Mechanical Ventilation.pptx

Mechanical Ventilation
Basic Modes
Speaker: Dr.Snigdha Singh
Assistant professor
Esi-pgimsr,Basaidarapur

Mechanical ventilation
Several models have evolved over time-
1. Negative pressure ventilation
2. Positive pressure ventilation
i. Simple pneumatic system
ii. New generation microprocessor controlled systems.
The basic function and applications remain common.

Indication for mechanical ventilation
Criteria for starting mechanical
ventilation are difficult to define
and the decision is often a clinical
one.

Indications( physical parameters)
Respiratory rate >35 or <5 breaths/ minute
• Exhaustion, with laboured pattern of breathing
• Hypoxia - central cyanosis, SaO2 <90% on oxygen
or PaO2 < 60 mmHg (8kPa)
• Hypercarbia - PaCO2 > 60 mmHg (8kPa)
• Decreasing conscious level
• Significant chest trauma
• Tidal volume < 5ml/kg or Vital capacity <15ml/kg

Indication (non- respiratory condition)
• Control of intracranial pressure in head injury
• Airway protection following drug overdose
• Following cardiac arrest
• For recovery after prolonged major surgery or trauma

Basic Ventilator Parameters
• Mode
• Tidal volume
• Frequency
• PIP
• Plateau Pressure
• PEEP
• Inspiratory Time
• Expiratory time
• I:E Ratio

Starting a ventilator: Mode
• Mode denotes interplay b/w patient and the ventilator
• Describes the style of breath support based on relationship between
the various possible types of breath and inspiratory – phase variables

Where to Start ?
• CPAP, IPAP, EPAP, NIV
• Pressure control, Volume control
• CMV, Assist Control, IMV, SIMV,
• PSV, ASV, MMV,
• APRV
• PCV, PRVC, PSV, VCIRV, Volume
• Support,
• Auto Mode,
• BiLevel, BiPAP,
• HFJV, HFOV

Objectives
• Understand how ventilators control breath delivery, phase and
control variables.
• Understand the basic modes of ventilation.
• Combinations, tailor-making, mix and match…

Mechanical Ventilation
Ventilators deliver gas to the lungs using
positive pressure at a certain rate.
The amount of gas delivered can be limited
by time, pressure or volume.
The duration can be cycled by time, pressure
or flow.

PHASE VARIABLES
A= what initiates a
breath - TRIGGER
ventilator (time)- triggered or patient
(pressure or flow) triggered
B = what controls / limits
it – LIMIT
flow-limited or pressure-limited
C= What ends a breath –
CYCLING
volume, time, flow or pressure cycled

Phase variables: Trigger
What causes the breath to begin (signal to open the inspiratory valve)
i. Machine (controlled): the ventilator will trigger regular breaths at a
frequency which will depend on the set respiratory rate, ie, they
will be ventilator time triggered.
ii. Patient (assisted): If the patient does make an effort to breathe and
the ventilator can sense it (by either sensing a negative inspiratory
pressure or an inspiratory flow) and deliver a breath, it will be
called a patient triggered breath.

Phase variables: Limit
Factor which controls the inspiration inflow
FLOW LIMITED: a fixed flow rate and pattern is set and maintained
throughout inspiration.
i. An adequate tidal volume (Ti dependent)
ii. Pressure will be variable (comp and resistance dependent)
PRESSURE LIMITED: the pressure is not allowed to go above a preset
limit.
i. The tidal volume will be variable (comp and resistance dependent)

Phase variables: Cycling
• Signal that stops the inspiration and starts the expiration.
• Without inspiratory pause: one signal
• With inspiratory pause: two cycling signals (one to close inspiratory valve and
the second to open the expiratory valve)
• Volume
• Time
• Flow
• Pressure : back-up form of cycling when the airway pressure reaches
the set high-pressure alarm level

PRESSURE CYCLED VENTILATION
Terminates inspiratory phase at a preset
PIP.
TV varies directly with lung
compliance and inversely with airway
resistance.
• Advantages: reduced barotrauma which
has been implicated secondary to high
PIP.
• Disadvantages: if lung compliance is
less, will lead to respiratory acidosis.
• Important to monitor patient’s expired
TV.

