Thanks to an unusual loophole in the strict rules of medical ethics, hundreds of trauma patients in California, Texas and a few other states will be taking a gamble when ambulances come to scoop them up after accidents or acts of violence.

Without waiting to get consent, paramedics will inject a fake blood product into half of the eligible patients chosen to take part in a new study. The other half will get a routine treatment of transfusion with saline solution until they reach the hospital.

For now, the artificial blood, known as PolyHeme, isn't approved for general use. But it will still slip into the veins and arteries of unconscious patients who won't be able to say no.