CRITICAL CARE

Central Sydney Health Service Royal Prince Alfred Hospital
� Set respiratory rate to maintain the minute ventilation (MV) that was recorded prior to
changing the ventilator settings (set f = old MV divided by new VT in litres). This may not
be possible as the maximum set respiratory rate (f) is 35
� Ensure that Autoflow is turned on.
� The airway pressure alarm must be set at 35 cm H2O.
This will limit the maximal airway pressure to 30 cm H2O.
� Turn the Flow Trigger “On” and set it to 2 L/min
� Adjust the Inspiratory time to start with an I:E ratio of 1:3. I:E ratio is displayed in the
bottom left corner of the “Ventilator settings” screen when Tinsp is selected.
� Adjust the FiO2 and PEEP as outlined in the section arterial oxygenation goal
(see below).
SUBSEQUENT VENTILATOR ADJUSTMENTS
TIDAL VOLUME AND INSPIRATORY TIME ADJUSTMENTS
� These may be necessary if the alarm “pressure limited, volume not constant” occurs.
This alarm indicates that the ventilator cannot deliver the programmed volume in the time
allowed whilst keeping the pressure under the alarm limit of 35 cm H2O (actual airway
pressure of 30 cm H2O). In this case the ventilator will deliver a lower tidal volume,
rather than exceed the pressure limit. There are two solutions to this problem.
1) Increasing the inspiratory time allows more time for the set tidal volume to be
delivered without exceeding the pressure limit. Initially, the Tinsp should change I:E
ratio from 1:3 to 1:2. If this does not help an I:E ratio of 1:1 should be used.
2) If the above does not resolve the alarm reduce the tidal volume in one ml/kg IBW
increments. This may be repeated every few minutes to a minimal tidal volume of
4 ml/kg IBW. The tidal volume should not be reduced below this. If a tidal volume
of 4 ml/kg is necessary, medical staff should be made aware.
� If the patient’s tidal volume is less than 6 ml/kg IBW, regular attempts should be made to
increase it, in 1 ml/kg IBW increments, back towards 6 ml/kg. The ability to do this will
be limited by the alarm “pressure limited, volume not constant” as described above. A
tidal volume of 8 ml/kg may be used after discussion with the ICU consultant and
documentation in the notes.
� If the patient is receiving 6 ml/kg IBW, attempts should be made to reduce the inspiratory
time to give an I:E ratio of 1:3.