Sensitivity and laboratory performances of a second-generation sub-epidermal moisture measurement device

The complex interplay between mechanical forces, tissue response and individual susceptibility to pressure ulcers

OBJECTIVE

The most recent edition of the International Clinical Practice Guideline for the Prevention and Treatment of Pressure Ulcers/Injuries was released in 2019. Shortly after, in 2020, the first edition of the SECURE Prevention expert panel report, focusing on device-related pressure ulcers/injuries, was published as a special issue in the Journal of Wound Care. A second edition followed in 2022. This article presents a comprehensive summary of the current understanding of the causes of pressure ulcers/injuries (PU/Is) as detailed in these globally recognised consensus documents.

METHOD

The literature reviewed in this summary specifically addresses the impact of prolonged soft tissue deformations on the viability of cells and tissues in the context of PU/Is related to bodyweight or medical devices.

RESULTS

Prolonged soft tissue deformations initially result in cell death and tissue damage on a microscopic scale, potentially leading to development of clinical PU/Is over time. That is, localised high tissue deformations or mechanical stress concentrations can cause microscopic damage within minutes, but it may take several hours of continued mechanical loading for this initial cell and tissue damage to become visible and clinically noticeable. Superficial tissue damage primarily stems from excessive shear loading on fragile or vulnerable skin. In contrast, deeper PU/Is, known as deep tissue injuries, typically arise from stress concentrations in soft tissues at body regions over sharp or curved bony prominences, or under stiff medical devices in prolonged contact with the skin.

CONCLUSION

This review promotes deeper understanding of the pathophysiology of PU/Is, indicating that their primary prevention should focus on alleviating the exposure of cells and tissues to stress concentrations. This goal can be achieved either by reducing the intensity of stress concentrations in soft tissues, or by decreasing the exposure time of soft tissues to such stress concentrations.

A systematic review on the impact of sub-epidermal moisture assessments on pressure ulcer/injury care delivery pathways

To assess all published studies which describe what happens to the delivery of pressure ulcer/injury (PI/PU) care pathways as a result of detecting raised sub-epidermal moisture (SEM) delta (∆ ≥ 0.6). We undertook a systematic review of the literature, and included original research studies using either a prospective or retrospective study design that report the impact that assessment using SEM assessments have on healthcare practitioners' delivery of PI/PU care pathways in adults at risk of developing PI/PUs. The review protocol was registered on PROSPERO (CRD42023416975). A literature search was conducted in May 2023, using PubMed, CINAHL, Scopus, Cochrane, EMBASE, Web of Science and Science Direct databases. Data were extracted using a data extraction tool including elements such as country, setting, sample size, intervention, control and quality appraisal was undertaken using the Evidence-based Librarianship. We identified nine papers published between 2017 and 2022. The majority of these studies were conducted in England (n = 6; 67%). The systematic review included studies conducted across multiple care settings including acute care, medical-surgical units, and palliative care, highlighting the importance of PI/PU prevention and management across diverse patient populations. The PI/PU care pathways implemented in the studies varied, but commonly included elements such as the application or increased use of pressure-redistributing mattresses/cushions, implementation of repositioning plans, management of incontinence and moisture, regular skin inspection, and assessment of patient mobility. Out of the nine studies identified, seven reported PI/PU incidence. A meta-analysis of seven studies (N = 18 451) demonstrated a statistically significant reduction in visual PI/PU development in favour of SEM-guided care pathways compared to usual care (the odds ratio = 0.36 [95% confidence interval: 0.24-0.53, p < 0.00001]). This systematic review provides evidence that implementing SEM assessments in patients at risk of developing PI/PUs prompts anatomy-specific clinical actions. The subsequent implementation of enhanced and targeted skin care interventions leads to consistent and sustained reductions in hospital-acquired PU incidence. The findings emphasise the importance of incorporating SEM assessments as part of comprehensive PI/PU prevention strategies in all care settings and patient populations. This systematic review is limited by the predominance of observational studies and variable study quality. Future research should focus on randomised trials in different care settings that monitor the efficacy of preventive interventions and their impact in reducing PI/PU incidence when implemented based on SEM assessments.

