Ministry of Health
Using HFOV on the Babylog
|Reviewed by Carl Kuschel
Click here to open the HFOV guideline
As well as being a conventional
ventilator, the Babylog 8000plus is able to provide high frequency
oscillatory ventilation (HFOV). However, it needs to be set up and used
differently to other oscillators (for example, the Sensormedics) for it to be
Although the Babylog is apparently
able to ventilate infants up to 4kg in weight, you should consider the
Sensormedics oscillator in babies over 2kg who have significant respiratory
The Babylog oscillates by rapid
switching of the expiratory valve. The use of a jet Venturi system provides an
active expiration phase.
- You must use non-compliant
tubing to use the HFOV function.
- Remember that the pressures generated at the
ventilator are attentuated by the ventilator tubing, the endotracheal tube,
and the baby’s airways so that the high pressures are not transmitted to the
Setting up the Oscillator
Choose a Mean Airway Pressure
- In general, set this 2-3 mbar
higher than the current MAP on conventional ventilation.
- Remember: High MAPs can
impair venous return to the heart and impair cardiac output. Consider this
as a potential problem in babies who require high MAPs for oxgenation but
- Obtain a chest radiograph after the baby has
been on the oscillator to check for lung expansion – aim for 8-9 posterior
- The default setting in NWH NICU
is 10Hz. With the Sensormedics, our recommendation is to leave the frequency
at 10Hz except under special circumstances.
- However, because of the limitations with
Amplitude with the Babylog (particularly at low MAPs), frequency may need to
change if the baby is not ventilating well at the maximum effective
amplitude (see next paragraph).
the frequency will
increase the ventilation
the frequency will decrease
Choose an Amplitude
Look at the DCO2 (Gas
- Although you can choose an amplitude between
0% and 100%, the amplitude delivered depends on the MAP – the lower the MAP,
the lower the amplitude before the maximum is reached.
- The amplitude is calculated the
pressure fluctuation as a percentage of the difference between MAP and 60
- For example, if the MAP is 15,
then 100% amplitude would be 45 mbar. Therefore, the pressure would be
from -7.5 to 37.5 mbar
- However, the airway pressure is limited to –4
mbar. Therefore, this limits the maximum effective MAP – you can set it at
100% but in the example above it will only deliver -4 to 34 mbar (total 38
mbar) which equals 84%! Therefore, the lower the MAP the lower the
amplitude that will be effective.
- The formula for this is:
Maximum effective amplitude (%) = (2 x (MAP + 4))/(60-MAP) x 100
- This is calculated using the formula: DCO2
= VT2 x frequency
- This value, by itself, is not
very useful. However, it is very useful to set this up as a continuous value
on the computer monitor so you can look for trends
- For example, with the changes in settings,
has DCO2 changed? Is DCO2 changing without any change
in the settings (i.e. is the baby’s respiratory status changing?)
- Be aware that DCO2 is
affected by leaks around the ET tube.
Display on the Computer
- Set up the computer screen so that the
following continuous parameters are displayed:
Adjusting Ventilation on HFOV
Weaning or increasing ventilation
should be done according to the clinical condition of the baby and the blood gas
It is important to understand
however the limitations of the machine when deciding how to increase or decrease
ventilation. For example, if the baby has a MAP of 14 and an amplitude of 78%,
increasing the amplitude will have no effect on ventilation unless the MAP is
Similarly, if a baby is on a MAP of
15 with an amplitude of 84%, decreasing the MAP to 13 will limit the maximum
deliverable amplitude to 72%.
However, altering the frequency may have quite
significant effects on ventilation. For babies that are difficult to
ventilate who are already at the maximum effective amplitude, consider reducing
the frequency to increase ventilation.