High-energy events in which a solid or liquid is converted rapidly to a gas can occur at 3 rates:
Deflagration: Rapid burning but minimal blast
Explosion: Subsonic ignition and blast wind (low-grade explosive)
Detonation: Supersonic ignition and blast wave (high-grade explosive)
An example of deflagration would be the rapid flash (without a bang) that results when an open pile of black powder (gunpowder) is ignited. The same black powder confined tightly in a container would cause a low-grade explosion. In high-grade explosives, the ignition wave travels through the material at supersonic speed and causes a supersonic blast (detonation) wave; common examples include nitroglycerin and trinitrotoluene (TNT— Examples of Low-Grade and High-Grade Explosives Examples of Low-Grade and High-Grade Explosives ).
In mass casualty incidents involving explosions, 3 concentric zones are identified:
In the blast epicenter (kill zone), any survivors are probably mortally injured, technical rescue capabilities and extrication are likely to be required, and advanced life support and high victim-to-care-provider ratios are required for any survivors. In the secondary perimeter (critical casualty zone), survivors will have multiple injuries, and standard rescue capabilities and moderate victim-to-care-provider ratios are required. In the blast periphery (walking-wounded zone), most casualties will have non–life-threatening injuries and psychologic trauma, no rescue is required, and basic support and self-help are needed.
(See also Overview of Incidents Involving Mass-Casualty Weapons Overview of Incidents Involving Mass-Casualty Weapons Mass-casualty incidents (MCIs) are events that generate sufficiently high numbers of casualties to overwhelm available medical resources. They include natural disasters (eg, hurricanes) and... read more .)
Pathophysiology of Explosive and Blast Injuries
Blast injuries include both physical and psychologic trauma. Physical trauma includes fractures, respiratory compromise, injuries to soft tissue and internal organs, internal and external blood loss with shock, burns, and sensory impairment, especially of hearing and sight. Five mechanisms of blast injury have been described (see table Mechanisms of Blast Injury Mechanisms of Blast Injury ).
The supersonic blast wave in primary blast injury compresses gas-filled spaces, which then rapidly reexpand, causing shearing and tearing forces that can damage tissue and perforate organs. Blood is forced from the vasculature into air spaces and surrounding tissue. Pulmonary involvement (blast lung injury) may cause pulmonary contusion, systemic air embolism (especially in the brain and spinal cord), and free-radical–associated injuries (thrombosis, lipo-oxygenation, and disseminated intravascular coagulation Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) involves abnormal, excessive generation of thrombin and fibrin in the circulating blood. During the process, increased platelet aggregation and coagulation... read more ); it is a common cause of delayed mortality. Primary blast injury also includes intestinal barotrauma (particularly with underwater explosions), acoustic barotrauma (including tympanic-membrane rupture, hemotympanum without rupture, and fracture or dislocation of ossicles in the middle ear), and traumatic brain injury Traumatic Brain Injury (TBI) Traumatic brain injury (TBI) is physical injury to brain tissue that temporarily or permanently impairs brain function. Diagnosis is suspected clinically and confirmed by imaging (primarily... read more .
Symptoms and Signs of Explosive and Blast Injuries
Most injuries (eg, fractures, lacerations, brain injuries) manifest the same as in other types of trauma. Blast lung injury may cause dyspnea, hemoptysis, cough, chest pain, tachypnea, wheezing, decreased breath sounds, apnea, hypoxia, cyanosis, and hemodynamic instability. Air embolism may manifest as stroke, myocardial infarction, acute abdomen, blindness, deafness, spinal cord injury, or claudication. Damage to the tympanic membrane and the inner ear may impair hearing, which should always be assessed. Patients with abdominal blast injury may have abdominal pain, nausea, vomiting, hematemesis, rectal pain, tenesmus, testicular pain, and unexplained hypovolemia. Traumatic brain injury Traumatic Brain Injury (TBI) Traumatic brain injury (TBI) is physical injury to brain tissue that temporarily or permanently impairs brain function. Diagnosis is suspected clinically and confirmed by imaging (primarily... read more may manifest immediately and resolve or leave residual neurocognitive affects of varying degree. There also is concern that multiple lower-level blast exposures may have a cumulative deleterious neurocognitive effect and perhaps lead to chronic traumatic encephalopathy Chronic Traumatic Encephalopathy (CTE) Chronic traumatic encephalopathy (CTE) is a progressive degenerative brain disorder that may occur after repetitive head trauma or blast injuries. (See also Overview of Delirium and Dementia... read more .
