For more than 50 years, doctors have sought to exploit the protective effects of cold on the human body, and therapeutic hypothermia to chill a patient's body temperature by a few degrees is now used for conditions ranging from heart failure to brain injury.
But at the University of Maryland in Baltimore, Dr. Samuel Tisherman is testing a more extreme form of hypothermia — with the goal of saving the most severely injured gunshot and stabbing victims from almost certain death.
A surgeon by training, Tisherman injects ice-cold salt water into the aorta, the largest artery in the body, to send body temperature plummeting from the normal 98.6 degrees Fahrenheit to the low 50s. At this temperature, his patients have no pulse and no brain activity, lying suspended between life and death for more than an hour without a single breath or heartbeat.
Ordinarily, only 5 to 7 percent of these critically injured patients survive. It’s a race against the clock as trauma doctors open the chest to clamp off the aorta to direct remaining blood to the brain, and then pump in fresh blood to try to restart the heart. But the effort is often futile; locating and sewing up the wounds often requires considerably longer than the five to six minutes it takes the brain to suffer irreversible damage and then death from lack of oxygen.
But preliminary evidence suggests that chilling the patient’s body before beginning emergency surgery helps preserve the brain and other vital organs.
“The hypothermia’s very protective,” Tisherman says. “It slows down all the chemical reactions in the body, and reduces your organs’ need for oxygen so the body can tolerate the cardiac arrest and the lack of blood flow from bleeding.”
Over the past two decades, Tisherman has successfully tested his approach in dogs and pigs. After placing the animals in cardiac arrest as a result of blood loss, he cools them to 50 degrees, stitches up the wounds, and then rewarms their bodies. Tests show the animals have no discernible brain damage.
Now he’s conducting the first clinical trial in humans, focusing on trauma patients who have suffered major gun or knife injuries in Baltimore, a city that in 2017 recorded the highest murder rate in the U.S.
“These patients have often lost half of their blood supply by the time they reach the hospital,” Tisherman says, adding that he anticipates results to be available within the next two years. “When we don’t detect a pulse anymore, we drop their body temperature as quickly as possible."
There aren’t many good options for treating such critically ill patients. And chilling the body so dramatically has risks of its own.
“It’s an abnormal state for a human being,” says Dr. Lance Becker, an emergency medical specialist at North Shore University Hospital in Manhasset, New York. “We’re fairly highly evolved to live at 98.6 degrees Fahrenheit, and being that cold can affect the body’s ability to clot, which is a challenge in trauma patients who are already bleeding. There’s been studies where mild hypothermia has been used for longer periods of time, and there seems to be increased risk of infections.”
But if the trial succeeds and the approach becomes standard practice in trauma centers across the U.S., Tisherman estimates that hundreds of thousands of lives a year could be saved. As he puts it, “If we can improve the survival rate from 5 percent to 15 percent or even 20 percent, that would be huge.”
Cooling in the field
Tisherman envisions extreme hypothermia being applied to other, more complex forms of trauma to give more time to investigate and repair injuries.
“If there’s been a car accident, the patient may have a ruptured spleen, a head injury, multiple bone fractures, as well as bleeding to the point of cardiac arrest,” Tisherman says. “It’s much more complicated to figure out where the injuries are, and where we need to operate, compared to just following the path of a bullet.”
Ultimately, it may be possible to give paramedics the training and equipment needed to apply therapeutic hypothermia to patients before they’re transported to the hospital.
As scientists understand more about how best to use it, extreme therapeutic hypothermia will become personalized — with patients given the optimum body temperatures to protect their bodies against specific kinds of injury.
“If we can figure out how best to make this work, it can really open up a new window for surgeons to bring many patients who are close to death, back from the brink and restore them to health,” he says.