Welch Allyn LC101 CO2 Module - User Manual - Manual (Page 55)

LC101 CO
2
Module OEM Implementation Manual
Welch Allyn OEM Technologies Confidential Page 55
Appendix A
Software Procedures
O
2
/N
2
O/Desflurane Compensation
The presence of oxygen, nitrous oxide and desflurane in the gas sample affects the
measurement of the CO
2
concentration. This section describes this effect and recommends a
method for applying the compensation when these gases are present.
Correction For O
2
As the N
2
in the sample gas is replaced by O
2
, the effect is a decrease in IR absorption. This
results in a lower than actual measured CO
2
value (CO
2
measured ). With the additional O
2
present, the raw measurement from the LC101 Module must be increased by a slight factor to
correct for the O
2
effect. It is recommended that O
2
compensation be made available to the user
via a menu selection or other means.
O
2
correction is recommended when the O
2
concentration is greater than 50%. At O
2
levels
equal to or less than 50%, the correction should not be used.
Correction For N
2
O & O
2
To correct for N
2
O in the sample gas, an assumption is made: if N
2
O is administered to the
patient, then the remaining balance of the administered mixture is O
2
. The combined effect of
these gases is two-fold: O
2
presence decreases IR absorption, and N
2
O presence increases
absorption. Though N
2
O does not directly absorb the filtered IR energy, it causes the CO
2
molecule to absorb and pass along some of its energy to the N
2
O molecule of similar molecular
weight. By passing off some of this energy, the CO
2
molecule is free to absorb even more energy
which leads to an increase in absorption.
Since the increased absorption effect due to N
2
O presence is greater than the decrease due to
O
2
presence, an optimal administered mixture of 25% N
2
O and 75% O
2
effectively cancels the
combined effect.