Sri Ramajeyam

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• Sri Ramajeyam
• Om Anandamayi Chaithanyamayi Sathyamayi Parame!
• Dr. S. Ahanatha Pillai, M.D.,D.A.,
• Emeritus Professor
• Dr. M. G. R. Medical University
• Former Professor of Anaesthesiology
• Madurai Medical College
• Govt. Rajaji Hospital
• Madurai

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DEPARTMENT OF ANAESTHESIOLOGY
Madurai Medical College
Madurai
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Basics of Ventilator Therapy

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• Ventilation Movement of Air
• Respiratory Physiology
• Movement of air in out of lungs
• Purpose
• Transfer O2 into Blood
• Removal CO2 from Blood
• Maintaining Normal Blood Gas

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Respiratory Failure

• Inability of the system
• to maintain Normal
• Blood Gas Levels
• Acid Base Status
• Respiratory Failure
  -Ventilatory Failure

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• Respiration External Internal (Tissue)
• Ventilation Utilisation of
  O2
• Mechanics Moving air
  Cell Metabolism in
  out of lung
• Al-Cap Mem Diffusion Release of
  CO2
• Perfusion O2 into Blood
• CO2 into Alveoli
• Ventilation ----- Perfusion -----
  Diffusion

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• Disorders of Breathing
• Airways
• Lungs
• Thoracic Cage Muscles (Apparatus)
• Brain (Central Control)

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Ventilator Therapy

• Useful only in Reversible
• Depression or Damage
• Brain (Central Control)
• Mechanics of Breathing (Apparatus)
• Lungs
• Pulmonary Oedema, ARDS Helpful
• Chronic - Irreversible Damage - ?

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Respiratory Mechanics

• The mechanical changes that happen
• in Respiratory apparatus which cause
• movement of air in and out of lungs
• Respiratory Apparatus
• Thoracic Cage
• Respiratory Muscles
• Lungs within Thoracic Cage

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• Mechanical Ventilation
• Common Indications
• Failure of Respiratory Mechanics
• Neurological G.B.S or N.M.Block
• Depression of Respiratory Center
• By Opioids, Head Injury etc

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Mechanical Ventilation

• A Machine performs
• the Work of Breathing
• instead of Inspiratory Muscles
• Expiration is always passive process

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Ventilator

• A device which causes
• bulk movement of gases
• in and out of lungs and
• takes over or assists the
• function of Respiratory muscles

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• The user should know
• what the Ventilator can do,
• not how it does that
• - J. S. Robinson

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Any Ventilator

• Has two basic components
• Brain
• A Control Mechanism
• to command what how to do
• Muscle
• A Driving Mechanism
• to carry out the command

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• Simplest Ventilator
• Divides the Minute Volume into
• Number of Breaths (Tidal Volume)
• Example Ambus Bag
• The Brain
• The Muscle

Belongs to operator
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Simplest Ventilator
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Types

• Negative Pressure Ventilators
• Positive Pressure Ventilators
• Negative Pressure Ventilator
• Creates extra thoracic Negative
• pressure intermittently
• Mimics normal respiration
• eg Tank Ventilators Cuirass

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Principle of Negative Pressure Ventilator
Tank Ventilator
Cabinet Ventilator or
Iron Lung

Cuirass Ventilator
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Emerson Tank Ventilator
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Iron lung ward Ranchos Los Amigos Hospital 1953
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Emerson Iron Lung
Used by Barton Hebert 1950 2003 - Louisiana
Museum Center for Disease control Prevention
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Modern Transparent Tank Ventilator
The Tank has clear acrylic lid a gasket around
neck The ventilator machine is seen as a Box
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Cuirass Ventilator
This patient has Hypoventilation during sleep
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Patient Supported by Cuirass
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Positive Pressure Ventilator

• All modern Ventilators
• The Principle is I.P.P.V
• Positive Pressure (Supra-atmospheric)
• applied to proximal airway
• forces air into Lungs Inspiration
• Expiration is allowed passively
• This is repeated - Intermittently

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Spontaneous Respiration
Inspiration
Expiration
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Positive Pressure Respiration - IPPV
Inspiration
Expiration
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_
2 cm
2 cm

_
0 (Atm)
15 cm
IE ratio 12
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Indications for Ventilation

• Apnoea or Impending Apnoea
• Hypoventilation
• Fatigue or Paralysis of Respiratory
• muscles (Myesthenia, Polyneuritis)
• Persistent Tachypnoea
• Paradoxical Respiration
• Flail Chest

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Advantages of Ventilation

• Takes over Work of Breathing
• Improves Gas Exchange
• Opens up collapsed alveoli (Recruiting)
• Permits Heavy Sedation Analgesia
• ignoring Respiratory Depression
• May reverse Pulmonary Oedema

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• Problems
• A common problem in
• patients supported by
• Mechanical ventilation is that
• they are hyperventilated, which
• leads to Respiratory alkalosis

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Respiratory Alkalosis

• Hypocapnoea (Hypocarbia)
• O2 Dissociation Curve Shift to Left
• Cerebral Vasoconstriction
• I.C.T. Reduced, Cerebral Oedema
• Inverse Steal in Brain pathology
• Hypotension
• Respiratory Centre Depressed

