Wound management is an exciting area of veterinary medicine and one in which veterinary nurses are assuming greater levels of responsibility. Understanding the pathophysiology and applying knowledge of the wound healing process, in addition to recognising best practice techniques in wound management, is essential for promoting good outcomes for veterinary patients. Practices often treat a number of wounds on a day-to-day basis. Many of these wounds, resulting from traumatic injuries and surgery, will require drains to assist with the healing process by reducing fluid accumulation within dead space. The classification of the wound, and the nature in which it was created, may give rise to various complications. For example, traumatic wounds, such as degloving injuries, are more likely to become infected than a wound created in aseptic surgical conditions (Aldridge, 2015), which could result in dehiscence of the wound edges. Veterinary nurses must apply their knowledge of wound classification and wound healing to direct high standards of nursing care and wound management, including the use of different drains, to reduce these complications. Consideration should also be given to novel drainage techniques and wound management protocols to ensure an evidence-based approach to patient care.
Normal wound healing
Once a wound is created, whether this be as a result of a surgical incision or trauma, the body's response will be to commence wound healing. The normal wound healing process occurs in three phases: inflammatory; proliferative; and remodelling (Figure 1). Failure of the normal wound healing process leads to complications such as chronic non-healing wounds, dehiscence and evisceration of abdominal wounds. The accumulation of fluid reduces tissue perfusion in the wound bed (O'Dwyer and Aldridge, 2014), in addition to providing a medium for bacterial growth (Watson and McFadden, 2019). This can impede the normal healing process, resulting in wound dehiscence (Carne, 2011). Occurrences such as these could lead to extended hospital times, increased risk of infection, and financial implications for clients. Therefore, to prevent this, some wounds will require the placement of drains to facilitate the removal of fluid.
Primary uses for drains in veterinary medicine include removal of fluid and exudate, prevention of seroma formation and to facilitate repeated wound lavage (Anderson and Smith, 2020). Drains may be placed in response to fluid accumulation, or prophylactically when larger volumes of exudate or fluid accumulation are predicted (Pope, 2017). To decipher whether drain placement is appropriate, the following indicators should be considered: likely contamination, and thus infection risk; and possibility for accumulation of large volumes of fluid. Both indicators are associated with delayed healing, pain and infection (Darrow and Lux, 2015).
Once a wound has been assessed and it has been decided that a drain should be placed, consideration should be given to selecting the most appropriate type of drain. Many types of drains are available for use in the veterinary practice and are classified by their action; either passive or active. Table 1 depicts different drain types and their action. For effective management, it is essential that veterinary nurses understand the reasons for choosing certain drains for certain wounds.
Table 1. Drain types available for veterinary patients (Day, 2014; Bell, 2016; Pope, 2017; Stanley, 2017)
| Drains | Actions | Comments |
|---|---|---|
| Penrose drain | Passive |
|
| Jackson-Pratt | Active suction |
|
| Thoracostomy | Active suction |
|
| Negative pressure wound therapy | Active suction |
|
Wound drains
Passive drains
Passive drains are open, allowing fluid to drain freely from the wound using gravity and capillary action along the drain itself (Pope, 2017). The drain should be placed at the lowest possible point of the wound: if fluid is to accumulate within a wound pocket or dead space, it will usually be at the bottom, consequently making sense for the drain to be placed in this part of the wound. There is no collection system attached to these drains meaning they are open systems with the potential for bacteria to ascend, potentially resulting in wound infection. These drains can require regular cleaning of the area around the exit point of the drain and kennel as a result of exudation, and to reduce the risk of ascending infection.
The most common passive drain is the Penrose drain (Figure 2). It is a soft, flexible tube surgically placed with one end embedded into the wound itself, and the other exiting through a ventral point created by a small incision. Penrose drains are either silicone or latex, however, it should be considered that some patients may be sensitive to latex, leading to local tissue reactions and potentially resulting in poor wound healing and increased discomfort (Watson and McFadden, 2019).
Passive drains are indicated in wounds with dead space and where fluid accumulation is anticipated, requiring further drainage of fluid after initial treatment, such as cat bite abscesses (Carne, 2011; Watson and McFadden, 2019). Passive drains are contraindicated for management of thoracic wounds, because of the potential for pneumothorax, and abdominal wounds as a result of respiratory movements that cause pressure changes and draw air and fluid into the abdomen (Watson and McFadden, 2019).
Active drains
Active drains are those which require active removal of fluid or exudate using a form of suction. For this to be possible, the drain must be airtight and thus active drainage systems are always closed. Usually, this is achieved by the drain having a collection bulb or chamber. The chamber is usually opened and squeezed to a collapsed state, removing air, then closed. Over time, it will return to its usual shape; this is what generates the suction necessary to draw out fluid or air from the wound (Figure 3). This action can be achieved against gravity, meaning the drain exit can be positioned anywhere that is considered appropriate while also reducing dead space (Watson and McFadden, 2019).
