What causes hypotension upon initiation of mechanical ventilation?

Hypotension upon initiation of mechanical ventilation can occur due to several physiological changes that take place with the introduction of positive pressure ventilation. One significant cause is the development of tension pneumothorax, which is a critical condition that can occur during mechanical ventilation.

When positive pressure is applied to the lungs, it can inadvertently increase intrathoracic pressure. In cases where air enters the pleural space (such as from a perforation or rupture of lung tissue), this can lead to tension pneumothorax. The accumulation of air in the pleural cavity compresses the lungs and major thoracic vessels, particularly the vena cava. As the venous return to the heart diminishes, cardiac output can be significantly decreased, resulting in hypotension.

This understanding aligns with the critical nature of monitoring patients when they are placed on mechanical ventilation, as it enables quick recognition of possible complications like tension pneumothorax that can directly affect hemodynamics. In contrast, the other options do not directly cause hypotension in the same acute manner related to the initiation of mechanical ventilation.