Use of nitrous oxide is contraindicated in all of the following surgeries except:

D.i.e. Excentration operation Diffusion hypoxia is seen during recovery phase after discontinuation of prolonged N20 anesthesia. It can be prevented by continuing 100% 02 inhalation for a few minutes after discontinuing N20Q. Second gas effect occurs in initial pa of induction of N20 anesthesia. N20 also shows bone marrow suppressionQ. Excentration is enucleation + wide dissection of periorbital tissue. In it there is no closed space formation so N20 can be used. In microlaryngeal lesser surgery, N20 is contraindicated d/t risk of airway fireQ