The mode of action of the SEM Assessment technology is to measure localised oedema by comparing the Biocapacitance marker across different tissue locations, e.g., in multiple sites around the sacrum or heels1. Once a number of SEM readings are taken in each area, the ∆ Delta is calculated.
A patient presenting with systemic oedema may be associated with higher individual SEM values however the ∆ Delta by its definition (variance between max and min values) will not be affected1 – this is crucial as the ∆ Delta is the prompt for action by the healthcare practitioner.
As described by Gefen (2020)2 if there is a condition of systemic oedema, e.g., lymphoedema or heart or kidney dysfunction, the SEM values acquired at adjacent points will be similar and hence, the SEM delta would be < 0.6. Accordingly, using the ∆ delta measure (rather than the individual SEM values) distinguishes a localized inflammatory process most likely indicating a PU is forming from a systemic increase in interstitial fluid content.
The localised oedema referenced results from a “mechanical insult” which is “fundamentally different from systemic oedema” typically caused by “sodium retention or due to a lymphatic disorder.”2
The localised nature of plasma fluid accumulation in soft tissues due to a forming pressure ulcer/injury (PI/PU) is inherently different from a systemic oedema mechanism, in both the pathophysiology and clinical outcomes.2
1. Gefen A., et al. (2020). The subepidermal moisture scanner: the technology explained. Journal of Wound Care. Vol 29, No 2
2. Gefen A., (2020). The SEM Scanner for early pressure ulcer detection: a 360-degree review of the technology. Wounds International. Vol 11 Issue 3