Somatosensory Evoked Potential Monitoring Research Articles

Use of intraoperative monitoring of somatosensory evoked potentials to prevent ischaemic stroke after surgical exclusion of middle cerebral artery aneurysms

The aim of this study was to assess the value of monitoring somatosensory evoked potentials (SEP) in the prevention of ischaemic stroke occurring during surgical exclusion of middle cerebral artery aneurysms. SEP monitoring was performed during the surgical exclusion of 131 aneurysms in 122 patients. All SEP variations over 30% were notified to the surgeon and those over 50% were considered as highly significant. If this happened, and in concert with the conduct of the operation, a return to the basal level was systematically sought. Post-operative ischemic stroke was observed after 15 (11.4%) operations, leading to a permanent neurological deficit in 12 (9.2%). During nine (6.9%) operations there was a highly significant SEP change that persisted, or was only partially reversed, after corrective procedure. Nine of these patients had a post-operative ischaemic stroke. In 25 (19%), operations there was a highly significant SEP change followed by complete recovery. Of these 25 patients, 2 suffered a post-operative ischemic stroke. Following 49 operations (37.4%) with less significant SEP modifications, 4 patients suffered a post-operative stroke (8%). A stroke did not occur in the 48 (36.6%) operations during which there was not a variation in SEP. The strokes were related to temporary clipping in 9 patients to definitive clipping in 3 to sylvian fissure opening in 1 to brain retraction in and to dissection of the aneurysm in 1 (1 case). Changes in the SEP correlated well with the occurrence of post-operative stroke. This early detection of ischemia directs attention to the need for measures such as withdrawal of temporary clipping or identification of another factor (e.g. release of brain retraction or repositioning of an occlusive clip) so that the risk of post-operative is reduced.

Pré-condicionamento isquêmico e monitorização da função medular na abordagem da aorta torácica descendente

To evaluate the effectiveness of acute ischemic preconditioning (IP), based on somatosensory evoked potentials (SSEP) monitoring, as a method of spinal cord protection and to asses SSEP importance in spinal cord neuromonitoring. Twenty-eight dogs were submitted to spinal cord ischemic injury attained by descending thoracic aorta cross-clamping. In the C45 group, the aortic cross-clamping time was 45 min (n=7); in the IP45 group, the dogs were submitted to IP before the aortic cross-clamping for 45 min (n=7). In the C60 group, the dogs were submitted to 60 min of aortic cross-clamping (n=7), as in the IP60 group that was previously submitted to IP. The IP cycles were determined based on SSEP changes. Tarlov scores of the IP groups were significantly better than those of the controls (p = 0.005). Paraplegia was observed in 3 dogs from C45 and in 6 from C60 group, although all dogs from IP45 group were neurologically normal, as 4 dogs from IP60. There was a significant correlation between SSEP recovery time until one hour of aortic reperfusion and the neurological status (p = 0.011), showing sensitivity of 75% and specificity of 83%. Repetitive acute IP based on SSEP is a protection factor during spinal cord ischemia, decreasing paraplegia incidence. SSEP monitoring seems to be a good neurological injury assessment method during surgical procedures that involve spinal cord ischemia.

Cerebral Monitoring of Somatosensory Evoked Potentials during Carotid Surgery: A Review of 100 Cases

The purpose of this study was to evaluate immediate and middle-term results of surgical carotid artery revascularization (CAR) with cerebral monitoring of intraoperative somatosensory evoked potentials (SEPs). Between 1998 and 2004, a total of 100 CARs in 86 patients were performed under general anesthesia with SEP monitoring. A shunt was inserted if SEP amplitude decreased by 50% or latency time increased by 10%. Immediate and middle-term results were analyzed retrospectively. The shunt insertion rate was 5%. Two transient ischemic attacks were observed, and one patient died postoperatively due to myocardial infarction. The cumulative stroke and death rate was 1% at 30 days. Intraoperative SEP monitoring with selective shunt placement can be used safely for carotid surgery. Randomized studies will be necessary to determine the respective indications for various cerebral monitoring techniques.

The Utility of Somatosensory Evoked Potential Monitoring During Cervical Spine Surgery: How Often Does It Prompt Intervention and Affect Outcome?

