Speaker: Chris Martin, Surgical Neurophysiologist (9:46) speaks at TxANA Conference Part I
In August, 2016, Neuro Alert exhibited at the TxANA Annual Convention & Trade Show. Here, Chris Martin, one of Neuro Alert’s Senior Surgical Neurophysiologists, was asked to present “Introduction to Intraoperative Neurophysiology” and “Intraoperative Monitoring Applications and Considerations.” In this six-part presentation, Martin walks us through the origins of Intraoperative Monitoring to present-day applications.Transcripts to follow:
Chris Martin, CNIM, Surgical Neurophysiologist:
I’d like to thank Bill for the invitation. I was very excited to to get it. I mean who doesn’t want to come to Houston in the middle of summer, but now it’s actually good to be back. I spent a good part of last year coming down to Houston Methodist and monitoring there and maybe worked with some of you there, but it’s just so critical because as neuromonitoring people and you anesthesia people — we really do work in concert to provide the best patient care possible so it’s an important opportunity to kind of make sure that we all are understanding each other’s perspectives.
So anyways lots to get to — let’s get started. Okay so I wanted to go over a little bit of the history of neuromonitoring, and it’s hard to kind of know exactly how far back to go. You can think of Galvani and Volta stimulating you know frogs legs — or if you wanted to look at anything to do with electricity itself goes back to ancient Greeks and Egyptians — but for our purposes we’ll start with Richard Caton, who in 1875 reported in the Proceedings of the British Medical Association, that he successfully recorded electrical activity off of the living brains of rabbits in this case. So that seems like a relatively momentous finding, but in fact he sort of faded into obscurity and nothing much was done on that until more than 50 years later when Hans Berger then cited Caton’s work in 1929 when he was discovering the Alpha frequency brain waves which is the beginning of EEG, so he had a system where a pen would deflect upwards for a negative charge and downwards for positive charge so if you get a pen deflecting up and down based on the charge it’s recording and sort of scroll some paper under then you can get a printout of that electrical activity which makes sense. EEG is electroencephalography — the writing of the electrical activity of the brain. So that was sort of the origins of EEG 1929 still in use today in the operating room.
In the sixties then with Harrington rods and and Luque wires no sublaminar wires and things like that surgeons became more able to make much more aggressive corrections on spinal deformities like scoliosis. With those more aggressive surgical techniques came an increase in iatrogenic equality and fortunately so they started to look for ways to sort of evaluate the integrity of the spinal cord while they’re doing these more aggressive procedures. Here is Pierre Stagnara, a French surgeon. Has anyone here or who might have done Stagnaro wake-up tests intraoperatively? No one? Yeah so what he essentially charged Madame Vauzelle, his anesthesiologist with doing was to wake the patient up, while they’re still prone just probably in an adolescent patient and keep them right on the edge of being able to respond to commands to wiggle their toes and move their extremities so they can be evaluated clinically but at the same time keep them comfortable enough that they’re not thrashing around with this giant gaping wound the entire length of their back. So that’s a very delicate technique thatMadame Vauzelle developed and was able to perfect, but you know Stagnara is the surgeon, it’s known as the Stagnara wake up test. To me it should be really the Vauzelle wake-up test, but he gets all the credit so let’s kind of give him one of those.
So that was a really sort of risky way of evaluating the neuro-integrity of the spinal cord. People were looking for alternatives to that where they can maintain the patient under general anesthesia so Betty Grundy, who’s an anesthesiologist in Cleveland, with Clyde Nash and Rich Brown helped them develop a technique to monitor the spinal cord function while still under general anesthesia and they decided to use somatosensory evoked potentials, which we’ll see are mediated up the dorsal column and are able to be recorded what without having to wake up the patient. So this was maybe an improvement over the more risky clinical evaluation.
A group in Japan at the same time, Tamaki and his anesthesiologist Shemoji had worked on a more invasive technique along those same lines trying to keep, you know, keep the patient under general but still be able to evaluate, and this involved subdurally placed electrodes, so it was more invasive. It didn’t catch on over here, but it was another attempt at maintaining the integrity of those pathways without having to wake up the patient.
The two groups got together in 1977 to really discuss the various techniques, and this was essentially the first neuromonitoring conference. At that conference Dr. Tamaki, the surgeon from Japan, said this following quote which I wanted to highlight specifically: “The evolution of anesthesiology has influenced and supported the development of intraoperative monitoring.” So I think that’s a critical statement that we’ll continue to see going forward.
Robert Levine then –another modality was developed and first used in the operating room in 1978, which is the brainstem evoked response. Shortly thereafter, Aage Moller in Dallas was working with Peter Ginetta and really invented the microvascular decompression technique using brainstem auditory evoked responses in order to safely be able to perform that surgery. So that’s kind of a case where a surgical procedure would not have been possible without concomitantly having some intraoperative monitoring to go with it.
The somatosensory evoked potentials as I said are an ascending sensory pathway and there’s plenty of case reports of intact SSEP’s and yet the patient wakes up with a motor deficit because it’s really not monitoring the motor pathways directly. You’re inferring what the integrity of the motor is from your SSEP’s so that was a short-coming that was early on realized, and Merton Morton then sort of looked for a way to run some signals through the descending motor pathways. In 1980 they developed this transcranial motor evoked potential technique. There’s Merton getting his head zapped to generate some motor evoked potentials in the classroom there. And the reason he’s in the classroom or the laboratory and not in the operating room doing these motors is because at the time in 1980 the typical technique from an anesthisia-point-of-view was nitrous, and halogenated gases and that technique precludes the recording of MEP’s in general. So this was a laboratory finding that wasn’t yet able to, you know, be used clinically in the operating room.
In an effort to sort of get around the pitfalls of that anesthetic technique at the time that was prevailing, it’s something called neurogenic MEP’s were investigated where again it’s more invasive — some needle electrodes were inserted in adjacent lamina in the spine and they’re attempting to stimulate you know proximal to where the wound was and then record something off distally to that. That way you’re bypassing all the synapses where your drugs are taking effect and it should be sort of relatively resistant if you’re just generating responses at high and low in the spinal cord.
In the meantime, techniques in anesthesia were evolving as well. So this 1991 paper talked about finally the use of propofol in the operating room and what kind of effect that would have on motor evoked potentials. So we’re starting to get, you know, some coming together of the anesthesia evolving, the intraoperative monitoring evolving, we’re getting into something close to where it is today.
Rich Toleikis who is a PhD but he was in the Department of Anesthesia at Rush University Medical Center, Chicago took a look at these neurogenic MEP’s in 2000, and using collision studies, was able to essentially disprove them as pure motor. What was happening was there was some orthodromic motor component to those responses but also some antidromic sensory, and if one or another of those elements of your response went away, you’re not sure whether that was the sensory motor. So they’re not really that useful, and they, therefore, fell out of favor, but we now have the transcranial evoked potentials which are a pure motor response. We now have some anesthesia techniques that are allowing us to use those in the operating room, and so that’s where we are today with the multimodality technique of motors sensory EMG.
That’s sort of the gold standard of neuromonitoring, but it really wasn’t until 2000, relatively recently, that that sort of became the gold standard. So as we’ve seen with the contributions throughout the history of neuromonitoring, really the development and advancement of it has been in collaboration with anesthesia and will continue to be so in the future. So it’s definitely something that you all can participate in if you find an idea that’s going to help improve the delivery of this intraoperative monitoring.
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