Expansion of an air-filled subdural space during nitrous oxide anesthesia

The long-term administration of nitrous oxide anesthesia during craniotomy as well as following closure of the parietal craniotomy flap (under no tension) leads to significant expansion of the residual air bubble trapped under the dura. A case is presented in which an extracerebral avascular space, filled only with gas, caused a marked shift of the intracranial structures and uncal herniation secondary to nitrous oxide anesthesia during craniotomy and postcraniotomy angiography.