Transcript Flow Patterns

Basic Pulmonary Mechanics
during Mechanical Ventilation
Points of Discussion
Basics , scalars and loops
1. Equation of motion
2. Airway pressures
3. Compliance
4. Resistance
5. Pressure-Time
6. Flow-Time
7. Pressure-volume loop
8. Flow-volume loop
9. Work of breathing
10.Hysterexis
Abnormalities
1. Air Leak
2. Auto PEEP and air trapping
3. Active Exhalation
4. Inadequate insp flow
5. Obstruction
6. Trigger sensitivity
7. Increased airway resistance
8. Inadequate flow support
9. Inadequate sensitivity
10.Atelectasis
11.Inadequate PEEP
12.Over-distension
Spontaneous Breathing
Exhalation
Inspiration
Precondition of Inspiration
Pa < Pb
• Pa < Pb
Gas Flow
– Spontaneous
breath
• Pb > Pa
– Mechanical
ventilation
Pb
Pa
Spontaneous Inspiration
Volume Change
Pressure Difference
Gas Flow
Mechanical Ventilation
Pressure Difference
Gas Flow
Volume Change
Airway Resistance
“The Feature of the Tube”
R=
D P
D F
Pressure Difference = Flow Rate x Resistance of the Tube
Compliance
D V
C=D P
Volume
DV
DP
Pressure
Volume Change =
Pressure Difference x Compliance of the Balloon
Tube + Spring Model
Resistive Forces
Elastic Forces
Basic Calculations
dP = R x Flow + dV / C st
Pressure
Cst = dV / (Pplat-PEEP)
Pplat
PEEP
time
R = (PIP-Pplat) / Flow
Lung Mechanics
resistance = Dpressure / Dflow
flow
transairway
pressure
transrespiratory
pressure
volume
transthoracic
pressure
elastance = Dpressure / Dvolume
Paw (cm H20)
Pressure vs Time
Spontaneous Breath
Expiration
Time (sec)
Inspiration
Pressure vs Time
Mechanical Breath
Paw (cm H2O)
Peak Inspiratory Pressure
PIP
Inspiration
Expiration
}
TI
TE
PEEP
Time (sec)
Spontaneous vs. Mechanical
Mechanical
Inspiration
Paw
(cm H2O)
Spontaneous
Expiration
Inspiration
Expiration
Time (sec)
Assisted vs Controlled
Pressure
(cmH20)
Assisted
Controlled
Time (sec)
Paw (cm H2O)
Components of Inflation Pressure
PIP
}
Pplateau
(Palveolar)
Transairway Pressure (PTA)
Inspiratory Pause
Expiration
Time (sec)
Begin Inspiration
Begin Expiration
Paw (cm H2O)
PIP
Pplateau
Pressure
} Transairway
(P )
TA
Exhalation Valve Opens
(Palveolar
Expiration
Time (sec)
Begin Expiration
Begin Inspiration
Paw (cm H2O)
PIP
Inflation Hold
(seconds)
Distending
(Alveolar)
Pressure
Expiration
Time (sec)
Begin Inspiration
Begin Expiration
PIP vs
Pplat
PIP
Normal
PIP
Paw (cm H2O)
High Raw
PPlat
PPlat
PIP
PIP
High Flow
PPlat
Time (sec)
Low Compliance
PPlat
Mean Airway Pressure
Lengthen
Increase
Increase
Increase
Increase
Inspiratory
peak
PEEP
Rate
pressure
FlowTime
Increasing Mean Airway Pressure
1. Increase flow
2. Increase peak pressure
3. Lengthen inspiratory time
4. Increase PEEP
5. Increase Rate
Pressure
Time
Flow vs Time
Flow (L/min)
Inspiration
Time (sec)
Expiration
Flow Patterns
SQUARE
ACCELERATING
DECELERATING
SINE
Flow Patterns and Effects of
Volume
SQUARE
DECELERATING
ACCELERATING
SINE
Inspiratory Flow Pattern
Peak inspiratory flow rate
PIFR
Beginning of expiration
exhalation valve opens
Flow (L/min)
Inspiration
Inspiratory
Time
TI
Expiratory Time
TE
Time (sec)
Beginning of inspiration
exhalation valve closes
Expiration
Total cycle time
TCT
Expiratory Flow Pattern
Beginning of expiration
exhalation valve opens
Flow (L/min)
Inspiration
Expiratory
time
TE
Duration of
expiratory flow
Expiration
Peak Expiratory Flow Rate
PEFR
Time (sec)
Flow (L/min)
Spontaneous Breath
Inspiration
Time (sec)
Expiration
Mechanical vs Spontaneous
Mechanical
Spontaneous
Inspiration
Expiration
Increased Expiratory Resistance
Flow
Time
Normal Resistance
Increased Resistance
Response to Bronchodilator
After
Flow (L/min)
Before
Time (sec)
PEFR
Long TE
Higher
PEFR
Shorter TE
Insufficient Expiratory Time
Flow
Time
End-Expiratory Flow
Air Trapping
Flow (L/min)
Inspiration
Normal
Patient
Time (sec)
}
Air Trapping
Auto-PEEP
Expiration
