Chapter 157 Wound Management
Most traumatic wounds seen in the small animal veterinary patient include bite wounds, abrasions or shearing injuries resulting from motor vehicle trauma, degloving, lacerations, and punctures. Wounds can also result from decubitus ulcers in the recumbent animal secondary to poor nursing care, or wounds can appear in postoperative surgical incisions that dehisce or become infected.
Although definitive repair of an open fracture should be done as soon as possible for patient comfort, initial care of the soft tissues should not be delayed if a surgeon is not immediately available or if the patient is not stable enough to undergo general anesthesia for several hours. Any exposed bone should be covered with sterile lubricating jelly and a sterile bandage but should not be pushed back below the skin surface because this can cause deeper contamination of the wound or further injury to the tissues. Similar guidelines exist for wounds with penetrating foreign bodies such as arrows, large wooden splinters, or knives. The foreign body may be tamponading a large vessel, and removal may lead to severe hemorrhage. These objects should be removed only under controlled surgical conditions.
Other wound classifications describe the length of time that the wound has been open because this relates to how quickly bacteria can multiply in a wound. Although this is important to know, it is not as vital as assessing the patient and the wound directly. It is more important to understand the local and systemic defenses of the patient and the types and virulence of bacteria that may be present in the wound so that appropriate treatment can be initiated.1
A basic understanding of the phases of wound healing gives the clinician an idea of how long it will take for a wound to improve in appearance and for making wound management decisions. Wound healing can be described in four phases: (1) inflammation, (2) debridement, (3) repair/proliferation, and (4) maturation.1 The phases overlap and the transitions are not visible to the naked eye.
The inflammatory phase occurs during the first 5 days after injury. Immediately after trauma there is hemorrhage caused by disruption of blood vessels, and then vasoconstriction and platelet aggregation limits the bleeding. Vasodilation follows within 5 to 10 minutes, allowing fibrinogen and clotting elements to leak from the plasma into the wound to form a clot and eventually a scab. The clot serves as scaffolding for invading cells such as neutrophils, monocytes, fibroblasts, and endothelial cells. Also contained in the plasma are inflammatory mediators (cytokines) such as histamine, prostaglandins, leukotrienes, complement, and growth factors.
The debridement phase occurs almost simultaneously with the inflammatory phase. It is marked by the entry of white blood cells into the wound. Neutrophils are the first to appear in the wound approximately 6 hours after injury. They remove extracellular debris via enzyme release and phagocytosis. Monocytes appear approximately 12 hours after trauma, and they become macrophages within 24 to 48 hours. The monocytes stimulate fibroblastic activity, collagen synthesis, and angiogenesis. Macrophages remove necrotic tissue, bacteria, and foreign material.
The repair phase, also called the proliferative phase,5,6 begins 3 to 5 days after injury and lasts about 2 to 4 weeks. This is the most dramatic healing phase and is characterized by angiogenesis, granulation tissue formation, and epithelialization. Fibroblasts proliferate and start synthesizing collagen, and then capillary beds grow in to form granulation tissue. Granulation tissue provides a surface for epithelialization and is a source of myofibroblasts that play a role in wound contraction. New epithelium is visible 4 to 5 days after injury and occurs faster in a moist environment.1 Wound contraction is first noticeable by 5 to 9 days after injury and continues into the maturation phase.6
Finally, the maturation phase occurs once adequate collagen deposition is present and is marked by wound contraction and remodeling of the collagen fiber bundles. It starts at about 17 to 20 days after injury and may continue for several years. Healed wounds are never as strong as the normal tissue; a scar is only about 80% as strong as the original tissue.6
Before handling the patient, the clinician and patient should be protected by the use of examination gloves. Initial stabilization of the patient should address oxygenation and circulatory requirements (see Chapter 2, Patient Triage). Intravenous catheter placement, fluid therapy, and supplemental oxygen may be required for the severely traumatized patients or patients in shock (see Chapters 19 and 65, Oxyen Therapy and Shock Fluids and Fluid Challenge, respectively). A complete blood count, biochemical analysis, urinalysis, and venous or arterial blood gas analysis should be performed on admission.
Direct pressure should be applied to any bleeding wounds. If bleeding cannot be controlled by direct pressure, surgical intervention is required. Bleeding of appendages can be controlled with tourniquets by using a pneumatic blood pressure cuff inflated to 200 mm Hg for not more than 1 hour.7It is important to remember that bite wounds commonly result from the penetration of both the upper and lower teeth. If bite marks are seen only on one side of the limb or trunk, then the other side should be shaved to search for the corresponding wounds. Wounds should be kept clean and moist and protected immediately from the hospital environment. A sterile, water-soluble lubricant and saline soaked sponges can be applied initially to the wounds and then covered with a sterile towel and soft padded bandage if the patient must be moved. It is important that the damaged tissue remain moist because desiccation impairs wound healing.
