Mathematically predicted (solid lines) and experimentally measured (dashed lines) thoracic dynamics caused by blast loading after detonation of 2.2 kg of Composition C4 to the right side of a sheep: (A) acceleration of the right rib cage peaked near 200 km/s2; (B) velocity of the right rib cage peaked near 40 m/s; (C) pleural pressure under the right rib cage peaked at more than 210 kPa (30 psi); and (D) airway pressure in the right lung exceeded 100 kPa (14 psi).
Pathophysiology
Mechanisms of internal organ injury following blast exposure are multifactorial, but stress and shear on biological tissues may result from overwhelming the elasticity of the tissue, thus causing damage in some ways similar to blunt trauma. An illustrative analogy is found in the Textbook of Military Medicine:
An aluminum beverage container that is pushed in only slightly will pop back to its original shape when the force is removed (and any work done by that force is recovered). The onset of damage occurs when the stress equals the tensile strength of the material. As the stress increases beyond the tensile strength, the work done by the excess external force will not be recovered.15
The primary effects of blast overpressure tend to more severely affect air-containing structures of the body. Differential velocities of stress waves traveling through water-density tissues and through air-density lumina create additional internal shear waves that can tear parenchyma at air-tissue interfaces. This can also occur at any location where a density transition is present.15–17
The Northern Ireland Hostile Action Casualty System was devised in an effort to quantify blast loading and its effects on various organ systems. The system estimates injury severity though use of five nonparametric groupings of charge-weight against three groupings of intervening distances.18 Investigators calculated overpressures in psi (1 psi = 6.895 kPa) then grouped them into descriptors of blast loading: < 20 psi = minor; 20–50 psi = moderate; 51–80 psi = severe; and > 80 psi = very severe. Of the 828 casualties registered into this database between 1970 and 1984, there were roughly equivalent numbers in each of the four groups (Table 29.1). No casualty in the first three groups died of “severe chest injury alone…with no serious external injury,” whereas 17% of those with very severe blast loading were in this category and presumably died of blast lung injury (BLI). Of the forty-two patients who died in a hospital, twelve did so during the initial ED resuscitation and fourteen during or shortly after an initial surgery. Half of the delayed deaths were due to severe head injury, and half were due to respiratory failure – whether from BLI, acute respiratory distress syndrome (ARDS), or a combination of both could not be established with certainty.
Relationship of blast loading to severity of injury in 828 casualties from terrorist bombings in Northern Ireland 1970–1984. Adapted with permission from the British Journal of Surgery 1989; 76(10): 1006–1010. The article did not specify whether the number of dead represented only those who did not reach medical care, or all deaths in non-disrupted casualties. Major, moderate, and minor injuries were not rigorously defined.
| Blast Loading Overpressure Categorization | ||||
|---|---|---|---|---|
| Minor <20 psi | Moderate 20–50 psi | Severe 51–80 psi | Very Severe >80 psi | |
| Number of cases | 255 | 135 | 200 | 238 |
| Total body disruption | 0.0% | 3.0% | 2.0% | 9.7% |
| Dead | 2.0% | 17.8% | 17.0% | 51.3% |
| Major injury | 5.5% | 9.6% | 19.0% | 11.3% |
| Moderate injury | 9.0% | 11.9% | 17.5% | 6.3% |
| Minor injury | 83.5% | 57.8% | 44.5% | 21.4% |
1 psi = 6.895 kPa
Injury Classification
The trauma caused by explosive detonations has traditionally been categorized by mechanism. Primary blast injury (PBI) is caused by the effects of the blast wave transmitting forces into the body. Secondary blast injuries are ballistic injuries from fragments, shrapnel, and debris energized by the explosion or associated blast wind. Tertiary blast injuries occur when people are displaced by forces of the blast front and blast wind – and are thrown through the air, tumble along the ground, and impact objects.
Further categorization is less standardized. The taxonomy described by Stuhmiller is useful in the description of quaternary blast injury and other trauma not directly related to the explosion. He depicted quaternary injuries as those resulting directly from “all explosion-mediated injuries not associated with pressure or wind effects,” most notably thermal, toxic, and asphyxiant mechanisms.17 Collateral injuries – such as crush from building collapse, fall from a height, or a motor-vehicle crash – would then encompass all other outcomes. Other authors have hypothesized a quinary category of a “hyperinflammatory state” that can lead to hemodynamic instability.18 Although the exact pathophysiology is uncertain, a toxicological response to the materials contained in many explosives has been suggested, which would move this cellular mechanism out of the quaternary blast injuries described by Stuhmiller.17
Obtaining a description of potential mechanisms of injury is important in the management of trauma victims, but these categorizations are more useful when devising equipment and tactics related to injury prevention. Those caring for these patients after an explosion need to know that presentations include a constellation of thermal, penetrating, blunt, crush, toxic, and other injuries, in some cases similar to those from non-blast mechanisms.
Injury Patterns and Initial Management
Because non-PBI mechanisms result in conventional trauma familiar to most healthcare providers, this section focuses on injury patterns primarily resulting from the blast wave itself.
