Grandparent able to make medical decisions?

My son spends alot of time with his grandmother since she baby sits him while I am at work and she takes him everyother weekend because I put in 36 hours of work in 3 days everyother weekend. Her and I were talking and in case of an emergancy is there a way I can give her power to make medical decisions when I am unable to be there. I work about an hour away from where she lives and the hospital is probably about another 15 mins away so if something were to happen it would take me probably over an hour and half to even get to him. I was just wondering if there was way I can give her legal rights to make quick decisions if I am unable to get there right away. Maybe something like POA but not quiet. Thanks