CHAPTER 21 Jennifer J. Devey1, Andrew Linklater2 and Rebecca Kirby3 1 Fox Valley Animal Referral Center, Appleton, Wisconsin 2 Lakeshore Veterinary Specialists, Milwaukee, Wisconsin 3 (Formerly) Animal Emergency Center, Gainesville, Florida A wound is a type of injury in which skin is torn, cut, or punctured (an open wound), or where blunt force trauma causes a contusion (a closed wound). The skin has many functions that include epidermal turnover, immune function, wound healing, vascular responsiveness, thermoregulation, barrier function, sebum production, and sensory perception. As wounds are caused by various types of external forces, internal injury may be present even when there is no evidence of significant external wounds. The etiology of wounds can be quite varied, with most naturally occurring wounds caused by some form of trauma and most hospital‐acquired wounds resulting from therapeutic intervention, such as placement of catheters or drainage tubes, and surgery. Minor injuries can include cuts, lacerations, abrasions, and contusions. Problems under the skin can become apparent when pathogens, such as parasites (bot fly larvae), bacteria (abscess formation), fungi or migration of a foreign object, cause inflammation of the skin and deeper tissues. All open wounds caused by bites or projectiles (such as sticks, iron rods, bullets, arrows) should be assumed to have substantial trauma to the underlying tissues. Complex mechanisms and forces come together to cause wounds. In general, the mechanism of injury is categorized as penetrating, blunt or thermal trauma, with a combination of mechanisms possible. Forces exerted on the tissues to cause wounds include compression (squeezing or condensing of tissues), shearing (tissues sliding over adjoining surfaces), torsion (rotation along fixed point), tension (pulling or drawing apart), and bending (impact in middle while ends are stable). Usually two or more mechanical forces are acting on tissues at any one time. Wounds resulting from traumatic injury can be classified by several methods, including the etiology, location, type of injury, wound depth and tissue loss or clinical appearance of the wound. Specific types of wounds can have a separate classification of their own, such as burns (Rule of 9 s), surgical wounds, and general wounds. General wounds are classified as superficial (loss of dermis only), partial thickness (involving the epidermis and dermis), and full thickness (involving the dermis, subcutaneous tissues, and sometimes bone). Surgical wound classifications are generally based on the degree of wound contamination and are described in Table 21.1 [1]. The class of wound has been shown to be a strong predictor for development of infection [2–4]. Open fractures can also be classified based on the degree of injury: Table 21.1 Surgical wound classification adapted by the Centers for Disease Control and used by the American College of Surgeons [1]. GI, gastrointestinal. Figure 21.1 A traumatic open distal radius ulna fracture in a dog. This would be classified as a type III open fracture. The healing process for surgical or traumatic wounds will go through at least four stages. Within the first few minutes of injury, there is vasoconstriction of the local vessels and platelets from the blood begin to stick to the injured site. This results in the activation of coagulation and the formation of a clot that slows or stops further bleeding (hemostasis stage). The inflammatory and debridement stages occur within minutes of the initial injury and can extend over several days. During this phase, damaged and dead cells, bacteria, and other pathogens or debris are removed by phagocytosis. Vasodilation and cytokine release allow fibrinogen and neutrophils in the area to form a scab, remove debris, and initiate angiogenesis. Platelet‐derived growth factors are released into the wound and cause the migration and division of cells during the following proliferative phase. This phase promotes the growth of new tissue. In this phase, angiogenesis, collagen deposition, granulation tissue formation, epithelialization, and wound contraction occur. This phase begins a few days after the wound occurs and can last for weeks. Finally, the maturation phase starts many days after the initial injury and can continue for years. Collagen is realigned along tension lines, and cells that are no longer needed are removed by programmed cell death. There are several patient factors that can affect the ability of the wound to heal. Age, obesity, poor nutritional status, dehydration, inadequate blood supply, depressed immune response, and the presence of chronic disease can all have a negative impact on wound healing. Malignancies can alter the cellular structure of tissues and negatively influence the healing process. Most wounds, whether natural or hospital acquired, will require a bandage (also called external coaptation) as part of the treatment plan. Almost every hospitalized patient will have some form of bandage, from a simple bandage protecting a peripheral catheter to a more complex dressing for open wounds or a splint or cast. The proper