Rosen & Barkin's 5-Minute Emergency Medicine Consult (789 page)

The physical forces that determine the wounding potential of gunshot and other penetrating wounds

• Wounding potential of bullet is determined by mass and velocity.
  
• The type and severity of a wound is determined by:
  
  • Wounding potential
    
  • Construction and shape of the bullet
    
  • Orientation of the bullet upon striking body
    
  • Deformity or fragmentation
    
  • What tissues the bullet traverse
    
• Traditional distinction between low and high muzzle
  velocity
  does not differentiate kind and severity of wounding:
  
  • A civilian hunting rifle or a large-caliber handgun with a hollow-point bullet may produce a more severe wound than a bullet with a full metal jacket from a “high-velocity” military rifle.
    
• Bullets wound by 2 main mechanisms—
  crush
  and
  stretch:
  
  • Sonic pressure wave that precedes bullet has no role in wounding.
    
  • Bullet crushes the tissue it directly passes through, forming a
    permanent cavity.
    
  • Stretch
    is produced by radial energy transferred from bullet as it slows down in tissue, forming a
    temporary cavity.
    
  • A bullet is stabilized in flight by
    spin
    transmitted from rifling in the barrel.
    
  • Spin minimizes
    yaw,
    which is the angle between the long axis of the bullet and its flight vector.
    
  • Without spin, a bullet would yaw to its most stable flight configuration, which is base and center of mass forward:
    
    • Not aerodynamically efficient
      
• As bullet enters tissue, spin of bullet is reduced and bullet will yaw.
  
• When yaw is 90°, a bullet crushes maximal amount of tissue, slows down the most, and maximal stretch injury occurs.
  
• Bullets designed to deform in tissue (soft point, hollow point) will expand on impact:
  
  • Increases amount of crush injury
    
  • Moves bullet center of mass forward
    
• Jacketed bullets prevent lead stripping in the barrel, which occurs at high muzzle velocities:
  
  • Jacketed bullets do not deform but may fragment.
    
  • Fragmentation increases surface area and crush injury.
    
• Bullets striking bone often fragment and may cause bone fragments to become secondary projectiles.
  
• Severity of wound also depends upon
  tissue composition and thickness:
  
  • Minimally elastic tissues, near-water-density tissue (brain, liver), fluid-filled (heart, bowel) and dense organs (bone) may be injured by the temporary cavity.
    
  • More elastic tissue, such as lung and skeletal muscle, may absorb the energy from temporary cavity formation and sustain minimal damage.
    
  • Extremities are often not thick enough for the bullet to fully yaw:
    
    • Temporary cavity formation is minimal.
      
    • Most damage is caused by direct crush injury of the bullet, its fragments, or secondary projectiles.
      
• Short-range shotgun blasts can produce severe wounds with compromise of the blood supply:
  
  • In short-range shotgun injuries, pellets may be greatly scattered in tissue secondary to the pellets striking each other.
    
• Stab wounds with knives and other sharp instruments are low-energy wounds with tissue injury from direct weapon contact.
  

DIAGNOSIS

• Severe underlying tissue damage and life-threatening injury may occur with even small entrance wounds.
  
• A knowledge of how different kinds of weapons and bullets wound, the trajectory of the bullet through the body, and the effect on different body tissues will allow the physician to carefully evaluate gunshot and stab wounds and their potential morbidity and mortality.
  

• Field personnel can provide information about weapon type and size, distance, and angle between the weapon and victim:
  
• This information may not be available or may be inaccurate.
  

• Evaluate for entrance and exit wounds:
  
• May estimate trajectory and potential for tissue damage
  
• Exit wounds are often stellate and larger than entranced wounds unless energy is dissipated at skin surface by special bullet type (hollow point, etc.).
  
• With high-velocity projectiles, exit wound may be much more extensive than entrance wound.
  
• Because of the elasticity of the skin, bullet can often be palpated subcutaneously.
  
• It is not always possible to differentiate entrance from exit wounds; clinicians do this poorly, so wounds should be described fully and classification as entrance or exit wounds should be avoided.
  

• ABCs must be stabilized prior to any workup.
  
• Account for all injury tracts.
  
• Place markers at wound sites.
  
• Examine all areas of the body for wounds (remember the perineum, axillae, and scalp).
  

