Introduction

One of the biggest issues facing Urgent and Emergency Care Settings (UEC) internationally is crowding, defined as when “the demands on an [emergency department] ED exceed the capacity” [1]. Crowding is known to lead to long wait times, delays for assessment, increased patient morbidity and poor health outcomes [2,3]. Whilst several strategies to reduce delays to assessment have been proposed, including frontloading triage teams and rapid assessment models [1,4], the issue of ongoing monitoring and reassessment of patients in crowded waiting rooms has yet to be clearly tackled.

A key component of patient assessment and reassessment in UECs is the recording of vital signs. Patient vital signs include heart rate, blood pressure, oxygen saturation, temperature, and respiratory rate. In UEC vital signs are recorded at least once, firstly as part of an initial assessment for patients’ presenting with illness conditions [5], and if needed, to monitor for clinical deterioration or improvements [6]. Despite the need to complete timely and regular recording of vital signs there is evidence that factors such as heavy nursing workload and ED crowding leads to incomplete or complete omission of recording [7,8].

One potential solution that may ease nursing workload caused by high numbers of patients and low throughput is the implementation of patient self-recorded vital signs using smartphone camera-based photoplethysmography (PPG). This may have utility for both initial assessment and ongoing monitoring of vital signs in stable patients, reducing the duration of the triage assessment and allowing nursing staff to focus on higher order tasks. Previous literature has implied high acceptability among ED patients with regards to using mobile devices to access and enter their personal and healthcare information. [9,10].

Camera PPG software to measure vital signs has been explored in various healthcare settings including cardiology [11], geriatrics [12], paediatrics [13], and intensive care [14]. Research within UEC settings reveals that camera PPG software could prove successful within ED triage [15,16], however previous work has focused on piloting the accuracy of the application [12,15,16] using small sample sizes and has not been widely trialled in a real-life uncontrolled scenario with a large population [17].

Aims and objectives

The main aim of the study is to determine the feasibility and acceptability of patient facial self-recorded vital signs for adult walk-in patients in the ED. The objectives are to:

• Explore the performance of facial recording of vital signs compared to standard methods
• Determine clinician acceptability of facial recording of vital signs in the ED

A secondary objective is to establish whether patients in urgent and emergency care settings are be interested in, or willing to use, mobile health technologies in their care.

Although reductions in crowding, improved utilisation of clinical staff time, and improved completeness of vital‑sign documentation are potential downstream benefits of patient‑recorded vital signs, these outcomes will not be evaluated within this feasibility protocol. The current study will focus on assessing usability, acceptability, feasibility, and preliminary agreement between smartphone‑derived and standard measurements. Evaluation of system‑level impacts will form part of future research.

Methods

Setting

For WP1 and WP2, recruitment will take place in the largest of 3 EDs in George’s, Epsom and St Helier Hospital Group in London. For WP3 (large scale survey) all 3 EDs will recruit participants. Recruitment will take place from 01 June 2025–31 December 2026.

Participants

Participants will be identified by members of the clinical or research teams working in any of the sites. Potential participants will be screened using electronic medical records to exclude patients in need of urgent medical assessment prior to approach. Screened patients will be approached by members of the research team and assessed against the eligibility criteria (Table 1). For WP2 (clinical staff questionnaire) we will email eligible staff members to request participation.

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Table 1. Eligibility criteria for the FacED feasibility study.

https://doi.org/10.1371/journal.pone.0326013.t001

For WP3, clinically stable participants will be approached in the ED whilst waiting to be seen. Posters with QR codes in waiting rooms at participating sites will also be used to allow patients to access the survey directly.

Study size

WP1: the smartphone vital signs recording work package will use convenience sampling. Agreement between smartphone‑derived vital signs and standard clinician‑measured vital signs will be assessed using the intraclass correlation coefficient (ICC). The ICC is the recommended metric when evaluating agreement between two continuous measurement methods obtained under similar conditions, as it quantifies the proportion of total variability that is due to true agreement rather than measurement error. The sample size for WP1 is based on achieving a precise estimate of the ICC, assuming an expected ICC of 0.75 for agreement between smartphone and standard measurements, a sample of 1,178 participants will be required to produce a 95% confidence interval with a width of 0.025. By recruiting 1,500 participants, we will allow for attrition and missing data while retaining sufficient precision in the ICC estimate to plan future evaluative studies.

The purpose of this study is to determine feasibility and acceptability; however, an estimate of measurement agreement is necessary to inform future definitive studies. Therefore, the ICC will not function as a co‑primary outcome, but rather as an important secondary metric to understand the likely performance of the technology under real‑world emergency care conditions.

WP2: uses a non-probability convenience sample of clinical staff working in the assessment areas of each of the sites. We aim to obtain a representative clinical staff (by profession and experience) and will recruit between 20 and 40 members of staff.

WP3: uses a non-probability convenience sample of patients presenting to the ED over the recruitment period. There is no sample size calculation for the survey on digital health use in the ED patients. Reason for attendance is not a factor in inclusion and based on previous work using similar recruitment methods we anticipate that 10,000 participants will be recruited over the study duration.

Variables

The outcome variables to assess the study aims are as follows:

• Feasibility: defined as the proportion of patients consented who were able to complete the vital signs recording using their smartphones. Feasibility also includes the proportion of participants who were able to complete the process without staff assistance and completeness of recorded measurements.
• Acceptability of self-recorded vital signs (patients): affinity for technology use – how comfortable, confident, and willing participants are when using digital or technological tools; and acceptability and patient experience of use of PPG application
• Performance: reliability of the platform to accurately measure the vital signs (blood pressure, heart rate, respiratory rate, oxygen saturation) recorded using a web-based PPG application compared to near simultaneous measurement of vital signs using a standard monitor. The Fitzpatrick skin‑tone scale will be used to support subgroup analyses of ICC to explore whether measurement agreement varies by skin tone [19].
• Acceptability (clinical staff): electronic survey of personal technical affinity and a usability evaluation of the patient-recorded vital signs

Data sources/measurement

The data collected in this study is anonymised and all participants will be assigned a unique identification (ID) number.

