2. ventilatory modes
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Transcript of 2. ventilatory modes
Definition of Mechanical
Ventilation
June 1, 2016
2
Mechanical ventilation is the
movement of gas in and out of
the lung by an external source
(an automatic mechanical device)
connected directly to the patient.
Purpose of MV
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3
Facilitate alveolar ventilation and carbon dioxide removal.
Provide adequate tissue oxygenation
Reduce the work of breathing
Relieve respiratory distress and Reverse respiratory muscle fatigue
Permit lung healing
Avoid complications
Mechanism of action of MV
Patient
lung
Expiration
Patient
lung
Inspiration
Expiratory valve
Leak
Continuous flowContinuous flow
spontaneo
us
Mechanical Ventilation
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Pressure Difference
Volume Change
Gas Flow Patient
lung
Inspiration
Classification of Mechanical
ventilators
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11
1- By power source:
a) Pneumatic
b) Electrical
2- By rate:
a) Conventional
b) High frequency
Classification of Mechanical
ventilators
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12
3- By pressure relationship to the patient:
a) Negative
b) Positive
4- By cycling mode at termination of inspiration:
a) Volume cycling
b) Pressure cycling
c) Flow cycling
d) Time cycling
e) Mixed cycling
Classification of Mechanical
ventilators
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13
5- Loop control of ventilator output:
a) Opened loop
b) Closed loop
Negative-pressure ventilators (iron lungs)
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•Non-invasive ventilation first used in Boston Children’s Hospital in 1928
•Used extensively during polio outbreaks in 1940s – 1950s
1st Positive pressure
ventilation
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18
• Invasive positive pressure ventilation first used at Massachusetts General Hospital in 1955
• Now the modern standard of mechanical ventilation
Volume control is good and
bad
Guaranteed tidal volume, even with variable
compliance and resistance
Less atelectasis compared to pressure
control
Can cause excessive airway pressure
The limited flow available may not meet the
patient desired inspiratory flow rate –
asynchrony
Leaks leads to volume lossHera NICU 2016
Pressure control is good and
bad
Limit excessive airway pressure
Improve gas distribution
Less tidal volume as pulmonary mechanic
change
Potentially excessive VT as compliance
improves
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Conventional Neonatal
Ventilators
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Pressure limited
Time cycled
Continuous flow
ventilators
In all pressure controlled
ventilation modes
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25
Tidal Volume supplied depend on:
1- PIP- PEEP2- Lung mechanics3- Respiratory drive
of the patient
Why volume control not
suitable of newborn?
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26
Use of small number of tidal volumes
Leak around un-cuffed ET
True tidal volume is influenced by ventilator
circuit compliance
Comprisable volume of the circuit including the
humidifier, can affect the tidal volume
Breath Types during mechanical
ventilation Mandatory (controlled)
Ventilator does the work
Ventilator controls start and stop
Spontaneous Patient takes on work
Patient controls start and stop
Assisted Patients triggers the breath
The ventilator delivers the breath as per control variable
Supported Patients triggers the breath
Ventilator delivers pressure support
Breath cycles at set flow
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Ideal ventilator design
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30
Achieve all the important goals of mechanical
ventilator
Provide a variety of modes that can ventilate
even the most challenging lung diseases.
Has monitoring capabilities to adequately
assess the ventilator and patient performance.
Has safety features and alarms that over lung
protective strategies.
Neonatal ventilator.
Ideal ventilator mode
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31
The mode which deliver a breath that:
Synchronized with the patient spontaneous breathing
Maintain adequate and consistent tidal volume and minute ventilation at low airway pressure.
Response to rapid change of lung mechanic or patient demands.
Provide the lowest possible work of breathing.
A mode of ventilation is only as good as the operator who applies it.
Anatomy of Pressure waveform
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Ti Te
Pre
ssu
re
Begin
inspiration
Cycle to expiration
Time
Flow determines rate
of rise and reaching
peak pressure
Pressure limited =
“PIP”
PEEP
∆pMAP
Classification of ventilatory
modes
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35
Trigger:
1- Machine ( IMV)
2- Patient ( SIMV, SIPPV, PS)
Control:
1- Pressure
2- Volume
3- Dual-control
Classification of ventilatory
modes
June 1, 2016
36
Cycling:
1- Time
2- Flow
3- Volume
Types of breaths during ventilation:
1- Mandatory ( controlled)
2- Spontaneous
3- Assisted
4- Supported
Intermittent Mandatory
Ventilation
Controlled Mechanical
Ventilation
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Trigger
Controll
ed
Cycling
Types of
breaths
Hazards of desynchronization
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39
Baby fighting with the ventilator
Inconsistent tidal volume delivery
Inefficient gas exchange
Increase the work of breathing
Abnormally high intra-thoracic and intra-pulmonary pressures leads to Barotrauma
Decreased venous return
Increase intra-cranial pressure leads to IVH
Sub-optimal training of respiratory muscle
So, synchrony is extremely important
and can be achieved by detecting infant’s
inspiratory effort and using it to trigger
positive pressure inflation (triggered-
ventilation).
Trigger sensitivity
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It determine how easy to the patient to trigger
the ventilator to deliver a breath.
Increase the sensitivity improve patient
ventilator synchronization.
High sensitivity my result in false or auto-
triggering.
