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Past, present and future of conservative oxygen therapy in critical care
  1. Daniel Martin1,2,
  2. David Harrison3,
  3. Paul Mouncey3,
  4. B Ronan O'Driscoll4,5,
  5. Mike Grocott6,
  6. Lorna Miller3,
  7. Doug Gould3,
  8. Alvin Richards-Belle3,
  9. Kathryn Rowan3
  1. 1 Peninsula Medical School, University of Plymouth, Plymouth, UK
  2. 2 Intensive Care Unit, University Hospitals Plymouth, Plymouth, UK
  3. 3 Intensive Care National Audit & Research Centre (ICNARC), London, UK
  4. 4 Respiratory Medicine, Salford Royal University Hospital, Salford, UK
  5. 5 Faculty of Biology, Medicine and Health, University of Manchester, Manchester, UK
  6. 6 Clinical & Experimental Sciences, University of Southampton, Southampton, UK
  1. Correspondence to Professor Daniel Martin, University of Plymouth, Plymouth PL4 8AA, UK; daniel.martin{at}

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Conservative oxygen therapy

Conservative oxygen therapy (COT) is the administration lower levels of supplemental oxygen than usual in order to tolerate a lower level of arterial oxygenation (either the partial pressure (PaO2) or haemoglobin saturation) than normal. Its purpose is to reduce a patient’s overall exposure to additional oxygen in order to minimise the risk of oxygen toxicity.1 This approach to oxygen therapy has also been called permissive hypoxaemia and the terms are frequently used interchangeably; here, we refer to all efforts to reduce supplemental oxygen administration or arterial oxygenation as COT. Studies have been conducted across a wide range of medical conditions, to determine whether COT improves patient outcomes and there appears to be a signal of benefit among acutely unwell patients.2 The intention in this article, however, is to focus only on critically ill patients admitted to intensive care units (ICUs). These patients often present with acute hypoxaemic respiratory failure and require high concentration oxygen to restore normal arterial oxygenation. There is concern that one of the central pillars of support for these patients, oxygen, may inadvertently be causing them harm, which we mistakenly ascribe to a worsening of their underlying pathology. There remains no consensus on how or when to use COT in critically ill patients and it is imperative we address these questions as soon as possible.

The past

Prior to the COVID-19 pandemic, a number of observational studies sought to understand the relationship between arterial oxygenation and survival using data from retrospective databases. Some findings supported the notion that hyperoxaemia was associated with harm3 while others did not.4 These early studies tended to rely on an extremely limited quantity of routinely collected data, commonly only using a single oxygenation value per patient. Their findings were at high risk of confounding by treatment indication and provided …

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  • Contributors All authors (DM, DH, PM, BRO’D, MG, LM, DG, AR-B and KR) contributed to the writing and editing of this article.

  • 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 All of the authors of this manuscript are investigators for the NIHR Health Technology Assessment funded UK-ROX (Intensive Care Unit Randomised Trial Comparing Two Approaches to OXygen Therapy) trial ( lecture and consultancy fees from Siemens Healthineers and Edwards Lifesciences. Director of Oxygen Control Systems. MG served as chair of the NHSE guidance on the management of critical care for adults with COVID-19. MG serves on the medical advisory board of Sphere Medical and is a director of Oxygen Control Systems. He has received honoraria for speaking and/or travel expenses from BOC Medical (Linde Group), Edwards Lifesciences and Cortex.

  • Provenance and peer review Not commissioned; externally peer reviewed.