A 72-year-old woman from Mumbai with a 15-year history of congestive heart failure presents with acute dyspnea and orthopnea. Physical examination reveals elevated JVP, bilateral ankle edema, and diminished breath sounds at both lung bases. Chest X-ray shows bilateral pleural effusions, more prominent on the right, with cardiomegaly and pulmonary edema. Thoracentesis of the right pleural fluid yields: protein 2.1 g/dL, LDH 180 IU/L, cholesterol 40 mg/dL. Serum protein is 7.2 g/dL and serum LDH is 420 IU/L. What is the next most appropriate step in the management of this patient?