CapnographyWellenform

Capnography Wellenform refers to the graphical representation of carbon dioxide concentration in exhaled breath over time, as displayed by a capnograph. This waveform, also known as a capnogram, provides crucial real-time physiological data for patients undergoing mechanical ventilation or anesthesia. The typical capnography waveform consists of several distinct phases, each corresponding to a specific physiological event during the respiratory cycle.

Phase I represents the beginning of exhalation, where inspired gas (low in CO2) is expelled, showing a baseline CO2 level close to zero. Phase II is the rapid rise in CO2 as alveolar gas, rich in carbon dioxide, begins to mix with the dead space gas. Phase III, the alveolar plateau, indicates the exhalation of predominantly alveolar gas, with a relatively stable and elevated CO2 concentration. The end-tidal CO2 (EtCO2) is the highest point reached in Phase III, representing the partial pressure of CO2 in the alveoli at the end of exhalation. Finally, Phase IV is the rapid drop in CO2 as the patient begins to inhale fresh, CO2-free gas, returning the waveform to baseline.

Deviations from the normal capnography waveform can signal various clinical problems. For example, an absent or significantly reduced waveform may indicate apnea, disconnection from the ventilator, or esophageal intubation. A drooping alveolar plateau can suggest bronchospasm or airway obstruction. Rebreathing of exhaled CO2 is indicated by a baseline that does not return to zero at the start of exhalation. Thus, continuous monitoring and interpretation of the capnography waveform are essential for effective patient management in critical care settings.