For WP1, participants will be asked to complete two types of data collection. A flow chart for WP1 can be found in Fig 1.

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Fig 1. Study flow diagram depicting the recruitment process for WP1.

https://doi.org/10.1371/journal.pone.0326013.g001

• A clinical research nurse will support the patient through the data collection phases if necessary. Completion of their vital signs using PPG technology on their smartphone accessed through a QR code link on a webpage. The webpage will not capture any personal information, and all data is removed once the participant leaves the website. Participants will be guided through the capture of their vital signs by a research nurse if needed. Clinical or research staff will near-simultaneously complete the patients vital signs using traditional methods. To ensure comparability, all clinical staff measuring vital signs using standard equipment will receive study‑specific training on timing, device placement, and measurement procedures. Near‑simultaneous measurement will be defined as occurring within two minutes of the PPG recording. Staff will record the timestamp of each measurement to verify this.
• Post-PPG recording participant acceptability data will be captured electronically using an online questionnaire. Participants will be able to complete the survey on their personal devices, following a linked QR code or can be provided with a handheld electronic device. The electronic survey contains the invitation to participate letter (participant information sheet), consent form and the questionnaire. Advantages of the electronic format include ease of administration, ease of data collection and reduced environmental impact versus the use of paper. The questionnaire has been designed to meet the study objectives, drawing from previous literature on digital technology acceptability and technical affinity. The questionnaire is comprised of 17 questions. There are 4 demographic questions, Fitzpatrick skin tone scale, and smartphone operating system. 8 questions including The Single Ease Question (SEQ) and System Usability Scale (SUS) [19–21] will be used to measure the usability of the software, and 5 questions will measure self-reported technical affinity [22] . The survey should take no longer than 5 minutes for each participant to complete, and participants will be notified of this at the start of the survey.
• Participant deprivation index and ED length of stay information will be captured from the hospital electronic patient record (EPR) by the research team and linked to the patient acceptability data following consent.

To determine levels of clinical staff acceptability of the use of PPG technology (WP2), participants will complete an electronic questionnaire designed to capture workplace demographics (profession and seniority), 5 questions will measure self-reported technical affinity [22] and 10 questions to determine the perceived usefulness of the PPG technology on their practice [23].

Finally, to establish whether patients in urgent and emergency care settings are be interested in, or willing to use, mobile health technologies in their care (WP3) we will collect data on age, gender, ethnicity, 1st language, educational attainment level and smartphone ownership. Self-reported technical affinity will be measured with 5 questions [22] and rating questions on areas where participants feel it is acceptable to use digital health technologies as part of their care. It will take participants approximately 15 minutes to complete.

Bias

Bias will be minimised in the study by collecting data through standardised reporting and assessment of measures and using a recognised evaluation questionnaires tool. The use of routine clinical measurements as the comparator may introduce bias due to inter‑observer variation and differences in training or technique. Standardisation procedures and training will be implemented to minimise this variability.

Exclusion of participants without English proficiency may limit generalisability and may disproportionately affect groups at higher risk of digital marginalisation. This issue will be explored in future work which will include language accessibility considerations in digital triage pathways.

Analysis and statistical methods

The electronic surveys will be hosted on the REDCap Platform under a password-protected personal account held only by the Chief Investigator and study team. REDCap provides compliance with General Data Protection Regulations and is ISO 27001 compliant. A link to the REDCap Data protection policy is provided within the participant information sheet.

Descriptive statistics will be used to characterise participants by age, gender, highest educational attainment, IMD and ethnicity. Feasibility will be reported with a percentage and 95% CI. Acceptability to patients as measured by SEQ and overall, SUS score will be summarised, using mean and standard deviation (SD). The association between acceptability to patients and age, educational attainment, IMD and ethnicity will be assessed using regression methods. Descriptive statistics will be used to summarise the findings of the acceptability to clinical staff survey.

Performance of the app will be assessed using the intraclass correlation coefficient (ICC) for the whole sample and for a priori defined subgroups. ICC’s take values between 0 and 1 where, 0 implies no agreement and 1 is perfect agreement and represents the proportion of the total variability in the observations that is due to the differences between pairs [24] . A priori subgroups for exploratory agreement analyses will include age, sex, Fitzpatrick skin tone, and Index of Multiple Deprivation category. These subgroup analyses will be descriptive and hypothesis‑generating only. The study is not powered for between‑group comparisons, and no adjustments for multiple testing will be made. Subgroup ICCs will be estimated using bootstrapped confidence intervals to provide stable descriptive estimates for planning future studies.

Patient and Public Involvement (PPI)

Effective patient and public involvement are of key importance to providing safe and effective emergency care. Discussions with ED service users informed the study design. Feedback emphasized the importance of clear instructions for internet application use and the brevity of questionnaires.

Ethics and dissemination

The study obtained UK NHS ethical approval by the London – Surrey Research Ethics Committee (REC number 25/PR/0222) on 4^th April 2025. Informed consent will be obtained prior to participants undergoing any activities that are specifically for the purposes of the study. Consent for WP1 will be taken electronically by a member of the research team. For WP2 and WP3 consent is ‘self-completed’ online and requires no input from the clinical or research teams. Research staff will not be aware of who has taken part and will not be able to identify any participants. There is no follow-up or other direct contact by research staff.

Findings from this research will be shared and discussed with the study steering committee in preparation of wider dissemination through journals and conferences.