Final answer:
The correct action for a nursing assistant is to assist the patient with using a pillow to splint while coughing after an abdominal aortic aneurysm repair.
Step-by-step explanation:
In the care plan for a patient who had a repair of an abdominal aortic aneurysm (AAA) 5 days prior, the most appropriate nursing action to delegate to an experienced nursing assistant is to assist the patient in using a pillow to splint while coughing. This task is within the scope of practice for a nursing assistant and aids in pain management and prevention of incisional herniation during coughing, which is a time of increased intra-abdominal pressure. Other tasks such as monitoring the quality and presence of pedal pulses, checking lower extremity strength, and teaching the patient signs of possible wound infection are more complex and require the clinical judgment and advanced knowledge of a registered nurse.