Document

Comments

Transcription

Document
Scientific Note 18
Trigger Settings in Ventilator Testing
The FlowAnalyser and CITREX calibration devices offer a variety of trigger settings. These
settings play an important role in accurately measuring volume and timing parameters which
are typically evaluated when testing and adjusting mechanical ventilators.
The versatility of the available trigger settings can be used to automatically analyse almost any
cyclic signal in technical applications such as ventilator component testing, valve and sensor
calibrations and other industrial or biomedical applications.
The following paper gives an overview on the available trigger settings and demonstrates the
importance to set them right in order to achieve precise measurement results.
Editorial
The Function of Triggers
Scientific Note 18
Triggers are used to identify start- and end-points in cyclic signals.
Christian Calame,
In measuring the flow and pressure of a ventilator the triggers detect the start of each inspiration and
Product Manager
the transition from inspiration to exhalation. This allows the calibration device (CITREX or
imtmedical 2015
FlowAnalyser) to determine a number of respiratory parameters such as respiratory rate, I:E ratio, as
Pressure
well as inspiratory and expiratory tidal volume.
Triggers help the calibration device to
identify the start of each breath and to
divide
between
inspiration
and
exhalation.
The accuracy of a number of parameters
depend on the correct trigger setting:
Flow
Vti
Vte
Trigger
Volume: Vti, Vte, Vi, Ve
Time:
Rate, Ti, Te, I:E, Ratio Ti/T
Other: Ppeak, Pmean,PEEP, Pplateau,
Cstat, PF Insp, PF Exp
Trigger
Trigger
Inspiration
If no trigger is detected, none of the
respiratory
parameters
can
be
measured.
Exhalation
1 / Rate
Effect of Triggers on Volume Integration
Inappropriately set triggers have a
catastrophic influence on tidal volume
accuracy:
Tidal volume is determined by integrating the
𝐸𝑛𝑑 π‘‡π‘Ÿπ‘–π‘”π‘”π‘’π‘Ÿ
𝑉𝑑𝑖 = |
∫
πΉπ‘™π‘œπ‘€ (𝑑) × π‘‘π‘‘|
Flow
area under the flow curve:
Vti
The initial inspiratory flow might be lost
due to an inadequate start trigger while
some of the initial expiratory flow might
count negative due to a wrongly set
end trigger.
π‘†π‘‘π‘Žπ‘Ÿπ‘‘ π‘‡π‘Ÿπ‘–π‘”π‘”π‘’π‘Ÿ
Positive flow is added to the tidal volume,
whereas negative flow is subtracted.
This is appropriate (and even smoothens out
small oscillations) but it may become catastrophic if the triggers are set inadequately.
Start Trigger
End Trigger
…and the same applies
expiratory tidal volume!
for
the
Then tidal volume (Vti, Vte) and minute volume
(Vi, Ve) can be significantly wrong.
Gewerbestrasse 8 | CH-9470 Buchs SG | [email protected] | www.imtmedical.com
1/3
Scientific Note 18 | Trigger Settings in Ventilator Testing
Trigger Source
Trigger Signal
The trigger source defines, which signal is
Each trigger source can be set to either watch
evaluated to detect the trigger criteria.
the pressure or the flow signal for the trigger
FlowAnalyser and CITREX allow different trigger
criteria. Start and end trigger can be set
sources:
differently, one to watch for a pressure, the
Low Flow
other for a flow criteria.
High Flow
The low flow channel requires a t-piece
External Trigger (High/Low Flow)
Low flow (FlowAnalyser only)
High flow
External (digital trigger) *)
ο‚·
ο‚·
ο‚·
connection to the PDiff+ inlet for pressure
Selecting high flow source with a flow trigger
works best for most adult ventilation
measurements.
measurement and triggering.
High Flow
*) With external triggering the user has to
choose whether to evaluate the data in the high
flow or the low flow measurement inlet.
Trigger Level
The moment when the pressure or flow signal
gets above (or below) the set trigger level, the
trigger is activated. For start and end trigger
Selecting +3 L/min start trigger and -3 L/min
end trigger works best for most adult
Start Trigger Level
