Title: A study within a trial to determine the effect of skin tone on the diagnostic accuracy of pulse oximeters.
Funder: Department of Health and Social Care

Abstract: The commonest way to measure the level of oxygen in a patient is by using a pulse oximeter; a clip that is usually placed on a fingertip and provides a value where 96-100% is considered normal. Pulse oximeters are used the world over in virtually every medical setting. During the COVID-19 pandemic there have been an extremely high number of patients presenting to hospitals with low oxygen levels and pulse oximeters are used to determine the severity of this lack of oxygen. If a patient’s oxygen levels are very low, they are admitted to hospital for specialist treatment; alternatively, if their level is only decreased a small amount, they may be sent home with a pulse oximeter to closely monitor their oxygen levels there. It is therefore imperative that pulse oximeters are accurate and reliable._x000D_ _x000D_ An increasing number of studies have shown that for patients with darker (pigmented) skin, pulse oximeters may over-estimate their true oxygen level. This is because the pulse oximeter shines light through the fingertip and skin tone may affect the device’s accuracy. Over-estimation of oxygen levels could under-estimate the severity of a patient's illness, lead to them receiving inadequate treatment and come to unnecessary harm._x000D_ _x000D_ Our aim is to determine whether skin tone affects the accuracy of pulse oximeters and confirm whether they over-estimate the level of oxygen in people with darker skin. We will do this by comparing the values from pulse oximeters to precise oxygen levels measured in blood samples, in patients with a range of different skin tones. The results will answer this question about pulse oximeters and provide information that will allow manufacturers to adapt how pulse oximeters work in the future._x000D_ _x000D_ We will adapt a trial (called UK-ROX) we are already running that was designed to study how oxygen levels affect patients on breathing machines in intensive care units (ICUs). Patients eligible to be enrolled in this trial will be offered the opportunity to participate in this additional diagnostic accuracy study. We will study several different pulse oximeters used by the NHS and for each patient, two of these will be placed on their fingers and the oxygen level compared to the oxygen level in a simultaneously taken routine blood sample. These blood samples (‘arterial blood gas samples’) are a normal part of caring for patients in ICU and are taken a number of times each day. The patient's skin tone will be measured using a special camera (called a handheld spectrophotometer) that accurately measures colour. We plan to enrol approximately 900 patients to this study, from 24 ICUs participating in the ICU-ROX trial over 12 months._x000D_ _x000D_ We have involved patients and the public in the design of this study and will be supported by the Centre for Ethnic Health Research (CEHR) in Leicester to help ensure all documentation and public messaging is conducted in a way that will be optimal for ethnic groups most affected by this research. Once the study is complete, we will publish the results in well-regarded medical journals and work with CEHR to reach out to public with our findings.

Lay abstract: Research question:_x000D_ What is the diagnostic accuracy of different pulse oximeters at peripheral oxygen saturation levels (SpO2) relevant to their use by patients at home and how does this vary in people with darker skin pigmentation?_x000D_ _x000D_ Background:_x000D_ Pulse oximeters are used in virtually every medical field and provide a non-invasive way of measuring arterial oxygenation. Their accuracy has recently been questioned and data shows this inaccuracy may be greater in patients with a darker skin tones when arterial oxygenation is low. This needs rapid and accurate investigation as it may be the cause of a substantial healthcare inequality._x000D_ _x000D_ Objective:_x000D_ To compare pulse oximeter-derived SpO2 values to co-oximeter-derived arterial oxygen saturation (SaO2) measurements from arterial blood gas (ABG) samples, for a range of fingertip pulse oximeters used by the NHS COVID Oximetry@home scheme, in an ethnically diverse group of adult patients with a broad spectrum of skin tones admitted to UK intensive care units (ICUs)._x000D_ _x000D_ Methods:_x000D_ We propose a study within a trial that will form a sub-study of the NIHR HTA funded UK-ROX trial, which is currently running in ICUs across the UK. UK-ROX is large-scale randomised controlled trial evaluating conservative oxygen therapy (a target SpO2 of 88-92%) versus usual oxygen therapy in mechanically ventilated adult patients admitted to ICUs in the UK. In order to in increase the number of patients eligible for the diagnostic accuracy study, we will also seek approval to enrol mechanically ventilated adult patients who have been screened for, but not enrolled into UK-ROX. 24 ethnically diverse ICUs enrolling patients into the UK-ROX trial will be randomly allocated two brands of pulse oximeter each to evaluate. Over a period of 24 hours for each participant, SpO2 values from the test pulse oximeters will be compared to simultaneous SaO2 values from ABG samples analysed on a standard ICU ABG co-oximeter machine. Patient skin tone will be objectively measured using a handheld spectrophotometer. The differences between SpO2 and SaO2 will be compared in different skin tone groups and across a range of arterial oxygenation levels._x000D_ _x000D_ Primary outcome:_x000D_ The accuracy of pulse oximeter derived SpO2 measurement, validated against co-oximeter-derived SaO2 from arterial blood gas samples._x000D_ _x000D_ Secondary outcomes:_x000D_ Diagnostic accuracy of SpO2 to predict SaO2 = 92% and presence of ‘occult hypoxaemia’._x000D_ _x000D_ Sample size:_x000D_ Based on observed data from UK-ROX, we anticipate 10,800 paired SpO2 and SaO2 measurements from 900 patients._x000D_ _x000D_ Timelines:_x000D_ We intend to begin the study in March 2022; after 1-2 months of set up we will recruit patients for 12 months then spend a maximum of 4 months analysis data and disseminating findings._x000D_ _x000D_ Impact and dissemination:_x000D_ Given the sensitivities around the study, beginning on its first day we will run a communications and engagement work package with our partners (the Centre for Ethnic Health Research) and PPI representatives. Its purpose will be to encourage engagement and communication with the wider public and community groups, and will continue to produce outputs to cover both progress during the study and the results at the end.

Research activity codes: 6.3 MEDICAL DEVICES
Health categories: RESPIRATORY;GENERIC HEALTH RELEVANCE