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Noyac said:
When mixing 2 different locals for a regional procedure, what is the toxicity of the solution? Additive, unchanged, diluted?
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Good question,
The toxicity is additive but there is no known numbers to go by to predict the toxic dose of a certain mixture, so I suggest considering the mixture to be one drug and the toxic dose the one for the more toxic drug of the two. Example: in a mixture of Lidocaine with Bupivacaine consider the whole amount to be Bupivacaine with a toxic dose of let's say 3mg/kg.
 
UTSouthwestern said:
Proportional.
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Do you mean that the two are proportional to each other, having a constant ratio? In otherwords, each local has its own toxicity and one is to stick with that known number.

Or are you saying that the two are additive as Plank stated.

I guess that since there has been 81 views but only two very experienced people have responded that not many people know the answer. I myself do not know the exact answer.

Plank, If I were to mix 30 cc of 2% lido with 30 cc of 0.5% Bupiv to a total of 60 cc. Are you calling it 60 cc of 0.5% bupiv or 60 cc of 0.25% bupiv since the original 0.5% is now diluted into twice the volume?

I will have more questions for those of you that give responses and I give my understanding later.
 
this is a way of looking at drugs that i am unfamiliar with. i'd be interested in seeing this discussion unfold.
🙂
 
Noyac said:
When mixing 2 different locals for a regional procedure, what is the toxicity of the solution? Additive, unchanged, diluted?
Click to expand...

Good question, Noy. Seems additive from an anecdotal experience of a colleague of mine, but we'll need sdn1977 to chime in for the academic answer.

Colleague relayed a case he saw where an axillary block...bupivicaine .5% 30mL....sub-optimal for surgery so GA with an LMA was the selected alternate choice....lidocaine 2% 4mL was given IV before the propofol....BOOM.....seizure.
 
Noyac said:
Do you mean that the two are proportional to each other, having a constant ratio? In otherwords, each local has its own toxicity and one is to stick with that known number.

Or are you saying that the two are additive as Plank stated.

I guess that since there has been 81 views but only two very experienced people have responded that not many people know the answer. I myself do not know the exact answer.

Plank, If I were to mix 30 cc of 2% lido with 30 cc of 0.5% Bupiv to a total of 60 cc. Are you calling it 60 cc of 0.5% bupiv or 60 cc of 0.25% bupiv since the original 0.5% is now diluted into twice the volume?

I will have more questions for those of you that give responses and I give my understanding later.
Click to expand...
My personal approach is to consider the whole mixture to be the more toxic drug , in your example Bupivacaine 0.5 %, although this might be exaggerated but since there are no established numbers this will allow you to err on the side of safety.
 
Planktonmd said:
My personal approach is to consider the whole mixture to be the more toxic drug , in your example Bupivacaine 0.5 %, although this might be exaggerated but since there are no established numbers this will allow you to err on the side of safety.
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I think many are viewing it this way.

What I don't understand here then is that the mg's of bupivicaine are unchanged. In my example we are dealing with 150mg of bupiv. The 150 mg are now in 60cc rather than 30cc. We didn't add 150 mg to the solution when we added the lidocaine. So your view of 60cc of 0.5% is hard for me to grasp. Why is it that many feel that we have doubled the dosage here?

Does the lidocaine have a synergistic (toxic) effect that makes the bupivicaine twice as toxic? Does that make sense? In other words, by adding lido to the bupiv have we increased the bupiv's toxicity? They both effect ion channels mostly Na. It has been studied and one study that I am familiar with (http://www.anesthesiology.org/pt/re...NX4KGT8ZfvcQqTp!-1697294916!181195628!8091!-1) shows that the mixture is less cardiotoxic than bupiv alone but equally hemodynamically toxic as bupiv alone. The lidocaine basically displaces from the Na channel more rapidly than bupiv which makes it less cardiotoxic. Also in the presence of bupiv, lido will cause the bupiv to displace more rapidly from the Na channel therefore, decreasing the bupiv toxicity. However, in the systemic sytem these agents bind the slower Ca channels causing hemodynamic effects. Since these are slower acting channels (this is how I read it) the two locals don't displace very rapidly and therefore the toxicity is greater, more like the bupiv alone.

