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by claude@2026-07, 2026-07-03
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This retrospective cohort preprint studied 81 hospitalised individuals (100 presentations) with nitrous oxide toxicity across six Sydney hospitals between 1 January 2020 and 31 July 2025, estimating weekly and cumulative exposure volumes and relating them to neurological outcomes and biomarker results. Higher cumulative nitrous oxide exposure was associated with worse neurological impairment, including subacute combined degeneration of the spinal cord and peripheral neuropathy, and showed a moderate correlation with neuropathy severity, while median homocysteine and methylmalonic acid were substantially elevated. For diagnosing subacute combined degeneration, vitamin B12 and holotranscobalamin had high specificity but low sensitivity, whereas homocysteine and methylmalonic acid were more sensitive but less specific. A major caveat is that the work is a preprint that has not been peer reviewed and the study uses retrospectively collected hospital data. The paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.
Abstract
Aims: : Recreational nitrous oxide (N 2 O) misuse is a growing problem. It can cause functional hydroxycobalamin (B 12 ) deficiency and severe neurological complications. Despite increasing harms, the dose-response relationship and clinical value of biomarkers remain unclear. This study aimed to characterise the demographics, patterns of use, outcomes, and biomarker utility in patients hospitalised with N 2 O toxicity, and to examine whether a dose-response relationship exists between exposure and toxicity. Methods: : This was a retrospective cohort study of hospitalised individuals with N 2 O toxicity between 1 January 2020 and 31 July 2025 across six Sydney hospitals. Weekly and cumulative N 2 O exposure volumes were estimated. Exposure volumes were compared with clinical outcomes and biomarker results to assess correlations and biomarker utility. Results: : Eighty-one individuals across 100 presentations were included. Higher cumulative volumes of N 2 O exposure were associated with worse neurological impairment, including subacute combined degeneration of the spinal cord (SCD)( p =0.006) and peripheral neuropathy (PN)( p =0.036), and showed moderate correlation with greater neuropathy severity (Spearman’s ⍴=0.43, p =0.001). Median homocysteine was 50 μmol/L(IQR: 32-114; normal 5-15) with a median half-life of 14.59 hours. Median methylmalonic acid was 0.68 μmol/L (IQR: 0.18-3.16; normal <0.27). Regarding diagnosis of SCD, B 12 and holotranscobalamin had high specificity (87% and 98%) but low sensitivity (22% and 5%); while homocysteine and methylmalonic acid were more sensitive (95% and 93%) but less specific (13% and 45%). Conclusions: : Cumulative N 2 O exposure is the strongest predictor of severe neurological outcomes in a dose-dependent manner. Homocysteine and methylmalonic acid are good screening tests for neurotoxicity but poor confirmatory tests.
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This is a preprint and has not been peer reviewed. Data may be preliminary.
Dose--Response Relationships Between Nitrous Oxide Exposure, Biomarkers, and Neurological Injury
Abstract
Aims: Recreational nitrous oxide (N 2 O) misuse is a growing problem. It can cause functional hydroxycobalamin (B 12 ) deficiency and severe neurological complications. Despite increasing harms, the dose-response relationship and clinical value of biomarkers remain unclear. This study aimed to characterise the demographics, patterns of use, outcomes, and biomarker utility in patients hospitalised with N 2 O toxicity, and to examine whether a dose-response relationship exists between exposure and toxicity. Methods: This was a retrospective cohort study of hospitalised individuals with N 2 O toxicity between 1 January 2020 and 31 July 2025 across six Sydney hospitals. Weekly and cumulative N 2 O exposure volumes were estimated. Exposure volumes were compared with clinical outcomes and biomarker results to assess correlations and biomarker utility. Results: Eighty-one individuals across 100 presentations were included. Higher cumulative volumes of N 2 O exposure were associated with worse neurological impairment, including subacute combined degeneration of the spinal cord (SCD)( p =0.006) and peripheral neuropathy (PN)( p =0.036), and showed moderate correlation with greater neuropathy severity (Spearman’s ⍴=0.43, p =0.001). Median homocysteine was 50 μmol/L(IQR: 32-114; normal 5-15) with a median half-life of 14.59 hours. Median methylmalonic acid was 0.68 μmol/L (IQR: 0.18-3.16; normal <0.27). Regarding diagnosis of SCD, B 12 and holotranscobalamin had high specificity (87% and 98%) but low sensitivity (22% and 5%); while homocysteine and methylmalonic acid were more sensitive (95% and 93%) but less specific (13% and 45%). Conclusions: Cumulative N 2 O exposure is the strongest predictor of severe neurological outcomes in a dose-dependent manner. Homocysteine and methylmalonic acid are good screening tests for neurotoxicity but poor confirmatory tests.
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Laxna Bhujel, Angela L. Chiew, Bhashita Jagarlamudi, et al.
Dose--Response Relationships Between Nitrous Oxide Exposure, Biomarkers, and Neurological Injury. Authorea. 19 March 2026.
DOI: https://doi.org/10.22541/au.177392033.30308482/v1
DOI: https://doi.org/10.22541/au.177392033.30308482/v1
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