Response of spinal cord blood flow and motor and sensory evoked potentials to aortic ligation

Intraoperative evoked potentials in patients with ossification of posterior longitudinal ligament

Preoperative somatosensory evoked potentials (preSEPs) are used to evaluate the severity of myelopathy, and intraoperative neurophysiological monitoring (IONM) is used to reduce iatrogenic damage during operations. However, the correlation between preSEPs and IONM on postoperative neurologic deterioration (PND) in ossification of the posterior longitudinal ligament (OPLL) has not been studied. Thus, under the hypothesis that the patients with deteriorated preSEPs would be more likely to have significant changes in intraoperative SEPs (ioSEPs), and that this would be correlated with PND, we investigated the prognostic value of preSEPs on IONM and PND. This retrospective study included 265 patients who underwent preSEPs and IONM between January 2015 and July 2019. Muscle strength, the sensory scale of the Japanese Orthopaedic Association score examined within 3 days preoperatively, and at 48 h and 4 weeks postoperatively, was analysed. PreSEPs and intraoperative SEPs (ioSEPs) were recorded by stimulating the median and tibial nerves. Intraoperative motor evoked potentials (ioMEPs) were elicited by transcranial electrical stimulation over the motor cortex. PreSEPs latency prolongation of the median and tibial nerves showed significant correlations with ioSEPs. PMD at 48 h or 4 weeks after surgery correlated with ioSEPs and ioMEPs amplitudes. Postoperative sensory deterioration (PSD) at 48 h or 4 weeks after surgery correlated with latency prolongation of ioSEPs. There was a positive correlation between amount of blood loss and maximum percentage of ioSEPs latency prolongation and a negative correlation with PMD at 48 h and 4 weeks postoperatively. PreSEPs predict significant changes in ioSEPs. Furthermore, bleeding control is important to reduce PMD in OPLL.

Quantitative analysis of motor evoked potentials in the neonatal lamb

Evoking motor potentials are an objective assessment method for neuromotor function, yet this was to our knowledge never done in neonatal lambs. There is neither a method for standardized quantification of motor evoked potentials (MEPs). We first aimed to evaluate the feasibility of MEP recording in neonatal lambs and test its validity. Second we aimed to develop an algorithm for its quantification and test its reliability since manual input is required. We recorded myogenic MEPs after transcranial motor cortex stimulation in 6 lambs aged 1–2 days. MEPs were also measured in one lamb undergoing Neuro-Muscular Blockade (NMB) and another undergoing lumbar spinal cord (SC) transection, both serving as controls. We computed 5 parameters using a custom-made algorithm: motor threshold, latency, area-under-the-curve, peak-to-peak amplitude and duration. Intra- and inter-observer reliability was analyzed. MEPs could be easily recorded, disappearing after NMB and SC transection. The algorithm allowed for analysis, hence physiologic readings of the parameters in all 4 limbs of all lambs were obtained. Our method was shown to have high intra- and inter-observer ( ≥70%) reliability for latency, area-under-the-curve and peak-to-peak amplitude. These results suggest that standardized MEP recording and analysis in neonatal lambs is feasible, and can reliably assess neuromotor function.

Development of a modified model of spinal cord ischemia injury by selective ligation of lumbar arteries in rabbits

STUDY DESIGN

Experimental study.

OBJECTIVE

The aim of this study is to develop a modified model of spinal cord ischemia in rabbits.

SETTINGS

Shenzhen Key Laboratory of Spine Surgery, Shenzhen, China.

METHODS

In total, 20 New Zealand rabbits were divided into the following four groups according to the level of ligation of bilateral lumbar arteries: (1) group A, sham group, no ligation, n=5; (2) group B, ligation of bilateral lumbar arteries at three levels (L2-L4, n=5); (3) group C, ligation of bilateral lumbar arteries at four levels (L2-L5, n=5); and (4) group D, ligation of bilateral lumbar arteries at five levels (L1-L5, n=5). The latency of motor-evoked potentials was measured intraoperatively and the modified Tarlov grades were scored, followed by a histological observation of spinal cord, on the seventh day after surgery.

