Description of the condition
Pressure ulcers, also known as bedsores, decubitus ulcers and pressure injuries, are localised areas of injury to the skin or the underlying tissue, or both. They often occur in areas with a bony prominence such as the sacrum (base of the spine) and heel (Vanderwee 2007), and are caused by external forces such as pressure, or shear, or a combination of both (EPUAP-NPUAP 2009).
Populations at risk of pressure ulceration include those with spinal cord injuries (Gefen 2014), and those immobilised or with limited mobility such as elderly people and people with acute or chronic conditions that might limit movement or bodily sensation, or both (Allman 1997; Berlowitz 1990; Berlowitz 1997; Bergstrom 1998; Brandeis 1994). Incontinence can also increase risk of ulceration by producing a detrimental environment for the skin (Brandeis 1994). Impaired nutritional status may also increase risk (Allman 1997; Donini 2005), however, there is currently limited evidence for the effectiveness of nutritional intake interventions for preventing or treating pressure ulcers (Langer 2003; Smith 2013).
Mobility produces relief from pressure within the body through regular, often sub-conscious, shifts in positions when sitting or lying. These movements, triggered by a reduction in oxygen levels at pressure points and possible discomfort, distribute pressure from contact at the surface, thus reducing the compression of soft tissue against bone (Gebhardt 2002). Populations with limited autonomous movement or conditions that dull body sensation, or both (as described above), are at risk of failing to achieve adequate pressure relief. Prolonged exposure of an area of the body to pressure or compression can interrupt the local blood circulation and trigger a cascade of biochemical changes that may lead to tissue damage and ulceration. Immobility can also lead to increased damage from shear and friction, for example, when people are pulled into position in chairs and beds.
Pressure ulcers vary in severity. One of the most widely recognised systems for categorising pressure ulcers is that of the National Pressure Ulcer Advisory Panel which is summarised below (NPUAP 2009).
Category/Stage I - non-blanchable erythema: "Intact skin with non-blanchable redness of a localized area usually over a bony prominence. Darkly pigmented skin may not have visible blanching; its colour may differ from the surrounding area. The area may be painful, firm, soft, warmer or cooler as compared to adjacent tissue. Category I may be difficult to detect in individuals with dark skin tones. May indicate "at risk" persons."
Category/Stage II - partial thickness: "Partial thickness loss of dermis presenting as a shallow open ulcer with a red pink wound bed, without slough. May also present as an intact or open/ruptured serum-filled or sero-sanguinous filled blister. Presents as a shiny or dry shallow ulcer without slough or bruising (bruising indicates deep tissue injury). This category should not be used to describe skin tears, tape burns, incontinence associated dermatitis, maceration or excoriation."
Category/Stage III - full thickness skin loss: "Full thickness tissue loss. Subcutaneous fat may be visible but bone, tendon or muscle are not exposed. Slough may be present but does not obscure the depth of tissue loss. May include undermining and tunnelling. The depth of a Category/Stage III pressure ulcer varies by anatomical location. The bridge of the nose, ear, occiput and malleolus do not have (adipose) subcutaneous tissue and Category/Stage III ulcers can be shallow. In contrast, areas of significant adiposity can develop extremely deep Category/Stage III pressure ulcers. Bone/tendon is not visible or directly palpable."
Category/Stage IV - full thickness tissue loss: "Full thickness tissue loss with exposed bone, tendon or muscle. Slough or eschar may be present. Often includes undermining and tunnelling. The depth of a Category/Stage IV pressure ulcer varies by anatomical location. The bridge of the nose, ear, occiput and malleolus do not have (adipose) subcutaneous tissue and these ulcers can be shallow. Category/Stage IV ulcers can extend into muscle and/or supporting structures (e.g., fascia, tendon or joint capsule) making osteomyelitis or osteitis likely to occur. Exposed bone/muscle is visible or directly palpable."
Pressure ulcers are relatively common, but complex, wounds. Prevalence estimates vary according to the population being assessed, the data collection methods used and decisions about whether or not stage I pressure ulcers should be included (since there is no active wound at this stage, but patients are 'at risk'). A large survey of hospital patients undertaken in several European countries returned a pressure ulcer prevalence (stage II and above) of 10.5% (Vanderwee 2007). In 2009, a USA estimate for pressure ulcer prevalence (stage II and above) across acute-care, long-term care and rehabilitation settings was 9.0% with prevalence highest in long-term acute-care settings (26%) (VanGilder 2009). In the UK, national pressure ulcer data are collected across community and acute settings - although data collection is not yet universal - as part of the National Health Service (NHS) Safety Thermometer initiative (Power 2012). Five per cent of patients across these settings were estimated to have a pressure ulcer in January 2014 (National Safety Thermometer Data 2014).
We note that all the prevalence figures quoted above are for at populations currently receiving medical care. The point prevalence of pressure ulceration in the total adult population was recently estimated using a cross-sectional survey undertaken in Leeds, UK. Of the total adult population of 751,485 the point prevalence of pressure ulceration per 1000 was 0.31 (Hall - personal communication). UK pressure ulcer prevalence estimates specifically for community settings have reported rates of 0.77 per 1000 adults in a UK urban area (Stevenson 2013).
