This articles will look at the initial management of traumatic wounds in small animal patients; from presentation, through to lavage. While some differences have been shown between cats and dogs in the speed and manner in which cutaneous wounds heal (Bohling et al. 2004), the initial management does not differ, and both species will be dealt with together in this article.
Triage and assessement of wound
Most of the wounds seen in veterinary practice are as a result of trauma. The initial triage and assessment of trauma patients focuses on the major body organ systems; the ‘ABCD’ of triage focuses on airway, breathing, circulation and disability, initial stabilisation addresses oxygenation and circulatory concerns (Aldridge and O'Dwyer 2013). While life-threatening conditions are the priority, temporary and emergency management wounds should not be neglected (Pead and Langley– Hobbs, 2007). Initially, to prevent dessication and further contamination of the wound, a sterile water soluble gel, or saline soaked gauze swab can be placed on the wound, and covered with a sterile towel or soft padded bandage; this protects the wound from the hospital environment.
Once the patient is stable, a secondary survey can be performed; this is a full physical examination of the patient, and at this stage the wound and the surrounding areas can be evaluated to assess damage to other structures. Survey imaging of the thorax and abdomen may be required to assess for any penetrating injury. With wounds affecting limbs radiography may be required to assess the impact of any trauma on bones and joints (Figure 1), also damage to underlying neurovascular structures should be assessed (O'Dwyer, 2007).
Overview of wound healing
A basic knowledge of the phases of wound healing gives clinical team members an idea of what to expect in terms of speed of healing, and a basis on which to make wound management decisions (Garzotto, 2009). More detailed descriptions of the process of wound healing are available (e.g. O'Dwyer, 2007), but the continuous process is commonly described as having four phases:
Management of acute open wounds
The basic steps indicated in the management of open wound have been described (see Box 1).
Acute wounds are expected to heal over a ‘normal’ period of time (Franz et al. 2007), as such management focuses not on accelerating the process, but on removing any impediments or deterrents to normal healing. In doing so the aim is to prevent delays or complications in healing, and prevent acute wounds becoming chronic wounds.
Common impediments to healing include: excessive bacterial population; the presence of necrotic tissue; seromas and haematomas; poor blood supply; and mechanical damage to tissue during surgery (Franz et al, 2008; Gregory, 2009). Impediments such as these prolong the ‘Debridement phase’ of healing, and delay the onset of the ‘Repair phase’.
Aetiology of wounds
Veterinary practices are commonly presented with patients that have sustained wounds due to a wide variety of aetiologies, and the patterns of trauma to tissues will likewise vary (White, 2009). An appreciation of the type of insult can give an idea of the resulting wound environment and the resulting impediments to healing, along with anticipated complications.
Other than just the level of contamination in a wound, the presence of foreign material and vascular damage will also have a profound effect on wound healing (Fowler, 2006). Which of these factors are present can be anticipated from the original insult:
Preventing further contamination
As mentioned previously, wounds should be covered with a sterile dressing as soon as possible after entering the clinic. Once issues affecting the major organ systems have been addressed, attention can turn to controlling contamination of the wound.
At this stage the patient may not be a suitable candidate for general anaesthesia, and a combination of adequate analgesia, sedation, local anaesthetic techniques and restraint may be required to allow intervention (Figure 5).
Bearing in mind that the aim is to prevent further contamination, and reduce that which is present, aseptic technique should be used throughout, with involved staff wearing sterile gloves, and preferably hat, mask and gowns.
Initially the wound should be packed, so that during the clipping of hair, further contamination is not introduced into the wound bed. This can be achieved with: a water solu-ble lubricant gel (KY jelly); a hydrocolloid gel (Intrasite, Smith & Nephew); with sterile saline soaked swabs; or a combination of gel and swabs (Figure 6).
The area surrounding the wound is clipped, ensuring the clipper blades are sharp, clean, and have no missing teeth; this minimises the chance of causing tissue trauma (Figure 7). Care should be taken to ensure the wound margins are not traumatised with the clippers; the hair here can be removed with scissors that have been wetted with sterile saline, so that the hair sticks to the blades and does not fall into the wound.
