Manage bite wounds: not just skin deep

Bite-wound management can present significant and daunting challenges to the veterinary practitioner. One reason is that the patient may present with several fairly small puncture wounds in the skin, but the damage underneath the skin may be far more serious and extensive due to the tearing and shearing caused by the large canine teeth.

Significant trauma to vital structures of the neck, thorax and abdominal cavity may not be immediately apparent at first glance. A bite-wound patient can also progress from being "stable" to "crashing" in a remarkably short time. The following discussion highlights major points in bite-wound management and is illustrated by a short case report.

Respiratory compromise:

In our practice, wounds to the head and neck of the canine victim account for a majority of all bite wounds inflicted by other dogs. This includes injuries to the upper respiratory tract, the larynx and the trachea. Also, bite wounds over the thorax may penetrate the pleural space causing a pneumothorax, hemothorax or a delayed pyothorax. If a bite-wound victim is in respiratory distress, it is important to determine whether it is upper-airway or lower-airway distress and should be treated accordingly.

In the upper airway, dogs can suffer from acute laryngeal paralysis if the recurrent laryngeal nerve, located adjacent to the trachea, is damaged from swelling or direct trauma. A common clinical sign associated with laryngeal paralysis is inspiratory stridor. Sedation with a low dose of acepromazine and/or butorphanol, or hydromorphone may be indicated. In cases that do not improve with sedation or in more extreme cases of cyanosis and hypoxia, immediate intubation and oxygen therapy may be necessary. A patient's temperature should be monitored closely as potentially life-threatening pyrexia may occur in cases of upper respiratory distress. The dog in Photo 1 suffered from bite wounds to the head and neck. On exploration of the wounds under anesthesia, there was significant soft-tissue damage in the ventral neck and evidence of penetration near the carotid sheath and trachea.

This dog is suffering from significant soft-tissue damage in the ventral neck and evidence of penetration near the carotid sheath and trachea as a result of bite wounds.

The damaged muscle was debrided and lavaged. When the patient was extubated, an inspiratory stridor and cyanosis were noted. Upon immediate re-intubation mucous-membrane color returned to normal. An oral examination revealed laryngeal paralysis. The suspected cause of the paralysis from inflammation effecting the recurrent laryngeal nerve along the trachea. A temporary tracheostomy was performed, and the tracheostomy tube was kept in place for four days while the swelling and inflammation resolved.

Lower-airway distress may be evident by tachypnea or dyspnea. Auscultation may reveal dull lung sounds, or crackles and wheezes. In a distressed and severely compromised patient, an immediate thoracocentesis may be indicated for diagnostic and therapeutic purposes. Radiography may prove helpful in making a diagnosis, but it is important to monitor for any respiratory distress and to minimize stress during this diagnostic test.

Shock

Every bite-wound victim should be evaluated for signs of shock. Patients in shock should be stabilized with intravenous fluids, broad-spectrum intravenous antibiotics, and, in some cases, a blood transfusion. Patients in shock should be monitored for sepsis and/or disseminated intravascular coagulation.

After initial stabilization, a full physical examination, including orthopedic and neurologic evaluation, should be performed. Bite wounds overlying the abdomen, with or without a puncture wound to the overlying skin, can cause significant internal damage, including internal hemorrhage, and gastrointestinal or urogenital perforation.

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Soft-tissue trauma

All patients with bite wounds penetrating the peritoneal cavity ideally should have a full abdominal exploratory after initial stabilization. Abdominal penetration may be evident by the herniation of abdominal contents, or the presence of free abdominal gas visible on radiographs, or by exploration of wounds with a blunt sterile instrument. All of the vasculature and organs should be evaluated for damage. The liver, spleen and vessels should be evaluated for active hemorrhage — a splenectomy or liver lobectomy may be necessary. If the gall bladder or bile ducts have been damaged, a cholecystectomy may be indicated. The gastrointestinal tract and the pancreas should be evaluated closely for perforation and cyanosis secondary to blood-supply disruption. Dogs that suffer from loss of circulation to a portion of the intestines can appear stable without exploratory until sudden collapse and death from sepsis and endo-toxemia days after the initial injury. Damage to the urogenital tract may require nephrectomy, ureter or urinary bladder repair. Evaluation of the diaphragm is also necessary to rule out a diaphragmatic hernia.

Management of individual wounds:

Of course, not all bite-wound patients are affected to this degree, but an exploration of the bite wounds is indicated in every bite-wound victim. Depending on the behavior of the patient and severity of wounds, exploration may be done awake with mild sedation or under general anesthesia. Each penetrating wound should be protected with a sterile lubricating jelly. The area around each wound should be clipped and cleaned. The wounds should then be probed with a blunt sterile instrument to evaluate the depth of penetration and lavaged copiously with sterile saline.

In many cases, wounds that extend under the skin and into muscle will need to be opened further to allow debridement of devitalized fat and muscle.

