Nitrous?

[pgg]

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Man I wish we had it available - it hasn't even been on our hospital formulary since the black-box warnings came out.

I also miss droperidol. Pharmacy took it away without consulting us.


I don't use much nitrous but I don't think it's the devil. I just don't see the point, outside of gentle (not fast) peds inductions, some old people, and the rare OB GA.

 

[pgg]

I'm with Jet. I love sevo. Iso is nice too if you have a really long case and want to save the hospital some money

I routinely run des for short/medium/long cases with 0.5 lpm fresh gas. It's not an expensive anesthetic. Turn it to 12 after induction, set the fresh gas to 0.5, put them on the vent, by the time the patient is prepped they're deep enough. Rarely, rarely see a big sympathetic surge.

Honestly we'd save more money if we abandoned propofol and went back to thiopental. But that's crazy talk, right? 🙂 As crazy as clinging to iso when des is available, maybe. 😉

I use des for everyone. Except mask inductions. And then I switch to des, usually.

 

[dhb]

I routinely run des for short/medium/long cases with 0.5 lpm fresh gas. It's not an expensive anesthetic. Turn it to 12 after induction, set the fresh gas to 0.5, put them on the vent, by the time the patient is prepped they're deep enough. Rarely, rarely see a big sympathetic surge.

Exactly how i do it

 

[beavis]

I routinely run des for short/medium/long cases with 0.5 lpm fresh gas. It's not an expensive anesthetic. Turn it to 12 after induction, set the fresh gas to 0.5, put them on the vent, by the time the patient is prepped they're deep enough. Rarely, rarely see a big sympathetic surge.

Honestly we'd save more money if we abandoned propofol and went back to thiopental. But that's crazy talk, right? 🙂 As crazy as clinging to iso when des is available, maybe. 😉

I use des for everyone. Except mask inductions. And then I switch to des, usually.

pgg, when you do this, do you turn your O2 % up really high? I have tried this low flow/high % des in the past, but my inspired O2 % always suffers due to the low flows.

Thanks,

Beav

 

[lord_jeebus]

pgg, when you do this, do you turn your O2 % up really high? I have tried this low flow/high % des in the past, but my inspired O2 % always suffers due to the low flows.

Thanks,

Beav

Most of the O2 you put in at these low flows is metabolized, so the FiO2 of your fresh gas can be quite different from the FiO2 in your circuit.

After running 50% FiO2 for a minute or so, I'll go down to about 0.4 L/min of O2 only. The inspired O2 concentration generally stays around 50-60%; if it trends up, my flows are higher than they need to be and I'll lower to 0.35 or 0.3. Alternatively, the same target is achieved by putting in just enough fresh O2 to keep the bellows from gradually collapsing.

 

[dhb]

pgg, when you do this, do you turn your O2 % up really high? I have tried this low flow/high % des in the past, but my inspired O2 % always suffers due to the low flows.

Thanks,

Beav

I leave the FiO2 at 1. After pre-ox, induction they have a good reserve of oxygen and they usually stay at 70% expO2, but yeah if you drop the FiO2 the exp O2 will plummet.

 

[epidural man]

Sorry dude can't argue with Miller. Although I use droperidol for rescue if I used decadron and zofran (both at 4 mg). I know the whole droperidol QT prolong at small doses is a crock of ****, but that dysphoria/agitated side effect I get every now and then is just not worth it. I used to use it religiously in routine c-sections during those slow OB closures to shut the mother up thanks to its sedative side effects. But every now and then I would give 1.25 mg and minutes later the patient would totally freak out so I would have to hit them with versed.

Uhhh...yes I can argue with Miller. Textbooks are frequently wrong...and, the chapter is written by one or two guys - and it isn't peer reviewed like an RCT in a high impact journal is. I know people that write book chapters. They do their best, no doubt, but they are just one person doing their best, filled with bias - as we all are.

I agree that NNT are difficult to nail down and to actually come up with one number is a daunting task. For example, if you were to try and define the NNT for gabapentin for neuropathic pain, you can find several different numbers.

Plus, that chart you show does not define prevention vs treatment - which have different NNT as well for both 5-HT3, and droperidol.

