Global Burden Related to Nitrous Oxide Exposure in Medical and Recreational Settings: An Individual Patient Data Meta-Analysis

Abstract

Background: The risk of adverse effects of nitrous oxide (N2O) exposure is insufficiently recognised despite its widespread use. These effects are mainly reported through case reports. Methods: We conducted an individual patient data meta-analysis to assess the prevalence of clinical, laboratory, and magnetic resonance findings in association with N2O exposure in medical and recreational settings. We calculated the pooled estimates for the studied outcomes and assessed the potential bias related to population stratification using principal component analysis. Findings: Eighty-five publications met the inclusion criteria and reported on 100 patients with a median age of 27 years and 57% of recreational users. The most frequent outcomes were subacute combined degeneration (28%), myelopathy (26%), and generalised demyelinating polyneuropathy (23%). A T2 signal hyperintensity in the spinal cord was reported in 68% (57·2%-78·8%) of patients. The most frequent clinical manifestations included paraesthesia (80%; 72·0%-88·0%), unsteady gait (58%; 48·2%-67·8%), and weakness (43%; 33·1%-52·9%). At least one haematological abnormality was retrieved in 71·7% (59·9%-83·4%) of patients. Most patients had vitamin B12 deficiency: vitamin B12 15 µmol/L (90·3%; 79·3%-100%), and methylmalonic acid >0·4 µmol/L (93·8%; 80·4%-100%). Interpretation: N2O can produce severe outcomes, with neurological or haematological disorders in almost all published cases. More than half of them are reported in the setting of recreational use. The N2O-related burden is dominated by vitamin B12 deficiency. This highlights the need to evaluate whether correcting B12 deficiency would prevent N2O-related toxicity, particularly in countries with a high prevalence of B12 deficiency. Funding Statement: INSERM UMR_S 1256. Declaration of Interest: Authors declare no conflict of interest