Study DesignRetrospective review of the results of somatosensory evoked potentials (SSEP) performed in cervical spine surgery.PurposeTo evaluate the utility of spinal cord monitoring during cervical spine surgery in a single surgeon's practice, based on how often it prompted an intraoperative intervention.Overview of LiteratureIntraoperative monitoring during cervical spine surgery is not a universally accepted standard of care. This is due in part to the paucity of literature regarding the impact of monitoring on patient management or outcome.MethodsSSEP for tibial, median, and ulnar nerves were monitored in 809 consecutive cervical spine operations performed by a single surgeon. The average patient age was 52 years (range, 2 to 88 years), with 472 males and 339 females. Cases were screened for significant degradation or loss of SSEP data. Specific attention was paid to 1) what interventions were performed in response to the SSEP degradation with subsequent improvement, and 2) whether SSEP changes corresponded with postoperative neurological deficits.ResultsSeventeen of 809 patients (2.1%) had SSEP degradation that met warning criteria and therefore prompted intervention. Release of shoulder tape (8) or traction (4) most often resulted in SSEP improvement. Failure of SSEP data to return to within acceptable limits of baseline was associated with neurological deficit (p=0.04). Two patients awoke with new postoperative neurological deficits, which resolved in 6 hours and 2 months respectively. Patients with ossification of the posterior longitudinal ligament (OPLL) were at seven-fold greater risk of intraoperative SSEP degradation.ConclusionsSSEP monitoring in this surgical population proved sensitive to perioperative factors which may increase the risk of postoperative neurologic deficit, and probably prevented neurological deficits in 15 of 809 patients (1.9%). Improvement in data following intervention appears to correlate well with unchanged neurologic status. Experience with intraoperative monitoring in this patient series has led to incorporation of these techniques as a standard of care in cervical spine surgeries performed by this surgeon.

Intraoperative somatosensory evoked potential monitoring during anterior cervical discectomy and fusion in nonmyelopathic patients—a review of 1,039 cases

Intraoperative somatosensory evoked potential (SSEP) monitoring has been shown to reduce the incidence of new postoperative neurological deficits in scoliosis surgery. However, its usefulness during cervical spine surgery remains a subject of debate. To determine the utility of intraoperative SSEP monitoring in a specific patient population (those with cervical radiculopathy in the absence of myelopathy) who underwent anterior cervical discectomy and fusion (ACDF) surgery. Retrospective review. A total of 1,039 nonmyelopathic patients who underwent single or multilevel ACDF surgery. The control group (462 patients) did not have intraoperative SSEP monitoring, whereas the monitored group (577 patients) had continuous intraoperative SSEP monitoring performed. A new postoperative neurological deficit. SSEP tracings were reviewed for all 577 patients in the monitored group and all significant signal changes were noted. Medical records were reviewed for all 1,039 patients to determine if any new neurological deficits developed in the immediate postoperative period. None of the patients in the control group had any new postoperative neurological deficits. In the monitored group there were six instances of transient SSEP changes (1 due to suspected carotid artery compression; 5 thought to be due to transient hypotension) which resolved with the appropriate intraoperative intervention (repositioning of retractors; raising the arterial blood pressure). Upon waking up from anesthesia, one patient in the monitored group had a new neurological deficit (partial central cord syndrome) despite normal intraoperative SSEP signals. ACDF appears to be a safe surgical procedure with a low incidence of iatrogenic neurological injury. Transient SSEP signal changes, which improved with intraoperative interventions, were not associated with new postoperative neurological deficits. An intraoperative neurological deficit is possible despite normal SSEP signals.

Perioperative Management to Improve Neurologic Outcome in Thoracic or Thoracoabdominal Aortic Stent-Grafting

