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.     

Experimental study on spinal cord monitoring--changes in spinal cord evoked potentials during vertical direction distraction of the spinal cord

Experiments were carried out on 18 adult dogs ranging from 9.0 to 11.5 kg. The dogs were intubated and anesthetized with Halothene oxygen, and then mounted on a stereotaxic spinal apparatus. Facetectomies and a discectomy between L1 and L2 vertebrae were performed readily to give traction force to the spinal cord. Spinal cord function was monitored by the first and second negative deflections (I and II, respectively) of the descending spinal cord evoked potentials (descending SCEP) elicited at T7 and recorded at L4 through bipolar catheter electrodes. Both of them were inserted at the midline of the dorsal epidural space. The study was conducted in two parts. In the first part, the cyclic distraction-release program was carried out until motor function was impaired. Distraction was increased in increments of 5 mm, each time maintained for 10 minutes and then totally released for 10 minutes. If neurological deficits in the hind limbs were confirmed by the wake-up test, which was performed every 10 minutes after distraction and release, the 10 minutes' release period was extended for a total period of 30 minutes. The first change in the experimental protocol was transient augmentation of the amplitude of the II deflection which was always observed on a slight distraction, while the I deflection did not change in its amplitude and latency. Each distraction produced a reversible slight reduction of the amplitudes with delay of latencies of the I and II deflections before motor disturbance occurred. However, at a certain traction level paraparesis accompanied by irreversible decrease of amplitudes and delay of latencies was observed, which was confirmed by the wake-up test. At this point, which was designated as the critical point, SCEPs were so time dependent that only a slight amplitude reduction was noted immediately after distraction, but it decreased quickly in a short time during this traction level. Histopathology and microangiography did not show any hemorrhage in the spinal cord of any of the specimens, although there were formation of perivascular space, rupture of a part of nerve fibers in the white matter and findings of acute degeneration in the grey matter. In the second part of this study, a small amount of distraction was introduced until the amplitude of the II deflection depicted transient augmentation, which had a mean amplitude of 167.8 per cent as compared to the control. This enhancement returned approximately to the normal value within 10 minutes by total release.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of spinal cord ischemia on compound muscle action potentials and spinal evoked potentials following spinal cord stimulation in the dog

We recorded the compound muscle action potentials (CMAP) from the soleus muscle and spinal evoked potentials (SpEP) from the caudal spinal cord after stimulation of the rostral spinal cord via epidural electrodes in 18 dogs. We examined the changes of CMAP and SpEP after the cord was made ischemic by clamping the aorta at different levels. Clamping the abdominal aorta below the artery of Adamkiewicz (five dogs) did not change either CMAP or SpEP significantly. When the thoracic aorta was clamped above the radicular and Adamkiewicz arteries (10 dogs), CMAP disappeared entirely within 5-10 min of occlusion, but SpEP showed only minimal latency prolongation limited to the late peaks in seven of 10 dogs. In the remaining three dogs, both CMAP and SpEP disappeared within 30 min of occlusion but with the more rapid deterioration of CMAP than of SpEP. Progressive ligation of lumbar arteries (three dogs) from caudal to rostral levels did not change CMAP until ligation of Adamkiewicz artery. Then CMAP disappeared, but SpEP remained unchanged. These findings suggest that CMAP and SpEP are mediated through different pathways and that CMAP reflect anterior cord function. The described electrophysiologic technique would be useful to monitor spinal cord motor function during surgery of the spine, spinal cord, or thoracoabdominal aorta.     

The influence of spine distraction on cat spinal cord blood flow and evoked potentials

The changes of spinal cord blood flow (SCBF) and spinal cord evoked potential (SCEP) due to spine distraction were analyzed in 30 cats. Spine distraction was performed at L1/2 level at which spinal bodies were separated surgically. SCBF was measured by means of a microsphere technique before, during and after spine distraction and SCEP elicited by spinal cord electrical stimulation was recorded simultaneously. With slight spine distraction (SCEP amplitude 80-100%), SCBF was increased significantly over normal value. SCBF was decreased significantly by further distraction (SCEP 50-80%), but was recovered over normal value after the release of distraction. When severe distraction (SCEP less than 50%) was applied, decreased SCBF around L1 level was irreversible. These results suggested that the disorder of SCBF regulating system due to spine distraction could be expected by analyzing changes of the SCEP.     

