Comen N10 - CO Display

CO
2
Monitoring
15-3
The total pressure of the gas mixture is measured by a cuvette pressure sensor.
To convert into any other unit, use the actual barometric pressure sent from the ISA sidestream (IRMA mainstream).
CO
2
(mmHg) = (CO
2
Concentration) x (Barometric Pressure from ISA (kPa)) x (750 / 100).
Take 5.0 vol% CO
2
@ 101.3kPa as an example: 0.05 x 101.3 x 750 / 100 = 38 (mmHg).
3) Effects of RH
As the NOMO section removes all condensed water, no water will reach the ISA gas analyzer. However, at an
ambient temperature of 37°C and a breathing gas with a relative humidity of 95% the gas reading will typically be
6% lower than the corresponding partial pressure after removal of all water.
When calibrating the O
2
measurement, the displayed value at the ambient temperature and RH level will be 20.8
vol%, not the actual partial pressure. The 20.8 vol% O
2
represents the actual O
2
concentration of the room air (water
saturation 0.7 vol %) (for example, 25°C and 23% RH @ 1013hPa). The monitor displays the actual partial pressure
at the current RH level when measuring the CO
2
, N
2
O and anesthetic gas (like all gases measured by infrared cell).
In the patient’s alveoli the water vapor in the respiratory gas is saturated (BTPS) at the body temperature.
Before the acquired respiratory gas in the sampling tube is transferred to the ISA sidestream gas analyzer, its
temperature becomes approximate to the ambient temperature. No water enters the ISA gas analyzer after the
Nomoline sampling tube removes all condensed water. The RH of the acquired gas is approximately 95%.
Use the following formula to calculate the CO
2
value at BTPS:
In the above formula:
EtCO
2
: EtCO
2
value [vol%] sent from ISA
Pamb: barometric pressure [kPa] sent from ISA
3.8 : typical partial pressure [kPa] of the water vapor condensed between the patient circuit and ISA
EtCO
2
(BTPS) = EtCO
2
concentration [vol%] at BTPS
It is assumed that the O
2
is calibrated by the room air at 0.7 vol% H
2
O (RH).
15.4 CO
2
Display
(1) CO
2
Waveform (2) Fractional inspired CO
2
(FiCO
2
)
(3) Airway Respiratory Rate (awRR) (4) End-tidal CO
2
(EtCO
2
)
(1)
(4)
(3)
(2)