Final answer:
The first action the nurse should take for a patient with acute kidney injury and hyperkalemia is to place them on a cardiac monitor to prevent and detect any life-threatening cardiac arrhythmias.
Step-by-step explanation:
When facing a patient with acute kidney injury due to dehydration, presenting with oliguria (reduced urine output), anaemia, and hyperkalemia (high potassium levels), the priority is to address life-threatening conditions first. Option C, Placing the patient on a cardiac monitor, should be the nurse's first action, as hyperkalemia can cause lethal cardiac arrhythmias. With the patient on a cardiac monitor, the healthcare team can continuously assess the patient's cardiac rhythm, ensuring immediate intervention if dangerous arrhythmias occur.
Other actions, such as administering epoetin alfa (Epogen) to manage anaemia and giving sodium polystyrene sulfonate (Kayexalate) for hyperkalemia, are also important but secondary to ensuring the patient's immediate cardiac safety. Inserting a urinary retention catheter may be considered to accurately measure urine output and kidney function, but this does not address the immediate risk posed by hyperkalemia.