Posted By Richard W. Vogel,
Thursday, February 1, 2018
In the Member Spotlight, we periodically introduce individual members of the ASNM to the society-at-large. We try to highlight some of their achievements and ask them interesting questions. We hope this affords members of the ASNM the opportunity to get to know each other. If you would like to recommend someone, including yourself, for the Member Spotlight, please contact Rich Vogel.
In this edition of Member Spotlight, we are shining the light on ASNM President Joseph Moreira, MD.
Position: ASNM President (May 2017 - May 2018)
As usual, we sent some questions to Dr. Moreira so we can learn a little about our President.
When your term as President ends, what do you hope to name as your greatest achievement?
My goal is to bring ASNM into the mainstream and work with other societies to have one voice and one consolidated set of practice guidelines. I would also like to improve communication in the field and surgeon and patient education. We should be the ones to choose what modalities are used on a given case and not have the surgeon arbitrarily select them.
What obstacles have you faced as President of the ASNM?
Bringing various factions and societies together on a unified front. So far so good but a lot of work left to do. I have worked on this with the current incoming president elects, Jeff Gertch and Rich Vogel and I am confident that as an executive committee going forward we will further the cause.
What predictions do you have about the future of the ASNM?
The ASNM’s member base will grow with all factions being well represented and involved. We will be a driving force amongst other societies and work together. We are the only pure IONM society in the US and need to lead the profession’s growth and education. If we can work with other societies and specialties, then we can flourish and grow.
What would you say is the best thing about attending an ASNM meeting?
The Bar! No … Apart from the educational content, the best part of the live conferences is the networking opportunity. We are all working in a vacuum most of the time, either in the OR doing our own case, or in an office. We rarely have the chance to openly discuss IONM and the industry with anyone. The ASNM meetings give us all the chance to relax, discuss, and learn new concepts. The mix of folks attending and gathering range from the new trainees to the seasoned, well experienced members at all levels
What is the most under-rated, or least known, benefit of being an ASNM member?
The open access to becoming involved. Anyone can join a committee, run for office, etc. This brings with it a new world of experience and accomplishment. We are a very open society to all involved in the field.
A little about you:
If I didn’t become a neurologist, I probably would have been a(n):
Anatomist, I love anatomy and its overall complexity and consistency. A fireman, besides the big trucks and awesome toys, I love to put out fires, that’s probably why I am drawn to IONM. A chef, love to cook.
Greatest technological advancement in neuromonitoring has been:
The development of multi-pulse train stimulation for MEPs is one of my favorites.
The best career advice I’ve ever received is:
Be brief, be bright, be gone!
A great article that everyone in the profession should read is:
Heuristic map of myotomal innervation in humans using direct intraoperative nerve root stimulation. (J Neurosurg Spine. 2011 Jul;15(1):64-70.).
I love this article because it is relevant to our everyday functioning in the OR, and expands on the range of muscles innervated by a specific root.
Litigating Intraoperative Neuromonitoring (IOM). (University of Baltimore Law Review. 2016 45(3), #3.).
This is a great 360 degree look at IOM and litigation and how to protect all concerned.
One of my favorite apps is:
Open Table, the quest for great food continues! Mapster, it keeps track of all your favorite places as you travel.
One of my pet peeves is:
My favorite film(s) of all time is/are:
Godfather and Blues Brothers.
At the top of my travel bucket-list is:
Mars, however to be realistic Italy, Ireland, Egypt. Favorite so far is Istanbul and Buzios, Brasil.
My favorite hobby is:
Playing the drums and cooking.
Posted By Richard W. Vogel,
Monday, January 22, 2018
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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
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
In the Literature
Posted By Richard W. Vogel,
Monday, January 15, 2018
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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:
- 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.
- 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.
- 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
- 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.
- 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.
- 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
- 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.
- 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.
Note: Opinions expressed in this blog belong to the authors of the post and do not represent the opinions of the ASNM.
In the Literature
Posted By Richard W. Vogel,
Friday, December 1, 2017
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Whether you practice neurophysiology in surgery, in the lab, or in the clinic, you probably use electrical stimulation to activate the nervous system on a daily basis. As you probably know, cathodal stimulation works best in some applications, while anodal stimulation works best in other applications.
Armed with this knowledge, you know precisely where to place electrodes on the body, and where to plug those electrodes in - black in cathode (-) and red in anode (+). But, what's the difference? What exactly is anodal or cathodal stimulation, and why does one work better than the other in some applications?