VOLUME CYCLED VENTILATION
Terminates inspiratory phase at a preset TV.
• Advantages: patient is guaranteed to
receive a preset TV under normal operating
conditions.
• Disadvantages: PIP may rise high enough to
cause barotrauma.

Flow cycled ventilation
• Terminates the inspiratory phase when inspiratory
flow reaches a predetermined minimal level.
• Measured during spontaneous ventilation
• Mostly seen in pressure support modes of
ventilation.

TIME CYCLED VENTILATION
• Terminates the inspiratory phase when a preset inspiratory time has
been reached.
• Advantages: ease to regulate I:E ratio especially when inverse ratio
ventilation is desired.
• Disadvantages: delivered TV is dependent on airway resistance and
compliance characteristics

BASIC DEFINITIONS
– Peak Inspiratory Pressure (PIP)
– Plateau pressures
– Positive End Expiratory Pressure (PEEP)
– Continuous Positive Airway Pressure (CPAP)

• Peak Inspiratory Pressure (PIP)-
The peak pressure is the maximum pressure
obtainable during active gas delivery.
This pressure a function of the compliance of
the lung and thorax and the airway resistance
including the contribution made by the
tracheal tube and the ventilator circuit.
• Plateau Pressure-
The plateau pressure is defined as the end
inspiratory pressure during a period of no gas
flow.
The plateau pressure reflects lung and chest
wall compliance.

• Mean Airway Pressure-
The mean airway pressure is an average of the system pressure over
the entire ventilatory period.
• End Expiratory Pressure-
End expiratory pressure is the airway pressure at the termination of the
expiratory phase and is normally equal to atmospheric or the applied
PEEP level

• Positive end expiratory pressure (PEEP) refers to the application of a
fixed amount of positive pressure applied during mechanical ventilation
cycle
• Continuous positive airway pressure (CPAP) refers to the addition of a
fixed amount of positive airway pressure to spontaneous respirations, in
the presence or absence of an endotracheal tube.
• PEEP and CPAP are not separate modes of ventilation as they do not
provide ventilation. Rather they are used together with other modes of
ventilation or during spontaneous breathing to improve oxygenation,
recruit alveoli, and / or decrease the work of breathing

Advantages:
• Ability to increase functional residual capacity (FRC)and keep FRC
above Closing Capacity.
• The increase in FRC is accomplished by increasing alveolar volume
and through the recruitment of alveoli that would not otherwise
contribute to gas exchange. Thus increasing oxygenation and lung
compliance
• The potential ability of PEEP and CPAP to open closed lung units
increases lung compliance and tends to make regional impedances to
ventilation more homogenous.

Disadvantages:
• High intra-thoracic pressures can cause decreased venous return and
decreased cardiac output
• May produce pulmonary barotrauma
• May worsen air-trapping in obstructive pulmonary disease
• Increases intracranial pressure
• Alterations of renal functions and water metabolism

Basic Modes of Ventilation
Controlled Mechanical Ventilation
Assist Control Ventilation
Intermittent Mandatory Ventilation
Synchronized Intermittent Mandatory Ventilation
Pressure Support
Combinations

Controlled mandatory ventilation (CMV)
• Breath -
MANDATORY
• Trigger – TIME
• Limit - VOLUME
• Cycle – VOL /
TIME

⚫FiO2
⚫Rate
⚫I-time
⚫PEEP
⚫PIP
⚫FiO2
⚫Rate
⚫Tidal Volume
⚫PEEP
⚫Peak flow
• Tidal Volume &peak
flow ( & MV) Varies
Pressure controlled Volume controlled
PIP( & MAP) & I:E
ratio Varies

Volume controlled Pressure controlled

Controlled mandatory ventilation (Volume-Targeted)
Time triggered, Flow limited, Volume cycled Ventilation

