a 51 y/o man has acute SOB 2 days post a cholecystectomy. He has no fever, chills, sputum production or pleuritic chest pain. On examination, Temp 37.2, HR 65, BP 120/70, RR 22, O2 91% on room air, there are diminished breath sounds and dullness over raw left base, Trachea shifted to the left side. CXR shows retrocardiac opacity that silhouettes the left hemidiaphragm. which of the following is the most likely problem of the patient?