Detection Of Spinal Cord Ischemia Research Articles

45. Intraoperative neurophysiological monitoring during aortic aneurysm repair: A single center experience and focus on methodological aspects

This study describes our experience with neuromonitoring in thoracoabdominal aortic aneurysms (TAAA) repair, focusing on the set up of a monitoring protocol, aimed to optimize the detection of spinal cord ischemia. A retrospective observational study was carried out on 62 consecutive patients (37 men; mean age 63.8 years) undergoing TAAA repair between February 2016 and March 2017. All patients underwent Motor Evoked Potentials (MEPs), Somatosensory Evoked Potentials (SSEPs), neurophysiological monitoring of peripheral ischemia, and continuous control of other intraoperative variables. The mortality rate was 9.6%, and the incidence of immediate and delayed neurological deficits was 6.4% and 3.2% respectively. Significant MEP changes occurred in 41.6% of patients, recovering in 85% of cases. Permanent MEPs changes occurred in 3 patients (15%), 2 of them developed immediate paraplegia. Significant SSEPs changes occurred in 6 patients (12.2%) and recovered in all but one, awaking with paraplegia. False negative and positive rate were both 1.6%. Our data are consistent with the literature. However, a consensus is still lacking with regard to an intraoperative protocol for monitoring, which limits the comparison of different studies. Our method demonstrated a good reliability and could contribute to the setup of a consensus protocol.

Neurophysiological Intraoperative Monitoring During Aortic Arch Surgery.

Circulatory management during replacement of the aortic arch is complex and involves a period of circulatory arrest to provide a bloodless field during arch vessel anastomosis. To guard against ischemic brain injury, tissue metabolic demand is reduced by systemically cooling the patient prior to circulatory arrest. Neurophysiological intraoperative monitoring (NIOM) is often used during the course of these procedures to provide contemporaneous assessment of brain status to help direct circulatory management decisions and detect brain ischemia. In this review, we discuss the characteristics of electrocerebral activity through the process of cooling, circulatory arrest, and rewarming as depicted through commonly used NIOM modalities, including electroencephalography and peripheral nerve somatosensory-evoked potentials. Attention is directed toward the role NIOM has traditionally played during deep hypothermic circulatory arrest, where it is used to define the point of electrocerebral inactivity or maximal cerebral metabolic suppression prior to initiating circulatory arrest while also discussing the evolving utility of NIOM when systemic circulatory arrest is initiated at more moderate degrees of hypothermia in conjunction with regional brain perfusion. The use of cerebral tissue oximetry by near-infrared spectroscopy as an alternative NIOM modality during surgery of the aortic arch is addressed as well. Finally, special considerations for NIOM and the detection of spinal cord ischemia during hybrid aortic arch repair and emerging operative techniques are also discussed.

Spinal Near-Infrared Spectroscopy Measurements During and After Thoracoabdominal Aortic Aneurysm Repair: A Pilot Study

Near-infrared spectroscopy (NIRS) is a noninvasive technique that allows continuous monitoring of regional hemoglobin oxygen saturation (rSo2). We evaluated its application to survey oxygenation of the spinal cord region during open thoracoabdominal aortic aneurysm (TAAA) repair and postoperatively in the intensive care unit (ICU). We also validated its association with motor-evoked potential (MEP) monitoring during the operation. The rSo2 curves of 15 patients (8 men; mean age, 64.2 ± 7.7 years) were measured continuously with NIRS at spinal cord levels of the thoracic vertebrae T3 (optode 1, reference spot) and T12 (optode 2) during open TAAA repair. T12/T3 ratios were calculated. NIRS measurements were continued in the intensive care unit and stopped 24 hours after the operation. MEP monitoring was performed in all patients during the procedure. No clinical signs of spinal cord ischemia were documented in any of the patients. Continuous NIRS measurements were successfully performed in all patients during and after the operation. T12/T3 ratios were significantly lower in the MEP ratios that were less than 50% compared with the MEP ratios that were 50% or higher (p= 0.037). NIRS is an easily applicable noninvasive tool for continuous surveillance of oxygenation of the spinal cord region during TAAA repair and postoperatively in the intensive care unit. The rSo2 curves provide useful information concerning hemodynamic changes in oxygenation of the spinal cord region and might contribute to early detection of spinal cord ischemia. Further investigation is needed before broad clinical implementation.

