Silver has been used as a topical antimicrobial agent for millennia in wound care, and is currently available in a variety of wound dressings. In modern medicine, silver is found in the form of silver oxide, silver sulphadiazine, silver nitrate, ionic silver and nano silver, used in the prevention and treatment of infection in both acute and chronic wounds. It is available in a range of formulations including creams, ointments and dressings impregnated with elemental silver or silver-releasing compounds (Thomas and McCubbin, 2003). However, silver dressings differ considerably in the nature of their silver content and in their physical and chemical properties.
Silver has a broad spectrum of antimicrobial activity (Bowler et al, 2004; Jones et al, 2004) and acts on multiple bacterial sites (Percival et al, 2005). White and Cutting (2006) have suggested that there is insufficient focus on the availability of the silver ion (Ag+), the active antimicrobial agent in silver dressings, and the amount of silver essential for an antimicrobial activity.
Laboratory studies have shown silver ions to be active against a broad range of potential wound pathogens, including many antibiotic-resistant bacteria, such as meticillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) (Lansdown, 2002; Parsons et al, 2005). Ip et al (2006) also evaluated the antibacterial activity of silver-impregnated or silver-coated dressings on several common wound pathogens including S. aureus, MRSA, Enterococcus faecalis, Pseudomonas aeruginosa, and Escherichia coli. Silver-impregnated dressings have also demonstrated bacterial activity against Gram-negative bacteria (Ip et al, 2006).
Silver dressings should be used with caution, as certain dressings, in particular silver sulphadiazine, cause staining of the skin and is toxic (Cutting, 2001).
How do silver dressings work?
The silver ion (Ag+) is the active antimicrobial agent in silver dressings (Lansdown, 2002).
In dressings, silver:
- Provides bactericidal action due to the Ag+ ion (Percival et al, 2005)
- Inhibits the bacterial DNA replication process (Michaels et al, 2009)
- Reduces the wall strength of bacteria (Percival et al, 2005)
- Increases the permeability of the bacterial cytoplasmic membrane and inhibits the respiratory enzymes, causing asphyxia of the bacteria (Percival et al, 2005).
Not all silver products are the same and the manufacturers’ instructions should be considered when treating different types of wound. It is also important to consider the amount of fluid (exudate) present.
There are many silver products available, how do I select the right one?
Each patient has different needs that need to be considered when choosing the correct product. The following questions can help with dressing selection.
How much exudate is the wound producing?
If the wound is producing medium to high volumes of exudate, a plus or superabsorbent product may be required. However, if exudate production is low, a light or thin dressing may be more suitable. Correct exudate assessment (based on colour and amount) and management is essential both to maintain a moist wound healing environment and to prevent the peri-wound skin from maceration.
Methods for assessing exudate have been suggested by Falanga (2000), Bates-Jensen (wound assessment tool) (Bates-Jensen, 2007) and a proposed national wound assessment form (Fletcher, 2010). The latter uses the term ‘wound moisture level’ rather than exudate, and is based on the World Union of Wound Healing Societies (WUWHS) document on exudate (WUWHS, 2007). Clinicians should also refer to their local policy on exudate assessment.
How fragile is the patient’s skin: adherent or non-adherent?
Non-adherent silver dressings do not stick to the skin and therefore need to be secured in place by another dressing, such as tape or light retention bandages. These dressings are suitable for use on fragile or damaged skin, where adhesive dressings may result in skin damage. There are a wide variety of adherent and non-adherent silver dressings on the market.
Is the dressing going to be used under compression?
Some silver creams and ointments are fluid in nature. This means that if pressure is applied, such as by compression bandaging, or by body weight if the dressing is placed on the sacrum or heel, the fluid in the dressing may leak out. In such circumstances, dressings which have the ability to wick and lock fluid away should be used.
Some silver dressings have a film-backing which prevents fluid leaking out of the back, which could prevent bandages or other dressings used to fix them in place from becoming wet.
Is antimicrobial action needed?
Silver has antimicrobial components, which help the dressings to kill microorganisms that may be responsible for local wound infection (Parsons et al, 2005). Antimicrobial dressings should only be used if infection is present, or if the patient is considered to be at an increased risk of wound infection.
Where is the wound? Is it in a place that is difficult to dress?
Some wound sites such as the sacrum or heel can be difficult to dress. Silver dressings can be used in most anatomical areas with ease.
Selecting a silver dressing
Selection of a silver dressing should be guided by:
- Volume of exudate
- Condition of skin
- Location of wound
- Use under compression
- Presence of infection.
Patient choice and preference should always be considered. This helps to build up a good nurse–patient relationship, and is in line with national policy.
Wound care specialists should ensure that the patient is not sensitive to any additives or agents in silver. Most silver products come with a precaution warning and should be avoided before magnetic resonance imaging (MRI) scans, or with electronic measurement procedures.
- Fluid-handling capacity
- Film backing in some silver products
- Secondary dressing may be required
- Can be used under compression
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