Today I hope to answer some of those questions for you because I believe that understanding stimulus polarity is important, and it will make you a better neurophysiologist.
Before we talk about how stimulators works, it is important to have a basic understanding of how a battery works.
How a Battery Works
The correct term for what we frequently refer to as a "battery", is a "cell", but I'm going to use the word battery to keep it simple. So, a battery is a charge-separating device. It stores electric energy by separating cations and anions into two separate compartments, or terminals (Figure 1).
- Cations are positively-charged ions (+).
- Anions are negatively-charged ions (-).
If you refer to the illustration in Figure 1, you will see that one terminal of the battery contains an excess of cations (+), and this is the positive terminal (+). Because it contains cations (+), the positive (+) terminal of the battery is called the cathode (+). The other terminal of the battery contains an excess of anions (-), and this is the negative terminal (-). Because it contains anions (-), the negative (-) terminal of the battery is called the anode (-).
When the battery is connected to a load, in this case a lightbulb, the device is powered by the flow of current. Conventional Current assumes that current flows out of the positive terminal, through the circuit and into the negative terminal. This was the convention chosen during the discovery of electricity, but they were wrong! Rather, Electrical Current is what actually happens, as electrons (-) flow out of the negative terminal (anode), through the circuit and into the positive terminal (cathode).
The take-home message is that, in a battery, current flows from anode to cathode. To learn more about batteries, go here.
How an Electrical Stimulator Works
In an electrical stimulator, the flow of anions (-) and cations (+) is controlled by the mechanics of the circuitry within the stimulator. The stimulator is unique in that the cathode is the negative pole (-) because it discharges anions (-), and the anode is the positive pole (+) because it discharges cations (+). At the end of the day, that's the fundamental difference between a battery and a stimulator.
Depending on how we configure the polarity, the stimulator will discharge either cations or anions into the body part being stimulated.
In cathodal stimulation, anions (-) are discharged into the body as current flows from the cathode (-), through the tissue, and back to the anode (+).
In anodal stimulation, cations (+) are discharged into the body as current flows from the anode (+), through the tissue, and back to the cathode (-).
Now, let's imagine that we place an electrical stimulator on the surface of the skin with a nerve bundle running underneath (Figure 2). Within the nerve bundle is a single nerve fibre (axon) upon which we will focus.
At rest, the inside of a cell is more negative than the outside of a cell. This occurs because there is a slightly greater number of negative charges than positive charges inside of the cell (intracellular space), and a slightly greater number of positive charges than negative charge outside of the cell (extracellular space). Because of the electrical difference, the cell is said to be polarized - just like a magnet, one side is more positive and the other side is more negative. If the electrical gradient were suddenly reversed, the cell would be depolarized, and we might see an action potential.
Cathodal Stimulation of Peripheral Nerves
When we use the term cathodal stimulation, what we mean is that negatively-charged anions (-) flow from the cathode, into the tissue, and back to the anode (Figure 3). As the electrical current flows from cathode to anode, negative charges (anions) tend to accumulate on the outer surface of the nerve membrane as they will be repelled by the negatively-charged cathode. This makes the outside of the membrane more negative. Consequently, the inside of the membrane becomes more positive due to accumulation of positive ions on the inside. This will result in depolarization, which, if sufficient in magnitude, will result in an action potential (nerve impulse or muscle activation).
Figure 3 illustrates activation of the axon under the cathode. As a result of stimulation, an action potential is sent in both directions along the length of the nerve, starting at the cathode. Something interesting happens underneath the anode, though! All of the negative charge from the extracellular space is attracted to the anode, leaving the outside of the cell excessively electrically positive relative to the inside of the cell. The cell is thus hyperpolarized under the anode, meaning that it is very, very difficult to activate.
If you apply the information above to the median nerve SSEP (Figure 4), then you can see why the anode is always distal, and the cathode is always proximal.
