GE HEALTHCARE E-PRESTN, Technical Manual

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Module Frames and Modules
8 - 6
2062973-004
where P(t), V’(t) and V(t) are the pressure, flow and volume measured at the D-lite at a time t,
Raw is the airway resistance, Compl is the compliance and PEEP
e
+PEEP
i
is the total positive end
expiratory pressure (PEEP
tot
).
1.2.4 Gas exchange measurement
The gas exchange measurement uses the D-lite flow sensor and the gas sampling system.
The basic data which is needed to obtain O
2
consumption and CO
2
production are volumes and
concentrations.
Concentrations have been corrected for delay and deformation during the transport of the gas
sample in a sidestream gas measurement sensor.
To obtain the amount of O
2
consumed in ml/min, the amount which is exhaled is subtracted
from the amount that is inhaled.
To obtain the amount of CO
2
produced in ml/min, the amount which is inhaled is subtracted
from the amount that is exhaled.
These amounts can be obtained by multiplying each measured volume piece (dv) by the
corresponding gas concentration:
Formula 4
and
Formula 5
Using inspiratory and expiratory minute volumes MV
i
and MV
e
and volume-weighted
inspiratory concentrations fi and fe, these equations can be rewritten as:
Formula 6
Formula 7
To obtain results which are less sensitive to errors in volume measurements, the so-called
Haldane transformation is used. This means taking advantage of the fact that the patient is not
consuming nor producing nitrogen: the amount of nitrogen inhaled is equal to the amount
exhaled fi
N2
× MV
i
=fe
N2
× MV
e
.
VO
2
and VCO
2
can then be written as:
Formula 8
Formula 9
with
f
Hald
= (1-fi
CO2
– fi
O2
– fi
N2O
- fi
Ane1
– fi
Ane2
) / (1-fe
CO2
– fe
O2
– fe
N2O
- fe
Ane1
– fe
Ane2
)
1.3 Main components
The respiratory modules consist of:
•
Gas sampling system