Intraoperative Somatosensory Evoked Potentials Research Articles

Protecting the Genitofemoral Nerve during Direct/Extreme Lateral Interbody Fusion (DLIF/XLIF) Procedures

ABSTRACT.A 77-year-old male presented with a history of severe lower back pain for 10 years with radiculopathy, positive claudication type symptoms in his calf with walking, and severe “burning” in his legs bilaterally with walking. Magnetic resonance imaging (MRI) revealed lumbar stenosis at the L3–L4 and L4–L5 levels. During the direct or extreme lateral interbody fusion (DLIF/XLIF) procedure, bilateral posterior tibial, femoral, and ulnar nerve somatosensory evoked potentials (SSEPs) were recorded with good morphology of waveforms observed. Spontaneous electromyography (S-EMG) and triggered electromyography (T-EMG) were recorded from cremaster and ipsilateral leg muscles. A left lateral retroperitoneal transpsoas approach was used to access the anterior disc space for complete discectomy, distraction, and interbody fusion. T-EMG ranging from 0.05 to 55.0 mA with duration of 200 μsec was used for identification of the genitofemoral nerve using a monopolar stimulator during the approach. The genitofemoral nerve (L1–L2) was identified, and the guidewire was redirected away from the nerve. Post-operatively, the patient reported complete pain relief and displayed no complications from the procedure. Intraoperative SSEPs, S-EMG, and T-EMG were utilized effectively to guide the surgeon's approach in this DLIF, thereby preventing any post-operative neurological deficits such as damage to the genitofemoral nerve that could lead to groin pain.

Localization of cervical and cervicomedullary stimulation leads for pain treatment using median nerve somatosensory evoked potential collision testing

Spinal cord stimulation (SCS) is being currently used to treat medically refractory pain syndromes involving the face, trunk, and extremities. Unlike thoracic SCS surgery, during which patients can be awakened from conscious sedation to confirm good lead placement, safe placement of paddle leads in the cervical spine has required general anesthesia. Using intraoperative neurophysiological monitoring, which is routinely performed during these cases at the authors' institution, the authors developed an electrophysiological technique to intraoperatively lateralize lead placement in the cervical epidural space. Data from 44 patients undergoing median and tibial nerve somatosensory evoked potential (SSEP) monitoring during cervical laminectomy or hemilaminectomy for placement or replacement of dorsal column stimulators were retrospectively reviewed. Paddle leads were positioned laterally or just off midline and parallel to the axis of the cervical spinal cord to effectively treat what was most commonly a predominant unilateral pain syndrome. During SSEP recording, the spinal cord stimulator was activated at 1.0 V and increased in increments of 1.0 V to a maximum of 6.0 V. A unilateral reduction or abolishment of SSEP amplitude was regarded as an indicator of lateralized placement of the stimulator. A bilateral diminutive effect on SSEPs was interpreted as a midline or near midline lead placement. Epidural stimulation abolished or significantly reduced SSEP amplitudes in all patients undergoing placement for a unilateral pain syndrome. In 15 patients, electrodes were repositioned intraoperatively to achieve the most robust SSEP amplitude reduction or abolishment using the lowest epidural stimulation intensity. In all cases in which a significant unilateral reduction in SSEP was observed, the patient reported postoperative sensory alterations in target locations predicted by intraoperative SSEP changes. Placement of cervical spinal cord stimulators for bilateral pain syndromes often resulted in bilateral but asymmetrical SSEP changes. In no cases were significant SSEP changes, other than those induced using the device to directly stimulate the dorsal surface of the spinal cord, observed. No case of new postoperative neurological deficit was observed. Somatosensory evoked potentials can be used safely and successfully for predicting the lateralization of cervical spinal cord stimulator placement. Moreover, they can also intraoperatively alert the surgical team to inadvertent displacement of a lead during anchoring. Further studies are needed to determine whether apart from assisting with proper lateralization, SSEP collision testing may help to optimize electrode positioning and improve pain control outcomes.

