Transcranial myogenic motor-evoked potentials after transient spinal cord ischemia predicts neurologic outcome in rabbits

Multipulse transcranial electrical stimulation (TES): normative data for motor evoked potentials in healthy horses

Background

There are indications that transcranial electrical stimulation (TES) assesses the motor function of the spinal cord in horses in a more sensitive and reproducible fashion than transcranial magnetic stimulation (TMS). However, no normative data of TES evoked motor potentials (MEP) is available.

Results

In this prospective study normative data of TES induced MEP wave characteristics (motor latency times (MLT); amplitude and waveform) was obtained from the extensor carpi radialis (ECR) and tibial cranialis (TC) muscles in a group of healthy horses to create a reference frame for functional diagnostic purposes. For the 12 horses involved in the study 95% confidence intervals for MLTs were 16.1–22.6 ms and 31.9–41.1 ms for ECR and TC muscles respectively. Intra-individual coefficients of variation (CV) and mean of MLTs were: ECR: 2.2–8,2% and 4.5% and TC: 1.4–6.3% and 3.5% respectively. Inter-individual CVs for MLTs were higher, though below 10% on all occasions.

The mean ± sd of MEP amplitudes was respectively 3.61 ± 2.55 mV (ECR muscle left) and 4.53 ± 3.1 mV (right) and 2.66 ± 2.22 mV (TC muscle left) and 2.55 ± 1.85 mV (right). MLTs showed no significant left versus right differences.

All MLTs showed significant (p < 0.05) voltage dependent decreases with slope coefficients of linear regression for ECR: − 0.049; − 0.061 ms/V and TC: − 0.082; − 0.089 ms/V (left; right). There was a positive correlation found between height at withers and MLTs in all 4 muscle groups. Finally, reliable assessment of MEP characteristics was for all muscle groups restricted to a transcranial time window of approximately 15–19 ms.

Conclusions

TES is a novel and sensitive technique to assess spinal motor function in horses. It is easy applicable and highly reproducible. This study provides normative data in healthy horses on TES induced MEPs in the extensor carpi radialis and tibialis cranialis muscles bilaterally. No significant differences between MLTs of the left and right side could be demonstrated. A significant effect of stimulation voltage on MLTs was found. No significant effect of height at the withers could be found based upon the results of the current study. A study in which both TMS and TES are applied on the same group of horses is needed.

SUMO-1 delays neuronal damage in the spinal cord following ischemia/reperfusion

The present study investigated the protective effects of small ubiquitin-like modifier 1 (SUMO-1) on spinal cord ischemic damage in rabbits. A trans‑activator of transcription (Tat)‑SUMO‑1 fusion protein was prepared, and transient spinal cord ischemia was induced by occlusion of the abdominal aorta for 15 min. Vehicle (glycerol) or 1 mg/kg Tat-1-SUMO‑1 was administered intraperitoneally to the rabbits immediately following ischemia/reperfusion. Administration of Tat-SUMO-1 did not lead to significant alterations in arterial blood gases [partial pressure (Pa)CO2 and PaO2], pH, or blood glucose levels prior to ischemia, 10 min after occlusion or 10 min after reperfusion. Mean arterial pressure was significantly decreased only during occlusion. Motor behaviors were assessed at 24, 48 and 72 h after ischemia/reperfusion using Tarlov's criteria. Administration of Tat‑SUMO‑1 significantly improved Tarlov scores 24 h after ischemia/reperfusion and the number of cresyl violet positive neurons was significantly increased in the ventral horn of the spinal cord compared with the vehicle‑treated group. However, Tarlov scores were consistently decreased at 48 and 72 h after ischemia/reperfusion in the Tat‑SUMO‑1‑treated group, and Tarlov scores and the number of cresyl violet positive neurons were not significantly different between the vehicle‑ and Tat‑SUMO‑1‑treated groups after 72 h. Tat-SUMO‑1 administration significantly ameliorated a reduction in Cu, Zn‑superoxide dismutase activity and an increase in lipid peroxidation 24 h after ischemia/reperfusion; however, these effects were not present at 72 h. These results suggested that Tat‑SUMO‑1 may delay, although not protect against, neuronal death by regulating oxidative stress in the ventral horn of the spinal cord and that combination therapy using Tat‑SUMO‑1 with other compounds may provide a therapeutic approach to decrease neuronal damage.