Pressure ulcers have a large impact on those affected; the ulcers can be painful, and may become seriously infected or malodorous. It has been shown that - after adjustment for age, sex and co-morbidities - people with pressure ulcers have a lower health-related quality of life than those without pressure ulcers (Essex 2009). The financial cost of treating ulcers in the UK was recently estimated as being between GBP 1214 for a stage I ulcer, to GBP 14,108 for a stage IV ulcer (Dealey 2012). In 2004 the total annual cost of treating pressure ulcers in the UK was estimated as being GBP 1.4 to 2.1 billion, which was equivalent to 4% of the total NHS expenditure (Bennett 2004). Pressure ulcers have been shown to increase length of hospital stay and the associated hospital costs (Allman 1999). Figures from the USA suggest that for half a million hospital stays in 2006 'pressure ulcer' was noted as a diagnosis; for adults, the total hospital costs of these stays was USD 11 billion (Russo 2008). Costs to the Australian healthcare system for treating pressure ulceration have been estimated at AUD 285 million per annum (Graves 2005).
Description of the intervention
There are two main strategies in the treatment of pressure ulcers, namely relief of pressure - commonly using specialist support surfaces (McInnes 2011) - alongside management of the wound environment using wound dressings. Other general strategies include patient education, pain management, optimising circulation/perfusion, optimising nutrition, surgical wound closure and the treatment of clinical infection (AWMA 2012; EPUAP-NPUAP 2009).
Dressings are widely used in wound care, with the aim of protecting the wound and promoting healing. Classification of dressings usually depends on the key material used in their construction. Several attributes of an ideal wound dressing have been described (BNF 2013), including:
the ability of the dressing to absorb and contain exudate without leakage or strike-through;
lack of particulate contaminants left in the wound by the dressing;
permeability to water and but not bacteria;
avoidance of wound trauma on dressing removal;
frequency with which the dressing needs to be changed;
provision of pain relief; and
Hydrogel dressings are the focus of this review; their properties are described below. As hydrogel dressings are likely to be evaluated against one of the many wound dressings available, a description of potential comparators, based on the British National Formulary structure (BNF 2013), is also provided. Dressings are listed below, by their generic names and, where possible, with examples of corresponding trade names and manufacturers. Dressing names, manufacturers and distributors may vary between countries.
1. Basic wound contact dressings
Low-adherence dressings and wound contact materials: these are usually cotton pads that are placed in direct contact with the wound. Examples include paraffin gauze dressing, BP 1993 and Xeroform (Covidien) dressing - a non-adherent petrolatum blend with 3% bismuth tribromophenate on fine mesh gauze.
Absorbent dressings: these can be applied directly to the wound or used as secondary absorbent layers in the management of heavily-exuding wounds. Examples include Primapore (Smith & Nephew), Mepore (Mölnlycke) and absorbent cotton gauze (BP 1988).
2. Advanced wound dressings
Alginate dressings: these are highly absorbent and come in the form of calcium alginate or calcium sodium alginate, and can be combined with collagen. The alginate forms a gel when in contact with the wound surface, which can be lifted off at dressing removal or rinsed away with sterile saline. Bonding to a secondary viscose pad increases absorbency. Examples include: Curasorb (Covidien), SeaSorb (Coloplast) and Sorbsan (Unomedical).
Foam dressings: normally these dressings contain hydrophilic polyurethane foam and are designed to absorb wound exudate and maintain a moist wound surface. These are produced in a variety of versions: some foam dressings include additional absorbent materials, such as viscose and acrylate fibres or particles of superabsorbent polyacrylate; while some are silicone-coated for non-traumatic removal. Examples include: Allevyn (Smith & Nephew), Biatain (Coloplast) and Tegaderm (3M).
Hydrogel dressings: these consist of cross-linked insoluble polymers (i.e. starch or carboxymethylcellulose) and up to 96% water. They are designed to absorb wound exudate, or rehydrate a wound, depending on the wound moisture levels. They are supplied as either flat sheets, an amorphous hydrogel or as beads. Examples include: ActiformCool (Activa) and Aquaflo (Covidien).
Films - permeable film and membrane dressings: these dressings are permeable to water vapour and oxygen, but not to water or micro-organisms. Examples includeTegaderm (3M) and Opsite (Smith & Nephew).
Soft polymer dressings: these dressings are moderately absorbent and composed of a soft silicone polymer held in a non-adherent layer. Examples include: Mepitel (Mölnlycke) and Urgotul (Urgo).
Hydrocolloid dressings: these are occlusive dressings usually composed of a hydrocolloid matrix bonded onto a vapour-permeable film or foam backing. This matrix forms a gel that provides a moist environment when in contact with the wound surface. Examples include: Granuflex (ConvaTec) and NU DERM (Systagenix). Fibrous alternatives have been developed that resemble alginates, are not occlusive, and that are more absorbant than standard hydrocolloid dressings. Examples include: Aquacel (ConvaTec).