Final point about droperidol - the 5-HT3s have no dose affect, meaning 4mg seems to work nearly as well as 8 or 12mg. But that isn't true with drop - more equals more effective. I like that. The chart does nothing to point this important fact out.

 

[wine thief]

re: cranis, do you not worry about pneumocephalus? or do you just use n2o at the end when the dura is closed?

 

[TheEleventhReel]

I do look Zippyesque when I pull my favorite party trick. Right as the drape comes down from a long case I lean over and say the patient's name. He opens his eyes. I say dude, there is a tube in your throat, do you want it out? He shakes his head yes. I say then reach up and pull it out. He reaches up and pulls it out. I only pull it off successfully 1/3 tries, but I am sure I can boost that to 2/3 before I retire. 😎


- pod[/QUOTE]

That's one of the most satisfying events in anesthesia for me. It makes you look like a rockstar.

 

[proman]

re: cranis, do you not worry about pneumocephalus? or do you just use n2o at the end when the dura is closed?

Not at all. The key is to use it before the dura is open. There is a concern if you start it after the dura has been opened. I don't buy it because if the nitrous is trapped in the subarachnoid space it would get absorbed extremely quickly. Out of the 1,000 cranis my residency hospital did annually I'd bet >75% were done with 0.5 MAC iso and 50% nitrous.

 

[cleansocks]

we like it as a background agent in a paralyzed tiva case just in case drip stops or iv dies

 

[cfdavid]

I do look Zippyesque when I pull my favorite party trick. Right as the drape comes down from a long case I lean over and say the patient's name. He opens his eyes. I say dude, there is a tube in your throat, do you want it out? He shakes his head yes. I say then reach up and pull it out. He reaches up and pulls it out. I only pull it off successfully 1/3 tries, but I am sure I can boost that to 2/3 before I retire. 😎


- pod

That's one of the most satisfying events in anesthesia for me. It makes you look like a rockstar.[/QUOTE]

Worked with an attending today whom I've never worked with before. Seriously, we did ALMOST what you described on three patients this morning, the only major difference is that we pulled the tube for them..... But, it WAS cool havin em scoot on over by themselves..... LOL Attending was a pretty cavalier dude...

This gig is fun as hell.

Oh, and while I can't yet quote the literature, I've been using a lot of nitrous lately which does seem to help with fast emergence.

 

[Ronin2258]

Out of the 21 anesthetics I have done since I started residency two weeks ago, I have only had 1 local/MAC, 1 spinal, 2 IV inductions, and the balance in inhalational induction with nitrous/sevo. I don't maintain them on nitrous. I usually switch them over to sevo or des, with oxygen/air mix. That second gas phenomenon is most impressive.

 

[Frank Rizzo]

Out of the 21 anesthetics I have done since I started residency two weeks ago, I have only had 1 local/MAC, 1 spinal, 2 IV inductions, and the balance in inhalational induction with nitrous/sevo. I don't maintain them on nitrous. I usually switch them over to sevo or des, with oxygen/air mix. That second gas phenomenon is most impressive.

They start you out on a Peds rotation, wtf?

 

[wine thief]

Not at all. The key is to use it before the dura is open. There is a concern if you start it after the dura has been opened. I don't buy it because if the nitrous is trapped in the subarachnoid space it would get absorbed extremely quickly. Out of the 1,000 cranis my residency hospital did annually I'd bet >75% were done with 0.5 MAC iso and 50% nitrous.

Wow. I have seen it at least once, when the resident started N20 at the end of the case before the dura was closed. Attending came in and switched it off. Not sure how long it was running. Pt didn't wake up. CT: Big pneumocephalus. He ended up doing OK.

 

[Ronin2258]

They start you out on a Peds rotation, wtf?

Nope. All adult patients. The boss is big on using it.

 

[pgg]

Nope. All adult patients. The boss is big on using it.

21 adult patients, 19 general anesthetics, 17 inhalational inductions? That's odd.

 

[RxBoy]

Nope. All adult patients. The boss is big on using it.

That is very bizarre.

I mean inhalation induction can be done... But why routinely?

I think your boss is big on saving money.

 

[proman]

Wow. I have seen it at least once, when the resident started N20 at the end of the case before the dura was closed. Attending came in and switched it off. Not sure how long it was running. Pt didn't wake up. CT: Big pneumocephalus. He ended up doing OK.