Inter-device agreement of sacral subepidermal oedema measurement in healthy adults during prolonged 60° head of bed elevation

AIM

To investigate the level of agreement between the SEM 200 and Provisio® subepidermal moisture sacral delta measurements, which may indicate increased pressure injury risk, in healthy adults during 120 min of prolonged 60° head of bed elevation. This position, which requires the elevation of the patient's upper body at a 60° angle above the horizontal plane for an extended period, is used by clinicians to prevent or manage a patient's medical or surgical conditions.

DESIGN

This prospective exploratory study recruited 20 healthy adults during October 2021 and collected sacral subepidermal moisture delta measurements using the SEM 200 and Provisio® devices.

METHODS

Delta measurements were taken at 20-min intervals over 120 min resulting in seven data collection timepoints. Descriptive statistics and a Bland Altman plot analysis were conducted.

RESULTS

A total of 280 sacral subepidermal moisture delta measurements were gathered or 140 per device. There were good levels of agreement between the two devices at baseline (T0) [mean 0.025; SD 0.137] and following 60- (T3) [mean 0.025; SD 0.111], 80- (T4) [mean -0.01; SD 0.177] and 100 min (T5) [mean 0.01; SD 0.129] of prolonged 60° head of bed elevation. Head of bed elevations can increase a patient's risk of sacral pressure injuries. In some countries, nurses have access to the SEM 200 and/or the Provisio® device, so our findings may increase nurses' confidence in the interchangeability of the device measurements, although further research is needed to confirm this. The SEM 200 and Provisio® subepidermal moisture scanners show promise in gathering similar objective pressure injury risk data which could prompt clinicians to implement prevention strategies.

IMPACT

Current pressure injury risk assessment is largely subjective in nature. This quantitative study on healthy human sacral tissue found a good level of agreement in the SEM 200 and Provisio® subepidermal moisture scanners, which may increase nurses' confidence in the interchangeability of the devices in clinical practice.

Measuring subepidermal moisture to detect early pressure ulcer development: a systematic review

OBJECTIVE

The aim was to assess evidence related to the measuring of subepidermal moisture (SEM) to detect early, nonvisible development of pressure ulcers (PUs).

METHOD

Using systematic review methodology, all quantitative animal and human research studies written in English were considered. In January 2021, PubMed, CINAHL, SCOPUS, Cochrane and EMBASE databases were searched. The primary outcome of interest was the validity of SEM measurement to detect early PU development. The secondary outcome was time to PU detection, sensitivity and specificity of SEM measurement, and the impact of SEM measurements on PU prevention. Data analysis was undertaken using RevMan and narrative synthesis.

RESULTS

A total of 17 articles met the inclusion criteria. In all studies, a consistent abnormal deviation in SEM measurements corresponded with evidence of visual PU development. Time to PU development, explored in four studies, showed earlier detection of PU development using SEM measurement. RevMan analysis identified the mean difference in time to PU development (SEM measurement versus visual skin assessment, VSA) was 4.61 days (95% confidence interval: 3.94-5.28; p=0.0001) in favour of SEM measurements. The sensitivity of SEM measurements was reported in four studies, and scores varied from 48.3% to 100.0%. Specificity was also reported in four studies and scores ranged from 24.4% to 83.0%. The impact of the detection of abnormal SEM measurements on PU prevention was explored by one study. Results showed a 93% decrease in PU rates when staff acted on the results of the SEM readings.

CONCLUSION

The findings of this review identified that SEM measurement detects PU development earlier than VSA. Furthermore, when staff responded to abnormal SEM measurements, prevention strategies were enhanced, with a subsequent reduction in visible PU development. SEM measurement may therefore be a useful addition to PU prevention strategies.

DECLARATION OF INTEREST

The School of Nursing & Midwifery, RCSI has a research agreement with Bruin Biometrics. Funding for the study was through an Irish Research Council PhD Enterprise Partnership Scheme with Bruin Biometrics. The authors have no other conflicts of interest.

