Final answer:
Continue to monitor vitals and maintain an open airway after an AED shock restores breathing and pulse in a cardiac arrest patient; prepare for transport to a medical facility.
Step-by-step explanation:
After a 75-year old female patient in cardiac arrest receives one shock from an AED and begins breathing at 15 breaths per minute with a strong carotid pulse, the next step is to continue monitoring her vital signs and maintain an open airway. It is important to ensure she is breathing effectively on her own and that her circulation is stable. The patient should also be prepared for transport to a medical facility for further evaluation and care. If breathing or circulation is inadequate, CPR may need to be resumed.