Pulse oximetry in primary care: factors affecting accuracy and interpretation

Paul Silverston; Marco Ferrari; Valentina Quaresima

doi:10.3399/bjgp22X718769

INTRODUCTION

The COVID-19 pandemic saw a rapid increase in the use of pulse oximetry devices (PODs) in primary care to triage and monitor large numbers of patients and to help decide which patients required admission to hospital. In the UK, this included providing 300 000 PODs to patients as part of the ‘virtual ward’ programme and there have been calls to extend the use of remote monitoring to patients with other medical conditions.¹^–³ However, the increased use of pulse oximetry has been accompanied by growing concern over the potential for PODs to produce inaccurate oxygen saturation (SpO₂) readings and the effect that this could have on critical decisions regarding the management of patients. This article discusses the factors that can lead to inaccurate SpO₂ readings and the implications that this could have for both GPs and patients.

THE ACCURACY OF PULSE OXIMETRY DEVICES (PODS)

In early 2021, both the Food and Drug Administration (FDA) and the Medicines and Healthcare products Agency (MHRA) issued safety communications regarding the potential for PODs to produce inaccurate readings.⁴^,⁵ The FDA’s assessment of the situation is well balanced and worth noting:

‘Pulse oximeters have limitations and a risk of inaccuracy under certain circumstances. In many cases, the level of inaccuracy may be small and not clinically meaningful; however, there is a risk that an inaccurate measurement may result in unrecognised low oxygen saturation levels. Therefore, it is important to understand the limitations of pulse oximetry and how accuracy is calculated and interpreted.’⁴

The accuracy of a POD is measured by comparing the SpO₂ reading to the arterial blood gas oxygen saturation (SaO₂) reading, across the range of SpO₂ values from 70–100%. Most manufacturers declare an accuracy of +/− 2–3% over that range. The typical accuracy (reported as Accuracy Root Mean Square …

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