A study of spinal cord ischemia during aortic cross-clamp--evoked spinal cord potential and histological analysis of the spinal cord

The relationship between the evoked spinal cord potential (ESP) and the histological findings of the spinal cord after thoracic aortic cross-clamp was studied. Thoracic aorta was cross-clamped in 23 dogs and ESP was monitored before, during, and after cross-clamping. Incidence of paraplegia and histological findings were studied after the dogs recovered from the procedure. Aortic cross-clamp was maintained for 60 minutes in 20 dogs (Group A). And cross-clamp was released 10 minutes after the amplitude of ESP became lower than 20% of control in 3 dogs. (Group B). In group A, three types of ESP changes were detected; ESP became lower or lost during cross-clamping in type 1 response, ESP remained unchanged in type 2 response, and ESP returned after transient loss during cross-clamping in type 3 response. Four of five dogs with type 1, none of nine with type 2, two of five with type 3 response showed paraplegia. One of the dogs with type 2 response showed paraparesis. ESP could not detected in one dog, in which traumatic spinal cord injury during laminectomy caused paraplegia. In Group B, all dogs showed type 1 response and paraplegia. Characteristic histological finding of the spinal cords of the dogs with paraplegia was the ischemic necrosis mainly in the gray matter. Necrotic foci were limited in the posterior horn in mild, in the anterior and posterior horn in moderate changes. And neurons were lost in entire gray matter in severe histological changes. In the spinal cords of the dogs with spastic paraplegia, severe histological changes were limited in the lower lumbar region.(ABSTRACT TRUNCATED AT 250 WORDS)     

Importance of extrasegmental vessels for spinal cord blood supply in a chronic porcine model

IObjective: Our purpose was to investigate the interaction of the important components of spinal cord blood supply in the pig model to enable its use for future studies of spinal cord protection. Methods: 25 juvenile pigs (20-22 Kg) underwent serial intercostal (IC) or lumbar artery (LA) ligation until disappearance of motor evoked potentials (MEPs). Pigs underwent sequential craniocaudal (IC/LA ligation alone (n=5); following clamping of both subclavian arteries (n=4)m, or clamping of the median sacral artery (MSA, n=4); preceded by clamping of the subclavian arteries (n=4), or of the MSA (n=4). Results were verified by Tarlov's scores and perioperative angiography. Results: All animals with MEP loss suffered postoperative paraplegia. Groups were equivalent with regard to stable arterial pressures throughout the experiment, temperature and other physiological parameters. Mean number of clamped IC/LA before MEP loss for cranio-caudal clamping direction was 12.8 +/-0.8 for segmental arteries isolated, 9 +/-0.8 if both subclavian arteries were ligated previously and only 4.3 +/- 0.5 IC if the median sacral artery was clamped before. Mean number of clamped LA for caudo-cranial clamping direction was 5.8 +/-0.9 for segmental lumbar arteries, 5.5 +/-0.6 LA if both subclavian arteries were ligated previously and 3.5 +/-0.6 if the median sacral artery was clamped before. Conclusion: This study confirms the importance of lumbar and MSA arteries to cord viability. It documents the interaction of the subclavian and MSA (roughly equivalent to the hypogastric arteries in humans) with segmental vessels in providing spinal cord blood supply. It also provides the physiologic basis for use of the pig model for studies of spinal cord protection in aortic surgery.     

Doppler ultrasonographic identification of the critical segmental artery for spinal cord protection.

