THOMAS PIRAINO: Hello.
My name is Thomas Piraino.
And I'm now going to discuss with you daily assessment
of mechanically ventilated patients.
The daily assessment of mechanically ventilated patients
should follow a systematic approach.
First, check that safety equipment is available in the room,
such as a manual resuscitator and suction.
Listen to and document breath sounds of the patient.
Check the endotracheal tube and document the position
and compare it to the previous assessment.
Check the inline suction catheter if one is being used.
If it requires changing, do so.
This could be due to it being clogged or it
has met the manufacturer's recommendation for when to change it.
If the patient has a heat and moisture exchanger,
please check the condition of it and make sure there
are no secretions within it.
Change when required.
Depending on hospital policy, this may be up to a few days.
Ensure connections are tight and secure.
Check that the humidifier chamber, if being used, is filling
and that the water source is sufficient.
Next, you can perform a general physiological assessment
of respiratory function.
First, start by reviewing the arterial blood gas for oxygenation and carbon
dioxide issues.
Make adjustments of the ventilator as appropriate.
If you don't have an arterial blood gas, you
can use a venous blood gas for pH and carbon dioxide,
and saturation for oxygenation.
Check the parameters that are most important to the mode you
are using to assess respiratory mechanics that may have changed.
In volume control, you need to check your peak pressure and plateau pressure
since minute ventilation will not have changed since the last time you
saw the patient.
Pressure control-- you need to check the tidal volume and minute ventilation,
since pressures would not have changed since the last time you saw the patient
and any change in respiratory system mechanics
would alter tidal volume and minute ventilation.
Pressure support would have the same concerns as pressure control.
It's always important to check and set alarms,
especially when changes have been made.
Not all ventilators have the same set of alarms available,
but the most common alarms are ones such as high respiratory rate, high and low
minute ventilation, high tidal volume, high peak area pressure, and apnea
alarms when you are using a spontaneous mode such as pressure support
ventilation.
Ventilators also have some alarms that are not
adjustable, including circuit disconnect or circuit occlusion.
Ventilator changes are often warranted by blood pH and oxygenation status
changes.
However, some safety measures also will prompt the changing
of ventilator settings, including if plateau pressure exceeds
levels such as 27 centimeters of water.
Always consider if higher PEEP, when being used,
is still appropriate for the patient.
This is something that should be considered every day when
higher PEEPs are being used, and attempts
to wean them should be aggressive.
Also assess for patient interaction.
If they have been on an assist control mode,
if they have now started triggering the ventilator,
you should assess the ability for ventilator liberation.
Patients should be allowed to make spontaneous efforts early
in the course of mechanical ventilation.
Generally speaking, if the patient is stable and/or improving medically,
the patient should be allowed to begin spontaneous efforts.
Daily attempts at assessing the patient's ability to come off
the ventilator should be considered.
The assessment for ventilator liberation should be done daily.
Criteria for assessing ventilator liberation
may differ between institutions, but the following
are common considerations for when to test it.
The patient is stable and/or improving medically,
the FiO2 requirements are 50% or less, the PEEP requirements
are 10 centimeters of water or less, and the patient
can make spontaneous efforts.
If they meet this criteria, a 2-minute test
of readiness for a spontaneous breathing trial can be performed.
One technique to assess readiness is to reduce all pressure settings,
while in pressure support ventilation, to 0.
If they are on an assist control mode, you
can switch them to pressure support and put all the settings to 0
for 2 minutes.
This 2-minute test is often referred to as the rapid shallow breathing index.
At the end of the 2 minutes, you divide the frequency
by the tidal volume in liters.
For example, if the patient had a respiratory rate
of 28 breaths per minute at the end of the test
and the tidal volumes were 300 milliliters, you would divide 28 by 0.3
and you would get 93.
If the value is less than 105, this is considered successful
as a screening tool and you would continue with the spontaneous breathing
trial.
There are different techniques used for spontaneous breathing trials
at different institutions.
The classic method is T-piece, which is removal from the ventilator,
and oxygen is supplied to the endotracheal tube
with a T-piece adapter.
Another technique is the same technique I
described for doing the rapid shallow breathing index, which
is removing all the support from the ventilator, while on pressure support,
so 0 on 0.
This is the closest to T-piece in terms of work of breathing.
However, the benefit is that it allows you to monitor the tidal volume, minute
ventilation, and respiratory rate with the ventilator
while performing the test.
Pressure support is another technique where
you would allow a low amount of pressure support
to augment inspiratory effort that may be
due to the presence of the endotracheal tube.
All of these tests are used to predict the extubation success of the patient.
They should be performed for a minimum of 30 minutes
and usually up to an hour, but they should not exceed more than two hours.
Sometimes, when patients are breathing spontaneously on a ventilator,
it is advisable to take over control from the patient.
When patients have high oxygen needs, it is advisable to reduce their effort
or simply take it away until they improve, and oxygen demand is lowered.
Patients with excessive inspiratory drive
also have potential to induce further lung injury.
All modern ventilators can measure a value called the occlusion pressure,
which is P0.1.
It's the pressure drop in the first 100 milliseconds of the triggered breath
and it represents the drive of the patient.
A P0.1 value greater than 4 is an example of an excessive effort.
In cases of patients making excessive efforts with high oxygen demands,
if sedation is not sufficient enough to reduce drive,
sometimes neuromuscular blocking agents may be required
to assist with lung protection.
The minute ventilation alarm is particularly important
when using pressure targeted modes.
When using pressure assist control, this alarm
usually means the respiratory system mechanics have changed
and it has affected tidal volume delivery.
When using pressure support, this alarm can
suggest the patient's drive has changed significantly with or without a change
in respiratory system mechanics.
The peak pressure alarm is particularly important in volume assist control.
This alarm usually means that respiratory system mechanics
have changed.
However, whether the change is due to resistance or elastance
will need to be assessed by looking at the peak pressure and plateau pressure.
Plateau pressure is not normally on alarm,
but keep in mind that increases in plateau pressure
will also increase peak pressure, so the peak pressure alarm will be set off.
When you measure the plateau pressure, changes in plateau pressure
are due to changes in respiratory system compliance or elastance.
Changes in PEEP and/or tidal volume will alter plateau pressure.
The value required to be changed depends on the individual patient's condition.
So whether or not you reduce PEEP and/or increase PEEP or increase or decrease
tidal volume will depend on the individual patient situation.
And finally, always consider the cardiovascular status of the patient.
Positive pressure applied to the lung can affect perfusion through the lungs.
High transpulmonary pressure can also reduce venous return.
A proper assessment of cardiac function, including
changes in blood pressure and heart rate,
should be done after every ventilator adjustment.