Thoracic or thoracoabdominal aortic stent-graft repair has shown a reduction in morbidity and mortality rates due to the procedure's advantages (no aortic cross-clamping, continuous distal aortic perfusion, no reperfusion injury). However, 3% to 12% of the patients are at risk of spinal cord ischemia. We investigated spinal cord protective measures with evoked potentials, cerebrospinal fluid drainage, and prevention of hypotension to minimize postoperative neurologic deficit. Between November 2000 and July 2005, vital parameters and spinal cord function were monitored, including cerebrospinal fluid pressure and transcranial motor-evoked and somatosensory-evoked potentials in 36 stent-graft procedures (31 patients) on the thoracic or thoracoabdominal aorta. Stent-graft placement was technically successful in all patients. We achieved a survival rate of 100% without neurologic deficit after fast-track extubation. Eleven of 31 patients exhibited changes in evoked potentials during stent-graft deployment. In 12 of 31 patients (including the 11 with evoked potential alterations), cerebrospinal fluid pressure exceeded 15 mm Hg. Cerebrospinal fluid drainage and vital parameter adjustment were executed in those instances. We observed intraoperative evoked potential total recovery in 10 of 11 patients after these interventions. Interventions to improve spinal cord perfusion led to total recovery of spinal function in most patients (10/11). Therefore, spinal cord protective measures with motor- and somatosensory-evoked potential monitoring, cerebrospinal fluid drainage, and prevention of hypotension can reduce the incidence of spinal cord ischemia and improve the neurologic outcome of patients undergoing endovascular thoracic or thoracoabdominal aortic repair.

Thoracic and Thoracoabdominal Aneurysm Repair: Is Reimplantation of Spinal Cord Arteries a Waste of Time?

The impact of different strategies for management of intercostal and lumbar arteries during repair of thoracic and thoracoabdominal aortic aneurysms (TAA/A) on the prevention of paraplegia remains poorly understood. One hundred consecutive patients with intraoperative monitoring of motor evoked potentials (MEP) and somatosensory evoked potentials (SSEP) during TAA/A repair involving serial segmental artery sacrifice (October 2002 to December 2004) were reviewed. Operative mortality was 6%. The median intensive care unit stay was 2.5 days (IQ range: 1-4 days), and the median hospital stay 10.0 days (IQ range: 8-17 days). Potentials remained unchanged during the course of serial segmental artery sacrifice, or could be returned to baseline levels by anesthetic and blood pressure manipulation, in 99 of 100 cases. An average of 8.0 +/- 2.6 segmental artery pairs were sacrificed overall, with an average of 4.5 +/- 2.1 segmental pairs sacrificed between T7 and L1, where the artery of Adamkiewicz is presumed to arise. Postoperative paraplegia occurred in 2 patients. In 1, immediate paraplegia was precipitated by an intraoperative dissection, resulting in 6 hours of lower body ischemia. A second ambulatory patient had severe paraparesis albeit normal cerebral function after resuscitation from a respiratory arrest. With monitoring of MEP and SSEP, sacrifice--without reimplantation--of as many as 15 intercostal and lumbar arteries during TAA/A repair is safe, resulting in acceptably low rates of immediate and delayed paraplegia. This experience suggests that routine surgical implantation of segmental vessels is not indicated, and that, with evolving understanding of spinal cord perfusion, endovascular repair of the entire thoracic aorta should ultimately be possible without spinal cord injury.

Neurophysiological Identification of Position-Induced Neurologic Injury During Anterior Cervical Spine Surgery

This study was a retrospective review of 3,806 patients who underwent anterior cervical spine surgery with multi-modality neurophysiological monitoring consisting of transcranial electric motor evoked potentials, somatosensory evoked potentials and spontaneous electromyography between 1999-2003. The objectives of this study were twofold: (1) to evaluate the role of transcranial electric motor evoked potential tceMEP and ulnar nerve somatosensory evoked potential (SSEP) monitoring for identifying impending position-related stretch brachial plexopathy, peripheral nerve entrapment/compression or spinal cord compression and (2) to estimate the point-prevalence of impending neurologic injury secondary to surgical positioning effects. Sixty-nine of 3,806 patients (1.8% showed intraoperative evidence of impending neurologic injury secondary to positioning, prompting interventional repositioning of the patient. The brachial plexus was the site of evolving injury in 65% of these 69 cases. Impending brachial plexopathy was most commonly noted immediately following shoulder taping and the application of counter-traction. Brachial plexus stretch upon neck extension for optimal surgical access and visualization was second in frequency-of-occurrence. Evolving traction injury to the ulnar nerve attributed to tightly-wrapped or malpositioned arms was observed in 16% of alerted cases, whereas evolving spinal cord injury following neck extension accounted for an additional 19%. This study highlights the role of tceMEP and ulnar nerve SSEP monitoring for detecting emerging peripheral nerve injury secondary to positioning in preparation for and during anterior cervical spine surgery.