Capillary-action dressings: these consist of an absorbent core of hydrophilic fibres held between two low-adherent contact layers. Examples include: Advadraw (Advancis) and Vacutx (Protex).
Odour-absorbent dressings: these dressings contain charcoal and are used to absorb wound odour, often in conjunction with a secondary dressing to improve absorbency. Examples include: CarboFLEX (ConvaTec).
3. Anti-microbial dressings
Honey-impregnated dressings: these dressings contain medical-grade honey, which is thought to have antimicrobial and anti-inflammatory properties and can be used for acute or chronic wounds. Examples include: Medihoney (Medihoney) and Activon Tulle (Advancis).
Iodine-impregnated dressings: these dressings release free iodine, which is thought to act as a wound antiseptic, when exposed to wound exudate. Examples include Iodoflex (Smith & Nephew) and Iodozyme (Insense).
Silver-impregnated dressings: these dressings are used to treat infected wounds, as silver ions are thought to have antimicrobial properties. Silver versions of most dressing types are available (e.g. silver foam, silver hydrocolloid etc). Examples include: Acticoat (Smith & Nephew) and Urgosorb Silver (Urgo).
Other antimicrobial dressings: these dressings are composed of a gauze or low-adherent dressing impregnated with an ointment thought to have antimicrobial properties. Examples include: chlorhexidine gauze dressing (Smith & Nephew) and Cutimed Sorbact (BSN Medical).
4. Specialist dressings
Protease-modulating matrix dressings: these dressings alter the activity of proteolytic enzymes in chronic wounds. Examples include: Promogran (Systagenix) and Sorbion (H & R).
The diversity of dressings available to health professionals (including variations within each type) can make evidence-informed decision-making challenging. Furthermore, whilst dressings may be viewed as 'inert' and cheap products, increasingly they are being formulated with an 'active' ingredient e.g. silver, or other anti-microbial products. With increasingly sophisticated technology being applied to wound care, practitioners need to know how effective these - often expensive - dressings are compared with more traditional, and usually less costly, options. There are limited data about the current use of dressings for the treatment of pressure ulcers although older studies have shown wide variation in practice and wound (wound type) care knowledge (Pieper 1995).
How the intervention might work
Animal experiments conducted over 40 years ago suggested that acute wounds heal more quickly when their surfaces are kept moist, rather than left to dry and scab (Winter 1962; Winter 1963a; Winter 1963b). A moist environment is thought to provide optimal conditions for the cells involved in the healing process, as well as allowing autolytic debridement (removal of dead tissue by natural processes), which is thought to be an important part of the healing pathway (Cardinal 2009). The desire to maintain a moist wound environment is a key driver for the use of wound dressings. Different wound dressings vary in their level of absorbency so that a very wet wound can be treated with an absorbent dressing (such as a foam dressing) to draw excess moisture away and avoid skin damage, whilst a drier wound can be treated with a more occlusive dressing to maintain a moist environment. Hydrogels are insoluble polymers that can bind a relatively large volume of water that can then be 'donated' to wounds to maintain a moist environment. Furthermore, if the hydrogel polymer matrix is not fully hydrated, it can absorb some wound exudate and help to optimise the moisture level of the wound. When hydrogel material is manufacturer in the form of a fixed structure via cross-linking of the polymers it is considered to be a hydrogel sheet dressing.
Why it is important to do this review
Pressure ulcers are a relatively common complex type of wound that have a negative impact on peoples' lives and incur high costs to health services. Dressings are a widely used treatment for pressure ulcers, and understanding the existing evidence base and potential uncertainty around the clinical and cost effectiveness of different dressing types is important for decision making in this area.
A key international guideline recommends that a dressing should be chosen "that keeps the wound bed moist", this recommendation was classed as being level C evidence, that is "supported by indirect evidence (e.g., studies in normal human subjects, humans with other types of chronic wounds, animal models) and/or expert opinion" (EPUAP-NPUAP 2009). The same guidelines suggests that hydrogel dressings are used to treat pressure ulcers in various scenarios but these recommendations are based on limited evidence (EPUAP-NPUAP 2009).
Two notable systematic reviews of treatments for pressure ulcers have included trials of dressings (Reddy 2008; Smith 2013). Reddy 2008 included eight trials of hydrogel in people with pressure ulcers. These studies were included as part of a much larger review that reviewed multiple interventions for treating pressure ulcers. The report stated that "No single dressing was consistently superior to other dressings in the trials of pressure ulcers we examined", however, because of the breath of the review, detailed examination of the effect estimates and quantifying uncertainty around the hydrogel trials was difficult. The search for trials for this review was done almost six years ago. The more recent review seems to include dressing interventions but does not mention hydrogels specifically (Smith 2013). We conclude that up-to-date and transparent information on the evidence for the use of hydrogel dressings to treat pressure ulcers is required.
This review is part of a suite of Cochrane reviews investigating the use of dressings in the treatment of pressure ulcers . Each review will focus on a particular dressing type. These reviews will be summarised in an overview of reviews that will draw together all existing Cochrane review evidence regarding the use of dressings to treat pressure ulcers.