I guess it happens. It also happens in patients without nitrous. I typically won't start it if I haven't started it from the beginning. But a nitrous induced pneumocephalous should resorb very quickly, right? I personally wouldn't avoid nitrous for that reason, but it's certainly on the differential for delayed emergence post craniotomy.

 

[Ronin2258]

Not only using nitrous, but interesting techniques as well.

Check this: Single Breath Induction, using sevo/nitrous. Did 2 today.

 

[bkell101]

Hey guys. Any papers out there on the effect of nitrous <30 min on the effects of methionine synthase and ponv?

I have had a had time titrating the sevo at the end of the case because we have medstudent/intern closures quite a bit and I've recently learned to use nitrous at the end of the case. Am I causing a significant increase risk in PONV with short duration?

Thanks.

 

[Doctor4Life1769]

Not only using nitrous, but interesting techniques as well.

Check this: Single Breath Induction, using sevo/nitrous. Did 2 today.

Please tell me how. I'm quite interested.

 

[BLADEMDA]

Hey guys. Any papers out there on the effect of nitrous <30 min on the effects of methionine synthase and ponv?

I have had a had time titrating the sevo at the end of the case because we have medstudent/intern closures quite a bit and I've recently learned to use nitrous at the end of the case. Am I causing a significant increase risk in PONV with short duration?

Thanks.

No. Keep using the nitrous that way. I do it all the time.

 

[lord_jeebus]

Hey guys. Any papers out there on the effect of nitrous <30 min on the effects of methionine synthase and ponv?

I have had a had time titrating the sevo at the end of the case because we have medstudent/intern closures quite a bit and I've recently learned to use nitrous at the end of the case. Am I causing a significant increase risk in PONV with short duration?

Thanks.

Doubt that such a PONV study has been done. As for methionine synthase's (irreversible) deactivation, the half time for that reaction on 70% N2O is about 45 minutes.

 

[btbam]

Hey guys. Any papers out there on the effect of nitrous <30 min on the effects of methionine synthase and ponv?

I have had a had time titrating the sevo at the end of the case because we have medstudent/intern closures quite a bit and I've recently learned to use nitrous at the end of the case. Am I causing a significant increase risk in PONV with short duration?

Thanks.

Turn sevo off early, turn FGF to 0.3-0.4 100% O2, close APL valve. Sevo will last forever and you can crank up flows as the med student finishes which will wash everything out very quickly. This technique gives you great leeway for variable timing with closures.

 

[jwk]

Turn sevo off early, turn FGF to 0.3-0.4 100% O2, close APL valve. Sevo will last forever and you can crank up flows as the med student finishes which will wash everything out very quickly. This technique gives you great leeway for variable timing with closures.

Ah, someone got the closed-system fever rotating through Grady. 😉

 

[Idiopathic]

Please tell me how. I'm quite interested.

here is how i do it. max dose sevo and 70% nitrous, flush the circuit (after preoxygenating). tell the patient you are going to have them breathe all the way out and then all the way in and hold their breath. place the mask over their face. when they let that breath out, they are asleep. occasionally it takes a second breath, but they almost universally bypass stage 2 (which is the reason i do it this way)

 

[deleted162650]

Ok so here's my take on nitrous. I came from a nitrous heavy residency program, and I still use it at the end of almost every case to wake pt's up (assuming no contraindication). N2O has probably been used more than any other anesthetic agent over the last 100+ years. Is it perfect - no, but it is still a great drug. There's just nothing that appraches it in terms of speed and cost.

The methionine sythase inhibition is clearly real, and very clearly dose dependent. Using 60-65% for the last 15-45min of case is not gonna have any clinically relevant bone marrow suppressing effect in the pt whose bone marrow is not otherwise at risk. I also think that 50% for 2 hours isn't gonna have any meaningful ill effects either. I will avoid it if the pt has some other b12 problem, or if its a pt that is gonna be making multiple trips to the OR and I'm concerned about cumulative effects (burns, complex trauma, complex plastics, belly washouts, etc.)

