Nitrous oxide optimum levels

Started by Stuart Mayfield, January 06, 2005, 03:08:30 AM

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Stuart Mayfield

At our institution, we have many who use nitrous oxide at or near 70% for msot cases unless contraindicated, and those who never use it for any case because of nausea, gas-filled cavities, marrow depression and the fact that sevo and desflurane seem to make it unnecessary.

I hold the middle ground. I use nitrous for all cases (unless directly contraindicated) at 50%. I find this gives me the best of both worlds. 50% O2 is plenty safety margin, yet the 50% nitrous allows for much quicker emergence (yep, even better than desflurane) and NO nausea side effects. I say NO in big letters because I am not entirely sure of this - I have no data to back it up. But informal feedback from my recovery nurses indicate that my patients have the fewest incidence of nausea out of all my peers.

I stand ready to be corrected, but I would need to see strong evidence in order to convince me to change my stance.

George Miklos

I think its probably a dose-response effect. Some nitrous causes X amount of nausea. Twice X causes twice the incidence of nausea.

Russell Coupland

There was a study I read a few years ago that showed that at about 50%, nitrous exerts very few side effects, certainly much less than expected. Sorry, can't give you a reference or citation.

Sandy Hancock

The only advantages nitrous oxide has over the smellies are, in my opioin, twofold.

It doesn't smell, so it can be useful at the start to stun a patient who doesn't like needles.

It is still unrivalled for speed of washout at the end of a case (maybe xenon is better?). I do not use it during maintenance, because its well documented adverse effects outweigh (for me) its minimal advantages *during maintenance*. At the end of a long case, I still use it often (with the patient denitrogenated and the sevo turned off) for the last 15-30 minutes and by the last stich the end-tidal sevo is about 0.3%. Turn off the nitrous and the patient is ready to walk by the time the dressings are on.

Therese Huntly

Quote from: Sandy Hancock on February 09, 2005, 12:14:37 AM
well documented adverse effects outweigh (for me) its minimal advantages *during maintenance

Don't you think that using nitrous even for short periods, and especially at the end of a case, will still cause side effects, in particular nausea?

More generally, what determines PONV as related to nitrous? Duration? Concentration? Total cumulative dose (time x concentration)?

I always thought that if you wanted to prevent PONV, then avoid nitrous altogether.

Sandy Hancock

I think (class 5 evidence here) at least part of the problem with nitrous oxide and PONV is due to distension of the gastric air bubble (and possibly other airspaces in the head?). I only turn it on at the end of fairly long cases where I have been using a high FiO2 (often 1.0), so the patient is fairly well denitrogenated. I think I mentioned this in my post.

Is it also possible that getting rid of a great deal of the smelly may help?