An open pneumothorax causes ventilatory inadequacy due to which mechanism?

An open pneumothorax causes ventilatory inadequacy due to which mechanism?

• A. Air entering the pleural space due to chest wall rupture
• B. Negative pressure created by inspiration draws air into the pleural space.
• C. Air accumulates causing positive pressure and lung collapse
• D. Exhalation increases intrapleural pressure causing ventilation failure

Answer: (B)

The key idea is that an open pneumothorax creates a direct path between the atmosphere and the pleural space through a chest wall wound, so ventilation is impeded by the way air moves into that space during breathing. When you inspire, the intrapleural pressure normally becomes more negative to suck air into the lungs. With a chest wall defect, that negative pressure pulls air not only into the lungs but also into the pleural space through the wound. This leak reduces the pressure that helps expand the affected lung, allowing that lung to collapse and reducing the tidal volume on that side, which leads to ventilatory inadequacy. The mechanism isn’t just that there’s a chest wall rupture; it’s specifically that the inspiratory negative pressure draws air into the pleural space via the defect, compromising lung expansion and overall ventilation.

The key idea is that an open pneumothorax creates a direct path between the atmosphere and the pleural space through a chest wall wound, so ventilation is impeded by the way air moves into that space during breathing. When you inspire, the intrapleural pressure normally becomes more negative to suck air into the lungs. With a chest wall defect, that negative pressure pulls air not only into the lungs but also into the pleural space through the wound. This leak reduces the pressure that helps expand the affected lung, allowing that lung to collapse and reducing the tidal volume on that side, which leads to ventilatory inadequacy.

The mechanism isn’t just that there’s a chest wall rupture; it’s specifically that the inspiratory negative pressure draws air into the pleural space via the defect, compromising lung expansion and overall ventilation.