Jennifer J. Devey, DVM, DACVECC
Little dogs presenting with bite wounds inflicted by larger dogs can be exceedingly challenging to manage. Appropriate wound care provided in a timely manner can help prevent significant morbidity and mortality. The seriousness of wounds should not be underestimated and in many cases aggressive surgical treatment is indicated as soon as the patient is cardiovascularly stable. In some situations the patient may never become cardiovascularly stable without surgery. Secondary problems with wound healing and patient morbidity may relate to inappropriate wound handling during the initial stages. Problems with sepsis from wounds come from inadequate debridement of necrotic tissue, insufficient irrigation, inappropriate choice of antibiotics and inadequate resuscitation.
First Aid Stabilization and Resuscitation
Evaluation of the patient should begin always with the ABC's (airway, breathing, circulation). There may be an obvious wound or wounds but the visible wound may be minor compared to an unseen injury such as airway disruption or pneumothorax. Patients should always be provided with supplemental oxygen (flow by, baggie or a non-tight fitting mask) on presentation. If it is determined that the patient is not in shock the oxygen can be discontinued. If the animal cannot breathe an airway will need to be established, which may require a tracheostomy. If the patient is showing signs of significant respiratory distress or is at risk for developing an airway obstruction the clinician may need to make a decision as to whether or not to anesthetize the animal and gain control of the airway. Once an injured patient is intubated the lungs should be ausculted bilaterally to ensure air is moving though all lung fields. If the patient has a sucking chest wound and is critical a chest tube may need to be placed through the wound immediately.
Large bore intravenous catheter(s) should be inserted and fluids started if the patient is in shock. Fluid therapy may consist of a combination of crystalloids, synthetic colloids and blood products depending on the status of the patient. Blood volume and blood pressure should be normalized unless the clinician is providing hypotensive resuscitation due to concerns for ongoing internal abdominal hemorrhage. Blood volume ideally should be estimated through measurement of central venous pressure but since central catheters are rarely placed during resuscitation, the distention of the jugular vein when the vein is held off at the thoracic inlet can be used as a subjective evaluation of central venous pressure. The hematocrit should be maintained as close to 30% as possible. Autotransfusion may be required in the patient with a significant hemoabdomen. Albumin should be maintained greater than 2.0 g/L with fresh frozen plasma. Patients at risk for or confirmed to be coagulopathic may need to receive plasma during the resuscitation phase. Small dogs are prone to hypothermia and fluids should be warmed.
Analgesics are always indicated once resuscitation has been started. Not only is pain detrimental to the overall well being of the patient but also it is detrimental to the healing process. Catecholamine release can lead to vasoconstriction and poor flow to the wound area. There are two key concepts to keep in mind. The first is that pain kills. The second is that no patient is too critical to receive analgesics. Doses may need to be decreased to 25 to 50% of normal in critical patients but all should receive appropriate analgesia. Patients with chest trauma should always have their pain aggressively controlled, since thoracic pain can interfere significantly with ventilation potentially leading to hypercarbia and hypoxia. Opioids are the primary class of drug used; they can be given intravenously, intramuscularly, subcutaneously, or epidurally. Pure mu agonists are preferred. The intravenous route is preferred over the intramuscular route (painful over time) and subcutaneous route (absorption is unpredictable). If the intramuscular route is used the injection should be given in the epaxial muscles since blood flow to this muscle bed is more consistent even in the face of alterations in tissue perfusion. Constant rate infusions of fentanyl or morphine are indicated in patients with significant pain and are very useful in patients who will require surgery. Local anesthetics (lidocaine, bupivacaine) can be injected as local or regional blocks. Intercostal blocks will help substantially to improve ventilation in dogs with fractured ribs. Pain related to the acidic nature of the local anesthetic can be modified by warming the drug to body temperature or by adding 10% of the volume as sodium bicarbonate. Nonsteroidal antiinflammatory drugs generally should be avoided. Some of the newer generation COX-2 specific drugs may prove to be safe to use in more critical patients; however, they are not recommended in patients with hypovolemia, compromised gastrointestinal perfusion (related to circulatory disturbances or underlying disease processes), and renal disease.
Active bleeding from wounds will need to be controlled. Capillary oozing and most venous hemorrhage can be controlled with pressure bandages. Pressure should be applied as a temporary measure to control arterial hemorrhage but definitive control of arterial bleeding using a hemostat followed by ligation should be achieved as soon as possible.
Gloves should be worn whenever wounds are evaluated since infections often come from the hospital environment, both from the floors and cage surfaces, as well as the nurses' and doctor's hands. The wound should be kept as clean as possible by covering it with a sterile dressing. Wounds should be kept moist using sterile water-soluble gel or saline-soaked gauze since desiccation interferes with wound healing. If the wound is over the chest wall a patch bandage should be placed over the wound. The ventral aspect of the bandage should not be adhered to the chest wall. This will prevent a tension pneumothorax from developing if the patient has a lung laceration. If the wound is associated with a fracture then a padded bandage or temporary splint should be applied until the patient can be completely evaluated. This helps prevent further mechanical injury to the tissues from the tearing effects of bone fragments. It also helps to prevent further injury to the bone and provides comfort to the patient. Radiographs can be taken through most bandage materials; therefore, an attempt always should be made to stabilize fractures prior to taking radiographs. Broad spectrum antibiotics should be administered.
