Mechanical Ventilation
The Basics
M.RADHA KRISHNAN
BPT,PGDRT,PGDRCM
SENIOR RESPIRATORY THERAPIST(ICU)
KMCH
COIMBATORE.
Mechanical Ventilation
Basic concepts

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Introduction
Indications
Modes
Initial Settings
Basic Physiology

Transairway pressure Gradient
• Gradient between mouth opening
pressure (Pao)and Alveolar
pressure (PA)
Basic Physiology
Negative pressure ventilation

Pre = Pao (Zero)
- Palv (Negative)
Positive pressure ventilation

Prs = Pao (+ve)
- Palv (0)
Basic Physiology
+ve
PI
PA
pressure CmH2o CmH20
ventiation
Inspiratio
n
20
0
End
inspiratio
n
20
20
∆P
FLOW
+20
In to
lungs
0
No flow
Expiration 0
20
-20
Out of
lungs
End exp
0
0
No flow
0
Delicate balance between Load and Capacity
Depressed Respiratory
Drive
Drug brain Stem
Muscular
Disorders
Myasthenia
Gravis
Electrolyte
Disorders
Prolonged
Increased Minute
Ventilation
Pain, Anxiety,
Excessive Feeding
Sepsis
Increased VD/VT
Increased Elastic
Loads
Low Lung
Compliance
Low Thoracic
Compliance
Intrinsic PEEP
Increased
Resistive Loads
Airway
Obstruction
Loads
Neuromuscular
Capacity blockade
Thoracic
Wall
abnormality
Neuromuscular
disorder
Type 1 Respiratory
Failure
 Def
PaO2 <60 mm Hg
PaCO2  45 mm Hg
 Etiology
Gas Exchange failure
V/Q Mismatch
Shunts
 Diseases
ARDS,Pulmonary
Edema, Pneumonia,
Pneumothorax, PE
Type 2 Respiratory
Failure

Def
PaCO2>45 mm Hg

Etiology
Ventilatory failure
Min. Volume

Diseases
COPD, Muscle
Weakness, Restrictive
Diseases
WHAT IS A VENTILATOR?
Any machine used to PUSH Gas
mixture (air & O2) in to the lungs.
This can be done by applying positive
pressure at the airway either
Invasively or Non invasively.

Classification of mechanical
ventilators
Negative pressure
ventilators
Tank ventilators
Cuirass ventilators

Positive pressure
ventilators
Origins of mechanical ventilation
The era of intensive care medicine began with positive-pressure ventilation
• Negative-pressure ventilators
(“iron lungs”)
• Non-invasive ventilation first
used in Boston Children’s
Hospital in 1928
• Used extensively during polio
outbreaks in 1940s – 1950s
• Positive-pressure ventilators
The iron lung created negative pressure in abdomen
as well as the chest, decreasing cardiac output.
• Invasive ventilation first used at
Massachusetts General Hospital
in 1955
• Now the modern standard of
mechanical ventilation
Iron lung polio ward at Rancho Los Amigos Hospital
in 1953.
Indications – simplified

Respiratory
• Restrictive

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ARDS
ILD
• Obstructive
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Bronchial asthma
COPD
Central airway obstruction
Non respiratory
• Restrictive

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Chest wall
Cardiac
• Normal


Airway protection
Respiratory drive dysfunction
Mechanical Parameters
Predicting Impending Failure
Criteria
Critical Values (Normal)
Muscle strength

Maximum Inspiratory Pressure
<-20 cm H2O (-50 to –100)

Peak Expiratory Pressure
<+40 cm H2O (+100 cm H2O)
Spiro metric data

Vital Capacity

Tidal Volume

Minute Volume
Bedside

PEFR

Respiratory Rate
<15mL/Kg
(65-75mL/Kg)
<5mL/Kg
(5-8mL/Kg)
>10L/min
(5-6L/min)
<100L/min
(400-600L/min)
>35/min
Modes
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CMV (Controlled Mandatory
ventilation)
ACMV
IMV
Synchronized intermittent mandatory
ventilation
CPAP
PS(Pressure support ventilation)
Mechanical Ventilation
Basic Concepts


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
Introduction
Indications
Modes
Initial Settings
VOLUME CONTROL

Normal
alveoli
emphysema
ARDS
VOLUME CONTROL
ADVANDAGE
The patients is
Guaranted to receive
a preset tidal volume
DISADVANTAGE
High Plateau
pressure leads to
Baro trauma
Pressure Control ventilation
ADVANTAGE