Measured versus predicted blood propofol concentrations in children during scoliosis surgery.

Propofol anesthesia is preferred during scoliosis surgery because it suppresses evoked potential spinal cord function less than other drugs and better enables the detection of spinal cord ischemia. In this study, we determined the difference between the true and predicted blood propofol levels during target-controlled infusions in children during scoliosis surgery. Arterial blood propofol measured concentrations (Cm) were compared with predicted concentrations (Cp) approximately every 30 minutes during the maintenance phase of anesthesia in 20 children. Whole blood propofol concentrations were measured using a point-of-care blood propofol analyzer. Anesthesia management was not affected by the study. The median performance error, median absolute performance error, wobble, and divergence were calculated. Children were aged 9 to 17 years and weighed 26.5 to 95 kg. The Paedfusor model was used in 16 children and the Marsh model in 4 children. In 154 blood propofol measurements, the mean difference between the Cm and Cp was 1.5 µg·mL (limits of agreement, -1.4 to 4.5 µg·mL), and the mean performance error was 44.7% (limits of agreement, -40.1% to 130.2%). The median performance error and median absolute performance error for the whole group were 39.8% (range, -20.9% to 103.3%) and 39.8% (range, 20%-103.3%), respectively. The performance errors improved with increase in duration of infusion (divergence, -2.2 [range, -1.03 to 0.13]). Cm was almost always larger than Cp except in 2 children who had consistently lower Cm than Cp (lowest Cm(s) were 1.74 and 1.96 µg·mL when the Cp was 3 µg·mL); both had the Paedfusor model and their body weights were 28 and 33 kg. Propofol target-controlled infusion models had poor performance characteristics in children undergoing scoliosis surgery. Point-of-care propofol assay may enable adjustment of the infusion to better achieve the intended blood level.

Optical Monitoring and Detection of Spinal Cord Ischemia

Spinal cord ischemia can lead to paralysis or paraparesis, but if detected early it may be amenable to treatment. Current methods use evoked potentials for detection of spinal cord ischemia, a decades old technology whose warning signs are indirect and significantly delayed from the onset of ischemia. Here we introduce and demonstrate a prototype fiber optic device that directly measures spinal cord blood flow and oxygenation. This technical advance in neurological monitoring promises a new standard of care for detection of spinal cord ischemia and the opportunity for early intervention. We demonstrate the probe in an adult Dorset sheep model. Both open and percutaneous approaches were evaluated during pharmacologic, physiological, and mechanical interventions designed to induce variations in spinal cord blood flow and oxygenation. The induced variations were rapidly and reproducibly detected, demonstrating direct measurement of spinal cord ischemia in real-time. In the future, this form of hemodynamic spinal cord diagnosis could significantly improve monitoring and management in a broad range of patients, including those undergoing thoracic and abdominal aortic revascularization, spine stabilization procedures for scoliosis and trauma, spinal cord tumor resection, and those requiring management of spinal cord injury in intensive care settings.