Brain
Severe open and closed head injury is the most common cause of death in blast-injured casualties.9,14,19 Evaluation and management of blast-induced TBI is generally similar to that of blunt and penetrating trauma from other mechanisms. Computed tomography (CT) is commonly employed, but should not be used for every patient. Rather, history and physical examination should guide clinicians. Mild cases of TBI are often missed, unless patients are properly screened for subtle functional impairments. In a 10-year study of accidental explosions, more than one-third of patients seen at the Maryland Institute for Emergency Medical Services Systems with a normal Glasgow Coma Score had some element of TBI that went undetected on the initial evaluation.20
The role of imaging has not been well-defined for TBI solely due to primary or quaternary mechanisms. During mass casualty situations, some authorities have recommended that CT be reserved for diagnosing intracranial mass lesions during the initial management phase – the period when casualties are arriving.21 Otherwise, CT or magnetic resonance imaging (MRI) can be deferred based on symptoms developed during observation while more immediately serious casualties are being managed.
Blast-induced TBI, which may be distinct from classic blunt or penetrating trauma mechanisms, ranges from mild to severe. The pathophysiology of damage is not well understood and often not apparent using conventional imaging techniques.22 Putative mechanisms of primary TBI are likely a combination of gross acceleration, skull deformation and rebound, surge of blood and cerebrospinal fluid from the blast-loaded thorax, air emboli from blast-injured lungs, micro-implosions in the brain substance, dysfunction of the blood-brain barrier, superoxide and toxicological effects, and electromagnetic pulse injury from superheated gases. Local biochemical and systemic metabolic derangements contribute to the injury patterns.23,24 A trial published in 2013 suggests that N-acetylcysteine administered within 24 hours of injury decreases immediate sequelae of mild TBI such as dizziness, hearing loss, headache, memory loss, sleep disturbances, and neurocognitive dysfunction.25
All blast-exposed individuals must be screened for TBI. Neurological deficits found on examination of blast victims range from subtle dysfunction to complete unresponsiveness. Key screening questions for potential neurological injury include: Do you have headache, vertigo, unsteadiness, or nausea?2 This may help identify patients at risk for mild TBI and allow early initiation of casualty protection and medical management. No specific assessment methodology for subtle neurocognitive deficits has proved superior in all settings, though one successful screening tool is the Military Acute Concussion Evaluation (MACE).26 Even patients believed not to have TBI should be provided detailed instructions regarding post-concussion syndrome and post-traumatic stress disorder (PTSD), which may be more closely related than previously suspected.
Eyes, Ears, Sinuses, and Throat
Auditory and ocular injuries were the most frequently missed in one Israeli report of mass casualty incidents.21 Healthcare providers should ask questions focused on visual and auditory symptoms:2
Do you have pain or problems with your eyes or ears? Any decreased vision represents a penetrating foreign body or intraocular hemorrhage until proven otherwise. Ringing, roaring, or decreased hearing is common, but determination of the long-term effect on hearing requires detailed audiometric testing on serial follow-up evaluations.
Foreign material and penetrating eye injuries are common after explosions. Hyphema14 and a variety of macular abnormalities,17 without obvious blunt or penetrating mechanisms, have been postulated as forms of PBI. The management of penetrating and non-penetrating eye injuries is beyond the scope of this chapter; however, ultrasound has been suggested as a screening tool for ocular damage in blast-injured casualties.28
Temporary hearing loss and tinnitus are common, the severity of which typically decreases at greater distances from the explosion. This can make communications challenging. Rupture of the TM also occurs frequently. Permanent hearing loss can result from irreparable damage to structures of the inner ear.29,30 Transient, intermittent, and/or permanent blast-induced vestibulopathy and dysequilibrium can also occur, most commonly due to tearing of microstructures within the cochlea. Symptoms can also manifest remotely after the injury, and should be considered in patients with vertigo and a history of exposure to blast overpressure. CT imaging of the temporal bones can be diagnostic for this injury.
Blast auditory injury (BAI) is not life-threatening, but should be considered after patients are stabilized. Practitioners should examine the ears using direct otoscopy. TM perforation, disruption of the ossicular chain, and gross contamination should be noted. Rupture and blood together could be indicative of concomitant TBI. In the absence of multiple casualties, an otolaryngologist should be consulted and the patient should be seen within 1 day if there is significant debris in the ear or the torn edges of the TM require realignment.
TM rupture may be a marker for TBI.31 It indicates exposure to blast overpressure, thus prompting mental-status and neurological examinations. On the other hand, contrary to previous expert opinions, the presence of TM rupture in patients without pulmonary manifestations in the first hour after injury does not appear to be a surrogate marker of sufficient blast overpressure to produce delayed-onset BLI.32 Absence of TM rupture makes BLI less likely, but does not completely eliminate the possibility.33
Chest
Blast waves that gain access to the upper respiratory tract can cause pharyngeal, laryngeal, and tracheal petechiae and ecchymoses.16,34,35 These findings may indicate sufficient blast loading to also cause BLI. However, blast waves do not cause BLI via an air pulse down the respiratory tract. Rather, BLI is caused by forces applied to the chest wall.
