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Rule of thumb
for estimating the system response over time:
*
T
= VC /
FG, where:
T
= Time constant of the system in minutes
VC = System volume in litres (breathing system,
ventilation hoses, residual volume of the lungs)
*
FG = Fresh gas flow in L/min
Example
for estimating the time constant of the system
(comprising breathing system and hoses):
VC = 6 [L]
*
FG = 3 [L/min]
T
= 2 [min]
In this example, the change of concentration in the
breathing system would have reached roughly 60 % of
the change in fresh gas concentration after approx.
2 minutes.
Tips for reducing condensation
Water vapour is released when CO
soda lime.
Moisture generation increases with the proportion of
rebreathed gas (low-flow mode).
The Cicero EM is optimised for this low-flow mode:
– the electric heater prevents condensation in the
breathing system,
– a large water container is integrated in the bottom of
the absorber vessel to collect condensate,
– the large cross-sections of the gas-conducting pipes
and valves minimise the danger of functional
deterioration due to condensate.
The following points must be observed for the practice
of low-flow anaesthesia, especially in the event of long
operations at low room temperatures:
Route the hoses so that the condensate can collect at
the lowest point and not run to the patient or into the
breathing system.
Regularly drain the condensate from the hoses.
Use water traps when performing operations longer
than 1.5 hours. Position the water traps at the lowest
point in the system, so that the condensate can flow
into the water traps.
Regularly empty the water traps.
is absorbed on the
2
Recommendation
If condensate is expected:
If condensate enters the breathing system, it can
adversely affect pressure and flow measuring.
In such cases, replace the breathing system with a
dry breathing system.
Protect the microbial filter from condensate. Although
the filter is insensitive to moisture, condensate in the
microbial filter increases its resistance!
Replace the microbial filter.
If condensate has entered the pressure measuring
line –
Replace the pressure measuring line and its filter.
Install the T-piece with the sample line filter, with the
connection at the top.
Replace the T-piece after every patient.
Fit the Y-piece with the Luer lock connection –
measuring connection at the top.
If microbial filters are used on the breathing system:
replace the Y-piece and hoses after every patient.
If microbial filters are used on the Y-piece:
replace the Y-piece and hoses daily.
If droplets of condensate form in the sample line –
replace the sample line.
If condensate has collected in the anaesthetic
scavenging line, empty the hose.
Replace the breathing system and piston/cylinder unit
daily.
Replace the soda lime daily.
Description
Tips for reducing condensation
169
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