TCeMEP Monitoring during Thoracic and Thoracoabdominal Aortic Aneurysm Repair

Michelle L. Nagel R.EEG/EPT, CNIM* and Leisha L. Osburn, M.S., R.EEG/EPT, CNIM**
*Synapse Neuromonitoring, Inc., 1365 N. Manchester Dr. Greenfield, Indiana 46140
**Clarian Health Partners Methodist Hospital, P.O. Box 1367. Neurophysiology Lab A1058, Indianapolis, Indiana 46206

Purpose:

The purpose of this study is to evaluate the effectiveness of multi-modality neural function monitoring, in predicting and preventing spinal cord motor tract injury during thoracic and thoracoabdominal aortic aneurysm procedures. We correlated TCeMEP changes, SEP changes, peri-operative events, and post-operative neurologic function. Challenges in recording techniques specific to this type of procedure have also been addressed.

Background Context:

SEP monitoring does not yield motor tract information and therefore is not predictive in motor tract injury during thoracic and thoracoabdominal aortic aneurysm surgeries.

Methods:

This is a retrospective chart review of 58 patients having undergone thoracic and thoracoabdominal aortic aneurysm repair. Neuromonitoring of these procedures was performed between May 2004 and July 2006 at a single institution by 4 cardiothoracic and cardiovascular surgeons. Both normothermic (9) and deep hypothermic circulatory arrest (DHCA) (49) techniques were employed. Upper and lower extremity cortical, subcortical and peripheral SEPs were recorded. TCeMEPs were recorded from the abductor pollucis brevis-abductor digiti minimi, vastus medialis, tibialis anterior, medial gastrocnemious, and abductor hallucis muscles bilaterally. After MEP changes were seen in a patient who was later found to have a cerebral stroke, EEG recording was added to the monitoring protocol. Significant change was defined as loss of responses during clamping for aneurysm repair during normothermic procedures and failure of responses to return with re-warming in DHCA. Challenges in stimulus delivery secondary to scalp edema prompted manipulation of stimulus delivery prior to reporting deviation from baseline recordings, especially upon re-warming in surgeries performed under DHCA. High risk patients (patients at continued risk for spinal cord ischemia), as determined by the surgeon, were followed to the cardiac intensive care unit and monitored for up to 72 hours until patients were able to follow commands and neurologic exams could be completed. Lumbar drains were placed successfully pre-operatively in 8 of 9 patients undergoing normothermic procedures.

Results:

The following risk factors were identified: 3 patients had seizure disorders; 4 patients had previous stroke; 3 patients had pacemakers. Additionally 3 patients had pre-existing deficit; 7 patients had diabetes; 21 patients had prior cardiac or vascular surgery. Of the 48 patients undergoing cardiac bypass, 43 patients had left leg cannulation and 5 patients had right leg cannulation. A total intravenous anesthetic technique (TIVA) was used in 56 out of 58 procedures. Inhalational agents were used briefly in 2 cases during induction. Neuromuscular blockade was used only for purposes of intubation, exposure (after baseline recordings) and to facilitate closure. With MEP loss, interventions included: increasing blood pressure, intravenous bolus of decadron, post-operative placement of lumbar drain, or drainage of CSF in patients with drains placed pre-operatively.

46 patients had MEP responses present and consistent with baseline at completion of the monitoring, with no new motor deficits post-operatively. 2 patients had unobtainable lower extremity MEP responses at completion of the monitoring, with normal motor function post-operatively. These false positives were later attributed to technical challenges in stimulus delivery caused by scalp edema. 4 patients had MEP loss with interventions leading to return of responses and no new motor deficit post-operatively. These interventions included increasing the blood pressure (1); drainage of CSF intraoperatively (1); giving decadron and placing a lumbar drain at closing (1); and placing a lumbar drain in the ICU after responses were lost within the first 24 hours post-operatively (1). 2 patients had loss of MEP responses and were found to have had cerebral strokes. 1 patient had prolonged absence of all MEP responses after re-warming, which lasted until several hours into the post-operative period. Though all responses did return in the ICU post-operatively, this patient never regained consciousness and was found to have had a severe cerebral anoxic insult. 1 patient had variable MEP responses after re-warming, which continued to be variable post-operatively during the ICU monitoring period. This patient was found to have suffered from a cerebral anoxic event. 1 patient with loss of MEPs intraoperatively had a lumbar drain placed at the end of the surgical procedure, with no return of MEPs and loss of lower extremity function. 1 patient with loss of MEPs intraoperatively had a lumbar drain placed at the end of the surgical procedure with no return of MEPs, and discovery of ineffective drain placement after 24 hours, with replacement and significant, high pressure CSF drainage, but no return of MEPs and no lower extremity motor function upon awakening.

