Wound management 2 – Penetrating injuries in dogs

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Wound management 2 – Penetrating injuries in dogs

Key points

When presented with a bite or bullet wound case, think “iceberg”: a small amount of surface damage often belies a large amount of damage in the deeper tissues!

Endoscopy allows early detection of esophageal perforations before clinical signs appear.

Penetrating wounds should be opened, explored, debrided, and lavaged; they are usually then best managed as open wounds. If wounds require closure, they should be closed over a drain.

If there is a penetrating wound (or suspicion thereof) or significant crush injury to the abdomen, exploratory celiotomy is indicated.

Foreign objects lodged in the body are best removed via a surgical approach in an operating theatre with an anesthetized, fully prepared patient.

Introduction

Penetrating wounds are often deceiving! An innocuous-looking skin puncture may overlie tissue that has been significantly compromised by strong forces, vascular damage, and/or inoculation of bacteria or foreign material. Even if the animal appears stable initially, continuing deterioration of damaged tissue can lead to necrosis, infection, inflammation, sepsis and death. Effective management of penetrating wounds requires first and foremost that the clinician recognizes small wounds can hide severe damage.

Forces and tissue damage

A dog bite can generate over 450 psi (pounds per square inch) of force [1], causing both direct and collateral damage to tissues. When the attacker’s canine teeth penetrate the skin and the attacker shakes its head, the elasticity of skin allows it to move along with the teeth, so only puncture holes are made in the skin. Subdermally, however, the teeth shear through a wide area of less mobile tissue, avulsing skin from muscle, tearing soft tissue and neurovascular structures, creating dead space, and inoculating bacteria and foreign material. All of this injury is further compounded by the crushing forces exerted by the premolars and molars.

Like bites, bullets cause both direct and collateral damage (Figure 1), imparting energy proportional to their mass and velocity [Kinetic Energy = ½ x mass x velocity²]. Dense tissues (e.g., liver, spleen,bone) absorb more energy than less dense, more elastic tissues (e.g., muscle and lung), which explains why cortical bone hit by a bullet may shatter into multiple pieces (each of which becomes a new projectile) while an identical bullet with the same energy can pass cleanly through a lung lobe. Cavitation – the pressure wave created by a projectile – can mean that a bullet may fracture bones, tear vessels, rupture bowel, and contuse organs that the missile never contacts directly.

Figure 1.(a) A bullet enters the body, carrying bacteria and debris (green) from the skin surface. The permanent cavity (white) is created as the bullet moves through tissue directly in its path. The temporary cavity (pink) is created as the cavitation energy moves ahead and perpendicular to the bullet (pink arrows), damaging tissue via compression.(b) Cavitation energy expands along paths of lesser resistance, such as the fascial plane between muscles (asterisks). Tissue that is not flexible or that is compressed against bone by cavitation can fracture (dashed lines), as can tissues that rebound back together after the cavitation energy dissipates. The bullet’s passage creates a vacuum that draws in more bacteria and debris.(c) Tissues can be damaged (mottled grey, dashed lines) by cavitation although untouched by the bullet.© Bonnie Campbell

The term “iceberg effect” can be used to describe bite and bullet wounds, because the small amount of damage seen on the skin often belies a large amount of damage underneath. In subdermal tissues, necrosis, hematomas, compromised vasculature, dead space, inoculated bacteria, and foreign material stimulate local inflammatory, immunologic, coagulation, and fibrinolytic cascades. With insufficient treatment, these cascades may overwhelm the body’s controls, resulting in systemic inflammatory response syndrome (SIRS) or sepsis (SIRS + infection) [2] [3] [4]. Patients can appear stable even as the body is ramping up to SIRS, and then acutely decompensate several days after injury. The clinician needs to think about the iceberg effect from the start and be proactive to stop progression to SIRS.

Other penetrating injuries can occur from sticks (e.g., when playing “fetch”, running into a stick in the field) or other environmental objects. The amount of energy imparted depends on mass and velocity (of the object or the dog, whichever is moving), and the iceberg effect occurs due to the blunt trauma associated with objects that are not aerodynamic.

Patient assessment

Immediately life-threatening injuries such as bleeding and respiratory compromise should be managed first. Wounds over the chest should be covered immediately with a sterile dressing in case they penetrate into the thorax. Ultimately, a full physical exam is performed, including orthopedic and neurologic assessments, and all wounds are examined. This may require extensive shaving; dogs that have been bitten typically have wounds in multiple locations [5] [6].

