Blast Injury

Aka: Blast Injury, Explosion Related Injury, Explosive Agents, Bombing Injury

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II. Causes: Explosive types (based on rate of burn)

  1. High order explosives (detonate)
    1. Result in a supersonic over-pressurization shock wave, expanding rapidly from detonation point
    2. Agents include Ammonium nitrate (ANFO), dynamite (TNT), Semtex
  2. Low-order explosives (deflagrate)
    1. Rapidly burns, but advances more slowly subsonic (<1000 m/s) than a high order explosive
    2. Devices and agents include pipe bombs, gun powder, and molotov cocktails (or other petroleum based bombs)

III. Risk Factors: Greatest Injury

  1. Enclosed space blasts (e.g. building, bus), underground or underwater blast
  2. Proximity to the explosive
  3. High order explosive
  4. Bombs encased with projectiles

IV. Mechanism

  1. Explosive detonation results in rapid conversion of solid or liquid to a gas, with a subsequent sudden release of energy
  2. Pressure peaks initially and then rapidly loses pressure
    1. Pressure falls below sub-atmospheric pressure
    2. Finally pressure returns to normal
  3. Fragmentation occurs when projectiles (e.g. nails, bolts, nuts) are housed within the bomb
    1. Typically result in most significant secondary injuries
  4. Pressure and fragmentation effects fall off exponentially with distance from the blast
    1. Doubling the distance from the blast, results in a 9 fold drop in experienced force

V. Adverse Effects: Primary Blast Injury

  1. Mechanism
    1. Injuries result from blast's direct pressure wave effects (especially high order explosives)
    2. Greatest injuries are to gas containing organs (middle ear, lungs, bowel) due to pressure gradient
  2. Associated injuries
    1. Pulmonary Barotrauma (Blast Lung)
      1. Most common lethal injury
    2. Pneumothorax
    3. Pulmonary Contusion
    4. Arterial Gas Embolism
      1. Results in Occlusion of the spinal cord or brain most commonly
    5. Gastrointestinal Barotrauma
      1. Most common in underwater blast injuries
      2. May include mesenteric shear injury, Liver Laceration, Splenic Rupture, intestinal rupture
    6. Genitourinary Barotrauma
      1. Testicular rupture may occur
    7. Globe Rupture
    8. Tympanic Membrane Rupture (or hemotympanum)
      1. Most susceptible to even low level blast injuries (5 PSI above barometric pressure)
      2. Ear Barotrauma is not a reliable indicator of greater internal injuries (e.g. lung, bowel)
    9. Traumatic Brain Injury
      1. Distinguish from Arterial Gas Embolism related CVA

VI. Adverse Effects: Secondary Blast Injury

  1. Mechanism
    1. Most common form of blast-related injury
      1. Most common form of lethal injury aside from building collapse
      2. Injury from flying debris (e.g. shrapnel)
      3. Radius of potential injury from epicenter is much greater than the blast pressure force itself
      4. Injured body parts are widely dispersed and often unpredictable
    2. Projectiles directly strike the blast victim
      1. Nails, bolts or nuts within the bomb casing
      2. Damaged people or materials are propelled by the blast force
  2. Precaution
    1. Deeper, serious injuries may exist despite relatively mild external wounds
    2. Treat all wounds as contaminated (avoid primary closure)
  3. Associated injuries
    1. Penetrating Trauma
    2. Blunt Trauma
    3. Fractures
    4. Soft Tissue Injury
    5. Traumatic amputation
    6. Compartment Syndrome

VII. Adverse Effects: Tertiary Blast Injury

  1. Mechanism
    1. Blast victim is propelled by the blast force (blast wind) against another object
    2. May result in blunt or Penetrating Trauma
  2. Associated Injuries
    1. Fractures
    2. Joint dislocations
    3. Compartment Syndrome
    4. Traumatic amputations
    5. Closed Head Injury

VIII. Adverse Effects: Quaternary Blast Injury

  1. Mechanism
    1. Environmental injuries and exposures related to the blast
  2. Associated injuries
    1. Burn Injury
    2. Inhalation Injury
    3. Toxin exposures (Carbon Monoxide Poisoning, Cyanide Poisoning)
    4. Chemical Weapon, Biological Weapon or Radiological Weapon exposure
    5. Exacerbation of chronic disease (e.g. Asthma Exacerbation or COPD exacerbation, Acute Coronary Syndrome)

IX. Adverse Effects: Late

  1. Acute Respiratory Distress Syndrome (ARDS)
  2. Disseminated Intravascular Coagulation (DIC)

X. Precautions

  1. One Blast Injury (e.g. Tympanic Membrane Rupture) predicts other blast injuries

XI. History: Blast Injury specific

  1. Background
    1. See AMPLE History
    2. Details of injury mechanisms and catastrophe
  2. Hearing Loss, Ear Pain, Tinnitus, Ear Drainage
    1. Ear Barotrauma (e.g. Tympanic Membrane Rupture)
  3. Dyspnea, cough or Hemoptysis
    1. See Pulmonary Blast Injury
    2. Pulmonary Barotrauma (most common lethal injury)
    3. Pulmonary Contusion
    4. Hemothorax or Pneumothorax
    5. Hemorrhagic Shock
  4. Chest Pain
    1. Chest blunt or Penetrating Trauma
    2. Hemothorax or Pneumothorax
    3. Pneumomediastinum
    4. Arterial Gas Embolism
  5. Nausea or Vomiting, Hematemesis, Abdominal Pain or bloody stools
    1. Abdominal blunt or Penetrating Trauma
    2. Bowel perforation
    3. Testicular rupture
  6. Eye Pain or Vision changes
    1. Globe Rupture