OBJECTIVE: The purpose of this study is to evaluate the possibility of identifying critical segmental arteries (CSAs) based on Doppler ultrasonographic hemodynamics. METHODS: In 18 mongrel dogs, the descending aorta was scanned directly with a 5-MHz linear probe through left thoracotomies and the flow velocities in segmental arteries were measured by pulsed Doppler. The aorta was cross-clamped between Th13 and L1, and flow velocity changes were recorded. According to flow increases, segmental arteries were divided into three groups: arteries with the largest flow increase (L-arteries), arteries with the smallest increase (S-arteries) and other arteries (O-arteries). Animals were divided into three groups. One aortic segment including an L-artery or an S-artery was perfused via a temporary shunt during 30-min aortic cross-clamping distal to the left subclavian artery (Group L or Group S) and neurological outcomes were compared with those of animals without shunting (Group N) after 24 and 48 h. RESULTS: L-arteries had significantly larger flow increases than S- and O-arteries (74.3+/-33.8, 20.4+/-9.8 and 33.3+/-17.8 cm/s, P<0.01). In Group N, five of the six animals were completely paraplegic (Tarlov Grade 0) and the other was Grade 1. In Group S, four animals were Grade 4 and two were Grade 0 after 24h. However, two animals showed delayed paraplegia. Therefore, four animals were Grade 0 and two were Grade 4 after 48 h. All animals in Group L were neurologically normal (Grade 4) at both after 24h (vs. Group N, P=0.0013) and 48 h (vs. Group N, P=0.0013; vs. Group S, P=0.019). CONCLUSIONS: Flow responses to aortic cross-clamping differed among segmental arteries and selective perfusion of L-arteries completely prevented paraplegia. Therefore, L-arteries were considered to be CSAs. Hemodynamic measurement of segmental arterial flow using Doppler ultrasonography could be clinically useful for spinal cord protection during thoracoabdominal aortic surgery.     

Development of spinal cord ischemia after clamping of noncritical segmental arteries in the pig.

BACKGROUND: Blood flow to the thoracolumbar spinal cord is thought to be critically dependent on the arteria radicularis magna. We investigated whether spinal cord blood supply becomes dependent on other, noncritical, segmental arteries if spinal cord perfusion pressure (SCPP) is decreased. The SCPP is equal to the mean arterial pressure (MAP) minus the cerebrospinal fluid (CSF) pressure (SCCP = MAP - CSF). METHODS: The thoracoabdominal aorta was exposed in 10 pigs. Functional integrity of spinal cord motor pathways was assessed with myogenic motor-evoked potentials after transcranial electrical stimulation (tc-MEPs). Using this technique, a group of segmental arteries not critical for spinal cord blood supply was identified. Before, during, and after clamping of the noncritical segmental arteries, spinal cord ischemia was produced by decreasing SCPP by means of increasing CSF pressure, and the SCPP threshold at which tc-MEPs showed evidence of spinal cord ischemia was determined. Ischemic SCPP thresholds, obtained during and after clamping of the noncritical segmental arteries, were compared with the ischemic threshold obtained before clamping (control value). RESULTS: Before noncritical segmental arteries were clamped, ischemic tc-MEP changes occurred when the SCPP was below 15 +/- 5 (SD) mm Hg. With a total of 9 +/- 3 (SD) segmental arteries clamped, the ischemic SCPP threshold was 48 +/- 14 mm Hg (p < 0.01). After the release of all clamps, ischemia occurred at a SCPP of 15 +/- 5 (SD) mm Hg. CONCLUSIONS: In this porcine experiment, clamping of originally noncritical segmental arteries significantly reduced the tolerance of the spinal cord to a decrease in SCPP.     

Importance of extrasegmental vessels for spinal cord blood supply in a chronic porcine model.

OBJECTIVE: Our purpose was to investigate the interaction of the important components of spinal cord blood supply in the pig model to enable its use for future studies of spinal cord protection. METHODS: Twenty-five juvenile pigs (20-22 kg) underwent serial intercostal (IC) or lumbar artery (LA) ligation until disappearance of motor evoked potentials (MEPs). Pigs underwent sequential craniocaudal IC/LA ligation alone (n=5); following clamping of both subclavian arteries (n=4), or clamping of the median sacral artery (MSA, n=4). Animals also underwent serial caudocranial clamping of LA/IC alone (n=4); preceded by clamping of the subclavian arteries (n=4), or of the MSA (n=4). Results were verified by Tarlov's scores and perioperative angiography. RESULTS: All animals with MEP loss suffered postoperative paraplegia. Groups were equivalent with regard to stable arterial pressures (64.6+/-3.1 degrees C) throughout the experiment, temperature (36+/-1.1 degrees C) and other physiological parameters. Mean number of clamped IC/LA before MEP loss for cranio-caudal clamping direction was 12.8+/-0.8 for segmental arteries isolated, 9+/-0.8 if both subclavian arteries were ligated previously and only 4.3+/-0.5 IC if the median sacral artery was clamped before. Mean number of clamped LA for caudo-cranial clamping direction was 5.8+/-0.9 for segmental lumbar arteries, 5.5+/-0.6 LA if both subclavian arteries were ligated previously and 3.5+/-0.6 if the median sacral artery was clamped before. CONCLUSION: This study confirms the importance of lumbar and MSA arteries to cord viability. It documents the interaction of the subclavian and MSA (roughly equivalent to the hypogastric arteries in humans) with segmental vessels in providing spinal cord blood supply. It also provides the physiologic basis for use of the pig model for studies of spinal cord protection in aortic surgery.     

