Final answer:
In tension pneumothorax, the mediastinum shifts away from the affected side due to the accumulation of air in the pleural space that increases intrapleural pressure, causing a mediastinal shift and leading to potentially life-threatening effects.
Step-by-step explanation:
The tension pneumothorax is a serious medical condition where the intrapleural pressure becomes positive due to air entering the pleural space and cannot escape. This causes the lung to collapse, and the increased pressure within the thoracic cavity forces the mediastinum to shift away from the affected side, known as a mediastinal shift. The mediastinum contains important structures such as the heart, trachea, esophagus, and major vessels. When it shifts, it can compress these structures and also reduce venous return to the heart, leading to a decrease in cardiac output and potentially life-threatening cardiovascular compromise.
The main answer to the question is that the mediastinum shifts away from the side of the tension pneumothorax, which is also known as an ipsilateral shift. This event occurs as the result of competing forces within the thorax being overcome by the air accumulating in the pleural space, leading to a positive pressure environment. The normal balance of forces is disrupted, as the elastic tissue of the lungs is overwhelmed, and the thoracic wall and pleural fluid can no longer contain the lung within the thoracic cavity. This explains why prompt medical attention, including the insertion of a chest tube to relieve pressure, is critical in managing tension pneumothorax effectively to re-establish normal chest wall compliance and pulmonary ventilation.