Monitoring for spinal cord ischemia by use of the evoked spinal cord potentials during aortic aneurysm surgery

Purpose: This clinical study was to evaluate changes of evoked spinal cord potentials (ESCPs) elicited by direct spinal cord stimulation and to determine their relation to spinal cord ischemia during aortic aneurysm surgery.Methods: We monitored descending ESCPs from the thoracic spinal cord and lumbar enlargement after cervical spinal cord stimulation (thoracic descending ESCP and lumbar descending ESCP), and segmental ESCP at lumbar enlargement elicited by bilateral tibial nerve stimulation in 22 aortic aneurysm surgical operations.Results: ESCP changes were classified into three types: (1) decrease of amplitude in lumbar descending ESCP and segmental ESCP; (2) decrease of amplitude in segmental ESCP alone; (3) decrease of amplitude in all ESCPs. The late negative waves of both lumbar descending ESCP and segmental ESCP were more sensitive than other components of ESCPs. Postoperative paraplegia occurred in the two cases that showed persistent diminution of amplitude in the late negative waves. Segmental ESCP was less reliable than lumbar descending ESCP, because it depended entirely on the adequate perfusion of the lower extremities.Conclusions: Lumbar descending ESCP was the best method for the spinal cord ischemia during aortic aneurysm surgery. Spinal cord ischemia could be detected by diminution in the amplitude of the late negative wave of lumbar descending ESCP. The recovery amplitude of the late negative wave after declamping correlated with the neurologic outcome. (J VASC SURG 1994;20:826-33.)     

缺血和再灌流对脊髓血流量及运动诱发电位的影响

本文采用家兔失血性休克模型，使血压下降至３０ｍｍＨｇ维持３０ｍｉｎ后再灌流，让血压回升到正常范围。观察缺血再灌流期 ＳＣＢＦ和 ＳＥＰ变化。缺血期平均动脉压 ３０～４０ｍｍＨｇ，脊髓 Ｔ１２及Ｌｌ节段灰质血流量减少５７％～６４％，白质血流量减少３２％～５０％；ＳＭＥＰ的潜伏期明显延长（Ｐ＜０．００１），各波的波幅降低并有２５％～６７％的波幅消失。再灌流期当血压回升到９０～１３０ｍｍＨｇ时，灰质血流量仍低于伤前（Ｐ＜０．０１），白质血流量无显著差异．ＳＭＥＰ潜伏期仍明显延长（Ｐ＜０．０５），除Ｐｌ波波幅下降有统计意义外，其它各波幅无差异，波幅消失占２５％～３３．３％。光镜下见脊髓存在损伤性病理变化，显示缺血再灌流后脊髓组织仍然存在继发缺血性病理损害和神经功能障碍。     

Somatosensory evoked potentials in the detection of spinal cord ischemia in aortic coarctation repair

Cortical somatosensory evoked potential (SEP) monitoring was used in 15 patients 2 to 50 years old undergoing repair of aortic coarctation to detect the onset of spinal cord ischemia during the cross-clamp period. Three different response patterns were observed. In 8 patients (53%), the SEP remained unchanged throughout the cross-clamping. This was designated a type 1 response. Six patients (40%) showed a gradual deterioration in the SEP after 15 minutes of cross-clamping (type 2 response). All SEPs returned to normal levels within 5 minutes of release of the clamp. One patient (7%) demonstrated a decline in SEP commencing prior to the application of the cross-clamp when an intercostal vessel was controlled with slings. The SEP completely disappeared within 5 minutes of cross-clamping, but after 19 minutes the repair was completed and the SEP returned within 3 minutes of reperfusion (type 3 response). No patient sustained neurological sequelae of repair. We believe that SEP monitoring offers the potential to identify the patient at risk of developing spinal cord ischemia intraoperatively before irreversible damage occurs. However, it is susceptible to deep halothane anesthesia, which abolishes all cortical responses and requires expert monitoring.     

Comparison of spinal cord evoked potentials and peripheral nerve evoked potentials by electric stimulation of the spinal cord under acute spinal cord compression in cats

STUDY DESIGN: Spinal cord evoked potentials and peripheral nerve evoked potentials after spinal cord stimulation were recorded under acute spinal cord compression in 19 cats. OBJECTIVES: To investigate the effects of acute compression upon grey matter and white matter by comparing both potentials. METHODS: We compared peripheral nerve evoked potentials, recorded at the biceps brachii branch of the musculocutaneous nerve, with descending spinal cord evoked potentials, recorded from the lumbar spinal cord, by stimulation to the C2 level, under compression of the C6 segment. RESULTS: The amplitude of both potentials decreased with increased compression. The second wave of peripheral nerve evoked potentials, which are motor fibre action potentials, decreased sooner than those of the spinal cord evoked potentials. CONCLUSION: These findings indicate that peripheral nerve evoked potentials are sensitive to acute damage of the segmented compression. This suggests that grey matter is more vulnerable to compression than white matter.     