This is very confusing for sure. If you read in the Conclusions of the article above it is stated that bupiv increases the QRS time (as we all know) and that addition of lido will further increase this time.
 
In addition, the guidelines for Local Toxicity are for IV dosing correct.

So what if you give 200mg of Ropivicaine and your block doesnt work but it aint intravascular. Can you give more?


Could you try again post op? Do you have to wait 4.5 half-lives before the drug is completely eliminated? 2 Half lives? Do you switch to an ester?
 
like one of my attendings likes to say, Life is a bell shaped curve. The recommended levels are for IV dosing but whos to say what blood level any given person has at any given time. Different blocks have theoretically different absorption rates but Im sure some people may absorb local faster from a pop fossa block than another may from an axillary. likewise some people have symptoms at lower blood levels than others. If the block doesnt work I would just let it be. Sometimes strange things happen. One case fem/sciatic block for a TKA took a couple of hours to set in. We had no idea why (combined stim/US with spread seen around the nerve) until we did the spinal and it took 15 minutes to start setting in. He apparantly had some kind of delayed reaction to local anesthetics. Also I try to avoid going over the recommended doses for medicolegal reasons. I do sometimes switch to an ester for OB purposes if amides arent working but havent tried it for nerve blocks.
 
Assuming that the whole dose is the more toxic drug makes no sense...

I consider toxicity to be additive. If my total of bupivicaine is 50% of the toxic dose (for that patient), the total amount of lidocaine I can add must be less than 50% of the toxic dose of lidocaine (for that patient).
 
Intubate said:
Assuming that the whole dose is the more toxic drug makes no sense...

I consider toxicity to be additive. If my total of bupivicaine is 50% of the toxic dose (for that patient), the total amount of lidocaine I can add must be less than 50% of the toxic dose of lidocaine (for that patient).
Click to expand...

Correct. Proportional toxicity.
 
Intubate said:
Assuming that the whole dose is the more toxic drug makes no sense...

I consider toxicity to be additive. If my total of bupivicaine is 50% of the toxic dose (for that patient), the total amount of lidocaine I can add must be less than 50% of the toxic dose of lidocaine (for that patient).
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That sounds good, I am not sure it is this simple though.
I don't think there is data about the behavior of local anesthetic mixtures and their pharmacodynamics.
 
1) if the block doesn't work then you don't add more local anesthetic... that is a surefire way to hurt the patient... just do a general or cancel the case

2) local anesthetics will affect intrinsic cardiac conduction times - sure some do so more than others (bupi > ropi)... just because you are mixing lidocaine with bupivacaine doesn't mean you aren't exposing cardiac tissue to more issues down the road... so in my sense it is proportional but the more you give the more trouble you potentially could have...

3) i still would like to know who came up with the idea of injecting 40ml of local anesthetic onto the brachial plexus when it basically bathes the carotid and jugular veins..... not my idea of smart, and yet we get away with it on a regular basis...

4) i think you will see far lower doses as more and more people become proficient with ultrasound guided placement of catheters in the plexus sheaths - thus allowing for lower doses that can be bolused instead of the whopper doses that we routinely use... so the future would look more like 10ml of mepivacaine and then a bupivacaine pump...

5) plus reimbursements are better with catheters
 
local anesthetic toxicity levels were determined by infusing animals with local anesthetic IV until they got seizures. how well does that translate to humans? my guess is poorly.

anesthesiologists specializing in regional anesthesia routinely go over the toxic levels of local anesthetics. the protocols for several studies give "toxic" levels of anesthetics in their blocks. For example, one study gave 50 ml of 1.5% mepivacaine + epi = 750mg to all pts which is basically over the toxic dose for all of them (unless you're over approximately 100kg). now of course, this isn't IV (or at least shouldn't be), but still...

so what does this mean? we have little idea what the hell the toxic dose of local anesthetics are. my suggestion is don't be stupid and inject 100ml 2% lidocaine IV, and always be prepared for toxicity in all cases.
 
