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
DEPARTMENT OF ANAESTHESIOLOGY
Madurai Medical College
Madurai
Basics of
Ventilator Therapy
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
Respiratory Failure
Inability of the system
to maintain Normal
●
●
Blood Gas Levels
Acid – Base Status
Respiratory Failure -Ventilatory Failure
Respiration External
Internal (Tissue)
Ventilation
Utilisation of O2
Moving air
in & out of lung
Cell Metabolism
Al-Cap Mem
Diffusion
Release of CO2
Perfusion
O2 into Blood
CO2 into Alveoli
Mechanics
Ventilation ----- Perfusion ----- Diffusion
Disorders of Breathing
● Airways
● Lungs
● Thoracic Cage & Muscles (Apparatus)
● Brain (Central Control)
Ventilator Therapy
Useful only in Reversible
Depression or Damage
● Brain (Central Control)
● Mechanics of Breathing (Apparatus)
● Lungs
Pulmonary Oedema, ARDS – Helpful
Chronic - Irreversible Damage - ?
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
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
Mechanical Ventilation
A Machine performs
the Work of Breathing
instead of Inspiratory Muscles
Expiration is always passive process
Ventilator
● “A device which causes
bulk movement of gases
in and out of lungs and
takes over or assists the
function of Respiratory muscles”
● “The user should know
what the Ventilator can do,
not how it does that”
- J. S. Robinson
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
Simplest Ventilator
● Divides the Minute Volume into
Number of Breaths (Tidal Volume)
Example – Ambu’s Bag
● The Brain
● The Muscle
Belongs to operator
Simplest Ventilator
Types
●
●
Negative Pressure Ventilators
Positive Pressure Ventilators
Negative Pressure Ventilator
 Creates extra thoracic Negative
pressure intermittently
 Mimics normal respiration
eg: Tank Ventilators & Cuirass
Principle of Negative Pressure Ventilator
Tank Ventilator
Cabinet Ventilator or Iron Lung
Cuirass Ventilator
Emerson Tank Ventilator
Iron lung ward
Ranchos Los Amigos Hospital 1953
Emerson Iron Lung
Used by Barton Hebert 1950 – 2003 - Louisiana
Museum – Center for Disease control & Prevention
Modern Transparent Tank Ventilator
The Tank has clear acrylic lid & a gasket around neck
The ventilator machine is seen as a Box
Cuirass Ventilator
This patient has Hypoventilation during sleep
Patient Supported by Cuirass
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
Spontaneous Respiration
Inspiration
Expiration
Positive Pressure Respiration - IPPV
Inspiration
Expiration
+
_
– 2 cm
+ 2 cm
+ 15 cm
0 (Atm)
+
_
I:E ratio 1:2
Indications for Ventilation
 Apnoea or Impending Apnoea
 Hypoventilation
 Fatigue or Paralysis of Respiratory
muscles (Myesthenia, Polyneuritis)
 Persistent Tachypnoea
 Paradoxical Respiration
 Flail Chest
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
Problems
“ A common problem in
patients supported by
Mechanical ventilation is that
they are hyperventilated, which
leads to Respiratory alkalosis”
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
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
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
Atrophy of Diaphragm
● Ventilation for
> 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
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
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
Exhaled Tidal Volume is the actual
tidal volume the lungs received
That is measured by
● Wright’s Respirometer
● Volumeter Bellows (Exp Spirometer)
● Transducers - Digital Display
The panel must have
Two Displays
 What we set on the Machine
 What actually the patient receives
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
East Radcliff Ventilator
(Positive – Negative pressure Respiratory pump)
Still it is better than a Bag, Mask & Hands
Modern Ventilators
Brain - Control Mechanism
● Microprocessor Modules
Muscle - Driving Power
●
●
●
Pneumatic
Electricity
Combined
– Air or O2
Ventilator Breath
(Mechanical Breath)
Each Cycle is divided into Four Phases
● Inspiratory Phase
● Changeover - Inspiration to Expiration
● Expiratory Phase
(Cycling)
● Changeover - Expiration to Inspiration
Basic Mechanical Breath
2 (Cycling)
1
3
+
0
_
4
Initiation of Inspiration
Any change can be done only on this