Aggressive attempts should be made to maintain normothermia since hypothermia can lead to cardiac arrhythmias, hypotension, coagulation problems, and sluggish blood flow. Warm water circulating blankets, fluid warmers, warm air circulating blankets, oat bags, warmed bubble wrap, and warming the inspired air are measures that can be taken to try and maintain the patient's body temperature.
The type of diagnostic tests required will be dictated by the type of wound. Blood work should consist of a minimum of a packed cell volume, total solids, electrolytes, glucose, blood urea nitrogen, and a blood gas. Albumin and coagulation parameters should be assessed in patients with more severe injuries. Ideally a complete blood cell count and a chemistry panel should be evaluated with older and more critical patients. An electrocardiogram should be performed in any patient with an auscultable arrhythmia or chest trauma. A thoracentesis to check for air and blood should be performed in every patient that has a wound over the thoracic cavity. Radiographs are indicated in any wound that may be associated with an open fracture, joints, and thoracic or abdominal cavities. Diagnostic peritoneal lavage should be performed in cases where the wound is over the region of the abdominal cavity and it is not certain if the abdomen was penetrated or not. Abdominal ultrasound is very useful for detecting free fluid within body cavities and may help diagnose intraabdominal injuries.
Proper assessment of most wounds requires some form of analgesia at a minimum and may require general anesthesia. The injury is painful and even if the patient is stoic attention should be paid to providing adequate analgesia. All wounds should be widely clipped in order to be able to assess them properly. This includes abrasions and bruises. Frequently, animals that are bitten have been impaled by both mandibular and maxillary 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 wound.
The goal of anesthesia in all patients is to ensure amnesia and analgesia. Analgesic drugs should be continued intraoperatively. If the patient seems to be responding to surgical stimuli additional analgesics may be indicated as opposed to just more inhalant anesthetic to mask the actual problem. This will help ensure a smoother recovery. In critical patients neurolept anesthesia (combination of an opioid and a tranquilizer) may be all that is required to provide adequate anesthesia. While some drugs such as ketamine provide some analgesia it should be kept in mind that many drugs commonly used such as propofol and isoflurane have no analgesic properties.
Patients should be preoxygenated and intravenous anesthetic agents should be used to provide rapid induction. Neurolept anesthesia may be all that is required. Once the patient is intubated the lungs should be ausculted bilaterally to ensure the air is moving through all lung fields. Drugs that decrease cardiac output or cause vasodilation should be avoided whenever possible. This includes inhalants such as isoflurane and sevoflurane which are two of the worst vasodilators available to veterinarians. Once the patient is intubated positive pressure ventilation should be instituted. Positive pressure ventilation should be continued until the patient is ventilating well on its own postoperatively based on assessment of capnometry or blood gases. In the author's experience hypoventilation is one of the major causes of instability during surgery as well as postoperative recovery problems.
Close monitoring is essential during anesthesia. Physical exam parameters as well as more advanced monitoring are indicated. Capnometry should be continually assessed intraoperatively and during recovery. Blood pressure monitoring preferably using a Doppler ultrasonic flow detector is indicated. Hypotension (systolic blood pressure less than 100 mm Hg and diastolic pressure less than 60 mm Hg) should be aggressively controlled. Vasoconstrictive agents should be used only if absolutely necessary since they may cause tissue hypoxia. Electrocardiography also should be assessed continually for evidence of tall T waves indicating myocardial hypoxia and premature ventricular contractions.
It is important to ensure that appropriate venous access is available intraoperatively if drugs need to be administered periodically. T-ports should be placed on at least one catheter since drug volumes are often very small and need to be given close to the catheter to ensure rapid absorption.
Overview of Surgical Management
The goal of surgical management of wounds should be to explore and remove any foreign material, control hemorrhage, and remove necrotic tissue. Many wounds will require the use of general anesthesia; however, superficial wounds that do not require extensive debridement can be managed under sedation and local anesthesia. The wound should be widely clipped and surgically prepped. This is very important since the extensive nature of the trauma can be easily underestimated based on external visualization.
