Assessment of Dressing Fluid Handling: A Comparison of Seven Absorptive Foam Dressings

Introduction

It has been demonstrated that moist wounds are able to heal faster due to increased granulation tissue, thicker and faster epidermal growth, increased collagen density and decreased number of inflammatory cells.1-3 Nevertheless, excessive exudate, rich in pro-inflammatory cytokines and matrix metallo- and serine-proteinases, which breakdown the extracellular matrix is equally detrimental. Excess exudate is commonly found in chronic wounds and its presence is one of the causes of a prolonged inflammatory state.

Therefore, adequate management of fluid exudate by means of the application of the most suitable wound dressing becomes of paramount importance. Wound dressings manage exudate by means of two mechanisms:

1. Direct absorption and retention
2. Evaporation of fluid through the back of the dressing

Here, we investigated seven different dressings with the aim of assessing the optimal fluid handling capabilities.

Methods

Seven foam dressings (designated Dressing A to G) were tested in triplicate for the properties detailed below. The free-swell absorbency (FSA), total fluid handling (TFH), and moist vapour transmission rate (MVTR) tests were performed according to the European standard BS EN 13726-1:2002.

Free-Swell Absorbency (FSA)
Pre-weighed dressings were soaked in ionic solution at 37°C for 30 min and weighed after removing the excess. Absorbency was calculated as follows:
Absorbency (g/dressing) = wet weight — dry weight

Retention Following Compression (RFC)
The dressings were allowed to absorb an amount of fluid representative of that produced by a highly exudating wound over 24 hrs at 37°C.2 Dressings were weighed after allowing fluid in excess to drip off (W1) and then compression (40 mmHg) was applied for 30 sec. After the dressing was reweighed (W2), the retention capacity was calculated as follows:
RFC (%) = (W2/W1) * 100

Total Fluid Handling (TFH)
To measure fluid transpired and absorbed, Paddington cups filled with ionic solution kept at 37°C and 20% relative humidity for 24 hrs were used. Total fluid handling was calculated as follows:
TFH (g/m2/24 hrs) = Fluid transpired + Fluid absorbed

Moist vapour transmission rate (MVTR)
Dressings mounted on Paddington cups filled with ionic solution were kept at 37°C and 20% relative humidity for 24 hrs. MVTR was calculated as the difference between the Paddington cup weight before (W1) and after (W2) incubation
as follows:
MVTR (g/m2/24 hrs) = (W1— W2) * (10,000/area of sample)
The MVTR values collected in this study were input into the Medetec MVTR calculator, which predicts the MVTR of
the dressing under ambient humidity and room temperature conditions similar to those seen in the clinic.4

Results

Free-Swell Absorbency
Dressing C showed the highest FSA capacity, the only dressing to absorb more than 100 g/dressing. Dressings D, E, F, and G showed the lowest absorptive capacity of ≤ 40 g/dressing. The absorptive capacity of Dressing C was
significantly greater than all the other dressings tested (p<0.01), aside from Dressing B (p=0.0552)

Retention Following Compression
Dressings A and C showed the highest retention following compression, retaining 99.9% of the fluid absorbed,
significantly more than the other dressings tested (p<0.05) aside from Dressing B (p=0.38). Dressing G showed
the lowest retention, retaining less than 70% of the fluid absorbed.

Total Fluid Handling
Dressings A and B handled the greater amount of fluid through a combination of evaporation and absorption,
significantly greater than the other dressings (p<0.05). Dressing B absorbed significantly more fluid than the other dressings tested (p<0.05). Dressing A evaporated the most fluid, while Dressing C evaporated significantly less fluid than the other dressings tested (p<0.05)

Moist Vapour Transmission Rate
The MVTR values varied considerably across the dressings. All tested dressings exhibited MVTR values of greater than
1000 g/m2/24 hrs other than Dressing C, which yielded an MVTR significantly lower than the other dressings tested. Dressing C was the only dressing to exhibit an MVTR less than 720 g/m2/24 hrs, which has been defined as the optimal MVTR required to provide a moist wound healing environment.5

Conclusions

Many of the dressings tested had poor retentive properties, which could result in chronic wound exudate being released back into the wound when the dressing is compressed. Furthermore, the majority of the wound dressings tested exhibited high transpiration, therefore potentially leading to the creation of a dry environment that may delay healing. The predicted values generated by the Medetec MVTR calculator, with conditions set at 25°C and 60% relative humidity, were all above 720 g/m2/24 hrs aside from Dressing C. Such value has been demonstrated to be the threshold below which an adequate moist wound healing environment is provided.5 Only Dressing C exhibited both high absorptive capacity and low MVTR.
This study suggests that dressings with high absorptive capacity and low MVTR may be more beneficial to optimizing a moist wound healing environment than those having a higher MVTR and lower absorptive capacity. These results highlight how some dressings may lead to low moisture level in the wound through excessive transpiration. We believe that health care professionals should take this evidence into account when selecting the foam dressing to provide the optimal moist wound healing environment.

References

1. Winter GD. Nature. 1962;193:293-294.
2. Junker JPE, Kamel RA, Caterson EJ, et al. Adv Wound Care. 2013;2:348-356.
3. Dealey C, Cameron J, Arrowsmith M. J Wound Care. 2006;15:149-153.
4. Thomas S. J Wound Care. 2010;19:194-199. http:medetec.co.uk/files/MVTR_calculator.html
5. Bolton L. J Wound Ostomy Continence Nurs. 2007;34:23-29.