2
Changeover from Insp – Expi (Cycling)
* Volume
Special Modes
Pressure
* Pressure
* Time
* Flow
+
0
–
1
* PSV
* PCV
* PAV
* IRV
* CPAP
* BIPAP
* APRV
3
Inspi Phase
* IMV
* SIMV
* MMV
Expi Phase
* NEEP
* ZEEP
* PEEP
Time
4
Changeover to Inspiration
* Time (CMV)
* Patient Triggered (Assist)
* Patient Triggered / Time (A/C)
All the possible modifications in a Mechanical Breath
Inspiratory Phase
● Pressure Support
● Pressure Control
● Proportional Assist
● Inverse Ratio
PSV
PCV
PAV
IRV
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
Expiratory Phase
● NEEP
● ZEEP
● PEEP
Positive End Expiratory Pressure
● CPAP
Continuous Positive Airway
Negative End Expiratory X
Expiratory Retard X
PEEP applied Spontaneous Breathing
NEEP
Negative End Expiratory Pressure
_
IPPV & NEEP
ZEEP
Zero End Expiratory Pressure
Expiratory Retard - Interrupted line is normal expiration
PEEP
Positive End Expiratory Pressure
PEEP
Positive End Expiratory Pressure
IPPV with PEEP
CPAP and Variants
● CPAP
Continuous Positive Airway
● BIPAP
Biphasic Positive Airway
● APRV
Airway Pressure Release
CPAP
Continuous Positive Airway Pressure
+
0
_
Patient breathes spontaneously on CPAP
Normal Inspiration and Expiration are seen
BIPAP
Biphasic Positive Airway Pressure
Time High
Time Low
Time High
Patient is breathing Spontaneously
APRV
Airway Pressure Release Ventilation
Patient is breathing Spontaneously
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)
Control Mode (CMV)
Controlled Mechanical Ventilation
A set rate of Mechanical breaths are delivered
at specific interval of Time
Totally ignores Patient's attempts
Assist Mode
Patient Triggered Ventilation
Patient's Inspiratory attempt is sensed, and
a Mechanical breath is delivered
No Inspiratory attempt - Apnoea - Danger
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
Special Modes
● IMV
● SIMV
Intermittent Mandatory
Ventilation
Not in use
Synchronised I M V
Very commonly used
● MMV
Mandatory Minute Ventilation
Not preferred
IMV
Intermittent Mandatory Ventilation
Patient breathes spontaneously
Certain number of Mandatory Breaths ordered
For example 4 Breaths / Minute
IMV
Intermittent Mandatory Ventilation
Mandatory breath may fall on any phase
If it falls on expiration Breath Stacking
Barotrauma or Volutrauma may occur
SIMV
Timing windows - Mandatory Breaths delivered only
during patient’s Inspiratory attempt No Asynchrony
IRV
Inverse Ratio Ventilation
Note: Long Inspiratory phase
Pressure may gradually increase to peak
Pressure may abruptly rise, maintain plateau
Adequacy of Ventilation
How to Assess clinically?
● Conscious Patient
● Chest Expansion
● Colour of periphery
● C V S Parameters
● Blood- Gas Study
– Comfortable
– Adequate
– Pink
– Normal
– Normal
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
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
Available Modes
Primary Modes Expiration Special M
● IMV
● CMV
● NEEP
● SIMV
● Assist
● ZEEP
● MMV
●A / C
● PEEP
Inspiration
Spontaneous
● PSV
● PCV
● PAV
● IRV
● CPAP
● APRV
● BIPAP
Ideal Initial Setting
● Tidal Volume
● Respiratory Rate
● Peak Insp. Flow Rate
● I : E Ratio
● Fi O2
● PEEP
● Wave Form
● Trigger Sensitivity
10 – 12 ml / Kg
10 – 12 / min
40 Lt / min
1:2
0.5
3 – 5 cm H2O
Decr. Ramp
1 – 2 cm H2O
Tidal Volume
Clinical Significance
● 10 – 12 ml / Kg
● 5 – 7 ml / Kg
● Larger Volume
– Ideal
– Micro Atelectasis
* Barotrauma
Stretch Damage
* Volutrauma
* C.V.S Decompensation
FiO2
Clinical Significance
●“ Should be
as High as necessary and
as Low as possible”
To prevent
● Hypoxia
● O2 Radical mediated lung injury
PEEP
Clinical Significance
● Keeping Fi O2 < 0.6
● Ideal level 5 – 10 cm H2O
● Useful effects of PEEP are
exhausted above 15 cm H2O
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
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
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
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
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
Ultimate Outcome
Depends on “Underlying disease”
● Reversible – Outcome is Good
● Irreversible – Ventilator Dependence
Ventilator associated complications
may modify the outcome
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