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Entonox (also known as Gas and Air) is a mixture of 50% Oxygen and 50% Nitrous Oxide, it is an odourless, colourless gas and has been used for pain relief for over 150 years.  It is used in hospitals particularly for pain relief in childbirth, and sometimes by dentists.  It is occasionally used in the short term in hospitals for pain relief in acutely painful conditions.  Nitrous oxide used to be used extensively in Anaesthesia: it is rarely used nowadays.

Entonox is inhaled by the patient via a mask or mouthpiece under the supervision of a nurse or doctor. Once deep breathing of the gas has started pain control is provided within 2 minutes. The gas is breathed continuously throughout the painful procedure, and the effects wear off rapidly after its use is stopped, however it is recommended that patients should not drive or operate machinery for 12 hours after use.

The effectiveness of Entonox relies on the patient making a tight seal around the mask or mouthpiece, this also means there is no possibility of overdose as someone who is asleep is unable to maintain this tight seal.

Entonox can safely be administered if patients are already taking other medication including pain killers.

Entonox is not used in longer term pain because there is a risk of harm to the bone marrow or nervous system.











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Pain Service Website, Gloucestershire Hospitals NHS Foundation Trust
Webmaster Dr J G de Courcy, Consultant in Pain Medicine and Anaesthesia
email: pain.webmaster[at]

Page updated 19/02/2016