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15. Flow and Pressure Triggering
15.1 Breath Detection Threshold (Flow
Triggering)
When the ventilator is used with a flow sensor the
flow waveform window contains a breath detection
threshold. The breath detection threshold needs to
be set in the following modes: CPAP, PTV, PSV and
SIMV. The ventilator monitors gas flow to detect a
patient breath. The level at which the threshold is
set describes what the ventilator will recognize as a
breath.
Setting the breath detection sensitivity too high may
allow the ventilator to interpret background noise in
the patient circuit as patient breathing. Setting the
breath detection sensitivity too low will mean that
the patient effort will not be detected and that the
apnoea alarm will be activated.
In the mode panel the user will find the “Set Trigger”
button. On first entering a mode where flow
triggering can be set the “Set Trigger” button will
flash, indicating that the breath detection threshold
needs to be set. Once the user has set a trigger
threshold on changing mode the “Set Trigger”
button will only flash for 15 seconds.
The Set Trigger Button
activates the breath
detection threshold in
the flow waveform
window.
On pressing the “Set Trigger” button the breath
detection threshold will start to flash.
The threshold is set in the same way as an alarm
threshold.
The default value for the threshold is 0.6 l/min and
the threshold increments in 0.2 l/min steps.
In the lung mechanics and measurement panel the
user will see the number of patient triggered
breaths, the Trigger value.
The ventilator colours the first 200 milliseconds of a
triggered breath orange and in the lung mechanics
and measurement panel the Trigger value flashes
white.
15.2 Breath Trigger Sensitivity
(Pressure Triggering)
The ventilator was designed primarily to be used
with the flow sensor, but the ventilator can be
operated without the flow sensor present. This
changes the mode of operation of ventilator from a
pressure ventilator with flow control to a pressure
ventilator.
If the ventilator is to be used without the flow sensor,
the user must take into account the following
differences in operation.
The ventilator used without the flow sensor will
monitor only pressure and no flow control
measurements will be present.
The TTV
plus
button will not be displayed.
Patient Leak Alarm Percentage button will not be
displayed.
In CPAP, SIMV, PTV and PSV the user will have to
set the Pressure Trigger Level once connected to a
patient.
No loops or flow based waveforms will be displayed.
When the ventilator is not being used with a flow
sensor the text NO FLOW SENSOR is displayed on
the screen.
Note: The cycle fail alarm threshold
autotracks the PIP parameter. The user must
be made aware that the cycle fail alarm will be
triggered when the set PIP value is close to or
equal to (0 to 3 mbar) the PEEP or CPAP
value.
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