Any problems using N2O during cases?

[HalO'Thane]

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As a first year anesthesiology resident I have started to love the use of N2O during my general anesthesiology cases. It decreases my volatile agent requirements and I therefore get a lot less hypotension when running deep anesthesia on sicker patients (particularly during periods of little surgical stimulation). Plus, it is fast as hell and patients wake up quick at the end of cases (even faster than Desflurane used alone). However, it seems to get a bad rap from some of the attendings at my institution. They feel it causes a higher incidence of post-op nausea and vomiting, which makes it especially crappy for same day surgery patients. There are also the textbook risks often cited of using N2O in closed air spaces (e.g. SBO, possible pneumothorax, glaucoma, middle ear surgery, etc.) My question to you guys then is how often do you use N2O for GA cases and in what situations would you avoid it?

 

[Noyac]

All situations. Personally.

 

[VentdependenT]

It most definitely increases nausea and vomiting whether its used in conjunction with a volitile or not.

It causes more N/V by itself than a volitile does by itself.

With current data perhaps leading to higher levels of oxygen leading to decreased post op infections, when I do use it, I use it at less than 50%.

Oxygen in high concentration does decrease nausea vomiting.

While it IS true that N20 can decrease you ET% of volatile used, most people end up increasing TOTAL FRESH GAS FLOW by using a 2L N20 1L O2, which probably uses more of the agent in the end. When using DES alone I run at least 500ml total flow, when running sevo I use 1L flow for 2MAC hours.

That being said, in the university setting, N2O is cheap, on every machine, and I do use it.

VENT.

 

[Mman]

I like the stuff, but am well aware that it has some not so nice side effects. The bone marrow suppression on cases of even a few hours in length is real and not that great for your older/sicker patients.

 

[Arch Guillotti]

It most definitely increases nausea and vomiting whether its used in conjunction with a volitile or not.


VENT.

Are you basing this on personal experience or published studies?

 

[canavarim]

I think use it whenever u can unless if u have a contraindication ..
don't worry about N/V , if u don't use it , then u are gonna replace it with a higher dose of VA , right ? they are emetogenic as well ...

 

[Gator05]

FWIW, analgesic effect tops out at ~35% N2O.

 

[ZA_Gasman]

Personally, I don't touch the stuff. We still have a lot of high flow semi-open circuit (Siemens Elema 900C) ventilators and I can't justify the pollution of the theatre environment for some perceived and minor benefits of Nitrous. There is almost always a pregnant person in the theatre (we have a very fertile department 😉 ) and I don't like the teratogenic risks.

There have also been some concerns about neuro toxicity of nitrous in children and James Cottrell (I think) has demonstrated increased apoptosis in rat brains following exposure to nitrous.

Other advantages to NOT using nitrous
1. No chance of hypoxic mixture (I pull the nitrous hose out of the wall)
2. No farting about continually adjusting ET Tube cuff pressure in long cases
3. Decreased PONV (already mentioned - underestimated IMHO) - what is the point of using expensive anti-emetics if I'm going to give an emetogenic gas?
4. The whole air-space issue with nitrous expanding air spaces - not a problem if I don't use it.
5. Less expense - Making nitrous is expensive - much more so than scrubbing and compressing air for the medical air line.

That said, I'm sure nitrous will always have it's proponents. This is only my opinion, which I try and bash into my interns and junior colleagues 🙄

Of interest, I'm not sure if anyone saw the editorial and article in BJA about 2 yrs ago, describing the use of nitrous as a source of nitric oxide to gain benefit in terms of ventilation perfusion ratios. Their premise was that nitric oxide in very small quantities is a contaminant of nitrous oxide, and these small quantities may have physiological effect. Haven't seen any other work like this so not sure if it is too esoteric, but it is out there...
ZA_G

 

[BigSkyDreams]

Howdy,

Keep in mind that your 'tea and toast' old ladies and vegans will be at greater risk of post-op B12 deficiency secondary to the ability of N20 to bind and wash it out.

Here

"...a rapid-onset, postoperative myeloneuropathy due to nitrous oxide anesthesia that inactivates marginal B12 stores has been described..."
Holloway KL, Alberico AM. Postoperative myeloneuropathy: a preventable complication in patients with B12 deficiency. J Neurosurg 1990;72(5):732-6

cuz I know you'd ask for it anyway

BSD

 

[Orthonut]

Howdy,

Keep in mind that your 'tea and toast' old ladies and vegans will be at greater risk of post-op B12 deficiency secondary to the ability of N20 to bind and wash it out.

Here

"...a rapid-onset, postoperative myeloneuropathy due to nitrous oxide anesthesia that inactivates marginal B12 stores has been described..."
Holloway KL, Alberico AM. Postoperative myeloneuropathy: a preventable complication in patients with B12 deficiency. J Neurosurg 1990;72(5):732-6

cuz I know you'd ask for it anyway

BSD

Interesting, thank you. I'm off to read the whole thing. It has become very popular to feed cats and dogs vegan diets (erm...cats are obligate carnivores?) and while for the most part nitrous isn't used that commonly in the private vet practice setting there are a fair number of practices that do use it.

