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Basic Pulmonary Mechanics during Mechanical Ventilation. Points of Discussion. Basics , scalars and loops. Abnormalities. Air Leak Auto PEEP and air trapping Active Exhalation Inadequate insp flow Obstruction Trigger sensitivity Increased airway resistance Inadequate flow support

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Presentation Transcript
points of discussion
Points of Discussion

Basics , scalars and loops

Abnormalities

Air Leak

Auto PEEP and air trapping

Active Exhalation

Inadequate insp flow

Obstruction

Trigger sensitivity

Increased airway resistance

Inadequate flow support

Inadequate sensitivity

Atelectasis

Inadequate PEEP

Over-distension

  • Equation of motion
  • Airway pressures
  • Compliance
  • Resistance
  • Pressure-Time
  • Flow-Time
  • Pressure-volume loop
  • Flow-volume loop
  • Work of breathing
  • Hysterexis
spontaneous breathing
Spontaneous Breathing

Exhalation

Inspiration

precondition of inspiration
Precondition of Inspiration

Gas Flow

Pa

  • Pa<Pb
    • Spontaneous breath
  • Pb>Pa
    • Mechanical ventilation

Pa<Pb

Pb

spontaneous inspiration
Spontaneous Inspiration

Volume Change

Pressure Difference

Gas Flow

mechanical ventilation
Mechanical Ventilation

Pressure Difference

Gas Flow

Volume Change

airway resistance
Airway Resistance

“The Feature of the Tube”

D P

R =

D F

Pressure Difference = Flow Rate x Resistance of the Tube

compliance
Compliance

Volume

D V

D P

Pressure

D V

C=

D P

Volume Change=

Pressure Difference x Compliance of the Balloon

tube spring model
Tube + Spring Model

Resistive Forces

Elastic Forces

basic calculations
Basic Calculations

dP = R x Flow + dV / C st

Pressure

Pplat

PEEP

time

Cst = dV / (Pplat-PEEP)

R = (PIP-Pplat) / Flow

lung mechanics
Lung Mechanics

transairway

pressure

transrespiratory

pressure

transthoracic

pressure

volume

elastance = Dpressure / Dvolume

resistance = Dpressure / Dflow

flow

pressure vs time spontaneous breath
Pressure vs TimeSpontaneous Breath

Expiration

Paw (cm H20)

Time (sec)

Inspiration

pressure vs time mechanical breath
Pressure vs TimeMechanical Breath

Peak Inspiratory Pressure

PIP

PEEP

Paw (cm H2O)

Inspiration

Expiration

TI

TE

}

Time (sec)

spontaneous vs mechanical
Spontaneous vs. Mechanical

Mechanical

Inspiration

Paw

(cm H2O)

Spontaneous

Expiration

Expiration

Inspiration

Time (sec)

assisted vs controlled
Assisted vs Controlled

Assisted

Controlled

Pressure (cmH20)

Time (sec)

components of inflation pressure
Components of Inflation Pressure

Pplateau

(Palveolar)

Begin Inspiration

PIP

}

Transairway Pressure (PTA)

Paw (cm H2O)

Inspiratory Pause

Expiration

Time (sec)

Begin Expiration

slide17

Exhalation Valve Opens

Begin Inspiration

Inflation Hold

(seconds)

Pplateau

(Palveolar

Paw (cm H2O)

Time (sec)

PIP

}

Transairway Pressure (PTA)

Paw (cm H2O)

Expiration

Time (sec)

Begin Expiration

PIP

Distending

(Alveolar)

Pressure

Airway Resistance

Expiration

Begin Inspiration

Begin Expiration

pip vs pplat
PIP vsPplat

PIP

High Raw

Normal

PIP

PPlat

PPlat

Paw (cm H2O)

Low Compliance

PIP

PIP

PPlat

High Flow

PPlat

Time (sec)

mean airway pressure
Mean Airway Pressure

Lengthen Inspiratory Time

Increase peak pressure

Increase PEEP

Increase Rate

Increase Flow

increasing mean airway pressure
Increasing Mean Airway Pressure

1. Increase flow

2. Increase peak pressure

3. Lengthen inspiratory time

4. Increase PEEP

5. Increase Rate

flow vs time
Flow vs Time

Inspiration

Time (sec)

