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Silent hypoxia in COVID-19: easy to recognise but hard to define
  1. Ashleigh Trimble1,
  2. Steve Goodacre2
  1. 1 Emergency Department, Sheffield Teaching Hospitals NHS Trust, Sheffield, UK
  2. 2 School of Health and Related Research (ScHARR), The University of Sheffield, Sheffield, UK
  1. Correspondence to Professor Steve Goodacre, School of Health and Related Research (ScHARR), The University of Sheffield, Sheffield, S1 4DA, UK; s.goodacre{at}

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Emergency physicians who worked during the COVID-19 pandemic are likely to remember the term ‘silent hypoxia’ (or ‘happy hypoxia’) being used to describe patients with marked hypoxia, potentially to a level incompatible with life, without any other clinical signs such as confusion, decreased conscious level or shortness of breath.1 2 However, silent hypoxia (or hypoxaemia) is surprisingly difficult to define, characterise or explain. Studies have generally defined silent hypoxia as presentation without signs of dyspnoea despite low oxygen saturation.1–4 Authors do not usually define dyspnoea in terms of RR, and the threshold for low oxygen saturation varies between studies.3–6

People with chronic obstructive pulmonary disease (COPD) often have hypoxaemia without signs of dyspnoea due to ventilation/perfusion mismatch and blunted ventilatory responses to hypoxaemia,7 but the mechanism for silent hypoxia in …

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  • Handling editor Ed Benjamin Graham Barnard

  • Contributors SG conceived the article. AT wrote the first draft. Both authors contributed to redrafting and approved the final draft.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.

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