Final answer:
The purpose of applying pressure over a hole with a dressing is to decrease the chance of atmospheric air entering the pleural space, which is essential to maintain the negative pressure crucial for lung expansion. This helps prevent a pneumothorax, which can impair respiration.
Step-by-step explanation:
The purpose of applying pressure over the hole with a dressing is to decrease the chance of atmospheric air entering the pleural space. This is critical for maintaining the negative intrapleural pressure that is essential for normal lung function. Due to the competing forces within the thorax, the inward pull from the elasticity of the lungs is balanced by the outward pull from the pleural fluid and thoracic wall, keeping the intrapleural pressure at approximately –4 mm Hg relative to the intra-alveolar pressure. The pleural cavity allows the lungs to expand and contract without friction. If atmospheric air enters this space due to injury or a puncture wound, it can cause a pneumothorax, potentially collapsing the lung and hindering respiration.
Applying pressure with a dressing helps prevent air from flowing into the pleural space from the atmosphere, which would disrupt the negative pressure that is crucial for lung expansion. A pneumothorax can drastically alter the ability to breathe and must be treated by sealing the opening and allowing the lung to re-expand, which is why immediate first aid involves such pressure dressings.