7-1
7 CO
2
Monitoring
7.1 Introduction
CO
2
monitoring is a continuous, non-invasive technique for determining the concentration of
CO
2
in the patient’s airway by measuring the absorption of infrared (IR) light of specific
wavelengths. The CO
2
has its own absorption characteristic and the amount of light passing
the gas probe depends on the concentration of the measured CO
2
. When a specific band of IR
light is passed through respiratory gas samples, some of IR light will be absorbed by the CO
2
molecules. The amount of IR light transmitted after it has been passed through the respiratory
gas sample is measured with a photodetector. From the amount of IR light measured, the
concentration of CO
2
is calculated.
The respiration rated range of sidestream EtCO
2
module is 0 to 120 bpm, and the data sample
rate is 50 Hz. And the EtCO
2
concentration reading is using the highest values respectively of
the temporal CO
2
waveform.
The respiration rated rate range of mainstream EtCO
2
module is 0 to 150 bpm, and the data
sample rate 100 Hz. And the EtCO
2
concentration reading is using the peak of the expired
CO
2
waveform（Averaging selections: 1 breath, 10 second, 20 second）.
The method used to determine the respiration rated range: Utilize a valve to permit switching
between the two sampling gases at different frequencies (simulating the range of specified
breath rates). Record the EtCO
2
value presented for each frequency. By drawing the
coordinate diagram which indicates the corresponding relationship between end-tidal value
and breathing frequency, the range of breathing frequency of EtCO
2
measurement accuracy
complying with the specification can be obtained.
Both mainstream CO
2
module and sidestream CO
2
module this ventilator is configured with
have the automatic atmospheric pressure compensation function.
The measurement provides:
1. CO
2
waveform.
2. End-tidal CO
2
(EtCO
2
) concentration: the CO
2
concentration measured at the end of the
expiration phase.
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