Effects of adenosine monophosphate-activated kinase in the ventral horn of rabbit spinal cord after transient ischemia

OBJECTIVE

To investigate the effect compound C, an adenosine monophosphate-activated kinase (AMPK) inhibitor, has on motor neurons of rabbit spinal cord after ischemia/reperfusion.

DESIGN

Compound C (30 mg/kg) was administered intraperitoneally to rabbits 30 minutes before ischemia and the animals were sacrificed at 15 minutes after ischemia/reperfusion to measure lactate levels and at 72 hours after ischemia/reperfusion for morphological study.

RESULTS

The administration of compound C did not produce any significant changes in physiological parameters such as pH, arterial blood gas (PaCO(2) and PaO(2)), and blood glucose in rabbit either at 10 minutes before ischemia or at 10 minutes after reperfusion. However, the administration of compound C did significantly ameliorate lactate acidosis at 15 minutes after reperfusion. In addition, the administration of compound C significantly improved the neurological scores of the rabbits and reduced the neuronal death seen in the ventral horn of their spinal cords at 72 hours after ischemia/reperfusion.

CONCLUSIONS

Inhibition of AMPK can ameliorate the ischemia-induced neuronal death in the spinal cord via the reduction of early lactate acidosis.

Methodology of motor evoked potentials in a rabbit model

Spinal cord ischemia (SCI) is a devastating complication of aortic operations. Neuromonitoring using motor evoked potentials (MEPs) is a sensitive modality to detect SCI in humans. We describe a leporine SCI model using MEPs to test pharmaceutical therapeutics and other neuroprotective adjuncts. In 80 rabbits, methods to obtain MEPs in normotensive and ischemic rabbits were developed. The effects of isoflurane, propofol, apnea, and hypotension on lower extremity MEPs were studied. Lower extremity MEPs disappear upon SCI induction in 78 of 78 (100 %) rabbits. Prior to SCI induction and during apneic episodes, lower extremity MEPs were lost in all (100 %) and upper extremity MEPs in one (25 %). Isoflurane was used in four experiments, with loss of lower extremity MEPs in all four (100 %) and loss of upper extremity MEPs in zero. With propofol upper extremity, MEPs were obtainable in 80 of 80 rabbits (100 %) and lower extremity MEPs in 78 of 80 rabbits (97.5 %) prior to SCI induction. The presence of these lower extremity MEPs prior to SCI induction was not correlated with systolic or diastolic blood pressure. Disappearance of MEPs occurred in all 45 rabbits with postoperative lower extremity impairment. MEPs in the leporine model correlate closely with paraplegia. MEPs are influenced by inhaled anesthetics and apnea but not by hypotension alone. Propofol anesthesia provides reliable MEPs. This study provides the basis for a reproducible model of SCI to be used for novel therapeutic drug development.

Can intraoperative motor-evoked potentials predict all the spinal cord ischemia during moderate hypothermic beating heart descending thoracic or thoraco-abdominal aortic surgery?

BACKGROUND AND AIM OF THE STUDY

Paraplegia is a serious complication of descending thoracic or thoraco-abdominal aortic aneurysm (DTAA or TAAA, respectively) surgery. The functional integrity of the spinal cord can be monitored with intraoperative motor-evoked potentials (MEPs). Herein, we evaluated the results and adequacy of MEP monitoring.