Diagnostic work-up is tailored to the patient’s injuries. Hematology and serum chemistry panels provide baseline values as well as evidence of organ compromise due to the injury itself, SIRS, or sepsis. Elevations in lactate and creatine kinase reflect the degree of tissue damage. Orthogonal radiographs, ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) can help determine the path of the penetrating injury, locate foreign material, and define orthopedic damage and internal injuries, although damage to soft tissues, including viscera, cannot be ruled out with imaging alone [3] [4] [7] [8]. If the number of intact bullets seen with imaging cannot be reconciled with the number of entry and exit holes seen on the patient, look for stray bullets with additional images or shave further to find additional wounds.

A number of key structures are at risk with penetrating wounds to the neck [9]. Severe hemorrhage may indicate laceration of a carotid artery or jugular vein; if necessary, both carotids and/or both jugulars can be ligated at the same time in dogs, assuming normal collateral circulation is intact. Tracheal perforation should be suspected in patients with neck wounds and extreme subcutaneous emphysema or pneumomediastinum (Figure 2). The esophagus is also at risk of puncture, but clinical signs may not be apparent for several days, during which time ingested food or water accumulates in the cervical tissues. It is thus prudent to scope the esophagus when there are deep wounds to the neck; tracheal damage can also be assessed while scoping.

Figure 2a. A nine-year-old Border Collie which had been attacked by another dog. Shaving revealed multiple cervical bite wounds (dorsal recumbency, cranial to the left).© Washington State University

Figure 2b. A nine-year-old Border Collie which had been attacked by another dog. Cervical radiographs show severe subcutaneous emphysema and pneumomediastinum. A 1 cm diameter puncture was found in the trachea at surgery.© Washington State University

Figure 2c. A nine-year-old Border Collie which had been attacked by another dog. Thoracic radiographs show severe subcutaneous emphysema and pneumomediastinum. A 1 cm diameter puncture was found in the trachea at surgery.© Washington State University

Surgical management

Surgical exploration is needed to fully assess the extent of trauma caused by penetrating injuries [2] [3] [7]. Furthermore, thorough debridement of devitalized, contaminated tissue is the only effective way to prevent or treat SIRS or sepsis. Thus, penetrating wounds should be opened, explored, debrided, and lavaged early on [2] [3]. If the damage ended directly below the skin, the surgery has been minor. If the damage continued into deeper tissue and/or if foreign material was lodged inside, surgery can prevent considerable morbidity and even mortality.

A large area should be prepped for surgery, since the path(s) of penetration may deviate in the deeper tissues. The surgeon should be prepared to enter the abdomen or chest if necessary. Entry and exit wounds are opened, the underlying tissue is visualized, and path of injury is followed to its deepest extent, debriding damaged tissue along the way (Figure 3) [2]. In bite wound victims, one can commonly insert a hemostat into one wound and exit it out a number of others due to avulsion of skin that has occurred (Figure 3a). When there are multiple bite wounds in an area, one longer incision can be made to access the tissue deep to all of these bite wounds at once.

An instrument or rubber tube can be inserted into the wound tract to aid dissection. It is common to see increasing tissue damage as one follows the tract into deeper tissue (Figure 3). Walls separating areas of dead space should be broken down and tissue that is clearly necrotic excised – no matter how much the clinician may wish to save it – as leaving it perpetuates inflammation, blocks granulation, and increases the risk of infection. Signs of necrosis include abnormal color and consistency (dry necrotic tissue is dark/black and leathery; moist necrotic tissue is yellow/gray/white and slimy) and lack of bleeding when cut (assuming the patient is not hypothermic or hypovolemic). Debridement should be continued until viable tissue is reached. Guidelines for debridement of tissue with uncertain viability are in Table 1.

Table 1. Guidelines for debridement of tissue with uncertain viability*.
“When in doubt, cut it out” if:	“When in doubt, leave it in” if:
removal is compatible with life	removal is incompatible with life
And	Or
there is only one opportunity to access and assess the tissue	there will be multiple opportunities to access and assess the tissue
And/Or	And
there is plenty of residual tissue so it will not be missed	the tissue will be valuable for later wound closure
Examples – damaged muscle deep in a wound; damaged spleen, jejunum, liver lobe, or lung lobe	Examples – damage to the one working kidney; damaged skin on a distal limb, where there is limited skin available for repair

* Uncertain viability i.e., it is unclear whether the tissue will survive; it has some signs of viability and some signs that it is dying; clearly necrotic tissue should be removed.