Resurrecting an old thread...
This question up yesterday and prompted discussion:

If you're running an IV lidocaine infusion as part of an opiate sparing strategy for an abdominal surgery, does this factor into your calculation for the maximum dose that can be infiltrated for blocks during the case? For example, if you had a small, 60kg patient receiving a lidocaine infusion at 1mg/kg/hour for 6 hours, and at case conclusion the surgeon wanted to infiltrate 60mL of 0.25% bupivacaine, prior to wound closure would you be on board or would you be inclined to attenuate his dose?
 
anesthesiadoc said:
Resurrecting an old thread...
This question up yesterday and prompted discussion:

If you're running an IV lidocaine infusion as part of an opiate sparing strategy for an abdominal surgery, does this factor into your calculation for the maximum dose that can be infiltrated for blocks during the case? For example, if you had a small, 60kg patient receiving a lidocaine infusion at 1mg/kg/hour for 6 hours, and at case conclusion the surgeon wanted to infiltrate 60mL of 0.25% bupivacaine, prior to wound closure would you be on board or would you be inclined to attenuate his dose?
Click to expand...
Definitely attenuate. 60 ml of plain 0.25% bupi is basically at the toxic limit for a 60 kg patient even without the lido. IV lidocaine half-life is 1.5 to 2 hours, so I would be very careful.

Btw, that's one reason I don't run lido infusions.
 
anesthesiadoc said:
Resurrecting an old thread...
This question up yesterday and prompted discussion:

If you're running an IV lidocaine infusion as part of an opiate sparing strategy for an abdominal surgery, does this factor into your calculation for the maximum dose that can be infiltrated for blocks during the case? For example, if you had a small, 60kg patient receiving a lidocaine infusion at 1mg/kg/hour for 6 hours, and at case conclusion the surgeon wanted to infiltrate 60mL of 0.25% bupivacaine, prior to wound closure would you be on board or would you be inclined to attenuate his dose?
Click to expand...

Definitely attenuate. Though i think there isn't really any good data for toxic doses. It makes no sense to have a wound infiltration max dose to be the same as IV toxic dose, since clearly IV dosing will have higher plasma levels..
 
Last edited:
Southpaw said:
Attenuate. Some epic posters in this thread - UTSW, Noy, Plankton, JPP, Tenesma. If you folks haven’t read Tenesma vs womansurg from way back when that’s just absolutely epic.
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Please post a link!
 
If the surgeon is going to put local in the surgical wound, why would you need to put local in their vessels?
 
FFP said:
Can't seem to find it.

P.S. I think this is it: Patients waking during surgery?
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That’s it. womansurg was a prominent poster at the time. After her run-in w Tenesma I never saw her post again. If she did it wasn’t for years later, and in typical bull-headed surgeon fashion, she never acknowledged defeat at the words and mind of Tenesma.
 
Psai said:
If the surgeon is going to put local in the surgical wound, why would you need to put local in their vessels?
Click to expand...

My observation is that surgeons are highly variable at the amount of effort they put in to doing an effective wound infiltration, with resulting efficacy in pain control.

Also, would not let them do 60mL of .25% on a 60kg patient. The lidocaine definitely counts, plus what kind of incision needs 60mL of LA anyway?
 
anesthesiadoc said:
Resurrecting an old thread...
This question up yesterday and prompted discussion:

If you're running an IV lidocaine infusion as part of an opiate sparing strategy for an abdominal surgery, does this factor into your calculation for the maximum dose that can be infiltrated for blocks during the case? For example, if you had a small, 60kg patient receiving a lidocaine infusion at 1mg/kg/hour for 6 hours, and at case conclusion the surgeon wanted to infiltrate 60mL of 0.25% bupivacaine, prior to wound closure would you be on board or would you be inclined to attenuate his dose?
Click to expand...

I wouldn’t let the surgeon do it but I routinely run lidocaine infusion throughout a big abdominal case and then do bilateral TAP blocks at the end. 20mL 0.25% bup + decadron each side, sometimes 10mL per side for RS blocks too (so 60mL total).
 
Remember this: IV > intercostal > caudal > epidural > brachial plexus > sc ? IM is almost like SC. Same goes for nerves in a fascial plane that is devoid of blood vessels.

The problem is when the surgeon injects next to the wound. That has a much higher chances of ending up intravascularly than a PNB.
 
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