Final answer:
For a patient with pneumonia on lactated Ringer's solution IV infusion with a serum potassium level of 4mEq/L, monitoring electrolyte levels is crucial to prevent potential hyperkalemia and maintain isotonic fluid balance.
Step-by-step explanation:
The nursing intervention that is most important for a client with pneumonia who is on an IV infusion of lactated Ringer's solution at 30ml/hr with a current serum potassium level of 4mEq/L is to monitor the patient's electrolyte levels, particularly potassium. Since lactated Ringer's solution contains potassium, the nurse must ensure that the infusion does not cause hyperkalemia in the patient, as the potassium levels in the solution and the patient's serum are the same. It is critical to maintain the isotonic balance of fluids and electrolytes to ensure patient safety and effective treatment.