Nitrous oxide (N2O) toxicity - Emergency Department guidance (haematology‑related toxicology)
Short summary
Nitrous oxide (N2O, “laughing gas”) causes two ED‑relevant problems: immediate harms from acute intoxication (hypoxia, trauma, barotrauma, aspiration) and a delayed functional vitamin B12 deficiency after repeated or heavy use that produces neurological injury and megaloblastic haematological disease. ED priorities are to treat life‑threatening airway/respiratory/circulatory problems, recognise the pattern of functional B12 deficiency, begin replacement promptly when indicated, and arrange timely specialist follow‑up (NICE NG239; RCEM).
Epidemiology and context
- Recreational use is common among young adults; harms and enquiries to poison centres have risen.
- Mortality from N2O is uncommon but can occur via hypoxic/asphyxial events.
- Possession and supply are controlled in the UK; clinicians should offer non‑judgemental harm‑reduction advice and signpost drug‑support services when appropriate (GOV.UK; RCEM).
Pathophysiology (brief and clinically relevant)
- N2O oxidises/inactivates cobalamin (vitamin B12) → functional B12 deficiency.
- Inactivation of B12 inhibits methionine synthase, impairing remethylation of homocysteine and disrupting methylation required for myelin maintenance.
- Functional B12 impairment also affects methylmalonyl‑CoA mutase function, causing accumulation of methylmalonic acid (MMA).
- Resulting problems include neurological demyelination (subacute combined degeneration) and megaloblastic changes in marrow.
- Acute harms also include oxygen displacement (hypoxia), barotrauma from pressurised canisters, and cold injuries from cartridge contact (frostbite).