With regards to PONV, all the potent volatiles are clearly emetogenic. The data on nitrous is actually mixed if you really look at it. I say if you can spare some of a known emetogenic agent witht the use of one that may or may not be, its usually a good thing. I also don't hear about many pts leaving the dentist's office puking their guts out because they got some nitrous (I'm sure it would still not be in use if this was going on). I do think Nitrous contributes to PONV if given for >1 MAChour (i.e. > 2 hours at 50% or ~85min at 70%) I think this is probably because this is when you start to get into real bowel distention which is nauseating. When used just for wake-up, I see very, very little PONV even in pts with a Hx or significant risk factors. I do admit though that I will give decadron (provided no brittle diabetes, etc.) and zofran to pretty much everybody.

I think a lot of the anti-nitrous literature/prpaganda out there is perpetrated by the makers of Des.

P.S I also have done a number of single breath inductions just like Idio describes with the same results. Definitley a fun way to put someone to sleep, especially the pot smokers with bong experience.

 

[Dawkter]

I agree completely. No other drug that we have available has the years (167 and counting) or number of exposures (likely in the billions). Our experience with nitrous is unparalleled.

I use it in cranis, spines at 50% + 0.5 MAC volatile. I'll go to 70% and shut off the volatile agent when closing starts. Consistently brisk wakeups without having to use a drug that causes hyperalgesia (remi). Its NMDA antagonism is also beneficial. I'll use high flow nitrous (7LPM with 3 LPM of oxygen) for open abdominal operations once the fascia is closed. Again, fast wakeups. Nothing beats the smoothness of an opioid/nitrous wakeup.

As for PONV, the avoidance of nitrous is associated with a relative risk reduction of only 12%. The use of TIVA instead of inhaled anesthetic only reduces risk by 19%. The avoidance of general anesthesia altogether results in a 9 fold decrease (and that's what we should really be doing if we can). This is found in the SAMBA guidelines for PONV.

I put together a flyer that was going to be part of a QA project during residency that never got off the ground on this. If anyone wants the full size PDF just PM.

Couple of questions from a newbie. How are you able to run 70% Nitrous? I did a case today where anywhere greater than 40% (4LPM nitrous 6 LPM O2) let to an immediate de-saturation to <90% from 100%. Also, very basic question but why do we need to use high flows with Nitrous? Lastly, has anyone run an entire case on Nitrous (for example a 10 minute cystoscopy)?

 

[ambiturner]

Couple of questions from a newbie. How are you able to run 70% Nitrous? I did a case today where anywhere greater than 40% (4LPM nitrous 6 LPM O2) let to an immediate de-saturation to <90% from 100%. Also, very basic question but why do we need to use high flows with Nitrous? Lastly, has anyone run an entire case on Nitrous (for example a 10 minute cystoscopy)?

I work at a nitrous friendly place. 70% nitrous in a person with healthy lungs, and we're talking all but the most frail patients, should not result in a SpO2 less than 95ish. I've run 20-21% oxygen on people and still had them saturating well, but you better make sure they don't cough because they're going to desat within a matter of seconds. Regarding high flows, I don't think you need high flows in fact that would be worse for the environment as nitrous is nasty on the atmosphere. I routinely run low flow (<1 L) with nitrous, you just have to make sure you are giving enough oxygen to meet the patient's metabolic demands (usually around 250cc). For an entire case, yes I have done entire cases in the several hours range with just nitrous on very old people (when the MAC can approach 1.0 on 70% N2O). If you want to do nitrous without volatile on younger people you need to add some narcotic (nitrous/narcotic technique) which is insanely smooth if done in the right circumstances (long hand cases are a great time to try this).

 

[deleted59964]

Couple of questions from a newbie. How are you able to run 70% Nitrous? I did a case today where anywhere greater than 40% (4LPM nitrous 6 LPM O2) let to an immediate de-saturation to <90% from 100%. Also, very basic question but why do we need to use high flows with Nitrous? Lastly, has anyone run an entire case on Nitrous (for example a 10 minute cystoscopy)?

