The indications for operative intervention in parapneumonic effusions (PPEs) are currently based on their anatomical, bacteriological and biochemical features. Because PPEs <10 mm in thickness on the lateral decubitus radiograph usually resolve with antibiotics, both the British Thoracic Society and the American College of Chest Physicians guidelines suggest that only PPEs with pleural fluid thickness (PFT) >10 mm on the lateral decubitus radiograph, ultrasound or CT scan should be sampled.1 2 3 However, Espana et al used a PFT cut-off point of 20 mm on the lateral decubitus radiograph for admitting patients with PPE and reported a significantly low outpatient mortality (0.5%).4

We examined the association between PFT and the development of pleural …