RESULTS

All 10 rabbits in Group A and Group B were electrophysiologically, neurologically and histologically normal. In Group C, moderate spinal cord ischemia injury was found in three of five rabbits: they had prolonged latency of motor-evoked potentials and neuronal karyopyknosis in the anterior horn of spinal cord, and the average Tarlov score was 4.2±0.8. In Group D, severe spinal cord ischemia injury was recorded in all the five rabbits: the latency of motor-evoked potential prolonged in one rabbit, whereas the waveform disappeared in four rabbits; loss of neurons and vacuolation of gray matter were seen in spinal cord sections, and the average Tarlov score was 0.6±0.9.

CONCLUSION

Selective ligation of lumbar arteries was a modified method to induce feasible and reproducible model of spinal cord ischemia in rabbits.

Nerve monitoring changes related to iliac artery compression during anterior lumbar spine surgery

BACKGROUND CONTEXT

There are no studies in the literature that correlate compression of the iliac vessels resulting in obstruction of blood flow with changes in nerve monitoring parameters during anterior lumbar surgery.

PURPOSE

To determine whether there is significant compression of the iliac vessels that can cause temporary nerve root ischemia or limb ischemia that could be responsible for loss of somatosensory evoked potentials (SSEP) while retractors are in place for exposure during anterior lumbar interbody fusion (ALIF).

SETTING

Patients coming to the operating room for ALIF from levels L2-L3 to L5-S1 would be studied for nerve monitoring changes during the procedure with particular attention to the intervals just before placement of a retractor, while the retractor was in place and immediately after removal of the retractor.

PATIENT SAMPLE

Forty-five consecutive patients were studied for changes in SSEP and oxygen saturation (SaO(2)) while undergoing ALIF.

OUTCOME MEASURES

Patients were considered to have lost saturation if the SaO(2) decreased to below 90%. Patients were considered to have abnormal SSEP with any increase in latency and decrease in amplitude.

METHODS

SSEP and SaO(2) were monitored continuously and simultaneously before exposure of the disc spaces, during exposure with retractors in place and after removal of the retractors.

RESULTS

Thirteen of 23 patients with exposure at L4-L5 had both loss of SSEP signals and loss of SaO(2) with exposure. All 13 patients had return to normal saturation and recovery of the SSEP signals within 15 minutes of removal of the retractors. Both of these are significant correlations (p<.001).

CONCLUSION

This study showed that the majority (57%) of patients undergoing ALIF at the L4-L5 level are subject to compression of the left iliac vessels enough to cause desaturation distally as measured by pulse oxymetry. This vascular compromise, as well as the return to normal saturation, correlates with changes noted in SSEP soon after both deployment and removal of the retractors used for exposure. The mechanism appears to be a transient ischemic response. Failure of the SSEP signals to recover may be diagnostic of left iliac artery thrombosis.

Spinal cord blood flow and pathophysiological changes after transient spinal cord ischemia in cats

OBJECTIVE

The goal was to study the hemodynamics and regional pathophysiological changes in the spinal cord after transient vascular occlusion in cats.

METHODS

We measured spinal cord blood flow (SCBF) continuously in the lumbar region with a laser-doppler flowmeter, before, during, and after spinal cord ischemia induced by balloon occlusion of the thoracic aorta, in 24 cats (divided into three groups) and simultaneously recorded the evoked spinal cord potentials (ESPs). In each group (n = 8), 10-, 20-, and 30-minute ischemic loading was performed. All animals were evaluated neurologically 36 hours later, and then their spinal cords were examined histologically.