Significance and cost-effectiveness of somatosensory evoked potential monitoring in cervical spine surgery

Intraoperative somatosensory evoked potential (SSEP) monitoring during cervical spine surgery is not a universally accepted standard of care. Our retrospective study evaluated the efficacy and cost-effectiveness of intraoperative SSEP in a single surgeon's practice. Intraoperative SSEP monitoring was performed on 210 consecutive patients who had cervical spine surgery: anterior cervical approach 140 and posterior approach 70. They were screened for degradation or loss of SSEP data. A cost analysis included annual medical costs for health and human services, durable goods and expendable commodities. Temporary loss of the electrical wave during cauterization resolved upon discontinuation of the cautery. We had no loss of cortical wave with preservation of the popliteal potential. A drop in the amplitude of the cortical wave was observed in three patients. This drop was resolved after hemodynamic stabilization in the first patient, readjusting the bone graft in the second patient, and interrupting the surgery in the third patient. The additional cost for SSEP monitoring was $835 per case and the total cost of the surgery was $13,835 per case. By spending $31,546 per year on SSEP, our institution is saving a total cost ranging from $64,074 to $102,192 per patient injured per year. Intraoperative SSEP monitoring is a reliable and cost-effective method for preventing postoperative neurological deficit by the early detection of vascular or mechanical compromise, and the immediate alteration of the anesthetic or surgical technique.

Quantifying the effect of isoflurane and nitrous oxide on somatosensory-evoked potentials

Anaesthetic techniques may have a significant effect on intraoperative-evoked potentials (EP). The present study is designed to compare Propofol anaesthesia with Isoflurane (with or without nitrous oxide) during intraoperative somatosensory-evoked potential (SSEP) monitoring in 15 ASA Grade I and II patients undergoing surgery for intracranial tumours. SSEPs in response to median and posterior tibial nerve stimulation were recorded under four different anaesthetic conditions: 1) Propofol infusion and ventilation with air-oxygen, 2) Isoflurane, 1.0 MAC and ventilation with air-oxygen, 3) Isoflurane 1.0 MAC and ventilation with nitrous oxide-oxygen, and 4) Return to Isoflurane, 1.0 MAC and ventilation with air-oxygen. Intraoperative monitoring of somatosensory evoked potentials is best recordable using Propofol. The morphology of the EP is reproducible with Isoflurane. This effect is exaggerated when it is advisable to avoid nitrous oxide.

Thoracic Pedicle Subtraction Osteotomy for Fixed Sagittal Spinal Deformity

STUDY DESIGN.: A retrospective clinical study. OBJECTIVE.: To find the corrective capacity of a thoracic pedicle subtraction osteotomy (PSO), determine if segmental correction is dependent on level, and to compute the impact of thoracic PSO on regional and global spinal balance. SUMMARY OF BACKGROUND DATA.: PSO is a technique popularized in the lumbar spine primarily for the correction of fixed sagittal imbalance. Despite several studies describing the clinical and radiographic outcome of lumbar PSO, there is no study in literature reporting its application in the thoracic spine. METHODS.: We retrospectively analyzed patients with fixed thoracic kyphosis who underwent thoracic PSOs for sagittal realignment. Segmental pedicle screw instrumentation and intraoperative neurophysiologic monitoring was used in all patients. Data acquisition was performed by reviewing medical charts and radiographs to determine sagittal correction (segmental/regional/global) and complications. Clinical outcome using the Scoliosis Research Society-22 (SRS-22) instrument was determined by interview. RESULTS.: A total of 25 thoracic PSOs were performed (mean: 1.7 PSOs/patient, range: 1-3) in 15 patients (9 M/6 F). The study population had an average age of 56 years (range, 36-81 years) and was followed up after surgery for a mean of 3.5 years (range, 24-75 months). The osteotomies were carried out in the proximal thoracic spine (T2-T4, n = 6), midthoracic spine (T5-T8, n = 12), and distal thoracic spine (T9-T12, n = 7). Mean correction at the PSO for all 25 levels was 16.3 degrees +/- 9.6 degrees . Stratified by region of the spine, thoracic PSO correction was as follows: T2-T4 = 10.7 degrees +/- 15.8 degrees , T5-T8 = 14.7 degrees +/- 4.6 degrees , and T9-T12 = 23.9 degrees +/- 4.1 degrees . Mean thoracic kyphosis (T2-T12 Cobb angle) was improved from 75.7 degrees +/- 30.9 degrees to 54.3 degrees +/- 21.4 degrees resulting in a significant regional sagittal correction of 21.4 degrees +/- 13.7 degrees (P < 0.005). Global sagittal balance was improved from 106.1 +/- 56.6 to 38.8 +/- 37.0 mm yielding a mean correction of 67.3 +/- 54.7 mm (P < 0.005). One patient, in whom there was segmental translation during osteotomy closure, had a decline in intraoperative somatosensory-evoked potentials. No patient sustained a temporary or permanent neurologic deficit after surgery. The mean SRS-22 Questionnaire score at final follow-up was 82.4 +/- 10.2. CONCLUSION.: Thoracic PSO can be performed safely. Segmental sagittal correction appears to vary based on the region of the thoracic spine the PSO is performed. The distal thoracic segments, which more closely resemble lumbar segments in morphology, rendered the greatest sagittal correction after PSO, approximately 24 degrees . There was no case of neurologic injury associated with thoracic PSO, and clinical outcomes according to the SRS-22 instrument were generally favorable.

