Breathing: It is taking air in (inspiration) and out of your
lungs (expiration). It can be consciously controlled
Breathing involves two stages — ventilation and gas
exchange. Ventilation is the movement of air in and out
of lungs and gas exchange is the absorption of oxygen
from the lungs and release of carbon dioxide.
Respiration is a process where the body breaks down
the oxygen, so that the cells in the body can use it .
Therefore ,Breathing is a physical process and
respiration is a chemical process
NORMAL MECHANICS OF SPONTANEOUS
VENTILATION AND RESPIRATION
Spontaneous breathing or spontaneous ventilation is
simply the movement of air into and out of the lungs.The
main purpose of ventilation is to bring in fresh air, for gas
exchange into the lungs and to allow the exhalation of air
that contains CO2.
It is defined as movement of gas molecules across a
EXTERNAL RESPIRATION is movement of O2 from the
lungs into bloodstream and of CO2 from bloodstream
INTERNAL RESPIRATION is movement of CO2 from the
cells into the blood and movement of O2 from the blood
Normal inspiration is accomplished by the expansion
of thorax or chest cavity. It occurs when the muscles of
inspiration contract. During contraction , the diaphragm
descends and enlarges the vertical size of thoracic cavity.
The external intercostal muscles contract and raise the
ribs slightly, increasing the circumference of thorax. The
activities of these muscles represent the “work” required
Normal exhalation is passive and does not require any work.
During normal exhalation, the muscles relax, the diaphragm moves
upward to its resting position, and the ribs return to their normal
position. The volume of thoracic cavity decreases, and air is forced
out of alveoli.
Negative pressure circuit
- Gradient between mouth and pleural space is the driving
- need to overcome resistance
- maintain alveolus open
• overcome elastic recoil forces
- Balance between elastic recoil of chest wall and the
Ventilation is the process by which Oxygen and CO2 are
transported to and from the lungs.
GAS FLOW AND PRESSURE GRADIENTS
Basic concept of Air flow is that, for air to flow through a tube or
airway, pressure at one end must be higher than the pressure at the
Air always flows from the high pressure point to the low pressure
point (pressure gradient).
The conductive airway begins at the mouth & nose, and ends at
the small airways near the alveoli.
Therefore, gas flows into the lungs, when the pressure in the
alveoli is lower than the pressure at the mouth and nose.
Conversely, gas flows out of lungs, when the pressure in the
alveoli is greater than the pressure at the mouth and nose.
When the pressure at the mouth and alveoli are same, as
occurs at the end of inspiration or the end of expiration, then no
gas flow occurs as there is no pressure gradient.
DEFINITION OF PRESSURES AND GRADIENTS IN
Airway opening pressure (Paw)/ Mouth pressure(PM) is often
called airway pressure (Paw). Unless pressure is applied to
mouth or nose, Paw is Zero (atmospheric).
Body surface pressure (Pbs) is the pressure at body surface .
This is equal to Zero unless the person is using a pressurized
chamber or a negative pressure.
Ppl = Intrapleural pressure; pressure in the intrapleural space ;
generally negative because the lungs are “naturally” smaller than
the chest wall; the negative pressure helps to keep the airways
open and helps the lungs from collapsing.
Palv = Intra-alveolar pressure; pressure within the alveoli;
positive on expiration, negative on inspiration, and
zero (same as atmospheric) when there no air movement.
Four basic pressure gradients are used to describe normal
1.Trans-Airway pressure (PTA): It is the pressure gradient
between the air opening and the alveolus
2. Trans-Thoracic pressure(Pw or Pt): It is the pressure difference
between the alveolar space(lung) and the Body surface.
Pw = PA - Pbs
(Pw represents the pressure needed to expand or contract the lungs and the chest
wall at the same time.)
