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Introduction to Sub-Epidermal Moisture

A pressure injury can also be known as a pressure ulcer, pressure sore, decubitus ulcer or bed sore. For ease of reading, this page will refer to the disease state as a pressure injury.

“A pressure injury is defined as localised damage to the skin and/or underlying tissue, as a result of pressure or pressure in combination with shear. Pressure Injuries usually occur over a bony prominence but also may be related to a medical device or other object.”1

Developing damage from pressure injuries and deep tissue injuries is always microscopic, detection in the earliest stages is clinically impossible without technology applications.

Prevention: keeping the skin intact, is therefore not effective under the current standard of care.

Inflammatory Response to Injury

Inflammation is the body’s first response to tissue damage and a mechanism to combat injury. The inflammation increases vasodilation and permeability of blood vessels, leading to leakage of plasma and fluid creating localised oedema in the tissue. Localised inflammatory oedema is described by the International Clinical Practice Guidelines (CPG)1 as one of the earliest signs of cell death in pressure injuries.

As the level of tissue damage increases, so does the inflammatory response. Accordingly, the resulting level of localised oedema in the skin and tissue, also known as sub-epidermal moisture (SEM) and persistent focal edema, increases.2 The CPG describe that this can be identified by a “biophysical marker called the Biocapacitance of the tissues.”1
These inflammatory changes in the skin and underlying tissues with the localised tissue oedema can occur from 3 to 10 days before damage and/or breakdown of skin is visible at the surface.3

Defining Biocapacitance

Biocapacitance is an electrical property of tissue that varies with the amount of interstitial moisture content. The greater the interstitial moisture, the higher the biocapacitance of the tissue. The higher biocapacitance is then interpreted by the Provizio® SEM Scanner.2

The Provizio® SEM Scanner

The Provizio SEM Scanner, is a CE-marked and FDA-authorised hand-held wireless device, that objectively alerts clinicians to specific anatomical areas of a patient’s body at increased risk for developing pressure damage, 5 days* earlier than visual skin assessments,4 regardless of skin tone5,6.

The scanner consists of a concentric sensor, an integrated pressure switch, and software that computes a “delta” (SEM ∆) value from a set of readings made around a common anatomical location.

When the sensor is pressed against an area on the skin, the Provizio SEM Scanner identifies the capacitance of the sensor and underlying tissue, which is affected by the moisture content within the tissue to a depth of approximately 4mm. The capacitance reading is converted into a unitless value (SEM) and displayed to the user. The device also computes a delta (∆) value for each set of measurements and displays this sub-epidermal moisture delta (∆) value to the user.

A SEM Δ < 0.6 at an anatomical site may suggest the tissue is at lower risk for pressure injuries

A SEM Δ ≥ 0.6 at an anatomical site may suggest increased risk for pressure injuries

Close-up view of the Provizio SEM Scanner, a handheld device for assessing pressure injury risk.

Current clinical decision making relies upon assessing a patient’s overall risk for pressure injury development and then completing a subjective skin and tissue assessment.7 Both methods suffer from not being able to direct clinicians to where the risk is building until damage is visible at the skin’s surface. Once pressure injuries become visible on the skin’s surface, tissue damage has already occurred.

Elevated SEM delta (∆) readings from the Provizio SEM Scanner, the detection effect, provide objective clinical information that directs clinicians to heels and sacrum’s at increased risk of developing pressure injuries, even before the damage is visible4 and should be regarded as a condition that requires treating, the treatment effect. This can facilitate earlier, anatomically specific interventions based on the facilities existing protocol and is designed to reverse the damaging effects of pressure and shear and prevent the pressure injury from breaking through the skin, the prevention effect.

International Clinical Practice Guideline 2019 (CPG)1

CPG recommendation 2.6 states that healthcare practitioners using their own qualified clinical judgement should, “Consider using a sub-epidermal moisture/edema measurement device as an adjunct to routine clinical skin assessment.”1

CPG recommendation 2.7 states that HCPs using their own qualified clinical judgement when assessing darkly pigmented skin should, “Consider assessment of skin temperature and sub-epidermal moisture as important adjunct assessment strategies.”1

For more information on the clinical and health economic evidence visit the Evidence page

1. European Pressure Ulcer Advisory Panel, National Pressure Injury Advisory Panel and Pan Pacific Pressure Injury Alliance. (2019). Prevention and Treatment of Pressure Ulcers/Injuries: Quick Reference Guide. Emily Hasler (Ed.). EPUAP/NPIAP/PPPIA
2. Gefen, A. (2018). The Sub-Epidermal Moisture Scanner: the principles of pressure injury prevention using novel early detection technology. Wounds International, 9 (3)
3. Moore Z., et al. (2016). Subepidermal moisture (SEM) and bioimpedance: a literature review of a novel method for early detection of pressure-induced tissue damage (pressure ulcers). International Wound Journal, 14(2), pp.331-337
4. Okonkwo H., et al. (2020). A blinded clinical study using a subepidermal moisture biocapacitance device for early detection of pressure injuries. Wound Repair Regen, (online) 1-11.
5. Bates-Jensen B., et al. (2009). Subepidermal Moisture Is Associated with Early Pressure Ulcer Damage in Nursing Home Residents With Dark Skin Tones. Journal of Wound, Ostomy and Continence Nursing, 36(3), pp.277-284
6. Osborne, C. et al. (2024). Shedding new light for nurses: Enhancing pressure injury prevention across skin tones with sub-epidermal moisture assessment technology. J Adv Nurs.
7. Moore Z., et al. (2019). Risk assessment tools for the prevention of pressure ulcers (Review) Cochrane Collaboration
* Median

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