Blast Injuries: Recognition and Management

Primary Problem:     

• Ruptured lung tissue

Secondary Problems:                 

• Ruptured esophagus, stomach or bowel wall

• Ruptured tympanic membranes (TMs) and sinus injury

Introduction:  
High-explosive (HE), thermobaric, and nuclear detonations cause extreme compression of molecules in surrounding air or water creating thin bands of locally high overpressure, which are propagated away from the origin of the explosion as a blast shock wave.  Most casualties within the injury radius of a HE detonation will have common penetrating (Figure 1 & Figure 2), blunt, and burn (Figure 3) injuries managed no differently than similar non-blast trauma.  

When the blast wave arrives at the surface of an object (vehicle, structure, or human body), it is transmitted into that object as a stress wave (Figure 4).  As the blast wave separates from the stress wave due to the latter moving slower through objects than the blast wave moves around them, pressure differentials cause forces that accelerate surfaces (Figure 5).  When transmitted into the human body, the shock wave causes stress-induced tears at air-tissue interfaces (Figure 6), which result in internal bleeding, weakening of tissue resistance to additional insults, and possible rupture with escape of air from the respiratory tract or spillage of gastrointestinal (GI) contents.

Massive hemoptysis can compromise the airway.  Management of any associated penetrating, blunt, and thermal trauma will not be discussed in this chapter.

Geographical Distribution:  
Worldwide.  In addition to its association with combat and acts of terrorism, blast injuries may occur as a result of industrial or training accidents.

Seasonal Variation:  
None.

Risk Factors:  
The closer a casualty is to an explosion, the more likely he will receive primary blast injury (PBI) from the effects of blast overpressure alone, particularly if behind cover and shielded from ballistic trauma.  

• Personnel in enclosures (buildings, ships, armored vehicles, etc.) are at greater risk, regardless of whether detonation occurred inside or outside the enclosure.  

• Personnel treading water are at higher risk for abdominal than thoracic blast injury from underwate explosion.  

• Fully submerged personnel are at equal risk of combined thoracic and abdominal blast injury, as are personnel in open air, but equivalency occurs at three times distance from explosion underwater compared to open air.  

• Body armor increases the risk of PBI, but decreases the risk of secondary blast injury from fragments, shrapnel, and debris due to its ballistic protection of vital structures.  

• Tertiary blast injury occurs when the high-velocity blast wind generated by pressure differentials accelerate personnel to tumble along the ground, strike solid objects (Figure 7), or impale themselves on other objects.  Secondary and tertiary mechanisms result in conventional blunt and penetrating trauma.

Associated Procedures:  

• Tourniquet application

• Endotracheal intubation

• Cricothyroidostomy

• Needle thoracentesis

• Tube thoracostomy

• Positive-pressure ventilation (PPV)

• Selective pulmonary intubation.

 

Lung Hemorrhage: Pulmonary contusion Hemoptysis Hemothorax Escape of Air: Pneumothorax Pulmonary pseudocyst Arterial gas embolism (AGE)

GI Tract Hemorrhage: Hematoma leading to obstruction Upper or lower GI bleeding Hemoperitoneum Escape of Contents: Mediastinitis Peritonitis

Ear Middle ear: Ruptured tympanic membrane (TM) Temporary conductive hearing loss Inner ear: Temporary sensory hearing loss Permanent sensory hearing loss

Focused Questions

Quantity – 

• Are you short of breath?  (Pulmonary contusion inhibits oxygen diffusion and requires more effort to inhale.  Pneumothorax and hemothorax decrease the volume of air that can be inspired.  Shock will cause the sensation of dyspnea due to poor tissue perfusion.)  

• Do you have chest pain?  (Chest pain indicates the possibility of penetrating or blunt trauma, pneumothorax, or myocardial ischemia or infarction due to coronary AGE.)  

• Do you have abdominal or testicular pain, nausea, urge to defecate, or blood in your stools?  (Penetrating and blunt abdominal trauma cause pain, but PBI of air-containing structures in the GI tract may cause any of the listed symptoms.)  

• Do you have eye pain or problems with your vision?  (Evaluate for penetrating or blunt eye trauma as described in the chapter on Ophthalmology.)  

• Do you have ear pain or problems with your hearing?  (Ruptures of TMs occur commonly but are not life-threatening, unless the casualty cannot hear life-saving commands or communications.)

Quality – 

• How bad is the [symptom above]?  (The severity of any single symptom or combination of symptoms must be evaluated relative to the casualty’s ability to carry out his duties and either facilitate or hamper mission accomplishment.)

Duration – 

• Did the [symptom above] occur at the time of the blast or develop later?  (Any positive finding indicates injury, but new symptoms appearing over time usually represents deterioration.)