3.Trans-Pulmonary pressure (PL or PTP )/Trans-Alveolar pressure
It is the pressure difference between the alveolus and the
pleural space. PL = PA - Ppl
4. Trans - respiratiory pressure (PTR ): It is the pressure
gradient between airway opening and the body surface
PTR = Paw - Pbs
During normal spontaneous inspiration, as the volume of
thoracic space increases, the intrapleural pressure becomes
more negative in relation to atmospheric pressure .
This negative intrapleural pressure goes from -5cm H2O at end
expiration to -10cm H2O at end inspiration. The negative
intrapleural pressure is transmited to the alveolar space.
A. Lung Volumes
1. Basic volumes:
a. Tidal Volume (VT, TV): volume of gas exchanged each breath; can
change as ventilation pattern changes .(500 ml)
b. Inspiratory Reserve Volume (IRV): maximum volume that can be
inspired, starting from the end inspiratory position (potential volume
increase at the end of inspiration).(3000ml)
c. Expiratory Reserve Volume (ERV): maximum volume that can be
expired, starting from the end expiratory position (potential volume
decrease at the end of expiration)(1200ml)
d. Residual Volume (RV): volume remaining in the lungs and airways
following a maximum expiratory effort (1300 ml)
2. Capacities:combined volumes
a. Vital Capacity (VC): maximum volume of gas that
can be exchanged in a single breath
VC = TV + IRV + ERV (4700 ml)
b. Total Lung Capacity (TLC): maximum volume of
gas that the lungs(and airways) can contain
TLC = VC + RV = TV + IRV + ERV + RV
c. Functional Residual Capacity (FRC): volume of
gas remaining in the lungs (and airways) at the end
FRC = RV + ERV (2500 ml)
d. Inspiratory capacity (IC): maximum volume of
gas that can be inspired from the end expiratory
IC = TV + IRV (3500 ml)
1. Frequency /Respiration rate (f or RR): breaths per unit
At rest: 12/min
2. Ventilation rate: total volume inspired or expired per
unit time ; sometimes called Minute Volume (MV) when
measured per minute; to avoid ambiguity, usually
measured as volume expired, VE’
MV or VE’ = f × TV , At rest= 12/min × 0.5L = 6 L/min
a. Peak velocity (e.g. peak expired flow rate) normal value
b. Timed vital capacity: volume of gas that can be expired from
the lungs with maximum effort in a given time .
1) Usually expressed as a fraction of the total volume expired
maximum effort, the Forced Vital Capacity (FVC)
2) Normal value of FEV1 / FVC ≥ 80%
Mechanical ventilation is a positive or negative pressure artificial
breathing device that can maintain ventilation and oxygen delivery
for prolonged periods. (It is indicated when the patient is unable to
maintain safe levels of oxygen or CO2 by spontaneous breathing
even with the assistance of other oxygen delivery devices)
HISTORY OF MECHANICAL VENTILATION
• The Roman physician Galen may have been the first to
describe mechanical ventilation.
• In 1908 George Poe demonstrated his mechanical respirator
by asphyxiating dogs and seemingly bringing them back to
ORIGINS OF MECHANICAL VENTILATION
Negative-pressure ventilators (“iron
•Non-invasive ventilation first
used in Boston Children’s
Hospital in 1928
•Used extensively during polio
outbreaks in 1940s – 1950s
•Invasive ventilation first used at
Mass achusetts General Hospital
•Now the modern standard of
Iron lung polio ward at Rancho Los Amigos Hospital in
• Ventilator delivers gas to lungs
using positive pressure at certain rate.
• The amount of gas delivered
can be limited by time, pressure ,
• The duration can be cycled by time ,
pressure and flow.