Spinal cord protection and thoracic aortic surgery

Spinal cord ischemia remains an important complication of open surgical and endovascular stent graft repair of thoracic and thoracoabdominal aortic aneurysm despite advances in operative technique. Identification of risk factors and interventions to prevent and treat spinal cord ischemia has the potential to prevent spinal cord infarction and the morbidity and mortality associated with paraplegia. Risk factors for spinal cord ischemia are aneurysm extent, open surgical repair, prior distal aortic operations, and perioperative hypotension. Augmenting spinal cord perfusion by increasing arterial pressure, lumbar cerebrospinal fluid drainage, and reattachment of segmental arteries are effective for the treatment of spinal cord ischemia. Early detection of spinal cord ischemia by intraoperative neurophysiologic monitoring and postoperative neurological examination is important to enable immediate treatment to prevent permanent paraplegia. Permanent paraplegia after thoracic and thoracoabdominal aortic aneurysm repair can be prevented in many high-risk patients by early detection and immediate treatment of spinal cord ischemia before it evolves to infarction. The mortality and morbidity associated with permanent paraplegia justifies the risks and uncertainties associated with established therapeutic interventions.

Technique for repair of suprarenal and thoracoabdominal aortic aneurysms

Suprarenal and thoracoabdominal aortic aneurysms represent significant surgical challenges. For patients with associated aortic dissections, current endovascular technology has not been matured to address branch reconstructions that derive from separate lumens, making open surgical reconstruction the only proven method for repair. The required exposures of the thoracoabdominal aorta are expansive, and the extent of aortic replacement mandates efficient technique. Furthermore, a well-orchestrated team of surgeons, nurses, anesthesiologists, and perfusionists are all integral to achieving good outcomes and keeping operative courses tightly managed. Techniques to address extensive aneurysms of the thoracoabdominal aorta are reviewed in detail here, and videos are provided on The Journal website to show relevant anatomical features.

Delayed response of transcranial myogenic motor-evoked potential monitoring to spinal cord ischemia during repair surgery for descending thoracic aortic aneurysm

The efficacy of transcranial myogenic motor-evoked potential (tc-MEP) monitoring during thoracic aortic surgery has been the subject of some reports, because tc-MEP monitoring can rapidly reflect changes in spinal cord blood flow during thoracic aortic cross-clamping. In this article, we present a case in which delayed loss of tc-MEP signals was observed after cross-clamping of the descending thoracic aorta. We must be aware that tc-MEPs recorded from the lower extremities can fail to provide rapid detection of spinal cord ischemia in the upper thoracic level after cross-clamping of the descending thoracic aorta.

Intraoperative spinal cord monitoring during descending thoracic and thoracoabdominal aneurysm surgery

Background Postoperative paraplegia is one of the most dreaded complications after descending thoracic and thoracoabdominal aneurysm surgery. In this study, intraoperative monitoring was applied during resection of descending thoracic and thoracoabdominal aneurysms to detect spinal cord ischemia and help prevent paraplegia. Methods Fifty-six patients (descending thoracic, 25; thoracoabdominal, 31) were monitored intraoperatively with both motor- (MEP) and somatosensory- (SSEP) evoked potentials. MEPs were elicited with transcranial electrical stimulation and recorded from the spinal epidural space (D wave) or peripheral muscles (myogenic MEP). SSEPs were obtained with median and tibial nerve stimulation. Results A total of 16 patients (28.6%) showed MEP evidence of spinal cord ischemia, only 4 of whom had delayed congruent SSEP changes. In 13 patients (23.2%), ischemic changes in MEPs were reversed by reimplanting segmental arteries or increasing blood flow or blood pressure. None of these 13 patients suffered acute paraplegia regardless of the status of SSEP at the end of the procedure, but 1 of them developed delayed postoperative paraplegia after multisystem failure. Three patients (5.4%) who had persistent loss of MEPs despite of recovery of SSEPs awoke paraplegic. Conclusions The results demonstrate that compared with SSEP, MEP, especially myogenic MEP, is more sensitive and specific in detection of spinal cord ischemia, and that intraoperative monitoring can indeed help prevent paraplegia.

