Pathophysiology
Clinical meaning
The pleural space normally contains a thin layer of serous fluid (~5-15 mL) that provides lubrication between the visceral and parietal pleurae during respiration. Negative intrapleural pressure (approximately -5 cmH2O) maintains lung expansion. When air (pneumothorax), blood (hemothorax), or fluid (pleural effusion) enters this space, the lung collapses as the negative pressure is lost. Chest tubes restore negative pressure by draining the pathological collection.