Final answer:
The first action that should be taken is to notify the registered nurse.
Step-by-step explanation:
The first action that should be taken in this situation is to notify the registered nurse.
The symptoms described, including pain, tenderness, redness, and warmth along the course of the vein, are indicative of phlebitis, which is inflammation of the vein.
Phlebitis can be caused by factors such as irritation from the IV catheter or an infection. In this case, the localized infection is likely, considering the presence of warmth, redness, and the patient's fever. It is essential to involve the registered nurse immediately to assess the situation further and determine the appropriate course of action.