What percentage of oxygen do we normally breathe in room air?

The normal composition of air at sea level consists of approximately 21% oxygen. This percentage is critical for various biological processes, particularly respiration in humans and many other organisms. When we inhale, the oxygen from the air is transported into the bloodstream, where it is used by cells for producing energy.

Understanding the oxygen level in room air is foundational for anyone working in medical settings where respiratory support is provided. It allows healthcare professionals to calculate the necessary supplemental oxygen when a patient's oxygen saturation levels fall below normal due to various medical conditions.

In contrast, other percentages provided in the choices are inaccurate. For instance, 12% is significantly lower than what is found in atmospheric conditions and would not support normal human respiration. Similarly, 50% oxygen is much higher and is typically found in controlled environments or during oxygen therapy. Lastly, 78% of air is actually made up of nitrogen, which is why it is not relevant when discussing the oxygen content in the atmosphere. Understanding these values is key to managing patient care effectively.