How accurate is a twitch with a popiteal block?

[Outrigger]

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I do popliteal blocks under U/S using an in plane, lateral to medial approach. I find that even with a twitch down to 0.30, when one begins injecting, it is frequently outside the fascia and you need to advance a little further to actually see spread around the nerve/nerves. In the old pre-ultrasound days, you would advance the nerve posterior to anterior 7 cm from the crease and get a very reliable block with the appropriate twitch. Has anyone else noticed this?

 

[ethilo]

My technique:
I always aim to inject in and place nerve catheters in the subparaneural space. I have the patient lie supine, knee propped up, 1 dirty hand with probe under their leg and the other staying sterile with a lateral approach. I find the bifurcation and target this point. With needling, I advance just on the deep aspect of the nerve. I was trained to "scoop the meatball," which is I put my needle tip just on the underside of the common peroneal, lift up on it with the needle, then pierce into the subparaneural space. You can frequently feel the "give" on the needle when you enter the space. We were also told in residency to imagine the subparaneural sheath like a pair of jeans, and you are trying to put the needle into the "crotch" of the jeans distal to where the internal body (nerve) is. You lift up one of the "legs" of the jeans with your needle and advance into this potential space there. I then do small "puffs" with saline to watch for a pocket/hydrodissection into the space. I then advance the needle more into that space if I create one, especially if I'm placing a catheter, to help give some buffer room to keep it from migrating out of the space. Slow and low pressure injection often results in component separation. While injecting I take the time to scan up and down the sciatic nerve to see local tracking within the subparaneural space. If it doesn't ever seem to be tracking right I readjust needle tip position.

 

[Arch Guillotti]

My technique:

Ditch the nerve stimulator.

 

[ProwlerturnGas]

You could be a million miles from sciatic nerve in the popliteal space and stim down to low level. Block failed. US only and get in perineural.

 

[dhb]

If i remember correctly a twitch at 0.4mA means the needle is subepineural 100% of the time.

 

[Outrigger]

If i remember correctly a twitch at 0.4mA means the needle is subepineural 100% of the time.

You can have a twitch at less than 0.4 and still not be subparaneural let alone subepineural. You can end up injecting in the subepimyseal compartment.

 

[dhb]

You can have a twitch at less than 0.4 and still not be subparaneural let alone subepineural. You can end up injecting in the subepimyseal compartment.

Really? Are you not stimulating muscle?
0.4mA on a thick sciatic is not going to acheive much.
Anyway i haven't used a NS in 15 years.

 

[Hoya11]

I do popliteal blocks under U/S using an in plane, lateral to medial approach. I find that even with a twitch down to 0.30, when one begins injecting, it is frequently outside the fascia and you need to advance a little further to actually see spread around the nerve/nerves. In the old pre-ultrasound days, you would advance the nerve posterior to anterior 7 cm from the crease and get a very reliable block with the appropriate twitch. Has anyone else noticed this?

feel the pop, see the twitch, inject and notice the twitch stop. in that order. notice the spread between the nerves separating the nerves in the sheath. reposition the needle a little to ensure good spread around both nerves in the sheath. youve got to feel the pop into the sheath as the key. you pop in and the twitch is very obvious

 

[JWebar]

My technique:
I always aim to inject in and place nerve catheters in the subparaneural space. I have the patient lie supine, knee propped up, 1 dirty hand with probe under their leg and the other staying sterile with a lateral approach. I find the bifurcation and target this point. With needling, I advance just on the deep aspect of the nerve. I was trained to "scoop the meatball," which is I put my needle tip just on the underside of the common peroneal, lift up on it with the needle, then pierce into the subparaneural space. You can frequently feel the "give" on the needle when you enter the space. We were also told in residency to imagine the subparaneural sheath like a pair of jeans, and you are trying to put the needle into the "crotch" of the jeans distal to where the internal body (nerve) is. You lift up one of the "legs" of the jeans with your needle and advance into this potential space there. I then do small "puffs" with saline to watch for a pocket/hydrodissection into the space. I then advance the needle more into that space if I create one, especially if I'm placing a catheter, to help give some buffer room to keep it from migrating out of the space. Slow and low pressure injection often results in component separation. While injecting I take the time to scan up and down the sciatic nerve to see local tracking within the subparaneural space. If it doesn't ever seem to be tracking right I readjust needle tip position.

Exactly what I do, though I tend to use a out-of-plane technique which makes is super easy to access the connective tissue between both nerves at the bifurcation. You don't really need a nerve stimulator. With the subparaneural technique onset is pretty short (10–15 minutes) and success rate is well above the 90% for surgical anesthesia using 20 mL of LA. Scanning proximal towards the "single" sciatic nerve and watching it divide into its 2 branches with your injectate is a great mark of successful injection.

 

[OneFellSwoop]

Step 1: get rid of twitch monitor.

Problem solved

 

[Mman]

I don't bring a nerve stimulator with me to do a popliteal sciatic block. Less than once a year I will make the nurse go grab one if the patient is so fat and anatomy so difficult to visualize that I am not sure what I am looking at, but for those I stop using it as soon as I get any twitch at all (around 1.00 mA) as just confirmation that I am actually seeing where the nerve is.

 

[Arch Guillotti]

I don't bring a nerve stimulator with me to do a popliteal sciatic block. Less than once a year I will make the nurse go grab one if the patient is so fat and anatomy so difficult to visualize that I am not sure what I am looking at, but for those I stop using it as soon as I get any twitch at all (around 1.00 mA) as just confirmation that I am actually seeing where the nerve is.

Same.

 

[gcc322]

My technique:
I have the patient lie supine, knee propped up, 1 dirty hand with probe under their leg and the other staying sterile with a lateral approach.

Do y’all really use sterile technique for single shots? Chloroprep and raw dog no glove.

 

[ethilo]

Do y’all really use sterile technique for single shots? Chloroprep and raw dog no glove.

I guess by "dirty" I mean I use a probe with nonsterile gel and by "stay sterile" I mean I up chloroprep the skin and hold the hilt of the needle without touching the needle. Exam glove or bare hands. I only glove up and stay sterile with catheters.

 

[dhb]

Do y’all really use sterile technique for single shots? Chloroprep and raw dog no glove.

I use alcohol gel , US gel is too messy, i don't like to clean up.
Why would be the reasoning behind using gloves? The probe is dirty? Or is it the needle?

 

[GassYous]

I use alcohol gel , US gel is too messy, i don't like to clean up.
Why would be the reasoning behind using gloves? The probe is dirty? Or is it the needle?

I just use regular gloves but sometimes you have to scan around and I can see how you could get things unsterile at the site But I think the chance of something bad happening from a single shot injection is pretty low.

 

[JWebar]

I just use regular gloves but sometimes you have to scan around and I can see how you could get things unsterile at the site But I think the chance of something bad happening from a single shot injection is pretty low.

Agreed. Have you ever heard of a clinically significant infection after a single shot? I haven't. Granted that its something that we may NOT hear about since its likely to be attributed to other causes (no one any idea of what we do).

 

[ethilo]

I just use regular gloves but sometimes you have to scan around and I can see how you could get things unsterile at the site But I think the chance of something bad happening from a single shot injection is pretty low.

I agree especially about pop blocks which is why I do some pretty wide-field pre-scanning sliding up and down so I can get the nerve to pop out in my mind's eye. Once it pops out and I have my window with the probe, I prep, local for skin, block

 

[Urzuz]

you are trying to put the needle into the "crotch" of the jeans

( ͡° ͜ʖ ͡°)​

But yes, ditch the nerve stimulator.