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Effects on CVS

• Thoracic Neg. Pump Abolished
• Venous Return Reduced
• Cardiac Output Reduced
• Pulm. Blood Flow Reduced
• Pulm. Cap.Pressure Raised
• Strain on Right Ventricle

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Patient - Ventilator Asynchrony

• Ventilator Muscle Overload
• With improper ventilator settings,
• patient fights the ventilator
• Results in need for
• More Sedation or Muscle Relaxant
• Undue delay in weaning process

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• Atrophy of Diaphragm
• Ventilation for gt 40 hours results in
• reduction of Diaphragm muscle mass
• Minimal amount of WOB prevents
• reduction of Diaphragmatic strength
• and maintains endurance
• Assist / Control Mode
• Prevents Respiratory muscle atrophy

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Oxygen Toxicity Stretch Injury

• Two possible injuries
• Excess O2 (High F i O2)
• O2 Free radical mediated lung injury
• Excess Flow
• Over distention Stretch injury
• Barotrauma in Poor compliance
• Volutrauma in Good compliance

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• Inadequate Tidal Volume
• Leaks Expansible Volume
• Leaks in the circuits may cause
• loss of gas that will not reach the lungs
• When positive pressure is applied,
• tubes of breathing circuit may expand
• and accommodate some volume of gases
• that will not be delivered to the lungs

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• Exhaled Tidal Volume is the actual
• tidal volume the lungs received
• That is measured by
• Wrights Respirometer
• Volumeter Bellows (Exp Spirometer)
• Transducers - Digital Display

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• The panel must have
• Two Displays
• What we set on the Machine
• What actually the patient receives

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Methods of Artificial Ventilation

• Self inflating resuscitator bag- Ambu
• Simple mechanical device- East Radcliff
• Sophisticated ventilators
• As long as the lungs are well ventilated,
• by some method, life can be saved
• 1952 Denmark polio epidemic had proved it

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East Radcliff Ventilator
(Positive Negative pressure Respiratory pump)
Still it is better than a Bag, Mask Hands
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Modern Ventilators

• Brain - Control Mechanism
• Microprocessor Modules
• Muscle - Driving Power
• Pneumatic Air or O2
• Electricity
• Combined

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Ventilator Breath (Mechanical Breath)

• Each Cycle is divided into Four Phases
• Inspiratory Phase
• Changeover - Inspiration to Expiration
  
  
• 
  (Cycling)
• Expiratory Phase
• Changeover - Expiration to Inspiration

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Basic Mechanical Breath
2
(Cycling)
1
3

0
4
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Initiation of Inspiration
Any change can be done only on this
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2
2
Special Modes
Changeover from Insp Expi (Cycling)
Volume Pressure Time Flow
IMV SIMV MMV
CPAP BIPAP APRV
1
3
Inspi Phase
Pressure
Expi Phase

• PSV
• PCV
• PAV
• IRV

NEEP ZEEP PEEP

0
Time
Changeover to Inspiration
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Time (CMV) Patient Triggered (Assist)
Patient Triggered / Time (A/C)
All the possible modifications in a Mechanical
Breath
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Inspiratory Phase

• Pressure Support PSV
• Pressure Control PCV
• Proportional Assist PAV
• Inverse Ratio IRV

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Change over from Inspiration to Expiration

• Volume Cycling Preset Volume
• Pressure Cycling Preset Pressure
• Time Cycling Preset Time (Pr or Vol)
• Flow Cycling Preset Flow
• Microprocessors can do all these in one
  
  
  
  

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Expiratory Phase

• NEEP Negative End Expiratory X
• ZEEP Expiratory Retard X
• PEEP Positive End Expiratory Pressure
• CPAP Continuous Positive Airway
• PEEP applied Spontaneous Breathing

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NEEP
Negative End Expiratory Pressure
_

• IPPV NEEP

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ZEEP
Zero End Expiratory Pressure

• Expiratory Retard - Interrupted line is normal
  expiration

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PEEP
Positive End Expiratory Pressure
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PEEP
Positive End Expiratory Pressure
IPPV with PEEP
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CPAP and Variants

• CPAP Continuous Positive Airway
• BIPAP Biphasic Positive Airway
• APRV Airway Pressure Release

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CPAP
Continuous Positive Airway Pressure

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_
Patient breathes spontaneously on CPAP Normal
Inspiration and Expiration are seen
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BIPAP
Biphasic Positive Airway Pressure
Time High
Time Low
Time High
Patient is breathing Spontaneously
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APRV
Airway Pressure Release Ventilation
Patient is breathing Spontaneously
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Initiation of Inspiration

• Change over from Expiration to Inspiration
• Modes (Independent Ventilator Breath)
• CMV (Controlled Mechanical) (Time)
• Assist (Assisted Ventilation) (Pt.Trig) X
• A / C (Assist / Control) (Pt.Trig Time)

