For veterinary nurses to effectively manage any type of wound it is important that they are able to first determine the type of wound and then understand the stage the wound is at in the healing process. This will enable the nurse to assist the clinician in planning the most appropriate protocol for managing the wound and optimizing healing.
By recognizing the stages of healing and the principles of wound management nurses are also better equipped to undertake dressing changes and give feedback to owners on the progress being made.
Stages of wound healing
A wound is described as the disruption of the continuity of cells and structures through injury. Wound healing is referred to as the physiological function that restores the continuity of tissues following injury (Hosgood, 2009).
Classically, wound healing can be divided into three phases inflammatory, proliferative and the remodelling phase (Hollis, 2010). The phases are not always distinct; overlap can be seen as one phase leads on to the next.
The inflammatory phase
The inflammatory phase begins immediately after the injury occurs and is triggered by the platelets and fibrin within the forming blood clot. Heat, redness swelling and pain can are all classic signs of inflammation. The fibrin attracts neutrophils to the injured site; their role is to destroy bacteria by attracting macrophages. The macrophages' role is to stimulate and inhibit other cells by releasing growth factors and enzymes. They debride necrotic tissue in the wound, reduce bacteria and organic debris and stimulate angiogenesis (the development of new capillaries). As the macrophages increase in numbers the debridement process begins, as does the transition into the proliferative phase. This phase lasts between 24–48 hours in a clean surgical wound (Hosgood, 2006).
The proliferative phase
The macrophages trigger the proliferative phase; fibroblasts lay down a new matrix, endothelial cells then migrate over this matrix laying down new capillaries and epithelial cells (epithelialization). This proliferation results in the production of granulation tissue; granulation tissue is so called because of its granular appearance which is composed of capillary loops.
Granulation tissue is resistant to infection and provides a surface for epithelial cells to migrate over. It helps to contract and reduce the wound size. Visible wound contraction is evident 5–9 days after injury (Hosgood, 2006). Over time collagen is laid down and a scar begins to form.
The remodelling phase
As collagen is laid down and the scar is formed the scar will remodel and strengthen over a period of days to weeks. The remodelling phase is underway by 7–10 days.
Wound classification
Wounds can be classified in various ways, initially as either open (Box 1) or closed. These can then be subdivided according to their aetiology or level of contamination. Classification enables appropriate decisions to be made of the type of wound management required based on the type of wound and the level of contamination. It also allows a prognosis to be made for the owner, with expectations of the length of time that treatment will be required.
Wound assessment
Every wound is different and should be assessed and treated accordingly. On presentation of a wound many factors should be considered. Full assessment should take place to determine whether there are other, perhaps more life threatening injuries. What has caused the injury and what is underlying the injury? A dog bite can be far more extensive than the visible puncture wounds of the skin.
Extrinsic factors such as degree of contamination, bacteria and infection, and length of time elapsed since the injury occurred are factors that can delay the healing process.
Other systemic factors will also influence the rate of wound healing, and healing may be delayed in immune-compromised patients, anaemic patients, those with poor oxygenation and malnutrition.
At initial presentation only a certain level of information can be gained by visual inspection (Figure 1), for example in the initial presentation of a cat with shear injury to a left hindlimb. General anaesthetic or heavy sedation would be required for a more thorough exmination (Figure 2). Orthopaedic injuries and further soft tissue damage can be better assessed at this stage.
Analgesia
Wound management can be painful and prolonged, and daily dressing changes can become distressful to a patient. Careful thought needs to go into appropriate pain management before, during and after dressing changes. Non steroidal anti-inflammatory drugs should be given throughout treatment to provide daily analgesia, with opiates given at the time of dressing changes in the early stages of wound healing, when inflammation is present and when pain is most severe. It may be necessary to sedate or fully anaesthetize a patient if the wound is large or extensive. Animals in pain are far more likely to interfere with dressings and potentially further damage their wounds, so adequate analgesia is essential.
Wound management
The first step following full assessment is to perform lavage (cleaning) of the wound. Lavage helps to remove gross contaminants and foreign materials at initial assessment. At subsequent dressing changes it helps to remove remnants of dressing materials and further dilutes bacteria, it also serves to debride the wound when performed under pressure, removing necrotic tissue and helping to control infection.
To prepare the wound for lavage at the initial assessment clip a wide area around the wound, applying sterile aqueous jelly to the wound to help avoid hair contamination by trapping loose hairs (Figure 3). Incontinence sheets help to protect the patient from the lavage fluid and contain any infected material (Figure 4). Gloves must always be worn when managing any type of wound, to prevent nosocomial (hospital acquired) infections (see below).
