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Inhalational Analgesic — Procedural Pain

Entonox (Nitrous Oxide 50% / Oxygen 50%)

Brand names: Entonox, Equanox

A ready-mixed inhaled gas of equal parts nitrous oxide and oxygen used as a rapid-onset, short-acting analgesic for procedures such as dressing changes and debridement in burns and plastics.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Inhaled nitrous oxide produces analgesia and light sedation through central effects including modulation of opioid and NMDA-receptor pathways, while the oxygen component maintains oxygenation.

Prescribing in practice

  • It is contraindicated where gas can expand in trapped spaces, including pneumothorax, bowel obstruction and recent intraocular or middle-ear surgery and decompression illness.
  • Prolonged or repeated exposure can inactivate vitamin B12 and impair folate metabolism, causing neurological and haematological harm, so cumulative use should be limited.
  • Adequate room scavenging and ventilation are needed to protect staff from chronic exposure.

Monitoring

Monitor conscious level and adequacy of analgesia during use; the short half-life means recovery is rapid once inhalation stops.

Counselling the patient

  • Breathe the gas through the mouthpiece during the painful part of the procedure.
  • It works quickly and wears off within minutes of stopping.
  • Tell staff if you feel very lightheaded, sick or unwell.

Evidence & guidelines

Entonox is a long-established inhaled analgesic for short painful procedures, with MHRA cautions regarding gas-filled spaces and vitamin B12 effects from repeated exposure.

Reference: AAGBI/Faculty of Pain Medicine Entonox Guidelines; BBA Burns Dressing Change Analgesia Protocol; Confirm identity and dosing against the manufacturer SPC (eMC) and NICE. Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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