The influence of regional spinal cord hypothermia on transcranial myogenic motor-evoked potential monitoring and the efficacy of spinal cord ischemia detection

Objective: Myogenic motor-evoked responses to transcranial electrical stimulation (transcranial myogenic motor-evoked potentials) can rapidly detect spinal cord ischemia during thoracoabdominal aortic aneurysm repair. Recent evidence suggests that regional spinal cord hypothermia increases spinal cord ischemia tolerance. We investigated the influence of subdural infusion cooling on transcranial myogenic motor-evoked potential characteristics and the time to detect spinal cord ischemia in 6 pigs. Methods: Regional hypothermia was produced by subdural perfusion cooling. A laminectomy and incision of the dura were performed at L2 to advance 2 inflow catheters at L4 and L6, to cool the lumbar subdural space with saline solution. Two temperature probes were advanced at L3 and L5, and 1 cerebrospinal fluid pressure line was advanced at L4. Spontaneous cerebrospinal fluid outflow was allowed. Spinal cord ischemia was produced by clamping a set of critical lumbar arteries, previously identified by transcranial myogenic motor-evoked potentials and lumbar artery clamping. The time between the onset of ischemia and detection with transcranial myogenic motor-evoked potentials (amplitude < 25%) was determined at cerebrospinal fluid temperatures of 37°C and 28°C. Thereafter, the influence of progressive cerebrospinal fluid cooling on transcranial myogenic motor-evoked potential amplitude and latency was determined. Results: The time necessary to produce ischemic transcranial myogenic motor-evoked potentials, after the clamping of critical lumbar arteries, was not affected at moderate subdural hypothermia (3.8 ± 0.9 min) compared with subdural normothermia (3.2 ± 0.5 min; P = .6). Thereafter, progressive cooling resulted in a transcranial myogenic motor-evoked potential amplitude increase at 28°C to 30°C and was followed by a progressive decrease. Response amplitudes decreased below 25% at 14.0°C ± 1.1°C. The influence of cerebrospinal fluid temperature on transcranial myogenic motor-evoked potential amplitude was best represented by a quadratic regression curve with a maximum at 29.6°C. In contrast, transcranial myogenic motor-evoked potential latencies increased linearly with decreasing subdural temperatures. Conclusions: Detection of spinal cord ischemia with transcranial myogenic motor-evoked potentials is not delayed at moderate subdural hypothermia in pigs. At a cerebrospinal fluid temperature of 28°C, transcranial myogenic motor-evoked potential amplitudes are increased. Further cerebrospinal fluid temperature decreases result in progressive amplitude decreases and latency increases. (J Thorac Cardiovasc Surg 1999;118:1038-45)

Spinal cord monitoring with myogenic motor evoked potentials: early detection of spinal cord ischemia as an integral part of spinal cord protective strategies during thoracoabdominal aneurysm surgery.

Spinal cord ischemia during resection of thoracoabdominal aortic aneurysms (TAA) can result in lower limb neurological deficits. Spinal cord monitoring can only improve outcome if ischemia is detected before irreversible damage has occurred and protective measures are readily available. Monitorin( spinal cord function with motor evoked potentials (MEPs) is a relatively new technique. With MEP. recorded from the muscle (myogenic MEPs), the vulnerable spinal motoneuronal system is exclusively monitored and ischemia is detected within minutes. Using a strategy aimed at maintaining and restoring spinal cord blood supply (distal aortic perfusion, sequential aortic clamping, and selective segmental artery reattachment), early detection of ischemia allows protective measures to be applied and adjusted immediately, ie, reattaching or safely ligating intercostal arteries, increasing proximal o distal aortic pressures as required, or inducing hypothermia. Recent improvements in the technique fo eliciting myogenic MEPs include multi-pulse stimulation paradigms and the use of a circumferentia cathode. This results in robust and reproducible signals, which are less susceptible to anesthetic interference and allow the use of a constant level of neuromuscular blockade. In conclusion, monitoring myogenic MEPs during a TAA repair has become clinically feasible. The fast detection of spinal cord ischemia allows timely guidance of protective measures.

