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

Abstract

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.

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

“…Two values are displayed on the device's screen: an individual value for every single scan and the SEM Delta (∆SEM) score. The delta value is a measure of the difference in the SEM values between potentially damaged tissue and nearby healthy tissue [44,45]. Calculation of a 'delta' value compares multiple measurements within a specific anatomy, some of which will be healthy tissue, compensates for systemic changes, overcomes the limitation of inter and intra-patient variability (such as changes in the patient's hydration status), and provides a measure of tissue health condition [45].…”

“…The delta value is a measure of the difference in the SEM values between potentially damaged tissue and nearby healthy tissue [44,45]. Calculation of a 'delta' value compares multiple measurements within a specific anatomy, some of which will be healthy tissue, compensates for systemic changes, overcomes the limitation of inter and intra-patient variability (such as changes in the patient's hydration status), and provides a measure of tissue health condition [45]. Clinical studies determined a threshold delta value of 0.6 as the cutoff so that a: a. Δ < 0.6 indicates a lower risk for a PI at the anatomic site, while; a, b. Δ ≥ 0.6 indicates an increased risk for PI at the anatomic site.…”

“…The delta value indicates compromised tissue that is likely to develop into a PI if an intervention is not implemented. As an objective measure, delta values overcome the limitations of the visual skin assessment and HCP variance in skill and technique [40,[44][45][46][47]. Consequently, when an elevated delta value is obtained, anatomically specific interventions can be implemented for a potential reversal of tissue damage before manifesting at the skin's surface.…”

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

“…Cause and effect level analysis at the patient demographic level was outside the scope of this study, particularly in light of other publications that address the characteristics of sub‐epidermal assessments made by the device at and around specific anatomies. Those studies show the device being neutral to patient skin tone and are unlikely to be adversely affected by patient‐specific factors, such as gender, race and comorbidities (Gershon & Okonkwo, 2021; Okonkwo et al, 2020). The authors are excited to continue researching SEM in combination with individual interventional modalities to determine their efficacy.…”

“…O'Brien et al, (2018) demonstrated that the device alerted HCPs to early and deep skin and tissue damage 4 days before damage was identified by visual skin assessment (VSA) with 100% specificity. Gershon and Okonkwo (2021) established the clinical significance of the SEM test in differentiating healthy and non‐visible damage under the skin before VSA for early and deep stage tissue damage. Okonkwo’s group demonstrated that the device alerted clinicians to tissue damage 4.74 days ± 2.39 days earlier than the diagnosis of a PI/PU by skin assessments with the diagnostic accuracy of the SEM test (SEM Scanner) exceeding clinical judgement alone in early and deep stage detection of developing PI/PUs at specific anatomies (Okonkwo et al, 2020).…”