Nitrous oxide is contraindicated in patients with pneumothorax, pneumo pericardium or intestinal obstruction, because it:

N20 is 35 times more soluble than N2 so when replaces N2O causes expansion of air containing cavity. Nitrous oxide has the potential to expand air containing cavities as it can diffuse into and accumulate in them. Hence it should be avoided in emphysema patients especially in those with bullae and pulmonary hypeension. Other Contraindication Pneumothorax, Acute intestinal obstruction with bowel distention, Intracranial air (pneumocephalus following dural closure or pneumoencephalograph cochlear implant surgery vitreo retinal surgery Tympanoplasty