The maintenance of moisture balance in a healing wound is hard to measure in vivo in real time on patients and requires heuristic judgment. Dressings that produce a moist wound environment and promote cell migration for wound healing are the benchmark of wound management.1 In the pursuit of moisture balance, the ideal dressing should possess a suitable water vapor transmission rate, an in vitro metric that, together with the water absorptive capacity of the dressing, regulates fluid balance.2
To my knowledge, there is no widely available clinical method that will facilitate the actual measurement of the moisture in the wound in the clinic (in vivo). However, indirect laboratory measurements of a given dressing, its properties, and the ability to wick or retain moisture in the wound or the periwound environment are replete in the literature, especially in hydrocolloid and hydrogel dressings.
In the laboratory, the moisture permeability of hydrogel dressings is determined by water vapor transmission rate.2 The moisture-fluid balance is the optimal condition for adequate wound healing, that is, a warm moist environment. Too much moisture leads to maceration, swelling, and disruption of the structures of the dermis.2 In an observational study, Milne et al3 advanced the concept that the moisture content of wounds can indeed be measured in clinical practice to assess the real-time moisture condition of the wound at the point of dressing change.3 Their study is the "the first large-scale" observational research that investigated wound moisture status at dressing change.3 They tested the WoundSense (Ohmedics, Glasgow, United Kingdom) sensor, which sits directly on the wound to evaluate the moisture status of the wound environment, without disturbing or removing the dressing. The investigators observed 588 dressing changes; of the 30 patients studied, 11 patients had an optimum moisture reading for at least 50% of the measurements before dressing change.3 The authors concluded that a "large number of unnecessary dressing changes are being made; they further suggest that the protocols established in this study if followed could reduce the number dressing changes and less perturbations to the healing wound bed3."
In a related study, Koyano et al4 explored the prevalence of skin tears and skin properties of older adults in a long-term-care environment in Japan.4 This cross-sectional study examined structural alterations in the epidermis and the dermis related to skin tears. After conducting a facility prevalence study, 18 patients with skin tears and 18 without skin tears were investigated. Their properties were evaluated by various techniques, including the use of the VapoMeter (Delfin Technologies, Kuopio, Finland),4,5 which is a portable instrument that produces a measurement of transepidermal water loss (TEWL) values and evaporation rates. This is an indirect measure of the skin's barrier function. The VapoMeter may be used either as a stand-alone device, or measurement data may be collected wirelessly to the Delfin Modular Core software.5 In this particular study, functional improvement of the skin barrier itself did not contribute to reduced skin tear prevalence. The authors found no significant difference between epidermal functions such as stratum corneum hydration, skin pH, and TEWL between patients with and without skin tears. They also speculated that Japanese subjects have higher water content and lower TEWL in their stratum corneum compared with white subjects.4 In a supporting study, Muizzuddin et al6 observed that East Asian and, to some extent, white skin were characterized by low maturation and a relatively weak skin barrier. African American skin was characterized by low ceramide levels and high-protein cohesion in the uppermost layers of the stratum corneum. This correlates with a high prevalence of xerosis in black skin and increased skin sensitivity in East Asian skin. Their results show that dermal properties at the level of the stratum corneum vary considerably among these ethnic groups.6 This contributes to an improved understanding of physiologic differences between these study populations. An excessively wet skin environment has a propensity to upset the skin fluid balance.
Maceration is defined as the softening and breaking down of the skin, resulting from prolonged exposure to moisture. Initially described by Charcot in 1877,7 maceration is related to extreme amounts of aqueous fluid in contact with the skin or wound surface for extended periods. This fluid may be produced by the wound itself (exudate) or may be a result of urinary incontinence, excessive sweating, or water lost through the skin as a result of TEWL.7,8 Proper moisture balance reduces the risk of maceration and dessication.
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