Welch Allyn Duet CO2 Module - User Manual - Manual (Page 8)

Duet CO
2
Module OEM Implementation Manual
Page 8 Confidential Welch Allyn OEM Technologies
Terminology
Capnography is the noninvasive measurement and graphic display of airway CO
2
concentration as a
function of time. The resulting waveform is called a capnogram. The evaluation of the capnogram is
useful in the assessment of the adequacy of carbon dioxide exchange in the lungs, integrity of the
patient’s airway, cardiopulmonary function and ventilator function.
Monitoring of CO
2
concentration at the end of expiration (point D) is referred to as End-Tidal CO
2
(ETCO
2
) monitoring.
76
CO
2
(mmHg)
Time
40
0
A B
C D
E
Mainstream vs. Sidestream
The patient’s expired gas may be sampled either directly off the airway external to the Duet Module or
aspirated from the patient through a cannula into the Module. The method used is dependent on the
patient’s airway status.
Mainstream capnography is used on intubated or tracheostomy patients. Intubation is the process of
inserting a tube into the patient’s trachea to deliver gases to the lungs. The sample chamber and CO
2
sensor are in line between the patient’s airway and the ventilator circuit. The signal is acquired external
to the Duet CO
2
Module while the module executes measurement calculation.
Sidestream capnography is used on patients who are intubated or non-intubated. The patient’s expired
gas is aspirated from the airway and transported to the Duet Module through a sample line. The
sidestream sample chamber and sensor are embedded within the Duet CO
2
Module. The Duet CO
2
Module performs signal acquisition and measurement calculation.
The Duet CO
2
Module is designed to accommodate both Welch Allyn OEM Technologies mainstream
and sidestream input, hence the name Dual End-Tidal (Duet) CO
2
Module.
Measuring Principle
CO
2
measurement is based on the infrared (IR) absorption characteristic of CO
2
molecules. The CO
2
sensor uses non-dispersive IR spectroscopy to measure the number of CO
2
molecules present in the
sample gas. CO
2
gas has a unique absorption band that is related to CO
2
molecule’s composition and
mass. CO
2
gas concentration is measured by detecting absorption in this band. The same
measurement technique is used for both mainstream and sidestream applications. Due to the nature of
the measurement technique employed, user calibration is not necessary with this system.