Prevent Baro
Trauma
DISADVANTAGE
Low lung compliance
and high airway
Resistances – Tidal
volume drops & drop
in minute ventilation
& Paco2
Accumulation &
respiratory acidosis
Common Modes

CMV (Control Mode Ventilation)

ACMV (Assist Control Mandatory
Ventilation)

IMV (Intermittent Mandatory Ventilation)

SIMV (Synchronized Intermittent
Mandatory Ventilation)

PSV (Pressure Support Ventilation )
CMV
CMV
Control Mode Ventilation

Every breath is mandatory and ventilator
triggered with no spontaneous breaths
• Mandatory breaths at a set frequency and tidal
volume delivered to the patient
• The inspiratory valve is closed to the patient
otherwise so that no additional breaths can be
taken
ACMV
ACMV
ADVANTAGE
WOB is very small

Pt maintain their
Own Pco2 or minute
Volume

DISADVANTAGE
Alvoelar
hyperventilation
IMV, volume-limited
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB, Scmidt
GA, & Wood LDH(eds.): Principles of Critical Care
IMV

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TYPE OF BREATH : ASSIST &
CONTROL
TRIGGERING : ASSIST & CONTROL
CYCLING : VOLUME CYCLED
COMPLCATION: BREATH STACKING
SIMV, volume-limited
Ingento EP & Drazen J: Mechanical Ventilators, in Hall JB,
Scmidt GA, & Wood LDH(eds.): Principles of Critical Care
CPAP
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
CPAP level
Time (sec)
CPAP

CPAP is PEEP is applied to the airway
of a patient who is breathing
spontaneously
PSV
Patient Triggered, Flow Cycled, Pressure limited Mode
Flow
(L/m)
Pressure
(cm H2O)
Flow Cycling
Set PS
level
Volume
(mL)
Time (sec)
PRESSURE SUPPORT
VENTILATION



Î Spontaneous Tidal Volume
Reduces RR
Reduces WOB
Initial Settings
Mode- ACMV
 Tidal volume : 7 to 8 ml/kg
COPD 6ml/kg & ARDS 5 to 6 ml/kg
 Fio2 100% or 60%
 RR NORMAL 16 to 18 b/m
 PEEP 5 CMH2O
 I:E RATIO 1:2 , COPD 1:4
 PIF 60L/MIN
 VC Monitor PIP & plateau , PC Monitor
Tidal volume & Minute ventilation

Recapitulation
Mandatory Breath
Limit
Spont.
Breath
Mode
Trigger
Cycle
CMV
Time
Pres.,Flow Volume/t
ime
No
A/CMV
Pressure or
Flow, Time
Pres.,Flow Volume/t
ime
yes
PSV
Pressure or
Flow
Pres.,Flow
SIMV
Pressure or
Flow/ Time
Pres.,Flow Volume/t
ime
Yes
PCV(PC
-CMV)
Pressure or
flow, Time
Pressur
e/ time
No
Flow
Only
SCALARS
Flow/Time
Pressure/Time
Volume/Time
LOOPS
Pressure-Volume
Flow-Volume
Flow (L/min)
Spontaneous Breath
Inspiration
Time (sec)
Expiration
Mechanical Breath
Flow (L/min)
Inspiration
Time (sec)
Expiration
Volume vs Time
Volume (ml)
Inspiratory Tidal Volume
Inspiration
Expiration
TI
Time (sec)
Paw (cm H2O)
PIP
}
Transairway Pressure (PTA)
Exhalation Valve Opens
Pplateau
(Palveolar
Expiration
Time (sec)
Begin Expiration
Begin Inspiration
Inflation Hold
(seconds)
Paw (cm H2O)
PIP
Distending
(Alveolar)
Pressure
Begin Inspiration
Expiration
Time (sec)
Begin Expiration
Inspiratory Flow Pattern
Peak inspiratory flow rate
PIFR
Beginning of expiration
exhalation valve opens
Flow (L/min)
Inspiration
Insp. 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
Inspiration
Flow (L/min)
Expiratory time
TE
Time (sec)
Duration of
expiratory flow
Expiration
Peak Expiratory Flow Rate
PEFR
Components of PressureVolume Loop
VT
Volume
(mL)
Paw (cm H2O)
PIP
Flow-Volume Loop
Inspiration
PIFR
FRC
VT
PEFR
Expiration
Volume (ml)
THANK YOU
Questions ?