Controlled Mandatory Ventilation (Pressure-Targeted)
Time Triggered, Pressure Limited, Time Cycled Ventilation

• Patient can not breath spontaneously
• Patient can not change the ventilator respiratory rate
• Suitable only when patient has no breathing efforts
Disease or
Under heavy sedation and muscle relaxants

• Asynchrony and increased work of breathing.
• Not suitable for patient who is awake or has own respiratory efforts
• Can not be used during weaning

CMV
Indications
• Under
anaesthesia
• Drug intoxication
• Neurologic
disorders
affecting
respiratory
neuromuscular fn
• Head injuries –
hyperventilation
• Delivering
unnatural I :E
ratios
Advantages
• Maintains precise
• Minute ventilation
• PaCO2
• Peak pressure
Disadvantages
• Ventilator cannot
respond to
patient’s
ventilatory needs
• Requires close
monitoring
• Requires heavy
sedation or
paralysis

Assist Control Ventilation
• A set tidal volume (volume control) or a set pressure and time
(pressure
• control) is delivered at a minimum rate
• Additional ventilator breaths are given if triggered by the patient
• Mandatory breaths: Ventilator delivers preset volume and preset
flow rate
• at a set back-up rate
• Spontaneous breaths: Additional cycles can be triggered by the
patient but
• otherwise are identical to the mandatory breath.
 A set tidal volume (volume control) or a set pressure and time (pressure
control) is delivered at a minimum rate
 Additional ventilator breaths are given if triggered by the patient
 Mandatory breaths: Ventilator delivers preset volume and preset flow rate
at a set back-up rate
 Spontaneous breaths: Additional cycles can be triggered by the patient but
otherwise are identical to the mandatory breath.

(pressure
flow rate
patient but
 Tidal volume (VT) of each delivered breath is the same, whether it is
assisted breath or controlled breath
 Minimum breath rate is guaranteed (controlled breaths with set VT)

(volume) Assist Control Ventilation (Pressure) Assist Control Ventilation

Assist Control Ventilation (Pressure)
• Breath –
MANDATORY
ASSISTED
• Trigger – PATIENT
TIME
• Limit - VOLUME
• Cycle – VOLUME /
TIME
Patient / Time-Triggered, Pressure Limited, Time Cycled Ventilation

Assist Control Ventilation (Pressure)

Assist Control Ventilation (Volume)
Patient / Time triggered, Flow limited, Volume cycled Ventilation

(pressure
flow rate
patient but
 Asynchrony taken care of to some extent
 Low work of breathing, as every breath is
supported and tidal volume is guaranteed.
 Hyperventilation
 Respiratory alkalosis.
 Natural breaths are not allowed
 Breath stacking
 High volumes and pressures

(pressure
flow rate
patient but
Hyperventilation and breath stacking can usually be overcome by
choosing optimal ventilator settings and appropriate sedation.

Assist Control Mode Ventilation
(ACMV)
Advantages
• Ventilator can respond
to changing ventilatory
needs
• Patient can increase
VE by increasing
respiratory rate
• Less work is required
to increase VE
Disadvantage
s
• Patient – ventilator
asynchrony
• Hyperventilation if
patient overtriggers
• Dynamic hyperinflation

Intermittent Mandatory Ventilation(IMV)
• Breath –
MANDATORY
SPONTANEOUS
VENTILATOR
• Limit - VOLUME
• Cycle - VOLUME

Intermittent Mandatory Ventilation(IMV)

Pressure controlled IMV Volume controlled IMV

Intermittent mandatory ventilation
(IMV)
⚫ Basically CMV which allows spontaneous breaths in
between
⚫ Disadvantage - In tachypnea can lead to breath
stacking
⚫ Not used now – has been replaced by SIMV
⚫ Breath stacking - Spontaneous breath immediately after a
controlled breath without allowing time for expiration (
SUPERIMPOSED BREATHS) - leading to dynamic
hyperinflation

