Nitrous oxide

Nitrous oxide is used at low dose for inhalational analgesia, e.g. carried by a 50% oxygen mixture - "Entonox", or at higher concentrations with other agents for induction and maintenance of balanced anaesthesia.

Nitrous oxide may be best avoided for inhalational anaesthesia in the following cases:

• when there is a need for high inspired oxygen concentrations
• in the first four weeks of pregnancy
• in long operations on patients with closed gaseous compartments - there is a high diffusibility causing an increase in volume and hence, for example, a pneumothorax may enlarge to compromise respiration
• cerebral vasodilation, increase in intracranial pressure
• where an alternative would suffice with less atmospheric pollution

Chronic exposure to nitrous oxide may interfere with folate metabolism, so resulting in all of the signs of deficiency, e.g. megaloblastic anaemia, neuropathy.