NOT a first aid class; perform medical care to your level of training

First Aid can be a challenging undertaking. The number one rule of thumb is "Do No Harm". Most states have Good Samaritan laws that provide some protection against civil litigation, at least for lay persons. Unfortunately, these laws are not consistent from state to state. Here is an article that discusses Good Samaritan coverage for Maryland, Pennsylvania, Virginia, DC, and West Virginia: Good Samaritan Laws By State.
The best advice is:

  • Get trained and certified
  • Don't exceed your training
  • Get professional help and turn over to them ASAP
  • This is a touchy subject - if you start CPR, don't stop until the professionals arrive and relieve you