Alleviating or Aggravating Factors – 

• How much exertion is required to cause any shortness of breath?  (Dyspnea at rest indicates shock due to external or internal hemorrhage, pneumothorax, or serious pulmonary contusion.  The more exertion required to elicit dyspnea, the less lung injury is likely.)

Using Basic Tools

General:  

• Identify sites of life-threatening external hemorrhage first.  (#1 cause of preventable death on battlefield.)  

• Categorize dyspnea by its severity at rest or by the degree of exertion that causes it.  (Do not purposefully exert the casualty just to see how much exertion elicits dyspnea.)  

• Altered mental status may be transient or not.  (May be due to head trauma, shock, or cerebral AGE.)

Vital Signs:  

• Tachycardia indicates stress from external or internal hemorrhage, hypoxia, exertion, dehydration, or anxiety.  

• Bradycardia is inappropriate but may be transient following a blast-induced vasovagal reaction stimulated by suddenly increased intra-pulmonary pressures.  

• Irregular heart rhythm may indicate cardiac irritability from shock or coronary AGE.  Rapid, shallow respirations are common after blast exposure, regardless of the degree of lung injury, but can also indicate other thoracic damage, shock, exertion, or anxiety.  

• Hypotension may result from hemorrhage, other causes of shock, or a vasovagal reaction.

Inspection:  

• Identify external abrasions, contusions, penetrating wounds (Figure 1 & Figure 2), and traumatic amputations (Figure 8 & Figure 9)   

• Watch for inadequate chest-wall movement.  

• Look for central and peripheral cyanosis (indicating hypoxia) and well-demarcated mottling or blanching of the tongue or areas of skin (indicating AGE).  

• Otorrhea or bleeding from the ears indicates TM rupture or basilar skull fracture.

Auscultation:  

• Listen for asymmetrical breath sounds, poor air movement, and wheezing.  Auscultation of bowel sounds is not necessary in the field.

Palpation:  

• Subcutaneous emphysema indicates an open external wound or rupture of an air-containing internal structure.  

• Abdominal tenderness may indicate internal hemorrhage or GI tract rupture.  

• Palpation of the spine or extremities may be appropriate to decide if the casualty can move under his own power or needs to be transported in an immobilized position.

Percussion:  

• When the environment is quiet enough, percussion may facilitate detection of air or fluid in the chest.

Clinical Tests:  

• A detailed neurological examination may identify subtle deficits.  

• The possibility of AGE should be evaluated as described in the chapter on Diving Medicine.

Pulse Oximeter:  

• A S_PO₂ < 95% on room air indicates some degree of lung injury, inadequate respirations, shock, or exposure to a chemical agent such as cyanide.  

• See the Assessment section of this chapter on using pulse oximetry to categorize the severity of blast lung injury.

Using Advanced Tools

Stool Guaiac:  

• If casualties with primary bowel injury have bleeding, it is usually gross hematochezia, but guaiac-positive stool indicates possible occult penetrating, blunt, or blast trauma.

Ophthalmoscope:  

• Magnification allows close inspection of the possibility of penetrating anterior-eye trauma.  

• Visualizing hemorrhage or a foreign body on funduscopic examination or the absence of a red reflex indicates posterior-eye trauma. 

• If air is noted in retinal vessels, it proves AGE.

Otoscope:  

• Look for ruptured TM.  

• Significant debris in the external canal should be left alone.

Cardiac Monitor:  

• Evaluate dysrhythmias occurring secondary to hypoxia, shock, or coronary AGE.

Hemoglobin & Hematocrit:  

• May be a useful baseline before travel to altitude or to assess slow hemorrhage during evacuation.

Prediction of Respiratory Problems

Insignificant pulmonary injury may be defined as no dyspnea with exertion after 1 hour of rest.  Significant pulmonary blast injuries may be classified as mild, moderate, or severe based on pulse oximetry.  This may help predict the likelihood of complications, requirement for positive-pressure ventilation (PPV), and need for higher-than-normal positive end-expiratory pressure (PEEP).

Blast injuries more likely to be initiated or exacerbated by decreased ambient external pressure on the casualty are pneumothorax, AGE, and bowel-wall stretching.  Reasses frequently!

