Professor Amit Gefen, Ph.D., Department of Biomedical Engineering, Tel Aviv University, Israel
Many factors contribute to the formation of pressure ulcers, and looking for potential preventive measures involves looking at all these factors together. As a result of looking at both clinical evidence and mathematical modelling, what seems like a simple, almost unbelievable, solution to a complex, challenging problem in healthcare is also simply innovative, taking existing materials and applying them in a novel way.
It is fairly common knowledge for healthcare practitioners providing day-to-day care that patients’ heels are the most common site for facility-acquired pressure ulcers, and also the most susceptible location for deep-tissue injuries. The use of multilayer, prophylactic dressings to prevent heel pressure ulcers (heel ulcers) is a relatively new preventive concept. It generally aims to minimize the risk for heel ulcers through mechanical cushioning and reduction of friction at the dressing-support interface. It also aims to reduce compressive and shear deformations in subdermal tissues.
Many studies’ results illustrate different aspects of preventing pressure ulcers. All acknowledge the significant clinical challenge of pressure ulcer prevention, particularly in the underresearched area of critical and trauma care and ICU patients, although the problem exists across the board.
Santamaria et al concluded during an investigation of the preventive application of multilayered soft silicone foam dressings (as an adjunct to standard prevention protocols) that significantly fewer patients (10 percent reduction in incidence) developed pressure ulcers within the intervention group. Their study echoes the findings of previous clinical studies and the mathematical models of our study, although results from other studies used dressings of differing construction and materials in both human and animal models1.
Preventive dressing use is clearly an idea with considerable promise and evidence on its side. It does, however, sound almost unbelievable when you tell practitioners who have struggled against this challenge throughout their careers in healthcare and wound management. Studies show, however, that dressings can change the microclimate at the skin/dressing interface, thus influencing pressure ulcer risk2,3.
A multi-intervention surgical ICU cohort study by Brindle showed benefits of prophylactic multilayered soft silicone bordered foam sacral dressings (the problem, of course is not unique to the heel) to reduce pressure ulcers4. Another study by Brindle and Wegelin used similar dressings in a cardiac surgery setting to reduce incidence of pressure ulcers5. Other studies looked at the reduction in ulcer incidence rates in ICU patients when using silicone dressings to reduce pressure friction and shear6,7.
The point at which many of these factors come together from a mathematical modelling point of view is where our studies come into play. One study reported mathematical modelling of the relationship between skin moisture levels under a dressing and pressure ulceration8. Current science, including our own work, shows that tissue exposure to sustained deformations is the primary cause for cell and tissue death, which leads to pressure ulcers, including heel ulcers.
Our recent study used finite element modelling to determine the protective efficacy of dressings in minimizing the risk of heel pressure ulcers. Finite element modelling is a computational method heavily used in traditional engineering design as well as in biomechanics research and the development of medical products for determining a state of loads in complex structures containing multiple interacting materials that are subjected to certain forces and are contacting surfaces or other structures (including biological tissue structures).
The procedure for solving the biophysical problem always begins with the division of the studied structures into small elements (hence ‘finite’ elements) with a simpler geometry (e.g., bricks or pyramids). Then, a powerful computer is employed for solving the set of equations governing the state of deformations and loads in the structure (or tissues) per each element, and between elements, which ultimately results in a map of the distributions of deformations and loads across and within the entire structure, or tissues.
This method is now being used in numerous product design processes of medical equipment and consumables, such as orthopaedic and cardiovascular biomedical devices.
All of this is a technical way to explain that our study developed finite element model variants of the posterior heel to evaluate the biomechanical performance of a multilayer dressing in prevention of heel ulcers during static supine lying. That is, bottom line – we examined whether applying a dressing preventively, before a heel ulcer could form, would be effective. And to find evidence to explain exactly why.
We compared exposures of the loaded soft tissues in the heel to deformations (including shear deformations) with and without a multilayer dressing on supports with different stiffness properties. The use of the multilayer dressing consistently and considerably reduced the internal soft tissue exposures to elevated deformation levels at the posterior heel, on all of the tested support surfaces, also when considering shear, for example due to elevation of the head of the bed.
The aforementioned multilayer design showed a clear benefit over a single-layer foam design in terms of dissipating local tissue deformations, by promoting internal shear in the dressing, which diverts loads from tissues. The multilayered design also showed a protective effect that was consistent on supports with different stiffnesses.
Most clinicians do not need to know the technical details behind mathematical modelling. They need to know, though, that the modelling explains the reasons why it works – and ultimately to know that preventive dressings do work. Recent randomized controlled trials confirmed the efficacy of the dressings. Taken together with this modelling work, the use of prophylactic multilayer dressings indicates great promise in pressure ulcer prevention.
Do you want to learn more about prophylactic dressings to prevent pressure ulcers? Join the Mölnlycke Health Care Proof into Practice Pressure Ulcer Prevention Pathway webinar. Sign up for the October 29th event to learn more about the clinical evidence supporting preventive treatment and international guidelines and putting both into practice.