1.Pressure controller: The ventilator maintains the same
pressure waveform, at the mouth regardless of changes in
2. Flow controller: Ventilator volume delivery and volume
waveform remain constant and are not affected by changes in
lung characteristics. Flow is measured
3. Volume controller: Ventilator volume delivery and volume
waveform remain constant and are not affected by changes in
lung characteristics. Volume is measured
4.Time controller: Pressure, volume, and flow curves can
change as lung characteristics change. Time remains
PHASES OF VENTILATORY CYCLES:
1. INITIATION OF INSPIRATION (triggering)
2. INSPIRATORY PHASE
3. CHANGE OVER FROM INSPIRATION TO
4. EXPIRATORY PHASE CYCLING
1.INITATION OF INSPIRATION
This is how inspiration is initiated in association with patients
breath. It can be by changes in time, flow or pressure
TIME TRIGGERING :
The rate of breathing is controlled by the ventilator. The breath
is controlled or mandatory. The patient cannot obtain air from
When pressure is the trigger , a decrease in the pressure
within the inspiratory circuit is sensesd and inspiration begins.
The sensitivity setting reflects the amount of pressure drop
baseline pressure that the patient must develop in the
ventilator circuit , on inspiration , to initate the flow of gas.
FLOW TRIGGERING: The ventilator delivers a constant
background flow (flow by).
Any change caused by patient effort is sensed by the flow
sensor. A breath is delivered to the patient. This requires
less work of breathing when compared to pressure
2. INSPIRATORY PHASE (Inspiration is timed from the beginning of
inspiratory flow to the beginning of expiratory flow)
A limit variable is the maximum value that a
variable(pressure, volume, flow, or time) can attain. This
limits the variable during inspiration but does not end the
3.CHANGE OVER FROM INSPIRATION TO
Of the four variables the ventilator can control to cycle out of
inspiration ( i.e.pressure, time, volume, or flow), only one can
operate at a given time.
The inspiratory phase of a volume-cycled breath is
terminated when the set volume has been delivered. In
most cases the volume remains constant even when lung
However, the pressures required to deliver the volume and
gas flow vary, as compliance and resistance change.
TIME – CYCLED VENTILATION
In this , the inspiration ends and expiration begins after a
pre-determined time interval is reached.
Cycling may be controlled by a simple timing mechanism or
by setting the rate and adjusting the I:E ratio, or percentage of
With time-cycled pressure ventilation, both volume and flow
vary. Ex- IPPB
With flow-cycled ventilation, the ventilator cycles into the
expiratory phase once the flow has decreased to a
predetermined value during inspiration.
Volume,pressure,and time vary according to changes in lung
Flow cycling is the most common cycling mechanism in the
When a preset pressure threshold (limit) is reached at the
mouth or upper airway, a ventilator set to pressure cycle ends
The exhalation valve opens, and expiratory flow begins.
The volume delivered to the patient depends on the flow
delivered, the duration of inspiration, lung characteristics, and
the set pressure.
The variable controlled during the expiratory time on the
ventilator is known as the baseline variable.
In all commonly used ventilator , pressure is the variable
controlled during expiration.
Exhalation occurs passively because of the elastic recoil of the
lung, but patient passively exhales to a controlled baseline
The end expiratory pressure when in equilibrium with
atmospheric pressure ,is zero.
A baseline pressure above atmospheric pressure is known as
Positive end- expiratory pressure (PEEP)
Acute lung injury (including ARDS, trauma)
Apnea with respiratory arrest, including cases from
Chronic obstructive pulmonary diseas(COPD)
Acute respiratory acidosis with partial pressure of carbon
dioxide (pCO2) > 50 mmHg and pH < 7.25, which may be
due to paralysis of the diaphragm due to Guillain-Barré
syndrome, Myasthenia Gravis, spinal cord injury, or the
effect of anaesthetic and muscle relaxant drugs
Increased work of breathing as evidenced by significant
tachypnea, and other physical signs of respiratory distress
Hypotension including sepsis, shock, congestive heart failure
Neurological diseases such as Muscular Dystrophy and
Amyotrophic Lateral Sclerosis.
