"Threshold-level" multipulse transcranial electrical stimulation of motor cortex for intraoperative monitoring of spinal motor tracts: description of method and comparison to somatosensory evoked potential monitoring

Numerous methods have been pursued to evaluate function in central motor pathways during surgery in the anesthetized patient. At this time, no standard has emerged, possibly because each of the methods described to date requires some degree of compromise and/or lacks sensitivity. OBJECT: The goal of this study was to develop and evaluate a protocol for intraoperative monitoring of spinal motor conduction that: 1) is safe; 2) is sensitive and specific to motor pathways; 3) provides immediate feedback; 4) is compatible with anesthesia requirements; 5) allows monitoring of spontaneous and/or nerve root stimulus-evoked electromyography; 6) requires little or no involvement of the surgical team; and 7) requires limited equipment beyond that routinely used for somatosensory evoked potential (SSEP) monitoring. Using a multipulse electrical stimulator designed for transcranial applications, the authors have developed a protocol that they term "threshold-level" multipulse transcranial electrical stimulation (TES). METHODS: Patients considered at high risk for postoperative deficit were studied. After anesthesia had been induced and the patient positioned, but prior to incision, "baseline" measures of SSEPs were obtained as well as the minimum (that is, threshold-level) TES voltage needed to evoke a motor response from each of the muscles being monitored. A brief, high-frequency pulse train (three pulses; 2-msec interpulse interval) was used for TES in all cases. Data (latency and amplitude for SSEP; threshold voltage for TES) were collected at different times throughout the surgical procedure. Postoperative neurological status, as judged by evaluation of sensory and motor status, was compared with intraoperative SSEP and TES findings for determination of the sensitivity and specificity of each electrophysiological monitoring technique. Of the 34 patients enrolled, 32 demonstrated TES-evoked responses in muscles innervated at levels caudal to the lesion when examined after anesthesia induction and positioning but prior to incision (that is, baseline). In contrast, baseline SSEPs could be resolved in only 25 of the 34 patients. During surgery, significant changes in SSEP waveforms were noted in 12 of these 25 patients, and 10 patients demonstrated changes in TES thresholds. Fifteen patients experienced varying degrees and durations of postoperative neurological deficit. Intraoperative changes in TES thresholds accurately predicted each instance of postoperative motor weakness without error, but failed to predict four instances of postoperative sensory deficit. Intraoperative SSEP monitoring was not 100% accurate in predicting postoperative sensory status and failed to predict five instances of postoperative motor deficit. As a result of intraoperative TES findings, the surgical plan was altered or otherwise influenced in six patients (roughly 15% of the sample population), possibly limiting the extent of postoperative motor deficit experienced by these patients. CONCLUSIONS: This novel method for intraoperative monitoring of spinal motor conduction appears to meet all of the goals outlined above. Although the risk of postoperative motor deficit is relatively low for the majority of spine surgeries (for example, a simple disc), high-risk procedures, such as tumor resection, correction of vascular abnormalities, and correction of major deformities, should benefit from the virtually immediate and accurate knowledge of spinal motor conduction provided by this new monitoring approach.     

The value of somatosensory and motor evoked evoked potentials in pre-clinical spondylotic cervical cord compression

This review focuses on the biomaterials used in urology, in particular, the properties of urethral catheters and ureteral stents currently being used in clinical practice. The importance of biomaterial type, biocompatibility, and encrustations are discussed and explained. Current management of bacterial infection and the importance of biofilms are presented, with recommendations based on published information.     

Somatosensory evoked potential monitoring in cervical surgery: identification of pre- and intraoperative risk factors associated with neurological deterioration

Cortical and subcortical somatosensory evoked potentials (SSEPs) were noninvasively monitored in 191 surgical procedures involving the cervical spine. In nine patients in the poorest neurological condition, SSEPs could not be monitored. Lower limb SSEPs were often too degraded to be useful. Upper limb responses were reliably recorded in 182 procedures, with a sensitivity of 99% and a specificity of 27% in 10 patients who developed neurological signs postsurgery. The aim of monitoring was to detect changes in spinal cord function at a time when neurological deterioration could be prevented or reversed, and these studies alerted the authors to certain clinical and SSEP risk factors associated with deterioration. Clinical and operative risk factors were: 1) poor pre-operative neurological function (one-third of Ranawat Class IIIb patients deteriorated); 2) use of instrumentation (the risk doubled in preoperatively unimpaired patients); 3) upper cervical and clival surgery (the risk tripled); and 4) and multisegmental surgery (increased risk with each additional level). There were SSEP changes in 33 patients. Fifty percent of patients with a complete loss had neurological damage, unlike those who had incomplete loss or whose electrical changes had recovered by the end of surgery. In the authors' view these "false positives" may represent real physiological changes, the effects of which might have been minimized by an alteration in the surgeon's response as a result of the warning. Although these initial studies have made this surgical team more alert to potential problems, the role of intraoperative SSEP monitoring is still being debated.     

