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Chapter 14: GAS Monitoring (Sidestream)
For professional use. See instructions for use for full prescribing information,
including indications, contraindications, warnings, precautions and adverse events.
The combination of ISA and monitor shall be considered a ME SYSTEM.
Measuring principle
Gas monitoring uses infrared (IR) spectroscopy method to measure and identify different gases.
Infrared spectroscopy is used to measure the concentration of molecules that absorb infrared
light. Since the absorption is proportional to the concentration of gas molecule, the concentration
can be determined by comparing its absorption.
For ISA AX+ or ISA OR+ sensor, absorption of nine different wavelengths of infrared light is
measured in order to identify the gases and measure their concentrations.
The measurement of CO2, N2O and anaesthetic agents in the breathing gas mixture is based on
the fact that the different gases absorb infrared light at specific wavelengths. Since ISA analyzer
analyzes the breathing gas mixture, the amount of infrared light absorbed by the gases is
measured continuously by the infrared spectrometer.
A microprocessor continuously calculates the CO2, N2O and anesthetic agent concentrations
from the infrared light absorption measurements using matrix calculations to identify which
anesthetic agents are present in the gas mixture.
The sampling flow rate for all applications of ISA analyzer is 50 ± 10 sml/min.
Measurable parameters by ISA sensor are:
EtCO2, EtN2O, EtAA (End tidal of these gases), FiCO2, FiN2O and FiAA (Fraction inspiratory
of these gases) and Air Way Respiratory Rate and MAC.
Fi and Et values are displayed after a breath and average of RESP value is updated regularly.
For more details, please refer to Technical Specification section.
NOTE:
It takes less than 10 seconds to display gas waveform data and 1 minute that the
accuracy and other operating specification of the system comply with technical
specification in Specification chapter.
MAC (Minimum alveolar concentration)
Minimum alveolar concentration or MAC is a concept used to compare the strengths of
anesthetic vapors; in simple terms, it is defined as the concentration of the vapor in the lungs that
is needed to prevent movement (motor response) in 50% of subjects in response to surgical
(pain) stimulus.
The MAC value may be calculated and displayed by using end-tidal (ET) gas concentrations
according to the following formula:
14-3
User Manual
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