care of the bandages can promote wound healing and prevent the development of a new secondary problem. The presence of wounds can have a significant impact on morbidity and mortality in the ICU small animal patient. The loss of fluids, electrolytes, and proteins through wound effusions can be substantial, affecting fluid balance and albumin status. Massive tissue damage can lead to systemic inflammation and the systemic inflammatory response syndrome (SIRS), and wound complications, such as necrotizing fasciitis or overwhelming sepsis, can lead to life‐threatening hemodynamic alterations. Even the improper application of a bandage or insufficient bandage maintenance can contribute to patient morbidity. Pain associated with the wound or banadage can lead to mutilation of the area by the animal. Because of the negative impact that wounds and bandages can have, appropriate diagnostic investigation to define the cause and nature of the wound and adequate monitoring procedures to optimize recovery should be instituted. Because the small animal ICU patient is likely to have a long list of medical problems, the presence of a wound or bandage may not be a priority at the time of initial admission. However, it is vital that the nature and classification of any wounds present are known and the plans regarding wound care and bandage support are clearly defined. Information from the history and physical examination may reveal underlying concerns that may affect wound healing. Clinicopathological laboratory testing and diagnostic imaging may be required to better define the extent and characteristics of the wound. The wound size, shape, and progress toward healing must be monitored. The history begins with the signalment (age, sex, breed). Wound healing may be impaired with older age. Both skin and muscle lose their tone and elasticity with age. Metabolism slows and circulation may be altered. Past medical problems become important since health problems such as malignancies, autoimmune diseases, hyperadrenocorticism, diabetes mellitus, and skin diseases can impact wound healing. A list of recent and current medications, to include injectable, oral, and topical drugs, can identify those (such as glucocorticosteroids) that might delay wound healing. The animal’s diet becomes important for assessing nutritional status and potential effects on wound healing. If a wound is present at admission, it should be determined if the skin defect was induced by trauma or developed spontaneously. Progression, regarding the time frame of wound development, changes in the wound character and overall changes in the health of the animal should be obtained. A history of trauma or possibility of bite wounds warrants careful examination for wounds hidden by hair or fur. The physical examination should include vital signs and an assessment of the perfusion and hydration status of the animal. Immediate identification of external hemorrhage is essential and hemostasis should be rapidly provided with application of a temporary compression bandage. Hyperdynamic perfusion (compensatory stage of shock) or severe hypotension can be a consequence of hemorrhage, significant fluid loss from effusive wounds, infection or systemic inflammation from massive tissue trauma. High body temperatures can be a result of systemic inflammation or infection secondary to dirty or contaminated wounds. Lower body temperatures can be a reflection of cold exposure (frostbite wounds) or poor circulation. The location of the wound will impact the likelihood of serious secondary complications. The hair or fur must be generously clipped from any body region that might have been affected. The skin is carefully examined for evidence of punctures, lacerations, subcutaneous emphysema, swelling or bruising. Wounds found around the head and neck raise concerns for bleeding, swelling or disruption of tissue within the nasal sinuses, brain, pharynx, larynx or trachea. Wounds over the chest region raise concerns for hemothorax, pneumothorax, pneumomediastinum, and lung parenchymal hemorrhage. Abdominal wounds raise concerns for rupture or perforation of an abdominal organ and abdominal hemorrhage. The limbs are examined for concurrent muscle, tendon, nerve or bone damage. Close examination of any wound is essential and the size, depth, tissue involvement, evidence of infection or debris, and underlying etiology (which may include parasites, foreign material) should be documented. Skin that is cool to the touch may be indicative of altered perfusion that may be secondary to an embolic event, compartment syndrome or necrosis. Bite wounds require specific attention because a significant injury deep to the skin wound is often present. For patients that are hospitalized, routine examination of any treatment‐induced wound (such as IV catheter, tube placement, incision site) and the evaluation of bandages are an important component of the physical examination performed each shift. Development of a new fever, pain, swelling or redness should stimulate the examination of catheter sites or unwrapping of a bandaged wound to address problems. Point of care (POC) testing