A variety of injuries may occur in the lungs due to tissue tearing. Blood can leak into the parenchyma, into the pleural space, or into the airways. Air can leak into the tissues, into the pleural cavity, or into the circulatory system. Box 29.1 summarizes the conditions resulting from air-tissue interfaces in the chest.
| Chest | Abdomen |
|---|---|
Escape of air into lung parenchyma results in traumatic pseudocyst into pleural space results in pneumothorax into vasculature results in systemic air embolism | Escape of air into bowel parenchyma results in pneumointestinalis into peritoneal space results in pneumoperitoneum into vasculature results in portal air embolism |
Escape of blood into lung parenchyma results in pulmonary contusion into pleural space results in hemothorax into airways results in hemoptysis | Escape of blood into bowel parenchyma results in bowel-wall hematoma into peritoneal space results in hemoperitoneum into bowel lumen results in GI hemorrhage |
| GI = gastrointestinal | |
The prototypical BLI is hemorrhage into the pulmonary tissues and small airways. This can range from subpleural petechiae to contusions of various shapes and sizes.34,35 The degree of damage is proportional to the peak chest-wall velocity.36 Figure 29.2 shows pulmonary contusions of various severities in different locations in a sheep model. Pulmonary lacerations can result in alveolar-venous fistulae; traumatic emphysema, if contained within the lung parenchyma; and hemopneumothoraces and bronchopleural fistulae, if involving the visceral pleura.
Blast lung injury from a sheep model. Note parenchymal contusions, the most severe of which are found in areas of the lung between reflecting surfaces such as the chest wall and diaphragm. Also note some hemorrhages located under the intercostal spaces.
Alveolar-venous communications can allow air to enter the pulmonary venous circuit, travel to the left heart, and be ejected as systemic air emboli. Organ infarction and death can occur within minutes. Air embolism can also occur following blunt or penetrating trauma.37 Bronchopleural fistulae can lead to unilateral or bilateral tension pneumothoraces.38 Both of these conditions can be rapidly and significantly exacerbated by positive-pressure ventilation (PPV).14,37 Some experts suggest that the commencement of PPV can accelerate death in initial survivors.
Medical personnel should ask targeted questions of casualties who can speak:2
“Are you short of breath?” Dyspnea may indicate tension pneumothorax, hemopneumothorax, pulmonary contusion, or shock from hypoxia, hemorrhage, or systemic air embolism.
“Do you have any chest discomfort?” Penetrating or blunt trauma, pneumothorax, and myocardial ischemia due to coronary air embolism can all cause chest pain.
“What does your pain feel like?” Pain associated with pneumothorax is typically sharp and focal, lateral or central, and aggravated by breathing until the lung is completely collapsed. Pain of pulmonary contusion is often described as dull and diffuse. Discomfort may wax and wane with respirations. Bronchospasm or difficulty expanding the chest may be described as tightness. Chest pain that seems consistent with an acute coronary syndrome may be due to air embolism to one or more coronary arteries.
“How much effort is required to breathe?” Dyspnea at rest may indicate shock due to external or internal hemorrhage; hypoxia due to airway obstruction or pneumothorax; or severe pulmonary contusion. Increased severity of dyspnea on exertion suggests the presence of BLI or pulmonary damage by another non-PBI mechanism.
Physical examination findings consistent with BLI include tachypnea; difficulty completing sentences in one breath; dry cough, with or without wheezing; hemoptysis of varying degrees; diminished breath sounds indicative of pulmonary contusion, pneumothorax, or hemothorax; inspiratory rales or dullness to percussion caused by interstitial edema, parenchymal hemorrhage, or hemothorax; and poor chest-wall expansion caused by decreased lung compliance. Rapid, shallow respirations are characteristic of BLI casualties.
Pizov et al. published a report on their observations regarding BLI severity of victims from bombings on commuter buses in Israel.38 They were able to classify injuries into mild, moderate, and severe based on plain chest radiography, arterial blood-gas (ABG) analysis, and the presence of bronchopleural fistulae. Contusion densities on chest radiographs ranged from localized unilateral to massive bilateral, whereas the paO2 to FIO2 ratio (PFR) was a marker of lung injury impairing oxygen diffusion.
Wightman and Gladish combined this classification with information from other studies to create the correlates of clinical information with the need for PPV (Table 29.2).14 Mild BLI, defined as one lung focally injured and a paO2 maintained over 5.6 kPa on an ambient FIO2 of 0.21, may require supplemental oxygen administration, but generally will not require PPV for respiratory compromise. Moderate BLI, defined as most of one lung or both lungs involved asymmetrically and an inability to maintain a paO2 of 17.4 kPa with an FIO2 of 0.60 using a non-rebreather mask (NRBM), normally requires some period of volume-controlled ventilation using reasonable levels of positive end-expiratory pressure (PEEP) or pressure support. Severe BLI, defined as the inability to achieve a paO2 of 8.1 kPa with an FIO2 of 0.93 using a bag-valve-mask (BVM) system, often requires pressure-controlled ventilation, inverse inspiratory-to-expiratory ratios, and permissive hypercapnia.
Severity categories for BLI reported by Pizov et al., which may help predict the necessity for use of PPV and PEEP. This table is in the public domain as a U.S. government work. It was adopted from the Annals of Emergency Medicine 2001; 37(6): 664–678. Assumptions are: ambient air has an FIO2 of 0.21, a non-rebreather mask delivers FIO2 in the range 0.50–0.70, and bag-valve-mask delivers FIO2 in the range of 90–96%.