Intermittent Mandatory Ventilation (IMV)
Pros:
• Freedom for natural
spontaneous
• breaths even on machine
• Lesser chances of
hyperventilation
Cons:
• Asynchrony
• Random chance of breath
stacking.
• Increase work of breathing
• Random high airway pressure
(barotrauma) and lung volume
(volutrauma)
Setting appropriate pressure limit is important to reduce the risk of barotrauma

Synchronized Intermittent Mandatory
Ventilation
• Ventilator delivers either patient triggered assisted breaths or time
triggered mandatory breath in a synchronized fashion so as to avoid
breath stacking
• If the patient breathes between mandatory breaths, the ventilator
will allow the patient to breathe a normal breath by opening the
demand (inspiratory) valve but not offering any inspiratory assistance.

Synchronized Intermittent Mandatory Ventilation
(SIMV)
• Breath – SPONTANEOUS
ASSISTED
MANDATORY
TIME
• Limit - VOLUME
• Cycle – VOLUME/ TIME

Synchronization window
Time interval just prior to time triggering in which the ventilator
is responsive to the patient’s inspiratory effort.

SIMV
If the patient makes a spontaneous inspiratory effort that falls in sync window, the ventilator is
patient triggered to deliver an assisted breath and will count it as mandatory breath

if patient does not make an inspiratory effort then ventilator will deliver a time triggered
mandatory breath.
SIMV

if patient does not make an inspiratory effort then ventilator will deliver a time triggered
mandatory breath.
SIMV
If the pt triggers outside this window, vent will allow this spontaneous breath to occur by opening the demand
(inspiratory) valve but does not offer any inspiratory assistance.

3 types of breathing:
1. Patient initiated assisted ventilation,
2. Ventilator generated controlled ventilation,
3. Unassisted spontaneous breath.

P-SIMV V-SIMV

Synchronized Intermittent
Mandatory Ventilation (SIMV)
Indications
• As a primary
mode of
ventilation
• As a partial
support
mode to
sustain work
of breathing
• Weaning
Advantages
• Decreased patient
ventilator
asynchrony
• Less chances of
hyperinflation
• Minimal
cardiovascular
effects of
mechanical
ventilation with
PEEP
• Prevents respiratory
muscle fatigue
• Greater patient
comfort
• Useful for weaning
Disadvantag
es
• Can increase
work of
breathing

Pressure controlled ventilation (PCV)
• Ventilator delivers pressure
limited breaths at preset
inspiratory pressure and
inspiratory.
• Time taken for airway pressure
to rise from baseline to
maximum.
• Breath – MANDATORY
• Trigger – TIME
• Limit - PRESSURE
• Cycle – TIME/ FLOW

Pressure controlled ventilation
(PCV)
•Reduction of
peak pressure
and barotrauma
•Ensures better
ventilation and
gas exchange
•Does not
guarantee
minute
ventilation
•Requires more
intensive
monitoring
Disadvantages
Advantages

Pressure Support Ventilation
Pressure (or Pressure above PEEP) is the setting variable
No mandatory breaths
Applicable on Spontaneous breaths: a preset pressure assist,
Flow cycling: terminates when flow drops to a specified fraction
(typically 25%) of its maximum.
Patient effort determines size of breath and flow rate.

6.Pressure support ventilation (PSV)
• After the trigger, ventilator
generates a flow sufficient to
raise and then maintain airway
pressure at a preset level for the
duration of the patient’s
spontaneous respiratory effort
• Breath – SPONTANEOUS
• Limit - PRESSURE
• Cycle – FLOW ( 5-25% OF
PIFR)

• Pressure (or Pressure above PEEP) is the setting variable
• No mandatory breaths
• Applicable on Spontaneous breaths: a preset pressure assist,
• Flow cycling: terminates when flow drops to a specified fraction
(typically 25%) of its maximum.
• Patient effort determines size of breath and flow rate

• It augments spontaneous VT decreases spontaneous rates and WOB
• Used in conjunction with spontaneous breaths in any mode of
ventilation.
• No guarantee of tidal volume with changing respiratory mechanics,
• No back up ventilation in the event of apnea.