Drains

Bite wounds cause dead space and introduce infection. These wounds should be left open or allowed to drain properly. For small areas of dead space, a Penrose drain is effective, or simply leaving the wound open is often adequate. Penrose drains operate via gravity and capillary action over the outer surface of the drain. They should exit through healthy tissue ventral to the wound to facilitate drainage. Penrose drains are normally left in place for three to five days. A bandage should be placed over the drain if possible or the patient should be provided with an Elizabethan collar to prevent removal of the drain by the patient. In larger areas of dead space and in the abdominal cavity, closed suction drains are indicated. In larger subcutaneous areas of dead space, a closed suction drain can be used. These can be made with a fenestrated sterile extension set, a needle and a red-top blood collection tube. The red-top tube creates the vacuum and collects the accumulated fluid. The tube will need to be changed periodically when the vacuum is no longer effective and/or when the tube is full. In contaminated abdominal cavities, J-vac drains (Photo 2) can be used. These need to be recharged on a regular basis to allow continuous suction of accumulated fluids. All closed suction drains exiting the peritoneal cavity should be secured with a pursestring skin suture.

In contaminated abdominal cavities, J-vac drains can be used and recharged regularly to allow continuous suction of accumulated fluids.

Case study

The emergency and surgical services at Red Bank Veterinary Hospital manages a high number of bite-wound patients. Many of these patients are very stable, but many are critically injured. The following case study is an example of a critical patient that was recently managed at the hospital.

A 2 year-old, 4 kg male intact Yorkshire Terrier was attacked by a large-breed dog two hours prior to presentation. The referring veterinarian provided very good initial stabilization with a hetastarch bolus, an intravenous enrofloxacin and ampicillin. On presentation, the dog was laterally recumbent, hypothermic (95.4F), tachycardic (180 bpm), hypotensive (70 mmHg) and had grey/pink mucous membranes. Multiple puncture wounds were present along the dorsum and ventral abdomen. A body-wall hernia was palpable on the ventral abdominal wall. The PCV had decreased from 35 percent to 19 percent, and total protein had decreased from 4.2 dl/L to 2.5 dl/L over two hours. Persistent abdominal hemorrhage was suspected. Diagnostics were performed including a complete blood count, chemistry screen, PT/PTT and blood type. The albumin was too low to register, the leukocyte count was low (5.6 x 109/L), and the PTT was prolonged at 162 seconds (normal 71-102). We were concerned about hemorrhage, sepsis and DIC. An emergency abdominal exploratory was planned. Fresh frozen plasma was started prior to induction of anesthesia. Warmed crystalloid fluids had been started on presentation.

A ventral midline laparotomy revealed a perforation in the duodenum at the duodenocolic ligament and a perforation in the mid-jejunum. The mesenteric adventitia was not present, and there was only a denuded web of mesenteric vessels visible. The distal portion of the right limb of the pancreas was avulsed from its blood supply and cyanotic. The right dorsal body wall and the epaxial muscles were significantly devitalized, actively hemorrhaging and the wounds penetrated the abdominal cavity and retroperitoneal space. There was retroperitoneal hemorrhage surrounding the right kidney. The right ureter and blood supply to the right kidney appeared intact. There were three additional large abdominal wall hernias.

Treatment consisted of two intestinal resections and anastomoses, a partial pancreatectomy, debridement of devitalized muscle and repair of the multiple hernias. A J-vac drain was inserted in the abdominal cavity and a urinary catheter was placed. A stockinette was placed over the patient's body.

Post-operatively, the dog was managed with ampicillin, enrofloxacin, intermittent plasma doses (four doses over two days), hetastarch, crystalloids with postassium supplementation, metoclopramide CRI, famotidine and warm compresses. Urine output was recorded. The dog had yellow liquid diarrhea and was regurgitating bile for eight to nine days post operatively. He also had hemo-globinuria for four days post incident. The J-vac drain was removed five days after surgery when the volume of fluid accumulation had decreased. After seven days, he would eat small pieces of boiled chicken when hand-fed. His blood glucose, packed cell volume, total protein and electrolytes were monitored routinely. At discharged from the hospital 14 days after being bitten, he was ambulatory, eating and drinking without regurgitation, and had a soft, normal-colored stool. One month later the owners reported that he was resuming normal activity and doing well.

Unfortunately, not all bite-wound stories end this well. Thanks to the excellent care by the referring veterinarian, rapid treatment by our emergency and surgical teams, and the willingness of the owners to allow us to pursue aggressive treatment, this was a success story.

Tara Britt graduated from the University of Pennsylvania School of Veterinary Medicine in 2002. She completed a rotating internship in small animal medicine and surgery at Red Bank Veterinary Hospital and is currently a resident in small animal surgery at Red Bank Veterinary Hospital in Tinton Falls, New Jersey.

Dr. Thacher, a dipl. of the American College of Veterinary Surgeons, is section head for the Department of Surgery at Red Bank Veterinary Hospital. He served as Chief of Staff of Affiliated Animal Health, a consortium of 17 small animal hospitals in the NY/NJ area and is former chairman of the Animal Medical Center's (AMC) Department of Surgery. Dr. Thacher has delivered numerous presentations on surgery throughout the United States and Europe. He received his DVM from the University of California, Davis in 1980.