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Working accuracy of pulse oximetry in COVID-19 patients stepping down from intensive care: a clinical evaluation
  1. Keir Elmslie James Philip1,
  2. Benjamin Bennett2,
  3. Silas Fuller2,
  4. Bradley Lonergan2,
  5. Charles McFadyen2,
  6. Janis Burns2,
  7. Robert Tidswell2 and
  8. Aikaterini Vlachou2
  1. 1National Heart and Lung Institute, Imperial College London, London, UK
  2. 2Critical Care, Royal Brompton and Harefield NHS Foundation Trust, London, UK
  1. Correspondence to Dr Keir Elmslie James Philip; k.philip{at}


Introduction UK guidelines suggest that pulse oximetry, rather than blood gas sampling, is adequate for monitoring of patients with COVID-19 if CO2 retention is not suspected. However, pulse oximetry has impaired accuracy in certain patient groups, and data are lacking on its accuracy in patients with COVID-19 stepping down from intensive care unit (ICU) to non-ICU settings or being transferred to another ICU.

Methods We assessed the bias, precision and limits of agreement using 90 paired SpO2 and SaO2 from 30 patients (3 paired samples per patient). To assess the agreement between pulse oximetry (SpO2) and arterial blood gas analysis (SaO2) in patients with COVID-19, deemed clinically stable to step down from an ICU to a non-ICU ward, or be transferred to another ICU. This was done to evaluate whether the guidelines were appropriate for our setting.

Results Mean difference between SaO2 and SpO2 (bias) was 0.4%, with an SD of 2.4 (precision). The limits of agreement between SpO2 and SaO2 were as follows: upper limit of 5.2% (95% CI 6.5% to 4.2%) and lower limit of −4.3% (95% CI −3.4% to −5.7%).

Conclusions In our setting, pulse oximetry showed a level of agreement with SaO2 measurement that was slightly suboptimal, although within acceptable levels for Food and Drug Authority approval, in people with COVID-19 judged clinically ready to step down from ICU to a non-ICU ward, or who were being transferred to another hospital’s ICU. In such patients, SpO2 should be interpreted with caution. Arterial blood gas assessment of SaO2 may still be clinically indicated.

  • respiratory measurement

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  • Contributors All authors contributed to concept of the study. KEJP, BB, SF and BL collected the data. KEJP analysed the data and wrote the first draft of the manuscript. All authors contributed to revisions of the manuscript and approved the final draft. KEJP confirms that he had full access to all the data in the study and had final responsibility for the decision to submit for publication.

  • Funding KEJP is supported by the Imperial College Clinician Scientist Scholarship. KEJP would like to acknowledge the National Institute for Health Research (NIHR) Biomedical Research Centre based at Imperial College Healthcare NHS Trust and Imperial College London for their support.

  • Disclaimer The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. The funders had no involvement in the project, its conduct, or decision to submit for publication.

  • Competing interests None declared.

  • Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting or dissemination plans of this research.

  • Patient consent for publication Not required.

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

  • Data availability statement No data are available. All relevant data are included in this publication. No other data will be made available due to patient confidentiality.