11 - Mechanical ventilation in patients with blast, burn and chest trauma injuries

Summary

Blast injuries

The recent increase in terrorist bomb attacks on urban civilian targets in Europe and the USA has emphasized the need for all relevant health provision team members to become familiar with the pathophysiology and treatment of the resulting injuries. Despite this, many surgeons and intensivists have little direct experience treating blast lung injuries.

The physics of explosions

Explosive devices instantaneously transform the explosive material into a highly pressurized gas, releasing energy at supersonic speeds (high order explosives) or subsonic speeds (low order explosives). High order explosives include Semtex, trinitrotoluene (TNT) and dynamite. Low order explosives include pipe bombs, petrol bombs or blasts caused by aircraft or motor vehicles used as missiles. The net result of any explosion, however, is the blast wave that travels out from the epicentre of the blast.

The blast wave rapidly reaches a peak (3 to 5 atmospheres) and then slowly (2 to 3 minutes) declines to sub-atmospheric pressure. The physical characteristics of the blast wave may be described in terms of velocity, wavelength and amplitude. It is the amplitude of the blast wave that principally determines the severity of the resulting lung injury. When compared with an explosion in an open space, an explosion within a confined space, such as inside a bus or a train, will have a blast wave that is amplified and more prolonged, resulting in injuries of greater severity and mortality.