Definitions 

Bhavani Shankar Kodali MD

Capnometry:

The measurement and display of carbon dioxide (CO₂) on a digitial or analogue monitor. Maximum inspiratory and expiratory CO₂ concentrations during a respiratory cycle are displayed.

Capnography:

 A graphic display of instantaneous CO₂ concentration (FCO₂) versus time or expired volume during a respiratory cycle (CO₂ waveform or capnogram)

Capnograms:

CO₂ waveforms which can be of two types: FCO₂ can be plotted against expired volume (SBTCO₂ curve /volume capnogram/ CO₂ expirogram) or against time (time capnogram) during a respiratory cycle.

PACO₂:

 Partial pressure of CO₂ in the alveoli.

PaCO₂:

 Partial pressure of CO₂ in arterial blood.

P_ETCO₂:

 Partial pressure of CO₂ at the end of expiration.

(a-ET)PCO₂:

 Arterial to end-tidal CO₂ tension/pressure difference or gradient.

PvCO₂:

 Partial pressure of CO₂ in mixed venous blood.