Learning Objectives

Discuss the etiology, general approach, diagnostic and therapy of the bite wounds in small animal patients.

The sources of trauma for tissues include lacerations, detachment or tearing of the skin and other tissues from the underlying tissue, bite wounds, stab wounds, gunshot wounds, poisonous snake bites, radiation injury, bed sores or inflicted by misapplication of plasters and bandages, burns, frostbite, perivascular injection of hypertonic drugs, among many others.

All veterinary clinics, whether or not designed for the management and treatment of trauma patients, commonly evaluate and treat these patients. The role of the veterinarian who provides the primary care to the patient with open wounds is vital, having a direct influence on the complexity of the case and the possibility of recovery.

Wound Classification

A wound can be defined as any physical or chemical event, caused by the interaction of external agents or not, that produces or induces cell necrosis, disturbances in tissue nutrition and disruption of the architecture and normal tissue continuity.

All wounds may, however, be classified into open or closed in relation to the integrity or not of the skin or mucous membranes.

Closed Wounds

In closed wounds, any tissue can be involved, the skin can be damaged, but do not presents continuity solutions and remains viable.

The forces of inertia, backlash and different tissue resistance may cause that some remote structures from the impact site can also be affected. This is particularly true in structures that are confined within bone boxes such as the brain (see TBI), and t issues such as the spleen which often fractures in absence of external signs of trauma. Ruptures and sprains mainly involve muscles, tendons and ligaments. Signs of this lesions include quick onset inflammation and lameness.

Open Wounds

Open wounds denote a continuity solution of the skin or mucous membranes. The underlying tissues can be damaged to varying degrees. Open wounds are contaminated at the time of injury, as the traumatic agent or foreign material is inserted into the wound. Further contamination can occur until the wound is closed.

Penetrating wounds are those induced by projectiles or sharp objects, which are inserted into an anatomical cavity such as the chest or abdomen, or in the lumen of hollow organs such as the intestinal loops, stomach or bladder. By definition they only have an entry hole. When there is also an exit hole these wounds are defined as puncture wounds.

A laceration is a wound created by the tearing of the tissues, in which the edges are irregular. The damage to the skin and the underlying tissues can be extensive, but is confined to the path of the traumatic agent.

Avulsions are wounds characterized by the detachment of tissues from their insertions. Skin and subcutaneous tissue can be severely avulsed from deeper tissues, varying in extensions even involving the entire trunk of the animal. Many of these flaps are so severely damaged that there is no doubt about its viability. Whenever there is doubt about the viability of a flap, it is preferable to clean, cut about 3 mm of the edges and suture in place.

Crush injuries can include various types of accidental injuries. Damage to the superficial and deep tissues is extensive. The severity of injuries caused by compression is determined by two factors; anatomical region involved and nature of force and length of time that region was under pressure.

Hernias are defined as the complete or incomplete protrusion of organs or tissues through an abnormal opening in the presence of skin or mucous membranes without solution of continuity. When these tissues protrude through a hole in the skin, it is called evisceration.

Principles of Treatment

The initial process of evaluation involves a physical examination that will determine the type, degree and extent of the various injuries received by the patient and their ability to put life in danger. Some wounds that have the ability to endanger the patient's life, require immediate action, such as penetrating thoracic or open pneumothorax ( see chest trauma ), and those involving massive bleeding due to the compromise of the integrity of large vessels such as the femoral.

Open wounds should be covered with a sterile dressing to prevent further contamination during handling of the patient. Fractured bones must be protected and may require some form of restraint to prevent further damage to the soft tissues, control shock or pain relieve. Once the patient is stable, we can turn our attention to the proper handling of these problems.

First Aid

External bleeding must be stopped applying pressure on the wound site with a clean bandage. If bleeding continuous, apply a new layer of bandage. The first bandage should always be kept in place, because if replaced we might as well be removing the forming clots and cause a larger hemorrhage. Once in the operating room, we can remove this bandages.

Definitive Treatment

The goal of treatment of all open wounds is to change a contaminated wound into a surgically cleaned wound that can be closed. The use of an aseptic technique, proper handling of tissues and proper hemostasis are essential.

All open wounds have some potential to become infected, and many are infected at the time of arrival. In the past it was accepted as a general rule that in the first 6 to 8 hours after injury wounds were contaminated, but not infected. This time reference, referred to as the "golden period", and was based on laboratory studies indicating that bacterial contaminants took more than six to eight hours to reach sufficient numbers to develop infection.