The alert applying value of somatosensory evoked potential examination in total vertebral osteotomy.

Objective To investigate risk factors related to changes in somatosensory evoked poten-tials (SEPs) in total vertebral osteotomy. Methods From April 2002 to December 2007, 118 patients with severe kyphoscoliosis deformity were treated with posterior total vertebral osteotomy. There were 68 males and 50 females with the mean age of 29 years (range, 4-73years). The pre-operative scoliosis Cobb angle was 70° (40°-130°) and kyphosis Cobb angle was 78° (32°-147°). The preoperative and intraoperative SEPs were recorded. The highest, lowest and mean arterial pressure (MAP) were recorded at the beginning, ending, and during the procedure. More than 50% decrease in SEPs amplitudes or more than 10% increase in latency was considered to be the warning threshold. Results The average blood loss volumn was 2000ml (800-6500 ml). The MAPs were less than 60 mm Hg in 14 patients, and 8 of those patients had false-posi-tive readings. There were 100 patients (84.6%) without monitoring changes and no postoperative neurologicdeficit, 1 patient (0.8%) with false-negative reading, 8 patients (6.8%) with true-positive readings, 9 patients (7.6%) had false-positive readings. Nine patients had a postoperative motor or sensory deficit. Higher false-positive rates were seen in patients with greater lability in MAP. In 12 patients, N50 latency increased and the latter two peaks amalgamated to form one slower wave. Conclusion False-positive readings are asso-ciated with high variability in MAP. The concussion, translation, rotation and distraction of the spinal cord and transient ischemia may cause the restrain of the SEPs. N50 latency increased and the latter two peaks a-malgamated to form one slower wave is the alert value possibly. Key words: Spine; Osteotomy; Evoked potentials, somatosensory; Monitoring, intraoperative

Intra-Operative Somatosensory-Evoked Potential Monitoring

To evaluate the usefulness of intra-operative somatosensory-evoked potentials (SSEPs) in monitoring spinal cord status via the posterior tibial nerve. 84 men and 28 women aged 16 to 66 years (72% were aged 20 to 40 years) with spinal trauma (63 in the lumbar and 49 in the thoracic spine) underwent posterior instrumentation and fusion using bone grafts. All 63 patients with lumbar spinal injury and 35 of the patients with thoracic spinal injury were treated with pedicular screws. The remaining 14 patients had their thoracic spinal injury fixed with sublaminar wires. Cortical scalp recordings were used. Baseline tracings were obtained prior to surgical intervention and after establishment of anaesthesia. If changes persisted for more than 15 to 20 minutes or if they did not show definite signs of resolution, event reversal was considered. Of the 112 patients, 74 (66%) had no changes in Cz-Fpz patterns and neurological status, whereas 14 (13%) showed improved patterns (2 of them had the same neurological status postoperatively) and 24 (21%) displayed deteriorated patterns prompting intervention. Of the 24 patients prompting intervention, 20 improved substantially (19 had no new neurological deficits and one had deteriorated neurological status) and 4 improved minimally (2 had no new deficit and 2 had new deficits), with 88% sensitivity and 78% specificity. 15 patients were true-positives with an identifiable cause; 21 were false-positives with no neurological deterioration or recognisable cause. Intra-operative SSEP monitoring helps identify acute neurological and systemic (hypoxia or hypotension) impairment and enables prompt correction. This makes surgery available to high-risk patients and enables surgeons to carry out more extensive procedures. It also provides valuable documentation in the event of medico-legal dispute.

Comparison between Sevoflurane/Remifentanil and Propofol/Remifentanil Anaesthesia in Providing Conditions for Somatosensory Evoked Potential Monitoring during Scoliosis Corrective Surgery