Monitoring of somatosensory evoked potentials: a primer on the intraoperative detection of spinal cord ischemia during aortic reconstructive surgery.

The acute interruption of blood supply to the spinal cord during thoracic and thoracoabdominal aortic reconstructions, if unabated, inevitably causes neurological injury secondary to regional hypoxia. Techniques that address the multifactorial nature of spinal cord ischemic injury have evolved to preserve neuromotor function. However, the overall incongruity of the spinal cord's vascular anatomy makes it virtually impossible to predict, with any degree of certainty, the duration of aortic cross-clamping (AXC) that can safely be endured. The sensitivity of evoked potential monitoring to the disruption of spinal cord perfusion has led to the emergence of this modality as an effective tool at the surgeon's disposal for the intraoperative assessment of distal aortic perfusion and cord viability during proximal AXC. Somatosensory evoked potentials (SSEP) provide invaluable diagnostic data as to the status of cord function, through the continuous appraisal of signal amplitude and latency. A latency increase, as small as 10% of the pre-AXC value, is linked to a reduction of spinal cord perfusion pressure and thereby associated with a high incidence of neurological impairment. Four discrete types of SSEP responses have been identified to represent differing surgical scenarios during AXC. The Type I response (deterioration of SSEP within 3 to 5 minutes) is indicative of a failure to maintain a distal pressure of at least 60 mm Hg, whereas a Type II signifies adequate distal aortic perfusion. Sudden loss of signal as witnessed in a Type III SSEP implies compromised critical intercostal vessels and indicates their expeditious reimplantation. A gradual (30 to 50 minutes) SSEP "fadeout" corresponds to marginal distal perfusion, suggesting the presence of extensive pathology. Intraoperative evoked potential monitoring, in conjunction with distal aortic perfusion, permits rapid identification and correction of compromised spinal cord blood flow, permitting repair of aortic lesions without the added liability of time constraints.

Clinical application of evoked spinal cord potentials elicited by direct stimulation of the cord during temporary occlusion of the thoracic aorta

Evoked spinal cord potentials elicited by direct stimulation of the cord were used to monitor spinal cord ischemia in 68 patients undergoing temporary occlusion of the thoracic aorta (29 thoracic nondissecting aortic aneurysms, 9 nondissecting thoracoabdominal aneurysms, and 30 dissecting aneurysms). "Immediate" postoperative paraplegia developed in three patients and "immediate" paraparesis developed in one, whereas "delayed" paraplegia developed in two others. During aortic crossclamping, four response patterns of the spinal cord potentials were obtained: (1) no change (n = 53), (2) change with return (n = 10), (3) change with inconsistent return (n = 2), and (4) change without return (n = 3). Neurologic complications occurred in 2%, 0%, 100% of these groups, respectively. Delayed paraplegia developed on the second postoperative day in only one patient with a false-negative result, and the potentials correlated well with this patient's clinical neurologic recovery. The aortic crossclamp time was significantly longer in the patients with "change with inconsistent return" and "change without return" than in the other two groups (p < 0.01). Femoral artery pressure and the cardiopulmonary bypass flow rate were also significantly lower in these groups than in the other two groups (p < 0.02 and p < 0.01, respectively). We conclude that intraoperative monitoring of direct spinal cord responses is useful for the early detection of spinal cord ischemia for assessing the efficacy of surgical countermeasures.

Intraoperative spinal cord monitoring during surgery for aortic aneurysm: application of spinal cord evoked potential