Iloprost protects the spinal cord during aortic cross-clamping in a canine model

BACKGROUND: Surgical procedures on the thoracoabdominal part of the aorta make the spinal cord vulnerable to ischemia. Paraplegia is the most severe complication following thoracoabdominal operations. In this study, iloprost was used as an agent to decrease the severity of ischemia and reperfusion injury to the spinal cord during aortic occlusion and declamping. METHODS: Twelve adult mongrel dogs weighing 17+/-2 kg were used in this study. The animals were randomly assigned to either group I, which received saline solution (6 dogs), or group II, which received prostacyclin. Group I was referred to as the control group and group II as the iloprost group. After baseline measurements were completed, the aorta was cross-clamped for sixty minutes distal to the left subclavian artery. No pharmacologic agents were used to control blood pressure in group I. Proximal and distal mean arterial pressures (DMAP) were monitored continuously. DMAP were considered as diastolic pressure in preocclusion and reperfusion periods. Iloprost administration was started at a rate of 5 ng/kg/minute five minutes before the aortic occlusion. This dosage was increased to 25 ng/kg/minute during aortic occlusion. RESULTS: Mean proximal arterial pressure was 147+/-12 mmHg in the control group and 116+/-13 mmHg in the iloprost group at occlusion (p<0.01). Mean distal arterial pressure was 19+/-7 in the control group and 37+/-5 in the iloprost group during clamping (p<0.05). Functional outcome was evaluated according to Tarlov scores 24 hours after the study. Although none of the animals recovered completely from the control group, 4 animals from the iloprost group recovered (p<0.05). Following the neurologic assessment, animals were sacrificed and specimens were taken for the electron microscopic study. Electron microscopic changes documented that severe mitochondrial damage and vacuolisation occurred in the control group. However these changes were more subtle in the iloprost group. CONCLUSIONS: As a result of this study we concluded that iloprost infused before and during clamping of the thoracic aorta mitigates the spinal cord injury due to ischemia and reperfusion following unclamping.     

Prevention of paraplegia in pigs by selective segmental artery perfusion during aortic cross-clamping

PURPOSE: During thoracoabdominal aortic aneurysm repair, a prolonged interruption of the spinal cord blood supply can result in irreversible spinal cord damage. The aim of this study was to investigate whether selective segmental artery perfusion during aortic clamping could prevent paraplegia in pigs. METHODS: Specially designed segmental artery perfusion catheters, which could be attached to an extracorporeal bypass graft system, were used. In experiment I (n = 10), it was assessed whether selective segmental artery perfusion could reverse electrophysiologic evidence of spinal cord ischemia and maintain transcranial motor evoked potentials (tc-MEPs) during 60 minutes of aortic cross-clamping. The abdominal aorta, containing critical segmental arteries, was bypassed through use of an aortoaortic bypass graft system. After the disappearance of tc-MEPs, an aortotomy was followed by selective segmental artery perfusion. In experiment II (n = 10), the aim was to determine whether selective segmental artery perfusion could prevent paraplegia. In five animals (group A), aortic cross-clamping was followed by selective segmental artery perfusion; five control animals (group B) underwent segmental artery blockade only. Postoperative hind limb function and spinal cord histopathology were evaluated on the third postoperative day. RESULTS: In experiment I, tc-MEPs disappeared within 3.7 +/- 3.7 minutes after cross-clamping and returned in all animals in 8.5 +/- 5.3 minutes after selective perfusion. During the study period, tc-MEP amplitudes recovered to a median of 49% (range, 28%-113%) of baseline values. Total bypass graft flow was 880 +/- 294 mL/min, of which 184 +/- 54 mL/min was directed to the selective perfusion catheters. The flow in individual catheters was 52 +/- 13 mL/min. In experiment II, all perfused animals demonstrated normal hind limb function, whereas four of five control animals were paraplegic on day 3 (P =.04) In the perfused animals, histopathologic examination showed either no spinal cord damage or eosinophilic neurons only, whereas in paraplegic controls there was infarction in large areas of the cord (P <.0001). CONCLUSION: In pigs, selective segmental artery perfusion can provide sufficient spinal cord blood flow to prevent paraplegia resulting from 60 minutes of aortic clamping, as shown by clinical outcomes and histopathologic examination.     

