23 - 2 BeneVision N22/N19 Patient Monitor Operator’s Manual
23.1 AG Introduction
The anesthetic 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.
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 absorbing 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 causes 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 monitoring is intended for adult, pediatric and neonatal patients.
• The AG module is configured with automatic barometric pressure compensation function.
• Perform the measurement in a well-ventilated environment.
• For the detailed information of BIS monitoring, see 27 Monitoring Bispectral Index (BIS).
• For the detailed information of RM monitoring, see 24 Monitoring Respiratory Mechanics (RM).
(1) AG menu hard key (2) Gas outlet
(3) BIS sensor connector (4) AG Measure/standby hard key
(5) Watertrap seat
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