Acceleromyography

[epidural man]

I love our acceleromyographs in the OR. I think they are one of the coolest monitors we have. I know they don't work a lot of the time, so I can imagine the same people that hate BIS probably hate acceleromyography because it can be unreliable.

But my problem is this - I don't really understand them, because in my residency days when I actually read about stuff and learned things - I don't remember learning anything about acceleromyography.

So I have a question or two. But first - the background to the question.

On our monitor - the output of the device shows a percentage of the TOF, which is what we are told is really important, and we base clinical decisions on this number.

However, with traditional qualitative peripheral nerve monitoring, we made judgements based on feel (did I feel no twitches? One twitch? two twitches? How many post-tetanic twitches did I feel? Was fade noticeable?)

Currently, with the quantitative monitoring (acceleromyography), I get a graphical output of the four twitches, which show a strength of the twitch based on the height of a bar graph, which in my mind is deceiving, because you may think that the percentage it is showing corresponds to the decrease in the bar height - but it isn't, it is a percentage of the first to fourth twitch (as far as I understand).

But it would seem to me that a MUCH MORE important measure, would be the strength of the twitches - or the percentage of the BAR HEIGHT - but as far as I can tell, no one even talks or mentions this parameter - even though it is shown graphically.

Because I want to know, what does a manual qualitative "one twitch" correspond to with an acceleromyograph? How much twitch height is that? Why does no one talk about the strength of the twitches, rather than the ratio? The ratio seems like crap to me anyway - half the time all four bars seem to decrease in strength at the same ratio - unlike what we where told should happen with non-depolarizers. Half the time with sux, they DON'T decrease in strength at the same ratio like we were told is suppose to happen.

So my question is - where can I learn more about the significant of the twitch strength/height? Where is that written down?

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[daneeka]

The usefulness of a ratio vs an absolute value is that what really matters is fade.

Looking at an absolute single twitch value height has plenty of disadvantages.
-A reduction in twitch height could mean many things. Sure, it might be residual neuromuscular block. Or the skin impedence might be high, or the electrodes not well attached or whatever.
-It doesn't mean anything unless you calibrated for baseline twitch height pre-NMBD

Before accelerometers/electromyographs, double-burst was good for residual block. Detectable fade = not reversed enough. It's more sensitive than doing TOF without an accelerometer.

But TOF with an accelerometer is the most sensitive way to look at residual block. Looking at the ratio automatically compensates for whatever other confounders may drop your twitch height - because these affect your first twitch just as much as your last twitch. So, your first twitch is construed as 'baseline' while the following twitches are evaluated as a % of this.

Above all, it is only fade that matters. This is because fade demonstrates that there is still antagonism at the pre-synaptic ACh receptors, which therefore means the synapse has difficulty recruiting more vesicles of ACh to send across to the NMJ. This will still be evident with fairly light levels of block where the T1 is back to normal.

This is a nice look at some of your questions:
Monitoring the Neuromuscular Junction

 

[epidural man]

The usefulness of a ratio vs an absolute value is that what really matters is fade.

Looking at an absolute single twitch value height has plenty of disadvantages.
-A reduction in twitch height could mean many things. Sure, it might be residual neuromuscular block. Or the skin impedence might be high, or the electrodes not well attached or whatever.
-It doesn't mean anything unless you calibrated for baseline twitch height pre-NMBD

Before accelerometers/electromyographs, double-burst was good for residual block. Detectable fade = not reversed enough. It's more sensitive than doing TOF without an accelerometer.

But TOF with an accelerometer is the most sensitive way to look at residual block. Looking at the ratio automatically compensates for whatever other confounders may drop your twitch height - because these affect your first twitch just as much as your last twitch. So, your first twitch is construed as 'baseline' while the following twitches are evaluated as a % of this.

Above all, it is only fade that matters. This is because fade demonstrates that there is still antagonism at the pre-synaptic ACh receptors, which therefore means the synapse has difficulty recruiting more vesicles of ACh to send across to the NMJ. This will still be evident with fairly light levels of block where the T1 is back to normal.

This is a nice look at some of your questions:
Monitoring the Neuromuscular Junction

Cool,

I'll take a look.

What you say makes sense if you don't have a baseline - but If I get a good baseline after propofol, then give the NMB, start the accelerometer - and watch the twitch height and TOF change, I feel like twitch height makes much more sense to give me an idea of when the patient won't reach up and grab the tube, or cough or buck with intubation - vs TOF - because if the twitch height is obviously 10% of what it was originally, yet TOF % is around 90%, I'm trusting twitch height.

Honestly, I am more interested in those numbers on the way in - then on the way out (I know...opposite of what is most important probably).