Excessive Secretions
Flow (L/min)
Inspiration
Normal
Patient
Time (sec)
Expiration
Air Leak
(Flow Trigger,
autotriggering)
Flow (L/min)
Inspiration
Time (sec)
Leak in LPM
Expiration
Active Inspiration or Asynchrony
Patient’s effort
Normal
Abnormal
Flow
(L/min)
Time (sec)
Excessive Inspiratory Time
Inspiration
Normal
Patient
Flow (L/min)
Increase WOB and “Fighting” of the ventilator
Time (sec)
}
Air Trapping
Auto-PEEP
Expiration
Obstruction vs Active Expiration
Obstruction
Flow
(L/min)
Active Expiration
Time (sec)
Normal
Abnormal
Trigger Sensitivity
Pressure
Time
Sensitivity level
Flow
Time
Volume vs. Time
Volume (ml)
Inspiratory Tidal Volume
Inspiration
Expiration
TI
Time (sec)
Active Exhalation
Volume (ml)
Time (sec)
Inadequate Inspiratory Flow
Inadequate Flow
Paw
(cm H2O)
Adequate Flow
Time (sec)
Volume (ml)
Air Leak
Air Leak
Time (sec)
Air Leak
Pressure
Flow
Expiratory flow area less
than inspiratory flow area
Inspired volume
Expired volume
Volume
Leak
FRC and PV Loop
Normal Compliance
VOLUME
TLC
FRC
0
Negative
Positive
DISTENDING PRESSURE
FRC
Components of Pressure-Volume
Loop
VT
Volume
(mL)
Paw (cm H2O)
PIP
Vol (ml)
Pressure-Volume Loop
(Type of Breath)
E
E
I
I
Controlled
Assisted
I: Inspiration
I
E
Paw
(cm H2O)
Spontaneous
E: Expiration
PEEP and P-V Loop
VT
Volume
(mL)
PEEP
Paw (cm H2O)
PIP
Inflection Points
Upper Inflection Point
 Upper Inflection Point:
Represents pressure
resulting in regional
overdistension
 Lower Inflection Point:
Represents minimal
pressure for adequate
alveolar recruitment
Volume (mL)
Lower Inflection Point
Pressure (cm H2O)
Decreased Compliance
Volume(ml)
Normal
Patient
Pressure (cm H2O)
Lung Compliance Changes and the P-V
Loop
Volume Targeted Ventilation
Preset VT
Increased
Normal
Decreased
Volume (mL)
Paw (cm H2O)
PIP levels
Normal
Pressure Targeted Ventilation
Increased
VT levels
Lung Compliance Changes and the P-V
Loop
Decreased
Volume (mL)
Paw (cm H2O)
Preset PIP
Hysteresis
Volume (ml)
Normal Hysteresis
Abnormal Hysteresis
Pressure (cm H2O)
Flow-Volume Loop
Inspiration
PIFR
Volume (ml)
FRC
VT
PEFR
Expiration
Work of Breathing
Volume (ml)
B
A
Pressure (cm H2O)
A: Resistive Work
B: Elastic Work
Work of Breathing
• WOB is a major source of caloric expenditure and oxygen
consumption
• Appr. 70% to overcome elastic forces, 30% flow-resistive work
• Patient work is a one of the most sensitive indicator of ventilator
dependency
• Comparison of Ventilator and Patient work is a useful indicator
during weaning process
• WOB may be altered by changes in compliance, resistance,
patient effort, level of support, PEEP, improper Ti, demand
system sensitivity, mode setting
• Elevated WOB may contraindicate the weaning process
WOB Measurements
WOB = ∫0
ti
V
P x Vdt
• Elasic work: ABCA
• Resistive work
– Inspiratory: ADCA
– Expiratory: ACEA
B
C
E
D
A
P
Work of Breathing
Measurements
WOB = ∫0 P x Vdt
ti
• Paw: Ventilator Work: The physical force required to
move gas into the lung, represents the total work of
the resp. system (patient + ventilator)
• Peso: Patient Work: done by respiratory muscles,
represents the pulmonary work of breathing
• Paw-Ptr: Imposed Work by the Endotracheal tube
P-V Loop and WOB
V
Normal Compliance
Increased Resistance
Decreased Compliance
Normal Resistance
P
V
Normal Compliance
Normal Resistance
P
V
P
Work of Breathing
Work per breath is depicted as a pressure-volume area
Work per breath (Wbreath) = P x tidal volume (VT)
Wmin = wbreath x respiratory rate
Volume
Volume
WR = resistive
work
VT
Volume
WEL = elastic work
Pressure
Pressure
Pressure
The total work of breathing can be partitioned between an elastic and resistive work. By analogy, the pressure needed to inflate a
balloon through a straw varies; one needs to overcome the resistance of the straw and the elasticity of the balloon.
