Ministry of Health
Basic Principles and
Guidelines for Conventional Ventilation
|Reviewed by Carl Kuschel
- Ventilation practices vary between (and
within) NICUs and neonatologists.
- This guideline is not intended to be
adhered to rigidly, but merely to provide some rationale behind
interpretation of blood gases and possible changes to ventilation
settings in response.
- There are limited randomised trial data
which establish that any one ventilation strategy or mode is superior.
- Many ventilation practices are based on
individual experience and on evaluating changes in blood gas parameters
and the clinical condition of the baby in response to changes in
Basic Principles of Ventilation
There are two goals of ventilation:
- Appropriate oxygenation
- Appropriate ventilation
Oxygenation is affected by several
factors such as the inspired oxygen concentration (FiO2), mean airway
pressure (MAP), the area of and diffusion across the gas exchange surface.
Ventilation refers primarily to the
amount of carbon dioxide exchanging at the alveolar level. Factors which
influence this include the gas exchange surface area and diffusion and the
amount of gas able to be moved in and out of the lungs.
There are several
modes of conventional ventilation,
which are explained in another section of the ventilation resource area.
So, when you set about changing the
settings, you need to think about what you are trying to achieve.
- Alter the FiO2
(turn the knob!)
- Alter the mean airway
- Change the tidal volume
(by changing the pressure, primarily)
- Change the frequency of
Target Blood Gas Values
- Ventilator settings in general
should be set to achieve
target oxygen saturations
as per unit policy.
- Ventilation settings that
should be set with the following guidelines in mind:
We have a philosophy of
relatively permissive hypercapnia. The rationale is to avoid
overventilating lung and thereby inducing injury through volutrauma and
barotrauma. At a pH above 7.25, metabolic function should be
relatively preserved. If there is a significant metabolic
component (that is, base excess <-4), then this may indicate that
oxygenation at a tissue level is impaired.
Exceptions to this guideline
- Infants with severe
chronic lung disease where high pCO2 levels with a lower pH
may be tolerated in order to further minimise ongoing lung injury.
- Infants with
where after discussion with a specialist a decision may be made to
maintain the baby in an alkalotic state (pH >7.45).
Before you Touch the Ventilator .....
at the blood gas result.
- Do you believe it? Does it fit
with the clinical picture the baby is giving you? Does it fit with
the expected course for the baby (e.g. improving compliance after
surfactant for RDS)?
- If it is vastly different
than you expect, is there some reason for it?
- Was there an air
bubble in the specimen?
- If a capillary gas, is
the perfusion awful? Did the baby bleed easily?
- Don't change anything
on the basis of a venous gas. The only reliable information
from a venous gas are the electrolytes and the glucose.
at the baby.
- Is the chest moving?
- What's the air-entry like?
- Is the baby struggling on
- Is the baby very
tachypnoeic or is the baby apnoeic?
at the ventilator.
- Is it cycling?
- Are you giving the baby
the ventilator settings you thought you were?
- What tidal volume (VT) is
the baby getting?
- Is there a significant
- Is it set up properly with
an appropriate inspiratory time and with appropriate pressures?
Click here to open the
respiratory function monitoring
at the nursing flow chart.
- How stable has the baby
been over the past few hours or days?
- Are there lots of
- How is the baby handling?
Changing the Ventilation Settings
Don't forget to tell the
bedside nurse what changes you have made, and don't forget to document your
Increase the FiO2
- The easiest solution.
- Remember that babies whose
oxygen requirements are changing significantly need to be clinically
reassessed and you should consider a radiograph if the FiO2
increases by more than 10%.
Increase the Mean Airway
- Increase the PIP (but this
may also affect ventilation)
- Increase the
(but this may just hold the lungs fully inflated at a high pressure).