XII. Exam

  1. See Trauma Primary Survey
  2. See Trauma Secondary Survey
  3. Head and Neurologic Exam
    1. Blood or drainage from auditory canal or nose
    2. Hemotympanum
    3. Globe injury
  4. Respiratory Exam
    1. Cyanosis
    2. Respiratory distress
    3. Hypoxia
    4. Apnea
    5. Rales or rhonchi
    6. Asymmetric breath sounds or chest movement
    7. Subcutaneous Emphysema
  5. Cardiovascular exam
    1. Arrhythmia
    2. Hypotension
      1. Hypotension compensatory mechanisms may be paradoxically absent in blast Trauma
      2. Systemic Vascular Resistance and Heart Rate may remain normal despite profoun Hypotension, blood loss
    3. Severe Bradycardia
      1. Seen especially with higher intensity blast injuries
  6. Abdominal exam
    1. Abominal tenderness, rigidity or guarding
  7. Neurologic Exam
    1. Glasgow Coma Scale
    2. Focal neurologic deficit
    3. Seizures

XIII. Labs: Initial

  1. Comprehensive metabolic panel
  2. Complete Blood Count (CBC) with Platelets
  3. Blood Type and Screen (consider cross-match)
  4. ProTime (PT/INR)
  5. Activated Partial Thromboplastin Time (aPTT)
  6. Urinalysis
  7. Urine Pregnancy Test

XIV. Labs: As Indicated

  1. DIC considered
    1. Thrombin Time
    2. Fibrinogen
    3. Fibrin split products
  2. Rhabdomyolysis considered (structure collapse, prolonged extrication, severe burns)
    1. Creatine Phosphokinase (CPK)
  3. Structural fire
    1. Carboxyhemoglobin
    2. Cyanide Level

XV. Imaging

  1. See FAST Exam
  2. Chest XRay
  3. Pelvic XRay
  4. Advanced imaging as indicated
    1. CT Head and CT Cervical Spine
    2. CT Chest (with or without Abdomen and Pelvis)
    3. CT Abdomen and Pelvis
      1. May miss intestinal Contusions and mesenteric injury
      2. Consider repeat imaging at 8 hours if persistent symptoms

XVI. Evaluation

  1. Initial Trauma Evaluation
    1. See Trauma Primary Survey
    2. See Trauma Secondary Survey
    3. See ABC Management (Cardiopulmonary Resuscitation)
    4. See MARCH Field Trauma Protocol
    5. See AMPLE History
    6. See FAST Exam
  2. Blast Injury specific evaluation (in order of highest lethality first)
    1. See History and Exam above
    2. Multiple Trauma
    3. Head Trauma
    4. Thoracic Trauma
    5. Abdominal Trauma

XVII. Management: Preparation after initial notification of catastrophe

  1. See Mass Casualty Incident
  2. Activate hospital disaster plan
    1. Activate available medical and surgical staff, nursing staff and allied health
    2. Use appropriate Personal Protection Equipment
    3. Sharpie markers are useful to mark patients, bed sheets
  3. Obtain details of catastrophe
    1. Explosion cause and type
    2. Toxin exposures
    3. Casualty location
  4. Expect "upside-down" triage
    1. Victims who are less injured (typically walking wounded) present before those more injured (due to self triage)
    2. Walking wounded self-triage themselves outside of EMS system, presenting individually to local hospitals
  5. Triage patients directly to their proper unit
    1. Acute surgical emergencies are triaged to the operating room
    2. Intensive Care unit patients are triaged to the ICU
  6. Anticipate total casualties
    1. Expect 50% of casualties in the first hour after an incident
    2. Double the number presenting in hour one, to estimate total casualties
    3. Structural collapse is associated with greater injuries, toxins (e.g. Carbon Monoxide), delayed presentations
  7. Stage and staff areas based on triage categories (typically assigned by EMS at scene)
    1. See Trauma Triage in the Field
    2. See JumpSTART Pediatric Multiple Casualty Incident Triage
    3. See SALT Mass Casualty Triage Algorithm
    4. Simple Triage and Rapid Treatment (START Triage)
      1. Patients are categorized into minor (green), delayed (yellow), immediate (red) and deceased/expected (black)
      2. Those in delayed group should be frequently reassessed for decompensation
  8. Prepare for expected injuries
    1. Closed Head Injury
    2. Chest Trauma
    3. Musculoskeletal Trauma
    4. Abdominal Trauma
    5. Open wounds

