Infected wounds are a constant clinical challenge. Broken skin offers microorganisms an entry point into the bloodstream. Likewise, an infected wound bed stops successful skin and tissue healing. Systemic antibiotics can help quell systemic infection, but they cannot always reach a wound in sufficient concentration to heal the infection. Thus, local wound care and dressing strategies for infected wounds are essential.
The normal process of wound healing
Most wounds go through predictable stages of healing from injury to restoration. The four stages are:
- Hemostasis – A fibrin clot forms to stop the acute bleeding. While the skin is broken, the clot and eschar act as a partial barrier to bacteria
- Inflammation – Immune cells (neutrophils, macrophages, etc.) are activated to fight off any invading microbes, releasing cytokines and other pro-inflammatory agents
- Proliferation – A flurry of cell growth and activity occurs, forming new skin, blood vessels, and extracellular matrix
- Restoration – The skin is essentially healed; the extracellular matrix remodels itself, the eschar flakes off to reveal new skin, and the barrier to microbial invasion is again fully intact
Unfortunately, a lot can go wrong during this complicated process, making an acute would become a chronic wound. Infection is one of the worst offenders, stalling the healing process in the inflammation or proliferation phase.
When contamination becomes infection
Bacteria cover every surface of the skin. Commensal organisms or even a few pathogenic microbes may contaminate a wound, but they do not become an infection until they are a multiplying and provoking an immune response. This immune response is a cellular process that can be witnessed on a macro level; an infected wound is purulent with white/green/yellow pus and is surrounded by warm, erythematous skin.
Contamination becomes infection when the wound itself promotes the colonization and expansion of aggressive microbes, specifically a humid, warm, nutrient-rich environment. Ironically, this is the same environment in which the cells that participate in wound healing also function best. While the first goal should always be to prevent wound infections, this is not always possible, so healthcare providers must know how to manage wounds once they have become infected.
Managing an infected wound
As mentioned, it is difficult to treat a wound infection with systemic antibiotics alone. To reach sufficient quantities in the wound, the dosage of the oral or intravenous antibiotic needs to be quite high, and even then, it may not be enough. Local synthetic and natural antibiotics can sometimes provide a solution to this difficult problem. Wound dressings are available that are impregnated with antibiotics against Staph spp., Strep spp., E. coli, Candida, and P. aeruginosa. Certain essential oils and even honey have been used successfully to either halt the multiplication of or kill bacteria in wounds without interfering with the healing process.
Taking a wound culture (The correct way)
Since many common bacteria are now partially or completely resistant to various antibiotics, a common approach is to start with a broad-spectrum antibiotic and then narrow the drug based on susceptibility studies. However, getting an accurate, usable wound culture is a tricky thing. There are so many different bacterial species in the wound, the one that ends up growing in the petri dish may not be the bug that is causing the infection. Many people perform a wound culture incorrectly; they causally drag a swab across the top of the wound for less than a second and send it off. The Levine Quantitative Swab Technique makes it more likely to sample the causative microorganism.
Levine Quantitative Swab Technique:
- Use normal saline to flush the wound
- Use sterile gauze to dry the wound bed
- Do not swab pus or obvious exudate (common mistake!); instead, swab a part of the wound bed that has viable, healthy-looking tissue
- To swab, cover an area that is 1 cm2 for at least 5 seconds (really, at least 5 seconds)
- To swab correctly, you will have to apply some pressure in a rotating (drilling) pattern—enough pressure that the wound expresses fluid to be expressed
Choosing the right dressing for a wound infection
Fortunately, many of the same principles that apply to non-infected wound management, also apply to infected wounds. The dressing should create an environment that is moist enough for healing to take place (neither an overly dry nor an overly moist wound will heal). Adequate blood flow is important, so the dressing should not compress the wound enough to impede blood flow. Fully occlusive dressings are good for dry wound beds, but ideally the dressing should be semi-permeable to allow for some air exchange. Wet-to-dry dressings should be avoided because they traumatize the skin when the dried dressings are removed.
Since infected wounds tend to be purulent and produce excess fluid, the best choice for dressing infected wounds are usually absorbent dressings such as alginates, collagens, and hydrocolloids. Alginates are highly absorbent, so they should only really be used on highly exudative wounds. As such alginates should be changed at least daily and the wound should be reevaluated at each dressing change to determine if a less absorbent dressing will suffice. Hydrocolloids are considered “painless” dressings because fluid makes them swell and release easily. On the other hand, hydrocolloid dressings may come off prematurely in highly exudative environments.
Medical tape and adhesives
Infected wounds require frequent dressing changes, each with its own wound assessment. The type of dressing can and often should change depending on the status of the wound. The choice of medical tape is actually an important part of infected wound management. Healthcare providers should choose a medical tape that holds strong when in use, but releases cleanly and easily when removed. The edges of wounds where medical tape is needed to secure dressings, can be friable and delicate. Hy-Tape does not get more aggressive the longer it is in use, so the zinc oxide-based adhesive releases without skin trauma.
Since the redness of an allergic reaction to medical adhesive can look virtually identical to cellulitis and worsening wound infection, it is essential to choose a latex-free medical tape such as Hy-Tape. Wound assessment should be about healing and the resolving infection, not contact dermatitis.