A machine learning algorithm for early detection of heel deep tissue injuries based on a daily history of sub-epidermal moisture measurements

Sub‐epidermal moisture is an established biophysical marker of pressure ulcer formation based on biocapacitance changes in affected soft tissues, which has been shown to facilitate early detection of these injuries. Artificial intelligence shows great promise in wound prevention and care, including in automated analyses of quantitative measures of tissue health such as sub‐epidermal moisture readings acquired over time for effective, patient‐specific, and anatomical‐site‐specific pressure ulcer prophylaxis. Here, we developed a novel machine learning algorithm for early detection of heel deep tissue injuries, which was trained using a database comprising six consecutive daily sub‐epidermal moisture measurements recorded from 173 patients in acute and post‐acute care settings. This algorithm was able to achieve strong predictive power in forecasting heel deep tissue injury events the next day, with sensitivity and specificity of 77% and 80%, respectively, revealing the clinical potential of artificial intelligence‐powered technology for hospital‐acquired pressure ulcer prevention. The current work forms the scientific basis for clinical implementation of machine learning algorithms that provide effective, early, and anatomy‐specific preventive interventions to minimise the occurrence of hospital‐acquired pressure ulcers based on routine tissue health status measurements.

Clinical profile of the SEM Scanner - Modernizing pressure injury care pathways using Sub-Epidermal Moisture (SEM) scanning

INTRODUCTION

Pressure injuries (PIs) are a global health concern. Current PI care standards, including skin tissue assessments (STA) and health care professional (HCP) clinical judgment, diagnose visibly manifested PIs on the skin's surface, i.e. after the damage has already occurred. However, objective assessment of early-stage, non-visible, pressure-induced tissue damage is clinically impossible within the current standard of care. The SEM Scanner is the first device authorized by the Food and Drug Administration (FDA) that addresses this unmet clinical need.

AREAS COVERED

This review describes the novel sub-epidermal moisture (SEM) scanning technology of the device and summarizes the clinical safety and efficacy data that support the use of the scanner in routine PI care practice.

EXPERT OPINION

The clinical strategy for developing the SEM Scanner is noteworthy. SEM technology using anatomy-specific data enables HCPs to provide early PI prevention interventions before visible signs of tissue damage develop while the damage is still reversible. When adopted into routine practice, the device identifies an increased risk of developing PIs 5 days (median) earlier than STA. FDA clearance was based on bench studies and data from three foundational trials that demonstrate the diagnostic accuracy of the device algorithm significantly exceeding clinical judgment (p < 0.001).

Our contemporary understanding of the aetiology of pressure ulcers/pressure injuries

In 2019, the third and updated edition of the Clinical Practice Guideline (CPG) on Prevention and Treatment of Pressure Ulcers/Injuries has been published. In addition to this most up‐to‐date evidence‐based guidance for clinicians, related topics such as pressure ulcers (PUs)/pressure injuries (PIs) aetiology, classification, and future research needs were considered by the teams of experts. To elaborate on these topics, this is the third paper of a series of the CPG articles, which summarises the latest understanding of the aetiology of PUs/PIs with a special focus on the effects of soft tissue deformation. Sustained deformations of soft tissues cause initial cell death and tissue damage that ultimately may result in the formation of PUs/PIs. High tissue deformations result in cell damage on a microscopic level within just a few minutes, although it may take hours of sustained loading for the damage to become clinically visible. Superficial skin damage seems to be primarily caused by excessive shear strain/stress exposures, deeper PUs/PIs predominantly result from high pressures in combination with shear at the surface over bony prominences, or under stiff medical devices. Therefore, primary PU/PI prevention should aim for minimising deformations by either reducing the peak strain/stress values in tissues or decreasing the exposure time.

Evaluating the impact on hospital acquired pressure injury/ulcer incidence in a United Kingdom NHS Acute Trust from use of sub-epidermal scanning technology

BACKGROUND

The incidence of pressure injury/ulcers is persistent despite multiple prevention strategies in hospitals across the globe. Current standard of pressure injury/ulcer care supported by subjective skin tissue assessments, risk assessment tools and clinical judgement is ineffective in consistent pressure injury/ulcer prevention.

AIM

A pragmatic study, aligning with SQUIRE guidelines, was conducted at Chelsea and Westminster hospitals to measure the impact of adding scanning technology to the prevailing standard of care pathway on the incidence of category 2-4 hospital-acquired pressure injury/ulcers.

