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Understanding Patient Grounding

Posted By Andrew Goldstein & Brett Netherton, Tuesday, November 14, 2017
Updated: Tuesday, November 14, 2017

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 As a field, we need to remove these outdated conventions from our practice and understand ground for true benefits and limitations.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.

Figure 1

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.

Figure 2

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.

Tags:  Education Highlight 

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Utilizing our New Website with Member Network and Blog

Posted By Administrator, Monday, November 13, 2017
Updated: Wednesday, August 30, 2017

Utilizing the new ASNM Website:

Website features:

  • Contemporary look with new ASNM logo
  • Responsive design
  • Efficient menu system
  • Blog
  • 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.

The Blog:

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.

Member Community:

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.

Tags:  Announcement 

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Member Spotlight - Learn More About Gene Balzer

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!

Tags:  Member Spotlight 

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President's Message - September 2017

Posted By Joseph J. Moreira, M.D., Thursday, August 31, 2017

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.

Tags:  President's Message 

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