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Predicting Motor Recovery After Surgery of Tumors in Motor Eloquent Areas

Posted By Christopher D. Halford BA, R. EEG/EP T., CNIM, Thursday, September 5, 2019

In this blog post, one of our members stepped up to the challenge of helping us review recent papers from the literature. Many thanks to Christopher Halford! If any readers would like help by writing summaries of recent papers, please contact me (ASNM President Rich Vogel). The post below was written by Christopher D. Halford BA, R. EEG/EP T., CNIM.

 

 In the article "Postoperative navigated transcranial magnetic stimulation to predict motor recovery after surgery of tumors in motor eloquent areas" by Seidel, et al., published in the June 2019 edition of Clinical Neurophysiology, the authors approach a very interesting topic. As the title says, they attempted to use post-operative transcranial magnetic stimulation (TMS) on patients to see if a present MEP could predict patient recovery following an intraoperative change in dcMEPs and/or tcMEPs that resulted in a post-operative motor deficit.

 Throughout the article the authors explain their methodology in great detail. They included essential information like the majority of the standards they used for establishing their criteria for changes in intraoperative MEP testing, the time frame used in the study to test the patient post-op, and a detailed chart showing the important information for each patient in the study including pre- and post-op strength changes, individual intraoperative MEP change (with recovery of signal or a lack thereof), recovery of strength from day one, one week, and one month post-op, etc. The authors make educating the reader of their testing and results, along with prior research done in this area (with many citations of pertinent scholarly articles to support each statement of fact or claim that guided their methods) a very high priority of their publication.

 Results:

 All of the 13 patients included in this study presented with a decrease in post-operative motor function compared to their pre-op exam. Within one week post-op (average=3.8 days) the researchers tested each patient and were able to record an MEP through navigated transcranial magnetic stimulation in 11 of the 13 patients. Ten of the 11 that had had a recordable MEP after TMS demonstrated a positive functional recovery by 30 days post-op, demonstrating this method has a positive predictive value (PPV) of 90.9%. Of the remaining two that did not have a post-op MEP after navigated TMS both had minimal to no recovery of function after one month post-op while one patient that had a post-op MEP from magnetic stimulation did not show improvement (based off of their progress criteria).

 Conclusion:

 In this article Seidel et al. show the reader the basis for his study done by other researchers (whose evidence and findings are stated and cited in this article) but they also expand these conclusions as well. As they point out, they extend their testing and results to lower limb motor function (as well as including upper limb) and propose the value of this technique for possible determination of patients that might benefit from aggressive post-op therapy that may have otherwise been seen as candidates that would benefit little from it. Also, the authors offer the prospective benefit of TMS for assessing more secondary and/or associative motor areas of the brain in a way not possible using only intraoperative tc or dcMEPs, which was also one of the key focuses of their testing.

 Limitations:

 The authors are very good about citing the sample size as the biggest limitation of their study. However with the solid outcomes of this limited sample size the authors have demonstrated that additional research will likely have merit. They also acknowledge that though the tumor locations for each resection were in different eloquent areas, each did have a limit of 3 to 8-cms distance from motor eloquent areas. Although the authors did inform the reader of most of their intraoperative criteria for evaluating and reporting change, it is still somewhat incomplete given that they didn’t list what specific surgical maneuvers were/could have been used to respond to intraoperative MEP changes, once an alarm criteria had been met. Also, more detailed stim parameters, anesthesia regimen/changes, and individual alarm criteria for each intraoperative change would be valuable for study reproduction. As mentioned they did provide much of these aspects but these key components would be crucial for complete replication.

 The IONM Big Picture Perspective:

 The article offers a potential technique of great value: a method that might indeed help determine the likelihood that a post-operative deficit is either going to be transient or permanent. Although this is an incredibly valuable determination (both to surgeons and patients/families), adaptation of this into the clinical setting could be a difficult task considering the cost of magnetic stimulators to those hospitals and facilities that don’t have preexisting needs for this technology. However, for those that do have this technology onsite, this could be a tremendous opportunity to consider research opportunities. If larger, repeated studies could further support the preliminarily data shown in this current article, then it could serve as evidential support for convincing hospitals to invest the necessary funds to acquire this technology and implement this type of monitoring. The development of a neuromonitoring test that would allow a surgeon to tell a patient, with confidence, that their new deficit will be only temporary has the potential to be a critical area where neuromonitoring could directly contribute to improving patient care. I encourage those that have the interest and the means to help to contact the authors, compile all information needed to replicate the study and move this research forward. 