The most common type of active drain used in practice is the thoracostomy drain (Anderson and Smith, 2020). Other examples are the Jackson-Pratt drain and negative pressure wound therapy (NPWT).
Negative pressure wound therapy: a novel drainage technique for incisional wounds
Although specific and novel protocols for its use are still emerging, NPWT is a relatively well-established technique for wound management in veterinary practice (Bristow et al, 2015). NPWT is a form of active drainage involving the application of a vacuum at sub-atmospheric pressure to the entire surface of a wound (O'Dwyer and Aldridge, 2014). Stimulation of angiogenesis as a result of evenly distributed mechanical forces within the wound bed, and migration of keratinocytes, encourages healing and opposes the action of fluid accumulation (O'Dwyer and Aldridge, 2014). The technique is most commonly used to manage traumatic wounds (Figure 4), however, its uses can be applied more generally to other wounds, including surgical wounds (Stanley, 2017). In human medicine, NPWT has been shown to be successful in reducing dead space, preventing fluid accumulation and increasing the speed at which deep cavity wounds, including those associated with thoracic and abdominal surgeries, are closed, thus reducing infection (Huang et al, 2014). A large-scale review to determine clinical recommendations concluded that NPWT was likely to be beneficial in reducing surgical site infections (SSIs), which affect around 25% of human patients, in addition to assisting surgeons in wound closure and incisional management (Willy et al, 2017). Although, another review evaluating whether the application of negative pressure for closed incisions reduced complications in wound healing yielded inconclusive results (Webster et al, 2019), multiple other potential benefits have been identified. The advantages of applying vacuum suction between 100 and 150 mmHg include increased blood flow, acceleration of the rate of granulation tissue formation, reduced bacterial contamination and increased likelihood of surgical flap survival (Stanley, 2017).
In veterinary medicine, to the author's knowledge, the overwhelming evidence surrounding the use of NPWT refers to use for management of open, traumatic wounds. However, some studies evaluating the effectiveness of NPWT for closed surgical incision management have been published. Perry et al (2015) investigated the use of NPWT to enhance wound healing of surgical incisions following high risk orthopaedic surgeries, specifically high energy fractures and arthrodesis of distal limbs. It was found that patients receiving wound drainage using NPWT experienced reduced digital swelling and wound discharge, compared with the control group. Nolff et al (2015) demonstrated successful application for NPWT for an incisional wound for a Rottweiler with previous history of wound healing complications. The patient underwent surgical excision of a thoracic wall mass, and as a result of the clinical history, the wound was considered ‘at-risk.’ The wound healed successfully and without complication (Nolff et al, 2015). Encouraging results were also obtained when comparing the use of negative pressure for abdominal drainage following partial closure of the abdominal wall as a treatment protocol for septic peritonitis in dogs. It was found that the application of NPWT was preferable to passive open drainage because of the perceived reduction in workload, regarding the necessity for repeated bandage changes, with the suspected reduction in patient discomfort linked to this (Spillebeen et al, 2017). In addition, it was suggested that NPWT can improve hygiene due to maintenance of improved and more accurate collection of drained fluid when compared with open drainage techniques (Spillebeen et al, 2017). Overall conclusions drawn from this paper outlined increased local healing and decreased morbidity in patients treated with NPWT when compared with passive open drainage of the abdomen. Although the two studies discussed offer interesting insight into the application of NPWT in partially to fully closed wounds, it is not possible to generalise results to all populations, and thus further research should be conducted to evaluate its use specifically for incisional wounds. NPWT may be a more costly approach to wound management initially, however, its benefits, especially reduced healing times, may outweigh this and result in savings from reduced, or eliminated, bandage changes and longer-term treatment.
Monitoring
All drains, both passive and active, should be monitored closely to ensure proper function and to identify complications early. As with all wounds, those with surgical drain placement should be monitored for signs of SSIs. Indications include erythema, oedema, exudation and pain in addition to pyrexia and behavioural changes such as lethargy and depression (Yon, 2019). The risk of ascending infection is present with all drains; however, the risk is considered lower in closed, active drainage systems when compared with open, passive drains (Reiffel et al, 2013). Patient interference is another complication which can result in premature removal of the drain and SSI, thus ensuring adequate techniques to prevent self-removal or interference, such as placement of buster collars or body suits, is necessary.
