A. End-Tidal Carbon Dioxide
B. Inspiratory point
C. Baseline Inspired Gas
D. Expired Air
Ans: B. Inspiratory Point.
The image shown is of a Capnograph.
- It represents the amount of carbon dioxide (CO2) in exhaled air, which assesses ventilation.
- It consists of a number and a graph.
- The number is capnometry, which is the partial pressure of CO2 detected at the end of exhalation. This is end-tidal CO2 (ETCO2) which is normally 35-45 mm Hg.
- The capnograph is the waveform that shows how much CO2 is present at each phase of the respiratory cycle, and it normally has a rectangular shape
- Phase I:
- Starts with exhalation.
- The first gases that pass over the capnography sensor usually do not contain carbon-di-oxide because they are the gases that fill the physiological dead spaces in the “conducting airway” (Lungs, bronchi, trachea, mouth, and nose). This phase is the baseline of the capnograph.
- Phase II:
- Phase II is known as the “Expiratory upstroke “ and trace the steep rise in CO2 level.
- This phase measures a mixture of dead space (No CO2) and alveolar (CO2).
- Phase III:
- The phase represents the “Expiratory plateau” which represents mostly alveolar gas exhalation.
- The plateau is indicative of the homeostasis of the patient.
- The gases released at the end of the expiratory plateau have the highest concentration of CO2.
- This is also known as the “End-tidal point” and is what is measured with calorimetry capnometry or capnography.
- Phase IV:
- This phase reflects the “Inhalational phase”, which brings oxygenated gases into the lung, returning the gas levels and the capnograph waveform to the beginning of a new cycle and the baseline
Causes of end-tidal carbon dioxide changes are as follows:
- Causes of high end-tidal carbon dioxide:
- Malignant hyperthermia, shivering, fever, sepsis, endocrine disease, hypoventilation.
- Cause of low end-tidal carbon dioxide:
- Hypothermia, low cardiac output, hyperventilation, pulmonary embolism.