Somatosensory evoked potential (SSEP) monitoring is an important tool in spinal corrective surgery. Anaesthesia has a significant influence on SSEP monitoring and a technique which has the least and shortest suppressant effect on SSEP while facilitating a fast recovery from anaesthesia is ideal. We compared the effect of sevoflurane/ remifentanil and propofol/remifentanil anaesthesia on SSEPs during scoliosis corrective surgery and assessed patients' clinical recovery profiles. Twenty patients with idiopathic scoliosis receiving surgical correction with intraoperative SSEP monitoring were prospectively randomised to receive sevoflurane/remifentanil anaesthesia or propofol/remifentanil anaesthesia. During surgery, changes in anaesthesia dose and physiological variables were recorded, while SSEP was continuously monitored. A simulated 'wake-up' test was performed postoperatively to assess speed and quality of recovery from anaesthesia. The effects of propofol and sevoflurane resulted in SSEP amplitude variability between 18.0% +/- 3.5% to 28.7% +/- 5.9% and SSEP latency variability within 1.3% +/- 0.4% to 2.6% +/- 1.2%. Patients receiving sevoflurane had faster suppression and faster recovery of SSEP amplitude compared to propofol (P < 0.05), although propofol anaesthesia showed less within-patient variability in Cz amplitude and latency (P < 0.05). On cessation of anaesthesia, time to eye-opening (5.2 vs. 16.5 minutes) and toe movement (5.4 vs. 17.4 minutes) was shorter following sevoflurane (all P < 0.05). These findings indicate that propofol produces a better SSEP signal than sevoflurane. However adjustments in sevoflurane concentration result in faster changes in the SSEP signal than propofol. Assessment of neurological function was facilitated more rapidly after sevoflurane anaesthesia.

Heat shock proteins HSP70 and HSP27 in the cerebral spinal fluid of patients undergoing thoracic aneurysm repair correlate with the probability of postoperative paralysis

An understanding of the time course and correlation with injury of heat shock proteins (HSPs) released during brain and/or spinal cord cellular stress (ischemia) is critical in understanding the role of the HSPs in cellular survival, and may provide a clinically useful biomarker of severe cellular stress. We have analyzed the levels of HSPs in the cerebrospinal fluid (CSF) from patients who are undergoing thoracic aneurysm repair. Blood and CSF samples were collected at regular intervals, and CSF was analyzed by enzyme-linked immunosorbent assay for HSP70 and HSP27. These results were correlated with intraoperative somatosensory-evoked potentials measurements and postoperative paralysis. We find that the levels of these proteins in many patients are elevated and that the degree of elevation correlates with the risk of permanent paralysis. We hypothesize that sequential measurement intraoperatively of the levels of the heat shock proteins HSP70 and HSP27 in the CSF can predict those patients who are at greatest risk for paralysis during thoracic aneurysm surgery and will allow us to develop means of preventing or attenuating this severe and often fatal complication.

頸動脈内膜剥離術における危険因子―術前のＷｉｌｌｉｓ動脈輪前方の形態学的評価と術中ＳＥＰの変化―

Cerebral ischemia during clamping of the carotid artery is a procedure-related complication in carotid endarterectomy (CEA). A correlation between the status of the circle of Willis, especially A1-A2 morphology, and the alteration of intraoperative somatosensory evoked potentials (SEP) was evaluated in 68 patients. All carotid endarterectomies were performed under general anesthesia without shunting. Patients were classified into 3 groups based on A1-A2 morphology in preoperative cerebral angiography. The amplitude of intraoperative SEP was decreased in 57.1% of patients with hypoplasia or absence of contralateral A1. On the other hand, amplitude was decreased in 26.7% of patients with hypoplasia or absence of ipsilateral A1 and in 11.4% of patients with patent bilateral A1. Incompleteness of the anterior part of the circle of Willis, especially hypoplasia or absence of contralateral A1, is a significant risk factor for developing of ischemia during clamping of the carotid artery.

Characteristics and distribution of somatosensory evoked potentials in the subthalamic region

The aim of the present study is to evaluate the topographical distribution of somatosensory evoked potentials (SSEPs) in the subthalamic area, including the zona incerta (ZI). Determination of this distribution may help in the correct placement of deep brain stimulation (DBS) leads. Intraoperative SSEPs were recorded from contacts of DBS electrodes at 221 sites in 41 patients: three patients with essential tremor and 38 with Parkinson disease who underwent implantation of DBS electrodes for the relief of severe tremor or parkinsonism. Two distinct SSEPs were recorded in the subthalamic area. One was a monophasic positive wave with a mean latency of 15.8 +/- 0.9 msec, which the authors designated subthalamic P16. Using both cephalic and noncephalic references, subthalamic P16 was only recorded in the ventral part of the ZI (mean 6.6 +/- 1.3 mm posterior to the midcommissure point, 4.8 +/- 1.2 mm inferior to the anterior commissure-posterior commissure line, and 9.7 +/- 0.6 mm lateral to the midline). When bipolar recordings were made, the traces showed a phase reversal at the caudal part of the ZI. The second potential is a positive-negative SSEP recorded throughout the entire subthalamic area. The mean latencies of the initial positive peak and the major negative peak were 13.6 +/- 1.1 msec and 16.4 +/- 1.1 msec, respectively. Several small notches were superimposed on the peaks, and their amplitudes were largest at the contact close to the medial lemniscus. The results indicate that intraoperative SSEPs from DBS electrodes are helpful in refining stereotactic targets in the thalamus and subthalamic areas.