If the animal has wounds associated with trauma, radiographs are indicated to assess for other more immediate, life-threatening injuries. These radiographs might include views of the spine, chest, abdomen, and pelvic region, in addition to appendages, if there is suspicion of a fracture. Blunt trauma, such as motor vehicle trauma or falling from heights, warrants chest and abdominal radiographs to assess for pulmonary contusions, pneumothorax or hemothorax, diaphragmatic hernia, and peritoneal effusion secondary to blood or urinary tract trauma. Cursory abdominal ultrasonography may also assist in detecting free fluid within the thoracic or abdominal cavity. A thorough neurologic assessment is also important, to rule out spinal or neurologic injury. Assessment of perfusion and sensation to the digits is important when severe trauma to peripheral blood supply and nerves might prohibit a successful outcome.
Once the patient has been thoroughly examined, stabilized, and all diagnostic tests performed, and if sedation or anesthesia can be administered safely, initial assessment and debridement of the wound should be done. The primary goal in the management of all wounds is to create a healthy wound bed with a good blood supply that is free of necrotic tissue and infection to promote healing.5 Most wounds will require daily debridement and bandage changes, and the clinician should not be discouraged if the wound cannot be closed initially. The following summarizes the steps for daily wound evaluation:
Initial debridement will require general anesthesia, local anesthesia, or neuroleptanalgesia. For future wound evaluations, the patient may require only sedation or analgesia and restraint, if surgical debridement is minimal. Local anesthetics are ideal for the patient that is not stable enough for general anesthesia and has injuries to the limbs. In these cases, wounds in the hind limb area can be debrided using epidural analgesia (see Chapter 164, Analgesia and Constant Rate Infusions) and forelimb wounds can be debrided using a brachial plexus block.8
Sterile lubricating jelly should be applied to the exposed wound to protect it from further contamination, and a wide area of fur clipped from the skin around the wound. Gross dirt from the skin around the wound should be cleaned by applying surgical scrub solution (chlorhexidine or povidone-iodine) to unbroken skin, but not to the surface of the wound because these solutions are damaging to exposed tissues.
Debridement should be done using aseptic technique: use sterile gloves, sterile gown, cap and mask, and the wound should be draped with sterile towels or water-impermeable drapes. At the time of initial assessment and subsequent bandage changes, necrotic tissue should be excised. All bite wounds should be explored, even if they look minor, because teeth exert a macerating or crushing force that can damage tissues deep below the skin surface (Color Plate 157-1). The hole around the bite wound should be trimmed and then tented up to evaluate the subcutaneous tissues. A probe, such as a mosquito or Kelly forceps, can be used to assess for dead space or pockets under the skin that could form hematomas, seromas, and abscesses.
Obviously necrotic tissue (black, green, or gray) is removed first. In areas that have ample skin for closure, initial trimming of skin can be done more aggressively. In areas such as the distal limbs, trimming of skin should be done conservatively, and time can be given to let questionable tissues “declare” themselves (Color Plate 157-2). Bone, tendons, nerves, and vessels are preserved as much as possible unless segments of these vital structures are completely separated from the tissue and obviously nonviable.
The wound can be lavaged with a variety of solutions. In wounds heavily contaminated with road dirt or soil, lukewarm tap water with a spray nozzle may be the most efficient way to remove debris.1 Maggots should be removed from severely necrotic wounds manually or with aggressive flushing. Chlorhexidine and povidone-iodine can be used in dilute form (chlorhexidine 0.05% solution: 1 part chlorhexidine 2% + 40 parts sterile water; povidone-iodine 1% solution: 1 part povidone-iodine 10% + 9 parts sterile saline) as initial lavage in contaminated and infected wounds because of their wide spectrum of antimicrobial activity. Povidone-iodine is more irritating to tissues, toxic to cells needed for wound healing, and inactivated by organic debris,1 so it may not be the ideal lavage solution. Lactated Ringer’s or normal saline are the most commonly used lavage solutions. An in vitro study demonstrated that normal saline and tap water cause mild and severe cytotoxic effects on fibroblasts, respectively, whereas lactated Ringer’s solution did not cause significant fibroblast injury.9
Lavage is performed by flushing with a bulb syringe or a 60-ml syringe with an 18-gauge needle. For efficiency, the syringe and needle setup can be connected to a three-way stopcock and an intravenous fluid bag to facilitate refilling.
Sugar has a bactericidal effect. Its osmotic action draws macrophages to the wound and accelerates sloughing of devitalized tissue.10 It is especially advantageous because it is effective and economical for large wounds. Indications include degloving and shearing injuries, infected wounds (Streptococcus, Escherichia coli, and Pseudomonas spp), burns, and other wounds that require further debridement. The wound is first debrided and lavaged. The area is then patted dry with a sterile towel before applying a coating (up to 1 cm thick) of granulated sugar. A wet-to-dry dressing is applied and changed daily, or more frequently if strike-through occurs. Sugar application is stopped when epithelialization begins.