A capnogram consists of four phases: 1. Phase I: Represents the baseline, where no CO2 is present (inspired air). 2. Phase II: Indicates the beginning of exhalation, with a rapid rise in CO2 levels. 3. Phase III: Plateau phase, where CO2 levels reach a peak, representing alveolar gas. 4. Phase IV: End-tidal point, the highest concentration of CO2 at the end of exhalation.
Abnormal capnogram shapes can provide clues to specific clinical conditions. For example, a "shark fin" pattern may indicate bronchospasm, as seen in asthma or COPD.
