A 56-year-old man with heart failure is admitted to the hospital with a 2-week history of increasing exertional dyspnea and fatigue. He also has type 2 diabetes mellitus. Medications are metformin, lisinopril, carvedilol, furosemide, metolazone, and digoxin.

On physical examination, blood pressure is 88/60 mm Hg, pulse rate is 95/min, and respiration rate is 20/min. He is somewhat confused and inattentive. Jugular venous distention is present to the angle of the jaw while sitting. Cardiac examination reveals an S3. There are bibasilar crackles on pulmonary examination. He has edema to the midthighs. Extremities appear mottled and are cool to the touch.

Serum creatinine level is 3.1 mg/dL (274 µmol/L); baseline value was 1.1 mg/dL (97.2 µmol/L). Serum sodium level is 133 mEq/L (133 mmol/L). Electrocardiogram shows no evidence of ischemia. Chest radiograph shows cardiomegaly and vascular congestion.

In addition to intravenous diuresis, which of the following is the most appropriate management?