| BLI Categorization | |||
|---|---|---|---|
| Mild | Moderate | Severe | |
| Bronchopleural fistulae | Absent | Possible | Present |
| Infiltrates on plain chest radiography | Unilateral | Bilateral but asymmetrical | Bilateral and diffuse |
| paO2-to-FIO2 ratio examples | >200 torr paO2 > 42 torr on FIO2 = 0.21 SPO2 > 75% on FIO2 = 0.21 | 60–200 torr paO2 36–120 torr on FIO2 = 0.60 SPO2 = 75–90% on FIO2 = 0.60 | <60 torr paO2 < 56 torr on FIO2 = 0.93 SPO2 < 90% on FIO2 = 0.93 |
| PPV requirement | Unlikely for a respiratory problem | Highly likely but conventional methods usually effective | Universal and unconventional methods often necessary |
| PEEP requirement | <5 cmH2O if PPV required | 5–10 cmH2O usually necessary | >10 cmH2O if volume-controlled PPV still used |
FIO2 = fraction of inspired oxygen; paO2 = arterial dissolved oxygen; SPO2 = arterial oxygen saturation as measured by pulse oximetry
Wightman used the oxygen-hemoglobin dissociation curve to estimate pulse oximetry (SPO2) measurements corresponding to PFR categorizations for use in the out-of-hospital setting. These recommendations assumed no major left or right curve shifts, no significant elevations in altitude, and no hemoglobin or mitochondrial toxins.2 Mild BLI is defined as any SPO2 reading at or above 75% hemoglobin saturation on ambient air. Moderate BLI exists with any reading at or above 75% on a NRBM. Severe BLI is diagnosed by a reading less than 90% when using a BVM.
BLI is uncommon from terrorist bombings in open-air civilian settings.39 Most victims close enough to high-order detonations to sustain BLI are killed by other blast mechanisms. One notable exception is the terrorist bombing event behind the U.S. Embassy in Nairobi, where BLI was a significant finding in victims. This was likely due to the charge detonating in a space surrounded by three multistory buildings that reflected the blast wave multiple times.40 In distinction, explosions in confined spaces create casualty populations with much higher proportions of survivors manifesting BLI – especially when devices did not generate many fragments or shrapnel, or victims were protected from significant secondary ballistic objects.41,42
Katz and colleagues described the connection between confined spaces and increased incidence of PBI in initial survivors.41 They reported on fifty-five casualties transported to two major medical centers in Jerusalem following detonation of a 6-kg device placed under a seat inside a commuter bus. Close to half of the casualties were evaluated and discharged from the EDs. All twenty-nine admitted patients had PBI of the ears, lungs, or bowel. For victims less severely injured but still admitted, there was a 29% (5/21) incidence of BLI and a 10% (2/21) incidence of “nonperforating bowel injury,” that is, presumptive blast intestinal injury (BII). In casualties with more severe injuries, 75% (6/8) had BLI and 25% (2/8) had BII.
Pizov and colleagues pooled data from two similar explosions in commuter buses to report on their experiences with managing BLI.38 Forty-seven victims were found dead at the scenes and one more died on ED arrival. Of the seventeen survivors, fifteen (88%) had BLI. Nine (60%) had pneumothoraces, which were bilateral in seven. Five had clinically significant bronchopleural fistulae.
Patients with tension pneumothorax require needle thoracentesis followed by tube thoracostomy. Unilaterally decreased breath sounds and evidence of clinical shock should prompt immediate pleural decompression. Air escape without clinical improvement should raise suspicion for bronchopleural fistula, which may require one or more chest tubes, independent lung ventilation by preferential intubation of the unaffected lung or use of a dual-lumen endotracheal tube, or interventional surgery. In mass casualty scenarios, chest tubes before radiography have been recommended for any serious thoracic injury. If bilateral tension pneumothoraces have been ruled out in patients with cardiac arrest, resuscitative thoracotomy should not be performed, because these casualties most often have non-survivable pulmonary contusions.21
Spontaneous, negative-pressure ventilation is preferred over PPV whenever possible.14 In a study of BLI patients admitted to the ICU at one Israeli medical center, 61% were intubated in the field or on arrival to the ED and 14% were intubated within 2 hours for progressive respiratory distress. The other 25% did not require mechanical ventilation.42 Noninvasive PPV has been used successfully to avoid endotracheal intubation in some patients.43 When invasive PPV becomes necessary, the initial use of PEEP up to 10 cmH2O is acceptable early in management.38 The need for more PEEP to maintain oxygenation should prompt a reassessment of ventilator mode, with consideration of pressure-control ventilation rather than the more commonly employed volume-control method.2
Systemic arterial air embolism should be considered any time a communication between the airways and the pulmonary venous circuit is suspected, such as with hemoptysis.44 Embolic infarction syndromes related to one or more vascular distributions may be noted on clinical examination.14,44 Semi-left-lateral decubitus or prone positioning have theoretical but unproven benefits.14 Otherwise unexplained cardiac arrest might also suggest systemic air embolism. When managing individual cases (i.e., not in a resource-constrained setting), if the side of injury can be determined, resuscitative thoracotomy with hilar twist may be lifesaving.
Optimal fluid management in patients with BLI is controversial, just as it is for pulmonary contusions due to blunt chest trauma. Colloids have been recommended over crystalloids for BLI, but outcome data are lacking. Following blunt trauma, neither the amount nor type of fluid seems to make a significant difference.45,46 Similar issues exist for blast and blunt TBI.14
ABG analysis is useful for stratifying patients into mild, moderate, and severe lung injury, regardless of etiology – for example, due to BLI (Table 29.2), blunt contusion, or ARDS (Table 2).14,38 The presenting PFR is predictive of outcome in blunt pulmonary contusion.45,46 Most other laboratory tests are unlikely to be helpful in early identification or management of PBI.47 During mass casualty situations, individual facilities will need to assess current resources and surge capacity to define specific laboratory protocols for blunt, penetrating, and thermal trauma.
