Intraoperative Neuromonitoring

In IONM, "you should learn crani's" means you should learn/do more. But why not go for more?

(Yes, back on this again)

I already got some pushback last month on a similar post that it's not worth it.... mostly boiled down to effort, higher stakes, and $.

Some made the counter points of passion.

I made some points of building optionality in an unknown future.

But here's a third reason to continue to poke around, get your hands dirty, and help make improvements in all aspects of our job.

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We spend a lot of our lives at work and you don't always want things to be easy and familiar.

Future you wants you to mentally/emotionally struggle a bit. Just like it wants you to move heavy weights (or other forms of struggling physically).

Our DNA has been molded to survive in scarce resources and thrive with struggle.

We weren't built to live the life of a house cat, but one that needs to figure out what to eat, how to not get eaten, and make due with shelter.

Consider this:

The tamer the animal, the smaller the brain... domesticated animals had brains about 25% smaller than their wild forebears.

The first year of IONM is a mental struggle. The next 30 depends on how you go about it.

My advice: be the cat that eats the rat, not the canned kibble.

Corticobulbar MEPs have come into favor for post-fossa surgery.

But what about blink reflexes? 😉

Like other reflexes, it has largely been abandoned due to the effects of anesthesia.

But corticobulbar MEPs aren't bulletproof, either. Stimulating centrally vs peripherally seems to be an ongoing complication. False positives with anesthetic fade are another concern.

In a small sample size, Aydinlar et all found utility in adding the blink response to their monitoring plan.

They were able to produce a case where the blink response demonstrated the change and corticobulbar MEPs were uneventful.

𝗪𝗵𝗮𝘁 𝘄𝗲𝗿𝗲 𝘁𝗵𝗲𝗶𝗿 𝘁𝗼𝘁𝗮𝗹 𝗳𝗶𝗻𝗱𝗶𝗻𝗴𝘀?

𝘈𝘤𝘤𝘰𝘳𝘥𝘪𝘯𝘨 𝘵𝘰 𝘰𝘶𝘳 𝘮𝘰𝘥𝘦𝘭, 𝘪𝘧 𝘢 𝘉𝘙 𝘸𝘢𝘴 𝘱𝘳𝘦𝘴𝘦𝘳𝘷𝘦𝘥, 𝘪𝘵 𝘱𝘳𝘦𝘥𝘪𝘤𝘵𝘦𝘥 𝘵𝘩𝘦 𝘱𝘢𝘵𝘪𝘦𝘯𝘵’𝘴 𝘰𝘶𝘵𝘤𝘰𝘮𝘦 𝘢𝘴 𝘯𝘰𝘳𝘮𝘢𝘭 𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯–𝘮𝘰𝘥𝘦𝘳𝘢𝘵𝘦 𝘥𝘺𝘴𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯; 𝘪𝘧 𝘱𝘦𝘳𝘮𝘢𝘯𝘦𝘯𝘵𝘭𝘺 𝘭𝘰𝘴𝘵, 𝘢𝘴 𝘴𝘦𝘷𝘦𝘳𝘦 𝘥𝘺𝘴𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯–𝘵𝘰𝘵𝘢𝘭 𝘱𝘢𝘳𝘢𝘭𝘺𝘴𝘪𝘴 𝘪𝘯 𝘵𝘩𝘦 𝘱𝘰𝘴𝘵𝘰𝘱𝘦𝘳𝘢𝘵𝘪𝘷𝘦 𝘱𝘦𝘳𝘪𝘰𝘥 𝘸𝘪𝘵𝘩 0.75 𝘴𝘦𝘯𝘴𝘪𝘵𝘪𝘷𝘪𝘵𝘺, 1 𝘴𝘱𝘦𝘤𝘪𝘧𝘪𝘤𝘪𝘵𝘺, 𝘢𝘯𝘥
0.968 𝘢𝘤𝘤𝘶𝘳𝘢𝘤𝘺; 𝘢𝘯𝘥 𝘵𝘩𝘪𝘳𝘥-𝘮𝘰𝘯𝘵𝘩 𝘱𝘦𝘳𝘪𝘰𝘥 𝘸𝘪𝘵𝘩 1 𝘴𝘦𝘯𝘴𝘪𝘵𝘪𝘷𝘪𝘵𝘺, 1 𝘴𝘱𝘦𝘤𝘪𝘧𝘪𝘤𝘪𝘵𝘺, 𝘢𝘯𝘥 1 𝘢𝘤𝘤𝘶𝘳𝘢𝘤𝘺.

