Understanding Phase II block by sux

[jihong]

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Trying to understand Phase II block by sux a little better. I know that phase II block occurs with repeated or extended periods of sux application in which the nerves become repolarized but desensitized and produce a twitch response identical to that of non-depolarizers.

My question is more clinical. How does a patient present when he's in phase II block? Texts say that phase II block manifests with tachyphylaxis (requiring increased doses to illicit the same response) and that increasing doses of sux would be required to maintain paralysis. However, if the nmj is desensitized to sux AND ACh, then wouldn't the patient still be paralyzed despite being unresponsive to sux? Since the patient is not responsive to ach as well, the patient would still not be able to move?

In other words, if I'm noting tachyphylaxis by requiring to increase sux, it means I want the patient paralyzed. Firstly, how would I know that I need increasing doses of sux unless the patient is moving/breathing/showing signs of movement unless that patient is reacting to ACh? But since in phase II block, the nmj is insensitive to ACh, that shouldn't be the case!

Confused...

 

[Planktonmd]

Trying to understand Phase II block by sux a little better. I know that phase II block occurs with repeated or extended periods of sux application in which the nerves become repolarized but desensitized and produce a twitch response identical to that of non-depolarizers.

My question is more clinical. How does a patient present when he's in phase II block? Texts say that phase II block manifests with tachyphylaxis (requiring increased doses to illicit the same response) and that increasing doses of sux would be required to maintain paralysis. However, if the nmj is desensitized to sux AND ACh, then wouldn't the patient still be paralyzed despite being unresponsive to sux? Since the patient is not responsive to ach as well, the patient would still not be able to move?

In other words, if I'm noting tachyphylaxis by requiring to increase sux, it means I want the patient paralyzed. Firstly, how would I know that I need increasing doses of sux unless the patient is moving/breathing/showing signs of movement unless that patient is reacting to ACh? But since in phase II block, the nmj is insensitive to ACh, that shouldn't be the case!

Confused...

Basically if you have a phase 2 block that means you have a block that acts like a non depolarizing block ( there could be some twitches, tetanic response, and post tetanic augmentation), and giving more Sux does not produce the expected disappearance of these twitches or that tetanic response at the usual doses (tachyphylaxis).

 

[narcusprince]

Plankton. Do you ever run Succ drips? Whats your technique? I vagually remember 3 amps in 250cc of lr on a micro dripper titrated to effect.

 

[jwk]

We used to do sux drips in the dark ages. It was available in a 1gm powder that could be spiked into an IV bag - we put a gram in 500cc. It was great for short procedures when our only other alternative was pancuronium, but it's nearly pointless to do it now with those newfangled rocuronium and vecuronium drugs that are all in vogue.

PS - sux powder was great for bowhunters 😉

 

[pgg]

I used a succ drip once during residency. I don't remember why, or the dosing details. But my attending put part of a dye ampule in the bag (methylene blue? indigo carmine?) so it'd be obvious from a distance that a paralytic was in the bag.

 

[Planktonmd]

A Sux drip as JWK stated used to be 1000 mg Sux powder in a 250 ml bag colored with Methylene blue so you can tell if you have Sux in the line,
It can be done with 3-4 vials of Sux in 250 ml bag as well, and it's a good alternative for cases where you need profound muscle relaxation but you don't want the commitment to a long lasting blockade, like rigid bronchoscopy procedures for example.
Sux drips are the proof that a phase 2 block is not such a bad deal after all.

 

[loveumms]

We will all be able to forget about sux when suggamadex is released 😉

 

[Sonny Crocket]

We will all be able to forget about sux when suggamadex is released 😉

We have sugammadex here in Scandinavia. It works well. But sux is still used most of the time for an RSI. Agree that it might be phased out one day but it doesn't look like any time soon.

 

[loveumms]

I was partially kidding ... since it's been years in the making. I work in academics and use sux about twice a year. Will always be asked on board exams (since it takes about 20 years to phase out old information).

 

[Random Anesthesiologist]

We used to do sux drips in the dark ages. It was available in a 1gm powder that could be spiked into an IV bag - we put a gram in 500cc. It was great for short procedures when our only other alternative was pancuronium, but it's nearly pointless to do it now with those newfangled rocuronium and vecuronium drugs that are all in vogue.

PS - sux powder was great for bowhunters 😉

I had a deer hit my car with an arrow sticking out of it a long time ago. Curare tipped arrow would have been welcome then.

 

[btbam]

I've only done a sux drip a couple times and it really is the ultimate titrate to effect drug. Put on a twitcher and do the 1 sec twitch or whatever the setting is then just open the microdripper. Too much and twitches disappear, slow the drip a little and voila twitches reappear.

 

[Planktonmd]

We will all be able to forget about sux when suggamadex is released 😉

No you won't!

 

[Planktonmd]

I was partially kidding ... since it's been years in the making. I work in academics and use sux about twice a year. Will always be asked on board exams (since it takes about 20 years to phase out old information).

Why is working in academics synonymous to not using Sux??? Just curious!

 

[Mman]

Why is working in academics synonymous to not using Sux??? Just curious!

resident get to practice mask ventilating for a longer time period

 

[narcusprince]

I use succ all the time. Sometimes appys here are 10-15 minutes. I use sux to intubate and no more relaxant. Btw I have had a psuedocholinesterase patient unknown to us on the table. It took awhile to get her back to full strength to extubate. Does not change my use of sux. And the myalgias are very similar to wave/particle duality if you ask about them then they have them but if not they are focused on the site of surgery.

 

[Twiggidy]

I used a succ drip once during residency. I don't remember why, or the dosing details. But my attending put part of a dye ampule in the bag (methylene blue? indigo carmine?) so it'd be obvious from a distance that a paralytic was in the bag.

This is exactly what my attending did. Only did it once. I think the procedure was a TURBT or something like that where the surgeon was concerned about obturator nerve stimulation. I was a first year (CA 1) at that point and afterwards it was pretty rare that I went back there or worked with that attending.

The sux in academics phenomenon is pretty funny. I think there was too much fear of a pseudocholinesterase def. patient or a cardiac arrest after sux that it scared people away. The when I went into cardiac and there was no need to extubate people so i didn't use it for an entire year. Now, only if i really fear the inability to ventilate/intubate or a full stomach emergency case, will i use it. When you hit private practice, i think you figure out ways to minimize muscle relaxation while also reducing the possibility of sux complications.