Identifying wound infections for veterinary nurses

Incidences of traumatic and bite wounds are high among both referral and primary care practices, and as veterinary nurses this is an area of veterinary medicine in which we can utilise a wide variety of skills that can be applied to various stages of the healing process, and have a profound effect on healing outcomes. Therefore, it is important for veterinary nurses to have a solid understanding of the full healing process including the distinct stages of healing, which factors can impede these processes, and the different techniques involved to optimise wound management.

There are numerous factors that can impede healing and lead to a prolonged inflammatory response with one of the major components, especially in heavily contaminated traumatic and bite wounds, being bioburden and biofilm formation leading to infection. All wounds should be considered contaminated (Patel, 2007); however, there is a difference between contamination, which should be easily rectified through good wound management techniques such as lavage and debridement, and a wound that has reached critical colonisation where the animal's host immune system has become compromised and the body's natural innate immune response can no longer deal with the level of bioburden without more invasive intervention techniques (Patel, 2007).

Infection versus inflammation

The inflammatory phase is the initial stage of wound healing and is initiated immediately an injury occurs. Haemostasis is triggered to stop haemorrhage and inflammatory mediators are called to the site of injury. Once haemostasis is achieved the blood vessels dilate releasing essential leukocytes, growth factors, enzymes, and nutrients into the wound bed (Maynard, 2015). Neutrophils are the first leukocytes to enter the site of injury as they are the most abundant in circulation (Maynard, 2015). Their numbers peak at around 24–48 hours (about 2 days) and will begin the process of destroying pathogens and removing damaged cells (Maynard, 2015). As the inflammatory phase progresses, monocytes enter the site and are converted to specialised cells known as macrophages, these continue to remove debris and pathogens and, as they do this, they secrete inflammatory mediators called growth factors, proteins, and enzymes to the site to facilitate healing and progress the wound into the proliferative phase (Maynard, 2015). This is a natural process that the body will carry out with or without intervention, but one of the aims of wound management is to facilitate this phase so that the wound can move through the natural stages of healing; this key step only becomes problematic when it becomes prolonged (Maynard, 2015). A severe inflammatory response has been linked to poor scar tissue formation and deregulation of cells within the wound bed; the cell pools of chronic wounds are decreased by mitigating factors such as infection, ischaemia and/or excessive exudate (Sorg et al, 2017).

A prolonged inflammatory response and inhibition of healing can be caused by infection or biofilm formation; it can be challenging identifying the difference between inflammation and infection as during the initial stages the difference in the signs and symptoms can often be subtle (Patel, 2007). To detect infection, we first need to be able to define it; infection can be associated with differing levels of contamination (Swezey, 2015). It is important to note that resident bacteria and transient bacteria are not the same: resident bacteria are naturally found on the skin surface and can provide a degree of protection against harmful pathogens, whereas transient bacteria are not permanent within or on the body and will colonise for days or weeks at a time (Bush, 2020). This is important to remember when managing a wound as the skin contains naturally occurring resident bacteria, and because of this every wound should be considered contaminated, but this does not mean it is infected; in fact, the bacterial level needs to reach a critical point where it overwhelms the innate immune response before signs of infection will begin to manifest. The differing degrees of contamination and infection are defined further in Table 1 (Swezey, 2015).

Signs and symptoms of infection

The signs and symptoms of infection can be similar to inflammation, but they tend to be exaggerated when wound size and extent are compared (Patel, 2007). If a wound is not progressing as expected infection or biofilm involvement should be considered a potential mitigating factor (Swezey, 2015).

