The goal of this clinical trial is to evaluate the safety and efficacy of sodium bicarbonate pleural lavage in treating complex pleural effusion in adult. The main questions it aims to answer are:

Will sodium bicarbonate pleural lavage reduce the failure rate of medical treatment (referral rate for surgery) for complicated pleural effusion？ Can sodium bicarbonate pleural lavage accelerating the rehabilitation of patients with complicated pleural effusion？ Will sodium bicarbonate pleural lavage improve the prognosis of patients with complicated pleural effusion?

Participants will will undergo catheter placement for continuous drainage of pleural effusion. Once at least 200 mL of pleural effusion has been drained:

Group A: Participants will receive a daily intrapleural injection of 200 mL of saline in 7 days; Group B: Participants will receive a daily intrapleural injection of 200 mL of 2.5% sodium bicarbonate in 7 days.

For patients with ultrasound evidence of pleural effusion loculations or drainage tube obstruction, intrapleural administration of urokinase may be performed at the discretion of the treating physician to ensure effective drainage.

Inclusion Criteria:

• Hospitalized patients aged 18 to 80 years, inclusive.
• Patients fulfilling any one of the following three criteria for complicated pleural effusion: A. Pleural fluid pH < 7.2; B. Pleural fluid glucose < 2.2 mmol/L and LDH > 1000 IU/L; C. Positive pleural fluid culture or smear for pathogens.
• Pleural effusion volume exceeding 300 mL, as determined by CT imaging using the formula D^2 * L (where D represents the maximum depth and L the maximum length), and for whom pleural effusion drainage is clinically indicated according to established guidelines or criteria.

Exclusion Criteria:

• Patients with known allergies to sodium bicarbonate or normal saline.
• Patients with severe coagulation disorders.
• Patients with severe heart or kidney failure.
• Pregnant or lactating women.
• Patients with pleural effusion caused by hospital-acquired interference, tuberculosis, fungal infections, or non-infectious causes.
• Patients unable to tolerate intrapleural administration.
• Patients with chronic lung diseases that may affect antibiotic efficacy, such as uncontrolled chronic obstructive pulmonary disease (COPD GOLD E group), bronchiectasis, or immunodeficiency.
• Patients who have experienced shock, major bleeding, trauma, or pulmonary surgery within the past 5 days.
• Patients with a history of lung or pleural surgery on the side of the pleural effusion.
• Patients who have recently had chest tubes placed due to pneumothorax, surgery, or pleural effusion.
• Patients currently enrolled in another drug or device clinical trial.
• Patients with poor compliance or difficulty in follow-up, or those with an expected survival of less than 3 months due to conditions other than pleural effusion.