Inhalation anaesthetic / analgesic
Nitrous oxide
Brand names: Entonox (50% N2O / 50% O2)
Adult dose
Dose: Self-administered Entonox demand-valve until adequate analgesia (typically 5–6 breaths)
Route: Inhalation
Frequency: PRN
Clinical pearls
- Labour analgesia, brief painful procedures (dressing changes, manipulations)
- Recreational misuse rising — counsel re neurological harm + B12
Contraindications
- Pneumothorax
- Bowel obstruction
- Recent diving (gas embolism)
- Pulmonary hypertension
- B12 deficiency
- Maxillofacial injury
- Recent ophthalmic surgery with intraocular gas
Side effects
- Megaloblastic anaemia / myelopathy with chronic abuse (B12 inactivation)
- Nausea
- Dizziness
- Diffusion hypoxia (post-cessation)
- Greenhouse-gas environmental concerns
Interactions
- CNS depressants
- Methotrexate (cytopenia)
Monitoring
- Sedation
- SpO2
Reference: BNF; AAGBI; MHRA; https://bnf.nice.org.uk/drugs/nitrous-oxide/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
Pathways
- Difficult Airway Algorithm (DAS) · DAS 2015; Royal College of Anaesthetists
- Major Haemorrhage Protocol · NICE NG24; UK MHP guidelines
- New-Onset Atrial Fibrillation · ESC 2020 AF Guidelines; NICE NG196
- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines
- Ventricular Tachycardia / Fibrillation · Resuscitation Council UK ACLS; ESC 2022 Ventricular Arrhythmia Guidelines