What happens during phase 2 of a normal capnogram?

During phase 2 of a normal capnogram, there is a rapid increase in the concentration of carbon dioxide (CO₂) detected as the exhaled air moves from the conducting airways, where CO₂ is relatively low, to the alveolar air, where CO₂ is much higher. This phase represents the mixing of air from the conducting airways and the alveoli.

As exhalation continues, the CO₂ concentration begins to increase sharply, indicating that the alveolar air is being expelled due to the stronger concentration gradient. This phase is critical for understanding the efficiency of gas exchange and the functioning of the respiratory system. The transition from lower CO₂ levels in the initial part of exhalation to the peak levels in phase 2 reflects how effectively the lungs are ventilating and exchanging gases.

Recognizing the significance of phase 2 helps clinicians monitor ventilatory status and detect potential respiratory issues, making it a key part of respiratory care practice.