Nirous oxide is contraindicated in all of the following except: September 2006

Ans. C: Patient in shock Overall, nitrous oxide is a very safe drug with few absolute contraindications. Absolute contraindications - Nitrous oxide is contraindicated in patients with significant respiratory compromise. The blood: gas paition coefficient of nitrous oxide is 34 times greater than that of nitrogen. This differential solubility means that nitrous oxide can leave the bloodstream and enter air-filled cavities 34 times faster than nitrogen. As a result, nitrous is contraindicated in patients in whom expansion of these air-filled cavities could compromise patient safety. This includes patients with pneumothorax, pulmonary blebs, air embolism, bowel obstruction, and those undergoing surgery of the middle ear and tympanoplasties. - Pneumoperitoneum - Pneumoencephalum - Acute intestinal surgeries and volvulus of gut as it may increase gut distension Relative contraindications - Nitrous oxide is known to interfere with vitamin B12 and folate metabolism. In patients with these preexisting conditions, nitrous oxide should only be used with full precautionary consideration and close monitoring. Paicular precautions should be taken in pediatric patients with underlying vitamin B12 deficiency (genetic or environmental) and conditions related to vitamin B12 deficiency. Nitrous oxide is relatively contraindicated in pregnancy. It is known to have potential teratogenic and fetal toxic effects, paicularly with chronic use. In vitro it depresses myocardium but in vivo this effect is not seen because of stimulation of sympathetic system, so it can be used safely for cardiac patients and for patients in shock.