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