First Aid does the emergency fixup:
"This is a character’s skill in performing emergency medical
treatment and using appropriate rapid-acting medications. First
Aid can be used to stop bleeding, relieve pain, set broken bones,
and stabilize patients who have suffered fatal injuries."
Medical Practice has a greater breadth and depth:
"Medical Practice is the diagnosis, study, and treatment of illnesses,
injuries, poisons and diseases. It includes the ability to accurately
prescribe suitable medications in proper doses to treat physical
and psychological conditions – failures in drug therapies can lead
to addiction, harmful side-effects, or even death in some extreme
circumstances.
Medical Practice also covers surgical procedures, both therapeutic
and elective (e.g. cosmetic)."
Some HARP SF equipment can be used with either First Aid or Medical Practice. In such cases, Medical Practice will have a lower maneuver difficulty because its practitioners know more. Some HARP SF equipment is only usable with Medical Practice.
Characters need both skills.
Best wishes,
Nicholas