Army researchers have developed a device that can tell when a wounded person is in danger of going into shock or dying from blood loss.

The life-saving device fits on a fingertip, and it's the first technology that gives early warning that a trauma patient is close to circulatory shock, the researchers say.

The device, called the Compensatory Reserve Index, can save lives, including soldiers wounded on the battlefield, by showing medics when a patient is about to go into hemorrhagic shock, according to a release from the Military Health System. Hemorrhagic shock is the leading cause of death among trauma victims.

Now, the CRI has been cleared by the U.S. Food and Drug Administration to be used in hospital settings and in treatment before a patient gets to the hospital.

Researchers at the U.S. Army Institute of Surgical Research at Joint Base San Antonio-Fort Sam Houston, Texas, collaborated with scientists and engineers at the University of Colorado and Flashback Technologies, Inc.

Their research found the compensatory reserve "is the single most important indicator for early and accurate assessment of imminent shock," Dr. Victor Convertino, USAISR senior scientist for U.S. Army Medical Research and Materiel Command's Combat Casualty Care Research Program, said in the release.

The device received FDA approval in December, paving the way for it to be fielded to combat medics on the battlefield, and also for emergency medical technicians treating civilians, Convertino said.

Measuring compensatory reserve in real time will "revolutionize medical monitoring" from diagnosis to guiding fluid resuscitation to providing feedback on how effective the invervention was, he said.  

How it works

CRI uses an algorithm to gauge the patient's ability to adjust to the loss of oxygen in body tissues because of blood loss, and indicates the point at which the patient may go into hemorrhagic shock or die.

The research team found that a patient's arterial waveforms, picked up from a standard pulse oximeter, which is carried by combat medics, could be used to generate the CRI. By analyzing individual arterial waveforms, the algorithm gains accuracy in predicting the body's ability to compensate for lack of oxygen in body tissues.

"Shock is deadly and unpredictable if it is not recognized and treated in early stages of hemorrhage," the researchers wrote in an article about the project, with Convertino, Dr. Michael Wirt, Dr. John Glenn and Dr. Brian Lein cited as the authors. "One of the most challenging aspects of providing effective treatment of shock is our inability to recognize its early onset."

To use the device, a standard pulse oximeter is placed on the patient's finger. The CRI uses the algorithm to determine whether the information from the oximeter indicates the patient needs resuscitation or immediate medical attention. 

Medics on the battlefield, especially those with limited experience, will benefit by seeing when a wounded warrior needs immediate priority, the researchers said.

Medics can see the early marker of the patient's status "well in advance of changes in standard vital signs," buying more time for intervention.

The CRI monitor is designed with a color bar graph indicator similar to a fuel gauge in a car. This shows the patient's level of compensation for blood loss. Green shows an adequate level, amber indicates "compromised," and red shows the patient is unstable.

The measurement of compensatory reserve can be integrated into current medical monitors or a pulse oximeter, displaying a "fuel gauge" reading that can be easily used and understood by combat medics as well as civilian medics, the researchers wrote.

The time it takes for paramedics and emergency medical technicians to diagnose an unstable bleeding patient was reduced by more than 40 percent when they saw and responded to the "fuel gauge" indicator, compared to reading vital signs alone, the researchers noted from data collected in studies.

They see the CRI as becoming a diagnostic tool that can be routinely used, one that can pick up what vital signs miss.

Taking a patient's vital signs using current methods may not be "smart" enough to reveal the danger because the vital signs may change very little during the early stages of hemorrhage, they say.

"Too often the use of standard vital signs does not allow us to distinguish those trauma patients with severe hemorrhage who are at greatest risks of poor outcomes in the early stages of blood loss prior to cardiovascular collapse when interventions and triage decisions would be most effective," the researchers wrote.

What's next

Data on the use of CRI is being collected in research studies involving patients with trauma, injury, Dengue hemorrhagic fever, renal dialysis and other conditions.

"More specifically to addressing the needs of military medical prehospital care is the ongoing data collection during air ambulance transport of battlefield casualties by the Israeli Defense Force," the researchers wrote.

The CRI will be an important tool for triage amid the stress of the battlefield, Convertino said.

"There's lots of noise, lots of adrenaline and not much equipment, which can make diagnosis especially hard for medics on the battlefield," Convertino said. "This device will help medics save lives on the battlefield."