The role of ALLEVYN™ Ag in the management of hard-to-heal wounds
21/11/11 | Complex wounds, Leg ulcers, Skin integrity | Lantis J, Price P
Hard-to-heal wounds are challenging to treat and have a significant impact on a patient’s quality of life and healthcare resources [1,2,3]. For clinicians, hard-to-heal wounds pose the dual challenge of providing cost-effective management, while improving patients’ wellbeing and concordance with treatment [1,4,5]. This paper examines the impact of hard-to-heal wounds on patients and reviews the clinical efficiency and cost-effectiveness of a topical antibacterial dressing containing silver sulfadiazine (ALLEVYN™ Ag, Smith & Nephew) in the management of patients with infected hard-to-heal wounds.
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The prevalence and costs of chronic wounds is increasing globally. This is reflected in the incidence of venous leg ulcers, which affect approximately 1% of the population worldwide and up to 2.5 million patients per year in the US alone. Pressure ulcers have an overall prevalence rate of around 10%, although this is often higher in individual facilities. The number of diabetic foot ulcers is expected to reach some 380 million by 2025, representing 7.1% of the adult population worldwide (www.idf.org). Venous leg ulcers alone typically consume 1-3% of healthcare budgets.
Defining hard-to-heal wounds
In the majority of cases, wounds close following a predictable sequence of overlapping stages. However, in some wounds, despite the best efforts of clinicians using standard therapies, closure is prolonged or never achieved. The challenge for clinicians is to predict when a wound is likely to become hard to heal.
Typically investigators have defined hard-to-heal ulcers as wounds that have[10,11]:
- Been present for over 12 months
- A bioburden of more than 105cfu/g
- A wound area of more than 10cm2.
A review by Margolis et al identified that a venous leg ulcer larger than 10cm2 and more than 12 months old has only a 22% chance of closure by 24 weeks. Others have shown wound closure rates of 30-35% in 'visually clean' venous leg ulcers at 12 weeks using a standard care regimen[13,14,15], while marginally improved closure rates of 55% at 12 weeks have been achieved where active therapy has been used.
There is a lot of data to show that older ulcers are more difficult to heal. There may be multiple reasons for this and the full picture is not clear, but as a consequence costs will be greater.
Such low rates of closure place a premium on:
- Reducing bioburden[6,17]
- Effective debridement
- Optimising the wound environment for closure .
These must all be achieved while maintaining adequate pain control.
White and Cutting state that bioburden in a wound may be one of the most important barriers to wound closure. Bioburden refers to the bacterial load present on the surface of the wound or in the tissue. It is thought that the higher the load, the greater the risk of infection or delayed closure. The bacterial diversity and density may also play a role in the delayed closure process, with the presence of specific bacteria linked to closure outcomes (including Pseudomonas aeruginosa, Staphylococcus aureus and β-haemolytic Streptococcus).
The presence of biofilms in the wound bed has been suggested as a major contributory factor to the failure of some acute surgical wounds to close. The presence of biofilms is also implicated in some chronic wounds becoming hard to heal. Biofilms are different from normal bacterial colonies in that they are usually composed of mixed microbial species in mutually supportive complex communities attached to the surfaces of a wound and distinct from their planktonic counterparts.
In addition, studies have shown that elevated levels of pro-inflammatory cytokines found in some hard-to-heal wounds can lead to the degradation of newly formed extracellular matrix (ECM) and other proteins, such as growth factors and receptors[25,26]. As a result, the wound becomes stuck in the inflammatory stage, and fails to progress to the proliferative phase. Some studies assume that these changes are due to a defect or disorder in the host's ability to regulate the inflammatory processes. Other studies have shown that biofilms can 'hijack' the host response to infection by producing a high level of virulence factors that can either dampen or re-orient the innate and adaptive immune response that usually maintains the inflammatory process.
Other contributors to delayed closure include patient-related elements such as diabetes, obesity, hyperglycaemia, tissue hypoxia, old age and restrictions in mobility, all of which need to be addressed as part of a comprehensive assessment, along with other wound-related factors such as wound size and depth, anatomical location, duration and wound-bed condition.
Impact of wellbeing on wound closure
In addition to the clinical challenges, there is increasing evidence to support a relationship between psychological and socioeconomic factors (such as a patient living alone or with poor nutritional status) and delayed wound closure. Living with a wound is associated with increased anxiety and poor quality of life[3,29].
To capture patient experiences, a large-scale survey was conducted in 15 different countries with over 2,018 patients and reported in a variety of studies [30,31,32]. Data from focus group work was consistent in showing that pain is one of the symptoms that patients find particularly distressing. Pain can impact on a patient's ability to cope, along with feelings of loss of control, 'uncleanliness' and a reduced sense of self-identity, which may also affect sexuality. In addition, the wound may affect the patient's ability to perform everyday activities, which can lead to social withdrawal and loss of financial independence.
