The compensatory reserve index can predict when a patient will go into shock from internal injuries. U.S. Army Institute of Surgical Research photo.
Battlefield medics and emergency responders have seen it before: a patient
with no visible wounds suddenly goes into shock from internal bleeding.
At that point, no matter how fast medical personnel respond, "the patient can still die," said Lt. Col. Will Smith, an emergency medicine physician in the Army Reserve. By the time a patient "crashes," or goes into shock, the body has difficulty keeping the brain and heart functioning. Early recognition and treatment of shock is paramount to saving the life of a patient with internal injuries, he said.
It's tough to predict shock before it happens, but that could be about to change. Researchers at the U.S. Army Institute of Surgical Research, in collaboration with colleagues at the University of Colorado, Children's Hospital Colorado and Flashback Technologies, Inc., have developed software that can predict when a patient will go into shock.
Clinical trials have been completed on the software, called a compensatory reserve index, and the results will be submitted to Food and Drug Administration within the next couple of months along with a request for approval of the software as a medical device.
Among the first people to try out the prototype has been Army Surgeon General Patricia Horoho, who called it a "game changer" during a visit to the Army Institute of Surgical Research in San Antonio last year.
"It could revolutionize how we take care of patients in both the pre-hospital as well as the hospital setting," agreed Smith, who heard about the device in March and immediately asked for a prototype. "If this device can be validated and receive clinical approval, then it has an amazing potential to save lives."
Smith, who is now deployed in the Middle East, is eager to try out the device, which combines the software with a common medical device called a pulse oximeter, a small portable instrument that measures heart rate and the level of oxygen in the blood.
A tool like the compensatory reserve index "would be very helpful" to predict which patients need to be flown to a Level 1 trauma center, he said.
Victor Convertino, the researcher at the institute whose work was instrumental in the development of the software, can barely contain his excitement. His enthusiasm is matched by others. Convertino received an award from the Journal of Emergency Medical Services earlier this year as a top innovator in the field.
The index will be important for triage, Convertino said, because battlefield conditions - lots of noise, lots of adrenaline and not much equipment -- make diagnosis especially hard.
"Combat medics feel for a pulse, talk to the patient. [But the patient has] a big rush of adrenaline. They'll say, 'I'm fine. I'm doing OK, don't worry about me.' The medic is getting all these signals that a casualty is OK.
Then all of a sudden they go out."
A collaborative research effort between the Army Institute of Surgical Research and the Department of Obstetrics at San Antonio Military Medical Center will provide an opportunity to test how well the compensatory reserve index tracks blood loss during childbirth. Convertino says postpartum hemorrhage is a major cause of maternal death, especially in the developing world.
"Obstetricians often have difficulty recognizing the actual amount of bleeding and predicting how well the mother will compensate. With this tool, we believe we're going to save the lives of mothers," he said.
The index tracks arterial waveforms, waves of blood pressure created as the heart pumps blood into the vessels. Within 30 seconds, it determines the rate at which the patient is using up his "compensatory reserve"- the body's ability to compensate for blood loss by directing blood flow to the heart and brain.
The body's compensatory reserve is like the gas that fuels a car's performance, Convertino said. The compensatory reserve index "is the gas gauge."
A small screen on the prototype uses green, yellow and red to denote how much of a patient's reserve has been used. Green indicates the patient is still strong, yellow that he is weakening, and red that he is in imminent danger of crashing.
After "training" the software to recognize the patterns in a patient's vital signs that precede shock, researchers analyzed old medical data from actual patients to see whether it could successfully predict shock. The software was so accurate that in one case it could have saved a patient by warning doctors well before she actually died.
"She was in the red [zone] hours before they lost her," Convertino said.
"Remember the story of Korey Stringer?" he asked. Stringer was an offensive tackle for the Minnesota Vikings football team who died of heatstroke during training in 2001. "This would have given fair warning that they had to get
him off the field."
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