Inefficiency of thoracic cage in generating pressure gradient
necessary for ventilation (chest injury, thoracic malformation)
Cardiac insufficiency (elimination WOB, reduce oxygen
Ventilatory failure or oxygenation failure due to
1. Increased airway resistance
2. Changes in lung compliance
4. V/Q mismatch
5. Intrapulmonary shunting
6. diffusion defect
Disorders of Pulmonary Gas Exchange
1. Acute respiratory failure
2. Chronic respiratory failure
3. Hypoxemia( not responding to supplemental oxygen and fluid
4. Acute hypercapnia ( with worsening acidosis)
5. Pulmonary disease resulting in diffusion abnormality
6. Pulmonary diseases resulting in ventilation-perfusion mismatch
UNDERLYING PHYSIOLOGICAL PRINCIPLES GUIDING
o Control of CO2 elimination
o Improved impaired oxygenation
o Assist respiratory muscles
FACTORS AFFECTING VENTILATION
3. Time constants for lung elasticity
4. Work of breathing
It is the change in volume per unit change in
• Static compliance= Exhaled tidal volume
• Dynamic compliance
= Exhaled tidal volume
Peak inspiratory pressure-PEEP
STATIC COMPLIANCE- is measured when there is no air flow.
• Reflects the elastic properties of the lung and the chest wall.
DYNAMIC COMPLIANCE -is measured when air flow is present.
• Reflects the airway resistance (non elastic resistance) and elastic
properties of lung and chest wall
Low lung compliance increases the work of breathing.
High compliance – exhalation is often incomplete due to lack of
elastic recoil by the lungs.
It is defined as airflow obstruction in the airways.
Normal airway resistance is between 0.6 and 2.4 cm H2o/l/sec
at a flow rate of 30 l/min.
Airway resistance varies directly with the length & inversely
with diameter of ET
Raw= pressure change/flow
Increase in airway resistance is equal to increase in work of
It is product of compilance and resistance.
The time constant is the time required, in seconds , to inflate a
lung region to 60% of its filling, if the filling pressure was to
Areas of the lung that have either increased resistance or
decreased compilance will have a longer time constants.
WORK OF BREATHING
The total work of breathing (WOB) is the sum of physiologic work
plus the work imposed by the breathing appratus .
The work that the respiratory muscles must perform to expand
the lung is that which will overcome elastic and non elastic forces :
compilance & resistance respectively.
When compilance decreases/ resistance increases a greater force
is required to move volume in the lung .
That is WOB increases.
1. Fraction of Inspired Oxygen (FiO2): Amount of oxygen delivered
to the patient. Adjusted to maintain O2 sat of > 90%. Concern
with oxygen toxicity with FiO2 > 60% required for 12-24 hours.
2. Respiratory Rate: Number of breaths/min. ventilator is to
3. Tidal Volume: Amount of air delivered with each ventilator
breath, usually set at 6-8 ml/kg.
4. Sigh: Ventilator breath with greater volume than preset tidal
volume, used to prevent atelectasis,however not always used.
5. Pressure limit: Limits highest pressure allowed by ventilator.
6. Positive End Expiratory Pressure (PEEP): Pressure maintained
in lungs at end of expiration used to improve oxygenation by
opening collapsed alveoli, improving ventilation/perfusion,
increasing oxygenation; can be used to reduce FiO2.
7. Adjuncts to Mechanical Ventilation
PEEP, CPAP, PSV
ventilator alarms must never be ignored or disarmed!!!!
9. Peak Inspiratory Pressure: Peak pressure registered on the
airway pressure gauge during normal ventilation; PIP value
used to set high and low pressure alarms; increased PIP may
indicate decreased lung compliance or increased lung
10. Minute Volume or Minute Ventilation (Ve): Respiratory rate
times the tidal volume.
