Electrospinogram and spinal and cortical evoked potentials in experimental spinal cord trauma.

Studies in 28 traumatized cats showed the following acute changes after spinal cord compression in the cord segment below the trauma: 1) increase in size of the spinal cord evoked potential; 2) increase in size of the electrospinogram; and 3) increase in frequency of the electrospinogram.     

Effect of graded hypoxia on cortical and spinal somatosensory evoked potentials.

Cortical somatosensory evoked potential (CSEP), spinal somatosensory evoked potential (SSEP), and electroencephalogram were recorded in rats under pentobarbital anesthesia. After baseline recordings in room air (21% O2), animals were subjected to a graded hypoxia at 15.75%, 10.5%, and 5.25% oxygen levels for 10 minutes. Each level of hypoxia was followed by a 15-minute reoxygenation period. With a moderate hypoxia (15.75% O2), measured latencies for the CSEP and the SSEP were not significantly different compared with baseline (p greater than 0.05). The CSEP amplitude showed a significant increase (p = 0.02) during reoxygenation after the moderate hypoxia. Change in the latency or amplitude of SSEP at 15.75% hypoxia or during the reoxygenation period was not significant compared with the room air (p greater than 0.05). No change in the electroencephalogram was noticed with the moderate hypoxia. At severe hypoxia (10.5% O2), 80% of the animals lost CSEP within 2 minutes. The loss of CSEP was concomitant with significant attenuation of the electroencephalogram waves. The SSEP was resistant to the severe hypoxia and was present in all animals. We concluded that hypoxia affects CSEP with the tendency to increase the amplitude at moderate hypoxia (15.75%) and loss of the latency and amplitude with severe (10.5%) and extreme (5.25%) hypoxia.     

Inhibitory amino acid effects upon cortical evoked potentials

The amplitude of both P1 and N1 waves of the cortical evoked potentials are significantly increased by topical application of GABA and taurine but not of glycine. This suggests a possible depressant effect of both GABA and taurine at superficial cortical layers.     

Pudendal cortical somatosensory evoked potentials

To determine normal reference latencies pudendal cortical somatosensory evoked potentials were evaluated in 20 healthy volunteers. The dorsal nerve of the penis or clitoris was stimulated electrically and the cortical response was recorded from the CZ-2 point (2 cm. behind the central vertex). Reproducible responses were obtained and reference values were established.     

Comparison of the effects of sevoflurane and propofol on cortical somatosensory evoked potentials

Background. Propofol (P) and sevoflurane (S) are potential anaestheticagents if electrophysiological monitoring is required duringspinal surgery. They allow rapid recovery and do not depresscortical somatosensory evoked potentials (SSEP) as much as otheragents. The effects of these agents on SSEP have not been comparedbefore. Methods. Twenty-four patients were allocated randomly to receiveeither S (n=12) or P (n=12). SSEP evoked by electrical stimulationof the posterior tibial nerve at the ankle were recorded beforeanaesthesia. The cortical potential P40 was recorded (latencyP40 and amplitudes N29P40 and P40N50). The anaesthetic concentrationwas adjusted gradually to obtain three predetermined rangesof values of bispectral index (BIS): 45–55, 35–45and 25–35. For each range, a stable state was maintainedfor 10 min and SSEP were recorded. Results. For the BIS 45–55 range, compared with preoperativevalues, P40 latency increased during S [mean change +2 (SD 0.6)ms] but not during P [+0.4 (0.2) ms (P= 0.12)] and both amplitudes(N29P40 and P40N50) decreased with S. Increasing S concentrationcaused a dose-dependent depression of SSEP. P did not have astatistically significant effect on the recordings and the signalsremained stable in each BIS range. Conclusion. Sevoflurane affected SSEP recordings in a dose-dependentfashion. Propofol had a minimal effect on SSEP recordings. Br J Anaesth 2002; 88: 785–9     

皮层体感诱发电位在脊柱脊髓疾患诊治中的应用

目的：评价皮层体感诱发电位（CSEP）在脊柱脊髓疾患诊治中的临床应用价值。方法：120例患者用Frankel分级判断脊髓功能，行CSEP术前检查，术中监护以及术后疗效评估，并分析应用不同标准的监测结果。结果：（1）CSEPⅠ型表现者全部为FrankelA级；Ⅱ型主要为B，C级，Ⅲ型主要为,C,D，Ⅳ型主要为D，E级。（2）Ⅰ-Ⅳ型CSEP表现者疗效分别为0,54.2%,82.8%,84.2%;(3)行椎体肿瘤切除，椎管内肿瘤切除，脊柱侧凸凹侧撑开及颈椎后路“单开门”时最易引发CSEP变化。（4）应用不同标准行术中监测灵敏度均为100％，特异度分别为85．6％，93．3％，误诊率分别为14．4％，6．7％，漏诊率均为0。结论：CSEP与Franke分级，临床疗效有良好的相关性；CSEP灵敏度高，可及时反映出脊髓功能的变化，提高脊髓手术的安全性；CSEP术中监测标准具有一定弹性，常因病情，体位及操作不同而变化。     