Continuous monitoring of cerebrospinal fluid oxygen tension in relation to motor evoked potentials during spinal cord ischemia in pigs

BACKGROUND: Perioperative assessment of spinal cord oxygenation might guide measures to prevent neurologic deficits secondary to ischemic or traumatic damage of the spinal cord. Although cerebrospinal fluid (CSF) partial pressure of oxygen (Po2) measurement has been used to detect spinal cord ischemia (SCI), the diagnostic value and the temporal resolution of CSF Po2 measurement compared with functional assessment of the spinal cord is unknown. This study compared CSF Po2 with transcranial motor evoked potentials (tcMEPs) for detection of experimental SCI. METHODS: The aorta and segmental arteries were exposed in 10 sufentanil-ketamine-anesthetized pigs (weight, 40-50 kg). Myogenic tcMEPs were recorded from the upper and lower limbs, and continuous assessment of CSF Po2 was provided by two Clark-type microcatheters inserted in the lumbar and thoracic intrathecal space. Graded lumbar SCI was produced by sequential clamping of segmental arteries. The relation between CSF Po2 and tcMEP during graded SCI was determined using linear regression. Diagnostic characteristics of CSF Po2 values for clinical SCI were determined using different cutoff points of CSF Po2. RESULTS: Lumbar CSF Po2 (baseline, 44 [interquartile range, 38-54] mmHg) decreased below 50% in all animals and was linearly related to loss of tcMEP amplitude in all animals. The median lumbar CSF Po2 during reduction of tcMEP to less than 25% of baseline was 11 (4-29) mmHg, whereas thoracic CSF Po2 remained constant (40 [28-50] mmHg). During absence of the tcMEP signal, lumbar CSF Po2 was less than 20 mmHg in 80% of the animals. Optimal sensitivity and predictive values of CSF Po2 measurement for SCI were in the range of 40-60% of baseline. CONCLUSIONS: The data indicate that intrathecal Po2 measurement is a sensitive monitoring technique to track real-time changes in local spinal cord oxygenation. Continuous monitoring of CSF Po2 might be applied for evaluation of patients who are at risk for direct or secondary SCI.     

A prolonged spinal cord ischaemia model in pigs. Passive shunting offers stable central haemodynamics during aortic occlusion.

OBJECTIVES: to evaluate the effect of a modified aortic shunt on central haemodynamic variables during experimental thoracic aortic occlusion in a prolonged spinal cord ischaemia model. MATERIAL AND METHODS: central haemodynamic variables were evaluated during aortic cross-clamping. In the shunt group (n=11), after the placement of proximal and distal aortic clamps, distal aortic perfusion was restored through an aortoiliac shunt via the left subclavian artery. In the no-shunt group (n=11), spinal cord ischaemia was achieved with only proximal aortic cross-clamping. The clamping time was 60 minutes in the shunt group and 30 minutes in the no-shunt group. RESULTS: in the no-shunt group, all animals needed inotropic support, vasodilators and buffers during the experiment. None of these drugs were needed in the shunt group. In the no-shunt group, cross-clamping caused a significant increase in mean arterial pressure and heart rate compared to baseline values. These variables were stable in the shunt group during aortic occlusion. In the reperfusion period cardiac output, heart rate and arterial pCO(2)were significantly higher in the no-shunt than in the shunt group. CONCLUSION: the present experimental spinal cord ischaemia model, using double aortic cross-clamping with shunt, offers improved central haemodynamics. This enables the study of prolonged selective spinal cord ischaemia without interaction from vasoactive drugs or systemic reperfusion.     