 References:

Seidel, K., Hani, L., Lutz, K., Zbinden, C., Redmann, A., Consuegra, A., . . . Schucht, P. (2019). Postoperative navigated transcranial magnetic stimulation to predict motor recovery after surgery of tumors in motor eloquent areas. Clinical Neurophysiology,130(6), 952-959.

 Disclaimer:

 The views, thoughts, and opinions expressed in this blog post  are solely those of the author(s). Blog posts do not represent the thoughts, intentions, strategies or policies of the author’s employer or any organization, committee or other group or individual, including the ASNM. The ASNM, along with the author(s) of this post, makes no representations as to the completeness, accuracy, suitability, validity, usefulness or timeliness of any information in this blog and will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. All information is provided on an as-is basis. Any action you may take based upon the information on this website is strictly at your own risk.

Tags:  In the Literature 

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Correlating MEPs and Preop Motor Function

Posted By Lanjun Guo, MD, MSc, DABNM, FASNM, Tuesday, June 5, 2018

This blog post will summarize a paper recently published by a member of the ASNM's Board of Directors, Lanjun Guo, MD, MSc, DABNM, FASNM. Dr. Guo trained as a neurosurgeon in China and is now a prominent clinical neurophysiologist practicing in California. She is active in multiple societies, including the ASNM and ISIN. The post below was written by Dr. Guo. Thanks for reading! RV

The Correlation Between Recordable MEPs and Motor Function During Spinal Surgery for Resection of Thoracic Spinal Cord Tumor

This paper examined the association between preoperative motor function of patients’ lower extremities and intraoperative motor evoked potential (MEP) recording.

 Patients undergoing thoracic spinal cord tumor resection were studied. Patients’ motor function was checked immediately before the surgical procedure. MEP responses were recorded from the tibialis anterior and foot muscles, and the hand muscles were used as control. Electrical current with train of eight pulses, 200 to 500 volts was delivered through two corkscrews placed at C3’ and C4’ sites. Anesthesia was maintained by total intravenous anesthesia (TIVA) using a combination of propofol and remifentanil after induction with intravenous propofol, remifentanil, and rocuronium. Rocuronium was not repeated. Bispectral Index was maintained between 40 to 50.

From 178 lower limbs of the 89 patients,  myogenic MEPs (m-MEPs) could be recorded from 100% (105/105) of the patients with 5 out of 5 motor strength in lower extremity; 90% (36/40) from the patients with 4/5 motor strength; only 25 % (5/20) with 3/5; and 12.5% (1/8) with 2/5 motor strength; None (0/5) were able to be recorded if the motor strength was 1/5. Therefore, it was concluded that the ability to record m-MEPs is closely associated with the patient’s motor function. They are difficult to obtain if motor function is 3/5 motor strength in the lower extremity. They are almost impossible to record if motor function is worse than 3/5.

Excerpt: Manual Muscle Test Grading Scale

Number Clinical Exam 
 0  No muscle movement. Flaccid paralysis.
 1  Visible muscle twitch, but no movement at the joint.
 2  Able to move in horizontal plane, but not against gravity.
 3  Able to move against gravity, but not against resistance.
 4  Able to move against resistance, but less than normal.
 5  Full strength against resistance

 Generation of m-MEPs depends on the excitability of the alpha-motor neurons in the anterior horns and excitability of the neuromuscular junction. Muscle MEPs can be generated only if the resting potential of alpha-motor neurons reaches the firing threshold, and thus, transmits this activity via motor axons of the peripheral nerves and neuromuscular junctions to the muscle.

The m-MEPs are affected by anesthetic drugs. Anesthetics impair the motor cortex’s ability to generate multiple descending volleys, the I waves. They also depress the excitability of the entire spinal cord, including the alpha-motor neuron pool. Because the D wave is resistant to anesthetic depression, the anesthetic effect at the alpha-motor neurons can be overcome at low anesthetic concentrations by high-frequency multipulse stimulation through transcranial stimulation.   The multiple D waves followed by stimuli to the motor cortex summate at the anterior horn cell to generate a subsequent myogenic response. The temporal accumulation of several cortico-motoneuronal excitatory postsynaptic potentials (EPSPs) is necessary to bring motor neurons from the resting state to the firing threshold during general anesthesia.