RR x vt = Ve Normal minute volume for adults is 5-10 liters
11. Ventilatory Mode
CMV, IMV, SIMV, A/C, PCV
Electrical failure alarms are a must for all ventilators
Alarms if RR goes above
or below set levels
Volumes go above or below
(i.e. VT/ minute volume)
Change in inspiratory or
peak airway pressure above
or below preset limits
BREATHS TYPES DESCRIPTION
MANDATORY A breath that is triggered , limited &
BREATH cycled by ventilator . Ventilator performs
all of the work of breathing throught the
the phases of ventilation
ASSISTED A breath that is triggered by the patient ,
BREATH then limited & cycled by the ventilator
PATIENT – CYCLED
SUPPORTED A breath that is triggered by the patient,
BREATH limited by the ventilator and cycled by
patient. A spontaneous breath with an
inspiratory pressure greater than baseline.
SPONTANEOUS A breath that is triggered , limited and
BREATH cycled by the patient . The patient performs
all of the work of ventilation
FULL VERSES PARTIAL VENTILATOR SUPPORT
Ventilatory support can be classified according to two general
1. FULL VENTILATORY SUPPORT (FVS)
It constitutes mechanical ventilation in which the ventilator
performs all of the WOB without any contribution from the patient.
The ventilator alone provides the minute volume of gases required
to satisfy the patient’s respiratory needs.
2. PARTIAL VENTILATORY SUPPORT(PVS)
PVS occurs when both the ventilation and the patient contribute
toward the WOB and meeting the minute volume of gases
required to satisfy respiratory needs.
The advantages of PVS include allowing the patient to respond to
increase in CO2 by increasing VE and promiting use of the
respiratory muscles , thereby preventing disuse atrophy.
POSITIVE PRESSURE VENTILATORS
• terminate inspiration
after delivering a
preset volume of gas
• delivered regardless
of required pressure to
• volume remains the
same unless high
• terminate inspiration
when a preset pressure is
• varying degrees of
resistance will interfere
with gas flow
• best used with drug
• not good for post-
operative or severe
NEGATIVE PRESSURE VENTILATORS
They exert a negative pressure on the external chest wall. This
causes decreasing the intrathoracic pressure during inspiration
which allows air to flow into the lungs, filling its volume.
Physiologically this type of assisted ventilation is similar to
1. It is used mainly in chronic respiratory failure associated
with neuromuscular conditions such as poliomyelitis, muscular
dystrophy, amyotrophic lateral sclerosis and myasthenia
2. Not used for serious patients
3. Simple to use
4. Do not require intubation
5. Adaptable for home use
Iron lung, body wrap and chest cuirass
COMPLICATIONS WITH NEGATIVE PRESSURE
Limited access for patient care.
Inability to properly monitor pulmonary mechanics.
• Encloses patients body except for the head and neck in a
tank and the air in it is evacuated to produce a negative
pressure around the chest.
• This negative pressure surrounding the chest &
underlying alveoli results in chest wall and alveolar
• The tidal volume delivered to the patient is directly related
to the negative presssure gradient.
• It is a form of negative pressure ventilation that was
intended to alleviate the problems of patient acess &
TANK SHOCK associated with iron lungs.
• It covers only the patient’s chest and leaves the arms and
lower body exposed.
• To overcome the problem of air leakage, individually
designed cuirass minimise air leaks, & they have been
used successfully to ventilate patients with chest wall
diseases such as scoliosis
POSITIVE PRESSURE VENTILATORS
Positive pressure ventilators inflate the lungs by exerting
positive pressure on the airway, forcing the alveoli to expand
during inspiration. Exhalation is passive.
Endotracheal intubation or tracheotomy is necessary in most
cases. There are three types of positive pressure ventilators,
which are classified by the method of ending the inspiratory
phase of respiration:
1. Pressure cycled Ventilators
2. Time Cycled ventilators
3. Volume Cycled Ventilators
4. Non-invasive positive
NONINVASIVE POSITIVE -PRESSURE
Positive pressure ventilation can be given via face mask that
covers the nose and the mouth, nasal masks or other nasal devices.
Ventilation can be delivered by volume ventilator, pressure
controlled ventilator, continuous positive pressure device or bi-
level positive pressure ventilator.