Figure 3a. A four-year-old Yorkshire Terrier bitten over the cranial thorax by another dog. Hemostats were easily passed from one bite wound to the next due to the disruption of underlying tissue. The skin overlying the hemostats was incised along the dotted line.© Washington State University

Figure 3b. A four-year-old Yorkshire Terrier bitten over the cranial thorax by another dog. Unhealthy tissue and a deep tract (probed with an instrument) were present below the incision.© Washington State University

Figure 3c. A four-year-old Yorkshire Terrier bitten over the cranial thorax by another dog. As the tract was opened up, additional tissue damage and multiple other puncture tracts (circled) were found. These tracts were followed, unhealthy tissue was debrided, and the surgery site closed over a suction drain after copious lavage.© Washington State University

Figure 3d. In this photo of a different dog, unhealthy muscle is being excised using a similar technique.© Washington State University

Debridement is followed by copious lavage at 7-8 psi, which maximizes removal of debris and bacteria while minimizing tissue damage (Figure 4). Avoid pressurized lavage on fragile organs. Lavage of abdominal and thoracic cavities should be with sterile saline alone, but antiseptic solutions (not scrubs) can be used in subcutaneous tissues and muscle. Appropriate concentrations are 0.05% chlorhexidine solution (e.g., 25 mL of 2% chlorhexidine + 975 mL diluent) or 0.1%-1% povidone-iodine solution (e.g., 10 mL of 10% P-I + 990 mL diluent for 0.1%; 100 mL of 10% P-I + 900 mL diluent for 1%).

Figure 4a.The desired lavage pressure of 7-8 psi is best achieved via a needle (16-22 G) on a standard intravenous drip set attached to a bag of fluids pressurized to 300 mmHg with an emergency pressure sleeve 22. Washington State University

Figure 4b.The desired lavage pressure of 7-8 psi is best achieved via a needle (16-22 G) on a standard intravenous drip set attached to a bag of fluids pressurized to 300 mmHg with an emergency pressure sleeve 22. Washington State University

Figure 4c.The debrided wound from the dog in Figure 2 is held open with a ring retractor (green) for lavage with 0.05% chlorhexidine solution.© Washington State University

The debrided wound is left open and managed with moist wound healing [10] and serial debridement and lavage as needed. The wound is closed once the veterinarian is confident it is free of contaminants, necrotic tissue, and unhealthy tissue that might necrose later. If a wound must be closed before that point, a drain (preferably a closed, active suction drain) should be placed and covered with a bandage [11]. Post-operative care also includes fluid support as needed, analgesics, and good nutrition with a recovery diet to support the healing process. In highly compromised patients, consider placing a feeding tube during anesthesia to ensure adequate nutrition during recovery.

More conservative debridement and lavage may be considered for superficial and/or low severity non-abdominal penetrating injuries [12] [13]. For example, damage caused by a single, non-tumbling, non-deforming bullet passing only through skin and muscle may be limited to the permanent cavity since these elastic tissues can handle a lot of cavitation energy. A similar effect may be created by penetration with a sharp, smooth, clean foreign body.

Wounds to the abdominal or thoracic cavity

Without surgery It can be difficult to determine if penetration of a body cavity has occurred. Penetrating wounds can be probed to assess their extent, but they may not follow a straight path and thus the probe may not be able to follow the tract to its end. Abdomino- or thoraco-centesis may reveal air, blood, urine, bile, ingesta, or purulence indicative of body cavity penetration, but a negative tap does not rule this out. Imaging may show free air/fluid, foreign material, or damaged tissues consistent with cavity penetration, but normal images do not rule out internal injury [3] [4] [7] [8] [14].

If there is a penetrating abdominal wound (or suspicion thereof) or significant abdominal crush injury, exploratory celiotomy is indicated at the time of presentation because:

There is a high risk of intestinal damage

Untreated intestinal perforation is life-threatening, and clinical signs may not be apparent until there is full-blown septic peritonitis and septicemia

Normal test results do not exclude internal injury (see above)

Intestines are constantly moving, so the damage cannot be reliably found just by following the wound tract through the body wall

While this “default celiotomy” approach will result in some negative abdominal explores, the risk-benefit ratio is squarely on the side of surgery even if penetration is unproven [2] [5] [13] [15].

Penetrating wounds over the thorax are opened, debrided, lavaged, and explored as for any wound; this may take the surgeon into the thoracic cavity. However, unlike an abdominal penetration, full exploration of the thoracic cavity is not the default, as:

The rib cage makes it challenging for penetrating objects that are not correctly aligned to enter the chest

The elasticity of the lung makes it less susceptible to penetration and associated collateral damage

The lungs are not laden with bacteria

Exploratory thoracotomy is indicated when hemothorax or pneumothorax is not responsive to stabilization measures.

