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Principles of operation
16.4.2
Optimization of the sample gas quality
In the case of an unusual waveform shape or if distortion of the measured etCO
values is suspected, changing the sampling site and using a heat and moisture
exchanger (HME) can be helpful.
Use only pure HMEs with a small volume for this which are listed in the list of
accessories.
Do not use fine-pored filters or HME filters, as undesired blockages (e.g., caused by
sputum) occur more abruptly with these than with pure HMEs. These blockages
would immediately cause negative pressure in the lungs.
4
No. Designation
1
2
3
4
Taking the gas sample as close to the patient as possible and using an HME if
necessary has the following advantages (among others):
– Optimization of the sample gas quality due to reduction of ventilation influences,
e.g., turbulence at the Y-piece
– Less distortion of the CO
– Less distortion of the measured etCO
– The undesired influence of the dead space between the Y-piece and the
sampling site is reduced. At the end of the expiration, the dead space already
contains fresh inspiratory gas for the next breath.
A blockage or soiling of the HME (e.g., caused by sputum) can have the following
effects in the previously described configuration:
– Increase of the HME resistance
– Negative pressure in the patient's lungs
– Increasing air trapping (detectable in the flow waveform as an incomplete
expiration before the start of the next inspiration)
322
3
Inspiration
Expiration
HME
Gas sampling
Instructions for use
1
2
waveform
2
values
2
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Atlan A100 (XL), A300 (XL), A350 (XL) SW 2.1n
2
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