Somatosensory evoked potentials and electromyography in spinal cord intraoperative monitoring

Intraoperative monitoring can be defined as an application of several electroneurophysiological techniques for nervous system monitoring throughout the surgery. The principal goal of monitoring is to identify new neurologic impairment early enough to find the cause and to prevent permanent deficits. This paper reviews monitoring techniques during surgery for spinal deformity.     

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)     

Surgical maneuvers placing the sciatic nerve at risk during total hip arthroplasty as assessed by somatosensory evoked potential monitoring

We investigated the influence of hyperthyroidism on relaxant responses of small mesenteric resistance arteries to beta-adrenoceptor agonists and to compounds stimulating the corresponding second-messenger system. Hyperthyroidism was induced by feeding rats for 28 days with 5 mg/kg L-thyroxine (T4)-containing rat chow. This treatment produced a stable hyperthyroid state, as indicated by several biochemical/metabolic and haemodynamic parameters. Preparations of small mesenteric arteries were mounted in an isometric wire myograph. Subsequently, concentration-effect curves were determined for isoproterenol, noradrenaline and salbutamol as well as for forskolin, dibutyryl-cAMP and theophylline. We also determined concentration-effect curves to the beta-adrenoceptor agonists in the presence of ICI 118,551 and CGP 20712A (i.e., in the presence of a selective beta 2- and beta 1-adrenoceptor antagonist, respectively). Apparent pA2-values were calculated to determine which beta-adrenoceptor subtype causes vasodilation. These experiments indicate that beta-adrenoceptor-mediated vasodilation involves both beta 1- and beta 2-adrenoceptors in mesenteric resistance vessels of both hyperthyroid and control rats. In our experiments hyperthyroidism has a sensitizing influence on vascular responses induced by the beta-adrenoceptor agonist isoproterenol and the selective beta 2-adrenoceptor agonist salbutamol. Sensitization to isoproterenol was abolished in the presence of ICI 118,551, whereas it was emphasized in the presence of CGP 20712A. Although this was not fully supported by the results obtained with noradrenaline, these results indicate that the sensitization to beta-adrenoceptor agonists is probably limited to the beta 2-adrenoceptor/G-protein complex and not associated with alterations of the corresponding second messenger system.     

Electroacupuncture and laser stimulation treatment: evaluated by somatosensory evoked potential in conscious rabbits

Tooth pulp generated somatosensory evoked potential (TPSEP) recordings were used to evaluate analgesic responses to Electroacupuncture (EA) and laser stimulation (Ls) treatments in Dutch-hybrid male rabbits. TPSEP recorded 100 trials at 30 minute intervals for 120 minutes. Three groups, EA, Ls and control were analyzed. The EA group received intermittent 4 Hz, intensity 2-10 volts electro-stimulation for twenty minutes. In the Ls group, a gallium aluminium arsenide (GaAlAs) laser diode with wavelength 780 nm, switched pulse frequency 9720 Hz, energy density 0.6 J/point was employed. Both EA and Ls groups received stimulation of the points Ho-ku (LI-4) and Tzu-San-Li (ST-36). Results showed tooth pulp generated noxious stimulation produced a consistent late near-field SEP waveform, which is similar to those recorded in humans and correlated to the sensation of pains, thus confirming that tooth pulp stimulation is a reliable dolormetric index. EA and Ls TPSEP recordings showed decreased peak-wave amplitude in late near-field components. These decreases correlate to analgesia. This technique provides an objective and reliable dolormetric index.     

Selective modification of somatosensory evoked potential during voluntary finger movement in humans

We examined changes in somatosensory evoked potentials (SEPs) during voluntary movement of fingers innervated by the stimulated nerve and those not innervated by the stimulated nerve and the relationship to the kind of movement modality. Analysis showed that the amplitude of most components at F3, C3', and P3, except for P45 at C3, N35 and P45 at P3, decreased during voluntary finger movement tasks. Further, we found that the components of P40 at F3, P45 at C3', and N35 at P3 were increased during the voluntary pulling movement of the second and the third digits compared to those during the voluntary pushing movement of the fourth and the fifth digits, whereas all other components were decreased at F3, C3', and P3. We also found that not all components of SEPs were decreased while some SEPs in middle latency were increased. In conclusion, we confirmed the selectivity in attenuation of the SEPs. Moreover, we noted an interesting finding that the selectivity of attenuation of the SEPs was most frequently observed in the N20, P30 (P25 at F3), N35 (N30 at F3), and P45 (P40 at F3) components at F3, C3', and P3.     