Signs of infection include:

• Erythema — redness of the surrounding tissue is common during the inflammatory phase but in infected wounds this rubor can create a poorly defined erythemal border, this is typically disproportionate to the size of the wound (Figure 1) (Swezey, 2015)
• Temperature — increases in localised heat around the site of injury might be noted, depending on the severity this may extend farther from the borders or may cause a systemic pyrexia (Swezey, 2015)
• Pain — the wound may become excessively painful; this may be disproportionate to the size and extent of the wound. In immunocompromised patients this may be the only noticeable sign that infection is present because of the body's inability to initiate an appropriate immune response (Swezey, 2015)
• Exudate — exudate may change in consistency, colour and odour. Noticeably it may become excessive, thicker, and malodorous, there may also be a disproportionate amount of exudate when compared with the wound size and extent. It may change from the expected clear or serous sanguineous colour to a more purulent, green, brown or haemorrhagic exudate (Figure 2) (Swezey, 2015)
• Functional decline — the patient may become systemically sick: hypotension, tachycardia, inappetence, pyrexia, lethargy and collapse can all be signs that an infection is present and may have now become a systemic issue. This may require immediate intervention if signs of sepsis or systematic inflammatory response syndrome (SIRS) is present (Swezey, 2015).

NERDS and STONES

In human medicine there are two useful acronyms that can be applied to veterinary medicine to assist in the identification of wound infections and the differentiation between an infection that is superficial or invading deeper tissues; these are ‘NERDS^©’ and ‘STONES^©’ (Sibbald et al, 2007). The differentiation between a superficial and deeper tissue infection can help to determine whether topical antimicrobial agents alone are required or if systemic antimicrobial or antibiotics may be required (Sibbald et al, 2007). If the wound exhibits two or more of the signs of NERDS (Table 2) or STONES (Table 3) then it may be indicative of a superficial or deep tissue infection and steps should be taken to rectify the bioburden and the correct treatment be carried out to prevent further damage (Sibbald, et al, 2007).

Checklists

The implementation of a wound checklist may help to identify wound infections more rapidly within the clinical setting. It is a well-established process in human medicine and becoming more popular in veterinary medicine with the use of surgical and anaesthesia checklists, pain scores and phlebitis scoring (RCVS knowledge, 2020). These could be used at each stage of wound presentation from admittance through to the end stages of management. It is a frequent occurrence, more so in primary care practice, that patient continuity may be difficult and various members of the team may be involved in the patient's care. The use of a checklist to prompt members of the team to monitor, record and note any changes within the wound bed, will help elicit a rapid response preventing further deterioration. These systems look to improve clinical outcomes and minimise mistakes; they have yet to be utilised within wound management, but the use of a simple checklist that prompts the recording of wound appearance, size, exudate level and colour, surrounding tissue and odour could prevent infection and biofilm formation before it becomes critical (RCVS Knowledge, 2020).

Conclusion

Veterinary nurses play a significant role in the identification of wound infections, but need to have a sound understanding of what is normal and abnormal to ensure any potential problems are highlighted before they reach a critical level. Knowing the difference between the signs of the body's normal inflammatory response, erythema, clear to serous sanguineous exudate, oedema, and necrosis compared with critical and severe colonisation of the woundbed leading to an exaggeration of these signs, is essential. The implementation of a checklist alongside care plans could help improve identification of infection and improve patient outcome and management of wounds overall.

KEY POINTS

• As veterinary nurses we can utilise our skills and expertise to have a positive impact on the wound healing process, but this requires a sound understanding of the normal phases of wound healing and the ability to identify what is abnormal.
• Wound infections are common in both primary care practice and referral settings because of the aetiology of most wound presented in practice being of a traumatic nature or bite wounds. The early recognition and prevention of infection are vital to ensure there are minimal to no delays in the healing process.
• The acronyms ‘NERDS’ and ‘STONES’ typically used in human medicine with regards to be identifying superficial and deep tissue infections can be applied to veterinary medicine to help in the early identification of complications in wound healing.
• The implementation of a wound checklist could help prevent vital steps from being missed during the early stages of management, these could also be adapted to be used at follow-up appointments to ensure any changes in the wound are identified and problems rectified before further deterioration occurs.