Differential Diagnosis

Rapid Unconsciousness – 

• Penetrating or blunt brain or cardiac trauma

• Vasovagal syncope

• Cerebral or cardiac AGE

• Chemical nerve-agent or cyanide inhalation

Airway Compromise – 

• Altered mental status

• Penetrating or blunt face or neck trauma

• Inhalation injury

• Massive hemoptysis

• Foreign-body aspiration

Ventilatory Insufficiency – 

• Pulmonary contusion

• Pneumothorax (all types)

• Rib fractures

• Bronchopleural fistula

• Chemical-agent or biological-toxin exposure

Shock – 

• External or internal hemorrhage

• Tension pneumothorax

• Hypoxia from pulmonary injury

• GI bleed (more often lower)

• Coronary AGE

Focal Neurological Deficits – 

• Head injury

• Spinal injury

• Peripheral nerve injury

• Cerebral or spinal AGE

Ruptured TMs – 

• Primary blast overpressure injury

• Basilar skull fracture

Plan 

If IV fluid is administered for controlled hemorrhage with shock or uncontrolled hemorrhage with altered mental status, bolus with one quarter the usual amount (crystalloid or hetastarch) and reevaluate to avoid exacerbating lung or brain injury.  Repeat boluses as necessary.

Procedures for Suspected Arterial Gas Embolism

• Essential:  Administer high-flow supplemental oxygen.  Use an aviator’s mask for extra pressure, if needed and available.  Evacuate to a hyperbaric chamber as soon as possible.  Pressurize the evacuation aircraft’s cabin to the atmospheric pressure at the destination, if using air transportation and it is technically possible in the aircraft used.

• Recommended:  Place the casualty in the coma position with his left side down (halfway between the left-lateral decubitus and prone positions) and his head at the same level as his heart (Figure 10).

Procedures for Massive Hemoptysis Compromising Airway

• Essential:  Perform selective intubation of the least injured side using the algorithm provided (Figure 11).  Use the lumen of the endotracheal tube to facilitate gas exchange in and out of the lung with lighter bleeding.  Use the cuff to prevent blood from the side of heavier bleeding crossing into the mainstem bronchus of the better lung.

Procedures for Suspected Tension Pneumothorax

• Essential:  Perform a needle thoracentesis to relieve life-threatening shock.

• Recommended:  Perform a tube thoracostomy (chest tube), if air is aspirated during needle thoracentesis, but respiratory difficulty and hemodynamic compromise are not relieved.  Although tube thoracostomies are generally not recommended during Tactical Field Care for penetrating trauma, severe pulmonary blast injuries can cause direct communications between large airways and the pleural space (bronchopleural fistula) where a 14-gauge catheter cannot evacuate air out of the pleural space faster than it enters.

Treatment of Suspected Pulmonary Contusion

• Primary:  Stop all activity.  Administer high-flow supplemental oxygen, if it is available.  Initiate PPV only if absolutely necessary.

• Alternative:  Wait at least 1 hour.  Resume tasks as tolerated.

• Primitive:  Only undertake activities at the lowest practical level of exertion (slower movement, less weight carriage, etc.).

Procedures for Ventilatory Assistance

• Essential:  Relieve tension pneumothorax.  Seal open pneumothorax (sucking chest wound).  Allow spontaneous breathing whenever possible.  Place casualty in the position he can breathe best.

• Recommended:  If positive-pressure ventilation (PPV) becomes required, use mouth-to-mask or bag-valve-mask/tube with slower and less-forceful delivies than are often used with other traumatic causes of respiratory problems.

Impact 750M Portable Ventilator (if available and operator qualified)

Initial Settings:                  

1. Connect high-pressure hose from oxygen source to 50-psi inlet

2. F_IO₂ will be 1.00 (100%) unless blender is used

3. Set mode to synchronized intermittent mandatory ventilation (SIMV)

4. Set respiratory rate to 12 breaths/minute (1 breath every 5 seconds)

5. Calculate tidal volume as 8 mL/kg

6. Set inspiratory time to 1 second (I:E ratio equals 1:4 over 5 seconds)

7. Set inspiratory flow to 8 mL/second for every kg of body weight

8. Attach PEEP valve to exhalation port, if needed

9. Test on balloon before attaching to airway adjunct

Persistent Hypoxemia:  Double-check that the definitive airway is still in place and its cuff is intact.  Ensure oxygen is being delivered to the ventilator unit.  Change the PEEP valve to a greater PEEP (up to 10 cmH₂O).

Peak Inspiratory Pressures > 35 cmH₂O:  Double-check that the definitive airway is in place.  Evaluate for tension pneumothorax, and correct if present.  Increase I:E ratio by proportionally increasing inspiratory time and decreasing inspiratory flow (e.g., 4 mL/sec per kg of body weight for 2 sec).  Consider selective intubation and independent lung ventilation with half the tidal volume.

Treatment of Vasovagal Syncope:  

• Primary:  Place the casualty’s head at the level of his heart and elevate his lower extremities.

