Introduction AG and O2 Concentration Monitoring
8 - 2 046-004667-00 A7™ Operating Instructions
8.1 Introduction
The Anaesthetic Gas (AG) module measures the patient's anesthetic and respiratory gases, and
incorporates the features of the O
2
module as well.
The AG (anesthesia gas) module determines the concentrations of certain gases using the infrared
(IR) light absorption measurement. The measured AG module gases absorb IR light. Each gas has its
own absorption characteristic. The gas is transported into a sample cell, and an optical IR filter selects
a specific band of IR light to pass through the gas. For multiple gas measurements, there are multiple
IR filters. This means that higher concentration of IR absorbing gas causes a lower transmission of IR
light. The amount of IR light transmitted after it has been passed though an IR absorbing gas is
measured. From the amount of IR light measured, the concentration of gas present can be calculated.
Oxygen does not absorb IR light as other breathing gases and is therefore measured relying on its
paramagnetic properties. Inside the O
2
sensor are two nitrogen-filled glass spheres mounted on a
strong rare metal taut-band suspension. This assembly is suspended in a symmetrical non-uniform
magnetic field. In the presence of paramagnetic oxygen, the glass spheres are pushed further away
from the strongest part of the magnetic field. The strength of the torque acting on the suspension is
proportional to the oxygen concentration. From the strength of the torque, the concentration of
oxygen is calculated.
The measurement provides:
1. An EtCO
2
waveform;
2. Measured parameters: EtCO
2
, FiCO
2
, EtN
2
O, FiN
2
O, EtAA, FiAA and MAC,
where, AA stands for any of the five anesthetic agents: Des (desflurane), Iso (isoflurane), Enf
(enflurane), Sev (sevoflurane), or Hal (halothane).
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