Philips IntelliVue MX800 - Measurement Principles; Measuring CO2 using M3014 A or X2

13 Monitoring Carbon Dioxide
212
Low etCO2 values: Leakages in the breathing system or sampling system may cause the displayed
etCO
2
values to be significantly too low. Always connect all components securely and check for leaks
according to standard clinical procedures. Displacement of the nasal or combined nasal oral cannulas
can cause lower than actual etCO
2
readings. Even with combined nasal oral cannulas, the etCO
2
readings may be slightly lower than actual in patients breathing through the mouth only.
Measurement Principles
For both mainstream and sidestream measurements, 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).
Measuring CO2 using M3014A or X2
The M3014A Capnography Extension or the X2 with the CO
2
option measures partial pressure of
carbon dioxide in a patient's expired gas using the mainstream method or the sidestream method.
The mainstream CO
2
measurement can be used, with appropriate accessories, with intubated adult,
pediatric and neonatal patients. The sidestream CO
2
measurement can be used, with appropriate
accessories, with intubated and non-intubated adult, pediatric, infant and neonatal patients. With
intubated patients, a sample of the respiratory gas is drawn from the patient's breathing circuit through
an airway adapter and a gas sampling tube. With non-intubated patients, the gas sample is drawn
through a nasal or oral-nasal cannula.