The pressure gradient inside the thorax changes with a pneumothorax. Normally, pleural cavity pressure is negative when compared to atmospheric pressure. When the chest wall expands outward, the lungs also expand outward because of the surface tension between the parietal and visceral pleura. The lungs tend to collapse because of elastic recoil. When there is communication between the alveoli and the pleural space, the air filling this space changes its gradient, equilibrium of the collapsed lung units is reached, or the rupture closes. The pneumothorax enlarges, and the lungs contract because of this vital capacity, and the partial pressure of oxygen decreases. The clinical presentation of a pneumothorax can range from asymptomatic to chest pain and shortness of breath. Tension pneumothorax can cause severe hypotension (obstructive shock) and even death. Elevated central venous pressure can result in distended neck veins and hypotension. Patients may experience tachypnea, dyspnea, tachycardia, and hypoxia.
