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Recreational inhalation of alkyl nitrites (“poppers”) may trigger the condition, and it can be missed when onset is sudden and severe. A 53-year-old man of Chinese ethnicity with learning disabilities collapsed in public, presenting unresponsive, cyanotic, hypothermic, and profoundly hypoxic despite high-flow oxygen. Arterial blood gas co-oximetry showed high methaemoglobin with normal pO2, creating a saturation gap; a nitrite bottle supported toxicity. Rapid improvement followed intravenous methylene blue, with safeguarding due to cognitive vulnerability.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":35,"@type":76,"position":81},"https://docshare.wps.com/document/healthcare/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/cyanotic-and-unresponsive-a-diagnostic-challenge-in-alkyl-nitrite-induced-methaemoglobinaemia/444456/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/cyanotic-and-unresponsive-a-diagnostic-challenge-in-alkyl-nitrite-induced-methaemoglobinaemia/444456.png","ImageObject",300,407,{"name":92,"@type":93},"McGucket","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-31","2026-09-29",true,{"@type":102,"interactionType":103,"userInteractionCount":39},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"Why is methaemoglobinaemia considered a diagnostic challenge in sudden hypoxia?","Question",{"text":112,"@type":113},"It may be overlooked when presentation is sudden and severe, especially without collateral history. A key clue is the “saturation gap”: low pulse oximetry readings alongside a normal arterial oxygen tension.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How does co-oximetry help confirm methaemoglobinaemia?",{"text":117,"@type":113},"Co-oximetry, part of arterial blood gas analysis, directly quantifies methaemoglobin levels. Conventional pulse oximetry can become unreliable at high methaemoglobin concentrations and often plateaus around 85%.",{"name":119,"@type":110,"acceptedAnswer":120},"What treatment led to rapid improvement in the reported case?",{"text":121,"@type":113},"Intravenous methylene blue produced rapid clinical and biochemical improvement, and the patient made a full recovery. Safeguarding measures were implemented due to his cognitive vulnerability.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},444456,1790815414,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":34,"category_name":35,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":39,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":24,"language":139,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":140,"faqs":141,"seo_title":142,"seo_description":67,"update_tm":143,"read_time":144,"preview_page_count":4},1236954412713,"https://us-avatar.wpscdn.com/davatar_29158cc5080c5b710cf443261637dec0","Review began 11/28/2025  \nReview ended 12/03/2025  \nPublished 12/07/2025  \n© Copyright 2025  \nBasu et al. This is an open access article distributed under the terms of the Creative Commons Attribution License CC-BY 4.0. , which permits unrestricted use , distribution , and reproduction in any medium , provided the original author and source are credited.  \nDOI: 10.7759/cureus.98627  \nOpen Access Case Report  \nCyanotic and Unresponsive: A Diagnostic Challenge in Alkyl Nitrite-Induced Methaemoglobinaemia  \nSayantan Basu 1, Rayna Koshy 2 , Verghese Kurien 3, Joseph Allen 4 , Purba Chakrabarty 4  \n1. General Medicine, Eastbourne District General Hospital, Eastbourne, GBR 2. Internal Medicine, New Cross Hospital, Royal Wolverhampton NHS Trust, Wolverhampton, GBR 3. General Internal Medicine, East Sussex Healthcare NHS Trust, Eastbourne, GBR 4. Internal Medicine, Eastbourne District General Hospital, Eastbourne, GBR  \nCorresponding author: Sayantan Basu, [sayantanbasu20091995@gmail.com](sayantanbasu20091995@gmail.com)  \nAbstract  \nMethaemoglobinaemia is a potentially serious condition in which haemoglobin is oxidised to a form that cannot carry oxygen effectively. Recreational inhalation of alkyl nitrites (“poppers”) may precipitate this condition and can be overlooked when the presentation is sudden and severe.  \nWe report a 53-year-old male of Chinese ethnicity, with multiple comorbidities, including learning disabilities, who collapsed in public and presented unresponsive, cyanotic, hypothermic, and profoundly hypoxic despite high‑flow oxygen. Arterial blood gas analysis revealed a high methaemoglobin level with a normal arterial oxygen tension, producing a marked saturation gap. A bottle of alkyl nitrites found in his possession supported a toxic cause. Intravenous methylene blue led to rapid clinical and biochemical improvement, and the patient made a full recovery. Safeguarding measures were implemented due to his cognitive vulnerability.  \nThis case highlights the diagnostic challenge of unexplained hypoxia, the essential role of co‑oximetry in confirming methaemoglobinaemia, considerations for enzyme deficiencies like G6PD, and the importance of harm-reduction strategies amid rising poppers use.  \nCategories: Hematology, Emergency Medicine, Substance Use and Addiction  \nKeywords: alkyl nitrites (poppers), diagnostic challenge, g6pd deficiency, hypoxia, jehovah’s witness,  \nmethemoglobinemia, methylene blue, vulnerable adult  \nIntroduction  \nMethaemoglobinaemia occurs when haemoglobin is oxidised to the ferric (Fe³⁺) state, preventing effective oxygen binding and delivery [1] . Severe cases may result in tissue hypoxia, neurological depression, and cardiovascular instability. It can be congenital (e.g., due to cytochrome b5 reductase deficiency, more common in populations like Native Americans or Ashkenazi Jews) or acquired, often from toxins or drugs.  \nRecreational alkyl nitrites (“poppers”) are a common acquired cause inducing methaemoglobinaemia through nitrite-mediated oxidation, though presentations may be delayed or unrecognised [2,3] .  \nDiagnosis is particularly challenging when patients present unresponsive or without collateral history. The characteristic “saturation gap”, i.e., low pulse oximetry readings despite normal arterial oxygen tension, should prompt consideration of methaemoglobinaemia or other dyshaemoglobinaemias. Co‑oximetry, performed as part of arterial blood gas analysis, is critical for diagnosis because it directly quantifies methaemoglobin levels, unlike conventional pulse oximetry, which becomes unreliable at high  \nmethaemoglobin concentrations and typically plateaus near 85%[4] .  \nEpidemiologically, recreational alkyl nitrite use has been rising in the UK, with national surveys consistently showing higher prevalence among younger adults and particularly within men who have sex with men (MSM) communities. Data from the Crime Survey for England and Wales indicate that poppers remain one of the ","cbCaifciGIumcCyV","https://ap.wps.com/l/cbCaifciGIumcCyV","pdf",1734874,"English","# Abstract\n# Introduction\n# Case Presentation\n## Imaging\n## Arterial blood gas and laboratory findings\n# How to cite this article","[{\"question\":\"Why is methaemoglobinaemia considered a diagnostic challenge in sudden hypoxia?\",\"answer\":\"It may be overlooked when presentation is sudden and severe, especially without collateral history. A key clue is the “saturation gap”: low pulse oximetry readings alongside a normal arterial oxygen tension.\"},{\"question\":\"How does co-oximetry help confirm methaemoglobinaemia?\",\"answer\":\"Co-oximetry, part of arterial blood gas analysis, directly quantifies methaemoglobin levels. Conventional pulse oximetry can become unreliable at high methaemoglobin concentrations and often plateaus around 85%.\"},{\"question\":\"What treatment led to rapid improvement in the reported case?\",\"answer\":\"Intravenous methylene blue produced rapid clinical and biochemical improvement, and the patient made a full recovery. Safeguarding measures were implemented due to his cognitive vulnerability.\"}]","Cyanotic and Unresponsive - A Diagnostic Challenge in Alkyl Nitrite-Induced Methaemoglobinaemia | PDF",1790708082,13]