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Principles of operation
16.3.4
Minimization of the fresh-gas consumption
If the ratio between the set fresh-gas flow and the patient's minute volume is low
(low-flow operation), the piston is moved back during expiration at a speed that
corresponds to the patient's expiratory flow. The volume exhaled by the patient is
therefore almost completely captured by the breathing system. The portion of gas
disposed of via the anesthetic gas scavenging system is minimized. This has the
following advantages:
– Minimization of the fresh-gas losses due to optimized utilization of the delivered
fresh-gas flow
– Optimization of the breathing gas climate control by capturing the largest
possible amount of humid expiratory gas in the breathing system
– Minimization of the dynamic resistance and easier exhalation for the patient
– Earlier availability of the pressure support in synchronized ventilation modes due
to earlier reaching of the piston start position
With larger set fresh-gas flows, the behavior described above is restricted. More
fresh gas and less exhaled patient gas is taken up by the breathing system. This
shortens the gas exchange times in the breathing system.
16.3.5
Compliance compensation
The volume delivered into the breathing circuit is not the same as the volume that
the patient ultimately receives. The determining factors for this difference in volume
are the elasticity of the breathing circuit and the compressibility of the gas contained
within it.
When the pressure in the breathing hose rises during inspiration, there is also
expansion of the hose material. The expanding breathing hose can hold a greater
volume, with the result that a lesser volume reaches the patient.
This device is equipped with dynamic compliance compensation, which
compensates for this volume difference during each breath. Volume is also fed to
the entire system so that the set tidal volume actually reaches the patient.
The basis for the compliance compensation is the breathing hose compliance
determined in the system test or in the leakage test.
16.3.6
Dynamically adjusted breathing system compliance
The required bottom start position of the piston is calculated based on the tidal
volume to be delivered plus a reserve volume for compliance compensation.
In mechanical ventilation modes, the higher the expected tidal volume, the lower
the start position of the piston. In Manual / Spontaneous mode, the piston start
position for the "Adults" patient category is also lower than for pediatric patients or
neonates. This enables the first automatic breath to be delivered without delay
when switching to a mechanical ventilation mode.
If the reserve volume is reduced at the end of the inspiration (e.g., due to leakage,
uptakes, or spontaneous breathing of the patient), the piston start position is
automatically lowered further in the mechanical ventilation modes.
The dynamic adjustment of the piston position reduces the dead space for the
ventilation to the minimum. This increases the ventilation precision and minimizes
the gas exchange times.
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Instructions for use
Atlan A100 (XL), A300 (XL), A350 (XL) SW 2.1n
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