METHODS AND RESULTS

Between March 2006 and April 2009, 33 patients (24 males and 9 females) were monitored with MEPs and reviewed retrospectively. The mean age was 50.7 ± 15.2 years. Eighteen and 15 patients underwent TAAA and DTAA repairs, respectively. We routinely used femoro-femoral partial bypass and cerebrospinal fluid (CSF) drainage. If the MEP demonstrated a significant change, prompt protective interventions were performed. During the procedure, 31 patients (93.9%) had a detectable MEP, of whom four had significant MEP changes and only one had an accompanying alteration in the somatosensory-evoked potential. In-hospital mortality occurred in two patients (6.0%) because of mesenteric ischemia and sepsis, respectively. Postoperative paraplegia developed in two patients (6.0%), one with an undetectable MEP and another with no significant intraoperative MEP change. Both patients had hypotensive events and impaired CSF drainage in the immediate postoperative period. Permanent paraplegia persisted in one patient. In four patients with intraoperative MEP changes, paraplegia did not occur.

CONCLUSIONS

Although intraoperative monitoring of MEP has been shown to be effective in detecting cord ischemia during DTAA or TAAA surgery, it is not definitive and cannot predict all neurologic deficits. Other postoperative preventive strategies such as CSF drainage and maintaining a high blood pressure are important to prevent paraplegia.

Excessively high systemic blood pressure in the early phase of reperfusion exacerbates early-onset paraplegia in rabbit aortic surgery

OBJECTIVE

We have demonstrated that therapeutic augmentation of systemic blood pressure during spinal cord ischemia plays an important role in minimizing spinal cord injury in both experimental and clinical aortic surgery. However, there remain concerns that excessively high blood pressure during spinal cord reperfusion may aggravate the reperfusion injury. The purpose of this study is to investigate the effect of high blood pressure during spinal cord reperfusion on postoperative neurologic outcomes after aortic surgery in rabbits.

METHODS

Experiments were performed using a rabbit spinal cord ischemia-reperfusion model in 2 randomly divided groups: (1) In the HR group, the mean blood pressure was maintained at a high level (121 +/- 1.3 mm Hg) during reperfusion with intravenously administered phenylephrine; and (2) in the CR group, the mean blood pressure was not medically controlled (75 +/- 9.1 mm Hg) during reperfusion. Neurologic and histologic assessments and evaluation of early reperfusion injury were performed.

RESULTS

In the HR group, slow and incomplete recovery of transcranial motor-evoked potentials (P = .02) and low neurologic scores (P < .005) were observed during spinal cord reperfusion compared with the CR group. At 48 hours of reperfusion, there were significantly fewer viable neuron cells, more apoptosis, and more perivascular edema with gray matter vacuolation in the HR group (P < .001 for each). At 3 hours, myeloperoxidase activity (P = .0021), vascular permeability (P = .0012), and superoxide generation (P < .0001) were significantly increased in the HR group.

CONCLUSION

Excessively high blood pressure in the early phase of spinal cord reperfusion increased reperfusion injury in the spinal cord, leading to exacerbation of early-onset paraplegia. Avoidance of spinal cord reperfusion with high blood pressure may be one management strategy in thoracoabdominal aortic surgery.

The value of motor evoked potentials in reducing paraplegia during thoracoabdominal aneurysm repair

OBJECTIVE

Paraplegia after thoracoabdominal aortic aneurysm (TAAA) repair mainly occurs in patients with Crawford extent I and II. We assessed the impact of monitoring spinal cord integrity and the subsequent adjusted surgical maneuvers on neurologic outcome in repairs of type I and II TAAAs.

METHODS

Surgical repair of TAAAs was performed in 112 consecutive patients with extent type I (n = 42) and type II (n = 70) aneurysms. The surgical protocol included cerebrospinal fluid drainage, moderate hypothermia, and left heart bypass with selective organ perfusion. Spinal cord function was assessed by means of monitoring motor evoked potentials (MEPs). Significant decreased MEPs always generated adjustments, including raising distal aortic and mean arterial pressure, reattachment of visible intercostal arteries, or endarterectomy of the excluded aortic segment with revascularization of back bleeding intercostal arteries.

RESULTS

Motor evoked potential monitoring could be achieved in all patients. By maintaining a mean distal aortic pressure of 60 mm Hg, MEPs were adequate in 82% of patients. Increasing distal aortic pressure restored MEPs in all patients. In 19 patients (17%), MEPs decreased significantly during aortic cross-clamping because of critical spinal cord ischemia. MEPs returned in all patients after spinal cord blood flow was re-established except in three patients with type II TAAA in whom MEPs could not be restored, and absent MEPs at the end of the procedure corresponded with neurologic deficit. Delayed paraplegia developed in two patients owing to hemodynamic instability with insufficient mean arterial blood pressure to maintain adequate spinal cord perfusion.

