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September 2008 Issue

Critically wounded soliders are quickly moved to a field hospital. UC researchers are studying how rapid movement and altitude changes associated with air medical evacuation may impact survival.
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Air Force Grant Targets Medical Evacuation

By Amanda Harper
Published September 2008

In the middle of an active war zone, your gut screams to move critically injured patients out of harm’s way as soon as possible.

But science cautions that may not be best for long-term recovery.

About 30 to 50 soldiers are critically wounded each month, requiring medical evacuation out of a war zone. Most are in transit to a full-service hospital within 48 hours.

Some critical care physicians question whether they are unintentionally doing more harm than good by moving critically injured soldiers so quickly.

UC researchers have received a grant in excess of $2 million from the U.S. Air Force School of Aerospace Medicine to determine the ideal time to fly that minimizes health complications to injured soldiers due to the rush to move them from the battlefield into a safe zone.

“There is a sense of urgency about getting these wounded soldiers to a cleaner, safer environment,” explains Col. Warren Dorlac, MD, co-principal investigator on the UC study.

“Our overriding goal is to protect patients from anything that could potentially lead to a cascade of medical complications that will jeopardize survival. But the reality is that evacuation is happening at a time when they are most prone to a secondary hit.”

Avoiding this “second hit”— such as a serious infection or pneumonia— improves survival dramatically.

Doing so is especially challenging, however, in the middle of a war zone where medical troops are often cared for in a maze of canvas and plywood hospital tents.

Dorlac and his colleagues believe there may be a direct link between inflammatory changes in the body and the timing of strategic medical evacuation movements.

For this study, UC researchers will investigate how early evacuation of combat casualties affects the body’s inflammatory response, possibly predisposing already critically wounded people to death from related complications.

“We need to understand the biological effects of the hypobaric environment so we can minimize the risk for additional injuries,” says Dorlac, director of the Cincinnati Center for Sustainment and Readiness Skills (C-STARS) housed in University Hospital.

Currently, no data exists on the impact of transport at altitude— characterized by reduced oxygen levels and decreased atmospheric pressure—on patients recovering from traumatic injuries.

“Determining the ideal time to fly could reduce infection, minimize hospital stays and result in fewer amputations and deaths for the soldiers defending our country,” adds Dorlac.

Because of the nature of a combat zone, the average medical evacuation plane quickly ascends to flying altitude within minutes. The plane is very different than a hospital intensive care unit—90 decibels of noise, lots of vibration and a pressurized environment that results in less oxygen to revive tissues and relieve stress on the body’s systems.

“When we send a patient up in an airplane, we’re essentially putting them into an environment we know can’t be good for them in an effort to move them to safety,” Dorlac adds. “A dark, quiet intensive care unit with very little stimulation or distraction is preferable. Even minor movements can cause a change in intracranial pressure.”

For this two-phase study, the UC team will create three animal models representative of traumatic military combat injuries: controlled hemorrhage, hepatic ischemia reperfusion and scald/burn.

The controlled hemorrhage model, characterized by a low but sustainable level of blood pressure, is meant to reflect a soldier who has experienced a heavy-bleeding wound but doesn’t reach a field hospital to receive fluids for several hours.

The hepatic ischemia reperfusion model represents a patient who needs serious abdominal surgery that requires re-establishing blood flow to a major organ. The scald/burn model corresponds to a blast burn wound from weapon fire.

“Each model has a different inflammatory response, all of them severe and relevant to injuries our soldiers experience during war,” explains Alex Lentsch, PhD, coprincipal investigator of the study and director of UC’s surgical research unit.

“By understanding how the inflammatory response evolves over the course of different injuries, flight times and altitudes,” he adds, “we will be able to better target care for patients who have been severely injured and need to be moved across country.”

After taking baseline biological measurements, researchers will test whether moving to an altitude of 8,000 feet increases the body’s inflammatory response. This information is necessary to determine an ideal time to fly that minimizes the risk for additional medical complications.

Cellular inflammation markers in the blood will be measured before and after flight to determine how different altitudes affect the body’s inflammatory response after injury.

The study’s second phase will focus on a more complex brain injury model using concepts learned in the initial research. Researchers will continue to look at the effect of flight timing and altitude on the patient’s inflammatory response but also monitor brain tissue oxygen levels and intracranial pressure.

“There is nothing known beyond anecdotal evidence about inflammation’s effects on the survival of patients with traumatic injuries, so we have a great opportunity to learn more about this problem and make an impact on the real world,” adds Lentsch.

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