Mindray BeneView T8, Operation Manual

Page: 143 / 290

14-1
14
Monitoring AG
14.1 Introduction
The anaesthetic gas (AG) module measures the patient’s anesthetic and respiratory gases, and
incorporates the features of the O
2
module and BIS module as well.
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
measurement, 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 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.
14.2 Identifying AG Modules
There are two AG modules: M-type and A-type. The M-type module cannot automatically
identify anesthetic gases, but the A-type module can.
For details on BIS, refer to the chapter
16 Monitoring BIS
.
Setup key
Gas outlet
Connector for AG watertrap
Connector for BIS sensor
Measure/standby
Indicator