Spinal cord evoked potentials elicited by direct stimulation of the spinal cord were monitored in 21 patients during thoracic or thoraco-abdominal aortic aneurysm surgery. Flexible catherer-type electrodes were used for both stimulating and recording. The basic pattern of the spinal cord evoked potential consisted of an initial spike and a subsequent polyphasic component. The earliest and most frequent alterations after cross-clamping of the aorta were changes in the configuration or amplitude of the polyphasic component. In 13 patients who exhibited no change except minor alterations of the polyphasic component during the initial test clamping for 15 or 20 min, subsequent graft replacements were safely performed without reimplantation of intercostal vessels. In 2 patients who had sudden cardiac arrests, the evoked potential completely disappeared. The polyphasic component disappeared first, followed by the initial spike. Another patient developed acute loss of the potential after the aneurysm was incised, presumably due to distal aortic hypoperfusion. In this case, prolonged distal hypotension resulted in flaccid paraplegia. Intraoperative monitoring of the spinal cord evoked potential is a useful method for the early detection of spinal cord ischemia during surgery requiring aortic occlusion.

Experimental and Clinical Use of Somatosensory Evoked Potentials in Surgery of Aneurysms of the Descending Thoracic Aorta

The use of somatosensory evoked potentials (SEP) for the detection of spinal cord ischemia in surgery of the descending thoracic aorta was studied in nine dogs. Also 18 patients (group A) operated upon without distal aortic perfusion and 10 patients (group B) operated upon with distal aortic perfusion were studied. Tibial nerve stimulated SEP was used. Crude SEP characteristics and the reliability of SEP were assessed. In dogs the preservation of SEP corresponded with absence of neurological damage (p less than 0.02). Loss of SEP and late or absent recovery were associated with presence of neurological damage histopathologically proved (p less than 0.05). In group A SEP recording was affected by peripheral ischemia whereas this phenomenon was absent in group B during perfusion. In group A no relation was observed between the preservation, loss, and recovery of signal and the presence of neurological damage. In group B loss and recovery of SEP corresponded with assumed reperfusion of the spinal cord. Additional SEP recording obtained from stimulation of the skin overlying the fourth lumbar vertebra and of the medullary conus were preserved over a longer period. In patients this type of SEP was especially useful and reliable in case distal aortic perfusion was not used.

Somatosensory evoked potentials in the detection of spinal cord ischemia in aortic coarctation repair: J.C. Pollack, M.P. Jamieson, and McWilham. Ann Thorac Surg 41:251–254, (March), 1986

Somatosensory evoked potentials in the detection of spinal cord ischemia in aortic coarctation repair: J.C. Pollack, M.P. Jamieson, and McWilham. Ann Thorac Surg 41:251–254, (March), 1986

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 halo-thane anesthesia, which abolishes all cortical responses and requires expert monitoring.

Intraoperative Detection of Spinal Cord Ischemia Using Somatosensory Cortical Evoked Potentials during Thoracic Aortic Occlusion

Paraplegia remains a devastating and unpredictable complication of surgical procedures requiring temporary occlusion of the thoracic aorta, interruption of important spinal radicular vessels, or both. Intraoperative monitoring of the physiological integrity of the spinal cord should permit the early detection of spinal cord ischemia, the judicious and timely institution of corrective measures, including bypass or shunting, and the preservation of important intercostal arteries in appropriate circumstances. A model of spinal cord ischemia was created by temporary proximal and distal occlusion of the canine thoracic aorta. Serial measurement of somatosensory cortical evoked potentials (SCEP) generated by peripheral nerve stimulation, reflecting the status of long-tract neural conduction, was used to monitor alterations in spinal cord function during ischemia. Twelve animals subjected to aortic occlusion demonstrated a characteristic time-related deterioration of the SCEP with virtual extinction of the signal at a mean interval (± standard error of the mean) of 12.4 ± 1.5 minutes. Six animals in which reperfusion was established immediately following the loss of the SCEP (Group 1) demonstrated complete recovery without neurological sequelae, as assessed by clinical and histological criteria. In 6 animals (Group 2), the period of aortic occlusion was extended for an additional 15 minutes following loss of the SCEP (27.3 ± 2.3 minutes); postoperatively, 4 of 6 animals sustained major neurological lesions characterized by spastic paraplegia and histological evidence of spinal cord infarction (Group 1 versus Group 2, p < 0.05).