U.S. doctors are preparing to test a new way to treat patients who arrive in hospital with devastating gunshot or stab wounds, by replacing part of their blood supply with ice cold salt water.

Patients with severe gunshot or stab wounds often have lost so much blood before they are picked up by emergency responders, they go into cardiac arrest shortly after arriving at hospital. At that point, surgeons only have minutes to repair the wounds before brain damage occurs. Few patients this badly injured survive.

But now surgeons at the University of Pittsburgh Medical Center have started a clinical trial to test a procedure in which they will inject ice cold saline water directly into the hearts of such patients. The aim: to try to send them into hypothermia.

Dr. Samuel Tisherman, the lead researcher on the experiment and a visiting professor from the University of Maryland, explains that cooling the body stops blood flow, giving doctors time to mend the wounds.

"The cooling is to decrease their need for oxygen in the brain and other organs and it's all just to buy time for surgeons to operate on them and stop the bleeding," he told CTV's Canada AM from Baltimore.

Tisherman says the procedure, called Emergency Preservation and Resuscitation, will drop the patient's normal body temperature from 98 degrees Fahrenheit to 50 to 55 degrees.

"That seems to be the optimal temperature to allow one to two hours of no blood flow for the surgeons to operate and get control of the bleeding," he said.

While the patients are in hypothermia, Tisherman says they will appear to be clinically dead.

"They won't have a pulse, they won't be breathing, there wouldn't be any brain waves and no brain activity. But they're not at a point where we would say that they're dead and we would stop all measures to help them," he said.

After surgeons have repaired the wounds, they will slowly warm the patient back up using a heart-lung machine – equipment that is already used frequently in cardiac surgeries.

The idea of inducing hypothermia to slow down blood flow is not new. Doctors have used chilling techniques to treat patients in cardiac arrest since the 1960s. But this would be the first time the procedure would be tested on trauma patients.

The team plans to test the approach only on patients who have arrived at the emergency department with “catastrophic penetrating trauma,” who have gone into cardiac arrest, and who are minutes away from death.

So far, the research team is still waiting for the right patients to come in. But they expect to see about one qualifying patient a month at the medical centre.

The technique will be tested on 10 patients before researchers review the data and consider tweaks to the technique. If all is going well, they will then test it again on another 10 patients.

With so few patients qualifying for the study, it could be several years before full results from the study are available.

Tisherman concedes that since the technique has never been used before on trauma patients, it's not known whether it carries the risk of brain damage.

But he says "brain damage is a concern in any kind of cardiac arrest" and there are few options left for patients whose hearts have stopped.

"Our goal is that patients not only survive, but they go back to being normal people and doing the things that they used to do," he says.