Lavage
Copious quantities of sterile isotonic fluid should be delivered under pressure. Isotonic solutions are used as they are non toxic and do not cause cell rupture or electrolyte imbalance (Anderson, 2009).
One method of delivering lavage fluid is by attaching a giving set to the fluid bag, and using a three way tap attach a 20 ml syringe and an 18 gauge needle (Figure 5). Fluids can then be aseptically drawn from the bag without the need for repeated needle insertion. The pressure used should be enough to dislodge foreign matter, but not enough to force bacteria and debris into the wound (Figure 4).
Alternatively, commercially available sterile irrigation sprays, eg Aquspray AnimalCare UK, provide a convenient solution to delivering lavage fluids
Debridement
Following clipping and lavage, the edges of the wound may need to be debrided to remove all necrotic and contaminated tissue. Debridement is the removal of devitalized or infected, contaminated tissue from a wound until surrounding healthy tissue is exposed (Stephen-Haynes and Thompson, 2007). The aim of debridement is to minimize infection and promote healing.
Debridement can be carried out in one of three ways: surgical (sharp dissection); mechanical (by the use of primary layer dressings); or by enzymatic debridement (chemical debridement). Surgical debridement is the most commonly used, performed by the veterinary surgeon; mechanical debridement is the second most common method, and can be performed by the veterinary nurse.
Adherent dressings, hydrogels and hydrocolloids can all be used as a means of mechanical debridement. This method is used during the early stages of wound management to remove debris that cannot be removed with lavage or initial surgical debridement, for example after a road traffic accident where grit may be present. This procedure needs to be carried out under general anaesthesia or heavy sedation. There is a possibility of damage to healthy tissue (see the primary layer section).
Principles of wound dressings
The aim of dressings in wound management is to create the optimal environment in which a wound can heal. George Winter's research in the 1960s pioneered the principle of moist wound healing. He proposed that a moist environment is most suitable for wound healing as it encourages cellular activity (Winter, 1962); this is contrary to the belief that wounds should be allowed to dry out and a scab to form.
Winter's research showed that when partial thickness wounds on the backs of pigs were covered with a polymer film to keep them hydrated the wounds healed twice as fast as those left to the open air to form a scab (Winter, 1962). His work began the concept of modern wound care and the advancement of dressings that promote moist wound healing.
Wound management and dressing types
For ongoing dressing changes it is important to keep accurate records, especially if different clinicians are involved in dressing changes, as management can become inconsistent.
A patient sheet detailing the following will allow continuity of care and give a good idea of the progress of the wound healing:
If possible photographs should be taken, these can be invaluable if different personnel are involved and can also be used to encourage owners in showing them the progression of the wound healing
Primary layer
The primary layer is the layer that is in direct contact with the wound. Following Winter's research indicating that wounds heal optimally in moist environments, dressings have evolved to provide ideal environments to improve the rate of healing. The primary layer has a number of functions (Box 2).
Primary layer dressings may be adherent or non adherent, absorbent or non absorbent, permeable or non permeable, passive, interactive or bioactive. Interactive dressings respond to the wound environment, they can rehydrate or debride necrotic wounds. Bioactive dressings have a biological effect on the wound and can stimulate formation of granulation tissue. A hydrocolloid is an example of both an interactive and bioactive dressing.
Adherent dressings are effective at debriding the wound, but are non specific as the gauze adheres and debrides both healthy and non healthy tissue, and can easily damage healthy areas of the wound and delicate structures. Healing can be delayed be repeated debriding of new granulation tissue and epithelial cells. Gauze swabs soaked in saline are a cost effective example of adherent dressings, commonly referred to as ‘wet to dry’ dressings. These dressings are notoriously painful to remove as they stick to the wound surface, and good analgesia, sedation or anaesthesia is required to change these dressings. It is reported in human wound management that wet to dry dressinga are painful to wear and remove (Hollinworth and Collier, 2000)
Hydrogels are insoluble hydrophobic polymers, they trap exudates and work to rehydrate the wound. These come in the form of impregnated sheets or as tubes of gel (Table 1). They have the advantage of not damaging the healthy granulation tissue, however, the healing process is slow requiring multiple dressing changes, which can become costly. A study has revealed that hydrogels increase contraction of limb wounds, but delay contraction of trunk wounds (Campbell, 2006).