The swabs are removed from the wound, or the gel is wiped out with sterile swabs (Figure 8). The skin surrounding the wound is then prepared using standard aseptic preparation with a suitable antiseptic (Figure 9) (e.g. chlorhexidine) at appropriate dilution, working from the wound outwards, taking care not to get antiseptic on the wound itself (concentrations of antiseptics suitable for aseptic skin preparation are cytotoxic to exposed tissue). The wound is now ready for lavage.
Lavage/irrigation
The aim of wound lavage (or irrigation) is to remove loose foreign material and necrotic tissue from the wound, while diluting the bacterial contamination present. In so doing, lavage aims to remove impediments to wound healing, and reduce the risk of infection.
As with a lot of areas in the human and veterinary medical world, the decision making behind how an individual clinician performs wound lavage is often based on a mixture of scientific reasoning and tradition or habit. The ideal lavage technique and pressures required for optimal results are still unclear in human literature (Chatterjee, 2005).
Variations exist in the technique employed for lavage, and in the choice of lavage fluid used.
However, some factors are agreed on:
Techniques
Lavage fluids are generally administered as a controlled jet directed over the wound surface. The pressure at which the fluid is applied is crucial to achieve the goal of removing impediments to healing; pressures need to be sufficient to dislodge debris and loose tissue, and overcome adhesive forces of bacteria, but excessive pressure will drive bacteria and debris deeper into the wound, and open up previously uncontaminated tissue planes.
Pressures of 8–12 pounds per square inch (psi) are strong enough to overcome adhesive forces of bacteria (Longmire et al. 1987). Pressures greater than 15 psi may cause wound trauma and drive bacteria deeper into wounds. Pressures lower than 4 psi are insufficient to remove surface contamination and bacteria.
In a practical situation correct pressures can be achieved with a 20 or 30 ml syringe, and a 19 gauge needle or intravenous cannula (Figure 10); this provides an output pressure range of 11–31 psi, but the end pressure of the jet that reaches the wound is probably about 8 psi.(Singer et al. 1994; Williams, 2009). The syringe can be rapidly refilled by incorporating a 3-way tap and a giving set attached to a bag of lavage fluids (Figure 11). An alternative technique which achieves similar pressures is to connect a fluid bag to a giving set with a 19 gauge intravenous (IV) cannula on the end, and squeeze the fluid bag with a pressure cuff or pressure bag inflated to 400 mmHg (Dulecki and Pieper, 2005). The stream of lavage fluid should be directed at 45 degrees to the wound bed to maximise dislodgement of debris (O'Dwyer, 2007).
Other techniques such as lavage with bulb syringes, or manually squeezing punctured fluid bags deliver insufficient pressures and are not as effective at reducing infection. (Longmire et al. 1987).
Volume of lavage fluid
In human medicine suggestions exist for the volume of lavage fluid deemed necessary based on the size of the presenting wound; volumes of 50–100 ml per centimetre of laceration or per square centimetre of wound have been suggested (Lammers, 2003). In veterinary texts suggestions are made regarding the minimum volume per wound — 500 ml (Pead and Langley-Hobbs, 2007). Required volumes are likely to be higher in veterinary patients due to an increased risk of contamination from hair, environment and patient interference. As mentioned previously, the greater the amount of contamination, the greater the volume of lavage required.
Choice of fluid
Controversies exist in the choice of lavage solution, and whether antiseptics should be added to the solution. Solutions need to be non toxic to tissues, reduce the number of microorganisms, not cause sensitivity reactions and be widely available and cost effective (Main, 2008). The author's current choices of lavage fluid are outlined in Box 2.
A lot of information in veterinary wound management is derived from human medicine, which in turn is often based on studies conducted on wound models in experimental animals.
