GE CARESCAPE, User Manual

Page: 302 / 548

Airway gases
●
E: With a scale, the height of the capnogram tells you the end-tidal CO
2
concentration. The monitor automatically calculates and display the EtCO
2
in
numbers. EtCO
2
approximates the alveolar CO
2
concentration because it is
measured when the patient exhales virtually pure alveolar gas.
●
1a and 1d = inhalation
●
1b and 1c = exhalation
EtCO
2
value % EtCO
2
value mmHg Indicates
4.5% to 5.5% 34 mmHg to 41 mmHg normocapnia
< 4% < 30 mmHg hypocapnia
> 6% > 45 mmHg
hypercapnia
Dips in capnogram
The dips seen in the capnogram during expiration are related to the sidestream gas
sampling, the continuous gas flow to the Y-piece, and patient’s cardiac contractions,
which cause intra-thoracic pressure changes and therefore flow variations.
The alterations in expired CO
2
waveform are cardiogenic movements of exhaled and
circuit gas at the sidestream gas sampling site. When the respiratory gas flow drops
below the gas sampling rate, a variable mixture of CO
2
free fresh gas and exhaled CO
2
rich gas is sampled. This causes variations in sampled CO
2
concentrations.
In the illustration below, CO
2
waveform is the one on top, and flow is the lower
waveform.
1. Expiration
2. Cardiogenic oscillations
302 CARESCAPE Modular Monitors 2062971-001