• Alternate:  Wait until casualty awakens.  Unlike syncope from fright, this may take up to 2 hours in a blast-injured casualty.

Treatment of GI Bleeding:  Same as outlined in the chapter on Gastrointestinal Problems.  

Treatment of Possible GI Tract Rupture

• Primary:  NPO.  Maintenance IV fluid.  Cefoxitin or ceftriaxone IV or IM.  Evacuate DELAYED for surgical care within 4 hours.  Monitor for peritonitis and sepsis.  Prochlorperazine or promethazine IV or IM, if needed to prevent recurrent vomiting.

• Alternative:  Maintenance PO water, if no IV and evacuation time > 4 hours.  Ciprofloxacin and metronidazole PO, if parenteral cephalosporins not carried or casualty is allergic to them.  Virtually any antibiotic coverage is better than nothing when time to definitive care is prolonged.

Treatment of Mediastinitis, Peritonitis, or Sepsis

• Primary:  One of two parenteral combinations: 1) cefoxitin (or ceftriaxone) AND metronidazole (or clindamycin); or 2) ampicillin/sulbactam (or piperacillin) AND gentamicin (or tobramycin).

• Alternative:  Oral combination of ciprofloxacin AND metronidazole.

Treatment of TM Rupture

• Primary:  Do not attempt removal of foreign debris.  Prevent water and other non-sterile material from entering the ear canal.  Manage pain as indicated.

• Empiric:  Prophylactic antibiotics are not indicated.  If infection of the TM (myringitis) develops, instill ophthalmological (for the eye) gentamicin 4 drops (not ointment) 4 times a day for 10 days.  Otological (for the ear) suspensions for otitis externa are contraindicated when the TM is ruptured.

• Alternative:  Amoxicillin/clavulanate or ciprofloxacin PO, if ophthalmological antibiotic drops are not available.

• Return Evaluation:  Inspect the area surrounding the ear, the external ear itself, the ear canal, and the TM daily for redness, swelling, or purulent drainage.  Pain when gently pulling up and back on the pinna or pressing on the cartilage just in front of canal also indicates otitis externa.

• Consultation Criteria:  The casualty should ideally be seen by an ear, nose, and throat (ENT) specialist within 3 days, or sooner if significant debris is in the canal.  Up to 2 weeks is acceptable, if no infection develops.

Evacuation Destination

• CASEVAC from the tactical environment to a higher level of medical care, then MEDEVAC to more definitive care.  The destination chosen should consider the following needs based on suspected diagnoses:

• Head Injury:  Facility with neurosurgery – URGENT-SURGICAL.  Intensive care at the same facility is desirable.

• Penetrating Torso Trauma:  Facility with general surgery – URGENT-SURGICAL.  Cardiothoracic and vascular surgery are desirable.

• Arterial Gas Embolism:  Facility with hyperbaric chamber – URGENT.  Other trauma services at the same facility are desirable.

• Pulmonary Contusion:  Facility with intensive care – URGENT.  Pulmonary and surgery services are desirable.

• GI Tract Rupture:  Facility with general surgery – PRIORITY.  A pulmonary service is desirable.

• TM Rupture:  Any facility with physician – ROUTINE.  An ENT service is desirable.

Notes

• AMS is most likely due to penetrating or blunt head trauma or shock from bleeding, but two unique features of blast injury are less common causes: 1) blast overpressure on the lungs can cause vasovagal syncope with bradycardia and hypotension, which may last minutes to hours even with conventional treatment; and 2) stress-induced tears in lung tissue may allow air into the pulmonary veins, which can then be ejected to the cerebral or coronary circulation causing a stroke or heart attack, respectively.

• Transient amnesia is common after any loss of consciousness caused by explosions.

• Pharyngeal petechiae (but not TM rupture) predict a higher likelihood of pulmonary contusion.

• Make sure the casualty can be easily moved between sitting and lying positions for respiratory management.

• Avoid PPV unless absolutely necessary, because it increases the risks for pneumothorax and arterial gas embolism.  AGE is the most common cause of death in immediate survivors and often occurs when PPV is initiated.

• It is better to place a possibly unneeded chest tube than have a tension pneumothorax during transportation.

• Development of a tension pneumoperitoneum affecting respirations is rare, but may require a 14-gauge needle paracentesis in the midline just above the umbilicus for decompression.

• Vertigo is usually due to head injury, not blast effects on the inner ear.  Meclizine can improve symptoms but can also sedate, thus impairing the casualty’s ability to function and making assessment of AMS more difficult.

• Morphine should be withheld in bradycardia and given with caution in respiratory difficulty.

• Evaluate for the necessity of a tetanus immunization booster.  

This section contributed by Lt Col John Wightman, USAF, MC