 However, transcranial stimuli only activate a small and variable subpopulation of the lower motor neuron pool to generate MEPs. Therefore, the m-MEPs are substantially more difficult to record in patients with underlying neurological abnormalities, such as spinal cord tumor. In practice, although a patient may maintain some motor function and can move their legs, MEPs may still not be recordable from muscles of the lower extremity.  There are previous studies correlating intraoperative recordings of m-MEPs during different types of spine surgery with the preoperative motor function, although the detailed information about the relation between the recordable MEPs and the grade of motor function were not reported.

 There are a number of methodological considerations in this study. The number of lower limbs with poor grade function was relatively small, only 33 lower limbs with 3/5 grade or less compared to 145 lower limbs with 5/5 or 4/5 grade. Different stimulation methods, such as different stimulating sites on the skull, different stimulation inter-stimulus interval, and /or different stimulating pulses, were not compared. Therefore, the recordable m-MEPs rate in clinical practice may be higher if different stimulating montages were tested.

 The current study provided evidence and confirmed the clinic experience that it can be difficult to obtain m-MEPs during a surgery when the patient has motor weakness, even the patient could still move legs. It also indirectly provide the information that if MEPs lost during surgery due to surgical manipulation, the patients may still have some motor function postoperatively, but most likely that would be worse than 3/5 motor strength.

References:

Guo L, Li Y, Han R, Gelb AW. The Correlation Between Recordable MEPs and Motor Function During Spinal Surgery for Resection of Thoracic Spinal Cord Tumor. J Neurosurg Anesthesiol. 2018 Jan;30(1):39-43.

Disclaimer:

The views, thoughts, and opinions expressed in this blog post  are solely those of the author(s). Blog posts do not represent the thoughts, intentions, strategies or policies of the author’s employer or any organization, committee or other group or individual, including the ASNM. The ASNM, along with the author(s) of this post, makes no representations as to the completeness, accuracy, suitability, validity, usefulness or timeliness of any information in this blog and will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. All information is provided on an as-is basis. Any action you may take based upon the information on this website is strictly at your own risk.

Tags:  In the Literature 

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Major Publication Questions Utility and Value of Neuromonitoring – ASNM Responds!

Posted By Richard W. Vogel, Friday, May 25, 2018

A recent paper published by Hadley et al1 in Neurosurgery claims that IONM has very little utility and value in spine surgery. They base this claim on a rather biased review of the literature and they call it a guideline.

It would all be a hard pill to swallow, but necessary nonetheless, if their observations were objective, if their findings were valid. Unfortunately, what we have come to call The Hadley Paper is little more than a biased repudiation of IONM in spine surgery, written by 4 neurosurgeons who don’t typically use IONM and seem to have little understanding of how it works.

You should have little doubt that this paper graced the inbox, or crossed the desk, of every spine surgeon with whom you work. Make no mistake, your surgeons are talking about it in their circles. We have already observed that some surgeons have discontinued using IONM simply based on this paper alone.

If they haven’t already, your surgeons may raise it as a topic of conversation with you. Whether that happens or not, you must be prepared to proactively educate your surgeons about the flaws in this paper and why it should be summarily dismissed.

The scale of the paper is so large, the reputation of the journal so prestigious, that this paper could have a significant impact on the future of our field. Indeed, many insurance carriers will likely use this paper to deny IONM claims and this could further drive down reimbursements and leave us in ruin.

This is a serious situation, and we want you to be aware of what is going on and what the ASNM is doing to help!

First, Drs. Bryan Wilent (Chair, Research Committee) and Rich Vogel (ASNM President-Elect) started a project last year, approved by the Board, in which the ASNM would write letters to the editor of journals in response to what we call bad literature. We loosely defined bad literature as papers invalidated by serious methodological flaws and having a high enough profile to do significant harm to our profession.

A few papers have come up for discussion, but we didn’t invest the energy because they were low profile and self-published. So, we didn’t write any letters for the first year, and then we saw The Hadley Paper.

Given the obvious and significant negative implications that come from publication of The Hadley Paper, the ASNM wrote our first Letter to the Editor2, on behalf of our membership, to point out some of the most egregious flaws. Incidentally, we weren’t the only Society to write a letter, but we were the first.

If you aren’t able to access The Hadley Paper due to limited institutional permissions, then you should at least read our Letter to the Editor of Neurosurgery. We have permission to post the original on our website.

