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15-1
Chapter 15 Monitoring Carbon Dioxide (CO
2
)
15.1 Introduction
CO
2
measuring principle is based on the fact that CO
2
molecules
absorb infrared light energy of specific wavelengths, with the amount
of energy absorbed being directly related to the CO
2
concentration.
When an IR light beam is passed through a gas sample containing
CO
2
, the electronic signal from a photo detector (which measures
the remaining light energy), can be obtained. This signal is then
compared to the energy of the IR source, and calibrated to
accurately reflect CO
2
concentration in the sample.
CO
2
mea
surement is used to monitor the patient’s respiratory status.
The monitor provides the mainstream and sidestream methods for
CO
2
monitoring.
 Mainstream measurement: directly insert a mainstream CO
2
sensor attached to an airway adapter into the patient’s breathing
system, allowing the inspired and expired gas to pass directly
across the IR light path. The major advantages of mainstream
sensors are fast response time and elimination of water traps.
When using mainstream CO
2
sensors, check the window for the
patient secretions pooled on periodically. Because that condition
may affect the accuracy of the measurement or even make the
sensor not work.

Sidestream measurement: sidestream CO
2
sensors are located
away from the airway, requiring a gas sample to be continuously
aspirated from the breathing circuit and transported to the
sensor by means of a pump. This type of system is needed for
non-intubated patients. When using sidestream CO
2
sensors,
there is a water trap or a part of the sampling tube with
dehumidifying function. Please periodically check the flow
sensor and tubing for excessive moisture or secretion buildup.
CO
2
monitoring is intended for adult, pediatric and neonatal patients.
15.2 Safety Information
Warning
Use the manufacturer approved accessories only.