METHODS

Six hundred and ninety-seven mixed-population patients at risk for pressure injuries/ulcers with a Waterlow score of ≥10 and a mean age ≥65 years were enrolled across four wards over a 6-month period. Scanning technology was added to the prevailing standard of care as a device adjunctive to clinical judgement for the detection of deep and early-stage pressure-induced tissue damage. Ward staff completed comprehensive device training by the device manufacturer. Clinical interventions were initiated by clinical judgement informed by injury/ulcer risk assessments, skin and tissue assessments and scanner readings. Incidence of reportable category 2-4 pressure injuries/ulcers from the prior 12-month period from the same wards were used as a control comparator population. All diagnosed category 2-4 pressure injuries/ulcers, unstageable and deep-tissue injuries were recorded.

RESULTS

Prior study 12-month pressure injury/ulcer incidence was 0.6% (5/892 patients) in ward A, 4.4% (9/206 patients) in Ward B, 1.1% (12/1,123 patients) in Ward C and 2.6% (16/625 patients) in Ward D. Two pressure injury/ulcers in Ward B were recorded during the study. Zero pressure injuries/ulcers were recorded in the remaining three wards resulting in an 81% incidence reduction across all four wards. Improved clinical decisions from clinical judgement based on Sub-Epidermal Moisture (SEM) Scanner data were reported in 83% patients (n=578/697).

CONCLUSION

Implementing scanning technology into routine clinical practice achieves consistent reductions in pressure injury/ulcer incidence.

Evaluating the sensitivity, specificity and clinical utility of algorithms of spatial variation in sub-epidermal moisture (SEM) for the diagnosis of deep and early-stage pressure-induced tissue damage

BACKGROUND

Sub-epidermal moisture (SEM) is a measurable biomarker detecting early pressure damage in order to objectively support current 'gold standard' skin tissue assessments (STA) for the detection of deep and early-stage pressure-induced injuries or ulcers (PI/PUs).

OBJECTIVE

A multi-site, dual arm, cross sectional, retrospective study was conducted to evaluate the sensitivity, specificity and clinical utility of spatial variation in SEM readings between healthy and damaged skin tissue.

METHOD

The study enrolled 175 subjects: 125 with confirmed PI/PUs or suspected deep tissue injury (sDTI), and 50 confirmed healthy subjects. Expert principal investigators and PI/PU healthcare practitioners (HCPs) evaluating all subjects were trained in SEM measurements but blinded to clinical interpretation of SEM readings. Sequential and spatial SEM readings of the sacrum and heels, subjects' demographic data, STAs, risk assessment tool scores (RATS), pain assessment and potential confounders were recorded. Independent statistical analyses were performed.

RESULTS

Mean spatial SEM measures within subjects with healthy tissue and within subjects with damaged tissue were statistically similar. Mean spatial SEM measures within anatomies of subjects with damaged tissue were significantly different (p<0.05). There was no significant difference between spatial readings in healthy subjects. Algorithms computing a range of SEM delta thresholds indicated a sensitivity of 82-87% and a specificity of 51-88% at an SEM delta ≥0.6. Receiver operating characteristic (ROC) curves computed areas under the curve (AUC) of 0.7809-0.9181 (95% CI: 0.7221-0.8817, 0.8397-0.9545, p<0.0001) exceeding clinical judgement.

CONCLUSION

These SEM data augment clinical decision-making for developing intact skin PI/PUs including sDTIs and Stage I PI/PUs. Informing HCPs of this subclinical, non-visible skin and tissue damage and providing opportunities for alternative PI/PU care pathways is an exciting prospect.

Anatomical variability of sub-epidermal moisture and its clinical implications

BACKGROUND

Technologies have been developed to monitor changes in dermal oedema, indicative of the early signs of pressure ulcers. However, there is limited information on the effects of regional differences in tissue morphology on these sub-epidermal moisture (SEM) parameters. This study was designed to investigate the absolute SEM readings across different anatomical sites using a commercial device.

METHODS

Twenty-four healthy participants were recruited to evaluate basal SEM values at different bony prominences, sampled by an experienced operator.

RESULTS

Distinct differences were observed in unloaded SEM values across different anatomical sites, notably between the upper and lower extremities. A high degree of variability was observed in particular sites, such as the heels. Moreover, SEM values at certain locations revealed significant relationships with age, BMI and gender (p < 0.05).

CONCLUSION

The study revealed a high level of variability between and within anatomical sites in a healthy cohort of participants. Determining the changes in local skin and sub-dermal tissue status using SEM may require consideration of both site specific and individual demographic factors, with further research needed in cohorts at risk of pressure ulcers.