Incidentally, Hadley and Colleagues respondedto our Letter with what can only be described as an affirmation of what we knew all along: they have little understanding of IONM and how it works. They’ve actually made matters worse by responding to us, and now we’re beginning to hear from spine surgeons around the country who contact us. They say, “[Hadley et al.] don’t speak for us and don’t represent us.”. Perhaps you'll understand why upon reading their reply.

The reader may also find amusing some of their ostentatious claims. As an example, Hadley et al. asserted that one of their authors was an expert because he studied critical appraisal of the medical literature for 5 years. Just to give you some perspective on that claim, of all the authors of the Letter to the Editor that the ASNM wrote, I’m probably one of the most junior by age, and I’ve been studying critical appraisal of the medical and scientific literature for 20 years.

More vexing than amusing is the unsubstantiated claims against the ASNM, made perhaps in an attempt to belittle our society and our profession. For example, Hadley et al. said, [the ASNM] is “perhaps unfamiliar with the rigorous, and sometimes frustrating, peer review process required before endorsement by our specialty societies, which may lead to extensive revisions and in-depth questions regarding statements and approach.” I’m sure this really irritated ASNM President, Dr. Jeff Gertsch, who recently oversaw the rewrite of our Professional Practice Guidelines. Anyway, if Hadley et al. had done a basic search of the literature, or our website, they would have found quite a few such guidelines authored by the ASNM that went through the very same process. 

This brings me to the second thing the ASNM is doing to help. Several of our members are heavily involved in the North American Spine Society (NASS). We now have a Section on Intraoperative Neurophysiological Monitoring. The Section is co-founded and co-chaired by ASNM Member Dr. Adam Doan and ASNM President-Elect Dr. Rich Vogel. Other founding members include Drs. Tony Sestokas, Bob Holdefer and John Ney, among others.

At the 2018 NASS Annual Meeting in Los Angeles, we will have our first symposium on IONM in which we have an objective review of the utility and value of IONM presented by surgeons, neurophysiologists, neurologists and a health policy economist. We will also have an abstract session in which a best paper is chosen.

Other work within NASS includes authoring a coverage policy on IONM, international speaking, and developing webinars and podcasts for 2019. All of this is being done by members of the ASNM, some of whom you elected to the Board. Inter-society cooperation is certainly the way to go!

Anyway, we thank you for taking the time to read this and we strongly recommend you take the time to read our Letter to the Editor. After all, we wrote it for you.

The ASNM is doing lots of things for you, and we hope to use our blog to be better at communicating to keep you in the know. Be sure to subscribe and keep reading!

References:

  1. Hadley MN, Shank CD, Rozzelle CJ, Walters BC. Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord. Neurosurgery. 2017 Nov 1;81(5):713-732.
  2. Vogel R, Balzer J, Gertsch J, Holdefer RN, Lee GR, Moreira JJ, Wilent B, Shils JL. Letter: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord. Neurosurgery. 2018 Jun 1;82(6):E190-E191.
  3. Hadley MN, Shank CD, Rozzelle CJ, Walters BC. In Reply: Guidelines for the Use of Electrophysiological Monitoring for Surgery of the Human Spinal Column and Spinal Cord. Neurosurgery. 2018 Jun 1;82(6):E192-E193.

Disclaimer:

The views, thoughts, and opinions expressed in this blog post  are solely those of the author(s). Blog posts do not represent the thoughts, intentions, strategies or policies of the author’s employer or any organization, committee or other group or individual, including the ASNM. The ASNM, along with the author(s) of this post, makes no representations as to the completeness, accuracy, suitability, validity, usefulness or timeliness of any information in this blog and will not be liable for any errors, omissions, or delays in this information or any losses, injuries, or damages arising from its display or use. All information is provided on an as-is basis. Any action you may take based upon the information on this website is strictly at your own risk.

Tags:  In the Literature 

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Raising Mean Arterial Pressure Alone Restores 20% of Intraoperative Neuromonitoring Losses

Posted By Richard W. Vogel, Monday, January 22, 2018

Anyone who works in neuromonitoring will tell you that the #1 reason why we lose MEPs or SSEPs during spine surgery is hypo-perfusion of the spinal cord. Indeed, the relationship between spinal cord perfusion and neuromonitoring (IONM) data is intimate: An adequately perfused spinal cord optimizes conduction-based data (i.e., MEP and SSEP), and a hypo-perfused spinal cord can cause loss of data or inability to acquire baseline data. Given that spinal cord perfusion is closely related to the mean arterial pressure (MAP), we always try to ensure that the MAP is maintained within an optimal range.

