Emergency War Surgery NATO Handbook: Part I: Types of Wounds and Injuries: Chapter
V: Blast Injuries
Pathology of Primary Blast Injury
United States Department of Defense
Primary blast injury is seen almost exclusively in gas containing organs: the ear and
the respiratory and gastrointestinal tracts. Of the three organ systems, the ear is the
most sensitive. The pinna and the external canal collect and in some cases, amplify
pressure signals so that the tympanic membrane, converting acoustic energy to mechanical
displacement, is displaced into the middle ear. At pressures of approximately 35
kiloPascals (kPa, with 7 kPa equalling 1 pound per square inch), the human eardrum may
rupture (Figure 18). Above 100 kPa, almost all
eardrums will be ruptured. The eardrum generally perforates inferiorly in the pars
tensa but there may be hemorrhage into the membrane without rupture. At higher
pressures, the drum may be almost obliterated and the ossicles can be dislocated or
fractured. Vestibular function is usually not affected.
Injury to the lung is the cause of the greatest morbidity and mortality. Grossly, one
sees diffuse, pleurally-based pulmonary contusions with a stiffened, heavy lung. The
costal surface may show transverse stripes called "rib markings" which, in fact,
are more closely associated with intercostal spaces. Lung weights may be two or three
times normal. Pleural rents or blebs may result in pneumothorax, hemothorax, or
mediastinal extravasation of air. Rib fractures or evidence of significant chest wall
damage are not seen in the absence of other mechanisms of trauma. Microscopically, the
hemorrhage is mainly intra-alveolar with some perivascular or peribronchial disruption and
bleeding. Alveolar walls are torn, sometimes producing giant blood-filled alveolar spaces.
Alveolar-pulmonary venous communications, the source of air emboli within the arterial
circulation, are created. These fistulae are responsible for most of the early mortality
resulting from primary blast injury. Critical vascular beds in the central nervous or
coronary arterial circulations can be occluded by entrained air emboli with subsequent
disastrous results.
The gastrointestinal tract may be damaged wherever there are collections of gas. Injury
to the gut is particularly severe in underwater blasts. While hollow visceral injury is
also present in airblast, it is generally overshadowed by the more dramatic presentation
of air emboli or acute respiratory insufficiency. The colon is the hollow viscus most
commonly disrupted. Gastric injuries are usually less common and less severe. Rarely, one
encounters rupture of the spleen or liver in the absence of superimposed blunt abdominal
trauma. Pathologically, injuries to the bowel range from subserosal or intramural
hemorrhage to frank rupture. The natural history of such bowel wall hemotomas is not
known, but it is clear that some can progress to perforation during the post-injury
course.
Figure 18
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Operational Medicine 2001
Health Care in Military Settings
Bureau of Medicine and Surgery
Department of the Navy
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Operational Medicine
Health Care in Military Settings
CAPT Michael John Hughey, MC, USNR
NAVMED P-5139
January 1, 2001 |
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