I don't know where you live, but I have worked in states with "Good Samaritan" laws (AZ and CA) and off duty medical personnel (from nurses to MDs) have always pitched in without fear of litigation.
That is the case in Alaska also. In Alaska, so long as you act within your training (within your "scope of practice") you are immune from civil liabilty.
Good Sam laws vary from state to state, and one should always be aware of the details in your state. In any area, it is always a good idea to maintain whatever level of training you have. Keep your certifications up to date. Do not act beyond your current level of training.