CONCLUSION

Monitoring MEPs is a highly reliable technique to assess spinal cord ischemia during TAAA repair. A surgical protocol including cerebrospinal fluid drainage, left heart bypass, and monitoring of MEPs can reduce the paraplegia rate significantly. Adjusted hemodynamic and surgical strategies induced by changes in MEPs could restore spinal cord ischemia in most patients, preventing early and late paraplegia in all type I patients. In type II patients, early paraplegia occurred in 4.2% and delayed neurologic deficit in 2.9%. Despite all available measures, complete prevention of paraplegia in type II aneurysms seems to be unrealistic.

The adverse effect of back-bleeding from lumbar arteries on spinal cord pathophysiology in a rabbit model

OBJECTIVE

The purpose of this study was to evaluate the adverse effect of back-bleeding from the lumbar arteries on spinal cord pathophysiology in a rabbit model.

METHODS

White rabbits were divided into 3 groups. Through laparotomy, the abdominal aorta was clamped below the renal artery and above the aortic bifurcation for 15 minutes. In group 1 (n = 13), back-bleeding from the lumbar arteries was drained from the aorta during aortic clamping. In group 2 (n = 10), back-bleeding was not drained. Group 3 (n = 6) was the sham-operated group. Postoperative hind limb function was evaluated using the modified Tarlov scale, and cell damage was analyzed by counting the number of intact motor neurons and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-positive neurons.

RESULTS

At 4 hours after operation, all animals were neurologically impaired in group 1 and normal in group 2. Motor neurons were significantly damaged in group 1 compared with groups 2 and 3 (P < .05). Forty-eight hours later, almost all animals were neurologically and pathologically damaged in groups 1 and 2. There was no difference in the number of normal motor neurons between the two groups, but the number of TUNEL-positive cells in group 2 was significantly larger than those in group 1.

CONCLUSIONS

Rabbits with 15-minute aortic clamping in the infrarenal portion showed delayed paraplegia, and those with back-bleeding from lumbar arteries showed early onset of paraplegia. The prevention of back-bleeding from intercostal arteries and lumbar arteries during thoracoabdominal aortic surgery was considered to reduce spinal ischemic injury.

Usefulness of transcranial motor evoked potentials during thoracoabdominal aortic surgery

BACKGROUND

The purpose of this study was to evaluate the efficacy of myogenic transcranial motor evoked potentials (tc-MEPs) for spinal cord ischemia in the repair of descending thoracic or thoracoabdominal aortic aneurysms.

METHODS

Intraoperative tc-MEPs was used in 72 patients who underwent the repair of descending thoracic (n = 24) or thoracoabdominal aortic aneurysms (n = 49) classed as Crawford I in 10 patients, II in 12, III in 23, and IV in 3. There were 52 men and 20 women, and their mean age was 64.9 +/- 12.8 years. Tc-MEPs were recorded by transcranial electrical stimulation and compound muscle action potentials.

RESULTS

The hospital mortality rate was 5.6% (n = 4), and the incidence of neurologic deficits was 11.1% (n = 8). All patients whose MEP amplitude recovered to more than 75% of the baseline showed normal spinal function, and 8 of 9 patients whose MEP amplitude decreased to below 75% of the baseline at the end of the procedure showed neurologic deficits postoperatively. The sensitivity of tc-MEPs was 100% and specificity was 98.4%. Latency in patients with postoperative paraplegia was 123% +/- 9% and was significantly prolonged at the end of the procedure.

CONCLUSIONS

Tc-MEPs were very sensitive and specific to spinal cord ischemia with reduced amplitude and prolongation of the latency period. Tc-MEPs are considered a useful monitor of spinal cord ischemia during descending thoracic or thoracoabdominal aortic surgery.