What happens when you accidentally reverse your stimulating electrodes when performing an SSEP test? The difficulty that you may experience in attempting to acquire an SSEP is explained by the phenomenon of anodal blocking (Figure 3). Thus, when bipolar electrodes have tips in the same orientation as a fiber, a fiber will be depolarized under the cathode, and hyperpolarized under the anode. If the hyperpolarization is large enough, an action potential initiated under the cathode may not be able to propagate through the region of hyperpolarization. If this is the case, the action potential will propagate in only one direction. While we often talk about the phenomenon of anodal blocking, you won't see this in the clinical scenario if you use appropriate stimulation parameters. For intraoperative monitoring of SSEPs, you should be using supramaximal stimulation. The high intensity stimulus will overcome any issues that may be experience as a result of anodal blocking.
Anodal Stimulation of Peripheral Nerves
When we use the term anodal stimulation, what we mean is that cations (+) flow from the anode, into the tissue, and back to the cathode (Figure 5). When applied to the surface of a nerve, anodal current will increase the concentration of cations (+) in the extracellular space under the anode. This will result in hyperpolarization, which, as I just mentioned, puts the cell in a heightened state of rest. So, what we see in Figure 5 is that the nerve axon becomes deactivated (hyperpolarized) under the anode.
The Importance of Cell Orientation
In all of the examples described thus far, the orientation of the cell under the stimulator has been horizontal with respect to the orientation of the anode and cathode (Figures 2-5). This is usually the case when stimulating nerves in the arms and legs.
What happens when the orientation of the cell is vertical with respect to the orientation of the anode and cathode? The answer is that things usually work exactly opposite to what we just discussed regarding horizontally-oriented cells.
This becomes particularly important in the brain where pyramidal cells of the cerebral cortex are vertically-oriented with respect to the surface where we stimulate.
Anodal Stimulation of Cerebral Cortex
Electrical stimulation of cerebral cortex is used for lots of reasons, but today I'm going to focus on motor evoked potentials (MEPs). If you use electricity (as opposed to a magnet) to evoke MEPs in your clinical practice, hopefully you know the following principle:
Whether you are stimulating the scalp over motor cortex, or directly stimulating the cortical surface, MEPs are always easiest to elicit and characterize when you use anodal, monopolar, pulse-train stimulation. Things change a little with subcortical stimulation, but that's a topic for a different day.
Starting with Fritsch and Hitzig (1870), many researchers have shown that monopolar stimulation of the motor cortex is more effective with an anode, as opposed to a cathode. Also, monopolar anodal stimulation seems to activate pyramidal cells directly.
One proposed mechanism is that anodal current enters (and hyperpolarizes) dendrites at the surface of the brain, then leaves and depolarizes the axon or cell body. One way to think about this illustrated in Figure 7.
Anodal stimulation is just the injection of positively-charged ions under the electrode. Because opposites attract, negatively charged ions migrate to the the very surface of cortex under the anode. You can think of this a current sink and the consequence is hyperpolarization of the apical dendrites of the pyramidal cell. In order to compensate for this current sink, a current source is generated distally such that positively-charged ions congregate around the other end of the pyramidal cell. This results in depolarization (activation) of the cell body, the axon hillock and the initial segment of the axon, which forms the corticospinal tract.
Of course, it isn't that simple! Computational simulations paint a more complex picture. As Figure 8 illustrates, the neural response to stimulation is likely a complex pattern of depolarization and hyperpolarization throughout the neural geometry of the cell, which is dependent upon stimulation parameters and the neural positions relative to the electrode. Clearly, when the long axis of the cell is oriented vertically relative to the orientation of an anodal stimulation electrode, the computation simulation supports hyperpolarization of the apical dendrites and depolarization around the axon hillock.
It all comes down to the orientation of the cell!
Think about this... when you place your monopolar stimulating electrode over the motor cortex and deliver anodal stimulation, your lowest threshold CMAPs are from the vertically-oriented cells just below your electrode. If you do transcranial MEPs, your electrode is probably C3 or C4, right? And, the electrode are just over the hand representation of the motor homunculus. You really have to increase the intensity to get MEPs from the legs, correct? This is because those "leg" cells are deep in the interhemispheric fissure and the cells are oriented horizontal to your anodal stimulating electrode. BUT, if you switch your polarity and deliver cathodal stimulation from the same electrode, MEPs from the legs are sometimes easier to elicit and hands become more challenging. This phenomenon works best when you are stimulation around threshold intensity. You can use this to troubleshoot your MEPs. If you begin stimulating and you get MEPs from the legs/feet at lower intensity than the arms/hands, then your polarity is probably reversed.