A plain chest radiograph is essential in victims with any traumatic torso-related complaint. This may also be used to confirm endotracheal, thoracostomy, and gastric tube placements. The cardiac silhouette may be enlarged as a result of right heart overload from increased pulmonary vascular resistance due to significant BLI.48 Although almost any radiographic finding might have a conventional traumatic cause, manifestations of BLI include interstitial or alveolar fluid, hemothorax, pneumothorax, or pulmonary pseudocyst.45,49 Infiltrates consistent with pulmonary contusions are the most common parenchymal findings. Pulmonary injury severity can also be categorized radiographically (Table 29.2).38
Additionally, as more emergency medical providers are trained in the use of ultrasound, this will likely become a useful tool in the rapid assessment of pulmonary and intra-thoracic injury. Ultrasonography is a relatively inexpensive method to screen large numbers of patients rapidly at the point of care, and also allows for out-of-hospital evaluation in ways not possible with traditional radiographs. This is especially true in the evaluation for pericardial effusion, pneumothorax, and hemothorax. There are currently no accepted standards for the use of ultrasound in the evaluation of blast chest trauma, however this is an emerging area of study.
Chest CT is an imaging option to quantify interstitial and alveolar fluid, and relate findings to ventilatory requirements of mild and severe categories, similar to those of Pizov et al.38 In one report of patients with non-blast trauma, all those with more than 28% airspace filling required ventilatory assistance; none with 0% to 18% filling did.50 Transthoracic and transesophageal echocardiography have been used to image air bubbles transiting cardiac chambers.
Abdomen
Box 29.1 summarizes conditions resulting from disruption of air-tissue interfaces in the abdomen. When stress-induced pressure differentials cause tissue tearing of air-containing structures in the gastrointestinal (GI) tract, these organs can bleed into the mesentery, bowel wall, or lumen. Figure 29.3 shows contusions of the bowel wall and intraluminal hemorrhage in a sheep model. Weakened parenchyma can rupture, releasing air and GI contents into intrathoracic, intraperitoneal, or extraperitoneal spaces. The colon is the organ most commonly affected, likely because of its larger gas content.48,51,52 Tension pneumoperitoneum has been reported.53
Blast intestinal injury from a sheep model. Note segmental parenchymal contusion in areas against the body surface. Also note intraluminal blood visible through other areas of relatively intact bowel wall.
Overall, the incidence of BII in initial survivors ranges from 1–33% depending on explosive energy, distance from the epicenter, wearing of body armor, air versus water medium, closed versus open airspace, and multiple other factors.52 Based on literature from World War II and Israeli Naval battles, BII is more common in victims exposed to underwater blasts.48 Fragments do not travel very far in water, but blast waves are propagated much greater distances than they are in air. Individuals treading water or buoyed upright by a flotation device have no TM exposure, only partial thoracic exposure, and full abdominal exposure to underwater blast fronts. Hence, the abdomen receives proportionally greater blast loading.15
Targeted questions to ask casualties are similar to those for blunt abdominal trauma:2
“Do you have abdominal or testicular pain, nausea, urge to defecate, or blood in your stools?” BII may cause visceral, parietal, or referred pain. Tenesmus and hematochezia are relatively common presenting complaints.
“What does your pain feel like?” Stretched bowel wall feels like a persistent gas bubble with possibly sharp and crampy waves as it is affected by peristalsis. Once the bowel ruptures, pain often decreases until peritonitis begins. The pain of peritonitis is commonly diffuse and severe, and may be associated with fever.
The abdominal, flank, back, genital, perineal, and rectal examinations are the same as for any other polytrauma patient, though the probability of bowel rupture is comparatively higher. Moreover, pathology can evolve over time as bowel-wall weakening can be delayed by several days following BII without immediate rupture.54–56 Blast-injured casualties with any abdominal signs or symptoms require serial examinations over several days.
Ancillary evaluation protocols for individual patients should be similar to those for blunt abdominal trauma, except clinicians must realize that the pretest probability of bowel rupture is higher, especially following closed-space explosions.14 Routine plain chest radiographs should be scrutinized for free intraperitoneal air. Focused assessment with sonography for trauma (FAST) or CT may be employed to visualize free intraperitoneal fluid. FAST may also be used as a rapid screening tool for intraperitoneal hemorrhage, whether or not combined with a specific triage methodology. However, a detectable amount of hemorrhage is an uncommon finding in intestinal perforation from any cause. CT, especially without GI contrast material, is also not particularly sensitive in detecting bowel rupture.52
Other Primary Blast Injuries
A syndrome of bradycardia and hypotension without blood loss has been described in blast-injured soldiers.34 Blast loads directed only toward the chest in animal models cause a unique, vagal nerve-mediated form of cardiogenic shock without compensatory vasoconstriction.57 This phenomenon occurs within seconds of exposure, and partially resolves over 1 to 2 hours. Pressure-sensitive pulmonary C-fiber receptors may be the initiating afferent limb of this reflex.58
Blast loading can also damage solid organs through displacement of body surfaces, shear-wave stretch, and acceleration at organ attachments. The heart and intra-abdominal solid organs may sustain petechiae, contusions, lacerations, or rupture. Mesenteric, retroperitoneal, and scrotal hemorrhages have also been reported.35
The combination of stress-wave induced shattering of bone and subsequent blast wind can tear off all or portions of the extremities and the head. Isolated torsos were all that were found of many victims exposed to the 1998 detonation of one metric ton of TNT-equivalent explosives behind the U.S. Embassy in Nairobi. Multiple traumatic limb amputations, with or without genital and intrapelvic injury, has become the signature IED injury in the Afghanistan conflict.59,60 Nonetheless, survival to reach definitive medical care is now common. Fourteen amputations occurred in survivors of the 2013 bombings at the Boston Marathon.
