Ventilation
Daniel Dunham
Ventilation
This entire presentation is applicable to
everyone from ECA to Paramedic
This presentation is not about
airways
This is not a comparison of ET Tubes, King
Tubes, Rescue breathing, or the adjuncts
used to assist in ventilation
This is only about the delivery of
mechanical ventilation
There are many ways to cause mechanical
ventilation.
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BVM
Ventilator
Mouth to mask
Negative pressure ventilation
However, the terms used to
describe ventilation are universal
Rate
The frequency at which ventilation occurs
Tidal Volume
The volume of air delivered with each
respiration
Minute Volume
Volume of air delivered each minute
Can be calculated by
(Breaths per minute) x (tidal volume)
Pip or PPeak
Peak Inspiratory Pressure
Measured in cmH2O, describes the amount
of peak pressure in the lungs during
inspiration
PIP
Excessive PIP can lead to lung damage;
Pneumothorax, ARDS (acute respiratory
distress syndrome), alveolar damage.
PEEP
Positive End-Expiratory Pressure
Measured in cmH2O describes the residual
pressure in the lungs at the end of
exhalation. A small amount of PEEP occurs
naturally during normal breathing as
residual lung capacity
PEEP is also how CPAP works.
Itime
Itime or Inspiration time
Measured in seconds
The amount of time it takes for inspiration
or positive pressure ventilation to occur
(from PEEP to Pip)
I:E ratio
Ratio that compares inspiration and
exhalation.
Normal breathing has a I:E ratio of ~1:2 (try
it yourself-- exhalation as fast as inhalation
doesn't happen naturally)
Ratios of 1:3 or 1:4 are not uncommon
(inhalation takes ¼ the time of exhalation)
Mean Airway Pressure
The average amount of air in all of the
airways over time.
The first line shows typical airway pressure
graph during ventilation over time.
Mean airway pressure is the average of the
area under the curve.
All of these properties can be
manipulated with a BVM and a
knowledgeable operator
What are we doing wrong?
What are we doing wrong?
“Rate is the only thing that's important”
“All patients can be ventilated at the same
rate”
“The more pressure I use the better the
patient will be oxygenated”
“How fast I squeeze and release the BVM
isn't important as long as it's done at the
right time/rate”
“You should always ventilate with 100%
oxygen / You should always ventilate with
room air”
What is the purpose of ventilation?
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Two major components to ventilation
Oxygenation
Removal of CO2
We can assess objectively, in the field,
exactly how well we are performing those
two functions
Assess Oxygenation
SpO2: goal 94-99%
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Hyperventilating intubated patients with 100% oxygen can
lead to problems, but these issues are less bad than
allowing hypoxia to occur
Always be aware of the limitations of SpO2
monitoring and consider them before making
changes to patient care based on it.
Assess CO2
EtCO2 monitoring
Normal is 35-45 mmHg
Can be assessed using King Tube, ET tube, normal breathing, or
even BVM ventilation (If you keep a good seal with mask)
Be aware of limitations of EtCO2
Ideal Ventilation
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Leads to...
SpO2 94-99%
EtCO2 35-45mmHg
PIP not excessive
PEEP appropriate to patient condition
Mean Airway Pressure
Mean airway pressure directly correlates to
oxygenation (SpO2)
Which graph has a higher mean for
the time period shown?
The curve on the left shows a simple and quick squeeze
and release. The curve on the right shows a reasonable
squeeze, slight pause, and gradual release, with a similar
respiratory rate.
Even though the time period is the
same, and the pressure is lower
The curve on the right will provide better
oxygenation.
This is because the alveoli will be exposed
to oxygen for a longer period of time,
allowing more oxygen to be moved to
bloodstream.
The shape on the left is more
representative of how we ventilate (short Itime, high PIP)
Since high PIP can be damaging, a slow
inspiration (without excessive force), a
slight pause, and slow release is the ideal
way to perform ventilations with a BVM
In patients with low SpO2 not
improving with ventilation
After ruling out pneumothroax, tube
displacement or inadequate mask seal, and
ensuring appropriate supplemental Oxygen is
attached, lengthening I:E ratio (or inverting) can
improve oxygenation drastically.
An inverted I:E ratio leads to a situation where the lungs are
always inflated, except to change air – take a slow deep
breath until it's time to exhale, exhale quickly, and inhale
slowly until it's time to breathe again (the lungs are always
inflated or working, never at residual capacity and resting).
Repeat. This is inverted I:E ratio.
For hypercarbic patients
A patient with an EtCO2 >45 is hypercarbic
High index of suspicion for bronchoconstriction
or for long periods with inadequate respiration
(seizures, CNS depression from overdose or
cerebral insult etc)
EtCO2 is a function of minute volume. The
higher the minute volume, the lower EtCO2 will
be. Slow respiration allows byproducts of
cellular respiration (CO2) to build up, meaning
more must be expired each breath.
For hypercarbic patients
Ventilate patients to maintain 35-45 mmHg. For all
patients, the change should be gradual, respiratory
rate for adults generally should not be greater than 24
(notable exceptions being DKA, malignant
hyperthermia or other conditions that increased
metabolic rate [fever, excited delirium etc]) . When
approaching appropriate EtCO2, slow respiratory rate
and find rate that will maintain value in desired range.
Consider reducing supplemental O2 with high
respiratory rates to maintain SpO2 94-99%.
Extra volume can also reduce EtCO2 but should be
done after increasing rate
For hypercarbic patients
Increase minute volume.
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First increase rate,
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If that is insufficient, increase tidal volume
Completely unrelated...
The first sign of malignant hyperthermia is
hypercarbia.
Malignant hyperthermia can be caused by
ketamine, succinycholine or other
depolarizing paralytics and, although rare,
is A Very Bad Thing and must be identified
early.
For hypocarbic patients
EtCO2 <35 should be a red flag. There are
few reasons why EtCO2 would be less than
35.
Esophageal intubation/displaced tube
Cardiovascular compromise/low cardiac
output/arrest
 Excessive respiratory rate or volume
 Regardless of EtCO2, respiratory rate should
never be less than 8-10.
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Intrathoracic pressure
Increasing PEEP, PIP, and MAP all
increase intrathoracic pressure.
Increased intrathoracic pressure can
reduce preload, causing a lower cardiac
output and blood pressure.
Special caution should be used in
hypotensive patients or patients in cardiac
arrest.
Intrathoracic pressure
You can reduce all these pressures by
squeezing bag less for each ventilation.
Always Remember
The goal of artificial ventilation is to mimic
as closely as possible normal breathing...
You shouldn't ventilate in a way that you
wouldn't breathe.