- Fritsch GT, Hitzig E. 1870. Über die elektrische Erregbarkeit des Grosshirns. Arch Anat Physiol Med Wiss 300–32. Translation in Von Bonin G. 1960. Some papers on the cerebral cortex. Springfield (IL): Charles C Thomas.
- Merrill DR, Bikson M, Jefferys JGR. Electrical stimulation of excitable tissue: Design of efficacious and safe protocols. J Neurosci Methods. 2005 Feb 15; 141(2):171-198.
- Nair DR, Burgess R, McIntyre CC, Lüders H. Chronic subdural electrodes in the management of epilepsy. Clin Neurophysiol. 2008 Jan;119(1):11-28. Epub 2007 Nov 26. Review.
- Ranck JB Jr. Which elements are excited in electrical stimulation of mammalian central nervous system: a review. Brain Res. 1975 Nov 21;98(3):417-40. Review.
- Stephani C, Luders HO. Electrical Stimulation of Invasive Electrodes in Extratemporal Lobe Epilepsy. In: Koubeissi MZ, Maciunas RJ, eds. Extratemporal Lobe Epilepsy Surgery. Montrouge, France: John Libby Eurotext; 2011. 261-313. Print.
Note: This article was originally published by Richard Vogel in 2015 and is being republished here for the benefit of ASNM members. The contents of this post are the work of the author and do not necessarily represent the views of the ASNM.
Posted By Joseph J. Moreira, M.D.,
Thursday, November 30, 2017
I hope this message finds you all well and that you had a wonderful Thanksgiving. It is now a family tradition that when things are either not going well, or we are complaining about life in general, that we force ourselves to think of 5 positive things. Yes, my partner is a psychotherapist! I am proud to update you on a number of items that I hope will brighten your day a bit.
The first order of business is to congratulate everyone on a well-run and successful election. I am very grateful to all the candidates that had the courage and spent the time to throw their hats in the ring and run for an office. It is a wonderful process to undertake as it gets you thinking about our field and what needs to be done to keep it moving in the right direction. It also gives each candidate a bit of exposure and helps them to network some and be recognized for their accomplishments. I urge all our members to consider being a part of this process and get involved in an election, a committee, a meeting, or whatever you have time for.
Our new President-Elect is Rich Vogel. He will become president after the Annual Meeting in 2019.
We also have 4 new Directors who will take office in 2019:
I am excited about our new board members and am looking forward to working with all of them. This society is in excellent hands and we owe the entire group that participated in this election a thank you for getting involved.
The second item I am grateful for is the recent board approval of our new Practice Guidelines for the Supervising Professional: Intraoperative Neurophysiologic Monitoring. This was over a year and a half in the making with the great efforts of an ad hoc committee comprised of original authors, board members, executive Committee members and general members. Great pains were undertaken to assure that the new document was properly updated. We strove to have the document reflect current practices while maintaining the highest quality of patient care. We will now submit the revision to other societies for their review and accept comments from them if any. The document will then be published after a final run through and consideration of any comments generated during the review period.
Item number three. We had one of our most successful Fall meetings ever in Baltimore. The main thrust was IONM and Medical-legal issues. Our Mock trial was a tremendous success and is the start of an all new type of creative format for our future meetings playing off a theme and using a more practical method of delivering the message.
That brings me to number four. Our Annual meeting will be held February 23-25 at the Swan and Dolphin in Disney World, Orlando, Florida. This will be held during President’s week off so please consider bringing the family. The meeting will be a new format of 2 tracks on day 1. Each session will have its own lectures, panel discussions and E poster presentations. The topics are cutting edge and all promise to be excellent. Please check out the agenda on our website.
Finally, number five. In keeping our promise to collaborate with other societies, May 1-6, 2018 we will be contributing to the 31st International Congress of Clinical Neurophysiology (ICCN) in Washington, DC. This is a great opportunity to hear from international neurophysiology experts and attend workshops and lectures. Note that this meeting is taking place during our usual Annual Meeting and that our Winter Meeting in Orlando is our Annual Meeting.
I look forward to seeing you all at the meetings and wish everyone a Happy, Joyous and Healthy Holiday Season.
Best Wishes, Joe
Joseph J. Moreira, MD
President, American Association of Neurophysiologic Monitoring
Posted By Administration,
Tuesday, November 14, 2017
Updated: Tuesday, November 14, 2017
ASNM is pleased to report the results of the 2018 Election:
Rich Vogel has been chosen as President-Elect.