The flashing trigger indication β€œTA”
(Trigger Activity) indicates the start
of a new inspiration.
Adjust trigger settings if this is not
the case.
Flow
different trigger levels can be set.
End Trigger Level
ventilation measurements.
Start Trigger
End Trigger
Rising / Falling Edge
Pressure
The positive / negative edge setting defines if
Trigger Level
Positive Edge
Negative Edge
the trigger is activated when the signal gets
above the set trigger level, or below
The signal with the sharpest rise or
fall should be selected for
triggering.
respectively.
For typical ventilation measurements positive
Start Trigger
End Trigger
edge is used for start trigger and negative
edge for end trigger.
Trigger Delay
To ensure correct volume measurement despite
noise or spikes in the signal. Trigger will be
of the set trigger delay, the volume integration
ignored if the signal returns below the trigger
always begins at start trigger, but will be
level within the set trigger delay.
displayed only after the trigger delay. This
Vti
becomes visible as a small step in the volume
curve. Spikes of the signal will not be counted
works well for most ventilation measurements.
for the volume measurement.
Delay
Volume
Trigger delay is set to 60ms by default which
Trigger Level
Flow
Trigger delay avoids false triggering due to
Start Trigger
Vti
Baseflow
Flow
Vti
Baseflow level
The base flow designates a constant flow which
The base flow setting produces acceptable
shall not be considered for the volume
results only with a constant base flow. Leakage
measurement. If there is a defined leakage or a
or ventilator base flow often are not constant,
base flow in the system, for example, where 3
and thus the measurement results are
l/min air is discharged constantly, the 3 l/min
compromised.
do not count as inspiration volume. By setting
Vte
base flow to 3.0 l/min the volume calculation in
our example could be corrected.
The base flow setting has no effect on
trigger levels.
Gewerbestrasse 8 | CH-9470 Buchs SG | [email protected] | www.imtmedical.com
2/3
Scientific Note 18 | Trigger Settings in Ventilator Testing
Preset Trigger Settings
FlowAnalyser and CITREX offer three preset trigger settings which work well in most cases of
mechanical ventilation.
Adult
Pediatric
High Frequency
Trigger Source
Internal High Flow
Internal Low Flow
Internal High Flow
Start Condition
Flow
Flow
Flow
End Condition
Flow
Flow
Flow
Start Trigger Level
3 L/min
1 L/min
3 L/min
End Trigger Level
– 3 L/min
– 1 L/min
– 3 L/min
Delay
60 ms
60 ms
10 ms
Baseflow
Disabled
Disabled
Disabled
The presets trigger settings are
configurable.
This may lead to misunderstanding
if a user expects them to always
revert to default values.
Pressure
Pressure contolled
Volume contolled
ventilation
ventilation
Flow
Flow
Pressure
Pressure / Volume Controlled Ventilation
Flow trigger works best for both, pressure
controlled and volume controlled
ventilation because of the sharp rise and
fall of the flow signal.
Flow Trigger or Pressure Trigger
Depending on the position of the calibration device, the same ventilation pattern will produce entirely different signals which have to be considered
A) Standard setup for mechanical
ventilation where the calibration device is
Pressure
when setting triggers.
Standard flow triggers are recommended.
Flow
EasyLungTM
in-line with the test lung.
CITREX
Start: Flow > 3 l/min, rising
End: Flow < -3 l/min, falling
Start
End
Start
End
B) Non-invasive ventilation setup where
ventilator and the intended leakage of a
non-invasive ventilation interface (mask,
whisper valve).
EasyLungTM
CITREX
The flow measurement includes
inspiratory tidal volume and leakage.
Pressure trigger is recommended.
Flow
Leakage
Pressure
the calibration device is between the
Start: Pressure > PEEP+1 mbar, rising
End: Pressure < PEEP+1 mbar, falling
Gewerbestrasse 8 | CH-9470 Buchs SG | [email protected] | www.imtmedical.com
3/3

Similar documents