Toxicity associated with recreational use of nitrous oxide in the United Kingdom

Nitrous oxide has been inhaled for its euphoric and dissociative effects since soon after its discovery in 1772. This study was performed to establish the current frequency and patterns of clinical toxicity associated with recreational use of nitrous oxide in the United Kingdom using data collected by UK National Poisons Information Service (NPIS) Units in Birmingham, Cardiff, Edinburgh and Newcastle. Methods: The UK Poisons Information Database (UKPID) was searched for enquiries relating to nitrous oxide and synonyms for the period January 2004 to October 2012. UKPID has stored records of enquiries to some NPIS Units since 2004 and all Units since 2007. Accesses to the NPIS poisons information database TOXBASE were quantified for the same period. Results: Of 44 telephone enquiries received relating to nitrous oxide, 25 concerned apparent recreational users, 17 males and 8 females, with a median age of 23 years (range 16-34). Exposure was classified as chronic or took place over 1 day or longer in 6 cases. The mode of use was often not well documented, but use of Entonox, a 50:50 mixture of nitrous oxide and oxygen (2 patients), canisters for production of whipping cream (6 patients) and inhalation from balloons (3 patients) were recorded. No significant changes in annual telephone enquiry rates were observed over the period 2008-2012, when all UK poisons enquiries were available for analysis. Access numbers for TOXBASE also did not change significantly between 2005 (n = 111) and 2011 (n = 106). Nine (36%) patients were asymptomatic. Neurological features were recorded in 4 patients including paraesthesiae/neuropathy (2 patients), which was associated with choreoathetoid movements in one, abnormal gait (1) and tinnitus with hyperaccusis. Other recorded clinical features included gastrointestinal symptoms (2 patients), tachycardia/palpitations (2), dyspnoea (2), stomatitis (2), chest pain, convulsion/syncope, dizziness, dry mouth, fever, rash, myalgia and anxiety (1 patient each). One patient had a coldinduced burn from handling a gas canister. Two of the patients with neurological features were treated with hydroxocobalamin. Conclusion: Enquiries to the UK NPIS concerning the recreational use of nitrous oxide are uncommon, but toxic effects similar to those recorded after therapeutic use are occasionally encountered, with neurological effects present in some patients. No recent change in the frequency of presentation has been detected.