Preliminary evidence supports the use of a novel biophysical marker—the measurement of sub-epidermal moisture—to detect tissue damage early, allowing wound care specialists to identify pressure/shear-induced tissue damage and intervene “when the damage is still microscopic and reversible”. This is the conclusion presented by Aglecia Moda Vitoriano Budri (School of Nursing and Midwifery, Royal College of Surgeons, Dublin, Ireland) and colleagues, writing recently in International Wound Journal.
Budri et al posit that technological-based approaches to wound detection may be more effective “than relying solely on visual skin assessments”, which they say is the current method for pressure-shear induced damage detection.
“From the epidemiological data, it is clear that pressure ulcers are still challenging clinicians throughout the world and within many different clinical settings,” they write. “The skin inspection process is still widely being performed using visual skin assessment. However, it is very challenging to visually diagnose a pressure ulcer in its early stages, as the problem usually starts in the sub-epidermal layers, making any visual identification of tissue damage very difficult. Thus, when the problem is discovered visually, it may already be too late to prevent its further development.”
They argue that more objective approaches based on the pressure ulcer aetiology “would substantially contribute […] to early detection of tissue damage present under intact skin”.
Enter sub-epidermal moisture measurements. Pressure or shear damage catalyses a local inflammatory response: when the first cells start to die after unrelieved pressure and/or shear damage, chemokines, cytokines, and other cell signalling molecules are released. These molecules “flag” the damaged cells, and guide the migration of local and systemic immune cells to that region. Budri et al explain how endothelial cells from the blood vessel walls are sensitive to certain chemokines, and respond by detaching from each other to enable the circulating immune cells to reach the affected area. This increased blood vessel permeability leads to plasma leakage, increasing the water content of the affected area and altering the electrical capacitance of the tissues. This sub-epidermal moisture can be measured using an electrical bioimpedance device.
Use of this “innovative” assessment meant that, on average, clinicians were able to confirm tissue damage five days prior to any visual presentation on the skin surface.
“The longer inflammation occurs, the more tissue degradation will happen, as continuous cell death causes further damage to the surrounding tissues,” Budri and colleagues explain. “This knock-on effect, which starts at a microscopic level (and can be detected by bioimpedance measurement) increases to a macroscopic level, enabling visualisation of the classic signs of inflammation: redness/ heat, swelling, and pain”, which can be measured by visual skin assessment.
Budri et al note two key advantages of this early detection of a pressure or shear-induced wound. Firstly, it enables early intervention, which “has the potential to prevent further aggravation of healthy surrounding tissue”. Secondly, if the problem is identified before the cell reaches the “death threshold”, wound care specialists can act early enough to completely avert pressure ulcer formation.