Continuous EEG–SEP monitoring of severely brain injured patients in NICU: methods and feasibility

Aims To evaluate the feasibility of a continuous neurophysiologic monitoring (electroencephalography (EEG)–somatosensory evoked potentials (SEPs)) in the neuro-intensive care unit (NICU), taking into account both the technical and medical aspects that are specific of this environment. Methods We used an extension of the recording software that is routinely used in our unit of clinical neurophysiology. It performs cycles of alternate EEG and SEP recordings. Raw traces and trends are simultaneously displayed. Patient head and stimulator box are placed behind the bed and linked to the ICU monitoring terminal through optic fibers. The NICU staff has been trained to note directly clinical events, main artefacts and therapeutic changes. The hospital local area network (LAN) enables remote monitoring survey. Results Continuous EEG (CEEG)–SEP monitoring was performed in 44 patients. Problems of needle detachment were seldomly encountered, thanks to the use of a sterile plastic dressing, which covers needles. We never had infection or skin lesions due to needles or the electrical stimulator. The frequent administration of sedative at high doses prevented us from having a clinically valuable EEG in several cases but SEPs were always monitorable, independently of the level of EEG suppression. The diagnosis of seizures and non-epileptic status was based on raw EEG, while quantitative EEG (QEEG) was used to quantify ictal activity as a guide to treatment. Conclusions EEG and EP waveforms collected in NICU were of comparable quality to routine clinical measurements and contained the same clinical information. A continuous SEP monitoring in a comatose and sedated patient in NICU is not technically more difficult and potentially less useful than in operating room. This monitoring appears to be feasible provided the observance of some requirement regarding setting, electrodes, montages, personnel integration, consulting and software.

Somatosensory- and motor-evoked potential monitoring during spine and spinal cord surgery

Prospective, observational study. Regional Trauma Center, Torino, Italy. Complex spinal surgery carries a significant risk of neurological damage. The aim of this study is to determine the reliability and applicability of multimodality motor-evoked potentials (MEPs) and somatosensory-evoked potentials (SEPs) monitoring during spine and spinal cord surgery in our institute. Recordings of MEPs to multipulse transcranial electrical stimulation (TES) and cortical SEPs were made on 52 patients during spine and spinal cord surgery under propofol/fentanyl anaesthesia, without neuromuscular blockade. Combined MEPs and SEPs monitoring was successful in 38/52 patients (73.1%), whereas only MEPs from at least one of the target muscles were obtained in 12 patients (23.1%); both MEPs and SEPs were absent in two (3.8%). Significant intraoperative-evoked potential changes occurred in one or both modalities in five (10%) patients. Transitory changes were noted in two patients, whereas three had persistent changes, associated with new deficits or a worsening of the pre-existing neurological disabilities. When no postoperative changes in MEP or MEP/SEP modalities occurred, it was predictive of the absence of new motor deficits in all cases. Intraoperative combined SEP and MEP monitoring is a safe, reliable and sensitive method to detect and reduce intraoperative injury to the spinal cord. Therefore, the authors suggest that a combination of SEP/MEP techniques could be used routinely during complex spine and/or spinal cord surgery.

The Use of Somatosensory Evoked Potentials to Determine the Relationship Between Patient Positioning and Impending Upper Extremity Nerve Injury During Spine Surgery: A Retrospective Analysis

Somatosensory evoked potential (SSEP) monitoring is used to prevent nerve damage in spine surgery and to detect changes in upper extremity nerve function. Upper extremity SSEP conduction changes may indicate impending nerve injury. We investigated the effect of operative positioning on upper extremity nerve function retrospectively in 1000 consecutive spine surgeries that used SSEP monitoring. The vast majority (92%) of upper extremity SSEP changes were reversed by modifying the arm position and were therefore classified as position-related. The incidence of position-related upper extremity SSEP changes was calculated and compared for five different surgical positions: supine arms out, supine arms tucked, lateral decubitus position, prone arms tucked, and the prone "superman" position. The overall incidence of position-related upper extremity SSEP changes was 6.1%. The lateral decubitus position (7.5%) and prone superman position (7.0%) had a significantly more frequent incidence of position-related upper extremity SSEP changes (P < 0.0001, Z-test for Poisson counts) compared with other positions (1.8%-3.2%). No patient with a reversible SSEP change developed a new postoperative deficit in the affected extremity. SSEP monitoring is of value in identifying and reversing impending upper extremity peripheral nerve injury.

