A 39-year-old woman presents with fever, dry cough, and chest pain for 20 days, and shortness of breath for the past week. Examination reveals dullness on percussion and absent breath sounds below the right second anterior rib, with tracheal deviation to the left. Pleural fluid analysis shows: positive mucin test, protein 29g/L, total cell count 700*10^9/L, RBCs 4*10^9/L, LDH 400U/L, and ADA >45. Which of the following is the most critical treatment measure?