Subepidermal moisture (SEM) and bioimpedance: a literature review of a novel method for early detection of pressure‐induced tissue damage (pressure ulcers)

Abstract

Current detection of pressure ulcers relies on visual and tactile changes at the skin surface, but physiological changes below the skin precede surface changes and have a significant impact on tissue health. Inflammatory and apoptotic/necrotic changes in the epidermal and dermal layers of the skin, such as changes in interstitial fluid (also known as subepidermal moisture (SEM)), may precede surface changes by 3-10 days. Those same epidermal and subepidermal changes result in changes in the electrical properties (bioimpedance) of the tissue, thereby presenting an objective, non-invasive method for assessing tissue damage. Clinical studies of bioimpedance for the detection of pressure ulcers have demonstrated that changes in bioimpedance correlate with increasing severity of pressure ulcer stages. Studies have also demonstrated that at anatomical locations with pressure ulcers, bioimpedance varies with distance from the centre of the pressure ulcers. The SEM Scanner, a handheld medical device, offers an objective and reliable method for the assessment of local bioimpedance, and therefore, assessment of tissue damage before signs become visible to the unaided eye. This literature review summarises pressure ulcer pathophysiology, principles of bioimpedance and clinical research using bioimpedance technology to assess pressure ulcers.

Utility of a sensor‐based technology to assist in the prevention of pressure ulcers: A clinical comparison

“…The SEM Scanner is a non‐invasive, portable wound assessment device designed to be used as an adjunct to clinical judgement in the detection of early pressure‐induced tissue damage (PUs or deep tissue injury) as part of PU prevention programmes. The SEM Scanner offers an objective method for the detection of early tissue damage before the damage becomes visible to the unaided eye …”

“…In the earliest stages of PU development, apoptosis, necrosis, and the inflammatory process lead to leakage from vasculature and other changes that modify the underlying structure of the damaged tissue. This results in an increase in the interstitial fluid or SEM, which is assessed by the scanner . These changes have been shown to occur 3–10 days before visually identifiable skin breakdown.…”

Use of prophylactic silicone adhesive dressings for maintaining skin integrity in intensive care unit patients: A randomised controlled trial

“…The sites of impaired skin integrity where PIs occur and the inflammatory reaction in the epidermis and dermis cause a change in the interstitial fluid . The SEM value may be a non‐invasive, reliable method for predicting the development of PIs, and it is currently used in PI prevention programmes …”

“…The relationship between change in the subepidermal moisture (SEM) value and skin assessment by visual discrimination was investigated in order to predict the occurrence of PIs as a non‐invasive and objective physiological index . The SEM value is a measurement of localised oedema and skin damage caused by pressure.…”

“…The SEM value is a measurement of localised oedema and skin damage caused by pressure. The use of the SEM value has been studied for blanching erythema and stages 1 and 2 PIs and for its discriminatory ability to differentiate between intact skin and tissue with pressure‐induced skin damage; the SEM value has been suggested as one of the objective indicators for predicting the occurrence of PIs …”