Utilization of somatosensory evoked cortical potentials in spinal cord injury. Prognostic limitations

The prognostic value of somatosensory evoked cortical potentials (SECP) for clinical recovery was studied in 71 patients with complete (28) and incomplete (43) spinal injuries. While the absence of an SECP was associated with no clinical recovery, the presence of an SECP was of little value in predicting the clinical state at the time of examination or the potential for recovery.     

Intra-operative recording of cortical somatosensory evoked potentials as a method of spinal cord monitoring during spinal surgery

The experience with cortical somatosensory evoked potential (SEP) recording during 13 cases of spinal neurological surgery is described. Good quality cortical SEPs were obtained in eight patients with a variety of intradural and extradural spinal disorders. The short latency components of these waveforms were stable during anaesthesia with nitrous oxide, 0.5% halothane and fentanyl. Fluctuations in signal amplitude were, however, common. In the one patient in whom the cortical SEP waveform was distorted intra-operatively, there was an increased neurological deficit. In one normal and four patients with impairment of dorsal column function, no intra-operative cortical SEP was recorded. In these five patients spinal SEPs were recorded rostral to the level of spinal disease. Monitoring spinal cord function using cortical SEPs can provide useful neurophysiological information, however, there are limitations to its utility. These relate to difficulties in signal acquisition, the low signal amplitude, attenuation of the signal during intramedullary surgery and uncertainties in signal interpretation. All these problems are exacerbated if the patient has a pre-operative clinical somatosensory deficit. Although most of these problems can be overcome using spinal SEP monitoring, intra-operative SEP recordings are not an infallible guide to spinal cord integrity since they reflect the functional status of only the dorsal column-medial lemniscus pathway.     

Experimental lumbar spinal stenosis. Analysis of the cortical evoked potentials, microvasculature, and histopathology

An animal model of lumbar spinal stenosis was developed in which the pathophysiology of this condition could be examined. Four experimental groups, each containing six dogs, were studied. One group had a laminectomy of the sixth and seventh lumbar vertebrae only; these animals served as controls. In the three other groups, a laminectomy was performed and the cauda equina was constricted by 25, 50, or 75 per cent to produce chronic compression. Cortical evoked potentials were recorded preoperatively, immediately after constriction, and at one, two, and three months postoperatively. Daily neurological examinations were carried out, and the neurological deficits were graded using the Tarlov system. After three months of constriction, the cauda equina of three dogs in each group was examined histologically, and the vascular circulation was examined by latex and India-ink injection with a modification of the Spalteholz technique. The animals in the control group showed no neurological abnormalities, no changes in cortical evoked potentials, normal microvascularity, and no histopathological changes in the nerve roots or the spinal cord. The dogs in which the cauda equina had been constricted 25 per cent had no neurological deficits, mild changes in cortical evoked potentials, slight histological changes, and venous congestion of the root and dorsal root ganglion of the seventh lumbar nerve. The dogs in which the cauda equina had been constricted 50 per cent had mild initial motor weakness, major changes in cortical evoked potentials, edema and loss of myelin in the root of the seventh lumbar nerve, and moderate or severe venous congestion of the root and dorsal root ganglion of the seventh lumbar nerve. The dogs in which the cauda equina had been constricted 75 per cent had significant weakness, paralysis of the tail, and urinary incontinence; two dogs recovered by the third month, but all had neurogenic claudication for three months. All six dogs had dramatic changes in cortical evoked potentials and had complete nerve-root atrophy at the level of the constriction. There was blockage of axoplasmic flow and wallerian degeneration of the motor nerve roots distal to the constriction and of the sensory roots proximal to the constriction, as well as degeneration of the posterior column. Severe arterial narrowing at the level of the constriction and venous congestion of the roots and dorsal root ganglia of the seventh lumbar and first sacral nerves were also present. Cortical evoked potentials revealed neurological abnormalities before the appearance of neurological signs and symptoms.(ABSTRACT TRUNCATED AT 400 WORDS)     

Somatosensory cortical evoked potentials: a review of 100 cases of intraoperative spinal surgery monitoring

A review of our experience with evoked potential monitoring of over 100 spinal procedures is summarized here. Typical results of somatosensory cortical evoked potential (SCEP) testing found that latency of responses increased slightly and amplitude decreased substantially from preanesthesia to predistraction with no further changes. SCEP results are effected by many factors, but when they are understood and recognized, evoked potential monitoring can play a significant role in recognizing potential problems and preventing postoperative neurological problems in patients undergoing spinal surgery.     