The effect of direct lidocaine injection into the clamped aortic segment on the spinal evoked potential: early diagnosis for spinal cord ischemia.

PURPOSE: The aim of this study was to identify a method to determine whether segmental artery reconstruction was indicated during aortic clamping. METHOD: Spinal cord evoked potential (SCEP) and regional spinal blood flow were studied in 24 adult dogs. Using the left heart bypass technique, aortic clamping divided the aorta into thoracic, abdominal, and terminal segments. After the occlusion of the descending aorta and discontinuation of the perfusion to the abdominal segment, animals were assigned to four groups: no treatment with perfusion to the terminal aorta (group IA), no treatment with cessation of bypass (group IB), 5% lidocaine administration (5 mg/kg) into the abdominal segment with perfusion to the terminal aorta (group IIA), and lidocaine administration with cessation of bypass (group IIB). RESULTS: Cessation of bypass reduced spinal blood flow and SCEP amplitude. Lidocaine injection allowed for a significant rapid decrease in SCEP amplitude in group IIB compared with group IB (24.2% +/- 13.4% versus 92.3% +/- 33.2%; p = 0.0039). The degree of spinal blood supply was reflected immediately in the magnitude of SCEP amplitude change by the direct lidocaine injection. (group IB versus group IIB; p = 0.023). CONCLUSION: The direct injection of lidocaine into the clamped aorta results in a rapidly change in SCEP in the threat of ischemia and can be used to make an early detection of the segmental arteries perfusing to the spinal cord.     

Prevention of spinal cord injury after cross-clamping of the thoracic aorta

Paraplegia has been a devastating and unpredictable complication following cross-clamping of the thoracic aorta. In this study, the effect of the pressure gradient between the aortic pressure distal to occlusion and cerebrospinal fluid pressure (CSFP), defined as relative spinal cord perfusion pressure (RSPP), on the development of spinal cord injury was investigated. In 32 mongrel dogs, the thoracic aorta just distal to the left subclavian artery was cross-clamped. After a complete loss of somatosensory evoked potentials (SEP) had been confirmed, the dogs were divided into six groups by an additional cross-clamp interval and RSPP as follows: Group I (n = 6): 0 mmHg for 10 minutes; Group II (n = 8): 0 mmHg for 20 minutes; Group III (n = 3): 7.5 mmHg for 20 minutes; Group IV (n = 3): 7.5 mmHg for 40 minutes; Group V (n = 6): 15 mmHg for 40 minutes and Group VI (n = 6): 15 mmHg for 60 minutes. RSPP was adjusted by either withdrawal of cerebrospinal fluid or injection of normal saline solution into the subarachnoid space. SEP were generated by the stimulation of bilateral peroneal nerves. The incidence of postoperative paraplegia was 0% in Groups I and V, 33% in Group III, 50% in Group VI and 100% in Groups II and IV. This study showed that RSPP plays an important role in the development of spinal cord injury during cross-clamping of the thoracic aorta. Therefore, RSPP should be maintained at as high a level as possible in order to prevent spinal cord injury even if SEP disappear during aortic occlusion.     

Evoked spinal potentials as a monitor of spinal cord viability

To determine the diagnostic and prognostic significance of evoked spinal potentials (ESPs), reproducible, compressive spinal cord lesions were produced in dogs under ESP monitoring. Both motor recovery and histologic findings were investigated in relation to the amplitude and persistence of the ESPs. Animals that had moderate, anterior compression (51% of canal width) in which the ESP was maintained had considerable motor recovery. Among animals that had submaximal compression (60%), motor recovery was good in those with persistent ESPs. The compression ratio at which ESPs terminated (67%) was termed the "electrophysiologic maximum tolerable compression." Continuous ESP expiration resulted in irreversible lesions and loss of motor recovery. Compressive spinal cord lesions of reproducible, graded severity were employed for the first time in our study of ESP. Persistence and amplitude were both useful in predicting not only the severity and extent of this type of lesion but also the recovery.     