| Primary dressings | Manufacturer | Product | Details and clinical use |
|---|---|---|---|
| Dry dressings | Smith & Nephew | Melolin | Simple dry dressing designed to absorb exudate from lightly exuding wounds. Typical use includes post surgery over sutures, on minor and bleeding wounds |
| Millpledge | Zorbopad | As melolin | |
| Smith & Nephew | Primapore | Simple dry dressing combining lightly non-adherent absorbent pad with a permeable adhesive border. Typically used post surgery over sutures to protect from immediate cross contamination | |
| BSN Medical | Leukomed | As primapore | |
| Animalcare | Treatpore | As primapore | |
| Film dressings | Smith & Nephew | Opsite flexigrid | Waterproof film dressing designed to protect wounds from cross contamination. Ideal for use post surgery over suture sites |
| BSN Medical | Leukomed T and T Plus | As above, Leukomed T Plus incorporates lightly absorbent pad | |
| Hydrogel | Smith & Nephew | Intrasite | Water-based gel, advanced dressing designed to provide moisture required for the optimal wound healing environment |
| Advancis Medical (Veterinary Distribution by Dechra Veterinary Products Ltd) | Citrugel | As above | |
| BSN medical | Cutimed Gel | As above | |
| Hydrocolloid | Convatec | Granuflex | Hydrocolloid sheet designed to assist debridement through autolytic hydration of necrotic tissue. Donates moisture so may also be used to maintain a moist environment on dry wounds. Soothing effect on nerve endings |
| Duoderm Extra Thin | Thin, low profile version of Granuflex. Can be used similarly to film dressing as includes a waterproof barrier if adhesion is good. Can be difficult to achieve good adhesion on angular areas, over fur or on damp skin | ||
| Foam dressings | Smith & Nephew | Allevyn | Triple layer foam dressing comprising non-adherent contact layer, hydrophilic middle layer and semipermeable film backing. Designed to absorb exudate and maintain a moist environment on low to medium exuding wounds |
| Advancis Medical (Veterinary Distribution by Dechra Veterinary Products Ltd) | Advazorb | Two layer foam comprising non-adherent, hydrophilic contact layer and semipermeable film backing. Designed to absorb exudate and maintain a moist environment on low to medium exuding wounds | |
| BSN Medical | Cutimed Siltec | Novel combination foam dressing combining a silicone contact layer to protect fragile wounds. Hydrophilic foam contains high absorption capacity polyacrylate granules. Dressing backed with a semipermeable film backing ensuring moisture maintenance during wear. Suitable for low, medium and more highly exuding wounds | |
| Andover Healthcare | PetFlex® AFD | All-in-one absorbent foam dressing and cohesive bandage for fast, effective treatment of puncture wounds, abrasions and lacerations. For small animal use | |
| Hydrofibre | Convatec | Aquacel | Absorbent dressing made up of strands of carboxymethylcellulose (CMC), a hydrophobic polymer, which removes and locks exudates into the dressing away from the wound bed |
| Convatec | Aquacel Ag | As aquacel with the addition of ionic silver | |
| Alginate | Convatec | Kaltostat | Absorbent, seaweed-based dressing which is also haemostatic |
| Aspen Medical | Sorbsan | Suitable for low to moderately exuding wounds. Sorbsan is seaweed based, but does not have haemostatic properties. The absorption is, however, more effective than Kaltostat | |
| Polyacrylate dressings | Advancis Medical (Veterinary Distribution by Dechra Veterinary Products Ltd) | Eclypse and Eclypse Adherent | ‘Nappy’ technology dressings. Sterile dressings containing polyacrylate crystals designed to absorb very high volumes of wound exudate. Suitable for using over drain sites and heavily exuding wounds |
| Non-adherent dressings | Smith & Nephew | Jelonet | Paraffin gauze. White soft paraffin-impregnated mesh dressing designed to protect granulation tissue. Should not be left in situ too long as new capillary growth can grow through the mesh. Can leave paraffin residue in the wound |
| Millpledge UK | Grassolind | As Jelonet | |
| Johnson & Johnson | N-A | Knitted viscose mesh used in the management of granulating wounds | |
| Advancis Medical (Veterinary Distribution by Dechra Veterinary Products Ltd) | Algivon | Absorbent, sterile manuka honey-impregnated dressing | |
| Scaffold dressings | Genitrix | Acell | Designed to promote epithelial migration across a wound bed by providing a matrix for cell growth. Derived from porcine, equine or bovine collagen they are intended to be left in the wound |
| Smiths Medical (Distribution by Dechra Veterinary Products Ltd) | VetBioSISt | As Acell | |
| Protective dressings | 3M available through Dechra Veterinary products | Cavilon | Protective barrier spray used to protect surrounding healthy tissue from excess wound moisture that can cause irritation and wound degradation |
Hydrocolloids are suspensions of polymers that are presented in adhesive sheets (Table 1), they rehydrate the wound and debride necrotic tissue. A disadvantage of these dressings is that they may prevent granulation tissue forming because the adhesive may stick to the wound edges.