The new Directors are:
Changes will take effect on May 1, 2018.
You can read about all of the candidates here.
Posted By Andrew Goldstein & Brett Netherton,
Tuesday, November 14, 2017
Updated: Tuesday, November 14, 2017
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Patient Grounding - Then and Now
Andrew Goldstein, BS, CNIM & Brett Netherton, MS, CNIM, FASNM
Current patient monitoring equipment standards require the use of isolated patient inputs including ground to minimize risk of harm due to unintended electrical currents. In the 1970s, increased awareness of electrocution risks led regulatory bodies to create standards phasing out the use of earth ground at the point of patient connection, as it was for previous generations of equipment (UL 544 1972, IEC 601-1 1977, ANSI/AAMI SCL 1978). However, many of the methodological conventions associated with the use of earth ground are still embedded in the performance of neurodiagnostics. As a field, we need to remove these outdated conventions from our practice and understand ground for true benefits and limitations.
Many of the problems encountered in discussing ground originate from the generic use of the term to represent several related but different concepts. We have earth ground, chassis ground, signal ground, isolated ground and technical ground. A discussion of all of the intricacies of the various types of ground is beyond the scope of this note so we will focus on earth ground and signal ground. These two concepts are the most relevant when discussing the issues of electrical safety and signal noise which are generally our main concerns regarding ground.
Earth ground refers to an electrical reference connected to the surface of the earth (see figure 1 below). In modern commercial and residential wiring, the ground pin of an electrical outlet is connected through wiring and/or the structure of the building to a conductor sunk physically into the ground. This is often water supply pipes, although there is some variation as the use of plastic plumbing elements becomes more common. At one time all grounds in electrical instrumentation were tied to an earth ground. The intent was to place various pieces of equipment at the same voltage potential avoiding the dangerous currents that could flow between equipment (through the patient) when differing voltages are encountered. The earth ground also had the capacity to shunt away unwanted electrical signals and reduce noise. In practice however, the earth ground introduced problems. Having everything referenced to the same earth ground, meant that if a break developed in a ground conductor, electrical current would find another path back to ground. This was especially a concern in wet environments as often encountered in operating rooms where there was a high probability of the current finding an easier path to ground through the patient. The noise reduction capacity of the earth ground was also compromised as more devices were attached to the ground conductor. The multiple resulting currents flowing through the ground introduced rather than reduced noise.
To counter these issues, isolation was introduced (see figure 2 below). Isolation is the breaking of the electrical pathways between two parts of a circuit. Through isolation the physical and electrical connection to earth ground is eliminated removing the path for currents to flow to a point of lower potential (the earth) through the patient. Multiple
levels of isolation exist in modern medical equipment resulting in there being no electrical pathway between any patient connection and earth ground. It is beneficial to understand that when the patient is no longer referenced (electrically linked) to earth, any voltages present on the patient no longer seek to drive currents to the lowest impedance pathway back to earth. The opportunity for dangerous currents and ground loops related to earth ground no longer exist with modern equipment. The patient connection labeled as ground on modern neuromonitoring equipment, sometimes referred to as isolated ground is more appropriately referred to as signal ground.
The signal ground does not have the high shunting capability that an earth ground had. Placing it on the patient in a region of high electrical noise will not cause the noise to be shunted or “grounded.” The main purpose of the signal ground to provide a common mode reference for the so-called active and indifferent electrodes that constitute the inputs to an amplifier channel. For this reason, the signal ground should be placed so that it sees the same noise signals as the active and indifferent electrodes to ensure that noise is optimally rejected.
What does this mean in practical terms?
The signal ground has no bearing on electrical safety. Furthermore, connecting any patient lead (including the one labelled ground) to an earth ground will actually create a safety hazard since it will defeat the isolation and reintroduce earth ground as a reference point.
Ground loops must also be thought of differently than in the past. The ground lead of each isolated circuit is a separate entity and having multiple grounds from separate circuits will not cause ground loops. Having multiple grounds from a single circuit however, can cause the noise problems associated with ground loops. Since it is possible to have multiple isolated circuits from the same device it is important to know the circuit configuration in order to place appropriate grounds. For example, some common 32 channel IONM systems consist of two separately isolated 16 channel amplifiers each of which have multiple places to connect the ground. It is important that a ground electrode be placed for each amplifier, and also that multiple grounds not be connected to the same amplifier.
