Final answer:
The nurse should place the patient on a cardiac monitor first due to the risk of hyperkalemia-related cardiac arrhythmias.
Step-by-step explanation:
The nurse should take the action to place the patient on a cardiac monitor first. This is because hyperkalemia can cause life-threatening cardiac arrhythmias, and it is important to monitor the patient's heart rhythm closely. Inserting a urinary retention catheter may be necessary, but it is not the priority in this situation.
Administering epoetin alfa (Epogen, Procrit) and giving sodium polystyrene sulfonate (Kayexalate) may be part of the treatment plan, but monitoring the patient's cardiac status takes precedence.