Currently, it is recognized that several factors including the type and virulence of the organism, location and type of injury, degree of blood supply, tissue type and resistance to infection, grade and type of pollutants, immune status of the patient, mechanism of injury and the initial wound management among some others, influence the wound to become infected.

Systemic antibiotic therapy should be implemented before handling the wound. If treatment is started during the first three hours, we will ensure an adequate level of antibiotic in the secretions present in the wound, before the bacteria become protected in the networks of blood clots.

This treatment should be effective against those bacteria most common in wounds, Staphylococcus, Streptococcus and Escherichia coli. Cephalosporins are a good choice because of its broad spectrum and good tissue penetration. In bite wounds, Pasteurella is the most predominant organism, and amoxicillin or ampicillin could be the antibiotics of choice. In heavily contaminated wounds a combination of antibiotics applied systemic and locally is a better choice. Antibiotics that are to be used locally must be water soluble, non-irritating and must be administered diluted in saline solution.

Wound Preparation

Before surgical treatment it is essential to prepare the wound properly. Patients require sedation or general anesthesia. The type of anesthesia used will depend on the patient's condition and the estimated duration of the surgical procedure.

In order to prevent further contamination of the wound with hairs and other contaminants, the wound must be protected while the area is being prepared. This is accomplished by applying a sterile hydrosoluble gel or sterile gauze soaked in saline covering the wound; or facing the edges of the wound using field forceps or by applying a temporary simple continuous suture. In wounds close to the eyes, you must protect the cornea and conjunctiva instilling an ophthalmic ointment on the eyelid fissure.

The use of hydrogen peroxide 5% for cleaning wounds is absolutely contraindicated. Its oxidizing properties are ineffective against anaerobic microorganisms due to the short period of contact, and its activity against aerobic bacteria is extremely low. The main disadvantage of the use of hydrogen peroxide lies in the ability to block almost completely the capillary with the subsequent necrosis making the healing process go slower.

Debridement of the Wound

Debriding a wound is the most important procedure in soft tissue management. The goal is to remove all devitalized, contaminated or infected tissue, as well as foreign detritus. This procedure removes tissue with great potential to enable the development and proliferation of bacteria. It also improves local circulation, allowing a greater flow of white blood cells, and cell growth factors, increases tissue oxygen levels and nutritional support, promoting healing.

Washing of the Wound

Abundant flushing of the wound is the next step in wound management. The mechanical effect of wound irrigation with solutions under pressure has a fundamental role in the removal of external contaminants, blood clots and tissue debris, as well as in reducing the bacterial population either by dragging or dilution.

The amount of fluid required to wash a wound properly, varies with the size, degree of contamination and type of wound. It requires extensive washing for effective cleaning. In humans it is recommended the use of 5 to 14 liters of sterile saline or Ringer lactates for the treatment of open fractures. In veterinary medicine literature refers a minimum of 1 to 2 liters, however, in highly contaminated wounds should a larger volume be used. Washing should be discontinued before tissues become discolored tissues and edematous, as if trapping water.

A suitable pressure of at least 7 psi, may be obtained using a saline bag, attached to an infuser drip. At its end a three-way can be attached to a 20 to 60 cc syringe in one of the outputs, and an 18 to 19 G needle is placed in the other. This provides a suitable pressure to remove contaminants without causing further tissue damage.

Repairing Procedures

After cleaning and debriding the wound we must decide for closing the wound using sutures or to allow closure by contraction and epithelialization. Whenever possible, wounds should be sutured.

At this point the doctor must choose either: 1) conduct a primary closure, with or without drainage, allowing healing by first intention, 2) opt for a delayed primary closure or healing by third intention, 3) allow the wound to heal by contraction and epithelialization, or healing by secondary intention.

Primary Closure

As a general rule, a wound may be sutured always when there is no contamination or infection, devitalized or necrotic tissues, and its edges can be apposed under a degree of tension that will not induce pressure necrosis.

Delayed Primary Closure

The delayed primary closure consist in suturing a 5 or more days old wound, having a layer of granulation tissue on its surface. To achieve this wound edges which are firmly attached firmly to the granular tissue must be cut and suture them above this tissue.

Healing by Contraction and Epithelialization

This treatment is reserved for those extensive wounds in which, due to trauma or posterior debridement do not have the sufficient amount of tissue for a primary closure without subjecting the tissue to considerable stress. Another indication are those wounds that are contaminated or excessive amount of tissue of doubtful vitality despite adequate debridement.

References

References are available upon request.