Note: This article was originally published in The ASNM Monitor Newsletter (June, 2014). We are reposting it in our blog to give ASNM members convenient access to this important educational material. Please feel free to leave questions and comments.
Posted By Administrator,
Monday, November 13, 2017
Updated: Wednesday, August 30, 2017
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Utilizing the new ASNM Website:
- Contemporary look with new ASNM logo
- Responsive design
- Efficient menu system
- Member networking community
Our new website is compatible on any device. The menu system has been reorganized to facilitate navigation and help you find information quickly.
If you’ve been a member of ASNM for a while, you probably remember our monthly newsletter, The Monitor, which was distributed via email and archived on our website in pdf format. In an effort to enhance communication with our membership and keep you in the know, we decided to roll the newsletter into a blog where we could post articles and updates as frequently as possible. Each post will be tagged, archived and easily searchable. The content will be similar to what we published in our previous newsletter.
We launched a new community on the ASNM website called SocialLink. A brand-new way to easily connect with fellow colleagues, share information across the ASNM network and manage your membership preferences.
Finding member information and updates are easier than ever thanks to this exciting new enhancement.
Posted By Richard W. Vogel,
Tuesday, September 19, 2017
We are happy to introduce our membership to the new “Member Spotlight” section of the ASNM Blog. In this section, we will periodically introduce individual members to the society-at-large, highlight some of their achievements and ask them interesting questions. We hope this affords members of the ASNM the opportunity to get to know each other. If you would like to recommend someone, including yourself, for the member spotlight, please contact Rich Vogel.
For our inaugural Member Spotlight, we chose Gene Balzer, PhD, FASNM.
Dr. Balzer, as he hates to be called, was the 2017 recipient of the prestigious Richard Brown Award. Gene has been monitoring cases continuously since 1982. He is a founding member of ASNM and was also a founding ABNM board member. Dr. Balzer has over 100 publications, book chapters and presentations. His contributions to the ASNM, and the field of IONM at-large, are extensive. We sent Gene a bunch of statements and asked him to complete the sentence. His responses are posted below:
The greatest technological advancement in neuromonitoring has been:
Nice question to ask the oldest guy in the bunch. First, it would be the miniaturization of the computers (keep in mind, my first machine weighed 684 lbs.). Second, it would be the internet, so I wasn’t solo in the OR (more below). Third, it would be the TcMEP.
The best career advice I’ve ever received is:
FLAP – Finish, Like A Pro(fessional). My dad would always tell us, "If you finish everything with the same vigor as you start, you will be amazed how many times you are successful." And, to go with that, he’d tell us, "You don’t get a chance to re-play the down (as in a down in football), so give your best effort all the way thru the play".
A great article that everyone in the profession should read is:
Everything you can get your hands on, and everything that comes out. Everything, well beyond the IONM literature alone, is a building block to recognizing impact on patient care and improving outcomes. And, keep in mind, unlike when I started (I would push the machine into the room and a carry a 3 ring binder full of articles related to anything to do with the case), now, you have full access to your library, and the world’s library, at your fingertips. But, my best answer remains to read, read and read. Nothing is a constant.
The best thing about attending an ASNM meeting is:
Truthfully, drawing on a bar napkin! The best thing about our Society, and profession, is the group is so small and everyone is so approachable. Sitting down with someone and asking questions and getting information, opinions and advice is readily available to every attendee. So, take advantage of it.
One of my favorite apps is:
Seriously, I am just happy when my phone rings and the person on the other end says “hello”! But, I would have to say, I do enjoy the TED talks app and getting snapchats from my kids, although I have no clue how to send one!
A common misconception about _________ is: _________.
A common misconception about life is that it is easy and fair. Life will throw you curve balls, sometimes sharp and difficult to handle; relax and deal with it. You can only be the best person you can be.
My favorite film(s) of all time is/are:
Well it would have to be Pretty Woman... “Hollywood, city of dreams, everyone has one, what’s yours”.
At the top of my travel bucket-list is:
Anytime I get to leave North Dakota in the Winter! Snow and cold are fun when your 10 years old, not some much when you have to shovel it.
My favorite hobby is:
Farming: helping plants and people grow and develop into something wonderful. Helping someone develop as a clinician, manager, leader is like growing great tomatoes.