Technical Challenges:

In two early cases, lower extremity MEP responses were not regained. These patients went on to have normal post-operative motor function. Technical challenges were identified with re-warming, regarding adequate MEP stimulus delivery in patients undergoing DHCA. Failure of transcranial stimulus delivery was prominent in patients with scalp edema. This difficulty was overcome in 37 patients by replacing MEP corkscrew stimulating electrodes with standard subdermal needle electrodes, and at times with further repositioning of the needle electrodes. In 3 patients, after these protocols were initiated, changing the MEP stimulus electrodes was still unsuccessful. One of these patients was found to have experienced a stroke and two had spinal cord injury.

Conclusions:

TCeMEP monitoring during TAAA repair can be technically challenging. Complicating factors include failure of stimulus delivery due to scalp edema and risk of stroke and anoxic brain injury. Our overall experience with MEP monitoring during TAAA repair showed TCeMEPs to be 100% sensitive and 96.5% specific before overcoming stimulus delivery problems, and 100% specific after protocols to address this were put in place. After overcoming the technical challenges with stimulus delivery and adding EEG recordings to rule out cerebral injury, we found TCeMEPs to be 100% specific and 100% sensitive. In our review of 58 cases in patients undergoing thoracic abdominal aortic aneurysm repair we have shown that multi-modality monitoring is an effective tool for lowering the risk of devastating neurologic deficit in this patient population.

Accepted for Publication AJET, July 2006

C5 Root Palsy Following Cervical Spinal Surgery

Intraoperative Neuromonitoring is invaluable in surgical procedures that place neural structures at risk. The main goal of any surgical intervention has been and continues to be the protection of the patient and prevention of iatrogenic complications. The implementation of Intraoperative electromyography (EMG) allows real time feedback to the surgeon during procedures regarding tolerance of individual nerve roots.

Cervical spinal surgery is commonly performed without Intraoperative Neuromonitoring because it carries a low risk of spinal cord injury. However, it is common that patients undergoing cervical spinal surgery suffer post-operative C5 root palsy. The C5 root is at higher risk because it is short in length. Because of resultant severe deltoid and bicep muscle weakness, this injury is debilitating to the patient. Often the patient cannot return to work for many months following rehabilitative therapy. Cervical root traction may contribute to post-operative C5 palsy and significant shoulder distraction (during patient positioning) may contribute to C5 palsy secondary to brachial plexus injury.

Each patient tolerates root traction or distraction differently. Cervical EMG monitoring is an important adjunct to cervical spinal surgery to alert the surgeon to activity seen in free-running EMG recordings.

EMG monitoring is a useful real time Intraoperative diagnostic tool during these procedures because it allows the surgeon to make appropriate alterations in
patient positioning and/or surgical activities when firing is noted.

Reference:

“Palsies of the fifth cervical nerve root after cervical decompression: prevention
using continuous Intraoperative electromyography monitoring.”

Juan C. Jimenez, M.D. Sepehr Sani, M.D. Berton Braverman, PhD. Harel Deutsch,
M.D, and John Ratliff, M.D.

Departments of Neurological Surgery and Anesthesiology, Rush University
Medical Center, Chicago and Chicago Institute of neurosurgery and
Neuroresearch Medical Group, Chicago, Illinois.

Michelle Nagel R.EEG/EPT, CNIM
Synapse Neuromonitoring, Inc.
Mnagel@synapseneuro.com

© 2019 Synapse Neuro Inc.