Monitorage cérébral par potentiels évoqués somesthésiques en chirurgie carotidienne. À propos d'une série de 141 carotides opérées

Objective To evaluate postoperative and mid-term results of carotid surgery (CS) with somatosensory evoked potentials (SEP) monitoring. Methods Between 1998 and 2006, 141 CS in 124 patients were performed under general anesthesia. Selective shunting was based on SEP abnormality. Shunting criteria were: reduction up to 50% of the amplitude or latency increasing up to 10%. Early results and follow-up data are analyzed retrospectively. Results Shunting rate was 6%, 3 strokes (two transient strokes) occurred and one patient died of perioperative myocardial ischemia. The cumulative stroke and death rate at 30 days was 1.4%. Conclusions Intra-operative SEP monitoring with selective shunting may be safely performed in carotid surgery.

Prevention and management of the neurological complications during the treatment of severe scoliosis

To discuss the prevention and management of the neurological complications during treatment for severe scoliosis. Seventy-one patients with the coronal Cobb angle more than 80 degrees underwent operation. The average coronal Cobb angle was 96.6 degrees (80 degrees - 135 degrees ), and 31 patients combined with kyphotic deformity with average sagittal Cobb angle 83.0 degrees (52 degrees - 145 degrees ). Fourteen patients were treated with posterior pedicle screw fixation alone, 21 combined with posterior wedge resection, 34 with staged operation, and 2 with combined anterior and posterior approach. Intraoperative somatosensory evoked potentials (SEP) monitoring and wake up test were used in 61 cases, and wake up test was used alone in 10 cases. The average coronal curve correction was 59.2% (average 39.6 degrees ) and sagittal curve correction was 61.6% (average 31.9 degrees ). Thirty-nine patients were followed up with average 51 months (5 - 81 months). Among them, 33 patients achieved solid spinal fusion and the rate of correction loss was 2.1%. Two patients underwent reoperation because of the breakages of the internal fixation. Among 8 patients with neurological dysfunction pre-operatively, 3 patients obtained complete recovery, 1 patient incomplete recovery, and the rest had not recovered because of post-poliomyelitis syndrome. Four of 5 patients developed neurological dysfunction post-operatively obtained complete recovery and 1 partial recovery. Halo-pelvic distraction and apical vertebra osteotomy are useful for increasing the correction rate and decreasing the neurological dysfunction. Intraoperative SEP monitoring combined with wake up test can call attention to early nerve injury. Early using of glucocorticoids and dehydration therapy promptly post-operatively is benefit to prevent neurological complications.

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.

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.

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.

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.

Intraoperative Somatosensory Evoked Potential Monitoring During Cervical Spine Corpectomy Surgery

Retrospective review. To review consecutive cases of cervical spine corpectomy surgery performed with intraoperative somatosensory-evoked potential (SSEP) monitoring. There is controversy about the utility of SSEP monitoring during anterior cervical spine surgery. There is no study in the literature that has specifically evaluated the utility of SSEP monitoring for cervical spine corpectomy surgery. Intraoperative SSEP tracings for 508 patients (average age, 55.7 years; 268 male, 240 female) who underwent anterior cervical fusion with single-level or multilevel corpectomies were reviewed. Intraoperative and postoperative records were analyzed to determine if any new neurologic deficits developed when the patients woke up from anesthesia. The overall incidence of a new postoperative neurologic deficit in this series of patients was 2.4% (11 with nerve root injury, 1 with quadriplegia). The incidence of significant SSEP changes was 5.3% (27 of 508 patients). The most common identifiable cause of SSEP changes was hypotension, and the most common neurologic deficit was deltoid (C5) weakness. One patient had irreversible SSEP changes, and he woke up with new-onset quadriplegia. The calculated sensitivity and specificity of intraoperative SSEP monitoring for detecting impending or resultant intraoperative iatrogenic neurologic injury were 77.1% and 100%, respectively. However, if the isolated nerve root injuries are removed from the analysis, then both the calculated sensitivity and the negative predictive values were 100%. Intraoperative SSEP monitoring can alert the surgeon to adverse iatrogenic intraoperative events with potential for neurologic injury. Most SSEP signal changes are reversible and do not result in a clinical deficit. Isolated nerve root injury appears to be the most common iatrogenic intraoperative injury during cervical spine corpectomy surgery.

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.

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.