>> List the different classifications of penetrating trauma.
>> Recognize the mechanisms of injury for penetrating trauma.
>> Understand the pathophysiology associated with penetrating trauma wounds.
>> Learn the treatments for patients with penetrating trauma.
Ballistics: The study of projectiles, their movement and impact. Although this term applies to any projectile, it’s most often used to refer to bullets and their damage.
Cavitation: The formation of a cavity, such as from a high-velocity projectile striking the body.
Hypotension: Lowered systolic and diastolic blood pressure.
Kinetics: The study of forces that produce or modify motion.
Perfusion: Supplying an organ or tissue with nutrients and oxygen via the circulatory system.
Yaw: The vertical axis of three-dimensional movement.
Most trauma cases you encounter in your career will be due to blunt trauma mechanisms, such as falls, motor vehicle collisions (MVCs) and similar events. However, you’ll certainly encounter patients who have sustained penetrating trauma. Penetrating trauma is an injury (or injuries) that occurs when an object pierces the skin and enters the body. Perforating trauma, a form of penetrating trauma, occurs when an object enters and exits the body. Both can have devastating consequences.
Overview and Incidence
The most common causes of penetrating trauma in the U.S. are gunshots and stabbings. Despite the widespread availability of guns in the U.S., penetrating trauma is relatively less common than one would expect.1 However, the U.S. still leads all economically developed countries in firearms-related deaths.2 In a recent study of 157,045 trauma patients treated at 125 U.S. trauma centers, researchers found the incidence of penetrating trauma to be significantly less than blunt trauma. Only 6.4% of all injuries were gunshots while only 1.5% were stab wounds.3 Yet, significant geographic variations and racial differences in the incidence of penetrating trauma exist. In a Los Angeles study of 12,254 trauma patients, 24% of patients treated had sustained penetrating trauma. In a similar Los Angeles study, penetrating trauma accounted for 20.4% of trauma cases, yet resulted in 50% of overall trauma deaths—most of which were due to gunshot wounds.4–5 Because of the higher mortality seen with penetrating trauma, EMS personnel must be quick to identify these injuries and rapidly deliver the patient to the closest appropriate trauma center.
Kinematics of Penetrating Trauma
Trauma results from the exchange of energy between an object and the human body. In the case of penetrating trauma, the object is often a projectile or knife. However, fence posts, nails, pencils and similar sharp objects can also penetrate the human body and cause injury.
The exchange of energy in trauma (both blunt and penetrating) can be described with the kinetic energy equation:
Kinetic Energy= Mass (Weight) x Velocity (Speed)2/2
Stated another way:
Kinectic Energy= 1/2 Mass (Weight) x Velocity (Speed)2
The greater the mass (or weight) of the object, the greater the resultant energy exchange. Dropping a 12 lb. bowling ball on your foot will cause more injury than a 5 oz. baseball. Velocity (speed), however, plays a more important role. Doubling the speed of an object increases the kinetic energy fourfold. In terms of ballistics, a small and fast bullet can cause more damage than one that’s large and slow. This is because velocity is more of a factor in energy exchange than mass. Thus, knife wounds tend to be less severe because they’re usually delivered with less velocity.
We typically classify the forms o-f penetrating trauma based on the rules governed by the kinetic energy equation (see Table 1 above). When discussing ballistics, we’re almost always talking about projectiles fired from a gun. A projectile fired from a gun will follow a flight path that’s typically divided into three stages: travel down the barrel of the gun, travel through the air and travel through the target (also called terminal ballistics). Generally speaking, projectiles fired from a rifle have considerably more energy than similar bullets fired from a handgun. Table 2 (above) illustrates the speed and energy of common handgun rounds. Energy and velocity are typically recorded as the bullet leaves the muzzle of the gun but can also be measured away from the gun.
Table 3 (above) illustrates the speed and energy of common rifle rounds. Certainly wounds from rifles, especially assault rifles, transmit a tremendous amount of energy and can cause significant damage to the human body. Although ballistics may seem unimportant to EMS providers, some basic knowledge will help you to estimate the potential for injury based on the caliber and type of the weapon involved.