Initial lab tests are not especially helpful in diagnosis but may be helpful in guiding resuscitation.

• Anteroposterior and lateral radiographs help localize bullet:
  
  • With placement of markers at wound sites, wound trajectory can be estimated
    
  • Fragments, fractures, pneumothoraces, or hemothoraces can be identified.
    
• US:
  
  • A positive FAST scan is highly predictive of a therapeutic laparotomy. A negative FAST scan does not exclude significant intra-abdominal injury.
    
  • US for pericardial effusion in potential mediastinal injuries
    
• CT scanning:
  
  • Identify location of projectile.
    
  • Location and amount of tissue damage (especially to the head and brain)
    
  • Abdominal CT is increasingly used in the evaluation of stable patients with penetrating back/flank or abdominal trauma.
    
  • In penetrating trauma of the thorax, an initial negative CT scan of the thorax obviates the usual practice of repeated chest radiographs.
    
• Angiography may be necessary if patient has potential vascular injury and surgical exploration is not otherwise warranted.
  

• Local wound exploration with clear delineation of the base of the wound tract that does not penetrate deep structures may be sufficient to evaluate stab wounds.
  
• Abdominal wounds that encroach the posterior fascia require further evaluation, either diagnostic peritoneal lavage or surgical exploration.
  
• Extent of tissue injury often apparent only on surgical exploration.
  

Organs at risk of damage can be inferred from weapon type, distance, locations of entrance and exits wounds, or projectiles on imaging.

• Tissues surrounding the projectile tract are also at risk of injury (i.e., from temporary cavity).
  
• Projectiles may fragment and create multiple injury tracts.
  

TREATMENT

• Gunshot and stab wounds to chest with unstable vital signs warrant a needle thoracostomy in the side of the chest with the entrance wound:
  
  • Relieves tension pneumothorax
    
  • If no improvement, a needle thoracostomy should be placed in the contralateral hemithorax.
    
• Impaled objects or projectiles should not be removed:
  
  • Immobilize with tape and gauze and transport.
    
• Clothing should be preserved if possible:
  
  • Clothing should be cut around holes made by the projectiles to preserve evidence.
    
• Patient should be transported to the closest trauma center.
  
• Hypotensive patient may be taken directly to the OR.
  

Stabilize airway, breathing, and circulation. Secure adequate IV access.

• Impaled objects should be removed only in the OR.
  
• In the ED, estimate tissue injury based on the above principles.
  
• Wound care includes appropriate exploration, irrigation, and debridement of devitalized tissue.
  
• All bullets are contaminated with bacteria and are
  not
  sterilized by being fired:
  
  • All nongrazing bullet wounds warrant empiric antibiotics.
    
• Early trauma, orthopedic, and vascular surgery consultation is necessary.
  

Prophylactic antistaphylococcal antibiotics should be prescribed for several days:

• Cefazolin 1 g IV q6h
  
• Cephalexin 500 mg PO q6–8h
  
• For penicillin-allergic patients or patients at risk for methicillin-resistant
  Staphylococcus aureu
  s then vancomycin 1 g IV q12h, clindamycin 300 mg IV/PO q6h, or sulfamethoxazole/trimethoprim DS 1 tablet BID can be prescribed
  
• Intra-abdominal wounds require broader coverage (many regimens available) such as cefotetan 1 g IV q12h, piperacillin/tazobactam 3.75 mg IV q6h, or the combination of ciprofloxacin 500 mg IV q12h with metronidazole 500 mg IV q8h
  

FOLLOW-UP

• Patients with neurovascular compromise and extensive tissue damage must be admitted for appropriate surgical intervention.
  
• Patients with nontrivial injury to the head, neck, torso, or abdomen should be admitted.
  
• Patients with injury from high-velocity projectiles or gunshot wounds should be admitted to a monitored setting for observation of neurovascular status.
  

Patients with minor penetrating extremity trauma or stabbing victims found not to have significant injury may be discharged with appropriate follow-up.

Emergent consultation of appropriate surgical specialists should be obtained for patients with potential injuries to vascular or nervous structures.

Patients not admitted to the hospital should have scheduled follow-up with a trauma surgeon or an appropriate surgical specialist (e.g., orthopedist for extremity trauma).