[/hijack]

 

[Bougie]

Just wondering if the above mentioned facts and studies relate to the use of nitrous through the length of an entire case. I personally use about 50% nitrous during the last 5-10 minutes of a case to allow me to bleed off VA but rarely use it through an entire case. Aside from the obvious contraindications (PTX, pneumocephalous, etc) are there studies that show even very brief use of nitrous cause PONV, myelosuppression, etc?

 

[VentdependenT]

Are you basing this on personal experience or published studies?

Got that off of some massive european trial adressing PONV. Can't remember the name of it. But its out there and should be pretty easy to locate.

 

[meddog1]

It most definitely increases nausea and vomiting whether its used in conjunction with a volitile or not.

It causes more N/V by itself than a volitile does by itself.

With current data perhaps leading to higher levels of oxygen leading to decreased post op infections, when I do use it, I use it at less than 50%.

Oxygen in high concentration does decrease nausea vomiting.

While it IS true that N20 can decrease you ET% of volatile used, most people end up increasing TOTAL FRESH GAS FLOW by using a 2L N20 1L O2, which probably uses more of the agent in the end. When using DES alone I run at least 500ml total flow, when running sevo I use 1L flow for 2MAC hours.

That being said, in the university setting, N2O is cheap, on every machine, and I do use it.

VENT.

I agree with VentdependenT and Bougie. You can get some pretty bad PONV. In the ambulatory setting that means a longer time for the PT in the PACU (= higher cost) and sometimes even an admission if the PT is VERY nauseated. The attendings where I work therefore get upset if we use it. Personally, (when there are no contraindications) I like it when coming close to wake-up on Pts (especially the obese ones) if I am using Sevo or Iso and I need to start blowing those volatiles off but need to keep the Pt out. In other words, I only use it for that end-point transition to wake up. As far as the lower flow with Sevo VentdependenT describes, I tend to run my flows a little higher secondary to the Compound A theory.

 

[HalO'Thane]

Thanks a lot for the quick and thorough responses. As a "newbie" I'm still constantly finding ways to better my anesthetic plan and figure out what strategies work best for me. Your guys' inputs will definitely help me out.

 

[TheSandMan]

It most definitely increases nausea and vomiting whether its used in conjunction with a volitile or not.

It causes more N/V by itself than a volatile does by itself.

With current data perhaps leading to higher levels of oxygen leading to decreased post op infections, when I do use it, I use it at less than 50%.

Oxygen in high concentration does decrease nausea vomiting.

While it IS true that N20 can decrease you ET% of volatile used, most people end up increasing TOTAL FRESH GAS FLOW by using a 2L N20 1L O2, which probably uses more of the agent in the end. When using DES alone I run at least 500ml total flow, when running sevo I use 1L flow for 2MAC hours.

That being said, in the university setting, N2O is cheap, on every machine, and I do use it.

VENT.

a little off topic, but am interested in what ventdependent said about higer O2 levels throughout the case. Is there good data out on this, or is it mostly speculation. in addition, what would the recommended % O2 be ?

 

[jwk]

I use N2O on just about every case, and my rate of PONV is no worse than those in my group that don't use N2O. I'm like canavarim - I need an indication NOT to use nitrous.

PONV is multi-factorial. Many of the drugs and potions we use besides N2O are emetogenic. Pain is emetogenic. Postural hypotension due to inadequate IV rehydration is emetogenic. Being female is emetogenic.

The other issues are at least interesting, but certainly far from being profound, overwhelming, practice-changing research.

I'm not sure where the comment that the analgesia effect of N2O tops out at 35% comes from. If it wasn't for that pesky need for O2, we might try 100%.

Finally, with all the talk about awareness in anesthesia - nitrous is good - no nitrous is bad.

 

[jwk]

.

 

[VentdependenT]

a little off topic, but am interested in what volatile said about higer O2 levels throughout the case. Is there good data out on this, or is it mostly speculation. in addition, what would the recommended % O2 be ?

I believe the study done was with 80% oxygen intraop and concerned infections involving colon surgery. Caviat was the patient was started on oxygen prior to going to or and continued on a high fio2 in the par/wherever for 5 hours post op.

It did show a decrease in infection.

Now I don't know if you call it good data or not but I'm seeing a little smoke so I'm hoping there is a fire.

 

[Arch Guillotti]

I use it all the time, especially in neuro cases.

 

[TheSandMan]

I believe the study done was with 80% oxygen intraop and concerned infections involving colon surgery. Caviat was the patient was started on oxygen prior to going to or and continued on a high fio2 in the par/wherever for 5 hours post op.

It did show a decrease in infection.

Now I don't know if you call it good data or not but I'm seeing a little smoke so I'm hoping there is a fire.

interesting. i will keep this in mind. thanks vent