Local Medical Responders
Destruction of structures and associated debris resulting from explosive blasts hampers initial rescue efforts of first responders. The threats of accidental or intentional secondary blasts; evolving hazards such as fire, smoke, toxic substances, and building collapse; and potential follow-up attacks with ballistic weapons can restrict local responders’ abilities to reach victims. Even when victims are located, single or combined threats can affect the speed and accuracy of clinical assessment prior to movement of patients out of these hazardous environments.
No matter how clinically contraindicated the rapid movement of blast victims may seem, the risks of lingering in an area of recent explosive activity to more adequately stabilize victims may be greater than any risk associated with early rescue or transportation. Organizations tasked with first response should anticipate the unique challenges of rapid evaluation, triage, initial treatment, and evacuation of individual or multiple blast victims.
Stein and Hirschberg described four out-of-hospital management phases based on their experiences with terrorist bombings in Israel.21 The “chaotic phase” is characterized by ambulatory victims self-evacuating or being transported from the scene by well-meaning bystanders. No professional responders have arrived, and no Incident Commander has assumed control of the situation. The “reorganization phase” begins with the arrival of law-enforcement, fire/rescue, and EMS assets. Triage is performed and resources are allocated for the most seriously injured casualties. The “site-clearing phase” involves evacuation of known patients and thorough searches for missed victims. In urban settings in Israel, scenes are typically cleared in less than 3 hours. The “late phase” encompasses the time required for all victims suffering from blast-related injuries to present for care. Minimally injured casualties and those with medical or emotional complaints usually seek care within 1–2 days of the event.
Einav and coauthors suggested three phases: rapid on-scene triage with a minimum of medical interventions; urgent evacuation of critically injured casualties to the nearest hospital for resuscitation and stabilization; and transportation of all other casualties to more distant and presumably less-burdened facilities, so as not to overwhelm those closest to the scene.61 A fourth phase might be the redistribution of casualties from less-capable hospitals to regional trauma or medical centers.
Singer and colleagues detailed the Israeli experience in out-of-hospital responses to terrorist attacks.62 The first medical team that arrives does not provide care. Its primary function is scene assessment and communication to Incident Command. Key transmission elements include: 1) type of event; 2) estimated casualty numbers; 3) location(s) of casualties; 4) safe approach and evacuation routes; and 5) estimated time of first casualty arrival at the closest hospital. As the next wave of medical teams arrive, they evaluate and manage casualties as they find them. Larger responses would allow additional medical teams to be assigned to different geographical regions.
Access
The potentially unstable environment associated with explosive blasts may limit search and rescue efforts. There is a dearth of best-practice recommendations for out-of-hospital responders. However, a few observations can be stated.
Significant rescue and response efforts require coordination among public safety agencies, including emergency management, fire/rescue, law enforcement, and public health. As such, emergency management partners should use the Incident Command System (ICS). Coordination with utility companies allows rapid response to situations that put rescuers at risk, such as ruptured pipelines or damaged power lines. Bomb squads or military explosive ordnance disposal teams may be required, if unexploded devices are discovered.
Explosions can cause collapse of buildings and other structures. Access to trapped victims falls under the discipline of urban search and rescue (US&R). Delayed access may result in natural progression of pathophysiological processes, with more complications from blast manifesting before medical personnel can make initial contact with victims or prior to extrication to medical teams at a casualty collection point (CCP). Conditions unfamiliar to EMS providers may exist. Some examples include confined-space hypoxia and hypercarbia; restriction of chest-wall expansion; dust, smoke, or toxic inhalations; prolonged, and possibly irreversible, hemorrhagic shock; compartment and crush syndromes; dehydration; and advanced wound infections and sepsis in delayed rescues. Delays in evacuation can similarly result in abnormally prolonged medical-responder patient-contact time prior to extrication and evacuation for stabilization or definitive care at a hospital or alternate site.
Collapse of smaller structures may result in larger proportions of victims surviving to hospital admission. With the collapse of larger structures, outcomes are less favorable, as was observed in those victims trapped inside the Murrah Federal Building in Oklahoma City. In that event, the relative risk of dying was over sixteen times greater in the collapsed portion than it was in other areas of the structure.9 The only fatality that did not occur as a direct result of the explosion was a rescuer with inadequate PPE who sustained a head injury caused by a falling object.
A “direct-threat environment” exists when responders are exposed to an active hazard. In some situations, scene security becomes a higher priority than casualty care, in order to prevent responders from becoming casualties themselves. When responders could be actively threatened by approaching the victim, it may not be appropriate to attempt immediate rescue. Casualties who can move under their own power should be directed to a safer location if possible. During a military-style attack, they should be told to either move to cover or remain still, so as not to attract attention and become a target again.
