurosurgical procedures on the spinal cord the use of SSEP monitoring in improving postoperative outcome is less well established.

Room E, 10/16/2000 9: 00 AM - 11: 00 AM (PS) The Efficacy of Electroencephalography and Somatosensory Evoked Potential Monitoring in Detecting Cerebral Ischemia during Carotid Endarterectomy under Regional Anesthesia

<b>Room E, 10/16/2000 9: 00 AM - 11: 00 AM (PS) The Efficacy of Electroencephalography and Somatosensory Evoked Potential Monitoring in Detecting Cerebral Ischemia during Carotid Endarterectomy under Regional Anesthesia</b>

Kathleen Mears Lecture: Intraoperative Evoked Potential Monitoring—A Historical Perspective

ABSTRACT.Published reports of intraoperative neurophysiologic monitoring first appeared in the 1970s describing the use of evoked potentials in orthopedic spinal surgery. The purpose of the monitoring, performed primarily at large academic institutions, was to provide feedback to surgeons of impending neurologic deficits caused by distraction and manipulation of the spinal column. Over the past two decades monitoring has included brainstem auditory and somatosensory EPs, EEG, EMG, and evoked motor responses to provide intraoperative data to surgical specialists, treating many conditions. The practice has spread to include small hospitals and private practice groups. Appropriate training and credentials required for technologists and interpreting physicians has been contentiously debated by professional societies. The purpose of this presentation is to provide a historical perspective of the many changes that have evolved this field.

Society of Neurosurgical Anesthesia and Critical Care. Orlando, Florida, October 16, 1998.

Society of Neurosurgical Anesthesia and Critical Care. Orlando, Florida, October 16, 1998.

The Efficacy of Electroencephalography and Somatosensory Evoked Potential Monitoring for Detecting Cerebral Ischemia during Carotid Endarterectomy under Regional Anesthesia

The Efficacy of Electroencephalography and Somatosensory Evoked Potential Monitoring for Detecting Cerebral Ischemia during Carotid Endarterectomy under Regional Anesthesia

226 Evoked potentials monitoring of lamotrigine and vigabatrin in epileptic children

226 Evoked potentials monitoring of lamotrigine and vigabatrin in epileptic children

Monitoring of median nerve somatosensory evoked potentials in carotid surgery.

The purpose of this study was to compare median somatosensory evoked potentials (SEP) in patients undergoing carotid endarterectomy (CEA) with routine shunting and nonshunting (excluding the option of selective shunting) and to evaluate the significance of a decrease in the amplitude of the cortically generated waveforms of the SEP and/or an increase in the central conduction time (CCT) on the one hand, and that of a loss of the cortical SEP, on the other. Somatosensory evoked potentials were recorded in 32 patients before, during, and after CEA with routine shunting or nonshunting. The N13 and N20 latency, the CCT, and the N20/P25 amplitude were evaluated. In addition, a meta-analysis of 15 previous studies was performed comprising a total of 3,136 patients. The intraoperative cortical SEP showed no differences between shunted and nonshunted patients, apart from the preclamping value of the N20/P25 amplitude which was lower in the nonshunted subjects. The number of patients with decreased and/or delayed cortical SEP (findings frequently used as criterion for selective shunting) was similar in the two study groups. A loss of the cortical SEP occurred in one patient operated on without an indwelling shunt. None of these patients had a new neurologic deficit after surgery. In the meta-analysis, the positive predictive value of decreased and/or delayed cortical SEP was extremely poor, that of absent cortical SEP was poor to moderate and the prevalence of new neurologic deficits was similar in patients undergoing CEA with routine shunting-nonshunting and those with selective shunting-nonshunting. Our study suggests that decreased and/or delayed cortical SEP are unreliable predictors of the neurological outcome of CEA patients and consequently an unsuitable criterion for selective shunting. The meta-analysis confirms this finding and shows that the neurologic outcome is not improved by using an indwelling shunt selectively based on SEP monitoring.

Incidence of sciatic nerve injury in operatively treated acetabular fractures without somatosensory evoked potential monitoring.

The authors investigated the incidence of sciatic nerve injury associated with the operative repair of acetabular fractures without somatosensory evoked potential (SSEP) monitoring. Retrospective case review of prospectively documented pre- and postoperative physical examinations. A level I trauma hospital. All the cases were reviewed of patients with open reduction and internal fixation of acetabular fractures who underwent posterior or extensile approaches (129) performed by the three senior authors from January 1991 through March 1995. Intraoperative SSEP monitoring was not used during any of the procedures. The procedures included sixty-five Kocher-Langenbeck approaches, thirty-four combined Kocher-Langenbeck and iliofemoral approaches, four extended iliofemoral approaches, and four triradiate approaches. One case of iatrogenic nerve injury resulted in a sensory deficit. No patient suffered an exacerbation of a preexisting nerve injury. The results of this study indicate that open reduction and internal fixation of acetabular fractures, using current techniques with visualization and protection of the sciatic nerve, can reduce the incidence of neurologic injury to a negligible level. There does not appear to be justification for the addition of SSEP or electromyograph modalities to the operative routine of experienced surgeons.