Every patient has different needs in terms of the mean arterial pressure (MAP) that will maintain adequate spinal cord perfusion, and thus function, and thus IONM signals. During spine surgery, we’re always working with anesthesia to maintain the appropriate pressure and we understand that achieving that optimal MAP can be challenging in some patients.

Sometimes the MAP slips too low, and we start to lose our signals. It’s a classic progression: MEPs deteriorate first, followed by SSEPs later. That’s because MEPs rely on conduction across the synapse between the upper and lower motor neurons. These synapses occur in the spinal cord’s ventral gray matter, they have a high metabolic demand, and they’re quite sensitive to changes in perfusion. So, the time to electrical failure is very short when blood supply is low. The SSEP pathway doesn’t synapse in the spinal cord and the dorsal column white matter tracts have a much lower metabolic demand. So, the time to electrical failure is much longer.

There’s an old saying in the world of stroke care: “Time is brain.”. The same is true in spine surgery: Time is spinal cord. When spinal cord perfusion falls below the functional threshold, the clock starts ticking as ischemia can ultimately cause an infarct. The penumbra between onset of ischemia and onset of infarct is what we call a critical window of opportunity to perform an intervention, and the first thing we usually do is request an increase in the MAP.

How frequently is this strategy effective? A recent article published in Spine1 assessed the effect of different interventions in restoring IONM signals in pediatric spine surgery. This was a multi-center prospective study of 452 patients undergoing posterior spinal deformity surgery. The results are exactly what we would expect, increasing MAP is highly effective first line of defense against spinal cord hypo-perfusion.

Of the 30 patients who had a significant IONM signal alterations in this study, 20% had return of signals due to an increase in MAP alone with no other interventions (MAP increased from x̅ = 68 to 86 mmHg). On average, signals returned to baseline after 16 min. In 60% of patients, MAP was raised from x̅ = 72 mmHg to 86 mmHg in conjunction with other interventions and signals returned to baseline after an average of 37 mins. The rest of the patients had signal changes unrelated to MAP. The authors argue that raising MAPs above 85 mmHg should be considered the first step in response to IONM signal changes, as this alone was successful in 20% of patients without sacrificing deformity correction.

A wonderful statistic not overly discussed in this paper was that there were zero bad spinal cord outcomes, meaning that performing some form of an intervention in each of the 30 alerts returned data to baseline, which was a strong predictor for success. All patients had return of signals at the conclusion of the procedure with one patient having postoperative neurological sequelae.

The rationale for having an adequate MAP extends well beyond making the neuromonitoring team happy. Increasing MAP in response to an IONM data change is universally used in spine surgery, and therefore serves as a common therapeutic intervention. However, we must never (ever) forget that an appropriate MAP during times of risk to the spinal cord is also prophylactic and makes the spinal cord more resilient to any iatrogenic or peri-surgical insult.

Interestingly, many of the alerts in this study occurred during pedicle screw placement, and not just during the correction. This suggests that MAP should be maintained at 85 mmHg during all times of risk, including screw/hook/sublaminar wire placement, osteotomies, etc. This can also include surgical exposure in certain populations like marked kyphoscoliosis patients who are at risk from positioning alone. Given that increased MAP is both therapeutic and prophylactic, maintaining MAP at 85 mmHg is likely a good idea in any cervical or thoracic spine surgery, regardless of diagnosis.

A final thought, increasing MAP doesn’t always equate to increasing spinal cord perfusion. Pure vasoconstrictors, like phenylephrine, increase MAP but their failure to increase cardiac output may do little to benefit spinal cord perfusion. In situations where hypo-perfusion is suspected, a better approach may be to consider epinephrine which increases heart rate, vascular resistance and cardiac contractility. The result of increasing the cardiac output is more blood flow to regions at risk for ischemic injury.