Intraoperative somatosensory evoked potentials to facilitate peripheral nerve release

The significance of intraoperative somatosensory evoked potentials (SSEP) monitoring is well known during spinal surgery. This technology could be beneficial during peripheral nerve surgery as well. In order to illustrate potential applications, two cases of successful peripheral nerve release demonstrated by on-line, intraoperative, SSEP are reported. Clinical and technical features: The first case presents a complex brachial plexus lesion involving two mixed sensory-motor nerves: median and ulnar. The second case involved an entrapment neuropathy of the lateral femoral cutaneous nerve, a pure sensory nerve (meralgia paresthetica). For each patient we elicited specific peripheral nerve SSEP (recorded using bipolar cephalic montage) by stimulating each nerve independently. In each case, during difficult nerve dissection and after having excluded other possible factors of intraoperative SSEP variations, an increase of the SSEP amplitude was observed, and later correlated with favourable patient clinical outcome. Two cases demonstrate that intraoperative SSEP monitoring may provide an effective tool to guide surgical dissection during peripheral nerve release. This technique has potentially beneficial clinical applications and warrants further investigation.

Change pattern of somatosensory-evoked potentials after occlusion of segmental vessels: possible indicator for spinal cord ischemia

Paraplegia was reported after occlusion of the segmental vessels during anterior spinal surgery. The aim of this study was to investigate the effect of occlusion of the segmental vessels on the somatosensory-evoked potential (SEP) monitoring and analyze its potential risk for cord ischemia. Thirty-one patients with thoracic scoliosis underwent anterior spinal surgery. T5-T11 segmental vessels on the convexity were occluded with microvascular clamps at the point 2 cm from the intravertebra foramen. The SEPs were recorded 5 min before occlusion and 2, 7, 12 and 17 min after occlusion. The SEPs were analyzed with two indices i.e. P40 latency and P40 amplitude. All SEP waveforms recorded during the test were regular and recognizable. Compared to 5 min before occlusion, the P40 latencies at 2 min and 7 min after occlusion significantly increased 3.39% and 2.76% on an average, the P40 amplitudes at 2 min after occlusion significantly declined 26% (peak to peak) or 22% (peak to baseline) on an average (P<0.05). But the changes of SEPs were temporary. The SEPs began to restore at 12 min after occlusion and returned to the pre-occlusion level at 17 min after occlusion. No neurologic complications occurred in all patients after surgery. These results suggest that SEP is a possible indicator for ischemia of the spinal cord which is a dynamic course and cannot be considered an "all-or-none" phenomenon. Without the factors such as developmental deformities of the spinal cord, vascular variation and potential cord ischemia, occlusion of the segmental vessels would be safe during the anterior spinal surgery.

Somatosensory Evoked Potential Monitoring During Anterior Cervical Discectomy and Fusion

A retrospective, multicenter clinical review was conducted. To examine our experience using somatosensory evoked potential (SSEP) monitoring during anterior cervical discectomy and fusion (ACDF) to determine if monitoring of the spinal cord with SSEPs was helpful in identifying reversible causes of neurologic impairment while performing the procedure. Recent studies have strongly supported the use of SSEP monitoring during complicated and upper-cervical spine surgery. The complete medical records of 163 patients who underwent ACDF, and who were monitored with SSEPs during the procedure between 1995 and 2002 were retrospectively reviewed. A single observer who was uninvolved with patient care abstracted these medical records. Demographic data, length of symptoms, workers' compensation status, primary diagnosis, preoperative neurologic status, number of levels fused, bone graft type, implants used, SSEP findings, postoperative neurologic status, complications, and recovery from complications were recorded. Final neurologic status was determined through phone contact with patients or outpatient charts of patients who could not be contacted personally. There were 3 false positive (1.8%) intraoperative SSEP findings in which SSEP changes intraoperatively did not reflect a neurologic deterioration after surgery. There was 1 false negative (0.6%) in which a new neurologic deficit occurred after surgery, despite no change in SSEP amplitudes during the operation. There were 2 true negatives (1.2%) in which SSEP monitoring showed a preexisting neurologic deficit, which did not change during the operation. In no instance were positive SSEP findings clinically useful in alerting the surgeon to potential intraoperative complications. Intraoperative SSEP monitoring is not helpful to the surgeon when performing routine ACDF. Additionally, ACDF is a safe procedure with a low rate of neurologic complications.

