Core Concepts & Takeaways

The course Objectives are

• Interpret blood oxygenation levels using pulse oximetry and capnography.
• Discuss how EtCO₂ measures ventilation and perfusion.
• Confirm the phases of the EtCO₂ waveform of a capnography.
• Analyze an EtCO₂ reading to:
  • Assess and monitor proper endotracheal tube placement.
  • Determine and monitor effective ventilation, and,
  • Determine and monitor effective perfusion.

An expert from the chapter Paramedic Recert EMS Care | 23-MCIT-F3-4102 | Capnography

It is essential to understand the features of the normal capnographic waveform, including contour, baseline level, and rate and rise of the carbon dioxide level.

A typical waveform has four distinct phases:

Phase I:  Called the respiratory baseline (A-B), it is the initial stage of exhalation; the gas sample is dead space gas, free of CO₂.

Phase II: Indicated by B-C, this is called the expiratory upslope. At point B, alveolar gas mixes with dead space gas, causing an abrupt rise in CO₂ levels.

Phase III represents the expiratory or alveolar plateau and is shown as C-D.  The gas sampled is essentially alveolar.  Point D reflects the maximal Et CO₂ level or the alveolar CO₂ level. The height of the waveform at point D correlates with the numeric value of exhaled CO₂ displayed on the cardiac monitor or defibrillator.

In Phase IV, or inspiratory downstroke (D-E), fresh gas is introduced. This displaces CO₂, causing the waveform to return to the baseline CO₂ level, approximately 0 mm Hg.

The duration (width) of each waveform corresponds to the duration of ventilation, and the space between waveforms corresponds with the patient’s respiratory rate.