Many patients who live with a wound over a long period of time indicate that symptom management is very important. Symptoms such as pain, odour and exudate can affect the way patients conduct their lives and they may worry that the wound will deteriorate, never heal or become infected. While patients report that their priority is for the wound to close, the ability to improve patient wellbeing appears to rely on appropriate symptom management, allowing them to get the most out of their daily living. For many patients, managing the symptom most important to them, rather than closure, can be the next step in care management.
The emphasis is on the need to address patient concerns through a holistic approach. Listening to patients can help clinicians gain their confidence and trust, leading to a partnership in which, for example, the patient feels able to discuss concerns about medication and clinicians can offer evidence-based advice to the patient on topics such as wound dressings and compression bandaging. A treatment plan can then be mutually agreed. The quality of the relationship between the patient and the clinician can impact positively on treatment outcomes, improve quality of life and help to reduce costs by improving concordance with treatment[1,4,16].
In addition, access to care and referral to clinicians with the appropriate knowledge and skills is vital for an early diagnosis and ensuring that appropriate treatment strategies are used to either achieve closure or manage the symptoms effectively. The importance of educating staff so that they know how to develop wound-care protocols and access resources cannot be underestimated. Such factors will vary in different parts of the world according to national and local standards and priorities for healthcare delivery.
Clinical approaches for hard-to-heal wounds
Management of wounds should focus on identifying problems early and using appropriate strategies and interventions to facilitate closure. According to several reports[34,18] hard-to-heal wounds are often treated using one strategy at a time. Due to an increase in antibiotic-resistant strains of bacteria, wound dressings containing topical antibacterials such as silver, iodine, honey or polyhexamethylene biguanide (PHMB) are popular choices, irrespective of the quality of the in vivo efficacy data, since they have a broad theoretical spectrum of antibacterial activity[35,36,37].
However, a lack of knowledge regarding the appropriate and timely use of these products could put patients at risk of delayed closure, while untreated local infection can lead to systemic sepsis . Using antibacterial dressings to stop local infection spreading may avoid unnecessary complications and costs, such as extended hospitalisation and, therefore, it is important to recognise and accurately identify the signs and symptoms of at-risk wounds.
The role of silver dressings
When the antibacterial properties of silver are used in wound-care products, it is the silver ions rather than the atoms that exert their effect. The theory is that on contact with wound fluid, silver atoms are slowly released from the dressing as positively charged ionic silver (Ag+). These silver ions kill pathogens in a variety of ways:
- Binding to the bacterial cell wall, weakening it and causing leakage from the cell and death of the bacteria
- Binding to bacterial cell oxidative enzymes, inhibiting their activity
- Binding to bacterial cell DNA to interfere with cell division and replication.
How far a dressing's antibacterial effect is influenced by the amount of silver contained in a dressing and the rate of release of Ag+ remains unclear[36,44].
One Cochrane review reported on three studies (n=847) using absorbent sustained-release silver dressings in venous leg ulcers, but failed to show faster closure rates at four weeks. Similarly, the VULCAN study did not show a difference in closure rates over 12 weeks for venous leg ulcers treated with a silver dressing when compared with an absorptive dressing.
However, the goal of using a silver dressing is not to close the wound, but rather to help reduce the bioburden and thus prepare the wound bed for closure. Therefore, large studies into the ability of a dressing that is intended to kill bacteria being used to close wounds, many of which may not have significant bacterial burden, would appear to be inappropriate. Indeed, very few studies report on bioburden, with the exception of one that examined a 0.9% cadexomer iodine dressing (IodosorbTM, Smith & Nephew), which was found to significantly reduce S. aureus levels over a six-week period in venous leg ulcers.
Other factors such as the dressing's capacity to manage exudate, promote autolytic debridement or maintain an optimum wound environment also need to be considered when selecting a silver dressing.
Infected wounds are more painful and may be associated with high exudate levels. This can lead to malodour and periwound maceration and leakage, requiring more frequent dressing changes. Treatment of the wound infection, by reducing bacterial load and reducing the inflammatory stimulus to the nervous system, should also result in a reduction in pain, malodour and exudate.
ALLEVYN Ag (Smith & Nephew) is described as a highly absorbent antibacterial foam dressing range that has been designed to manage exudate and provide an effective bacterial barrier. It comprises a triple-layered structure of hydrocellular foam containing silver sulfadiazine, a perforated wound contact layer and an outer highly breathable top layer.
Silver sulfadiazine (SSD) is a silver compound that was first developed in 1968 and is effective against a variety of pathogens. It has been used by clinicians as a topical antibacterial agent for burns and other wound types, including venous leg ulcers[48,49,50]. As exudate is absorbed into the dressing and away from the wound, the SSD within the central layer is released as positively charged ions at a bactericidal concentration for up to seven days.
In vitro, ALLEVYN Ag has been shown to have a broad spectrum of bactericidal activity against Gram-positive and Gram-negative bacteria, antibiotic-resistant strains, anaerobes, fungi and yeast[52,53].