How large must a hole be in the thorax for tension pneumothorax to occur?

A tension pneumothorax occurs when air enters the pleural space and cannot escape, leading to increased pressure and compromising respiratory and circulatory function. For this condition to develop, a hole in the thorax must be sufficiently large to allow air to permit air entry more easily than it can exit.

The diameter of the trachea is often used as a reference point when considering the size of such a hole. A hole that is two-thirds the diameter of the trachea is considered adequate because it allows enough air to enter the pleural space quickly, enough to create a significant pressure gradient that leads to tension pneumothorax. The trachea has a diameter of about 1.5 to 2 centimeters in adults, so a hole two-thirds the diameter would typically present a significant enough opening to allow for rapid air accumulation.

If the hole were smaller, it might not facilitate sufficient airflow to create the high pressure typically seen in tension pneumothorax. Conversely, a hole larger than the trachea would certainly lead to air entering but can also be associated with more catastrophic injuries. Thus, while larger openings are also dangerous, the crucial threshold for tension pneumothorax typically aligns with that two-thirds comparison.