Adam Doan, DC, D.ABNM

Rich Vogel, PhD, D.ABNM

References:

1Yang J, Skaggs DL, Chan P, Shah SA, Vitale MG, Neiss G, Feinberg N, Andras LM. Raising Mean Arterial Pressure Alone Restores 20% of Intraoperative Neuromonitoring Losses. Spine (Phila Pa 1976). 2017 Oct 18. Find on PubMed

Tags:  In the Literature 

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Brachial Plexus Injury in Cervical Spine Surgery

Posted By Richard W. Vogel, Monday, January 15, 2018

The ASNM Monitor Blog is pleased to add a new series entitled, In the Literature. Posts published with this tag will review articles in the literature to help you follow the latest developments in the science and practice of IONM. 

 Today, we’re reviewing an article1 on the prevalence of brachial plexus injury during cervical spine surgery. The article is titled, Brachial Plexopathy After Cervical Spine Surgery. It is open access and available to download here if you wish.

 This study is a retrospective, multicenter case series of 12,903 patients who underwent cervical spine surgery at 21 different facilities. In this large sample of patients, only 1 patient experienced post-operative brachial plexopathy. So, the incidence was 0.78%.

 The results of this study suggest that brachial plexus injury is an extremely rare complication of cervical spine surgery. In their review of the literature, the authors cite a previously published paper by Hasegawa et al.2 which reported a much higher occurrence of 2.2% brachial plexopathy following c-spine surgery.

 The authors’ explanation for the disparity in the prevalence of brachial plexopathy between the two studies may be a result of several factors, such as:

  1. The retrospective nature of the study by Than et al. renders it prone to recall bias, which can decrease the prevalence rate that gets reported.
  2. The present study was composed of 12,903 patients whereas the study by Hasegawa et al. was composed of 857 patients. The larger number of patients in the present study resulted in a higher denominator when calculating the percentage of brachial plexus injuries. This may result in a more accurate estimation of the injury rate.
  3. The study by Hasegawa et al. collected data mostly in the 1980s and 1990s. This was prior to routine use of neuromonitoring in cervical spine surgery, and prior to the routine use of MEPs. The more recent study by Than et al. collected data from 2005 to 2011. Patients in this study likely received more optimal neuromonitoring and more advanced surgical techniques. This could also explain the lower prevalence of brachial plexopathy in recent years.

The one patient who presented with brachial plexopathy in the present study actually developed Parsonage-Turner Syndrome (brachial neuritis), but it didn’t appear until a few days after surgery. While there’s no mention of neuromonitoring for this patient, it is worth noting that MEPs and SSEPs can only predict neurologic function in the immediate postoperative period. Delayed deficits are rarely, if ever, detected with neuromonitoring.

Positioning issues are common in surgery. The authors of this blog post have personally detected malpositioning and compression of the extremities in hundreds of patients. Isolated changes in SSEPs or MEPs served as the warning sign. Following an intervention, such as repositioning the limb or removing compression, the data almost always returned to baseline and the patients woke without deficits. These alerts are classified most accurately as true positives. If we had not intervened, then the patient would likely have emerged from surgery with some type of deficit, such as brachial plexopathy.

 Our experience mirrors those described by Schwartz et al.3 in which the most common cause of changes in MEPs and/or SSEPs during ACDF surgery was impending injury to the brachial plexus. In fact, 65% of all data changes during ACDF were related to impending position-induced brachial plexopathy.

 How does brachial plexopathy develop in cervical spine surgery? In the present paper, the authors identify upper extremity traction as the main time of risk to the brachial plexus. This is when the surgeon is taping down the shoulders. The second greatest time of risk to the brachial plexus is extension of the neck (in anterior surgery), as this places additional traction on the brachial plexus. With this in mind, it makes the most sense to get baseline SSEPs and MEPs prior to both of these maneuvers. This would help to quickly and accurately determine the cause if there are any abnormalities in your data.

 How would this play out? First, you would establish baselines. The surgeon would then tape the shoulders in traction, and you would run another test to ensure that there are no changes from baseline. If there are changes, then you recommend that the surgeon loosen the tape on the impacted shoulder. Next, the surgeon extends the patient’s neck, and you would run another test to ensure that there are no changes from baseline. If there are changes, then you recommend that the surgeon move the patient’s neck to a more neutral position.

 Imagine if you establish baseline after these positioning maneuvers in an ACDF and you find abnormalities in the baseline data. It may be far more difficult to determine if these abnormalities in the data reflect the patient’s true baseline, or whether they are the result of one or both of the positioning maneuvers. You’d have to undo the maneuvers to help identify the root of the abnormalities. You might even have to wake the patient to perform a neuro exam. We’ve heard of this happening before. It’s quite disruptive and totally unnecessary.

