Bite wounds are one of the most common traumatic injuries presented in general practice. The delay between injury and examination can vary greatly, determining how the bite wound is managed. However, there may be other contributing factors that may affect the healing process.
Most bite wounds originate as a result of a large dog versus small dog attack scenario, however many domestic incidences also occur in multi-dog households. Common locations for bites are around the face, head, neck and leg area (Yuill, 2011), although it is not un-common to treat wounds in other locations, so a thorough examination is vital to establish the extent of damage caused (Figure 1). Bite wounds can be challenging to assess. External trauma often disguises further injury to underlying tissue, often referred to as the iceberg effect (Campbell, 2013). An in-depth discussion with owners prior to examination should be conducted at this stage, as it can be difficult to determine the best method of wound management until a full assessment has been made. Owners should be made aware of the potential cost implications of stabilisation, medication, laboratory testing, the management of extensive wounds and even hospitalisation in severe cases.
Immediate management
On presentation a clinical history should be obtained, followed by a full clinical examination to assess any major life-threatening injuries. This can help to establish underlying medical issues that could affect treatment, and any factors delaying wound healing or altering management plans. Life-threatening injuries should be dealt with before any wounds. Wounds can be covered with sterile lint-free dressings until the patient is stable to help minimise further bacterial contamination (Campbell, 2013).
Injuries to the thoracic cavity, tracheal lacerations, major haemorrhages and abdominal wall ruptures should take priority. Vital signs should be taken, oxygen therapy and adequate analgesia should be considered to prevent any further decompensation of the patient, then intravenous fluid therapy or blood products, if required, can be administered. A basic blood panel should be checked to rule out organopathies, coagulopathies and signs of systemic inflammatory response syndrome (SIRS) or sepsis. Once the patient is deemed stable enough to undergo further investigations, the wounds can be explored further — this will usually require a sedative or general anaesthetic.
It is imperative to clip a wide radius of hair from around any wounds, ensuring correct personal protective equipment is worn, sterile gel can be applied into wound deficits to help prevent further contamination. Clipping the hair allows for an accurate analysis of wound depth and severity, ascertaining whether any body cavities have been penetrated (Figure 2). Dog bites exert a tremendous crushing force of up to 150–450 psi (Williams and Moores, 2012), not only affecting visible external tissue, but also extending to the deeper underlying tissues which can cause penetration of body cavities, bruising, and even internal organ damage or haemorrhage. For this reason, radiographs, ultrasound scans or computed tomography (CT) scans may be necessary to determine any organ involvement.
The canine teeth of dogs and cats penetrate tissues deeply causing puncture wounds, while the molars and premolars are designed to tear and shear, resulting in avulsion injuries (Figure 3, Williams and Moore, 2012). In many cases the biting animal will shake their ‘prey’ causing underlying tissue to avulse from the dermal layer, resulting in a significant amount of dead space, which allows for the accumulation of blood or serum. This can influence and cause delays in the healing process, as the build-up of fluid can prevent the underlying tissue from efficiently adhering to the dermal layer, acting as a medium for bacteria to proliferate. It is therefore important to fully investigate and measure the amount of dead space present, a depth gauge can be used for this, as this may need to be addressed later in the healing process.
Antibiotic therapy
All bite wounds are classed as dirty wounds as there will inevitably be a significant bacterial burden, transferred from both the penetrated external skin surface and directly from the oral flora of the biting animal. High volumes of bacteria are often driven deep into underlying soft tissue and although the variety of these vary between animal species, Pasteurella spp. is predominantly isolated in dog and cat bite wounds, closely followed by Streptococcus spp. and Staphylococcus spp. (Abrahamian and Goldstein, 2011). In many wound cases, anti-biotics are often given unnecessarily, due to a lack of understanding and misinterpretation of the inflammatory phase. In bite wounds, however, antibiotic treatment is often necessary and the veterinary surgeon's decisions over antibiotic selection should ideally be based on culture and sensitivity swab results.
