 A unique aspect of EMS is that there are two hierarchies of authority, as the chain of command is separate to medical authority.Certified first responders may be sent to provide first aid, sometimes to an advanced level.Their duties include the provision of immediate life-saving care in the event of a medical emergency; commonly advanced first aid, oxygen administration, cardio-pulmonary resuscitation (CPR), and automated external defibrillator (AED) usage.