1. your patient had a large Aa gradient - many do not.
2. no

 

[deleted59964]

3. no

 

[Mman]

here is how i do it. max dose sevo and 70% nitrous, flush the circuit (after preoxygenating). tell the patient you are going to have them breathe all the way out and then all the way in and hold their breath. place the mask over their face. when they let that breath out, they are asleep. occasionally it takes a second breath, but they almost universally bypass stage 2 (which is the reason i do it this way)

What's the point of the pre-oxygenation if you are exhaling it all and replacing with nitrous + sevo + remaining oxygen? I mean we preoxygenate before an IV induction because the patient will go apneic. An inhalation induction keeps the patient breathing and you lose most of your preoxygenation anyway.

 

[twoliter]

Wow. I have seen it at least once, when the resident started N20 at the end of the case before the dura was closed. Attending came in and switched it off. Not sure how long it was running. Pt didn't wake up. CT: Big pneumocephalus. He ended up doing OK.

If I remember big Miller right, he/they say it's ok to use N2O up to dura closure and then cutting off. There is bound to be at least a small amount of pneumocephalus with or without N2O (just as there is routinely pneumoperitoneum for a few days after abdominal surgery. So the problem isn't pneumocephalus in and of itself, it's the size / concern of tension pneumocephalus, which is where the fear of N2O comes from. But since there will likely be at least a small pneumocephalus at the time of dura closure, if you've been using N2O up to that point, the pneumo will be mostly N2O. Then if you cut the N2O off, it will resorb back into the blood stream via gradient. However, if you start it after dura closure (or keep it going after dura closure), the room air pneumo will then increase in size due to taking up nitrous faster than the nitrogen resorbs back into the blood stream.
That's per Miller, and that's what makes sense to me.

 

[Triple AAA]

There are too many posts to read in this thread, and I'm sure many of them echo sentiment that I am about to share. I personally have always been a believer in N2O and try to use it whenever possible, unless there are specific contraindications, which include:

1. Any case in which the surgical field is above the level of the heart (ie, sitting cranies, C-section, etc) due to risk of air embolus. Even here, once the pt is supine and closure has started, I usually turn on N2O.

2. Any patient who has a congenital heart defect, due to risk of paradoxical embolus.

3. Any pregnant patient, due to risk (albeit questionable) of birth defects. In C-section, once the baby is out, I'll turn on N2O.

4. Any case that goes longer than 3-4 hrs due to risk of bone marrow suppression, etc. For that matter, any chemo patient with baseline bone marrow suppression should not have N2O either.

5. Any case in which N2O interferes with neuro-monitoring. Once the neuro monitors are off, I turn on N2O.

6. Any patient/case in which oxygenation is compromised (lung isolation, any pt with problems oxygenating, etc)

7. Any open bowel surgery. Again, once bowel has closed, N2O goes on.

8. Any laparoscopic/robotic procedure which involves insufflation of the belly. Again, once the scopes are removed N2O goes on.

9. Any cranies due to increased CMRO2 and cerebral vasoconstriction.

Those are the big ones I can think of. Most of these are conditions inherent to the procedure itself, which usually go away once the procedure is done and the closure starts. There are few instances in which I would avoid N2O altogether for the entire procedure (2, 4, 6).

I really don't buy the PONV argument, it's kind of a moot point when you've been using volatile gas the entire case and plan to administer anti-emetics. I also have rarely seen significant diffusion hypoxia in the absence of pre-existing problems with oxygenation. As far as methionine synthase inhibition for the fetus, I really couldn't see it being an issue by the 3rd trimester. Remember, once that baby comes out, we almost universally use N2O to mask them down. (in addition to volatile gas). Then again, if a C/S comes down to GA, the fetus probably isn't doing too well to begin with.

 

[Sublimazing]

There are too many posts to read in this thread, and I'm sure many of them echo sentiment that I am about to share. I personally have always been a believer in N2O and try to use it whenever possible, unless there are specific contraindications, which include:

1. Any case in which the surgical field is above the level of the heart (ie, sitting cranies, C-section, etc) due to risk of air embolus. Even here, once the pt is supine and closure has started, I usually turn on N2O.

2. Any patient who has a congenital heart defect, due to risk of paradoxical embolus.

3. Any pregnant patient, due to risk (albeit questionable) of birth defects. In C-section, once the baby is out, I'll turn on N2O.

4. Any case that goes longer than 3-4 hrs due to risk of bone marrow suppression, etc. For that matter, any chemo patient with baseline bone marrow suppression should not have N2O either.