XVIII. Management: Blast specific injury management

  1. See Pulmonary Blast Injury
  2. See Arterial Gas Embolism
  3. Acute Stabilization
    1. See Trauma Primary Survey
    2. See Trauma Secondary Survey
    3. See ABC Management (Cardiopulmonary Resuscitation)
    4. See MARCH Field Trauma Protocol
  4. Abdominal Trauma
    1. Abdominal complications may be delayed 2-14 days
    2. Observe symptomatic patients for 6-8 hours regardless of normal CT Abdomen results
    3. Consider repeat imaging at 6-8 hours
  5. Mild Traumatic Brain Injury
    1. Seemingly mild head injuries can have longstanding effects
  6. Tympanic Membrane Rupture
    1. Risk of longterm Hearing Loss (one third of patients)
    2. Consider evaluation with otolaryngology
    3. May evaluate for ossicle disruption, or increased risk of Perilymphatic Fistula or Cholesteatoma
  7. Eye Injury
    1. Serious Eye Injury is common in blast survivors
    2. Evaluate foreign body Sensation, Vision change
  8. Traumatic amputation
    1. Very high mortality (due to rapid Exsanguination)
    2. Associated with multi-system injury
    3. Lower extremities are most commonly involved
    4. Immediate Tourniquet application at scene, followed by emergent surgical evaluation
  9. Wound contamination
    1. Consider all blast wounds contaminated
    2. Debride foreign material and non-viable tissue
    3. Extensive Isotonic Saline irrigation
    4. Tetanus prophlaxis (Td or Tdap and consider tetanus Immunoglobulin)
    5. Consider blood bourne pathogen exposure in specific cases (Hepatitis B Vaccine, HIV Postexposure Prophylaxis)
    6. Consider empiric antibiotic coverage
      1. Clostridium perfringens
        1. First-Line: Penicillin
        2. Alternatives: Erythromycin, Chloramphenicol, Cephalosporins
      2. Pseudomonas aeruginosa (severely contaminated blast wounds)
        1. First-Line: Amioglycosides
        2. Alternatives: Carbapenems (e.g. Imipenem), Zosyn
      3. Open Fractures
        1. First-Line: Cefazolin
        2. Alternatives: Clindamycin, Vancomycin, Aminoglycoside

XIX. Management: Specific Cohorts

  1. Pregnancy (second and third trimester)
    1. Evaluate for Placental Abruption
    2. Obtain Fetal Monitoring and Ultrasound
    3. Consider RhoGAM in Rh Negative women
    4. Consider obstetrics Consultation
  2. Extremes of age (increased mortality risk)
    1. Children
      1. High risk of Pulmonary Barotrauma (Blast Lung, Pulmonary Contusion)
      2. Have high index of suspicion if Rib Fractures or Chest Contusions
      3. Chest XRay in most Pediatric Trauma
    2. Elderly
      1. High index of suspicion for orthopedic injury
      2. Chest Trauma is associated with greater morbidity

XX. Management: Disposition

  1. Emergent surgical Consultation for TTA Level I patients, positive FAST Scan or other immediate surgical emergency
  2. Consider transfer of multiple Trauma or significant Trauma to the head, chest, or Abdomen to Level I Trauma Center
  3. Admit those with significant, but non-surgical findings on exam or diagnostics
    1. Significant Burn Injury
    2. Suspected arterial Air Embolism (or risk)
    3. Chemical Weapon exposure
    4. Radiation exposure
    5. White Phosphorus contamination (risk of Calcium and Phosphorus abnormalities)
    6. Abdominal Pain despite normal CT Abdomen
    7. Vital Sign, chest or Abdomen abnormalities
    8. Non-extremity penetrating injuries
    9. Pregnant women beyond first trimester (risk of Placental Abruption)
  4. Observe for 6-8 hours (with Oxygen Saturation) those with positive history or exam findings (see above)
    1. Closed-space or under-water blast exposures
    2. Isolated Tympanic Membrane exposures
  5. Observe for 4 hours, patients exposed to open-space blasts without significant findings
  6. Communication may be difficult after Blast Injury (due to Deafness, Tinnitus)
    1. Written communication and instructions may be needed

XXI. Prognosis

  1. Closed Head Injury is the most common cause of death
  2. Bimodal mortality distribution
    1. Greatest mortality immediately after blast
    2. Second peak in mortality is delayed affecting the most severely injured
  3. Blast victims (contrasted with other Trauma victims)
    1. More severe injuries
    2. Require extended ICU, hospital, and rehab stays

XXII. Resources

  1. CDC
    1. http://www.cdc.gov/masstrauma/preparedness/primer.pdf
  2. American Trauma Society (ATS)
    1. http://www.amtrauma.org/?page=BlastPrimer
  3. ACEP
    1. http://www.acep.org/blastinjury/

XXIII. References

  1. (2016) CALS Manual, 14th edition 1: 42-3
  2. Jagminas (2015) Crit Dec Emerg Med 29(5): 2-11
  3. Swaminathan and Bucher in Herbert (2019) EM:Rap 19(8): 5-6
  4. DePalma (2005) N Engl J Med 352(13): 1335-42 [PubMed]

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