Wound and body cavity irrigation form an important part of any surgical procedures. "Dilution is the solution to pollution." The use of sterile isotonic solutions is preferred. Tap water has been used to irrigate wounds without complication; however, tap water is not ideal due to its hypotonicity. Antibiotics should not be added to irrigation fluids since this may lead to bacterial resistance and extreme care should be exercised when adding disinfectants to irrigation fluids. Body cavities should be irrigated with sterile isotonic fluid only. Irrigation can be provided using mechanical lavage systems designed for wound irrigation or using a 35 ml syringe and an 18- to 19-gauge needle. Pressure generated by the irrigator ideally should not exceed 7-9 PSI although some commercial irrigators generate 15 PSI which appears to be safe. Irrigation should not be done blindly or up into holes since this may force infection or foreign material further into the wound or potentially into healthy tissues. This can actually make the wound worse.
Hemostasis generally is achieved by direct pressure, suturing of wounds (compression of vessels), electrosurgery, ligation of vessels, vascular clips, omental packing, use of superglue, use of hemostatic agents or removal of the organ that may be bleeding. There are numerous products available for hemostasis many of which are based on gelatin, fibrin, bovine thrombin, seaweed and a variety of other natural products that have hemostatic qualities. Electrosurgery is indispensable for rapid and efficient control of hemorrhage in critically ill or injured patients who are predisposed to being anemic and have coagulopathies. It causes heat-induced protein denaturation and tissue coagulation and can be used to control hemorrhage from arteries up to 1 mm and veins up to 2 mm in diameter.
The skin should always be incised in order to be able to visualize and assess the entire wound. Most mistakes in wound care come from a lack of knowledge about the extent of the trauma because the wound was not adequately explored. Tissues should be debrided back to bleeding edges whenever possible using sharp dissection. This is especially important with fat and muscle. Bone and ligament should be removed if the surgeon is certain it is nonviable but if there is any doubt the tissue should remain since removal may interfere with subsequent function of the affected area. Skin edges of wounds should be debrided using sharp dissection back to bleeding edges unless this might cause problems with wound closure. Scissors generally should not be used since they may cause crushing of the tissue, which can compromise circulation to the wound edges and cause problems with healing.
Wounds should be irrigated again prior to closing the skin to remove any additional foreign material and blood. The presence of blood provides an ideal medium for bacterial proliferation. If there is any doubt about viability of tissues the wound should not be closed initially. Instead wet-to-dry dressings should be placed and the wound should be revaluated on a daily basis. Daily debridement should be performed as necessary until the health of the tissues is assured. Wounds should be cultured prior to closure since multiple species of bacteria have been identified in dog bite wounds and no one antibiotic has been shown to be effective.
The amount of suture left in wounds should be minimized. Skin sutures should not be placed tightly since again this may compromise circulation. Wounds should not be closed under tension since this will compromise wound healing. Skin can either be mobilized by undermining of healthy tissues or grafting should be used as needed.
Dead space can only be closed effectively using active suction drains or bandages. Both drains and bandages will help enhance wound healing and prevent seroma formation. Sutures can be used to approximate tissues but cannot close dead space. Using sutures to "close dead space" should be avoided since it can create compartmentalization and the amount of foreign material (suture) left in the wound is increased.
Two types of drains exist--passive and active. Passive drains such as Penrose drains allow wound exudate to drain by gravity or overflow. The most serious complication associated with Penrose drains is the risk of ascending infection and ideally Penrose drains should be covered with a sterile dressing. Active drains remove wound fluids by application of negative pressure. Fenestrated drains are attached to a suction bulb that is primed by removal of air. These are available commercially in sizes ranging from 4 to 20 French. Drain suction bulbs are emptied as necessary--usually 2-4 times per day and cytology is evaluated as indicated. Drains are left in place until they are no longer functional or until they are no longer needed. Drainage will slow down within 72 hours in most wounds. If a large amount of dead space was created the drains may need to stay in place for up to 5-14 days.
Bandages are designed to protect the wound and encourage wound healing. They can also provide support to underlying tissues and help improve patient comfort and mobility. Contaminated or infected wounds should have wet-to-dry dressings placed until the wound is clean. When wet-to-dry bandages are removed they will help mechanically debride remaining foreign material and necrotic tissue. These dressings should be compromised of wide-meshed gauze, which will entrap particulate matter, soaked in 0.9% saline. Bandages should be placed over all surgical incisions for at least 24 hours until a fibrin seal has formed.
Postoperatively these patients will require close monitoring and treatment with a minimum of fluid therapy, analgesics, and antibiotics. Analgesics should be given on a scheduled basis but should also be given as needed since every patient's injury and tolerance to pain is different. Supplemental oxygen and/or ventilatory support may also be required. Urinary catheters should be placed in patients with difficulties with either ambulation or urination. Other treatment such as chest tube aspiration and care, care of suction drains and bandage changes will vary depending on the type of injury and the surgery performed. Monitoring will be dictated by the underlying trauma and status of the patient; however, a minimum of temperature, heart rate, respiratory rate and effort, and blood pressure should be assessed hourly until the patient is normothermic and stable. Critical patients will require blood work postoperatively; the tests will vary with the patient. Enteral nutritional support should be started within 6 to 12 hours which may require placement of a feeding tube.
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