Ministry of Health

NZ Government

    
 ©Copyright
 Published: 29/11/2011

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.

1. Check for a leak.
   
   This is the most common reason for an alarm. The Tidal Volume (V_T) measured is the expired V_T. 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.

2. Check the set tidal volume.

   Aim for a V_T of 4-8ml/kg per breath. If the set V_T 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 V_T is delivered results in adequate ventilation.
   

3. 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?
   

4. 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 V_T. The ventilator may alarm, even though on the assisted breaths the V_T is reached. The easy way to change this is to set the ventilator to PSV, where every breath is assisted.
   

5. Change the Alarm Delay

   In the alarms screen, check the delay.  This is usually set at 10 seconds.  If the V_T alarm is frequently going off, yet resets before you get there because the baby receives a breath more than the set V_T, consider increasing the delay (e.g. to 15 seconds).
   

6. 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