Ministry of Health
The Low Tidal Volume Alarm
|Reviewed by Carl Kuschel
This is the alarm which causes the most auditory distress. This should only
alarm if you are in Volume Guarantee (VG) mode - you need to ensure that you
have set up the VG mode properly (see
Setting Up Volume Guarantee).
The following plan is suggested to troubleshoot this problem.
- Check for a leak.
This is the most common reason for an alarm.
The Tidal Volume (VT) measured is the expired VT.
Therefore, if there is a large leak (usually >30%), the ventilator has
trouble delivering enough inspiration to get a decent expiration past the
sensor. If the leak is large, either turn off the VG (recommended) or change
to a larger tube (if appropriate). Sometimes a change in position will
have a dramatic effect on the size of the leak.
- Check the set tidal volume.
Aim for a VT of 4-8ml/kg per
breath. If the set VT
is too high, the ventilator will have trouble delivering it with the preset
pressure limits. The key to setting this up properly is to ensure that
whatever VT is delivered results in adequate ventilation.
- Check the maximum set PIP.
The set Peak Inspiratory Pressure (PIP) is a maximum PIP. The ventilator will give slightly more than this if
required, but if it has to do this a lot, it will alarm. Adjusting the PIP
higher than was previously set for the same volume delivered means that
compliance has changed. The key is to think "why?" – is there a pneumothorax
or something else affecting compliance, is the lung disease progressing
naturally (as in RDS), is there a pulmonary haemorrhage or pulmonary oedema,
or did you have the PIP set too low to start with?
- Check the mode (SIMV vs. PSV)
If the mode is set to SIMV and the baby is
breathing well above the ventilator set rate, the volume received with
spontaneous breaths may be less than the set VT. The ventilator
may alarm, even though on the assisted breaths the VT is reached.
The easy way to change this is to set the ventilator to PSV, where every
breath is assisted.
- Change the Alarm Delay
In the alarms screen, check the delay.
This is usually set at 10 seconds. If the VT alarm is
frequently going off, yet resets before you get there because the baby
receives a breath more than the set VT, consider increasing the
delay (e.g. to 15 seconds).
- Turn the VG off
If none of the above work and the alarm is
driving you insane, turn the VG off and ventilate the baby using pressure
and not volume.
Other Ventilation Links