When exudate is high primary dressings need to be changed every 24 hours, or in some cases twice daily if strike through is present
Absorbent dressings can be used as either the primary or secondary layer. Foam dressings absorb exudates while keeping the wound environment moist and allowing granulation to occur (Table 1)
Secondary layer
The secondary layer plays a number of roles: it acts as padding and to hold the primary layer in position; it absorbs exudates and ensures an even pressure across the dressing. Soft orthopaedic wool is used for this layer; the amount used will be dependent on the nature of the wound and the amount of exudate.
Tertiary layer
The third layer is the outermost layer and is used to protect the primary and secondary layers; a cohesive type dressing is used. These often provide a degree of waterproofing to prevent soaking and soiling of the under layers during exercise.
The future of wound dressings
Honey preparations
The use of honey is becoming more popular and preparations are available on the veterinary market in the form of tubes of honey and impregnated sheets.
Honey had been used to treat wounds since 2000 years BC (Forrest, 1982), it has been shown to have many properties including anti-inflammatory effects, antibacterial and antimicrobial activity, analgesic properties and stimulation of tissue growth.
Honey releases low levels of hydrogen peroxide which in turn releases low levels of oxygen; this is thought to assist monocytes and macrophages in increasing in numbers when oxygenation in the wound is poor. In addition, honey is hypertonic and is able to draw fluid into the wound from surrounding tissue. This aids in the reduction of inflammation and increase in debridement (Molan, 1992). The oxygen and high sugar content in honey makes it difficult for bacteria to survive, and this gives honey its anti-bacterial property.
| Antimicrobial | Manufacturer | Product | Clinical use |
|---|---|---|---|
| Honey | Advancis Medical | Activon range | Burns, slough, infection, necrotic and barrier layer |
| Medihoney | Medical Medihoney | Superficial wounds and burns, necrosis and slough | |
| Aspen Medical | Mesitran | Indicated for rehydration, promotes autolytic debridement | |
| Silver | Smith & Nephew | ActiCoat 7 | Barrier layer over partial and full thickness wounds |
| Urgo | UrgoCell Silver | Low to moderately exuding, infected or critically colonized wounds | |
| Coloplast | Biatain Ag | For medium to heavily exuding wounds | |
| Convatec | Aquacel Ag | As a primary dressing for moderate to heavily exuding wounds | |
| Molnlycke | Mepilex Ag | Low to moderately exuding wounds | |
| Andover Healthcare | PetFlex® AFD Silver I | All-in-one silver ion-embedded foam pad dressing and cohesive bandage for treatment of lacerations and wounds | |
| Iodine | Smith & Nephew | Iodosorb | Topical treatment of chronic exuding wounds |
| Systagenix | Inadine | Prevention of infection in ulcerative and minor wounds | |
| Smith & Nephew | Iodoflex | Topical treatment of chronic exuding wounds | |
| Polyhexamethylene biguanide (PHMB) | Active Healthcare | Suprasorb X + PHMB | Light to moderately exuding critically colonized and infected wounds |
| Covidien | Kendal AMD | Moderately to heavily exuding wounds | |
| Covidien | Kerlix AMD | Primary or secondary dressing to help prevent infection |
Sterile medical grade honey is produced by pathogen free bees for use in the clinical field. Manuka honey has been shown to be more potent and produce enhanced effects compared with standard honey (Molan, 1992).
Silver dressings
In human medicine silver release dressings are well established in the management of acute and chronic wounds and burns. It has been shown to have antibacterial properties and has been used in the management of meticillin-resistant Staphylococcus aureus (Lansdown, 2005).
Larval therapy
Larval or ‘maggot therapy’ uses the larvae of the green bottle fly, Lucilia sericata, to debride necrotic or infected tissue from wounds. This technique has been used in treating wounds for centuries (Thomas, 2000), but was recently reintroduced to human and veterinary medicine as an alternate means of wound management. The technique works because the larvae only ingest necrotic and devitalized tissue; a digestive proteoltyic enzyme is secreted and this liquefies the tissue, enabling the larvae to ingest it. This secretion prevents growth of bacteria including meticillin-resistant Staphylococcus aureus.
Preventing nosocomial infections
Conclusion
George Winter pioneered the concept of moist wound healing and it is from his research that current wound dressings have derived. Every wound requires different management as no two wounds are the same. Nurses play an important role in the effective management of wounds. It is necessary for the nurse to be aware and understand the various stages of wound healing and its classification. With a thorough understanding of the expected healing of a wound the nurse will be better equipped in the planning of protocols for wound management.