I agree with what Mike A said above,
ASK PERMISSION and OBTAIN IT, if a person is not concsious, consent is implied, as well as there is implied consent if it is a child and the parent/guardian is not present, otherwise consent must be by the parent.
I will simply elaborate on the negligence part.
If you have ANY type of training like 1st Aid/CPR, ONLY do what you are trained to do.
If you dont have any training at all, GET SOME, otherwise, do only what you do actually know how to do.
If you do anything that exceeds your training, is when you get beyond the Good Samaritan factor and into the negligence realm.
I am and authorized Instructor for 1st Aid/CPR/AED/WHID/Wilderness Survival and a couple more I think, this is covered in the materials for 1st Aid only very briefly. The primary focus being Permission, and doing only what you absolutely know how to do.
I would not be able to dispense medication, or perform a tracheotomy for instance, that is beyond my official training and would be negligent.