I'm going to hug my family a little tighter tonight. 46th school shooting of the year, and the 47th also happening in Colorado.
This is very different than bleeding from, say, a major artery in a leg. In that case the issue isn't loss of piping to the brain, it's losing blood until the total blood volume in the body isn't sufficient to maintain a workable blood pressure, and yes that can take multiple minutes before a person loses consciousness.