The Use of Somatosensory Evoked Potential Monitoring to Produce a Canine Model of Uniform, Moderately Severe Stroke with Permanent Arterial Occlusion

The Use of Somatosensory Evoked Potential Monitoring to Produce a Canine Model of Uniform, Moderately Severe Stroke with Permanent Arterial Occlusion

The Use of Somatosensory Evoked Potential Monitoring to Produce a Canine Model of Uniform, Moderately Severe Stroke with Permanent Arterial Occlusion

To develop a reliable canine model of cerebral infarction of moderate size, we compared infarctions caused by permanent occlusion of the following vessels in 42 dogs: 1) the middle cerebral artery (MCA), 2) the MCA and azygous anterior cerebral artery (ACA), 3) the MCA, azygous ACA, and posterior cerebral artery (PCA), and 4) sham-operated controls. The infarction volume was determined at 6 hours in half the animals and at 6 days in the others. Studies of somatosensory evoked potentials (SSEPs) and regional cerebral blood flow (rCBF) were performed before and after arterial occlusion, and good correlation was observed between the decrease in amplitude of the SSEPs and the decrease in rCBF observed after arterial occlusion. Only the groups in which the MCA and azygous ACA were occluded showed moderate infarctions of relatively consistent size. Analysis involving all groups revealed that the animals with SSEP amplitude preserved after vessel occlusion had only small infarctions; thus, preservation of SSEP amplitude after occlusion of the MCA and azygous ACA could in the future be used prospectively as a rejection criterion to improve the uniformity of infarction size. Conversely, animals with loss of SSEP amplitude after vessel occlusion had infarctions of moderate to large size; thus, loss of SSEP amplitude after MCA occlusion alone could in the future be used prospectively as a rejection criterion. When these rejection criteria were retrospectively applied to the groups in which both the MCA and azygous ACA were occluded, the resulting mean infarction volumes +/- 1 SEM) for the acute and chronic subgroups were 20.3 +/- 2.8% and 38.2 +/- 4.5% of the hemisphere, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effet des anesthésiques sur les potentiels évoqués sensoriels

The authors have reviewed the main effects of anaesthetic agents on sensory evoked potentials (EPs) in the auditory, somatosensory and visual modalities. Knowledge of EP changes induced by anesthetic drugs is important to avoid false alarms when monitoring neural structures at risk during surgery. Intraoperative EP monitoring is all the more efficient as the following points are taken into account: 1) whatever the sensory modality considered, EPs are more attenuated by volatile halogenated agents than by intravenous drugs; 2) the cortical components of EPs are more sensitive to anesthetic drugs than the brainstem components; 3) in each modality, the first component of the "primary cortical complex" is less attenuated by anaesthetic agents than the following cortical waves; 4) continuous administration of anaesthetic agents rather than acute administration (bolus) is preferred during EP monitoring. EPs also represent an objective means to assess the depth of surgical anaesthesia, since they may provide a reliable index of cortical depression. Amplitude changes of middle-latency auditory responses (Pa/Nb) seem to be a good marker for estimating depth of anaesthesia with the aid of EPs.

THERAPEUTIC EMBOLIZATION OF NEUROVASCULAR LESIONS

SUMMARY Interventional neuroradiologic procedures have become the preferred treatment for certain vascular disorders of the central nervous system as a result of the development of new catheters and embolic agents and improved imaging techniques. Whether these procedures are used preoperatively or as definitive treatment, the risk of embolization has decreased with increasing experience, and they compare favorably with the risk of surgery and other treatment modalities. Although devascularizing procedures decrease or eliminate the blood supply to vascular lesions, transluminal angioplasty and thrombolytic therapy increase blood flow to tissues and are effective treatments for symptomatic cerebral vasospasm and iatrogenic cerebral emboli, respectively. Conscious sedation is the preferred anesthetic technique for therapeutic angioembolization because of the ability to perform repeated neurologic assessment. For the uncooperative, obtunded, and pediatric patient, general anesthesia is required for immobilization, control of the airway, and ventilation. Evoked-potential monitoring and preembolization testing with Amytal sodium have decreased the incidence of neurologic complications significantly. Patients with cardiovascular instability and elevated intracranial pressure are at increased risk if controlled hypotension is necessary during embolization. Complications associated with therapeutic embolization can result in stroke, paralysis, or death. An anaphylactic reaction to contrast media can produce airway obstruction and cardiopulmonary compromise. Resuscitation equipment and emergency drugs should always be available. Acute pulmonary embolism may occur if an arterial injection of embolizing material is carried through an AVM to the venous circulation and thence into the lung. Closure of a large AVM may result in acute systemic hypertension and pulmonary edema; this is a common complication of occlusion of a vein of Galen AVM in an infant. Intracranial hemorrhage is another serious complication of neuroembolic procedures. Emergency management includes airway control, hyperventilation and barbiturate administration for elevated intracranial pressure, and maintenance of cardiovascular stability to preserve cerebral perfusion pressure.