The prevention of spinal cord ischemia during the operation on the thoracic aorta utilizing the evoked spinal cord potential (ESP)

The evoked spinal cord potential was used for the moniter of the spinal cord ischemia during the operation on the thoracic aorta. At first, experiments were performed on 23 dogs. Following laminectomy and 1t. thoracotomy, evoked spinal cord potential to the stimulation from bipoler electrodes in the midline dorsal subdural space at the level of near L1 were recorded from needle electrode in the intervertebral disk at the level of Th4-5. After baseline measurements, the thoracic aorta was occluded in all dogs by aortic cross-clamping (AXC) distral to the origin of the left subclavian artery. Then 3 types of changes were detected. TYPE-I (n = 8) showed loss of the ESPs during AXC and return after reperfusion. TYPE-II (n = 10) showed no changes during and after AXC. TYPE-III (n = 5) showed return of ESPs after transient loss of them even during AXC. Five of 7 dogs (71%) in TYPE-I and 1 of 5 dogs (20%) in TYPE-III developed paraplegia, but all of them in TYPE-II avoided paraplegia. Secondly, ESP was used for the moniter of spinal cord ischemia during operation on 13 patients. Ten patients showed no changes of ESPs, but 3 showed loss of ESPs during AXC and return after reperfusion of them. No paraplegia appeared. We have concluded that intraoperative ESP monitering is a more reliable indicator of the spinal cord ischemia than other methods previously reported.     

马尾神经慢性压迫的病理变化与脊髓诱发电位和MRI之间的关系

目的:探讨犬马尾神经慢性压迫的病理变化与脊髓诱发电位(CESEP)和M RI之间的关系,为临床诊治该病和判断预后提供实验依据。方法:家犬10只,2只为对照组,8只为实验组,在L5~L6椎板下,潜行置入可控式硅胶水囊,对照组不注水,实验组每周注入0.5m l,在压力为20m m H g(第4周)、60m m H g(第7周)及120m m H g(第9周)和120m m H g持续1周(第10周)后随机抽取2只犬,用诱发电位和M RI检查后处死动物,观察其相应的组织学变化。结果:当压力<60m m H g,椎管狭窄<50%时,诱发电位潜伏期延长,波幅下降,但无统计学意义,M RI示硬膜外脂肪存在,马尾神经无压迫,病理学无器质性变化;当压力≥60m m H g,椎管狭窄≥50%时,诱发电位潜伏期延长,波幅下降,有显著性差异。M RI示硬膜外脂肪消失,受压处硬膜囊明显变细,局部马尾信号增高,病理学示神经纤维出现不可逆变化。结论:随着压力和压迫时间的增加,马尾神经的病理变化逐渐加重,诱发电位和M RI均有相应变化,M RI示椎管狭窄≥50%时病理学上神经纤维出现不可逆变化。     

Continuous Monitoring of Cerebrospinal Fluid Oxygen Tension in Relation to Motor Evoked Potentials during Spinal Cord Ischemia in Pigs

Background: Perioperative assessment of spinal cord oxygenation might guide measures to prevent neurologic deficits secondary to ischemic or traumatic damage of the spinal cord. Although cerebrospinal fluid (CSF) partial pressure of oxygen (Po2) measurement has been used to detect spinal cord ischemia (SCI), the diagnostic value and the temporal resolution of CSF Po2 measurement compared with functional assessment of the spinal cord is unknown. This study compared CSF Po2 with transcranial motor evoked potentials (tcMEPs) for detection of experimental SCI.

Methods: The aorta and segmental arteries were exposed in 10 sufentanil-ketamine-anesthetized pigs (weight, 40-50 kg). Myogenic tcMEPs were recorded from the upper and lower limbs, and continuous assessment of CSF Po2 was provided by two Clark-type microcatheters inserted in the lumbar and thoracic intrathecal space. Graded lumbar SCI was produced by sequential clamping of segmental arteries. The relation between CSF Po2 and tcMEP during graded SCI was determined using linear regression. Diagnostic characteristics of CSF Po2 values for clinical SCI were determined using different cutoff points of CSF Po2.

Results: Lumbar CSF Po2 (baseline, 44 [interquartile range, 38-54] mmHg) decreased below 50% in all animals and was linearly related to loss of tcMEP amplitude in all animals. The median lumbar CSF Po2 during reduction of tcMEP to less than 25% of baseline was 11 (4-29) mmHg, whereas thoracic CSF Po2 remained constant (40 [28-50] mmHg). During absence of the tcMEP signal, lumbar CSF Po2 was less than 20 mmHg in 80% of the animals. Optimal sensitivity and predictive values of CSF Po2 measurement for SCI were in the range of 40-60% of baseline.     

