Selecting the Ventilator and the Mode

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Selecting the Ventilator and the Mode

• Chapter 6

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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 patients 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?

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Invasive VS Non-invasive

• Artificial airway
• Translaryngeal airways oral or nasal
  endotracheal tubes
• Tracheostomy tube
• Mask

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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

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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

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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

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Control Variablesthe independent variable used
to establish gas flow to the patient

• Volume Control
• Volume provided to the patient is constant and
  independent of what happens to pressure when the
  patients lung characteristics change or when the
  patients 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 Control
• 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

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Modes of Ventilationbreath 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 IE
• PC-CMV (PCV) set IP, rate, IT to adjust IE
  time cycled

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Modes of Ventilationbreath 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

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Modes of Ventilationbreath type and timing of
breath delivery

• Spontaneous Modes
• Spontaneous breathing
• Breathing spontaneously through the ventilator
  circuit (Briggs adaptor, T-piece)
• Ventilator monitors the patients 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

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Pressure Support Ventilation

• Ventilator provides a constant pressure during
  inspiration once it sense the patients 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)

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Other Ventilator ModesClosed Loop Ventilation

• Bilevel PAP
• PRVC
• Paug Pressure augmentation, VAPS
• MMV
• APRV
• PAV
• Familiarize yourself with these (p 96-98).

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Clinical Rounds 6-1 p. 84What 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)

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Clinical Rounds 6-2 p. 86Volume targeted breaths
with Changing Lung Characteristics

• 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

Figure 6-1 Graphs for constant flow,
volume targeted ventilation p. 86
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Clinical Rounds 6-3 p. 87Pressure targeted
breaths with Changing Lung Characteristics

• 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

Figure 6-2 Graphs for pressure targeted Ventilatio
n p.87
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Clinical Rounds 6-4 p. 89Pressure or Volume
Ventilation

• A physician wants to make sure that a patients
  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.