Researchers at the University of Pittsburgh Medical Center have begun a clinical trial that pushes the boundaries of conventional surgery — and, some say, medical ethics.

By inducing hypothermia and slowing metabolism in dying patients, doctors hope to buy valuable time in which to mend the victims’ wounds.

But scientists have never tried anything like this in humans, and the unconscious patients will not be able to consent to the procedure. Indeed, the medical center has been providing free bracelets to be worn by skittish citizens here who do not want to participate should they somehow wind up in the E.R.

“This is ‘Star Wars’ stuff,” said Dr. Thomas M. Scalea, a trauma specialist at the University of Maryland. “If you told people we would be doing this a few years ago, they’d tell you to stop smoking whatever you’re smoking, because you’ve clearly lost your mind.”