Presurgical functional localization of primary somatosensory cortex by dipole tracing method of scalp-skull-brain head model applied to somatosensory evoked potential

Glutathione S-transferase activity of both the microsomal and soluble fractions was determined in a variety of aquatic macrophytes. The examined enzyme extract was prepared from a combination of leaves and shoots. Four different model substrates were used. The highest conjugation rate was obtained for 1-iodo-2,4-dinitrobenzene, followed by 1-chloro-2,4-dinitrobenzene, p-nitrobenzoyl chloride, and 1,2-dichloro-4-nitrobenzene. Comparison of several samples of Nuphar lutea L. from two different lake areas revealed increased glutathione S-transferase activity in plants from the site contaminated with polyaromatic hydrocarbons.     

Comparison of cerebral oximeter and evoked potential monitoring in carotid endarterectomy

PURPOSE: To assess the cerebral oximeter, which measures regional oxygen saturation (rSO2) continuously and noninvasively, as a cerebral monitor during carotid endarterectomy (CEA). The rSO2 was compared with Somatosensory Evoked Potentials (SSEPs) as an indicator for shunting and as a predictor of postoperative neurological deficits. METHODS: Seventy-two consenting patients undergoing CEA with general anaesthesia were studied. Normocarbia, normothermia and normotension were maintained. Cerebral monitoring consisted of bilateral median nerve SSEPs and the INVOS 3100 cerebral oximeter with the sensor pad placed on the ipsilateral forehead. Decreases in SSEP amplitude of 50% and in rSO2 of 10% were considered clinically significant. Neurological assessment was performed at emergence from anaesthesia, 24 hr postoperatively and at discharge. The rSO2 changes were compared with SSEP changes and with neurological deficits. Statistical analysis was with chi square and analysis of variance P < 0.05 was considered significant. RESULTS: During carotid artery clamping, rSO2 decreased from 72 +/- 8% to 68 +/- 9% and mean arterial blood pressure increased from 92 +/- 14 mmHg to 98 +/- 14 mmHg. In four patients, the carotid artery was shunted because of SSEP changes after cross-clamping. Five patients had > or = 10% decreases in rSO2 following clamp application. Changes in both SSEP and rSO2 occurred in two patients. Three of the four shunted patients had transient postoperative neurological deficits. One patients had a transient deficit without changes in either monitor. There were no persistent postoperative deficits. Compared with SSEPs, rSO2 had a sensitivity of 50% and a specificity of 96%. CONCLUSION: Clinical experience with this evolving technology is ongoing. Its role in neurovascular procedures has yet to be established.     

The cortical representation of somatosensory evoked potentials of the phrenic nerve

Parasitic third-stage larvae of the sheep abomasal nematode Haemonchus contortus develop and molt in vitro to the fourth stage (L4) in 48-72 hr, at which time they begin feeding. Coincident with the third molt, larvae begin to secrete significant amounts of protein into culture fluids, including a zinc metalloproteinase. This culture-derived zinc metalloproteinase differs from a previously described metalloproteinase from infective third-stage larvae (L3[2M]), which mediates the ecdysis process. These differences include time of expression, molecular mass, and substrate specificity. The purified proteinase, from cultures of L4, has a molecular weight of approximately 46 kDa, functions as an endopeptidase, and digests several native proteins of host origin including fibrinogen and fibronectin.     

The effect of thoracic paravertebral blockade on intercostal somatosensory evoked potentials

Streptococcus pneumoniae strains have emerged that are resistant to penicillin (MICs >0.06 microg/mL) and many other beta-lactams. However, some older compounds such as amoxicillin have potency against these pneumococci with altered penicillin-binding proteins, but are labile to beta-lactamases produced by other prevalent respiratory tract pathogens. The interactions of amoxicillin with an enzyme-stable cephalosporin (cefixime) with a long elimination half-life were examined by the checkerboard dilution method versus 39 S. pneumoniae strains (13 resistant, 15 intermediate, and 11 susceptible to penicillin). Among 24 strains with evaluable drug interaction tests, 17 (71%) demonstrated partial or complete synergy. This favorable interaction produces a cefixime susceptibility category change from resistant or intermediate to susceptible for 16 of 28 strains (57%), when combined with < or = 1 microg/mL amoxicillin. Thus, the use of two currently available oral beta-lactams (amoxicillin twice a day + cefixime once a day; three total doses) appears to be a potential alternative treatment with greater spectrum for community-acquired respiratory tract infections pending clinical trial results.     