• Provides pressure support to overcome the increased work of
breathing imposed by the disease process, the endotracheal tube, the
inspiratory valves and other mechanical aspects of ventilatory
support
• Allows for titration of patient effort during weaning.
• Helpful in assessing extubation readiness

Pressure support ventilation
(PSV)
Indications
• Spontaneously
breathing
patients who
require
ventilatory
support ,sp
when MV> 10
l/min and
RR>20/min
• Spontaneously
breathing
patients with a
history of COPD
or evidence of
muscle
Advantages
• Decreases work
of breathing with
minimal
cardiovascular
compromise
• Patient
determines own
RR,inspiratory
time, inspiratory
flow rate, VT
• Improves patient
comfort
• Helps in
weaning
Disadvantage
s
• Can be used
only if there is
adequate
respiratory drive
• Unsuitable for
severe acute
respiratory
failure

7)Positive end expiratory
pressure (PEEP)
⚫ Increases the end expiratory or baseline airway
pressure to a value greater than atmospheric
(0cmH2O) on ventilator manometer
⚫Keeps alveoli partially inflated
⚫Provides protection against the development of
shear forces during mechanical inflation
⚫ Not a stand alone mode, applied in conjunction
with other modes

Positive end expiratory pressure
(PEEP)
Indications
⚫Intrapulmonary shunt
⚫Refractory hypoxemia
⚫ Decreased FRC
⚫Decreased lung compliance
⚫Maintaining pulmonary function in non-
cardiogenic pulmonary edema, especially ARDS

Positive end expiratory pressure
(PEEP)
BENEFITS
1. Restore FRC/ Alveolar
recruitment
2. ↓ shunt fraction
3. ↑Lung compliance
4. ↑PaO2 for given FiO2
DETRIMENTAL
EFFECTS
1. Barotrauma
2. ↓ VR/ CO
3. ↑ PVR
4. ↓ MAP
5. ↓ Renal / portal bld
flow

How much PEEP to
apply???
Lower inflection point – transition
from flat to steep
part
- ↑compliance
- recruitment
begins (pt. above
closing vol)
Upper inflection point – transition
from steep to
flat part
- ↓compliance

LIP –
atory airway
al P < UIP –
ntion
s
UIP differ for
s
How much PEEP to apply??

Selection of degree of PEEP
⚫Lowest level of PEEP which maintains PaO2 > 60
mmHg on a FIO2 < 0.6
⚫Ensures optimal oxygenation
⚫Ensures maximal oxygen transport
⚫Best compliance
⚫Lowest Qs/Qt ratio
⚫Lowest Vd/Vt ratio
⚫Lowest PaCO2 –PetCO2 gradient

8) Continuous positive airway
pressure (CPAP)

Continuous positive airway
pressure (CPAP)
⚫ CPAP is actually PEEP applied to spontaneously
breathing patients.
⚫But CPAP is described a mode of ventilation without
additional inspiratory support while PEEP is not
regarded as a stand-alone mode

9)Biphasic positive airway
pressure (BiPAP)
• Single ventilation mode which covers entire spectrum
from mechanical ventilation to spontaneous breathing
• Permits spontaneous breathing
⚫Two pressure levels are set P high & P low
⚫Two time intervals are set T high & T low
⚫Spontaneous breathing possible at both levels
⚫Changeover between 2 pressure levels is synchronized
with exp & insp

.
Can provide total / partial ventilatory support
1. BiPAP – CMV – if pt not breathing
2. BiPAP – SIMV- spontaneous breathing at lower pressure
level only + mandatory breaths by switching between 2
pressure levels
3. CPAP – both pressure levels are identical in spontaneously
breathing patient
4. Genuine BiPAP _Spontaneous breathing at both the
pressure levels

Advantages
1. Allows unrestricted spontaneous breathing
2. Continuous weaning without need to change
ventilatory mode – universal ventilatory mode
3. Reduced atelactasis
4. Less sedation needed

SIMV + PS Ventilation
Spontaneous
breath with PS

Thank you!! You have done it!!!

Mechanical Ventilation.pptx

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