Monitoring the fluid output of the drain should be incorporated into care plans to include drain specific details, fluid output and any issues that have arisen. Although there are no studies investigating compliance with drain management in veterinary medicine to the author's knowledge, in human medicine, compliance with wound drain care was found to be as low as 20% among healthcare professionals, which may have contributed to complications associated with delayed removal (Lyons et al, 2015). It has been suggested that collected drain fluid should be emptied every 6 hours (McFadden and Oberhaus, 2019). In the author's experience, intervals of between 4 and 6 hours have been adopted with some preference for emptying when full to reduce the frequency of opening up the drainage system; frequent opening of a closed drainage system increases the chance for contamination and ascending infection. If the volume of output is less than expected, it should be considered that the drain may be blocked. Blockages may be caused by internal structures or materials such as fibrin and blood clots, in addition to drain failure caused by lack, or absence, of pressure (Watson and McFadden, 2019). Active suction drains placed into the abdomen can become blocked by omentum or blood clots, and thoracostomy tubes can be blocked by thoracic tissue (Murgia, 2015; Watson and McFadden, 2019); therefore care should be taken not to place excessive pressure on the syringe plunger when aspirating in order to not damage tissues if manually aspirating. Fluid output, characteristics such as presence of blood clots, colour and viscosity, should be noted to enable observations to be made about deteriorations or improvements in wound healing.
Placement of drains may lead to local inflammation as a result of the body recognising it as ‘foreign’ (Watson and McFadden, 2019). This can lead to pain and discomfort in addition to that caused by the initial trauma or surgical incision. Therefore, it is essential to ensure that adequate analgesia is provided to maintain patient comfort and to reduce the likelihood of self-trauma or removal of the drain.
Handling
It is probable that all traumatic wounds would have undergone lavage before drain placement, meaning bacterial contamination should be significantly reduced, as demonstrated by Hamil et al (2020). However, when handling drains, aseptic technique should be demonstrated in all cases. A study conducted by Nolff et al (2016) found the 48% of bite wounds in dogs provided positive bacterial cultures with 6% of these being multidrug resistant (MDR). Although these statistics were in reference to pre-lavaged wounds, MDR bacteria pose a threat to all veterinary patients, especially those with open wounds. Furthermore, the study conducted by Hamil et al (2020) found that in dogs with acute traumatic cutaneous wounds, 22% of dogs contracted SSIs, although there was no correlation between bacterial species present in the initial wound swabs before intervention. Although this study has a small sample size of 64 dogs, it could be suggested that the results imply that the infections observed were as a result of other hospital factors. Thus, aseptic handling and adoption of barrier nursing protocols should be demonstrated to reduce the risk of cross contamination of dangerous bacteria to other patients, and those handling the wound. However, without appropriate preparation of the wound bed and management of the drain itself, infection risks will still be significant even with aseptic handling, highlighting the necessity for optimal wound management from presentation.
Dressings
Frequently used dressings include those that are passive and adhesive. Dressings are protective barriers between the wound and the environment; however, strikethrough of exudate facilitates bacteria passing through the dressing to contaminate the wounds and therefore dressings must be removed and replaced before it is observed (Gray, 2018). Yet, overly frequent dressing changes may increase the risk of contamination and ascending infection if not handled aseptically. Veterinary nurses must therefore monitor dressings closely and change them only when considered necessary. Additional dressings may be required to hold drains in place, for example, elasticated netting can be used to position the collection chamber of drains to avoid them dragging along the floor and creating tension on the wound and stoma site (Figure 5).
Drain removal
Ensuring the drain removal timing is correct is paramount. The longer the drain is left in situ, the greater risk of bacterial colonisation at the drain site as a result of ascending infection (McFadden and Oberhaus, 2019). However, if drains are removed too early, there is an increased risk of seroma formation (Shaver and Hunt, 2014). In a recent study examining complications associated with drain placement, no association was found between the length of time the drain was in place and the incidence of complications, however, in alignment with human medical evidence, it is recommended that drains should be removed as early as possible to reduce the risk of infection (Bristow et al, 2015). Some fluid production is considered normal resulting from an inflammatory response to the presence of a drain, however, when production drops below 2–4 ml/kg/day, the drain should be removed (Carne, 2011; McFadden and Oberhaus, 2019). Exact volumes of fluid output cannot be measured from passive drains; however, removal should be decided once the volume of exudate has reduced and the appearance has improved (Carne, 2011).
Conclusion
There are many considerations when caring for a patient with a wound drain. Education of veterinary staff, including knowledge of different drain types and their requirements regarding safe handling and maintenance, is essential to reduce morbidity and mortality. Advancements in wound management and novel drainage techniques are fast emerging and veterinary nurses should ensure they keep up to date with best practice protocols, while taking an evidence-based and holistic approach to patient care.
KEY POINTS
- Veterinary nurses are often heavily involved in managing a variety of wounds and therefore must be informed on how best to approach their care.
- Understanding normal wound healing, and recognising complications when they arise, is essential to demonstrate best practice.
- The appropriate use of drains can enhance and accelerate the process of wound healing.
- Novel techniques, such as negative pressure wound therapy, can aid wound healing and reduce hospitalisation times, contributing to better outcomes.
- Drain removal should take place at the correct time to reduce the risks of infection and wound breakdown.
- A holistic approach to wound management, including regular observation of vital parameters and effective pain management, is imperative for delivery of excellent nursing care.