Clinical Usefulness of Somatosensory Evoked Potentials for Detection of Brachial Plexopathy Secondary to Malpositioning in Scoliosis Surgery

A retrospective longitudinal study of 434 consecutive pediatric patients who underwent surgical correction of scoliosis, while being monitored for positional brachial plexopathy. To evaluate the effectiveness of intermittent monitoring of ulnar nerve somatosensory evoked potentials (SSEPs) for detecting brachial plexus injury caused by malpositioning during scoliosis surgery. Continuous intraoperative SSEP monitoring for spinal cord function has been well reported, and is widely accepted as the standard for spinal deformity correction surgery to detect and avoid neurologic injury. The use of SSEPs for the monitoring of ulnar nerve function intraoperatively as an indicator of brachial plexus function is becoming more accepted as a valid and useful technique to minimize intraoperative neurologic injuries during deformity corrections. A review was conducted to assess the effect of ulnar nerve SSEP monitoring, as a measure of brachial plexus function, during anterior, posterior, or combined approach surgeries. The type of scoliosis, type of surgery and positioning, and surgical event at noted amplitude decrease were included in an analysis of variance for repeated measures, and a Student t test was performed for significant differences. A total of 27 patients had ulnar nerve amplitude decreases of > or =30%, resulting in a point prevalence of 6.2% for positional brachial plexopathy during positioning for all scoliosis surgeries. A significant difference was noted between the types of positioning, with prone positioning accounting for a higher rate of brachial plexopathy compared with anterior approach positioning (P < 0.01). No statistical difference exists as to the type of scoliosis present and the incidence of brachial plexopathy (P < 0.01). Avoidance of neurologic injury to the brachial plexus during scoliosis surgery is possible by early detection with ulnar nerve SSEP monitoring.

VALUE OF SOMATOSENSORY EVOKED POTENTIALS FOR SPINE PATHOLOGY STUDY

Objective. To analyze the efficacy of dynamic neurophysiologic monitoring for diagnosis and treatment of patients with spine diseases and injuries during decompression and decompression/stabilization surgery of the spine. Materials and Methods. Somatosensory evoked potentials (SSEP) were recorded in 297 patients with the spine diseases and injuries. Besides, 118 patients underwent intraoperative monitoring of SSEP and neural evoked potentials. Patients with abdomen dysfunction were examined by cystometry, profilometry, and urofluometry. Results. Neurophysiological examinations for spine injuries allow to verify the level of spinal cord conductor injury and to assess the degree of functional disorders in spinal cord structures. In degenerative spine the changes in SSEP parameters occur only in disturbed spinal arteriovenous and venous circulation accompanied by expressed motor and sensitive conduction disorders. The SSEP study is most informative when inflammatory process is localized in the cervical or thoracic spine. In different forms of dysraphic status (diastematomyelia, syringomyelia, Chiari malformation) the SSEP study can not be a determinative diagnosis method. Conclusion. Considering the relative simplicity of SSEP study and its value for dynamic examination of spinal cord conductors, it can be recommended as an obligatory test to assess indications for spine surgery for vascular disorders associated with degenerative-dystrophic diseases of the spine.