𝘚𝘪𝘮𝘪𝘭𝘢𝘳𝘭𝘺, 𝘸𝘩𝘦𝘯 𝘧𝘢𝘤𝘪𝘢𝘭 𝘊𝘰𝘔𝘌𝘗𝘴 𝘸𝘦𝘳𝘦 𝘱𝘳𝘦𝘴𝘦𝘳𝘷𝘦𝘥, 𝘰𝘶𝘳 𝘮𝘰𝘥𝘦𝘭 𝘢𝘯𝘵𝘪𝘤𝘪𝘱𝘢𝘵𝘦𝘴 𝘯𝘰𝘳𝘮𝘢𝘭 𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯–𝘮𝘰𝘥𝘦𝘳𝘢𝘵𝘦 𝘥𝘺𝘴𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯 𝘢𝘯𝘥, 𝘪𝘧 𝘭𝘰𝘴𝘵, 𝘴𝘦𝘷𝘦𝘳𝘦 𝘥𝘺𝘴𝘧𝘶𝘯𝘤𝘵𝘪𝘰𝘯–𝘵𝘰𝘵𝘢𝘭 𝘱𝘢𝘳𝘢𝘭𝘺𝘴𝘪𝘴 𝘰𝘵𝘩𝘦𝘳𝘸𝘪𝘴𝘦. 𝘐𝘵 𝘱𝘦𝘳𝘧𝘰𝘳𝘮𝘦𝘥 𝘸𝘪𝘵𝘩 0.937 𝘢𝘤𝘤𝘶𝘳𝘢𝘤𝘺, 0.5 𝘴𝘦𝘯𝘴𝘪𝘵𝘪𝘷𝘪𝘵𝘺, 𝘢𝘯𝘥 1 𝘴𝘱𝘦𝘤𝘪𝘧𝘪𝘤𝘪𝘵𝘺 𝘧𝘰𝘳 𝘵𝘩𝘦 𝘱𝘰𝘴𝘵𝘰𝘱𝘦𝘳𝘢𝘵𝘪𝘷𝘦 𝘱𝘦𝘳𝘪𝘰𝘥 𝘢𝘯𝘥 𝘸𝘪𝘵𝘩 0.968 𝘢𝘤𝘤𝘶𝘳𝘢𝘤𝘺, 0.667 𝘴𝘦𝘯𝘴𝘪𝘵𝘪𝘷𝘪𝘵𝘺, 𝘢𝘯𝘥 1 𝘴𝘱𝘦𝘤𝘪𝘧𝘪𝘤𝘪𝘵𝘺 𝘧𝘰𝘳 𝘵𝘩𝘦 𝘵𝘩𝘪𝘳𝘥-𝘮𝘰𝘯𝘵𝘩 𝘱𝘦𝘳𝘪𝘰𝘥.

Their recommendation is a further look at the utility of adding BR to your monitoring plan. It might just be a helpful complement.

𝗪𝗵𝗼 𝘄𝗮𝗻𝘁𝘀 𝘁𝗼 𝘀𝗵𝗮𝗿𝗲 𝘁𝗵𝗲𝗶𝗿 𝗲𝘅𝗽𝗲𝗿𝗶𝗲𝗻𝗰𝗲?


Intraoperative Neuromonitoring of Blink Reflex During Posterior Fossa Surgeries and Its Correlation With Clinical Outcome

The most common change in adult spinal correction surgery? Anesthesia? Positional? Legitimate guesses, but not it. Results below.

A new paper's results showed a different story.

Those are secondary issues of doing the surgery, but it was the actual maneuvers of the surgery that, by a large amount, were the cause of the most signal changes.

Sounds reasonable, but not always the collective experience when speaking to others in the field.

Or my own, which would have positioning and anesthesia much higher.

See the below results for adult spinal deformity cases and let me know if it matches your experience.

The most frequent causes of IONM changes were due to surgical maneuver (86.3%), followed by changes in blood pressure/temperature (11.4%), unknown cause (1%), patient positioning (.7%), oxygenation (.3%), and anesthesia (.3%).



Cottone, C., Kim, D., Lucasti, C., Scott, M. M., Graham, B. C., Aronoff, N., ... & Patel, D. (2024). Causes of Intraoperative Neuromonitoring Events in Adult Spine Deformity Surgery: A Systematic Review. Global Spine Journal, 21925682241242693.

See you all there!

Conflicting IONM signal changes lead to the rule "When you hear hoof beats, think horses, not zebras." And so we troubleshoot, but here's when to break it...

Well, not break it, but start considering zebras after we troubleshoot.

(Almost) without fail, if you're getting something screwy, something got screwed up.

Can't get a TOF?

Well, either some mm relaxants were slipped in, or you're recording or stimulating from the wrong areas.

We check our pods and smack our heads for mixing up our rights and lefts (or something else).

For the most part, we should be able to spot most screw-ups if we either don't see the response we expect, or it's inverted.

But when things check out, we increasingly consider differentials out of the ordinary.

Sometimes it's some anatomical variant outside of what we learned from Netter's textbooks. Other times, it's potentially an underlying condition.

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In the case study cited below, they had changes that weren't as straightforward as you'd assume in this C3-7 ACDF when troubleshooting checked out.

+ EMG in the bicep, loss of bilateral lower extremity SSEP, loss of hand/leg tcMEP responses...

All with an intact ulnar nerve SSEP.

So let's think through this...

- EMG in the Delt puts us upper/mid cervical (C4-7). Textbook calls it C5.
- we lost B LE SSEP after, so we know the dorsal column was affected. It's affecting the cord.
- we lost L hands (no BSL on R hands) and lower extremity, but not rostral muscle groups.

BUT, the ulnar nerve SSEP (C8-T1) was preserved. How could we spare that one tiny section of the spinal cord?

It's easy to get blinders on and think through possible effects due to the surgical injury, If you weren't able to get your mind out of the level of the cord, you might not have come to a potentially correct differential.

Martin-Gruber anastomosis explains it. (If you don't know what this is, Google it and look at the image).

We don't start with Martin-Gruber (it's rare), but we need to know when a horse is a zebra.

And have a good reason to add/remove it from our differential list.



Shore, S., Sabetta, Z., Schneider, L., Taylor, Z., Chyatte, D., & George, T. Martin-Gruber Anastomosis Explains Bizarre Intraoperative Neuromonitoring Data: A Case Report. World J Surg Surgical Res. 2024; 7, 1521.