The theory isn't that complicated when reduced to its essentials. When you have major blood loss, you go into shock. For a short time, this increases your chances of survival by increasing your blood pressure and adjusting other parts of your body chemistry. But, it you stay in shock too long it starts the process of ushering you into your traumatic death in an irreversible way.
An epilepsy drug called valproic acid tricks your body into thinking it doesn't need to go into shock. In the modern world, where there are other ways to deal with blood loss and medical tools to revive people once they reach a hospital, this trick is a good thing. A person whose body doesn't think they are in shock is more likely to avoid lasting harm from the incident if a hospital can be reached in time.
This isn't the sort of drug that it makes sense to have in the drug cabinet at home, but it is the sort of treatment that could become a standard part of an emergency medical technician's arsenal.
At this point, there is a theoretical basis for the treatment, there are some successful rodent trials, and there is progress towards the "safe" part of the Food and Drug Administration's "safe and effective" requirement for new drugs that is established because the drug is already used to treat epilepsy. But, developers are initially looking at using the drug in a battlefield setting, and if it works, it could make a significant difference in emergency trauma care survival rates.
Even slight differences in treatment approaches make a huge difference in survival rates. For example, a delay of just five or ten minutes in the time it takes to reach a hospital in certain kinds of serious accidents doubles the likelihood that a patient will die. Some of that time sensitivity may come from the way the shock reaction works, which a quick valproic acid injection could change.