Download Selecting the Ventilator and the Mode

Selecting the Ventilator and
the Mode
Chapter 6
Criteria for Ventilator Selection
• Why does the patient need ventilatory support?
• Does the ventilation problem require a special mode?
• What therapeutic goals can be achieved by using a
ventilator?
• Does the patient need to be intubated or can a mask be
used?
• Will therapeutic intervention take place in an ICU or the
patient’s home?
• Will ventilatory support be provided for a brief period of
time or will long-term assistance be required?
• How familiar is the staff with the ventilator under
consideration?
Invasive VS Non-invasive
• Artificial airway
– Translaryngeal airways – oral or nasal
endotracheal tubes
– Tracheostomy tube
• Mask
Noninvasive Ventilation
NPV: negative pressure ventilators
CPAP: continuous positive airway pressure
Used to improve oxygenation
Treat obstructive sleep apnea
NPPV: noninvasive positive pressure ventilation
Advantages of NPPV
– Avoids complications with
artificial airways
– Provides flexibility in
initiating and removing
ventilation
– Reduces requirements for
sedation
– Preserves airway defenses
– Reduces need for invasive
monitoring
Disadvantages of NPPV
– Can cause gastric
distention
– Skin pressure lesions
– Dry membranes –oral
nasal, eye irritations
– Claustrophobia
– Poor sleep
Invasive Positive Pressure
Ventilation
• Full ventilatory support: the ventilator
provides all the energy necessary to
maintain effective alveolar ventilation
• Partial ventilatory support: any degree of
mechanical ventilation in which the set
rates are lower than 6 breaths/min and the
patient participates in WOB to help
maintain effective alveolar ventilation
Type of breath delivery
• Mandatory
– Ventilator controls the timing, tidal volume or both
• Spontaneous
– Patient controls the timing and the tidal volume
• Assisted
– Characteristics of both spontaneous and mandatory
breaths
– All or part of the breath is generated by the ventilator
– The patient triggers and cycles the breath
Control Variables:
the independent variable used to establish gas
flow to the patient
Volume Control
Pressure Control
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Volume provided to the patient is
constant and independent of what
happens to pressure when the
patient’s lung characteristics change or
when the patient’s effort changes
Use when consistent tidal volume
delivery is important; goal is to
maintain a certain level of PaCO2
Guarantees a specific volume delivery
and Ve regardless of changes in lung
compliance and resistance
Disadvantages: Peak and alveolar
pressures rise when lung conditions
worsen = alveolar over distention;
delivery of flow may be fixed and not
match patient demand; inappropriate
trigger settings
•
•
•
Pressure remains constant whereas
volume delivery changes as lung
characteristic change
Used when the limiting of pressure
delivery is important
Allows the clinician to set a maximum
pressure, reducing the risk of lung
over distention, uses a descending
flow pattern; may be more comfortable
for pts who can breathe spontaneously
Disadvantages: volume delivery
varies, tidal volume and minute
ventilation decrease when lung
characteristics deteriorate
Modes of Ventilation
breath type and timing of breath delivery
• CMV: all breaths are mandatory and can be
volume or pressure targeted; breaths can be
patient or time triggered
– Time triggered breaths in CMV is called control mode
– A/C mode is time or patient triggered
– Sensitivity settings (pressure or flow)– increased
WOB or auto-cycling
– Response time: time increment between when a
patient effort is detected and when flow from the
ventilator to the patient begins
– VC-CMC [set Vt, rate, flow to adjust I:E]
– PC-CMV (PCV) [set IP, rate, IT to adjust I:E] time
cycled
Modes of Ventilation
breath type and timing of breath delivery
• IMV / SIMV: periodic volume or pressure targeted
breaths occur at set intervals (time triggered), between
these mandatory breaths the patient breathes
spontaneously at any desired baseline pressure without
receiving a mandatory breath
– SIMV operates in the same way as IMV except that mandatory
breaths are normally patient triggered rather than time triggered;
at predetermined intervals the machine waits for the patients
next spontaneous effort and then assists the patient by