5. Any case in which N2O interferes with neuro-monitoring. Once the neuro monitors are off, I turn on N2O.

6. Any patient/case in which oxygenation is compromised (lung isolation, any pt with problems oxygenating, etc)

7. Any open bowel surgery. Again, once bowel has closed, N2O goes on.

8. Any laparoscopic/robotic procedure which involves insufflation of the belly. Again, once the scopes are removed N2O goes on.

9. Any cranies due to increased CMRO2 and cerebral vasoconstriction.

Those are the big ones I can think of. Most of these are conditions inherent to the procedure itself, which usually go away once the procedure is done and the closure starts. There are few instances in which I would avoid N2O altogether for the entire procedure (2, 4, 6).

I really don't buy the PONV argument, it's kind of a moot point when you've been using volatile gas the entire case and plan to administer anti-emetics. I also have rarely seen significant diffusion hypoxia in the absence of pre-existing problems with oxygenation. As far as methionine synthase inhibition for the fetus, I really couldn't see it being an issue by the 3rd trimester. Remember, once that baby comes out, we almost universally use N2O to mask them down. (in addition to volatile gas). Then again, if a C/S comes down to GA, the fetus probably isn't doing too well to begin with.

I had never heard number 2, can you please elaborate on this one. Does size of the defect matter? ASD vs VSD? We treated a ton of peds and special needs patients with the full gamut of septal defects and none of my attendings mentioned it...and I don't remember it being brought up in that A+A that came out last year-ish. But I'm interested to hear about it.

Thanks!

 

[Triple AAA]

I had never heard number 2, can you please elaborate on this one. Does size of the defect matter? ASD vs VSD? We treated a ton of peds and special needs patients with the full gamut of septal defects and none of my attendings mentioned it...and I don't remember it being brought up in that A+A that came out last year-ish. But I'm interested to hear about it.

Thanks!

No matter how much you try to de-air the IV tubing, there will always be minute amounts of air bubbles present. This would not usually be a big deal if not for the increased risk of CVA this would cause in patients with a R to L shunt. As N2O has the potential to expand these bubbles, it should be avoided. N2O can also increase PVR and exacerbate R to L shunting.

With that said, I have seen N2O used in children with CHD during induction and then discontinued once they are sufficiently deep, prior to placement of the IV. I am no pediatric anesthesiologist myself, but it's a risk that I prefer to avoid.

 

[deleted59964]

There are too many posts to read in this thread, and I'm sure many of them echo sentiment that I am about to share. I personally have always been a believer in N2O and try to use it whenever possible, unless there are specific contraindications, which include:


3. Any pregnant patient, due to risk (albeit questionable) of birth defects. In C-section, once the baby is out, I'll turn on N2O.

Oh dear.
Doctor - when do birth defects develop?

hint : C section is about 2 trimesters after I won't use N2O

 

[Triple AAA]

Oh dear.
Doctor - when do birth defects develop?

hint : C section is about 2 trimesters after I won't use N2O

Yes, thank you, I know when organogenesis occurs. (hence the 'albeit questionable'). In spite of this, I have many former attendings and current colleagues who won't TOUCH nitrous with a 10 foot pole on any pregnant patients.

 

[deleted59964]

why?

 

[deleted171991]

A more interesting question would be: why don't we use N2O for pain relief during labor, like many other Western countries?

Answer: For the same reason we are not doing elective lap chole's with LMAs. Uneducated juries and liability.

 

[OB1🤙]

1. Any case in which the surgical field is above the level of the heart (ie, sitting cranies, C-section, etc) due to risk of air embolus. Even here, once the pt is supine and closure has started, I usually turn on N2O.

2. Any patient who has a congenital heart defect, due to risk of paradoxical embolus.

1 and 2 are total bunk, I hate to say.

 

[deleted59964]

A more interesting question would be: why don't we use N2O for pain relief during labor, like many other Western countries?

Answer: For the same reason we are not doing elective lap chole's with LMAs. Uneducated juries and liability.

i didn't realise you don't use entonox in labour either - wtf

 

[BuzzPhreed]

I personally have always been a believer...

Are you sure you're not also a Belieber?

