Final answer:
A chest tube's purpose is to reestablish the negative pressure necessary for lung function by balancing the inward and outward forces in the thorax and maintaining pleural adhesion.
Step-by-step explanation:
The purpose of a chest tube is to reestablish negative pressure in the pleural space. This is critical for maintaining normal lung function as the lungs are attached to the inside of the chest wall by liquid adhesion, resulting in a negative gauge pressure of -4 to -8 mm Hg during exhalation and inhalation, respectively. If air enters the chest cavity, pleural adhesion is compromised and the lungs may collapse. Suction is applied to reestablish the negative pressure, which is crucial for lung inflation. This process is governed by competing forces in the thorax: the inward pull from lung elasticity and alveolar surface tension is balanced by opposing forces from the pleural fluid and thoracic wall, leading to a slight outward pull that maintains the necessary negative intrapleural pressure for lung expansion.