Flow (L/min)

Expiration

flow patterns
Flow Patterns

SQUARE

DECELERATING

ACCELERATING

SINE

flow patterns and effects of volume
Flow Patterns and Effects of Volume

ACCELERATING

SINE

DECELERATING

SQUARE

inspiratory flow pattern
Inspiratory Flow Pattern

Total cycle time

TCT

Beginning of expiration

exhalation valve opens

Peak inspiratory flow rate

PIFR

Inspiration

Inspiratory

Time

TI

Expiratory Time

TE

Flow (L/min)

Time (sec)

Beginning of inspiration

exhalation valve closes

Expiration

expiratory flow pattern
Expiratory Flow Pattern

Beginning of expiration

exhalation valve opens

Duration of

expiratory flow

Peak Expiratory Flow Rate

PEFR

Inspiration

Expiratory time

TE

Time (sec)

Flow (L/min)

Expiration

spontaneous breath
Spontaneous Breath

Inspiration

Time (sec)

Flow (L/min)

Expiration

mechanical vs spontaneous
Mechanical vs Spontaneous

Mechanical

Spontaneous

Inspiration

Expiration

increased expiratory resistance
Increased Expiratory Resistance

Flow

Time

Normal Resistance

Increased Resistance

response to bronchodilator
Response to Bronchodilator

After

Before

Time (sec)

Flow (L/min)

Long TE

PEFR

Shorter TE

Higher PEFR

insufficient expiratory time
Insufficient Expiratory Time

Flow

Time

End-Expiratory Flow

air trapping
Air Trapping

Air Trapping

Auto-PEEP

Normal

Patient

Inspiration

Time (sec)

Flow (L/min)

}

Expiration

excessive secretions
Excessive Secretions

Normal

Patient

Inspiration

Time (sec)

Flow (L/min)

Expiration

air leak flow trigger autotriggering
Air Leak (Flow Trigger, autotriggering)

Inspiration

Time (sec)

Flow (L/min)

Leak in LPM

Expiration

active inspiration or asynchrony
Active Inspiration or Asynchrony

Patient’s effort

Normal

Abnormal

Time (sec)

Flow

(L/min)

excessive inspiratory time
Excessive Inspiratory Time

Air Trapping

Auto-PEEP

Normal

Patient

Inspiration

Increase WOB and “Fighting” of the ventilator

Time (sec)

Flow (L/min)

}

Expiration

obstruction vs active expiration
Obstruction vs Active Expiration

Obstruction

Active Expiration

Time (sec)

Flow (L/min)

Normal

Abnormal

trigger sensitivity
Trigger Sensitivity

Sensitivity level

Pressure

Time

Flow

Time

volume vs time
Volume vs. Time

Inspiratory Tidal Volume

Volume (ml)

Inspiration

Expiration

TI

Time (sec)

active exhalation
Active Exhalation

Volume (ml)

Time (sec)

inadequate inspiratory flow
Inadequate Inspiratory Flow

Adequate Flow

Inadequate Flow

Paw

(cm H2O)

Time (sec)

air leak
Air Leak

Air Leak

Volume (ml)

Time (sec)

air leak1
Air Leak

Pressure

Flow

Expiratory flow area less

than inspiratory flow area

Expired volume

Inspired volume

Volume

Leak

frc and pv loop
FRC and PV Loop

Normal Compliance

TLC

VOLUME

FRC

FRC

Negative

Positive

0

DISTENDING PRESSURE

components of pressure volume loop
Components of Pressure-Volume Loop

VT

Expiration

Volume (mL)

Inspiration

PIP

Paw (cm H2O)

pressure volume loop type of breath
Pressure-Volume Loop(Type of Breath)

E

E

Vol (ml)

E

I

I

I

Paw

(cm H2O)

Spontaneous

Controlled

Assisted

I: Inspiration E: Expiration

peep and p v loop
PEEP and P-V Loop

VT

PEEP

PIP

Volume (mL)

