Oridion - Overview: Capnography Waveforms

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Capnography Waveforms: Interpreting the Capnogram

A capnogram is the graphical waveform depicting carbon dioxide concentration throughout respiration. End-tidal CO₂(EtCO₂) refers to the measurement of carbon dioxide concentration at the end of exhalation.

Terminology & the Normal Capnograph
A Normal Capnogram

EtCO₂
End-tidal carbon dioxide: measurement of the concentration of CO₂ at the end of exhalation. A normal range for EtCO₂ is 35-45 mmHg (4.5%-6%).

Capnometry
Measurement and numerical display of CO₂ concentration at the patient?s airway.

Capnography
A numerical measurement and waveform display of CO₂ concentration at the patient?s airway.

Capnogram
Graphic representation of C02 concentration over time.

Anatomic Dead Space
The portion of inhaled gases that fills the conducting airways and never reaches the alveolar membrane to participate in gas exchange.

PaCO₂
Partial pressure of CO₂ in arterial blood.

a-ADCO₂
Difference between EtCO₂ and PaCO₂ normally 2-5 mmHg.

A Normal Capnogram

The diagram below shows the shape of a normal capnogram.

A-B: A near zero baseline?Exhalation of CO₂-free gas contained in dead space.
B-C: Rapid, sharp rise?Exhalation of mixed dead space and alveolar gas.
C-D: Alveolar plateau?Exhalation of mostly alveolar gas.
D: End-tidal value? Peak CO₂ concentration?normally at the end of exhalation.
D-E: Rapid, sharp downstroke?Inhalation