Immediate ischemic preconditioning based on somatosensory evoked potentials seems to prevent spinal cord injury following descending thoracic aorta cross-clamping

Delayed ischemic preconditioning has demonstrated neuroprotective effects in spinal cord ischemia. We investigated the effects of immediate ischemic preconditioning based on somatosensory evoked potentials monitoring in a model of spinal cord injury due descending thoracic aorta occlusion in dogs. Twenty-one dogs were submitted to spinal cord ischemia induced by descending thoracic aorta cross-clamping for 45 min. Control group underwent only the aortic cross-clamping (n=7), group A underwent one cycle of ischemic preconditioning (n=7) and group B underwent three equal cycles of ischemic preconditioning (n=7), immediately before the aortic cross-clamping. Ischemic preconditioning cycles were determined by somatosensory evoked potentials monitoring. Neurologic evaluation was performed according to the Tarlov score at 72 h of follow-up. The animals were then sacrificed and the spinal cord harvested for histopathology. Aortic pressures before and after the occluded segment were similar in the three groups. Ischemic preconditioning periods corresponded to a mean ischemic time of 3+/-1 min and a mean recovery time of 7+/-2 min. Severe paraplegia was observed in three animals in Control group, in four in group A and in none in group B. Tarlov scores of group B were significantly better in comparison to the Control group (P=0.036). Histopathologic examination showed severe neuronal necrosis in the thoracic and lumbar gray matter in animals who presented paraplegia. Immediate repetitive ischemic preconditioning based on somatosensory evoked potentials monitoring seems to protect spinal cord during descending aorta cross-clamping, reducing paraplegia incidence.

Intraoperative monitoring of blood flow insufficiency during surgery of middle cerebral artery aneurysms

The usefulness of motor evoked potential (MEP) monitoring to detect blood flow insufficiency (BFI) in the cortical branches of the middle cerebral artery (MCA) and lenticulostriate arteries (LSAs) during MCA aneurysm surgery was investigated based on the correlation between MEP and somatosensory evoked potential (SEP) monitoring. Fifty-three patients with MCA aneurysms underwent surgery accompanied by intraoperative MEP and SEP monitoring. There was no postoperative motor paresis in 43 patients in whom MEP and SEP results remained unchanged. In the other 10 patients, nine manifested transient MEP changes; in five of these, SEP changes did not occur. The transient MEP changes were thought to be attributable to BFI of the MCA cortical branches in two patients, the LSA in three, and either the MCA branches or the LSA in four patients. Of these nine patients, six did not present with postoperative motor paresis; transient motor paresis was recognized in the other three. In the 10th patient, MEP waves disappeared and did not recover. This patient's SEPs remained at 70% of the control level, and he developed severe hemiparesis. A postoperative computerized tomography scan revealed a new low-density area in the corona radiata and putamen. Blood flow insufficiency in both the LSA and MCA cortical branches that perfuse the corticospinal tract can be detected by intraoperative MEP monitoring. Somatosensory evoked potential monitoring is not reliable enough to detect BFI in the MCA branches and the LSAs.

Cerebellar-evoked potentials and nitrous oxide in healthy subjects

INTRODUCTION: Evoked Potential monitoring has become common practice during major spinal surgery. The aim is to alert the surgical team to impending ischaemic damage and avoid permanent neurological injury. The most common modality used is Somatosensory Evoked Potential (SSEP) monitoring. However, SSEPs have some important limitations. They are known to be influenced by commonly used anaesthetic agents.(1). SSEPs are carried via the dorsal columns so monitoring of SSEPs alone may allow a ventral cord defect to go undetected. Cerebellar Evoked Potentials (CEPs) have been reported as a potential monitor of ventral cord integrity. (2,3). A pilot study in the intraoperative setting has suggested that CEPs are robust during general anaesthesia.(4). The purpose of this study is to characterize these evoked potentials and to determine the effect of nitrous oxide in healthy volunteers.

Effectiveness of Intraoperative Somatosensory Evoked Potential Monitoring During Cervical Spinal Operations on Animals with Spinal Cord Dysfunction

We conducted somatosensory evoked potential (SEP) monitoring on 3 dogs with cervical spinal cord dysfunction caused by various diseases throughout operative procedures to examine whether the intraoperative SEP monitoring was effective for prediction of spinal cord conductive function. The SEP was recorded on the scalp via stimulation of the ulnar nerve. Stable SEP was recorded in all animals examined. Its amplitude was decreased by surgical manipulations of the regio vertebralis, but the amplitude gradually recovered once the manipulations were halted. The latency showed small variation throughout the operations. This evidence suggests that intraoperative SEP monitoring may provide continuous and instantaneous information regarding the functional integrity of the central nervous system.