 

[psychbender]

If I remember big Miller right, he/they say it's ok to use N2O up to dura closure and then cutting off. There is bound to be at least a small amount of pneumocephalus with or without N2O (just as there is routinely pneumoperitoneum for a few days after abdominal surgery. So the problem isn't pneumocephalus in and of itself, it's the size / concern of tension pneumocephalus, which is where the fear of N2O comes from. But since there will likely be at least a small pneumocephalus at the time of dura closure, if you've been using N2O up to that point, the pneumo will be mostly N2O. Then if you cut the N2O off, it will resorb back into the blood stream via gradient. However, if you start it after dura closure (or keep it going after dura closure), the room air pneumo will then increase in size due to taking up nitrous faster than the nitrogen resorbs back into the blood stream.
That's per Miller, and that's what makes sense to me.

So, in residency, we went to a nearby (huge name) Mecca institution for a month of nothing but cranis, since our Neurosurgeons mostly did spines (and at the time, there was limited hospital support for the few surgeons that kept trying to bring cranis to the hospital). The general recipe for most there was 40% nitrous, 1/2 MAC iso, fentanyl or remifentanyl infusion, with the nitrous run the entire case, and it was the last thing to come off. The desired outcome was a very rapid emergence from anesthesia, regardless of case duration, for neuro exam prior to extubation. It worked beautifully for the few dozen cranis I did there. I had not done that before, nor have I done it since, for the concerns you mentioned, but speaking to the attendings, including the neurointensivists, they did not see any significant increase in complications using this technique. I know at least one other SDN member of this forum currently works (and trained?) at that hospital, so maybe she can shed some light on if they still do things this way, and if they have yet had any poor outcomes associated with this technique.

 

[michigangirl]

No matter how much you try to de-air the IV tubing, there will always be minute amounts of air bubbles present. This would not usually be a big deal if not for the increased risk of CVA this would cause in patients with a R to L shunt. As N2O has the potential to expand these bubbles, it should be avoided. N2O can also increase PVR and exacerbate R to L shunting.

With that said, I have seen N2O used in children with CHD during induction and then discontinued once they are sufficiently deep, prior to placement of the IV. I am no pediatric anesthesiologist myself, but it's a risk that I prefer to avoid.

I'm with Triple AAA on this one-- the place one encounters this a lot is the peds cath lab. Lots of shunts from holes that should or shouldn't be there. Everyone knows how anal pedi anesthesiologists are about air bubbles. If the child is a cyanotic HD patient, unlikely to use nitrous for induction simply because of the risk of worsened hypoxia on induction if baseline sats are 75% not interested in 65%-- if tolerated in an older patient to smooth out an induction may do 50:50 if they walk in on RA. But all before the IV goes in. Particularly in a training hospital. I can go on and on about why air bubbles are bad during our pre-op or induction with a resident/fellow, but it's inevitable that someone at some point is going to allow a few air bubbles to go in through the IV during boluses of meds, or when the bag runs dry. Nitrous is a great drug, but not mandatory by any means, so not worth risking bigger bubbles 🙂

 

[Triple AAA]

1 and 2 are total bunk, I hate to say.

Are you saying that sitting cranies do not have a legitimate risk of air embolus, or that N2O would be safe even if that were to happen?

 

[Triple AAA]

Are you sure you're not also a Belieber?

No, I'm more of a One Direction kinda guy 😛

 

[deleted162650]

Are you saying that sitting cranies do not have a legitimate risk of air embolus, or that N2O would be safe even if that were to happen?

N2O shouldn't be problem in the setting of an air embolus provided you turn it off as soon as the embolus occurs. Any N2O within the air embolus will be rapidly resorbed into the blood stream. Now failure to recognize the embolus and leaving the N2O on is another story which will certainly make matters worse.

 

[Triple AAA]

N2O shouldn't be problem in the setting of an air embolus provided you turn it off as soon as the embolus occurs. Any N2O within the air embolus will be rapidly resorbed into the blood stream. Now failure to recognize the embolus and leaving the N2O on is another story which will certainly make matters worse.

I think this is why many practitioners (myself included) would rather avoid N2O in the first place for these scenarios. Can it be done? Sure. Is it worth the risk? To me, probably not.