Diagnosis of Explosive and Blast Injuries
Imaging studies as indicated by findings
Patients are evaluated as for most multiple trauma casualties (see Approach to the Trauma Patient: Evaluation and Treatment Evaluation and Treatment Injury is the number one cause of death for people aged 1 to 44. In the US, there were 243,039 trauma deaths in 2017, about 70% being accidental. Of intentional injury deaths, more than 70%... read more ), except that special effort is directed at identifying blast injury, particularly blast lung (and consequent air embolism), ear trauma, occult penetrating injury, and crush injury. Apnea, bradycardia, and hypotension are the clinical triad classically associated with blast lung injury. Tympanic membrane rupture has been considered to predict blast lung injury, but pharyngeal petechiae may be a better predictor. Chest x-ray is done, which may show a characteristic butterfly pattern. Cardiac monitoring is done in all patients. Patients with possible crush injury are tested for myoglobinuria, hyperkalemia, and ECG changes.
In blast injuries, less seriously injured patients often bypass prehospital triage and go directly to hospitals, possibly overwhelming medical resources in advance of the later arrival of more seriously injured patients. On-scene triage differs from standard trauma triage mainly in that blast injuries may be more difficult to recognize initially, so initial triage should be geared toward identifying blast lung, blast abdomen, and acute crush syndrome in addition to more obvious injuries.
Treatment of Explosive and Blast Injuries
Attention should be given to airway, breathing, circulation, disability (neurologic status), and exposure (undressing) of the patient (see Approach to the Trauma Patient: Evaluation and Treatment Evaluation and Treatment Injury is the number one cause of death for people aged 1 to 44. In the US, there were 243,039 trauma deaths in 2017, about 70% being accidental. Of intentional injury deaths, more than 70%... read more ). High-flow oxygen and fluid administration are priorities, and early chest tube placement should be considered. Most injuries (eg, lacerations Lacerations Lacerations are tears in soft body tissue. Care of lacerations Enables prompt healing Minimizes risk of infection Optimizes cosmetic results read more , fractures Overview of Fractures A fracture is a break in a bone. Most fractures result from a single, significant force applied to normal bone. In addition to fractures, musculoskeletal injuries include Joint dislocations... read more , burns Burns Burns are injuries of skin or other tissue caused by thermal, radiation, chemical, or electrical contact. Burns are classified by depth (superficial and deep partial-thickness, and full-thickness)... read more , internal injuries, head injuries Traumatic Brain Injury (TBI) Traumatic brain injury (TBI) is physical injury to brain tissue that temporarily or permanently impairs brain function. Diagnosis is suspected clinically and confirmed by imaging (primarily... read more ) are managed as discussed elsewhere in The Manual.
Because air embolism may worsen after initiation of positive-pressure ventilation, positive-pressure ventilation should be avoided unless absolutely necessary. If it is used, slower rates and lower inspiratory pressure settings should be chosen. Patients suspected of having air-gas embolism should be placed in the coma (or recovery) position, halfway between left lateral decubitus and prone, with the head at or below the level of the heart. Hyperbaric oxygen (HBO) therapy may be useful (see Recompression Therapy Recompression Therapy Recompression therapy is administration of 100% oxygen for several hours in a sealed chamber pressurized to > 1 atmosphere, gradually lowered to atmospheric pressure. In divers, this therapy... read more ).
If acute crush syndrome is diagnosed or suspected, urinary catheterization Bladder Catheterization Bladder catheterization is used to do the following: Obtain urine for examination Measure residual urine volume Relieve urinary retention or incontinence Deliver radiopaque contrast agents or... read more is done to allow continual monitoring of urine output. Forced diuresis using an alkaline mannitol solution to maintain urine output up to 8 L/day and a urinary pH of ≥ 5 may help. Arterial blood gases (ABGs), electrolytes, and muscle enzymes should be monitored. Control hyperkalemia with calcium, insulin, and glucose (see Hyperkalemia: Treatment Treatment Hyperkalemia is a serum potassium concentration > 5.5 mEq/L (> 5.5 mmol/L), usually resulting from decreased renal potassium excretion or abnormal movement of potassium out of cells. There are... read more ). Hyperbaric oxygen therapy may be particularly useful in patients with deep tissue infections. Monitoring for compartment syndrome Compartment Syndrome Compartment syndrome is increased tissue pressure within a closed fascial space, resulting in tissue ischemia. The earliest symptom is pain out of proportion to the severity of injury. Diagnosis... read more is done clinically and by measuring compartment pressure. Patients may need fasciotomy if the difference between diastolic blood pressure and compartment pressure is < 30 mm Hg. Hypovolemia and hypotension may not be apparent initially but may suddenly occur after tissue release and reperfusion, so large volumes of intravenous fluid (eg, 1 to 2 L Ringer's lactate or normal saline) are given both before and after reperfusion. Fluids are continued at a rate sufficient to maintain a urine output of 300 to 500 mL/hour.
The views expressed in this article are those of the author and do not reflect the official policy of the Department of Army, Department of Defense, or the US Government.
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