Monday, April 15, 2013

What Do We Know About Blast Injuries: Speculating About the Boston Marathon Bombing

Remains of a low order device
The Disease Management Care Blog's thoughts and prayers go out to the Boston Marathon bombing victims and their families. Like all Americans, it hopes the death rate remains low and is confident that the survivors' recovery will be a credit to the world-class skill of the physicians and nurses staffing Boston's ERs, operating rooms and ICUs.

While it was digesting the horrific details, the DMCB was struck by the likelihood that the Afghan and Iraq wars as well as multiple terrorist attacks have enhanced our ability to deal with blast injuries.

What have we learned?

As outlined in this abstract, the initial explosion results in "primary" injury, fragment or shrapnel injuries are "secondary," being bodily thrown results in "tertiary" blunt injury while the burns and other trauma are "quaternary."  It's difficult to survive a primary injury because the supersonic compressive air wave travels though the human body and "shears" any organ with an air/water interface, such the lung and intestines; that's also why ear drums rupture.

According to the CDC, primary injuries are more likely with "high order" explosives such as military grade bombs or TNT.  "Low order" gun powder (the image above is from a "pipe" bomb) or petroleum-based devices are less likely to result in supersonic shock waves. That - and reports of "white smoke" - may account for the initially low mortality rate at the Marathon. Interestingly, body armour does not protect against a primary injury and a ruptured ear drum is a poor predictor of its presence.

Unfortunately, the stress wave can also cause bone fractures and, if severe enough, "transosseous" amputation.  The DMCB was dismayed by reports of some of the victims losing their limbs, which suggests the devices were large if "low-order" bombs.  Amputations were common in the '05 London terror bombings because the victims were in close proximity to the devices and the blast waves were at ground level.  Initial reports from Boston suggest the devices were placed in trash receptacles, which, if it turns out to be true, would fit the pattern.

If victims are in shock from bleeding, the DMCB's uneducated first impulse would be to correct the low blood pressure and give lots of intravenous fluids and blood.  It turns out that combat surgeons have discovered that kind of aggressive therapy can increase the rate of death and complications. The best current approach appears to be the use of "hypotensive resuscitation" and more liberal use of blood products (plasma, platelets and pack cells or whole blood) versus fluids

If you live in Boston and want to donate blood, you can check this out.

Given the standard emergency triaging, the DMCB suspects the secondary, tertiary and quaternary victim counts are still being compiled.  In addition, it will be some time before we understand the incidence of traumatic brain injuries and their associated symptoms of unbalance, hampered motor function, disordered vision, decreased communication and depression. The etiology and our ability to predict it remains a topic of research.

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