THE EFFECT OF NITROUS OXIDE ON INTRACRANIAL PRESSURE IN PATIENTS WITH INTRACRANIAL DISORDERS

The effect of induction of anaesthesia with 66% nitrous oxide on intracranial pressure was studied in 12 patients with intracranial disorders. The pressure rose in all cases (mean change 27 mm Hg) to a plateau, which was reached after 5 min. Arterial carbon dioxide tension and arterial blood pressure were essentially unaltered; when measured (4 patients only) central venous pressure was unaffected. Cerebral perfusion pressure decreased on average from 71 mm Hg (range 106-36 mm Hg) to 45 mm Hg (range 71-16 mm Hg). When nitrous oxide was discontinued, intracranial pressure fell immediately to control levels. The most likely mechanism for the intracranial pressure elevation is cerebral vasodilatation leading to increased intracranial blood volume. The consequences may be moderate to marked decrease in cerebral perfusion pressure and, in the diseased brain, focal ischaemia and tentorial herniation. The intracranial hypertension caused by nitrous oxide could be efficiently counteracted by hyperventilation. It is concluded that nitrous oxide should not be used for induction of anaesthesia in patients with intracranial pathology.