Datex-Ohmeda F-LM1, Technical Reference Manual

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Functional description
1 FUNCTIONAL DESCRIPTION
1.1 General
CO
2
monitoring determines the carbon dioxide concentration in exhaled gas and converts this data
to a carbon dioxide value and a corresponding waveform.
The CO
2
board is designed for use with Datex-Ohmeda sensors and cables.
1.2 Measurement principle
CO
2
measurement is based on the infra-red absorption characteristic of CO
2
molecules. The CO
2
sensor uses non-dispersive infra-red spectroscopy to measure the amount of CO
2
present at the
end of exhalation (EtCO
2
). The sensor is optically tuned to measure the concentration of CO
2
molecules present in the airway adapter. Based on these sensor measurements, the CO
2
board
calculates the end tidal and inspiratory CO
2
value, breaths per minute, and generates a
corresponding waveform.
1.2.1 Mainstream CO
2
sensor
Mainstream measurement employs a CO
2
sensor and an airway adapter in the circuit of intubated
patients. The CO
2
sensor has six basic components: an infra-red (IR) source, detector, chopper
wheel, heater, thermistor, and non-volatile memory.
Airway adapter / Sampling
Chamber Windows
Infrared Source
Sample
Optical Filter
Dark
Rotating Chopper
Wheel
Reference Gas
Cell
Photodetector
Open
Figure 1 CO
2
measurement principle
The IR source emits energy that is directed toward an IR detector. The detector generates a voltage
based on the amount of energy it receives. In the IR path between the source and detector are
three components: a filter, allowing only a specific IR wavelength to pass; the gas sample in the
airway adapter; and a chopper wheel with three distinct areas: a CO
2
reference cell, an opening,
and a dark, or closed, area.
Document No. 8000060-1
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