One of my pet peeves is:
Lack of accountability, not finishing like a pro…
If I didn’t become a neurophysiologist, I probably would have been a(n):
Truthfully, I don’t really know, I started doing this when I was 19 years old, doing ABR’s in the Neonatal nursery, and I have no regrets. I have met, befriended and learned from 3 generations of people passionate about this patient care activity.
If you would like to contact Gene Balzer, he can be found in the Membership Directory at the top of this page.
That concludes our inaugural Member Spotlight. Please be sure to subscribe to this blog so you can stay up-to-date on communications from the ASNM!
Posted By Joseph J. Moreira, M.D.,
Thursday, August 31, 2017
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Greetings to all in the IOM community. If you are reading this address then you are looking to the ASNM for information of some kind, or just curious to see what we have to offer. If you have visited us previously or are a member then you will notice that we just launched our new website. I want to extend a thank you to our two board members that orchestrated the new web design from the start, Dr. Richard Vogel and Dr. Bryan Wilent. Great job! Here is a brief message from Rich and Bryan:
“We're very excited to announce that our website has been redesigned to enhance your experience as a member of the ASNM. The new website features a modern, responsive design with a new menu system that simplifies navigation on any device. The website now contains a blog, which replaces the old Monitor Newsletter. From the blog, you can expect frequent posts from the ASNM to keep you up-to-date on news and announcements from the ASNM, including upcoming meetings and webinars, interesting case studies, clinical commentary, recently-published literature, and other news from around the neuromonitoring community. Finally, the website will include a member community, like a social network, that provides a new way to connect with fellow colleagues, share information across the ASNM network and manage your membership preferences. We encourage you to explore the new website and all of its features, and don’t forget to subscribe to our blog!”
I had the honor of taking the reigns over during our Annual Meeting in Cleveland. We celebrated the 40th anniversary since the first IOM meeting was held there. I was humbled by the experience of meeting the pioneers of our field. It was an amazing sight to see our youngest and brightest at the meeting mingling with the likes of Dr. Tamaki, Schramm, Nuwer, Nash, Kartush, Moller, Sloan and Koht. Drs. Koht and Eccher and the rest of the planning committee did an outstanding job of coordinating and creating this event. Thanks to all involved.
One of this year’s themes is about growth as a field and as a society. We are considering a corporate membership plan that would give IOM companies and institutions a discounted rate for a group membership. The larger we grow as a society the more presence and influence we will have. Our offerings will also grow with a larger membership base. I encourage our current members to recruit others in the field to join and perhaps participate on a committee or in any way possible.
Another main theme is about improving communication. One of the messages I have taken away from my few months as President is that we all aspire to improve the ground operations of the IOM field. It all comes back to a common theme of excellent communication with the patient as the central focus. We have recently heard many different messages and ideas of how our field can improve, but the common theme is communication. The link between the personnel in the OR and the supervising professional, the surgeon/anesthesiologist and the IOM team, and so on, are critical to the benefit of the patient. As there is always room for improvement, I urge all of us to step back and examine how we communicate daily before, during and after our surgeries and enhance the process in any way possible.
Our third theme this year is about collaborating with other societies. I had the opportunity to attend the annual ASET meeting this month along with the ASNM’s Executive Director Carol Ingmanson. We participated as a vendor and promoted the ASNM. Carol did a great job of setting up and coordinating the trip and we added several members and potentially a few more corporate sponsors. We are also planning a joint meeting May 1-6, In Washington DC, just before the International Congress of Clinical Neurophysiology (ICCN). More details to follow.
If you have not already made plans to attend please look at our upcoming Fall Meeting in Baltimore on September 9-10. We have a very interesting and practical agenda. “What to do When Something Goes Wrong and Hot Topics” We are featuring a Mock Trial and several talks on managing and avoiding potential legal issues. Drs. Eva Ritzl, Trey Lee and Robert Minahan and the rest of the planning team have done an excellent job of creating a very new and innovative meeting. Thanks to all!
Our Annual 2018 Meeting will be held early this year on February 23-25 at Disney’s Swan and Dolphin Resort in Orlando. Great family destination!
Last but certainly not least please check out our Webinar schedule. Our next webinar is on 10/11 with Dr. Charles Yingling, “A Comprehensive Guide to Corticospinal Tract Mapping and Monitoring”
Thank you all for logging in, I look forward to seeing you all in Baltimore and at future meetings.
Joseph J. Moreira, M.D.