provides immediate information at the cage side and will include packed cell volume (PCV), total protein (TP), creatinine, blood glucose, blood lactate, blood electrolytes, acid–base balance, blood smear for platelet estimate, coagulation profile, and urinalysis. The PCV and TP can imply blood loss, anemia or hypoproteinemia. Evaluation of the clotting profile, with the platelet estimate, can identify a coagulopathy that might be contributing to bruising, bleeding or swelling from a wound. A low blood glucose can be a result of wound‐related sepsis and a high blood glucose may be a stress response but if it persists, warrants investigation for diabetes mellitus which can impair healing. A high blood lactate suggests poor tissue oxygenation and anaerobic metabolism, harmful to wound repair. An elevated creatinine can be a result of dehydration or renal impairment, both potentially negatively impacting wound healing. A complete blood cell (CBC) count and serum biochemical profile should be submitted to assess for underlying diseases or conditions that can affect wound healing in patients with significant wounds. Samples can be collected from an impression smear, skin scraping, wound drains or aspirates of a swollen area. Cytology and gram staining of samples collected can be examined for pathogens, debris or abnormal cell types and may be useful in guiding the initial empirical antibiotic therapy. Wounds that are grossly infected (such as abscesses) or contaminated (such as bite wounds) warrant collection of samples for bacterial culture and susceptibility to help direct antibiotic therapy (see Chapter 14). Depending on the geographic location, specific diagnostic testing for fungal disease, such as blastomycosis or coccidioidomycosis, may require collection of samples for fungal titers, fungal cultures, and urine antigen testing. When wounds are not healing with appropriate wound management or are associated with swellings or masses or are located at mucocutaneous junctions, then collection of incisional or excisional tissue biopsies for histopathology or macerated tissue culture may be indicated to investigate for underlying etiologies (such as resistant infections, neoplasia or autoimmune skin diseases). Imaging techniques (radiographs or ultrasound focused assessment with sonography for trauma (FAST) exams) for examination of inappropriate collections of fluid or air within cavities or wounds may be indicated, particularly in those patients suffering from significant trauma. Chronic wounds may warrant imaging studies to determine if there is involvement of underlying tissues. Occasionally, contrast studies (such as a fistulogram for chronic draining tracts) or advanced imaging (computed tomography (CT) or magnetic resonance imaging (MRI)) may be ordered to investigate the extent of a wound, vascular supply, for neuroorthopedic disease that is identified on examination or to identify the presence of foreign material. Patient monitoring includes frequent assessment of the physical perfusion parameters (heart rate, pulse intensity, capillary refill time (CRT), mucous membrane color, temperature) and hydration parameters (skin turgor, mucous membrane moistness, eye position within socket). Skin wounds usually need to be inspected at least once daily to ensure healing is progressing appropriately. Exceptions to this include wounds that have hydrocolloid dressings (generally changed every 5–7 days) and bandages over skin grafts (usually changed every 3–5 days). Gloves should be worn whenever wounds are exposed to help prevent contamination and nosocomial infection. The skin around the wound should be assessed for evidence of swelling, crepitus, heat, pain, odor, and discharge. By outlining any affected skin areas with a nontoxic permanent marker, it is possible to determine if the damage is progressing or resolving. Covering catheter and other hospital‐acquired wound sites with external coaptation and regular bandage maintenance is necessary. Venipuncture sites and catheter (long‐ and short‐term) sites should be inspected daily. Every catheter (vascular, epidural), tube (tracheostomy, thoracostomy, feeding), and drain (Penrose, suction) site should be assessed by direct visualization and palpation at least once daily. Hourly examination of vascular catheter sites for swelling, pain or heat should be part of the critical care nursing routine (see Chapter 20) when fluids or drugs are being infused at that site. Each time a limb bandage is changed, sensation should be assessed on the lateral and medial aspects of the limb. Blood flow can be evaluated based on tissue color and temperature, bleeding, and the presence of pulses. If there is any concern for arterial blood supply, a Doppler ultrasonic flow probe should be placed over the regional arteries and flow subjectively assessed. Significant swelling of distal extremities accompanied by rapid bleeding with a needle prick in patients that have experienced crush‐type injuries is consistent with venous congestion that may lead to significant complications. The temperature of the surrounding skin can be assessed using infrared