User's Manual

Patient Monitor User Manual Monitoring AG
- 126 -
18.9 N
2
O and O
2
Compensations
The following models need O
2
compensation: IRMA AX+, IRMA CO
2
, ISA AX+, ISA CO
2
. The
following models need N
2
O compensation: IRMA CO
2
and ISA CO
2
. For the compensation
details, please refer to the following table.
O
2
Range SetO
2
Range
0~30 vol% 21
30~70 vol% 50
70~100 vol% 85
N
2
O Range Set N
2
O Range
0~30 vol% 0
30~70 vol% 50
18.10 Effects of humidity

The partial pressure and the volume percentage of CO
2
, N
2
O, O
2
and anesthetic agents depend on
the amount of water vapor in the measured gas. The O
2
measurement will be calibrated to show
20.8 vol% at actual ambient temperature and humidity level, instead of showing actual partial
pressure. 20.8 vol% O
2
corresponds to the actual O
2
concentration in room air with 0.7 vol% H
2
O
concentration (at 1013 hPa this equals for example 25°C and 23% RH). The measurement of CO
2
,
N
2
O, and anesthetic agents (e.g. all gases measured by the IR-bench) will always show the actual
partial pressure at the current humidity level.
In the alveoli of the patient, the breathing gas is saturated with water vapor at body temperature
(BTPS).
When the breathing gas flows through the sampling line, the gas temperature will adapt to
ambient before reaching the gas analyzer. As the NOMO section removes all condensed water, no
water will reach the ISA gas analyzer. The relative humidity of the sampled gas will be about
95%.
If CO
2
values at BTPS are required, the following equation can be used:
where:
EtCO
2
= EtCO
2
value sent from ISA [vol %]
Pamb = Ambient pressure sent from ISA [kPa]
3.8 = Typical partial pressure of water vapor condensed between patient circuit and ISA [kPa]
EtCO
2
(BTPS) = EtCO
2
gas concentration at BTPS [vol%]
O
2
is assumed to be room air calibrated at a humidity level of 0.7 vol% H
2
O.