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Control Mode (CMV)
Controlled Mechanical Ventilation
A set rate of Mechanical breaths are delivered at
specific interval of Time Totally ignores
Patient's attempts
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Assist Mode
Patient Triggered Ventilation
Patient's Inspiratory attempt is sensed, and a
Mechanical breath is delivered No Inspiratory
attempt - Apnoea - Danger
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Assist / Control Mode

• Inspiratory attempt is sensed and Assisted
• If there is no attempt within the back up time,
  then
• a Mechanical Breath is delivered

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Special Modes

• IMV Intermittent Mandatory
• Ventilation Not in
  use
• SIMV Synchronised I M V
• Very commonly used
• MMV Mandatory Minute Ventilation
• Not
  preferred

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IMV
Intermittent Mandatory Ventilation
Patient breathes spontaneously Certain number of
Mandatory Breaths ordered For example 4 Breaths
/ Minute
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IMV
Intermittent Mandatory Ventilation
Mandatory breath may fall on any phase If it
falls on expiration Breath Stacking Barotrauma or
Volutrauma may occur
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• SIMV

Timing windows - Mandatory Breaths delivered
only during patients Inspiratory attempt No
Asynchrony
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IRV
Inverse Ratio Ventilation

• Note Long Inspiratory phase
• Pressure may gradually increase to peak
• Pressure may abruptly rise, maintain plateau

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Adequacy of Ventilation

• How to Assess clinically?
• Conscious Patient Comfortable
• Chest Expansion Adequate
• Colour of periphery Pink
• C V S Parameters Normal
• Blood- Gas Study Normal

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Modes Settings

• Mode is a primary method to
• Ventilate lungs
• Eg CMV, Assist / Control (A / C)
• Setting is a modification or
• addition to the primary mode to
• improve the quality of Ventilation
• Eg PEEP, IRV

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Available Modes

• Unfortunately many Newer Modes
• have been introduced merely on the
• basis of Technical ability rather than
• as a result of a defined clinical need
• or demonstrable advantage to the
• patient.
• J. Denis Edwards

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Available Modes

• Primary Modes Expiration Special M

• IMV
• SIMV
• MMV

• CMV
• Assist
• A / C

• NEEP
• ZEEP
• PEEP

Inspiration
Spontaneous

• PSV
• PCV
• PAV
• IRV

• CPAP
• APRV
• BIPAP

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Ideal Initial Setting

• Tidal Volume 10 12 ml / Kg
• Respiratory Rate 10 12 / min
• Peak Insp. Flow Rate 40 Lt / min
• I E Ratio 1 2
• Fi O2 0.5
• PEEP 3 5 cm H2O
• Wave Form Decr. Ramp
• Trigger Sensitivity 1 2 cm H2O

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Tidal Volume

• Clinical Significance
• 10 12 ml / Kg Ideal
• 5 7 ml / Kg Micro Atelectasis
• Larger Volume
• Barotrauma
• Volutrauma
• C.V.S Decompensation

Stretch Damage
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FiO2

• Clinical Significance
• Should be
• as High as necessary and
• as Low as possible
• To prevent
• Hypoxia
• O2 Radical mediated lung injury

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PEEP

• Clinical Significance
• Keeping Fi O2 lt 0.6
• Ideal level 5 10 cm H2O
• Useful effects of PEEP are
• exhausted above 15 cm H2O

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PEEP CPAP

• PEEP IPPV CPAP Spontaneous Breath
• Advantage (Splinting of Airways)
• Holds lung in more expanded position
• and out of range of airway closure
• Increases FRC improves O2 diffusion
• Indications Not yet rigidly defined
• ARDS, RDS of New born

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Effects of PEEP on Alveoli

• A. Atelectatic Alveoli before PEEP application
• B. Optimal PEEP reinflates alveoli to normal
  volume
• C. Excess PEEP over distends the alveoli
  compress pulmonary capillaries, cause dead space

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PEEP CPAP

• Disadvantages
• Decreases Venous Return
• Reduction of Cardiac Output
• Increases interstitial alveolar water
• Increase in ADH
• Retention of Sodium Water
• Rise in ICT parallel to the increase
• in mean intra thoracic pressure

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Weaning from Ventilator 47

• It is easier to connect a patient
• on a ventilator but,
• it is difficult to wean him off
• It may take a few minutes to
• many days to wean
• Weaning is decided only when
• the original problem is cured

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• Weaning
• Patient is awake is able to cough
• Chest expansion is good
• Gas Exchange is good - O2 CO2
• Normal Pa O2 breathing air 21 O2
• No Chest Infection
• X-Ray No Atelectasis, Oedema,
• Consolidation, Pneumothorax

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Ultimate Outcome

• Depends on Underlying disease
• Reversible Outcome is Good
• Irreversible Ventilator Dependence
• Ventilator associated complications
• may modify the outcome

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Some Key Points

• If ventilator support is required,
• start it in time without any delay
• before irreversible damage occurs
• When in doubt, consult a colleague,
• even a junior for a second opinion
• Hourly assessment and modulation of
• settings will give excellent results
• Lot of wisdom is needed to decide,
• that can be acquired by experience

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Thank You