The role of pleural pressure in inducing pneumothorax and other adverse effects of positive pressure ventilation.

Mechanical ventilation, essential for critically ill patients, contrasts with natural respiration, primarily due to differences in pleural pressure (P_pleural ). Natural inspiration decreases P_pleural , pulling the lungs away from the thoracic wall, whereas positive pressure inspiration increases P_pleural , pushing the lungs against the thoracic wall. This shift has several consequences. First, elevated P_pleural during positive pressure ventilation can lead to cyclic airway closure, particularly in the dependent lung regions. This increases the risk of atelectasis, that impairs oxygenation and may lead to further complications such as pneumonia. Second, the increase in P_pleural disrupts the balance maintained by negative P_pleural and capillary forces. This disruption reduces the lubricating pleural fluid between the pleurae, increasing friction and shear stress on the lung tissues, which may lead to damage and conditions such as ventilator-induced lung injury and pneumothorax. Furthermore, airway closure can worsen lung compliance, making mechanical ventilation more challenging and increasing the risk of lung overstretching. This necessitates careful management of ventilation settings, particularly the use of positive end-expiratory pressure (PEEP) and recruitment maneuvers to minimize these adverse effects. Protective strategies, such as synchronizing mechanical ventilation with the patient's breathing efforts, prone positioning, and careful application of PEEP, are crucial in reducing P_pleural and its associated risks. Since negative pressure ventilation (NPV) inherently lowers P_pleural , it may help avoid many of the adverse side effects previously discussed. Therefore, reconsidering and reintroducing NPV in a modern context should be seriously explored.