When a projectile strikes the human body, it slows, and energy is transferred to the body. Remember, as detailed in the law of conservation of energy, energy can be neither created nor destroyed. It can only be changed. Numerous factors affect the injury or injuries created by projectiles. These are often hard to quantify but include the size and shape of the projectile (mushroom), the velocity of the projectile, the spin (if any) and yaw (twist or oscillate about a vertical axis) and tumble of the projectile, fragmentation of the projectile, the distance from the gun to the target and the type of tissue struck. Various body tissues respond differently to a projectile based on their density, resiliency, content and similar factors.
Connective tissues that readily absorbed kinetic energy would serve to limit tissue damage. Bones, on the other hand, readily break and fragment when contracted by a projectile. The effect of penetrating trauma on organs depends on the organ type. Solid organs are dense and have low resiliency. They’re vulnerable to fracture with significant injuries. Hollow organs, on the other hand, are either fluid- or air-filled (or both). Because of the density of fluid as opposed to air, fluid-filled organs tend to sustain greater damage than those, such as the lung, that are air-filled.
Injury begins when the tip of the projectile impacts the body tissue. The tissues are then pushed forward and laterally and subsequently collide with adjacent tissues, causing damage. Generally speaking, injury from penetrating trauma occurs through three different mechanisms.
1. Tearing and crushing of the tissues: This occurs along the projectile track and from fragments that may break off from the projectile.
2. Cavitation: When a high-energy projectile travels through the relatively liquid human body, it forms a cavity along the track of the bullet. In actuality, there is both a permanent and a temporary cavity formed. As a bullet moves through the tissues the energy of the bullet causes a temporary radial stretching, forming a cavity that soon closes as the energy is dissipated. However, within the central portion of the projectile path there will be enough tissue damage to cause a permanent cavity. For low-velocity weapons, such as knives, there’s little difference between the permanent and temporary cavity. As the energy of the projectile increases, however, the size of the temporary cavity increases accordingly. In essence, a considerable amount of damage is done by the formation of the temporary cavity. This is why high-velocity/high-energy weapons can cause so much more damage.
3. Shock wave: This is a rapid change in pressure, temperature or density secondary to the projectile. In high-energy, high-velocity weapons, shock waves can sometimes approach 200 atmospheres of pressure. The shock wave generated by the bullet usually lasts only a few microseconds. However, the result can be extremely damaging.
Several factors related to the bullet affect the subsequent injury. One of these is the bullet’s profile. The profile is the size and shape of the bullet as it contacts the human body. The larger the profile, the greater will be the rate of subsequent energy exchange. Most bullets will rotate or tumble somewhat on their axis during travel. Yaw often takes the bullet slightly off of its course. This can occur during travel through the air or as the bullet strikes the body. Short, high-velocity bullets tend to yaw and rotate more severely when they strike human tissue. Rifles contain grooves within the barrel (rifling) that imparts a spin on the projectile that serves to minimize yaw and tumble. Thus, the greater the yaw or tumble of a projectile, the more rapid the subsequent delivery of kinetic energy and resultant damage.
The shape of the bullet also affects the subsequent energy delivery. Some bullets are designed to expand when they strike an object, causing more injury. Various international military conventions, such as the Hague Convention of 1899 and the Geneva Convention of 1949, forbid the use of expandable bullets in war. Military bullets must have a full metal jacket. However, expandable bullets are widely available in the civilian sector and used in hunting, security and similar endeavors.
Pathophysiology of Penetrating Trauma
Penetrating trauma can impact all body regions, cavities and structures. These can include the head, neck, chest, abdomen and pelvis, and the extremities.
Head trauma: Penetrating head trauma has a high morbidity and mortality rate. It has been estimated that 50% of all trauma deaths are due to traumatic brain injury. Gunshot wounds to the head account for approximately 35% of these deaths. In the civilian sector, gunshot wounds account for the vast majority of penetrating head injuries. These may be accidental, self-inflicted (suicidal), or due to homicide or assault. Penetrating head trauma by suicide is associated with a higher rate of mortality than other types of penetrating brain injury. In the military sector, penetrating head injuries from shrapnel, shell fragments and debris are more common.6
Neck trauma: Penetrating neck injuries occur in approximately 5–10% of all trauma cases. The incidence of penetrating neck trauma in a military setting is considerably higher due to the lack of body armor protection for the neck. Numerous high-risk structures traverse the neck, including the spinal cord and column, the carotid arteries, the jugular veins, the vertebral arteries, the trachea, the esophagus and other significant structures. Thus, penetrating trauma to the neck can cause bleeding, respiratory, neurological problems, or any combination of these.