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。     

The vascular supply to the spinal cord and its relationship to anterior spine surgical approaches

Background contextThe understanding of vascular supply to the spinal cord is important given that the evolution of surgical approaches to the spine may bring along the potential for more frequent complications, especially a rare but devastating complication: that of spinal cord ischemia or infarction. To maximally avoid this complication, the relationship between the spinal cord vascularity and the anterior spine surgical approach needs further study.PurposeTo provide a theoretical basis that will allow the spinal surgeon to take appropriate steps to avoid spinal cord ischemia during anterior spinal surgery through anatomic means.Study designSpinal cord vascular casting assessment with cadaveric specimen.MethodsTwenty adult cadaveric specimens (11 men and 9 women) were obtained for the latex perfusion and vessel dissection. In addition, nine patients (seven men and two women) underwent superselective angiography of the spinal cord. The segmental arterial anastomosis and radiculomedullary vessels in the thoracolumbar region were shown and reviewed.ResultsThere were approximately 21 pairs of segmental arteries in the thoracolumbar region. Adjacent segmental arteries were networked with each other. The latex infusion specimens demonstrated 72 anterior radiculomedullary arteries and 177 posterior radiculomedullary arteries in all 20 samples. The anterior and posterior spinal arteries were also networked with each other at several levels. Superselective spinal angiography was consistent with the latex infusion specimens showing.ConclusionsThe variety of anatomy of spinal cord arterial networks is shown, and the relation between the blood supply of certain spinal levels and the potential ischemic complications during the anterior surgical approach is discussed. It is hopefully of benefit to surgeons, after fully understanding the anatomy of these spinal vascular supply structures, that there may be even greater avoidance of vascular compromise in these challenging operations.     

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.     

Influence of preservation or perfusion of intraoperatively identified spinal cord blood supply on spinal motor evoked potentials and paraplegia after aortic surgery

Permanent ligation of arteries supplying blood to the spinal cord in operations for aortic aneurysm can lead to spinal cord ischemia, which can result in either paraparesis or paraplegia. This report describes a rapid method of intraoperative identification of those arteries that supply the spinal cord by use of an intrathecal platinum electrode to detect hydrogen in solution that has been injected into the aortic ostia. Preservation or perfusion of those identified arteries supplying the spinal cord may decrease the rate of postoperative neurologic complications. Of 28 porcine experiments with postoperative observation for 24 hours, there were 3 initial pilot experiments in which saline saturated with hydrogen was injected into the temporarily cross-clamped aorta. Twenty animals were then randomized to (1) preservation of only the vessels sequentially identified to supply blood to the spinal cord from T-13 to L-5 (n = 10); (2) division of the vessels supplying the spinal cord (n = 10). A further five animals underwent perfusion experiments wherein the identified cord arteries were perfused by a shunt, the other nonsupply arteries were divided, and the aorta was kept clamped for 45 minutes. Spinal motor evoked potentials were elicited with an intrathecal electrode and were highly sensitive for paralysis. Paralysis occurred in 0/3 pilot (p less than 0.013 vs division); 8/10 division; 1/10 preservation (p less than 0.0017 vs division); and perfusion 1/5 (p less than 0.025 vs division). Results of a pilot study in eight humans shows that the technique can be used to rapidly identify segmental arteries supplying the spinal cord, to determine if distal perfusion is supplying the spinal cord with blood flow, and if reattached segmental arteries are patent.     

The arterial supply of the human spinal cord: A new approach to the arteria radicularis magna of Adamkiewicz

Summary The arteria radicularis magna (Adamkiewicz's artery) was studied in 30 human spinal cords after arterial injection. The artery was present in all cases, between T 8 and L 2, and was identified by its diameter and position. The arteria radicularis magna was the main blood supply to the lowest region of the spinal cord. In one out of three cases it accompanied the ventral root at T9, and in 80% of the cases studied it was found on the left side. The arteria radicularis magna had a posterior component in 63% of the cases. We did not observe specific radiculo-medullary arteries in the conus medullaris region.