Pressure-Dependent Pneumothorax Following Pleural Drainage in a Non-expandable Lung: A Case Report and Literature Review.

Pressure-dependent pneumothorax is an under-recognized but clinically significant phenomenon that complicates pleural fluid drainage, particularly in patients with non-expandable lungs due to malignancy or chronic pleural fibrosis. Unlike pressure-independent pneumothorax, this condition arises from the pronounced transpleural pressure gradient generated during therapeutic thoracentesis or chest drainage. This negative pressure transiently distorts the visceral pleura, allowing air to enter the pleural space until an equilibrium is reached. The resulting pneumothorax typically remains stable and resolves spontaneously without intervention. However, it is frequently misdiagnosed as a pressure-independent pneumothorax, leading to unnecessary interventions, such as chest drain insertion or even surgical management. We report the case of a 65-year-old man with stage IV lung adenocarcinoma and malignant pleural effusion who developed basilar pneumothorax after chest drainage. Although the air leak was initially presumed to be iatrogenic and was treated with negative suction, persistent bubbling and minimal radiographic changes prompted re-evaluation. Clamping of the chest drain and serial imaging confirmed stable pneumothorax with fluid reaccumulation, consistent with pressure-dependent physiology. Removal of the drain resulted in no progression. This case highlights the importance of recognizing pressure-dependent pneumothorax to avoid unnecessary intervention. Awareness of this mechanism, together with pleural manometry or clinical criteria, can inform individualized management, prevent prolonged air leaks, and improve outcomes in patients undergoing pleural drainage.