Relationship between duration of spinal cord ischemia and postoperative neurologic deficits in animals

Twenty hogs were administered the following procedures before, during, and after overdistraction of the spinal column at T5-T6: somatosensory (SEP) and neurogenic-motor evoked potentials (NMEPs), hydrogen clearance procedures, Stagnara wake-up tests, and aortic-injection of silastic plastic. To ensure that overdistraction was possible, a nonosseous, circumferential osteotomy was made at T5-T6 and distraction applied in one-ratchet increments using Harrington instrumentation. Overdistraction was maintained for 3, 5, 6, 10, 15, 20, 25, or 30 minutes. Results indicated that the duration of overdistraction, as represented by lost NMEPs, was always correlated with the animal's clinical status on wake-up test. If overdistraction was maintained more than 6 minutes, 100% of the animals demonstrated positive wake-up results; if maintained between 5 and 6 minutes, 75% demonstrated positive wake-up results; and if maintained less than 5 minutes, only 25% demonstrated positive wake-up results. Time-to-loss of the NMEPs and SEPs, after onset of overdistraction, fell within two groups: slow and fast. In the slow group, it required slightly more than 20 minutes (mean = 20.6) for the potentials to be lost, while in the fast-loss group data were lost in slightly less than 4 minutes (mean = 3.6). Blood flow studies and inspection of the spinal cord revealed that the mechanism of action for the slow group appeared to be ischemia of the spinal cord that extended several centimeters above and below the site of maximum distraction. In the fast-loss group, it appeared that gross structural damage, with some very localized ischemia, were the mechanisms of actions influencing the integrity of the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between duration of spinal cord ischemia and postoperative neurologic deficits in animals

Stagnara wake-up tests, blood flow measures, somatosensory evoked potentials (SEPs), and neurogenic-motor evoked potentials (NMEPs) were elicited from 20 hogs before and after spinal cord overdistraction at L3-L4. Overdistraction was maintained from 5 to 30 minutes after loss of NMEPs. Results suggest that the longer the duration of overdistraction the greater the likelihood of paraplegia. Blood flow measures indicated that reduced perfusion was greatest at the distraction site but extended proximally and distally. Finally, NMEPs were more sensitive to onset of overdistraction and a more valid indicator of paraplegia than SEPs. NMEPs should provide the surgeon with more time for initiation of intervention techniques than SEPs. Because NMEPs and SEPs provide information regarding different spinal cord tracts, the authors continue to use both methods for monitoring the functional integrity of the human spinal cord during corrective spine surgery.     

Prevention of spinal cord ischemia after cross-clamping of the thoracic aorta--monitoring of spinal cord perfusion pressure and somatosensory evoked potentials

The pressure difference between the mean distal aortic pressure (MDAP) and the cerebrospinal fluid pressure (CSFP), defined as the spinal cord perfusion pressure (SCPP), as well as somatosensory evoked potentials (SEP) were monitored intraoperatively to detect and prevent intraoperative spinal cord ischemia in 24 patients who required cross-clamping of the descending thoracic aorta. A temporary axillo-femoral shunt, utilizing a 10 mm woven Dacron tube graft, was employed in 10 patients and partial cardiopulmonary bypass was employed in fourteen. Ischemic SEP changes were seen in six patients. Two patients, whose SCPPs were 32 and 35 mmHg, showed a complete loss of SEP and subsequently developed paraplegia. In the other four cases, increase of the MDAP and/or withdrawal of cerebrospinal fluid were performed to increase the SCPP to more than 60 mmHg when ischemic SEP changes occurred. The SEP gradually recovered in two of these cases. The ischemic SEP changes seen in one patient, who had the longest aortic cross-clamping time, (175 minutes) returned to normal immediately after unclamping. In another case, who had a thoracoabdominal aortic aneurysm, the intercostal arteries were reimplanted since the ischemic SEP changes did not revert. These four patients recovered without any neurological deficit. In the other 18 cases without ischemic SEP change, SCPP was kept at more than 40 mmHg during aortic cross-clamping. We conclude that the SCPP should be maintained at more than 40 mmHg during aortic occlusion, and increased to more than 60 mmHg when ischemic SEP changes occur, by increasing MDAP and/or withdrawing cerebrospinal fluid in order to prevent postoperative paraplegia.     

