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14Monitoring Carbon Dioxide
Use the CO2 measurement to monitor the patient’s respiratory status and to control patient
ventilation.
There are two methods for measuring carbon dioxide in the patient’s airway:
• Mainstream measurement uses a CO2 sensor attached to an airway adapter directly inserted into the
patient’s breathing system. This method is available with the M3014A Capnography Extension and
the M3016A Mainstream Extension to the M3001A Multi-Measurement Server.
• Sidestream measurement takes a sample of the respiratory gas with a constant sample flow from the
patient’s airway and analyzes it with a remote CO2 sensor built into the measurement system. Philips
offers the sidestream CO2 measurement in the M3014A Capnography Extension and the
Microstream method of sidestream CO2 measurement in the M3015A Microstream CO2
Measurement Extension.
In both cases, the measurement principle is infrared transmission, where the intensity of infrared light
passing the respiratory gas is measured with a photo detector. As some of the infrared light is absorbed
by the CO2 molecules, the amount of light passing the gas probe depends on the concentration of the
measured CO2.
When using a wet ventilator circuit, monitor mainstream CO2 if available, in preference to sidestream
CO2.
The partial pressure is calculated from the gas concentration by multiplying the concentration value
with the ambient pressure.
The measurement provides:
•a CO
2 waveform.
•an end tidal CO
2 (etCO2) value: the CO2 value measured at the end of the expiration phase.
• an inspired minimum CO2 (imCO2): the smallest value measured during inspiration.
• an airway respiration rate (awRR): the number of breaths per minute, calculated from the CO2
waveform.
Depending on the Max Hold setting configured for your monitor, the etCO2 numeric shows either
the highest CO2 value measured within the configured time period (Max Hold set to 10 sec or 20
sec) or the etCO2 numeric shows breath-to-breath value (Max Hold set to Off).
Refer to your Gas Module Instructions for Use, if you are using a Gas Module to monitor CO2.