 

[daneeka]

You're probably right that done properly absolute twitch height can be just as useful - I'm just far too lazy to put it on at induction.

Do you find that with your low twitch height, but good TOF % situation, does the twitch height continue to improve with time/more reversal?

Luckily we can unlearn all this stuff pretty soon with the wonders of sugammadex!

 

[epidural man]

You're probably right that done properly absolute twitch height can be just as useful - I'm just far too lazy to put it on at induction.

Do you find that with your low twitch height, but good TOF % situation, does the twitch height continue to improve with time/more reversal?

Luckily we can unlearn all this stuff pretty soon with the wonders of sugammadex!

Yes, it seems to.

Sugammadex is really a great thing.

I think merk priced it wrong. if they made it cheaper, it would be used 1000x more. I don't understand how they can't figure that out. I'm basically ******ed and I know that if you sell 1000 vials at $20, you make more money than selling 100 vials at $90.

 

[Ronin786]

Yes, it seems to.

Sugammadex is really a great thing.

I think merk priced it wrong. if they made it cheaper, it would be used 1000x more. I don't understand how they can't figure that out. I'm basically ******ed and I know that if you sell 1000 vials at $20, you make more money than selling 100 vials at $90.

It's not going to stick at $90 for long. Once enough people are using it, that price is going to skyrocket. People aren't going to want to go back to Neo/Glyco.

 

[dhb]

It's not going to stick at $90 for long. Once enough people are using it, that price is going to skyrocket. People aren't going to want to go back to Neo/Glyco.

If you don't buy into the new trend of deep neuromuscular block is better for surgery then Neo/Glyco is fine. If both products are priced the same then of course Suggamadex is superior.
I don't like using rocuronium: too much variability.

 

[BLADEMDA]

Sugammadex for reversal. Problem solved.

 

[epidural man]

If you don't buy into the new trend of deep neuromuscular block is better for surgery then Neo/Glyco is fine. If both products are priced the same then of course Suggamadex is superior.
I don't like using rocuronium: too much variability.

I hate the drug. it is ridiculously variable.

however, now with suggamadex being cheaper than neostigmine, I only use it.

 

[epidural man]

The usefulness of a ratio vs an absolute value is that what really matters is fade.

Looking at an absolute single twitch value height has plenty of disadvantages.
-A reduction in twitch height could mean many things. Sure, it might be residual neuromuscular block. Or the skin impedence might be high, or the electrodes not well attached or whatever.
-It doesn't mean anything unless you calibrated for baseline twitch height pre-NMBD

Before accelerometers/electromyographs, double-burst was good for residual block. Detectable fade = not reversed enough. It's more sensitive than doing TOF without an accelerometer.

But TOF with an accelerometer is the most sensitive way to look at residual block. Looking at the ratio automatically compensates for whatever other confounders may drop your twitch height - because these affect your first twitch just as much as your last twitch. So, your first twitch is construed as 'baseline' while the following twitches are evaluated as a % of this.

Above all, it is only fade that matters. This is because fade demonstrates that there is still antagonism at the pre-synaptic ACh receptors, which therefore means the synapse has difficulty recruiting more vesicles of ACh to send across to the NMJ. This will still be evident with fairly light levels of block where the T1 is back to normal.

This is a nice look at some of your questions:
Monitoring the Neuromuscular Junction

Daneeka,

I finally read the article - pretty cool. Thanks for sharing.

According to the graph, a twitch height reduction of about 50% corresponds to about 85% blockage. That's good info!

 

[drmwvr]

I hate the drug. it is ridiculously variable.

however, now with suggamadex being cheaper than neostigmine, I only use it.

If the proper "hygiene" is observed rocuronium, it isn't so bad. If it stays out of refrigeration or languishes in a cart or omnicell forever, it is less predictable. When Zemuron was first introduced, you could set your watch by it because the sales representatives would be very attentive to how the drug was cared for. People liked it and used it a lot so there wasn't much that sat around for very long. But with suggamadex, it doesn't matter. I like it because I hate mixing vecuronium.

 

[deleted682700]

What is the incidence of bronchospasm with suggamedex. I am Leary of new drugs and will wait for 10 year post marketing data from practitioners

 

[pgg]

What is the incidence of bronchospasm with suggamedex. I am Leary of new drugs and will wait for 10 year post marketing data from practitioners

It's been 9 years since it was approved in the EU, so you don't have long to wait.

Also, the risk of adverse events is probably dose dependent. IIRC the initial studies were done with 16 mg/kg doses, the amount you'd need to immediately reverse an RSI dose of rocuronium. Most of us are only using 2-4 mg/kg for routine reversal at the end of a case.