RESULTS

The amplitude of ESPs decreased 10 minutes and disappeared 20 minutes after occlusion. SCBF increased to as much as 2 times the control values after reperfusion and decreased gradually in all groups. Then, in all animals in the 10-minute group and six animals in the 20-minute group, SCBF returned to the control values, which were subsequently maintained throughout the experiment, and ESPs returned to normal patterns within 1 hour. For all animals in the 30-minute group and two in the 20-minute group, hypoperfusion after recirculation, irreversible amplitude changes in ESPs, postischemic paraparesis, and pathological ischemic changes in the lower thoracic and lumbar spinal segments were recognized.

CONCLUSION

Our results showed that > 20-minute occlusion of the thoracic aorta in cats resulted in irreversible spinal perfusion disorders and that the monitoring of SCBF and ESPs could be useful for predicting potential neurological deficits. Furthermore, postischemic hypoperfusion may have an important role in the development of secondary spinal cord ischemia, resulting in severe neurological dysfunction. This observation suggested the possibility of therapeutic modification of the secondary processes inducing hypoperfusion after spinal ischemia.

Response of spinal cord blood flow to the nitric oxide inhibitor nitroarginine

OBJECTIVE

The extent to which nitric oxide (NO) is involved in the modulation of spinal cord blood flow (SCBF) in the uninjured and injured cord is unknown. To elucidate these questions, the following experiments in anesthetized rats were conducted.

METHODS

Because NO is an unstable free radical with a half-life of seconds, its role can be understood through the study of the NO synthase inhibitor L-NG-nitroarginine (L-NOARG). L-NOARG was administered intravenously for 30 minutes at a dose of 100 or 500 micrograms/kg/min in 12 and 10 uninjured animals, respectively. SCBF fluctuations at C7-T1 were measured using laser doppler flowmetry. In a second set of 12 rats, L-NOARG (500 micrograms/kg/min) was administered 10 minutes before spinal cord injury using a modified aneurysm clip at C7-T1 and continued for 30 minutes thereafter.

RESULTS

In the uninjured animals, L-NOARG was associated with a dose-dependent increase in mean arterial pressure of 20 to 80% above baseline (P = 0.0001), together with a dose-related decrease in SCBF (P = 0.0373). In the injured animals, L-NOARG was associated with a 48% increase in mean arterial pressure. With L-NOARG, the changes in SCBF from baseline after injury were similar to those of noninjured controls (n = 25) and significantly less than injury controls (n = 18) or those receiving phenylephrine (n = 8).

CONCLUSION

NO synthase inhibitors, by reducing available NO, cause systemic vasoconstriction and a decrease in SCBF in the uninjured spinal cord. In the injured spinal cord, the administration of L-NOARG results in a redistribution of blood flow with an augmentation in posttraumatic SCBF at the injury site.

Efficacy of high dose amino acid solution on spinal cord injury induced by focal Nd:YAG laser irradiation

In this experimental study, a neodymium:yttrium-aluminium-garnet (Nd:YAG) laser was used to induce highly reproducible focal spinal cord lesions in anaesthetized guinea pigs. The efficacy of high dose amino acid solution (HDAAS) on this injury is investigated. Experiments were performed on 36 animals divided into three groups; sham operated controls, laser irradiated surgical controls, and amino acid groups. Acute responses to injury were evaluated with somatosensory (SSEP) and motor evoked potentials (MEP) and functional recovery was assessed for 8 weeks using the inclined plane technique. In the laser irradiated surgical control group, MEP disappeared one hour after the laser injury, but SSEP revealed changes of amplitude and latency. In this group, the average value of the inclined plane at 24 hours after the laser application was 45.3 +/- 1.4 degrees. In the amino acid group, at the sixth hour of injury, MEP and SSEP changes improved with infusion of HDAAS for 4 hours. This improvement was statistically significant (for latency of SSEP U = 140 p < 0.05). Inclined plane value at 24 hours after the laser application was 65.5 +/- 1.2 degrees in this group. This study showed that application of Nd:YAG laser irradiation on the spinal cord induced spinal cord injury which presented as paraparesis, HDAAS may provide significant therapeutic protection in secondary damage following this injury and may have a potential role in the treatment of acute spinal cord injury.