Intraoperative Somatosensory Evoked Potentials Monitoring of Pelvic and Acetabular Fractures

The efficacy of intraoperative somatosensory evoked potential (SSEP) monitoring was evaluated in the surgical management of 82 patients with pelvic and acetabular fractures. The injuries consisted of 45 acetabular fractures, 30 pelvic ring disruptions, and seven combined injuries. Preoperative neurological deficits were recorded in 34% of the study group (29% of those with an acetabular fracture and 47% of those with a pelvic ring injury). Three patients sustained an iatrogenic sciatic nerve injury during the study period (all of which were documented in the first 40 cases). Two patients sustained an exacerbation of an existing sciatic nerve injury. In the group of pelvic fractures, hazardous parts of the exposure, reduction, and fixation were identified by the SSEP monitoring. Removal of the provocative stimulus by the surgeon led to reversal of the SSEP abnormalities, and none of this group of patients sustained an iatrogenic injury. When the intraoperative SSEP changes were noted during an acetabular fracture fixation, immediate attempts were made to relieve the excessive tension on the sciatic nerve by replacing or removing a retractor, flexing the knee, extending the hip, or dividing the femoral insertion of the gluteus maximus. None of the SSEP changes were associated with the lacerative injury to the sciatic nerve. For the method to be clinically effective in reducing the incidence of neurological deficit, even subtle changes in the SSEP tracing must be recognized immediately by the neurophysiologist so that a corresponding corrective measure can be rapidly undertaken by the surgeon to remove the offending stimulus.

Evoked-Potential Monitoring during Dorsal Root Entry Zone Surgery

Spinal cord evoked potentials (SCEP) in response to epispinal stimulation were measured in an experimental animal model designed to define further the value of electrophysiological monitoring during dorsal root entry zone (DREZ) surgery. Thirteen cats underwent microsurgical stereotactic thermal radiofrequency lesions of the DREZ. The postmortem histological examination of the location and extent of the lesions were compared with the intraoperative electrophysiological and postoperative neurological effects. Despite the use of the stereotactic microsurgical technique, the sizes and the configurations of the DREZ lesions varied greatly. Changes in ascending and descending SCEP correlated highly with the extent of the histologically defined injury to the dorsal and lateral columns. SCEP monitoring during experimental DREZ surgery provided a sensitive indication of lesion invasion into the dorsal or lateral columns. The high degree of correlation between changes in descending SCEP and extension of the surgical lesion into the lateral column indicates that the SCEP technique is more sensitive than somatosensory cortical evoked potentials in the intraoperative electrophysiological assessment of corticospinal tract function, and it may prove to be a useful surgical adjunct during DREZ surgery in humans.

Evoked-Potential Monitoring during Dorsal Root Entry Zone Surgery

Somatosensory evoked potentials (SEP) were monitored intraoperatively in 15 patients who underwent spinal cord radiofrequency thermal dorsal root entry zone (DREZ) lesion procedures to treat chronic deafferentation pain. We found a significant correlation between transient latency shifts (recovery to prelesion values in the postlesioning period) of the first positive peak of the SEP (P1) during lesion production and the patients' subsequent postoperative neurological status (p less than 0.01). Transient increases in P1 latency above 2 ms were associated with detectable but transient postoperative sensorimotor deficits that resolved weeks to months after surgery. In 1 patient, the intraoperative P1 latency failed to return to baseline values; this patient had irreversible postoperative sensorimotor dysfunction. In 9 patients, we confirmed the value of recording bilateral SEP, using the contralateral side of the spinal cord (with no lesions) as a control. This experience has resulted in an improved SEP monitoring strategy: we now reconsider the risk-benefit ratio of additional DREZ lesions if early lesion production results in increased P1 latency. Rapid normalization of the P1 latency indicates that any postoperative deficits likely will resolve. Failure of P1 latency to return to control levels during the surgical wound closure period (approximately 1 h) indicates the high probability of permanent neurological deficits.