A client with heart failure (HF) returns to the clinic two weeks after adjustments were made to the prescribed cardiac glycoside, diuretic, and potassium supplement. The client's lungs are clear, heart rate is 58 beats/minute, and serum potassium level is 2.9 mEq/L (2.9 mmol/L). Which action is most important for the nurse to implement? Reference Range: Potassium (K+) [3.5 to 5 mEq/L (3.5 to 5 mmol/L)