Trauma is an important cause of hospitalization and death in the U.S. The Centers for Disease Control and Prevention estimates 29.6 million Americans were treated for an injury in hospital emergency rooms in 2004. About two million of these victims required hospitalization. Trauma is the leading cause of death for Americans 44 and under. In 2002, about 161,000 people in the U.S. died from an injury. Motor vehicle accidents (as a driver, passenger or pedestrian), falls and firearms are the leading causes of injury for people of all ages.

Hemorrhage Control

When an injury occurs, blood vessels are broken and bleeding occurs. Normally, the body tries to "heal" the wound by forming a clot to seal the leak. The clot develops when specialized blood cells, called platelets, bind to collagen and form a plug. A fibrin mesh forms over the area to stabilize the plug.

A large wound or break in a major blood vessel can overwhelm the ability of the body to repair the injury, leading to hemorrhage, or uncontrolled loss of large amounts of blood. When serious blood loss occurs, there is less blood to bring oxygen to the vital organs. Heart rate may raise to increase the amount of blood to the lungs and brain. At the same time, blood pressure may drop. Eventually, the tissues are starved for oxygen. Metabolic changes enable cells to produce energy without oxygen. But this process leads to production of lactic acid, changing the pH of the blood and leading to a condition, called metabolic acidosis. If not corrected, organs start to fail. The patient loses consciousness and may die.

Uncontrolled bleeding is the cause of 30 to 40 percent of trauma deaths. Researchers estimate many trauma deaths are caused by hidden or inaccessible sites of bleeding within the body, like the liver, spleen and kidneys.

Controlling Hemorrhage

In severe injuries, hemorrhagic shock can lead to death within minutes. Doctors must work quickly to stop the bleeding and replace lost blood and fluid. For injuries that are close to the surface, doctors can sometimes seal the broken vessel(s) using electrocautery, or heat. The treatment shrinks and closes off the target vessel, allowing blood clots to move in and seal the site.

Wounds that are deep inside the body may only be accessible through surgery. That puts the patient at further risk of bleeding. In addition, it can take time for the surgeon to locate the site(s) of bleeding.

Sounding Out a New Option

Researchers are testing another possible treatment for hemorrhage control, using high-intensity focused ultrasound (HIFU). Ultrasound devices use sound waves. Currently, they are best known for a diagnostic application, producing images inside the body, like a fetal ultrasound on a pregnant woman.

HIFU has an energy intensity that is about four to five times greater than diagnostic ultrasound. When focused on a blood vessel, the sound waves create an intense beam of acoustical energy, producing a high temperature at the target site and sealing the injured vessel. Yet the surrounding tissue is unharmed.

Shahram Vaezy, Ph.D., a Bioengineer with the University of Washington, compares HIFU to a magnifying glass and sunlight. A magnifying glass focuses the individual beams of sunlight onto one spot. Each of the individual rays converges on the target, increasing the amount of heat and, if held in place long enough, producing a burn. But away from the point of convergence, the sun's rays are separate beams that produce little or no extra heat. HIFU works on a similar principle with sound waves, focusing the energy from each sound wave onto a single, target spot.

Currently, HIFU is in pre-clinical (laboratory) study and has not yet been tested on humans. Grant O'Keefe, M.D., is a Trauma Surgeon at Harborview Medical Center in Seattle and is working on the research team. He says the ultrasound beams can be used to target areas of bleeding deep inside the body (like the liver and pelvis) that would normally only be accessible through surgery. HIFU may be combined with diagnostic ultrasound to locate the site of bleeding and apply the treatment.

Researchers envision HIFU being used in trauma rooms or even at the scene of an accident to control bleeding before a victim reaches the hospital. The U.S. military is also looking at HIFU applications for soldiers who are wounded on the battlefield, hopefully buying time until the patient can be transported to an appropriate medical facility.

For general information on trauma:

American Association for the Surgery of Trauma

Centers for Disease Control and Prevention

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