Localization of functional regions of human mesial cortex by somatosensory evoked potential recording and by cortical stimulation

Previous studies have shown that characteristics of posttraumatic temporomandibular disorders (pTMD) differ considerably from those of nontraumatic or idiopathic temporomandibular disorders (iTMD). Both the rate of recovery and the amount of treatment required appear to be different for both groups. In this blinded study, 14 patients with iTMD and 13 patients with pTMD were examined. Patients submitted to a variety of reaction-time tests and neuropsychologic assessments to test their ability to cope with simple and more complex tasks with and without a variety of cognitive interferences. Clinical examination was used to assess signs of TMD. Eleven of the subjects (six iTMD, five pTMD) consented to a second phase of the investigation, whereby the patients were studied with single-photon emission computerized tomography (SPECT) using 99mTc-hexamethylpropyleneamineoxime (HMPAO). For simple and complex reaction-time tests, the pTMD group was significantly slower than the iTMD group (P < .05 to P < .001). Other neuropsychologic assessment tools such as the Consonant Trigram Test and the California Verbal Learning Test indicated that pTMD patients were more affected by both proactive and retroactive interferences and were more likely to perseverate on a single thought. In clinical examination, pTMD patients demonstrated greater reaction to muscle palpation than did iTMD patients (P < .05). The SPECT results suggested that there were mild differences between the two populations, and further ther studies are required to confirm this finding. The results lend support to the concept that there are differences between pTMD and iTMD populations. It is suggested that although patients with pTMD may have some similarities to those with iTMD, the former population may benefit from being handled somewhat differently and should be assessed and treated using a more broad, multidisciplinary treatment paradigm. These results must be confirmed in studies of larger populations.     

How reliable is the predictive value of SEP (somatosensory evoked potentials) patterns in severe brain damage with special regard to the bilateral loss of cortical responses?

Acrosin, Arysulfatase A, and beta-N-acetylglucosaminidase are three key enzymes localized within the mammalian acrosome that play a pivotal role in the penetration of the oocyte. The objectives of this study were to compare two methods of enzyme extraction based on the activities of these enzymes from equine spermatozoa. Method A utilized a 0.5 M Tris-maleate buffer containing 0.1% Triton X-100 and Hyamine 2389. Method B used 0.05 M Tris-HCl, 0.05 M MgCl2 in 0.05 M Tris-maleate, followed by 0.05 M Tris-maleate containing 0.1% Triton X-100. Results indicated that acrosin was initially bound in an acrosin-acrosin inhibitor complex; this complex was dissociated after incubating the extract in 2 mM HCl. Significant (P < 0.001) increases in acrosin activity were found after-acid extraction from 0.076 U/mg after Method B to 0.327 U/mg after Method A. Arylsulfatase A activity was found to have a higher mean activity (P < 0.03) after Method A (0.012 U/mg) as opposed to Method B (0.007 U/mg). Similarly, beta-N-acetylglucosaminidase was found to have a higher mean specific activity (P < 0.001) after Method A (0.037 U/mg) as compared to Method B (0.008 U/mg). This is the first report of the quantification of these enzymes from equine spermatozoa which can ultimately be used as an index of acrosomal damage in cryopreserved semen, and provide additional insight into biochemical alterations between normal vs. abnormal semen.     

Intra-operative facial nerve monitoring. Its predictive value after skull base surgery

A 65-year-old man was admitted with a diagnosis of arteriosclerosis obliterans. He had a 3-month history of intermittent claudication of the right leg. Physical examination revealed absence of pulsation of the right posterior tibial artery. Contrast angiography of lower extremities showed several obstructive lesions below the right popliteal artery. As interventional and surgical approached were not indicated, the patient was treated with exercise with heparin pretreatment (5,000 IU). As a result, walk distance on a floor was increased from 400 m to 2,000 m, and repeat magnetic resonance angiography revealed increased flow to the right lower extremity. Thus, he was successfully treated with exercise and heparin pretreatment without any side effects.     

Two cases of severe metabolic acidosis after monitoring of evoked spinal cord potential

Evoked spinal cord potential (ESCP) elicited by direct spinal cord stimulation has been applied to monitor the spinal cord function during spinal surgery. We report here two patients who showed excessive muscle contraction and developed severe metabolic acidosis as a result of the stimulation of spinal cord to measure ESCP. These changes were prevented by vecuronium administration prior to ESCP monitoring. These results suggest that excessive muscle contraction by direct spinal cord stimulation may lead to metabolic acidosis. In conclusion, the use of a non-depolarizing muscle relaxant is recommended to prevent the adverse effects of ESCP monitoring.