Noninvasive intraoperative monitoring of motor evoked potentials under propofol anesthesia: effects of spinal surgery on the amplitude and latency of motor evoked potentials

We present the results of intraoperative monitoring of motor evoked potentials from 34 patients undergoing spinal surgery under total anesthesia with intravenously administered propofol. Intraoperative recording was performed with transcranial electrical stimulation. Two groups of patients were studied: 1) a control population of 26 patients undergoing lumbar discectomy for prolapsed intervertebral disc, all of whom had normal preoperative motor conduction; and 2) a population of 8 patients undergoing neurosurgical procedures for spinal tumor (5 patients) and spinal arteriovenous malformation (3 patients), all of whom had abnormal preoperative neurological signs and abnormal preoperative motor conduction. In the first group, electromyographic responses were recorded intraoperatively either from the 2nd dorsal interosseous muscle of the hand (5 patients) or from the 1st dorsal interosseous muscle of the foot (21 patients). In the second group, responses were recorded intraoperatively either from the 1st dorsal interosseous muscle of the foot (7 patients) or from the anterior tibial muscle (1 patient). Intraoperative monitoring of motor function was successful in 88.5% of the patients in the control group. Propofol anesthesia caused a reduction in response amplitude to 7% of baseline values obtained from conscious relaxed subjects. Intraoperative monitoring was successful in 87% of the patients in the pathological group. We observed significant changes in both amplitude (greater than 50%) and/or onset latency (greater than 3 ms) from the intraoperative baseline that indicated either improvement (3 patients) or deterioration (2 patients) in motor conduction within minutes of surgical maneuvers anticipated to alter spinal cord function. Only permanent complete loss of intraoperative motor conduction (1 patient) correlated with a significant change in the postoperative neurological state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Peroxide lipid and evoked spinal potentials in experimental spinal cord ischemia

The author of this report has studied peroxide lipid and evoked potentials of the spinal cord during ischemia and after reperfusion. In addition, he has studied effects of vitamin E (V.E.) upon ischemic spinal cord. The ischemia of the spinal cord was experimentally produced by clamping the thoracic aorta of Wistar rats and subsequently removing the clamps. Wistar rats were given diet containing 2 IU/100 g (control group) or 50 IU/100 g (V.E. group) of alpha-tocopherol acetate for 6 weeks before experiments. In the V.E. group the quantity of thiobarbituric acid reactive substance (TBARS) in the spinal cord after clamp removal was lower than the control group. The V.E. content in the spinal cord indicated a negative correlation to the TBARS values. The evoked spinal potentials in both groups disappeared due to spinal cord ischemia. The control group displayed wave form loss earlier than the V.E. group. It is conceivable that lipid peroxidation correlate to the tissue damage following spinal cord ischemia and reperfusion, and V.E. has the preventive effect to the damage.     

Compound muscle action potentials and spinal evoked potentials in experimental spine maneuver

In this study, the authors evaluated the effects of spine manipulations, similar to those used in scoliosis surgery, on the compound muscle action potential (CMAP) and spinal evoked potential (SEP) in 25 cats: a distraction maneuver was performed in ten, a rotation in five, and a combined (distraction and rotation) procedure in ten cats. Compound muscle action potential was only minimally changed by the rotation maneuver alone in all five cats. Distraction resulted in earlier deterioration of CMAP than SEP; when CMAP was no longer elicitable in ten cats, seven still showed measurable SEP. All ten cats became paraplegic. With the combined procedure, both CMAP and SEP were abolished earlier than with distraction alone. This was observed in all ten cats becoming paraplegic. The authors further extended the study to ten rabbits having experimentally induced scoliosis. Following corrective surgery with distraction and derotation, eight rabbits lost both CMAP and SEP. Two lost CMAP with still recordable SEP. All ten rabbits became paraplegic. These findings suggest that monitoring CMAP is a more sensitive measure than SEP, and that the spinal cord is more vulnerable to a combined distraction and derotation maneuver than to either one alone.