If a responder proceeds to a casualty and encounters a hazardous situation, most medical interventions would be inappropriate until both patient and provider are in a safe location. On the battlefield, care under fire is usually confined to control of rapidly exsanguinating external hemorrhage. Immediate airway issues from blast injuries are rare. Basic remedial maneuvers require a constant position, and adjunctive interventions can be dangerously time-consuming in a direct-threat situation. If the responder subsequently moves to a position of safety, more interventions could be undertaken and the casualty could be moved using field-expedient lifts, carries, or other available methods.
An “indirect-threat environment” occurs when rescuers are not experiencing an active threat, but are at risk because of proximity to a hazard. Potential risks and benefits must be weighed before any decisions on access and rescue are made. Safety is a prime function of the ICS. Evolving sensor technologies may facilitate locating victims, and even assessing their physiological statuses. This information will better inform decisions regarding responder risk versus patient benefit.
Out-of-Hospital Triage
Although triage is usually discussed in the context of a disaster or mass casualty scenario where inadequate resources exist to meet medical needs, triage occurs daily in medical settings around the world. It can be applied to any decision related to allocation of resources.
Undertriage refers to categorizing victims into a lower acuity category than their conditions warrant and risks excessive morbidity and mortality from delays in care. On the other hand, overtriage categorizes victims into higher acuity categories than necessary and commits resources that might be needed elsewhere. Whereas undertriage mostly affects individual casualties, the overtriage rate has been postulated to have a linear relationship to mortality in the overall population of critical casaulties.63 However, no evidence is available demonstrating this assertion. All publications to date on the subject describe only associations. It is equally valid to postulate that the strain of working at mass casualty events with higher mortality rates results in more overtriage. Since no studies currently exist demonstrating a cause and effect relationship, either interpretation is equally valid (see Chapter 14). Nonetheless, during resource-constrained responses, incorrect triage decisions have far-reaching consequences on the community affected by the disaster.64
Three general domains for the application of field triage have been suggested: targeting, treatment, and transportation.2 Each must also be viewed in the context of potential hazards for the responders. For instance, care provided to a bleeding victim might be different in a structure partially on fire than it would be on a street with traffic blocked.
“Triage for targeting” refers to locating and accessing victims of an explosive blast. Reconnaissance by aircraft may be helpful in assessing the affected area, but there are limited best practices or technological solutions to support the process of victim location beyond rescuers conducting thorough on-the-ground searches. This may be hampered by debris or hazardous materials dispersed by the energy of the explosion and the blast wind; lack of technical expertise to enter collapsed structures or buildings on fire; or inadequate security to neutralize the threat of additional armed attacks.
Assigning personnel assets to geographical areas with the highest probability of containing salvageable victims should be coordinated through the ICS. External assistance in the form of specialized search-and-rescue teams and equipment may be necessary.
“Triage for treatment” in the out-of-hospital setting involves sorting casualties based on required medical interventions. This presumes that patients requiring the most immediate lifesaving interventions are the ones who will be triaged to the highest priority category, if adequate resources are available to treat everyone.
There are a number of triage systems available for use in mass casualty settings (see Chapter 14). Simple Triage and Rapid Treatment (START) and Secondary Assessment of Victim Endpoint (SAVE)65 encompass one such system, which has been commonly employed in the United States for many years. However, the SALT (Sort, Assess, perform Lifesaving interventions, and Treatment and Transportation) methodology66 has received considerable attention in recent years. Internationally, there are other triage systems commonly in use, such as Triage Sieve and Sort in the United Kingdom and an algorithm created by CareFlight in Australia. There are no prospective studies of the performance of any triage system during an actual disaster. Most published articles examined medical records retrospectively, which has led to any conclusions being severely hampered by missing data and small numbers of critically injured patients, the group that would presumably most benefit from rapid and accurate triage.
Most field triage systems divide casualties into some combination of five categories (listed in order of priority): immediate, delayed, minimal, expectant, and dead. However, the Magen David Adom (MDA) Israeli National EMS system uses three categories: urgent, non-urgent, and dead. MDA has the advantage of being a nationwide network with centralized organization in a relatively small geographical area, but many response systems in other communities could adopt a similar approach.
Immediate or urgent casualties are those for whom immediate lifesaving intervention is required. However, the resources needed to save the life of any given casualty in this category are as variable as the conditions that cause the life-threatening problems. When immediately available, and not anticipated to be needed elsewhere, most communities and cultures have an expectation that the necessary resources will be committed. However, if these resources are not available in the timeframe required, cannot be obligated to a single patient, or must be redistributed to many patients (e.g., the time a medical provider can spend with a single patient, or the need for large amounts of resuscitative fluids or blood), casualties in the immediate category might be reclassified into the expectant category.
Other victims would be non-urgent in the Israeli system. Delayed casualties are categorized based on the triage officer’s brief assessment as those not needing immediate lifesaving intervention, but without a potentially life-threatening condition excluded. Minimal casualties are those believed to have conditions not requiring intervention during the mass casualty situation in order to prevent undue mortality, morbidity, or suffering.
Although the expectant category derives from medically austere military settings with typically longer evacuation times, it may be necessary to use this designation in civilian settings when needs outstrip resources. Many EMS educators teach an approach to expectant casualties as if they are “expected” to die, or are otherwise labeled as “unsalvageable.” A better approach (for these casualties, who would have otherwise been categorized as immediate) would be to “expect” reevaluation, and initiate more aggressive management once sufficient resources become available.