The Neonatal flow sensor
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Hot wire anemometer
Sensitive to 0.17 mL
0 - 30 lpm range
Weighs 10 grams
0.5-1 mL added
deadspace
Virtually no resistance
Inexpensive
6 month use
Flow Sensor Measurement
Principle
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Hot wire anemometer:
• Two tiny platinum wires are heated to 400°C
• One wire is shaded to determine direction of gas flow
• Wire cooling is proportional to gas flow
• Flow is integrated with time for volume measurement
Limitations of the flow sensor
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48
If ET leak, expiratory tidal volume may be
underestimated.
Imposing 1 ml of a dead space , which may
increase the WOB in very tiny preterm.
If less than the expected expiratory tidal
volume due to ET leak is registered as a
negative flow and trigger a ventilator breath,
auto-triggering.
Limitations of the flow sensor
June 1, 2016
49
Humidity; water will create significant
fluctuations of accuracy.
Secretions- surfactant; reading above or below
baseline in the presence of zero flow
Very delicate-breaks easily, wears-out due to
processing and age
Assist/Control
Synchronized Intermittent Positive Pressure
Ventilation
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2016
Trigger
Controll
ed
Cycling
Types of
breaths
Trigger window
Synchronized Intermittent
Mandatory Ventilation
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Trigger
Controll
ed
Cycling
Types of
breaths
Trigger windo
w
A/C Vs SIMV
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56
More stable tidal volume
Less tachypnea
Smaller blood pressure fluctuation
Smaller tidal volume
Lower work of breathing
Faster weaning from mechanical ventilator
Paw
V•
insp
exp
Patient or
vent ilator
initiated
inspiration PSV cycled
expiration
Peak flow
Drop to 15%
of peak flow
Pressure Support Ventilation
Set Pinsp
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PSV Vs A/C
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59
PSV, Allow the newborn more control over the
respiratory pattern, with synchronization at the
end of inspiration not only the beginning.
PSV, Decreasing asynchrony by minimize the
chance of active expiration against high
positive pressure.
PSV, Automatically adjust Ti according to
change in patient time constant breath by
breath.
PSV, Allow the infant to sigh as needed to
prevent atelectasis.
Synchronized intermittent
mandatory ventilation &
pressure support
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60
Trigger
Controll
ed
Cycling
Types of
breaths
Proportional Assist Ventilation (PAV)&
Neurally adjusted ventilatory
assistance(NAVA)
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61
New ventilatory modes designed to assist
spontaneous ventilation
The breath delivered is similar to PS but the
pressure support level is variable and is
proportional to patient spontaneous effort
a) The harder the patient work = the more
support by ventilator
b) The less the patient work = the less
support is provided
Volume Guarantee
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63
Working principle of Volume Guarantee. According to a set tidal volume, inspiratory pressure is automatically regulated by the ventilator.
Volume Guarantee (Dual-Control
Mode)
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64
Several breaths may be needed to reach the target tidal volume after a sudden change.
Maximum
pressure
Principle of working of Volume
Guarantee
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Test breath
Measure Vt
Inspiratory
pressure
Same
inspiratory
pressure
Inspiratory pressure
Compare to set VtMore
Equal
Less
Why volume targeted ventilation in
neonate?
Consistent VT Stable PaCO2 Stable CBF Less IVH
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Open the lung and keep it
opened
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The benefit of
Volume Targeted
Ventilation can not
be realized without
ensuring that the
tidal volume is
evenly distributed
throughout
an (open lung)
Volume guarantee why?
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69
It is volu-trauma than baro-trauma
More stable tidal volume
Wean PIP if lung mechanics improved
Less hypo-capnea
Work better with A/C than SIMV
Bio-trauma decreased with TV 5ml/kg
Faster weaning from mechanical ventilator
Pressure Support + Volume
Guarantee
Concept of “Auto-weaning”
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PIP
C lung
Vt
ExtubateTime
Mandatory Minute Ventilation
MMV
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72
Guarantee a minimum minute ventilation ( RR x TV)
If the patient maintain a MV above the set MV this mode will function like PS mode
If the patient MV falls below the set MV the mode will deliver mandatory breaths ( SIMV or IMV + VG), only the numbers of breaths that required to return patient MV to the set MV
Depends on the patient ventilatory drive
When the spontaneous breathing increased, fewer mandatory breaths will be provided
Adaptive Support Ventilation
!!!???
June 1, 2016
75
Body weight
Sex
ASV delivers pressure-controlled breaths using an adaptive (optimal) scheme .
“Optimal” means minimizing the mechanical work of breathing
The machine selects a tidal volume and frequency that the patient’s brain would presumably select if the patient were not connected to a ventilator.
This pattern is assumed to encourage the patient to generate spontaneous breaths.
Different ventilatory modes
and their characteristics
Weaning byPIPInspiratory
time
Ventilator
respiration
rate
Assistance
of each
breath
Inspiratory
trigger
Ventilatory
mode
RR&
PIP
Fixe
d
Fixe
d
Fixe
dNoNoIMV
RR&
PIP
Fixe
d
Fixe
d
Fixe
dNoYesSIM
V
PIPFixe
d
Fixe
d
Variabl
eYesYesAC/
SIPP
V
PIPFixeVariablVariablYesYesPS