A clinical study on intra-operative spinal cord monitoring with spinal evoked potentials for scoliosis

Spinal cord monitoring with the spinal cord evoked potentials using direct spinal cord stimulation is a safe and reliable method. The purpose of this study was to determine the degree of the potential change that is permissible to avoid severe neurological complications. Three hundred and fifty-four patients with spinal disorders were monitored with this method. The peak amplitude of the potential used as an indicator of the spinal cord function was evaluated quantitatively. The amplitude changes of those with neurological complication were compared with those without complication. The results in 135 patients with scoliosis were analyzed. False negative results were obtained in two patients who had only slight paresthesia. In the patients with normal spinal cord function, up to 50% reduction of the amplitude was permissible. Spinal monitoring is also useful in the improvement of operative technique because it can immediately disclose injury to the cord resulting from surgical misconduct.     

Experimental study of spinal cord evoked potentials in cats

Assessment of function of the spinal cord utilizing spinal cord evoked potentials (SEP) has become a useful diagnostic tool. In the present study, various aspects of characteristics of SEP were analyzed. The basic waveform of conductive SEP consisted of two major components, namely, N1 and N2, whose conduction velocities along the dorsal surface of the cord were 74 m/s and 55 m/s, respectively. Halothane inhalation caused reduction of N2 amplitude, whereas asphyxia caused latency delay of N2. Significant amplitude reduction of N1, N2 (p less than 0.005) and considerable latency delay of N1 were noted in ventral epidural recording. Although there was no relationship between severity of injury and the appearance of positive potentials, N2 tended to be positive-going in heavy injury. Findings of positive potentials showed that N1 originated in the area of ventral gray matter through the ventro-lateral column and N2 through the dorsal column.     

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.     

An experimental study of spinal cord evoked potentials and histologic changes following spinal cord heating

To study the safety of hyperthermia cancer treatment, canine spinal cords were heated with radio waves to between 43 C and 47 C for 30 minutes. Spinal cord evoked potentials (SCEP) studied by epidural recording after epidural stimulation showed shortened latency and unchanged amplitude at 44 C or below. At 45 C or above, reduction of amplitude combined with shortened latency was observed, a phenomenon that has not hitherto been reported. After heating to 45 C, SCEP recovered with the reduction of temperature, but histologic examinations showed pigment exudation, vacuolation, and hemorrhage. These results suggest that tolerable spinal cord temperature should not exceed about 44 C.     

Recording of spinal somatosensory evoked potentials for intraoperative spinal cord monitoring

The authors' experience with intradural and epidural recording of spinal somatosensory evoked potentials (SSEP's) during 26 cases of spinal surgery is described. The techniques of monitoring spinal cord function provided good quality SSEP waveforms in patients both with and without neurological deficits. The SSEP configuration and peak latencies remained stable for up to 5 hours during anesthesia with nitrous oxide, halothane, and fentanyl. Patterns of baseline SSEP's were characteristic of different spinal segments. Distortion and asymmetry of these baseline patterns were seen in several patients with spinal neoplasms. Loss of waveform components during surgery occurred with profound hypotension, overdistraction of the vertebral axis, dorsal midline myelotomy, and removal of intramedullary tumors. Persistent loss of waveform components was associated with an acquired neurological deficit. Fluctuations in the amplitude of the SSEP's were common but were not associated with postoperative neurological deficits. Spinal cord monitoring by means of SSEP recording would appear to be useful during extradural spinal surgery, but there are limitations associated with this technique during some types of intradural surgery.     

脊髓诱发电位的实验研究

为探索脊髓诱发电位（Spinalcordevokednotentials，SCEP）在术中监测的安全范围，将刺激和记录线电极分别置于24只大耳白兔T7～T8、L4～L5间隙硬障外，记录正常电位后对脊髓施加纵向牵张力，至实验要求的波幅。波幅下降至正常的80％组脊髓组织结构轻微改变，脊髓功能正常；下降至50％组及＜50％组则出现不可逆损害。结果表明，SCEP波形稳定，其波幅下降至80％是脊髓损伤的危险信号，下降至50％或50％以下将产生不可逆的脊髓损伤。