<prompt> All are false about N20 except-Little effect on respirationGood muscle relaxantLighter than airNo diffusion hypoxia  <response>: Ans. is a i.e., Little effect on respiration Nitrous oxide N2O o It is colourless, odourless, heavier than air, nonirritating and noninflammable gas. o It is also called laughing gas. o MAC is 105 least potent - even pure N20 at 1 atmospheric pressure can not produce adequate anaesthesia, o It has good analgesic but poor muscle relaxant activity. o It is supplied under pressure in blue coloured steel cyclinders. o It has very low blood solubility - induction is quick and smooth with rapid recovery, o Second gas effect and diffusion hypoxia occur with NzO only. o N2O is generally used as a carrier and adjuvant to other anaesthetics - A mixture of 70 N2O 25 - 30 O2 0.2-2 another potent anaesthetic is employed for most of the surgical procedures, o Entonox is a mixture of 50 N2O and 50 O2. o It has little effect on respiration, heart and BP. o It can cause bone marrow depression and vit B12 deficiency. o N2O is the only anaesthetic reported to produce hematologic toxicity and neurotoxicity with long term administration. o Both toxicides are the result of the interaction of N2O with vit B12. o Complete bone marrow failure can be expected after several days of continuous exposure, o Bone marrow changes are preventable by pretreating patients with large doses of folinic acid. o Other manifestations of vit B12 deficiency eg. megaloblastic anemia, subacute combined degeneration of cord may also occur. o Methemoglobinemia and laryngospasm may occur. o It is contraindicated in patients with air cavities like pneumothorax, pneumoperitoneum and volvulus - expansion and increase in pressure occur. 