Analgesia
Adequate analgesia should be considered both for its anti-inflammatory properties and to address pain associated with the trauma, which has been shown to contribute to delays in wound healing (Upton and Solowiej, 2010). A multimodal approach to analgesia may be necessary. Adequate analgesia prior to dressing changes may be required, especially if the patient will not tolerate conscious bandaging. The patient's pain response can be monitored, and analgesia tailored using a pain scoring chart; the veterinary surgeon can then use this as a guide to decide the most suitable analgesia. Opioids, such as methadone, or partial opioids, such as buprenorphine can be used. Care should be taken when using non-steroidal anti-inflammatories (NSAIDs), especially in hypovolaemic patients. For long-term analgesia considerations, provided NSAIDs are not contraindicated due to organopathies, they will usually be suitable for the duration of treatment. Ensuring adequate analgesia can be paramount to allowing a more thorough investigation and treatment of the wound but can also prevent the learned association of pain that may occur with dressing changes or the anticipation of pain, which could result in ongoing difficulty in treating the patient effectively.
Owner expectations and informed consent
Liaising with owners is important at this stage to establish a wound management plan. Obtaining informed consent for procedures, discussing cost implications and the expected time scale. Informed consent is essential — owners should be made aware of the various complications that could arise during the wound healing process, such as graft failures, bandaging complications due to poor compliance or allowing patient interference (Chin, 2016). Implementing effective communication between the owner and veterinary staff using informational handouts, tailored treatment plans and owner involvement, can help improve patient outcomes, owner compliance and prevent unnecessary complaints (American Animal Hospital Association (AAHA), 2009).
Wound management
After the full extent of damage has been established, the wound should be treated by second intention healing initially, as determining tissue viability can take up to 5 or 6 days (Figure 5) (Hollis, 2017). During this time oedema, bruising, ischaemia and necrosis can develop due to hypoxia, a compromised blood supply or devitalisation of tissue caused by the crushing effect.
Lavage
Wound lavage and debridement should be performed once the patient is stable. Delays can increase the potential for the bacterial bioburden, potentially leading to sepsis or SIRS (Campbell, 2013). Lavage should be performed under pressure, ideally using a 19/20G needle attached to a 20/35 ml syringe generating an optimal pressure of 8-15PSI (Hollis, 2016). This process aids in the removal of visible and microscopic contaminants from the wound, while avoiding driving bioburden deeper into the tissue. Initial wound cleansing can be performed in contaminated wounds using a chlorhexidine 0.05% solution (10 ml chlorhexidine gluconate diluted in 500 ml water), but care should be taken as it has been proven to have cytotoxic effects on fibroblasts and keratocytes, which are important in wound healing (Kirk, 2014). As the granulation bed begins to proliferate, the authors recommend transitioning to a more osmotically stable, warmed sterile solution, such as Hartmann's or 0.9% saline. Lavage can either be performed by using the above method or if irrigation is required for a larger area, a drip line can be connected to the fluid bag using a three way tap with an 18G needle and syringe attached (Kirk, 2014).
Debridement
Once the wound beds have been prepared, tissue viability should be assessed, and an appropriate form of debridement performed to remove unwanted and unhealthy tissue. Staged debridement may be required to allow for devitalised tissue and vascular damage to fully present itself over the subsequent days. There are many forms of debridement which can be broken down into four main subgroups: surgical; mechanical; chemical or enzymatic; and autolytic.
Surgical
Mainly dependent on the tissue appearance; blue/black, thin, leathery or white tissue can be associated with nonviability and may require surgical debridement. This is performed using sharp debridement techniques to remove any nonviable tissue using a sterile scalpel blade and scissors; this is highly selective, and care should be taken not to disrupt areas associated with essential structures such as major blood vessels, nerves or ligaments (Winkler, n.d).
Mechanical
Mechanical debridement in the form of wet-to-dry dressings work by applying saline soaked sterile swabs to the wound, then allowing them to dry over for a maximum period of 24 hours. The adhered dressing is then physically removed. This method of debridement is non-selective, meaning it has a chance of removing healthy tissue along with the unhealthy and requires the patient to be at least sedated for the removal as this process is often painful (Campbell, 2015).
Dependent on the wound location, debridement pads can be used to perform a more delicate form of mechanical debridement, which may be required in order to remove slough and necrosis attached to exposed underlying structures, such as over tendons and between digits.
