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Clinical Review Lesson of the week

Toxicity after intermittent inhalation of nitrous oxide for analgesia

BMJ 2004; 328 doi: (Published 03 June 2004) Cite this as: BMJ 2004;328:1364
  1. Mark Doran, consultant neurologist (,
  2. Sahir S Rassam, specialist registrar in anaesthetics1,
  3. Lucy M Jones, clinical nurse specialist pain management1,
  4. Simon Underhill, consultant in anaesthesia and pain management1
  1. 1Wrexham Maelor Hospital, Wrexham LL13 7TD
  1. Correspondence to: M Doran
  • Accepted 12 March 2004


A mixture of nitrous oxide and oxygen in equal proportions (Entonox or Equanox) is an effective analgesic and is considered safe with minimal side effects. The mixture is ideal for treating short term pain. We report a serious neurological problem in a patient using such a mixture to control pain from the daily packing of a large perineal cavity.

Case report

A 21 year old man presented with a short history of being unable to stand. He had had a series of serious operations for the treatment for inflammatory bowel disease over a four year period—colectomy, ileostomy, and laparotomy with the formation of an ileoanal pouch. He developed pelvic sepsis requiring the laying open of an extensive perineal abscess.

The provision of postoperative analgesia for a perineal abscess proved difficult, during daily changes of packs to the cavity. Doctors gave paracetamol, diclofenac, regular oral slow release opioids, morphine tablets, and a 50:50 mixture of nitrous oxide and oxygen for managing the incident pain while changing dressings.

The hospital gave the man a 300 litre cylinder of the mixture as a short term arrangement over the Christmas period to provide analgesia for dressing changes. The man was to be readmitted after two weeks …

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