A client is being treated for syndrome of inappropriate antidiuretic hormone (SIADH). On examination, the client has a weight gain of 4.4 lbs (2 kg) in 24 hours and an elevated blood pressure. Which intervention should the nurse implement first?

A. Measure ankle circumference: Measuring for edema can help assess fluid retention but does not actively address the urgent need to manage worsening fluid overload in SIADH. B. Monitor daily sodium intake: Monitoring sodium intake is important because SIADH can cause hyponatremia, but controlling fluid volume is more urgent when signs of overload are present. C. Obtain serum creatinine levels daily: Monitoring kidney function is useful but does not immediately correct the fluid retention that is causing weight gain and elevated blood pressure. D. Ensure client takes a diuretic every morning: Administering a diuretic is a direct intervention to promote fluid excretion, helping to manage acute fluid overload and prevent complications like pulmonary edema or heart failure.