The cause of wounds is broadly divided into traumatic or iatrogenic aetiology. There are important additional considerations to make when evaluating or nursing the patient depending upon the aetiology. In a patient that has experienced trauma, the wound may be only one of a multitude of injuries and it is important that thorough patient evaluation is performed. If the wound has been caused by a high velocity impact, such as a road traffic accident or a fall, then thoracic and abdominal radiography should be considered to exclude the presence of a traumatic hernia. Bite wounds overlying a body cavity, in particular where an animal has been picked up in the jaws of a larger animal, should also lead to thoracic and abdominal imaging to evaluate for internal injury (Figure 1). The superficial appearance of a bite wound can often hide the severity of the underlying injuries and what can be seen must be considered to be the “tip of the iceberg”.
Traumatic wounds are likely to have significant contamination from environmental debris; bite wounds are a particularly high risk for infection due to bacterial inoculation from the penetration of teeth into deeper tissues, concurrent with crushing injury which devitalises tissues and provides the optimal bacterial multiplication site (Frykfors von Hekkel et al., 2020).
Iatrogenic wounds are those that occur related to prior surgical intervention. Wound breakdown is a recognised complication of any surgical procedure. It may occur due to patient-related factors affecting healing, such as an endocrine disorder, concurrent medication or patient interference. Wound breakdown can also occur due to tension, excess mobility or skin necrosis, in particular if a large or complex wound reconstruction has been required (Figure 2). If the open wound is a prior surgical wound that has broken down, it is important to consider that there is a greater risk that the wound may be infected with a multidrug resistant organism. This is important to plan appropriate nursing care and minimise the possible contamination of areas of your practice or hospital.
First aid management
Following appropriate analgesia and patient stabilisation, thorough evaluation of the wound and lavage is the next step. It is important that this is performed under sedation or general anaesthesia to allow extensive clipping, lavage and decontamination, probing and debridement as necessary, and to maintain patient welfare. Lavage is performed using a set-up with a fluid bag and giving set and a three-way tap, to provide a suitable pressure for dislodgement of debris and bacteria from within the wound (Figure 3). The optimal fluid for wound lavage is isotonic, so compound sodium lactate and 0.9% sodium chloride are appropriate.
A bacteriology swab taken from within the wound immediately following lavage is likely to be the most representative of remaining bacterial contamination that may progress to wound infection. It may be worthwhile, however, to take a swab of the wound before lavage if prior surgery has been performed to optimise detection of hospital-acquired infection. Thorough documentation of the nature and extent of the wound should be recorded in the clinical notes, to allow assessment of wound healing and progress to be reviewed as necessary.
Appropriate wound management can be time consuming and costly in the initial stages. Debridement typically requires general anaesthesia and surgical management in the first instance and this may need to be repeated if progressive loss of skin viability is evident, requiring daily sedation or general anaesthesia. The use of open weave gauze swabs is very effective as a debridement dressing; removal is painful and therefore sedation or general anaesthesia is essential. It is important to recognise when healthy granulation tissue develops and to change the primary dressing material at this stage, as otherwise the wet-to-dry dressings will damage delicate epithelising tissue from progressing with wound healing. For more gentle debridement, the use of a hydrocolloid gel is effective. This may be possible to change less frequently. Some clinicians may choose to start with wet-to-dry dressings and to switch to use of a hydrocolloid gel once more gentle debridement is required. This also allows moist wound healing to occur. If drainage is required from the wound and there are also concerns about the vascularisation of the wound, the use of negative pressure wound therapy can be very beneficial. This does not, however, replace the need for initial surgical wound debridement if there is necrotic tissue in the wound bed. A bolus tie-over dressing is a very useful technique to secure the dressing to wounds in places that are difficult to comfortably dress (Figure 4).
In a wound with good tissue viability, or where en bloc debridement of affected tissue can be achieved, it may be suitable for primary closure to be performed. Due to the contaminated nature of wounds, it would often be appropriate to place a dependent drain (eg Penrose drain) exiting via a separate stab incision. If there is a greater degree of tissue contamination and stepwise wound debridement is required, then delayed primary closure would be preferable. Where there has been significant compromise to tissue and wound contamination and there is a resulting tissue deficit, second intention healing with open wound management may be considered; for large defects a reconstructive technique such as use of an axial pattern flap (Field et al., 2015) or a free skin graft may be used (Riggs et al., 2015; Figure 5).
The chronic wound
Wounds are a common clinical presentation in first opinion and referral veterinary practice. The healing capacity of the skin in the dog and cat is tremendous and their abundant skin, over the dorsal neck and flank in particular, allow for simple primary closure when dealing with many wounds. There are, however, situations when we are faced with non-healing wounds and the management can be tricky. Systematic evaluation of the patient and the wound are essential to troubleshoot the issue and resolve the problem. Many of the plans for addressing a non-healing wound could and should have been considered in management of all wounds, thereby decreasing the likelihood of encountering those that become non healing.
What are the possible causes for a non-healing wound?
- Excessive tension or movement
- Poor vascularity
- Large size
- Infection: could there be a multidrug resistant organism or mycobacterial infection? Is there a nidus for infection?
- Management factors
- Endocrine disease or medication factors
Bacterial wound infection, possibly with multidrug resistant bacterial isolates, may impair wound healing. It is important, however, to remember that even in the face of multidrug resistant infections, and in fact particularly so, appropriate wound management is the mainstay of management. Progressive and regular debridement and drainage from the wound is essential to create a healthy wound bed. It is normal that bacterial isolates will be obtained from the surface of a wound; however, it is typically the presence of poorly vascularised tissue, necrotic tissue or lack of drainage from dead space that allows infection to establish. Whether or not you have antibiotics available to augment your management of the non-healing infected wound, thorough and regular wound management is the most important.
A non-healing wound should always have a biopsy. Even if it does not appear that there is a mass, the issue with healing may be due to neoplasia. Squamous cell carcinoma may readily manifest as a non-healing wound, as may an ulcerated mast cell tumour or inflammatory mammary carcinoma – there are of course many more examples. Tissue biopsy is also important for extended culture. Wound management is expensive – it is not a good financial saving to bypass a biopsy of the wound.
When a wound has been managed chronically, there may be a fundamental underlying reason why the wound is not healing and often it will be multifactorial. It is also important to consider that our interventions may be contributing to the poor progression of wound healing. For example, a wound on the paw or limb may be able to progress to healing via contraction and epithelialisation if left undressed, with appropriate precautions taken to maintain the health of the wound, whereas abrasion from ongoing dressing may stop the process of epithelialisation from working effectively.