Intrinsic PEEP and Work of
Breathing
VT
VT
Volume
When present, intrinsic PEEP contributes to the work of breaking and
can be offset by applying external PEEP.
Dynamic
Hyperinflation
FRC
Pressure
PEEPi
PEEPi = intrinsic or auto PEEP; green triangle = tidal elastic work; red loop = flow resistive work; blue rectangle = work expended
in offsetting intrinsic PEEP (an expiratory driver) during inflation
The Pressure and Work of Breathing can
be Entirely Provided by the Ventilator
(Passive Patient)
Ventilator
+
₊
+
+
+
₊
The Work of Breathing can be
Shared Between the Ventilator
and the Patient
The ventilator generates positive pressure within the airway and the patient’s
inspiratory muscles generate negative pressure in the pleural space.
AC mode
PAW
patient
PES
Paw = Airway pressure, Pes= esophageal pressure
machine
time
Work of breath
Resistive Work
Pressure
Elastic Work of Lung
Elastic Work of Chest
Paw
Work to inflate the chest wall
Inflation
Deflation
Volume
Pes
Relationship Between the Set
Pressure Support Level and the
Patient’s Breathing Effort
The changes in Pes
(esophageal
pressure) and in the
diaphragmatic
activity (EMG)
associated with the
increase in the level
of mask pressure
(Pmask = pressure
support) indicate
transfer of the work
of breathing from
the patient to the
ventilator.
Carrey et al. Chest. 1990;97:150.
Partitioning of the Workload Between
the Ventilator and the Patient
How the work of breathing partitions between the patient and the ventilator
depends on:
• Mode of ventilation (e.g., in assist control most of the work is usually done by the ventilator)
• Patient effort and synchrony with the mode of ventilation
• Specific settings of a given mode (e.g., level of pressure in PS and set rate in SIMV)
Abnormalities
•
•
•
•
•
•
•
•
•
Air-leak
Air trapping
Increased airway resistance
Inadequate flow support
Inadequate sensitivity
Atelectasis
Inadequate PEEP
Airway obstruction
Over-distension
Air Leak
Volume (ml)
Air Leak
Pressure (cm H2O)
Air Leak
Inspiration
Flow
(L/min)
Volume (ml)
Air Leak in mL
Normal
Abnormal
Expiration
Air Trapping
Inspiration
Flow
(L/min)
Does not return
to baseline
Volume (ml)
Normal
Abnormal
Expiration
Increased Airway Resistance
Inspiration
Flow
(L/min)
Volume (ml)
Normal
Abnormal
“Scooped out”
pattern
Decreased PEFR
Expiration
Increased Raw
Higher PTA
Vol (mL)
Pressure (cm H2O)
Airway Secretions/Water in the
Circuit
Inspiration
Flow
(L/min)
Volume (ml)
Normal
Abnormal
Expiration
Airway Obstruction
F
F
V
V
Before Suction
After Suction
Optimising PEEP
V
V
P
PEEP: 3 cmH2O
P
PEEP: 8 cmH2O
Inadequate Sensitivity
Volume
(mL)
Increased WOB
Paw (cm H2O)
Atelectasis
Lost FRC
Replaced FRC
V
V
P
P
Overdistension
With little or no change in VT
Volume (ml)
Normal
Abnormal
Pressure (cm H2O)
Paw rises
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