Passport 12/Passport 8 Operator’s Manual 17-1
17 Monitoring AG
17.1 Introduction
The anaesthetic gas (AG) module measures the patient’s anesthetic and respiratory gases by connecting to the airway of
intubated patients or collecting the gases with specified accessories. It also incorporates the features of the O
2
module
and BIS module. The AG measurement is applicable for adult, pediatric and neonatal patients. AG monitoring is for
Passport 12 patient monitors only.
The AG module determines the concentration of certain gases using the infrared (IR) light absorption measurement. The
gases that can be measured by the AG module 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. The higher the concentration of gas in a given volume the more
IR light is absorbed. This means that higher concentration of IR absorbing gas cause a lower transmission of IR light. The
amount of IR light transmitted after it has been passed through 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.
AG module can identify two anesthetic gases in a mixture automatically and distinguish between them according to
their contributions to the MAC value for display as the primary and secondary anesthetic agents.
NOTE
The AG module is configured with automatic barometric pressure compensation function.
Perform the measurement in a well-ventilated environment.
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