Chemical or enzymatic
Maggot larvae physically feed on dead tissue and release special chemicals into the wound that breakdown dead tissue into a liquid form that the larvae can easily remove and digest. During this process the actively feeding larvae also remove bacteria, which are then destroyed within their gut (BioMonde, 2018). Alternatively, topical products are available which act as synthetic proteases to aid debridement of nonviable tissue.
Autolytic
Autolysis occurs naturally within the wound during the first 3–5 days. This is performed by the white blood cells and allows sparing of the healthy cells and leaves the matrix molecules intact. This has become favoured over mechanical debridement, as it allows the best environment possible to support the body's natural healing process, which is achieved through moist wound management (Campbell, 2015).
Antimicrobials
During the inflammatory phase topical application of antimicrobials can reduce bioburden and help promote healing. Silver-based dressings or hyperosmotic dressings in the form of medical grade manuka honey are the most common. Honey works via an osmotic effect by dehydrating organisms, reducing inflammation and oedema and promoting the formation of the granulation tissue (Murgia, 2016). Usually during this phase, a high amount of exudate will be expected so absorbent foam dressings should be used in conjunction with these products, and dressing changes carried out every 24–48 hours.
Wound closure
After the wound has transitioned through the inflammatory phase and begins to proliferate, a decision can be made regarding closure — either by second intention (Figure 5), the natural process of contraction assisted by open wound management, or via delayed primary closure, achieved by surgical intervention. The decision should be made based on a variety of factors, such as wound size, location, movement and tension, but it is also important to consider how the patient is tolerating regular bandage changes. Issues include the possible need for multiple sedations, an assessment of patient and owner compliance, and importantly weighing up the cost and anticipated time frame of repeat bandage changes versus surgical intervention. It is a common error to surgically close bite wounds prior to proliferation of the granulation bed (Figures 6 and 7), as it often results in surgical dehiscence and more extensive deficits to manage than the original presentation. The Veterinary Wound Library regularly receives requests for advice on managing bite wounds that have dehisced following premature closure (Figure 8), therefore it is important to ensure that the wound bed has been prepared sufficiently and is no longer showing signs of inflammation; such as redness, oedematous tissue, purulent exudate, a sloughy (yellowy) appearance, and that all areas of necrosis have been debrided (The Veterinary Wound Library, 2018).
If a decision has been made that closure by delayed primary intention will be the best course of action, it is advisable to have a definitive surgical plan in place prior to anaesthetising the patient. This ensures that closure is possible and that factors which could increase the likelihood of dehiscence will have been considered, especially in areas of high movement or tension, therefore hopefully avoiding postoperative complications. Alternatively, reconstructive surgery may be required to prevent these associated issues. Multifilament suture materials should be avoided in cases associated with a high volume of bioburden such as bite wounds, as they absorb fluids and ‘wick’ them along the suture, potentially transporting bacteria into the wound site and increasing the risk of dehiscence (Coles et al, 2018).
If dead space is still present from the initial trauma, or created during surgical closure, a surgical drain should be placed to prevent the build-up of free fluid which will otherwise increase the risk of complications. Closed suction drains are preferential due to the reduced risk of bacteria entering the wound; and the mode of action is more effective at removing fluid than passive drains, as exudate is actively drawn out of the wound (Williams and Moores, 2012). They do however require regular emptying using an aseptic technique when handling and monitoring to ensure that the fenestrations at the end of the drain have not been drawn out of the wound. A method of attaching the drain to the patient will need to be considered, such as use of a body suit or a stockinette. Alternatively, passive drains, such as Penrose drains, are more cost effective and require less monitoring, however they do increase the potential for environmental contamination due to exposure of the open wound created at the exit site. Ideally an absorbent dressing should be placed over the site to absorb exudate produced by the wound and prevent it from macerating surrounding tissue.
Conclusion
Bite wounds are always classed as contaminated wounds and should therefore be treated as such. The levels of bioburden should always be considered and addressed promptly to prevent wound regression and secondary systemic effects. Premature surgical closure will have an increased risk of dehiscence, therefore managing these wounds by secondary intention until they progress to the proliferative phase of healing, will improve the prognosis. Expert advice from specialists in the field can be obtained through The Veterinary Wound Library, where individual case assistance can be provided from an independent perspective (Figure 9).