Fortunately, the mortality rate for patients with penetrating neck trauma is actually declining due to better imaging techniques and improved surgical strategies. From a prehospital standpoint, the biggest risk for patients with penetrating neck trauma is airway compromise and significant hemorrhage. These can be controlled in many cases until the patient is delivered to the trauma center and operating room.7
Chest trauma: Because of the size and location of the thoracic cavity, penetrating injuries to the chest are common. These can damage the chest wall, lungs, tracheobronchial structures, esophagus, diaphragm, great vessels and the heart. As one would expect, penetrating injuries of the heart are highly lethal with a fatality rate approaching 70–80%. The ventricles, primarily the right ventricle because of it larger size and proximity to the anterior thoracic wall relative to the left ventricle, are most commonly affected.
These injuries often result in an immediate pericardial tamponade that reduces cardiac output, causing shock. Similarly, injuries to the great vessels of the chest (especially the aorta, superior vena cava and pulmonary vessels) are also common with penetrating chest trauma. In fact, more than 90% of all great vessel injuries are due to a penetrating mechanism of injury. Historically, these injuries were uniformly fatal. However, the ability to now rapidly image the thorax and the great vessels and perform rapid emergency surgical intervention has reduced the mortality rate significantly.
Lung injuries are common with thoracic penetrating trauma and can cause pneumothorax, hemothorax or both. In addition to lung injuries, tracheobronchial injuries can also occur with penetrating trauma. These injuries are almost always associated with injuries to other thoracic structures, such as the great vessels. Esophageal injuries are relatively rare. However, they can have significant long-term complications. The diaphragm, the muscle separating the abdominal cavity from the thoracic cavity, is frequently injured in penetrating trauma to the trunk (chest and abdomen). Diaphragmatic injuries occur in approximately 45% of gunshot wounds and 15% of stab wounds to trunk.8
Abdominal/Pelvic trauma: The abdomen and pelvis are also quite vulnerable to penetrating trauma. These two body cavities contain numerous organs and associated structures. As with other types of penetrating trauma, most penetrating injuries to the abdomen result from gunshot wounds. The abdominal and pelvic structures injured in cases of penetrating trauma are somewhat dependent on the mechanism of injury (see Table 4 above).
The fatality rate for abdominal penetrating wounds varies significantly based on the structures injured and the magnitude of the injury. The average mortality rate for all penetrating abdominal injuries is approximately 5%. Intra-abdominal vascular injuries have a higher mortality rate. Interestingly, most deaths from penetrating trauma occur within six hours of hospital admission and often in the emergency department or operating room.
Most deaths from blunt abdominal trauma tend to occur later (within 72 hours) and occur in the intensive care unit setting. Factors associated with increased mortality from penetrating abdominal trauma include the presence of shock on admission to the hospital, massive hemorrhage, a long time interval between the injury and subsequent surgery, female gender and coexisting brain injury.9 The organs and structures of the pelvis are relatively well protected from penetrating trauma. However, projectiles that enter the pelvis can certainly damage genitourinary and reproductive structures. This is particularly prevalent in pregnant patients where the gravid uterus fills the pelvic cavity and the lower portions of the abdomen. External structures, such as the penis and scrotum, can also be injured with penetrating trauma.
Extremity trauma: Penetrating injuries to the extremities are common. The mechanism is somewhat different between the civilian and military experience. The widespread usage of body armor in the Iraqi and Afghan conflicts resulted in an increased relative incidence of extremity trauma. Although the torso is well protected from injury with body armor, the extremities are vulnerable. Any of the anatomical structures within the extremity—bone, muscle, tendon, ligament, nerve or blood vessel—can be affected. Most extremity injuries are not life threatening. However, vascular extremity injuries can be both life and limb threatening. Injuries to nerves and tendons can result in lifelong disabilities. Although gunshots and stab wounds are seen in penetrating extremity trauma, there are other causes. These include nails and similar sharp objects, liquid under pressure (such as grease), and lacerations and punctures with various tools (saws, drills). Again, the energy with which these are applied is related to the severity of the result of trauma.
