Mindray iMEC8 Vet - 15 Monitoring Carbon Dioxide (CO ); Introduction

15-1
15 Monitoring Carbon Dioxide (CO
2
)
15.1 Introduction
CO
2
monitoring is a continuous, non-invasive technique for determining the concentration of CO
2
in the patient’s airway
by measuring the absorption of infrared (IR) light of specific wavelengths. The CO
2
has its own absorption characteristic
and the amount of light passing the gas probe depends on the concentration of the measured CO
2.
When a specific band
of IR light is passed through respiratory gas samples, some of the IR light will be absorbed by the CO
2
molecules. The
amount of IR light transmitted after it has been passed through the respiratory gas sample is measured with a
photodetector. From the amount of IR light measured, the concentration of CO
2
is calculated.
There are two methods for measuring CO
2
in the patient’s airway:
1. Mainstream measurement uses a CO
2
sensor attached to an airway adapter directly inserted into the patient’s
breathing system.
2. Sidestream/Microstream measurement samples expired patient gas at a constant sample flow from the patient’s
airway and analyzes it with a CO
2
sensor built into the monitor.
The measurement provides:
1. A CO
2
waveform
2. End tidal CO
2
value (EtCO
2
): the CO
2
value measured at the end of the expiration phase.
3. Fraction of inspired CO
2
(FiCO
2
): the smallest CO
2
value measured during inspiration.
4. Airway respiration rate (awRR): the number of breaths per minute, calculated from the CO
2
waveform.