Which phase of a normal capnogram is characterized by the presence of inspired air?

The phase of a normal capnogram characterized by the presence of inspired air is Phase I. During Phase I, the capnogram reflects the beginning of exhalation where the first portion of the expired gas primarily consists of fresh, inspired air that has not participated in gas exchange. Consequently, this phase typically shows a low level of carbon dioxide (CO2) since the inspired air contains minimal CO2.

In contrast, Phase II marks the transition where mixed air from the lungs starts to enter the airway, leading to a gradual increase in CO2 concentration. Phase III follows, representing a plateau where the exhaled gas primarily reflects alveolar air, which has a higher concentration of CO2. Phase IV does not exist in a standard capnogram but would rather refer to inspiratory phases after the exhalation process.

Understanding the phases of the capnogram is crucial for respiratory care professionals as it provides insights into the patient's ventilatory status and the efficiency of gas exchange in the lungs.