thermometry. If there is a significant difference in temperature between the healthy skin and the affected area, the animal should be carefully examined to ensure this is a local rather than a more diffuse problem. The goals of wound care are to preserve viable tissue, restore damaged tissue to a normal condition and function, provide an environment that maximizes the development of wound strength, and avoid problems such as infection that interfere with wound healing. Factors that promote good wound healing include: Healing of wounds requires diligent care of the whole patient. Emphasis should be placed on fluid balance, oxygenation, immune status, nutrition, and nursing care from the Rule of 20. The animal may have varying degrees of immune system dysfunction secondary to underlying disease, immunosuppressive drugs and malnutrition, each potentially increasing the risk of infection [4,6,7]. Patient morbidity can also be attributed to inappropriate wound management. Sepsis can occur secondary to wounds and is usually due to a combination of one or more of the following factors: inadequate debridement of necrotic tissue, insufficient irrigation, inappropriate choice of antibiotics, and inadequate patient resuscitation. Urgent wound care includes patient stabilization, appropriate analgesia (examples include fentanyl 2–5 μg/kg IV, hydromorphone 0.05–0.1 mg/kg IV, methadone 0.1–0.3 mg/kg IV) (see Chapter 19), and hemostasis. Once these are achieved, a sterile, water‐soluble lubricant is applied directly to an open wound, followed by the removal of surrounding hair and cleansing of the surrounding skin. Further injury can be prevented by bandaging, immobilizing the area, and placing an Elizabethan collar on the patient. Administration of antibiotics in the early stages may be warranted in traumatic wound care. A sterile dressing should be placed on every wound as soon as possible to minimize the risk of nosocomial infection. Wounds should never be handled unless gloves are worn. Hand washing with an antibacterial soap or an alcohol‐based rub is required prior to donning gloves. Sterile instruments and sterile suture should be used when treating all wounds. It may not be possible to perform definitive wound care immediately after urgent wound stabilization. A delay in definitive care can have advantages, such as allowing time to stabilize the patient and time for tissues to “declare” themselves. Disadvantages, such as increased risk of bacterial contamination, can be minimized with timely and appropriate initial wound management. In general, wounds that are kept moist will maintain overall tissue hydration, which helps prevent cell death, encourages angiogenesis, phagocytosis and growth factor production, improves the rate of epithelialization, and may be less painful [9]. Wounds should not be allowed to form a crust as a wound with no crust will epithelialize almost twice as fast [8]. Definitive wound care includes hemostasis, debridement, irrigation, antisepsis, drainage, and closure. The procedures and extent of intervention will vary depending on the nature and extent of the wound. Hemostasis during wound care is important during all stages of wound healing. The presence of blood in the wounded tissues can delay healing by inhibiting the migration of fibroblasts, inhibiting angiogenesis, and facilitating colonization with organisms. Various mechanical, thermal, and chemical methods are available to decrease the flow of blood into the wound site. Without adequate control, bleeding from transected or penetrated vessels or diffuse oozing from large denuded surfaces may interfere with the view of underlying structures. Achieving complete hemostasis before wound closure also will help prevent formation of postoperative hematomas. Collections of blood or fluid in the incision can prevent the direct apposition of tissues necessary for complete union of wound edges. The presence of blood provides an ideal culture medium for microbial growth and can lead to serious infection. When clamping or ligating a vessel, care must be taken to avoid creating excessive tissue damage. Necrotic tissue increases the risk of infection [9] and should be debrided back to bleeding edges. Surgical debridement of devitalized tissues is usually performed using sharp dissection with a scalpel blade or scissors. Scissors are generally avoided in skin debridement because they have a tendency to crush tissue. Healthy muscle edges may not bleed but will typically contract when incised. Embedded debris should be removed from exposed tissues and bone by gently scraping the tissues or bone with the edge of a scalpel blade. Minor debridement can be performed using certain dressings including wet‐to‐dry, honey and sugar bandages [10–12]. Crush injuries with venous or tissue congestion often experience delayed healing. Leeches are an effective method of reducing excessive venous congestion while the tissues are healing [13]. Figure 21.2 shows leeches on a wound and discusses application. Figure 21.2 Medicinal leeches applied to a wound where significant venous congestion and tissue swelling are noted. Application of leeches: (1) leeches are obtained from a medicinal leech source, (2) the skin is cleaned with chlorhexidine and rinsed with saline, (3) the leech may be held in place with a syringe case until attachment occurs, (4) the leech is left in place until it is full and detaches (10–30 minutes, but it may be longer). Some evidence supports that one leech can decongest and increase perfusion to approximately 2 cm2 area of skin, removing approximately 5 mL of fluid each. Leech species include Hirudo, Hirurdinaria, and Macrobdella [14]. Irrigation is always indicated after debridement and may be warranted whenever a bandage covering an open wound is changed. Sterile isotonic fluids are preferred. There is conflicting evidence regarding the use of antiseptics in irrigation fluids, as they may interfere with wound healing [15]. Irrigation with chlorhexidine at 0.05% has not been shown to negatively impact wound healing in dogs [16] and may actually aid wound healing [17]. The appropriate concentration (0.05%) of chlorhexidine must be used since higher concentrations have been shown to interfere with wound healing [18]. Tap water has been used to irrigate larger wounds without complications [19], and can be used as a first step when large wounds are present. Antibiotics should not be added to irrigation fluids since this is not effective and can lead to bacterial resistance. The ideal pressure for irrigation systems is unknown. Excessive pressure can lead to tissue trauma and infection [7]. One study demonstrated that use of a 35 ml syringe and needles from 16 to 22 G in size routinely generated pressures well above 15 PSI, which could lead to tissue trauma [20]. Most surgeons agree on a pressure of 8–12 PSI, the pressure necessary to dislodge bacteria [21]. Irrigation can be performed with mechanical lavage systems or by using a 1 L fluid bag pressurized to 300 mmHg with any size of needle or catheter [20]. The ideal volume of irrigation is also unknown, although 50–100 mL of irrigation fluid per cm of laceration or cm3 of wound has been recommended [22]. Irrigation should not be done blindly into puncture wounds since this may force foreign material or bacteria further into the wound or into healthy tissues. The classification of the wound based on the degree of contamination (see Table 21.1) has been shown to be a strong predictor for development of infection [2–4]. Wounds become infected secondary to the environment or due to the migration of endogenous bacteria, with the majority coming from the latter source [23]. Factors shown to provide an additional risk for wound infection include inadequate skin disinfection, inadequate preparation of the surgical team, hypothermia during the surgical procedure, and prolonged anesthetic and surgical time [6,23,24]. The size of the laceration and the presence of contamination has also been shown to increase the risk of infection [7,25,26]. Potential risk factors and options to minimize their impact are listed in Table 21.2. Table 21.2 Risk factors for wound contamination and infection and methods to decrease those risks.
Wounds and bandages
Introduction
Classification
Description
Clean
Uninfected surgical wound with no inflammation and internal tracts (respiratory, GI, genital, urinary tract) are not entered; includes surgical wound incisions made after nonpenetrating trauma, if it meets the above criteria
Clean‐contaminated
Surgical wound in which internal tracts are entered under controlled conditions and without unusual contamination; no signs of infection and no major break in technique occurs.
Contaminated
Open, fresh, accidental wounds; surgical procedures with major break in sterile technique (such as open cardiac massage) or gross spillage from GI tract; incision with acute nonpurulent inflammation is included
Dirty or infected
Old traumatic wounds with retained or devitalized tissue; wounds with existing infection or perforated viscera; suggests organisms causing postoperative infection were present in the wound before surgical procedure
Diagnosis and monitoring procedures
History and physical examination
Point of care and clinicopathological laboratory testing
Diagnostic imaging
Patient monitoring
General wound care
Initial wound management
Definitive management
Hemostasis
Debridement and congestion
Irrigation
Antisepsis
Risk factor
Methods to minimize
Inadequate skin disinfection and preparation
When preparing for surgical manipulation of a wound, cleansing the area with a chlorhexidine or iodine solution is necessary
Inadequate preparation of surgical team
The surgical team should be fully prepared, having necessary monitoring, surgical and bandage equipment, appropriate clipping and preparing as well as surgical materials
Hypothermia during the procedure
Use a variety of warming devices (warm air blowers, warm IV fluids, circulating warm water blankets) to minimize
Prolonged anesthetic time
Having an experienced surgeon and anesthetist with necessary materials “at the ready” will help minimize surgical time
Size of injury
Only necessary incisions should be made
Presence of contamination
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