You need to watch that the inspiratory time is shorter than the
- Increase the PEEP (we
don't do this often, except for pulmonary haemorrhage)
Decrease the FiO2
- The easiest solution
(unless the baby is already in room air - if in room air, then we
generally accept high saturations or PaO2)
Decrease the MAP
- If the PEEP is higher than
5, then you can drop this down (if the reason for the high PEEP - e.g.
pulmonary haemorrhage - has resolved)
- Decrease the PIP (but this
may adversely affect ventilation)
- Decrease the
inspiratory time if it is too long
with a Low PaCO2
Decrease the tidal volume
- Do this first if the baby
has good chest movement and/or high tidal volumes
- Decrease the difference
between the PIP and PEEP (usually by decreasing the PIP)
- Note that there are
no rules on how much to drop the PIP by - you need to look at the chest
movement and look at the delivered tidal volume on the ventilator.
In general, dropping the PIP by 2mbar (or more if significantly
overventilated) is about the right amount. But look at the tidal
- If the baby is on
drop down the set tidal volume.
Decrease the frequency
- Drop the rate. If
the gas is just a bit alkalotic, drop by 5. If really alkalotic,
you might want to drop it by 10 or more.
- Note that for modes
where every breath is assisted (e.g. PSV, SIPPV), it is futile to
reduce the rate if the baby is breathing above the back up rate.
So wean the pressure (or VT) instead.
with a High PaCO2
Increase the tidal volume
Do this first if the baby has no chest
movement and/or low tidal volumes
- Increase the PIP till you
get some chest movement but look at the tidal volume too.
- In general, you should not
increase the PIP too high as you may find that the tidal volume
increases significantly. But you need to give enough pressure to
get chest movement.
- Remember that if
you are having to put the PIP up a lot to get the same tidal volume in
that you were giving previously,
is going down. Ask yourself "Why?". Look at the baby,
listen to the air entry, and think about a radiograph, particularly if
the FiO2 is going up.
- If the baby is on
increase the set VT. But you may have to increase the PIP as well.
Increase the frequency
- Increase the rate.
If a bit acidotic, increase by 5. If really acidotic, you may need
to increase it by 10 or more.
- For fast rates, it is
really important that the expiratory time is longer than the inspiratory
time. The Babylog will let you know if you get it the wrong way
around. You may need to decrease the inspiratory time accordingly.
- If you find you need to
give more than 70 breaths per minute, think about
as a ventilation mode. Speak to the specialist on duty.
Balance is Important
- Don't forget to balance your ventilator settings. For example, if a
baby is in 100% oxygen but with low pressures settings, it may be
preferable to reduce the FiO2 but increase the pressures.
- Similarly, if the baby is on high pressure
settings but a low rate, it may be better to give a faster rate and lower
When Do I Do the Next
An easy answer at last : "It
depends ....". So what does it depend on?
How abnormal the gas is
- If it is really outside
the normal range you are targeting, you probably want to check it quite
soon to see whether your changes have had the effect you thought they
would (that is, in 15-30 minutes).
How stable the baby is
- The specialist on duty
should be able to give you some guidance on how often gases need to be
- If the baby is stable and
you're not doing too much with the ventilation, you don't need to check
it too soon after the change. Some babies who are chronically
ventilated may only need a gas once a day.
- You can look at other
things like the new tidal volume to see whether you think your changes
have had any sort of effect.
- But if the baby is really
unstable, you may wish to do gases often to see where they are heading.
- If you have given
surfactant, you might want to check a gas within an hour to see what
effect any change in
is having on gas exchange.
How confident you are
- If you are new to
ventilation, you may need reassurance with a gas soon after you make
- However, try to avoid too
many tests just to reassure yourself (particularly if the nursing staff
need to take a capillary sample).
- Blood letting is the most
common reason for babies needing transfusions in the first week or two
When the nurses tell you
- If they are worried, they
tell you (...and you should listen).
I'm really worried that I
will be told off on the ward round if I get it all wrong .....
- There are many ways to
ventilate babies. All the consultants have different styles and
experiences, and have their "favourite" modes. No single mode has
been shown to be significantly better than another (other than
synchronised modes are probably better than untriggered modes).
- Some babies do well on one
mode and settings one minute, then they may seem to need something else.
- Believe it or not, all the
consultants had to learn by trial and error, and they don't always get
- What is most important is
that you understand what happens when you make a change to a ventilator
setting. No one can necessarily predict what will exactly happen
to a blood gas as a result of that change.
- And if you are not sure
what to do, ask someone (including the consultant.