Paw (cm H2O)

inflection points
Inflection Points

Upper Inflection Point

Lower Inflection Point

  • Upper Inflection Point: Represents pressure resulting in regional overdistension
  • Lower Inflection Point: Represents minimal pressure for adequate alveolar recruitment

Volume (mL)

Pressure (cm H2O)

decreased compliance
Decreased Compliance

Normal

Patient

Volume(ml)

Pressure (cm H2O)

lung compliance changes and the p v loop
Lung Compliance Changes and the P-V Loop

Volume Targeted Ventilation

Preset VT

Increased

Normal

Decreased

Volume (mL)

Paw (cm H2O)

PIP levels

lung compliance changes and the p v loop1
Lung Compliance Changes and the P-V Loop

VT levels

Increased

Normal

Pressure Targeted Ventilation

Decreased

Volume (mL)

Preset PIP

Paw (cm H2O)

hysteresis
Hysteresis

Volume (ml)

Normal Hysteresis

Abnormal Hysteresis

Pressure (cm H2O)

flow volume loop
Flow-Volume Loop

Inspiration

PIFR

Volume (ml)

FRC

VT

Flow (L/min)

PEFR

Expiration

work of breathing
Work of Breathing

Volume (ml)

B

A: Resistive Work

B: Elastic Work

A

Pressure (cm H2O)

work of breathing1
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 Measurements

WOB =∫0ti P x Vdt

  • Elasic work: ABCA
  • Resistive work
    • Inspiratory: ADCA
    • Expiratory: ACEA

V

B

C

E

D

P

A

work of breathing measurements
Work of Breathing Measurements

WOB =∫0ti P x Vdt

  • 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
P-V Loop and WOB

V

Normal Compliance

Increased Resistance

Decreased Compliance

Normal Resistance

P

V

Normal Compliance

Normal Resistance

V

P

P

work of breathing2
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

WEL = elastic work

WR = resistive work

Volume

Volume

Volume

VT

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
Intrinsic PEEP and Work of Breathing

When present, intrinsic PEEP contributes to the work of breaking and can be offset by applying external PEEP.

Volume

VT

VT

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
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 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

machine

PES

time

Paw = Airway pressure, Pes= esophageal pressure

work of breath
Work of breath

Resistive Work

Elastic Work of Lung

Pressure

Elastic Work of Chest

Paw

Pes

Work to inflate the chest wall

Inflation

Deflation

Volume

relationship between the set pressure support level and the patient s breathing effort
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
Partitioning of the WorkloadBetween 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
Abnormalities
  • Air-leak
  • Air trapping
  • Increased airway resistance
  • Inadequate flow support
  • Inadequate sensitivity
  • Atelectasis
  • Inadequate PEEP
  • Airway obstruction
  • Over-distension
air leak2
Air Leak

Volume (ml)

Air Leak

Pressure (cm H2O)

air leak3
Air Leak

Inspiration

Flow

(L/min)

Volume (ml)

Air Leak in mL

Normal

Abnormal

Expiration

air trapping1
Air Trapping

Inspiration

Flow

(L/min)

Does not return

to baseline

Volume (ml)

Normal

Abnormal

Expiration

increased airway resistance
Increased Airway Resistance

Inspiration

Flow

(L/min)

Volume (ml)

Normal

Abnormal

“Scooped out”

pattern

Decreased PEFR

Expiration

increased raw
Increased Raw

Higher PTA

Vol (mL)

Normal Slope

Lower Slope

Pressure (cm H2O)

airway secretions water in the circuit
Airway Secretions/Water in the Circuit

Inspiration

Flow

(L/min)

Volume (ml)

Normal

Abnormal

Expiration

airway obstruction
Airway Obstruction

After Suction

Before Suction

F

F

V

V

optimising peep
Optimising PEEP

PEEP: 3 cmH2O

PEEP: 8 cmH2O

V

V

P

P

inadequate sensitivity
Inadequate Sensitivity

Volume (mL)

Paw (cm H2O)

Increased WOB

atelectasis
Atelectasis

Replaced FRC

Lost FRC

V

V

P

P

overdistension
Overdistension

With little or no change in VT

Normal

Abnormal

Volume (ml)

Pressure (cm H2O)

Paw rises