 Some of these very same issues were discussed in a 2015 Editorial by Epstein and Stecker4. With respect to establishing baseline MEPs and SSEPs before positioning, they pose the question, “Why can’t we and our monitoring colleagues get this right?” They recommend establishing baselines before any maneuvers are performed that pose risk to the nervous system, regardless of whether the risk is to the spinal cord, nerve roots or peripheral nerves.

 In the context of a spinal fracture, deformity, a stenotic spinal canal, or pathology involving the spinal cord, the risk actually begins with intubation because it requires extension of the neck. Awake fibreoptic intubations are typically ordered by the surgeon in these situations so a neurological exam can be performed before unconsciousness is induced. If an awake intubation is not possible in these situations, then Epstein and Stecker recommend that MEP and SSEP baselines be established in the period of time between induction and intubation. These baselines should accurately reflect the preoperative status of the patient.

 There is at least one densely-populated geographic region of the US where almost all of the hospitals have a protocol to acquire pre-intubation baselines on all patients undergoing cervical spine surgery, regardless of diagnosis or severity of risk. This technique requires that almost all neuromonitoring electrodes be placed in pre-op holding (usually after a little Versed). All of the needles get placed in holding except in the head and feet. When the patient comes in the OR, all the electrodes get plugged in. Anesthesia induces unconsciousness with a Propofol injection and manual respiration begins through a mask as the monitorist quickly places electrodes in the patient’s head and feet. Then, the monitorist quickly tests MEPs and SSEPs to establish baseline. After that, anesthesia proceeds with intubation. The teams who do this regularly have excellent preparation and communication. The whole process takes less than a minute. This pre-intubation baseline protocol is extremely rare outside of this one particular geographic region, and probably not necessary in most patients.

 Following intubation, the next stage of risk to the nervous system is positioning of the patient. If it’s an anterior approach, then the risky maneuvers include shoulder traction and neck extension. If it’s a posterior approach, then the risky maneuver is prone positioning of the patient. We are of the opinion that MEP and SSEP baselines should always be established before performing these maneuvers. A separate paper just published in 2017 reported neuromonitoring data changes immediately following neck extension in 2.4% of patients undergoing ACDF surgery5. In most of the affected patients, signals returned to baseline immediately following repositioning of the neck. In a small portion of affected patients, signals were never recovered and they emerged from surgery with new neurologic deficits.

 Unfortunately, some surgeons don’t want to get baselines before positioning the patient, particularly in ACDF surgery, because they think it will slow them down. This is a flawed perspective, though, because it should take less than a minute to acquire baselines in a typical ACDF surgery. So, there is no good reason to not establish neuromonitoring baselines prior to positioning for cervical spine surgery. With this in mind, we believe it is best practice for the neuromonitoring team to recommend pre-positioning baselines to the surgeon before cervical spine surgery, regardless of diagnosis. If the surgeon declines, it is best practice to document this recommendation along with the fact that the surgeon declined.

 Rich Vogel, PhD, DABNM

 Adam Doan, DC, DABNM

 References:

  1. Than KD, Mummaneni PV, Smith ZA, Hsu WK, Arnold PM, Fehlings MG, Mroz TE, Riew KD. Brachial Plexopathy After Cervical Spine Surgery. Global Spine J. 2017 Apr;7(1 Suppl):17S-20S.
  2.  Hasegawa K, Homma T, Chiba Y. Upper extremity palsy following cervical decompression surgery results from a transient spinal cord lesion. Spine (Phila Pa 1976). 2007 Mar 15;32(6):E197-202.
  3. Schwartz DM, Sestokas AK, Hilibrand, AS, Vaccaro AR, Bose B, Li M, Albert TJ. Neurophysiological identification of position-induced neurologic injury during anterior cervical spine surgery. J Clin Monit Comput 2006; 20: 437–444
  4. Epstein NE, Stecker MM. Intraoperative neuro-monitoring corner editorial: The need for preoperative SSEP and MEP baselines in spinal surgery: Why can't we and our monitoring colleagues get this right? Surg Neurol Int. 2014 Dec 30;5(Suppl 15):S548-51.
  5. Appel A, Korn A, Biron T, Goldstein K, Rand N, Millgram M, Floman Y, Ashkenazi E. Efficacy of head repositioning in restoration of electrophysiological signals during cervical spine procedures. J Clin Neurophysiol 2017; 34:174-178.

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