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14
14Monitoring Carbon Dioxide
Use the CO
2
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 CO
2
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 CO
2
sensor built into the measurement system. Philips
offers the sidestream CO
2
measurement in the M3014A Capnography
Extension and the
Microstream method of sidestream CO
2
measurement in the M3015A Microstream CO
2
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 CO
2
molecules, the amount of light passing the gas probe depends on the concentration of the
measured CO
2
.
When using a wet ventilator circuit, monitor mainstream CO
2
if available, in preference to sidestream
CO
2
.
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
(etCO
2
) value: the CO
2
value measured at the end of the expiration phase.
• an inspired minimum CO
2
(imCO
2
): the smallest value measured during inspiration.
• an airway respiration rate (awRR): the number of breaths per minute, calculated from the CO
2
waveform.
Depending on the
Max Hold setting configured for your monitor, the etCO
2
numeric shows either
the highest CO
2
value measured within the configured time period (Max Hold set to 10 sec or 20
sec
) or the etCO
2
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 CO
2
.