However, whereas normal saline is used extensively in human wound lavage, and is seen as the ‘standard’ solution, most veterinary texts recommend Hartmann's solution (Lactated Ringers) as the wound lavage solution of choice. This choice seems to be based on a paper (Buffa et al. 1997) that described the effects of wound lavage solutions on canine fibroblasts in a Petri dish (in vitro). The cells were exposed to phosphate buffered saline, normal saline, tap water and Hartmann's solution, for time periods of between 30 seconds and 10 minutes. Tap water damaged the fibroblasts at all time intervals, and normal saline caused cytotoxic effects after 10 minutes. Neither phosphate buffered saline, nor Hartmann's caused any significant fibroblast injury. No clinical randomised veterinary study exists to confirm the significance of this finding on the healing and infection rates of acute wounds.
While both normal saline and Hartmann's are isotonic, and evidence suggests lavage should be carried out with a fluid that has similar osmotic pressure to that found in living cells, recent human literature has looked at the use of ordinary drinking water as an alternative lavage solution for acute wounds. Drinking water has the advantage of being readily available and cheap. A study on contaminated musculoskeletal animal wound models showed identical reduction in bacterial counts following lavage with identical volumes of normal saline and drinking water (Svoboda et al, 2008), even in open fractures. While studies in humans have shown no difference in infection rates or healing rates when comparing normal saline to drinking water (Griffith et al. 2001; Hall, 2007) in the lavage of acute wounds.
The addition of antiseptics to lavage fluid can have cytotoxic effects on important cells involved in healing, such as keratinocytes and fibroblasts. Hydrogen peroxide and povidone-iodine reduce proliferation and migration of fibroblasts in a dose-dependent fashion. Chlorhexadine and silver-containing antiseptics also reduce proliferation at high concentrations, but at lower concentrations they may actually enhance epithelial growth (Thomas et al, 2009; Morton and Phillips, 2012). If chlorhexadine is used in a wound, it should be used at low concentrations (a solution of 0.05%); used at this dilution chlorhexadine causes no significant difference in wound contraction or epithelialisation compared to sterile saline or Hartmann's in dogs (Lozier et al. 1992), while achieving 100% bacterial kill rates against Staphylococcus intermedius, a common skin commensal bacteria.
The addition of antiseptics is often used in infected wounds; the aim of lavage is to reduce bacterial levels to a where the immune system can prevent critical colonisation or infection (Atiyeh et al. 2009). Lavage of a 6 hour old wound with 9 litres of saline or tap water reduced bacterial counts to 71% of the pre-lavage levels in a contami-nated wound model (Svoboda, 2008); in an infected wound these remaining levels of bacteria may exceed the critical bioburden and infection may ensue. The use of an antiseptic in the lavage fluid may lower residual bacterial counts by killing as well as diluting.
Addition of antibiotics to lavage solution is not recommended (O'Dwyer, 2007; Williams, 2009). Antibiotics may cause a sensitivity reaction in the patient, they are unlikely to maintain effective local levels for a suitable length of time, they are costly, and the promotion of resistance is a concern (Crowley et al. 2007).
Soap or surfactants are commonly used in lavage of open fractures in human patients, where their use has been shown to reduce the complication rate compared with lavage with normal saline (Bhandari, 2012). Soaps have lipophillic components which block bacterial cell adhesion in a wound, so assisting their removal. Soaps may also be of use in chronic wounds where they are more effective at removing adherent denatured proteins, such as dry fibrin and blood compared with saline or Hartmann's (Kaehn, 2009).
Once lavage is completed, a bacteriology swab can be taken from the wound bed to obtain a culture and sensitivity of any remaining bacterial contamination. If debridement of the wound is required to remove necrotic tissue this can now be carried out; the area surrounding the wound is aseptically prepared again prior to surgical debridement. Lavage is usually continued during surgical debridement.
Conclusion
The benefits of wound lavage in removing impediments to healing in the wound environment are without question, as is the idea that the greater the volume of fluid used, the greater the benefits. Well established techniques exist to enable delivery of lavage fluids at the correct pressure, using equipment that is readily available in veterinary practice. What is less clear is the choice of solution used in lavage, whether to add antiseptics or surfactants, and whether different wound types require different solutions. The author's current choices of lavage fluid are outlined in Box 2. The majority of veterinary clinicians will use isotonic crystalloids as their lavage solution of choice; current trends in human medicine in the use of drinking tap water and surfactants may impact on the veterinary world in the future.