Nitrous Oxide

General Anaesthetics: Nitrous oxide is used for maintenance of anaesthesia and, in sub-anaesthetic concentrations, for analgesia. For anaesthesia it is commonly used in a concentration of 50 to 70% in oxygen as part of a balanced technique in association with other inhalational or intravenous agents. Nitrous oxide is unsatisfactory as a sole anaesthetic owing to lack of potency, but is useful as part of a combination of drugs since it allows a significant reduction in dosage of the others. A mixture of nitrous oxide and oxygen containing 50% of each gas (Entonox®, Equanox®) is used to produce analgesia without loss of consciousness ('gas and air'). Self-administration using a demand valve is popular in obstetric practice, for changing painful dressings, as an aid to postoperative physiotherapy, and in emergency ambulances.

Analgesics: Nitrous oxide in sub-anaesthetic concentrations as an analgesic. A mixture of nitrous oxide and oxygen containing 50% of each gas (Entonox®, Equanox®) is used to produce analgesia without loss of consciousness. Self-administration using a demand valve is popular in obstetric practice, for changing painful dressings, as an aid to postoperative physiotherapy, and in emergency ambulances.

General Anaesthetics: Breathing 100% nitrous oxide causes respiratory depression as a result of severe hypoxaemia. Normally used with at least 50% oxygen to avoid this unwanted action. It can also result in mild nausea or lingering dizziness if too much is inhaled in too short a time. Nitrous oxide may have a deleterious effect if used in patients with an air-containing closed space since nitrous oxide diffuses into such a space with a resulting increase in pressure. This effect may be dangerous in the presence of a pneumothorax which may enlarge to compromise respiration. Special care is needed to avoid hypoxia if an anaesthetic machine is being used; machines should incorporate an anti-hypoxia device. Exposure of patients to nitrous oxide for prolonged periods, either by continuous or by intermittent administration, may result in megaloblastic anaemia owing to interference with the action of vitamin B12. For the same reason, exposure of theatre staff to nitrous oxide should be minimised. Depression of white cell formation may also occur.

Analgesics: It can result in mild nausea or lingering dizziness if too much is inhaled in too short a time.

General Anaesthetics: For light anaesthesia, using suitable anaesthetic apparatus, a mixture with 25–30% oxygen. For analgesia, as a mixture with 50% oxygen, according to the patient's needs.

Analgesics: A mixture of nitrous oxide and oxygen containing 50% of each gas (Entonox®, Equanox®) breathed via an on demand apparatus ('gas and air').

General Anaesthetics: See eBNF.

Analgesics: See eBNF.

General Anaesthetics: Disinhibition of higher centres occurs in the early stages of anaesthesia or analgesia, leading to euphoria - sometimes manifest as laughter (hence "laughing gas").

Analgesics: Useful for emergency analgesia and for obstetrics because of rapid onset and breath to breath control. Must be used with at least 50% oxygen to avoid hypoxaemia.