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14.2 Alarms
14.2.1 High and Low Alarm Operation
The high and low alarm thresholds warn the user to
a positive or negative increase in the pressure
waveform.
The high and low alarms are limited so that the user
cannot set them so far above or below the pressure
waveform that in practice they are turned Off. These
alarm thresholds are limited to 15mbar above and
below the pressure waveform for conventional
ventilation and 20mbar for HFO or HFO+CMV.
The high and low alarm thresholds autotrack the
pressure waveform. If the user has set a high/low
threshold and then changes the PIP or Delta P
(dependant on mode of ventilation) the threshold
will move to 5mbar of the pressure waveform
(conventional) and 10mbar (HFO). This will happen
when any adjustment is made to the waveform.
If a user set autotracked high or low alarm threshold
is crossed, a high/low alarm is triggered but
ventilation is continued.
The high and low alarms also have two invisible
ventilator set thresholds at 5mbar and 20mbar
above the high and below the low user set
thresholds.
Crossing the 5mbar ventilator set threshold
If the high or low alarm threshold is exceeded by
more than 5mbar the ventilator drops the fresh gas
supply for 3 seconds. It maintains the mean
pressure and stops ventilating. This is true for all
modes of ventilation. The ventilator will re-instate
the fresh gas supply after 3 seconds and then
restart ventilation a further 5 seconds after re-
instatement of the fresh gas. The high or low
pressure alarm will sound until the condition is
cleared. If the ventilator encounters the same
conditions after restarting ventilation the fresh gas
pressure relief cycle is repeated.
Crossing the 20mbar ventilator set threshold
If the high or low alarm threshold is exceeded by
more than 20mbar the ventilator drops all the gas
supplies for 6 seconds. It does not maintain the
mean pressure and stops ventilating. This is true for
all modes of ventilation. The ventilator will re-instate
the fresh gas supply after 6 seconds and then
restart ventilation a further 2 seconds after re-
instatement of the fresh gas. The high or low
pressure alarm will sound until the condition is
cleared. If the ventilator encounters the same
conditions after restarting ventilation the fresh gas
pressure relief cycle is repeated.
Note: The user must be made aware that the
Low Alarm threshold will only autotrack down
to 1mbar in conventional ventilation. If the
user wishes to set the alarm lower than 1mbar
then this has to be done manually. If the alarm
threshold is manually set lower than 1mbar
and a pressure related parameter is adjusted
the low alarm threshold will return to 1mbar.
The user will have to manually re-adjust the
alarm threshold to the required level.
Warning: If the user sets the low alarm
threshold below 1mbar the ventilator will not
be able to detect a patient circuit
disconnection of the following type:
Inspiratory limb disconnection from the ET
manifold complete with coloured restrictor.
(In this case the low alarm will not be
triggered as it is set to 0mBar or less, also the
leak alarm will not activate as the restrictor is
still on the inspiratory limb.
The ventilator will also not instantly detect an
ET tube disconnection from the flow sensor, if
the low alarm is set to 0 mbar or less. The
ventilator will alarm with a “Breath Not
Detected” alarm after 20 seconds.
Warning: If the user encounters a high or low
alarm condition where there is a pressure
spike 20mbar or greater and no gas flow is
present, this is indicative of a pneumatic unit
component failure.
If the user deems this to be the case the
following actions must be followed:
a) Check the alarm thresholds are set
correctly.
b) Press the Reset button to restart
ventilation.
If the pressure spike is generated the
ventilator will cut all gases again.
c) Remove the patient immediately to an
alternative form of ventilation
d) Remove the ventilator from service.
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