Penetrating wounds into internal organs are debrided and lavaged. The small diameter of intestine makes adequate debridement difficult, so affected areas are treated with resection and anastomosis. Liver lobectomy, splenectomy, and lung lobectomy are usually the most efficacious ways to manage wounds in these tissues. More complex procedures may be required to resect damaged tissue in non-redundant organs.

Removal of penetrating objects

There are risks associated with removing a foreign body lodged in tissues; these include bleeding from holes in major vessels previously plugged by the foreign body, additional tissue damage caused by barb-like projections on the foreign body, and/or leaving behind fragments of foreign material (e.g., pieces of bark from a stick). It is therefore best to remove foreign material via a surgical approach in an operating theatre with an anesthetized, fully prepped patient. Because foreign material can migrate due to body motion or gravity, images used to guide surgery should be current.

Retained organic or non-organic material can cause inflammation, infection, and/or chronic draining tracts, so removal is indicated if the reaction is causing significant clinical signs or if vital structures are at risk should the object migrate. The inflammation associated with steel shot (which is 99% iron) tends to be self-limiting after two to eight weeks in dogs, so it may not need to be removed. Lead bullets in soft tissues are typically walled off by fibrous tissue and do not pose a poisoning risk [12] [16] [17]. However, lead in the gastrointestinal tract or in contact with cerebrospinal fluid can cause toxicosis, and lead within a joint can cause destructive synovitis, so removal of bullets in these areas may be prudent [17] [18] [19].

Two dissection techniques can be used to remove a penetrating object. In the first, an incision is made alongside the foreign body or down its tract until the material can be removed without resistance. In the second technique, the entire tract and foreign body are removed as a unit, similar to removing a neoplasm with margins (Figure 5). This technique maximizes the chance of removing all foreign material and associated unhealthy or contaminated tissue. After removing the foreign body with either technique, surrounding tissue is debrided further as needed, lavaged, and the tract is left open to heal on its own or closed over a drain [11].

Figure 5a. A 4-year-old castrated male Border Collie crossbreed presented for a recurrent draining tract cranial to the left shoulder that had been treated with antibiotics, surgical exploration, and drainage. Five months earlier, the dog had surgery for a hard palate injury from playing with a stick. Serial radiographs around the draining tract had not shown any foreign body, but the stick, which must have entered the neck after penetrating the oropharynx, was seen on MRI.© Washington State University

Figure 5b.The stick and surrounding tract were dissected out en bloc from the neck.© Washington State University

Figure 5c. The stick can be seen emerging from the excised tract after removal.© Washington State University

Use of antibiotics

The question can be asked: are antibiotics indicated for all penetrating wounds? Such wounds are contaminated with bacteria and debris, and the risk of infection increases with the amount of tissue damage and vascular compromise. While antibiotics are typically given during surgery, proper debridement and lavage are pivotal to minimizing the risk of contamination turning into infection; antibiotics do not replace the need for local wound care [3] [20]! Antibiotics can be stopped post-operatively for shallow, minimally contaminated wounds surgically converted to clean [3] [19]. Post-operative antibiotics are clearly indicated in patients with extensive tissue damage, open joint or fracture, sheared bone, SIRS, immunocompromise, and actual infection [1] [2] [19] [21]. In between these two groups, the decision is less clear cut and must be tailored to the individual, factoring in the need to avoid unnecessary use of antibiotics due to multi-resistant bacteria. For patients with infected wounds, antibiotic choice is ultimately based on aerobic and anaerobic cultures. Culture of a piece of tissue cut from deep in the wound is the most reliable, followed by culture of purulent material; culture of the wound surface is least desirable due to surface contaminants.

Conclusion

Recognition of the iceberg effect is important for thorough treatment of penetrating wounds. Early, pre-emptive debridement and lavage of penetrating wounds prevents the development of SIRS or sepsis several days after injury. If penetration of the abdominal cavity cannot be ruled out, the abdomen should be explored due to the high risk for intestinal perforation.

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Bonnie Campbell

DVM, PhD, Dip. ACVS

Dr. Campbell received her DVM and PhD degrees from Cornell University. She completed a small animal surgical residency at the University of Wisconsin and is a Diplomate of the American College of Veterinary Surgeons. Dr. Campbell is now a Clinical Associate Professor of Small Animal Soft Tissue Surgery at Washington State University, with particular clinical interests including wound management and reconstructive surgery. She gives continuing education programs both nationally and internationally and has served as president of both the Society of Veterinary Soft Tissue Surgery and the Veterinary Wound Management Society.