synchronously delivering a mandatory breath
– SIMV designed to avoid breath stacking
– Spontaneous breaths may be pressure supported
– Monitor WOB
– Potentially fewer cardiovascular side effects, may be used for
weaning
Modes of Ventilation
breath type and timing of breath delivery
Spontaneous Modes
• Spontaneous breathing
– Breathing spontaneously through the ventilator circuit (Brigg’s
adaptor, T-piece)
– Ventilator monitors the patient’s breathing and can activate
alarms
– Some ventilators require considerable effort to open inspiratory
valves to receive flow
• CPAP
– Spontaneously breathing through the ventilator circuit
– Improving oxygenation in patients with refractory hypoxemia and
a low FRC
• PSV
– Special form of assisted ventilation, always patient triggered
Pressure Support Ventilation
• Ventilator provides a constant pressure during
inspiration once it sense the patient’s effort
• The inspiratory pressure, CPAP, and sensitivity
are set, Patient establishes the rate inspiratory
flow and inspiratory time
• Vt is determined by the pressure gradient, lung
characteristics, and patient effort
• PSV is used to:
– Overcome WOB
– Reduce WOB
– Provide full ventilatory support in the assist mode
(PSmax)
Other Ventilator Modes
Closed Loop Ventilation
• Bilevel PAP
• PRVC
• Paug Pressure augmentation, VAPS
• MMV
• APRV
• PAV
Familiarize yourself with these (p 96-98).
Clinical Rounds 6-1 p. 84
What type of breath is it?
• A patient receives a
breath that is patient
triggered, pressure
targeted and time
cycled. What type of
breath is it?
• This is a mandatory,
pressure targeted,
ventilator cycled
breath
• A patient breathes
spontaneously at a
baseline pressure of
8cmH2O
• This is a spontaneous
breath, patient
triggered and cycled
(CPAP)
Clinical Rounds 6-2 p. 86
Volume targeted breaths with Changing
Lung Characteristics
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•
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Figure 6-1 Graphs for constant flow, volume
targeted ventilation; p. 86
What is the approximate inspiratory time?
About 1 sec
What type of waveform is used?
Constant flow waveform, descending ramp
(decelerating)
What is the approximate tidal volume
delivery for each breath?
Vt = 500ml
What are the peak inspiratory pressures in A
B and C?
A = 14cmH2O; B = 25cmH2O; C = 12
cmH2O
What types of lung or thoracic abnormalities
can result in reduced compliance?
Pneumonia ARDS pulmonary
fibrosis/scarring ascites burns surgical
incisions
What would happen to the PIP if compliance
went unchanged but airway resistance
increased?
PIP increases as more pressure is required
to deliver the gas flow
Clinical Rounds 6-3 p. 87
Pressure targeted breaths with Changing
Lung Characteristics
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Figure 6-2 Graphs for pressure targeted•
Ventilation; p.87
What type of pressure curve is delivered in
A, B, and C?
The pressure curve is constant
What type of flow waveform is present
during inspiration in A, B, and C?
A descending ramp (decelerating)
Compare the flow-time curve during
inspiration in C to that in A. What is the
difference between the two?
A drops to zero just at the end of inspiration;
C drops to zero before the end of inspiration
Look at the dotted line in C that starts at the
flow waveform just when flow drops to zero
during inspiration. Look at the volume-time
curve (C). What do you notice about this
volume-time curve compared to those in A
and B? Why is it flat at the top?
The volume curve in C has a short plateau
at the top that begins when flow drops to
zero during inspiration and ends when
exhalation starts. It is flat because the
volume is not changing.
Why is volume delivery higher in B than in
A?
the lungs in B are more compliant than the
lungs in A
Clinical Rounds 6-4 p. 89
Pressure or Volume Ventilation
• A physician wants to
make sure that a patient’s
PaCO2 stays at the
normal level 50mmHg.
Would volume or
pressure ventilation best
meet this requirement?
• Volume ventilation should
be used since it
guarantees volume
delivery and minute
ventilation.
• Ventilating pressure can
become very high in
patients with ARDS. To
prevent excessive
pressures, what
independent variable
would be most
appropriate, volume or
pressure?
• Pressure targeted
ventilation since the goal
is to avoid high
pressures.