What does "end-tidal CO2" represent during ventilation?

End-tidal CO2 represents the level of carbon dioxide present in the air that is exhaled at the end of exhalation. This measurement is crucial during ventilation as it provides valuable information about a patient's respiratory status and metabolic function.

Analyzing the end-tidal CO2 can help assess how effectively the lungs are expelling carbon dioxide, which is a byproduct of metabolism. Elevated levels of end-tidal CO2 may indicate hypoventilation or impaired gas exchange, while decreased levels can suggest hyperventilation or inadequate perfusion. Monitoring this parameter is essential for ensuring that ventilation is adequate, particularly in critical care settings.

In contrast, the other options focus on different gases or phases of breath that are not applicable to end-tidal measurements, such as levels of oxygen, nitrogen, or carbon monoxide, which do not directly relate to carbon dioxide levels at the end of exhalation.