Whichever methodology is applied, two dynamics are critical: the responders must be intimately familiar with the chosen technique; and they must reassess patients and reassign categories dynamically to optimize victim benefit and allocation of resources. Casualty receivers must also be aware of the system or systems used in their communities, so they are prepared for the types of casualties presenting in each triage category. One caveat to this is that excessive retriaging can also create bottlenecks in patient flow, leading to delays in definitive care.
“Triage for transportation” is less understood outside of the military. It should be self-evident that patients incapable of moving themselves to treatment facilities will ultimately require evacuation. Most of the world’s military organizations use triage to sort patients into categories for allocation of scarce transportation resources. In the U.S. Army and Marine Corps, for example, “urgent” patients are those requiring a higher level of treatment within the next 2 hours. “Priority” patients are those who require additional treatment within 4 hours. “Routine” patients require movement to a higher level of care setting within 24 hours, so this would rarely apply to a civilian disaster setting in the developed world. Nonetheless, significant constraints on the availability of evacuation assets, long distances, and lack of suitable destinations may force consideration of this category. Civilian agencies also have the option of changing the expected time frame, for example to 6 or 12 hours, instead of 24 hours.
Some casualties can be placed in a “convenience” category when their conditions would not be expected to deteriorate if care could not be rendered for longer than 24 hours. If this category is employed, these patients would be placed on a medical conveyance only when extra space is available, and no medical attention is required during transportation (e.g., a patient with an uncomplicated pregnancy who requires management in a non-combat zone setting). Because this classification is used by the military for individuals with a medical condition who need only physical movement out a given location, it would likely have limited utility in civilian disaster settings.
The Israeli MDA uses only “urgent” and “non-urgent” triage categories for making treatment and transportation decisions. In a paper that defined mass casualty incidents as those of “large enough scale to recruit most of the rescue teams…within a defined region, regardless of the actual number of casualties,” Einav and colleagues examined evacuations from urban and rural scenes of terrorist bombings over a 2-year period.61 Approximately one in every five victims were deemed to be urgent, although a few incidents were not related to explosions, and those that did result in blast-injured casualties encompassed both open-air and closed-space detonations. However, even in large urban areas, less than half of these critical casualties were evacuated to trauma centers, although most of the remainder were transported to other medical centers as opposed to smaller hospitals. The vast majority of patients arrived at the closest facility, whether self-evacuated or transported by ambulance.
Ideally, critically injured blast casualties should be managed at trauma centers, when available.67 Children should be transported to hospitals with pediatric capabilities.68 Consideration should be made for the reintegration of injured children and parents, as separation may lead to social disruption and impediments to care. Less critical casualties should be dispersed to less-burdened facilities farther away from the incident.62 Use of helicopters, which represent high-value, low-density assets in any disaster response, must be carefully considered. Effective transportation systems for critical casualties require significant community and regional preparedness before an event, but evacuation processes are made even more complex by ongoing threats following initial explosions. Difficult on-the-spot decisions must be made in determining the best mode of transportation (e.g., ambulance or nonmedical vehicle of convenience, ground or air) and best destination for casualties who did not self-evacuate, based on triage category and specific injury types.
Out-of-Hospital Care
Once patients are adequately assessed in a relatively safe environment, the individual out-of-hospital care each victim receives should not be affected by the specifics of post-blast settings. This is true as long as due consideration is given to the potential for exceeding available time, personnel, equipment, and supply resources. Civilians responding to a threatening environment should be aware of the tactical emergency casualty care (TECC) recommendations.69 These guidelines discuss appropriate care in direct and indirect threat, time-constrained, and resource-limited situations.
Mass casualty out-of-hospital care may require EMS providers to employ techniques with which they are less familiar. Examples include use of methods other than direct pressure to control hemorrhage, since this action consumes medically trained personnel resources that may be more effective elsewhere. Exsanguinating extremity hemorrhage may necessitate control with a proximal tourniquet, either by applying a prefabricated or field-expedient device or inflating a sphygmomanometer to a pressure higher than systolic blood pressure. The use of tourniquets in modern wartime has shown that correctly placed extremity tourniquets improve survival.70,71 They may also have applications in disaster medicine, but specific use criteria are needed in the civilian setting.72 Clot enhancing agents such as kaolin, microporous polysaccharide microsphere, mineral zeolite, or poly-N-acetylglucosamine (chitosan) may be useful adjuncts, or applied primarily for truncal or proximal extremity wounds where tourniquets cannot be used.73
Although rarely reported in the literature, massive hemoptysis from severe BLI may compromise a victim’s airway. If simply allowing patients to attain their own best position for oxygenation and ventilation is ineffective, one lifesaving intervention is to selectively intubate the least injured lung, if sufficient time and resources are available.14 This can be accomplished blindly as depicted in Figure 29.4.74 In 99% of cases, a standard endotracheal tube passed orally to its full depth will cause the tip and balloon to sit in the right mainstem bronchus. After cuff inflation and a few ventilations, unilateral isolation should be assessed. If more blood passes around the tube than through the tube, then the right lung is protected from left-sided hemorrhage. If more blood passes through the tube, the right lung is likely the origin, and the left lung must be selectively intubated.2
Algorithm for blind selective-mainstem intubation.
Related posts:
Full access? Get Clinical Tree