In essence, prehospital assessment and treatment of the patient with penetrating trauma is essentially the same as that of the patient with blunt trauma and follows the tenets of the trauma life support courses. However, some subtle differences are worthy of noting.
All the victims of penetrating trauma should undergo a primary assessment to detect any immediate life threats. This includes airway maintenance, assessment of breathing and ventilation, control of hemorrhage and support of circulation, determination of neurologic status and adequate exposure of the patient for detailed examination.
Generally speaking, C-spine immobilization isn’t indicated in penetrating trauma unless there’s a direct injury to the spinal column or spinal cord.10 Although spinal injuries can occur with penetrating trauma, they’re uncommon and typically stable when present.
In a study of 282 penetrating trauma patients in Los Angeles, 8% of patients with gunshot wounds had a spinal injury. However, none of the patients had an unstable fracture requiring surgical stabilization. No spinal injuries were associated with stab wounds.11 In a similar study of 1,069 patients with a penetrating neck injury, only four patients (0.4%) had unstable C-spine injuries. All four had sustained gunshot wounds and had neurological deficits at the time of presentation.12 In a New Orleans study, C-spine immobilization of penetrating trauma victims was associated with an increased risk of death.13
Following the primary assessment, EMS personnel should proceed to the secondary survey. The secondary survey should be a rapid systematic exam beginning at the head. Generally speaking, penetrating trauma to the head is readily evident. However, hair and blood can mask subtle wounds. Prehospital personnel should always maintain a high index of suspicion for penetrating head trauma, remembering the high mortality rate associated with these. Most penetrating neck wounds are also readily evident.
These may or may not involve the great vessels or spinal cord. Any significant bleeding or airway issues should be addressed. Penetrating injuries to the trunk should be quickly assessed. It can be difficult to determine whether a penetrating injury involves the chest, abdomen, pelvis or any combination of these.
In actuality, the exact location of the injury within the trunk makes little difference the prehospital setting. These patients often require detailed imaging and surgical exploration. You should quickly assess the chest and abdomen. Remember to look at the back. Be sure to look for exit wounds—especially with gunshots.
With gunshot wounds, remember that there may be both an entrance and exit wound on opposite sides of the trunk. The track between the entrance wound and exit wound can allow you to visualize the possibly injured structures. Penetrating extremity injuries are usually readily evident. The primary risk with these is hemorrhage from vascular injury. Fortunately, most extremity-related bleeding can be controlled with standard methods.
Penetrating trauma is a surgical disease. As detailed earlier, patients with penetrating trauma tend to die sooner than those with blunt trauma. Following a rapid assessment, patients with penetrating trauma should be transported to the appropriate level trauma center. Such supportive measures as airway maintenance, hemorrhage control and maintenance of body temperature should be provided en route. IV access should be obtained en route (do not delay transport to place an IV), if possible. In patients with hypotension (shock), administer enough fluid (usually 1–2 L of an isotonic solution) to maintain the systolic blood pressure of at least 90 mmHg.
The goal of permissive hypotension to restore enough fluid volume to maintain end-organ perfusion—not restore all lost blood volume. In patients who are normotensive, IV access should be obtained en route but fluids withheld unless the patient develops hypotension.
Penetrating trauma is a serious emergency that requires prompt prehospital identification, transport, and often, immediate surgical intervention. It’s easy to miss some penetrating wounds unless you do a detailed secondary assessment. Remember that penetrating injuries to the head, neck and chest have significant morbidity and mortality. Victims of penetrating trauma have the best outcomes when they’re treated in a comprehensive trauma center that allows rapid assessment, necessary imaging and quick access to surgical care in the operating room setting. The role of prehospital personnel is to detect these injuries, provide essential emergency care and ensure that the patient is delivered to the closest appropriate facility.14 JEMS
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14. American College of Surgeons Committee on Trauma. Advanced Trauma Like Support, Eighth Edition. American College of Surgeons: Chicago, 2008.
This article originally appeared in April 2012 JEMS as “Breakng the Surface: Arm yourself with knowledge about penetrating trauma.”