The most comfortable mode for the
patient is pressure controlled ventilation
with pressure support.
This eases the work of
breathing and enhances the gas
Indications for NIPPV
1. Acute or chronic respiratory failure
2. Acute pulmonary edema
4. Chronic congestive heart failure with a sleep rated breathing
5. Obstructed sleep apnea
1. Hemodyanamically unstable
3. Inability to protect airway
4. Excessive secrections
5. Unco-operative patients
6. Patients with facial odema , trauma,
• Pressure support ventilation (PSV)
• Adaptive support ventilation (ASV)
• Proportional assist ventilation (PAV)
• Volume assured pressure support (VAPS)
• Pressure regulated volume control (PRVC)
• Volume ventilation plus (VV+)
• Pressure control ventilation (PCV)
• Airway pressure release ventilation
• Inverse ratio ventilation (IRV)
• Automatic tube compensation (ATC)
• Is not an actual mode on the ventilator since the
rate and tidal volume are determined by the
• It provides inspiratory flow to the patient in a
• Used with adjunctive modes like PEEP
Positive End Expiratory Pressure (PEEP)
• PEEP is positive pressure that is applied by the ventilator at
the end of expiration.
• This mode does not deliver breaths, but is used as an
adjunct to CV, A/C, and SIMV to improve oxygenation by
opening collapsed alveoli at the end of expiration.
•Improves oxygenation by
•Improved oxygenation will
allow the Fio2 to be lowered
•Increased lung compliance
•Increased incidence of
•Potential decrease in venous
•Increased work of breathing
•Increased intracranial pressure
Complications from the increased pressure can include
decreased cardiac output, pneumothorax, and increased
This offers independent control of inspiratory and expiratory
pressures while providing pressure support ventilation.
Can be used as a Cpap device by setting IPAP and EPAP at
the same level
It is provided via a nasal or oral mask, nasal pillow, or mouthpiece
with a tight seal with a portable ventilator.
It is most often used for patients who require ventilator assistance
at night, such as patients with severe COPD or sleep apnea.
CONTINUOUS POSITIVE AIRWAY PRESSURE
It is simply a spontaneous breath mode, with the baseline
pressure elevated above zero.
Improves oxygenation by increasing FRC
Decreases physiological shunting
Improved oxygenation will allow the Fio2 to be lowered
Increased lung compliance
Increased incidence of pulmonary brotrauma
Potential decrease in venous return
Increased work of breathing
Increased intracranial pressure
Pressure lesion on the skin
Irritation of eyes
•Where FRC is increased (ARDS, Pneumonia, lung collapse)
•Improved V/Q mismatch
•In post operative patients & In ARDS premature
infants (to treat HYPOXIA)
• If patient breath spontaneously helps to maintain airway
-Surgical emphysema -Bullae
-Undrained pneumothorax - Excessive secrections
CONTROLLED MANDATORY VENTILATION (CMV)
• Patient has no control over ventilation
• Breaths are delivered at a rate and volume that are
deterimned by adjusting ventilator , regardless of patient’s
attempts to breath(i.e. controls both the tidal volume and
respiratory rate of the patient).
• Should only be used with a combination of sedatives,
respiratory depressants and neuromuscular blockers.
• Patients fighting or bucking the ventilator ,means the
patient is severely distressed and vigrously struggling to
• Teatnus or seizure activites
• Complete rest for the patient for 24 hrs
• Crushed chest injury patients (in whom paradoxical chest
wall movement produced due to spontaneous inspiratory
• Where complete control is mandatory (i.e. undergoing
• Patient who are unable to breath at all (GBS, Anaesthetic
• Rests muscles of respiration
• Heavy sedation is required
• More haemodynamic depression
• Risk of intrinsic PEEP is significant
• Patient does not like to be controlled (uncomfortable)
• Disconnection or ventilator fails to operate is a primary
hazard- in a sedated or apneic patient is the potential for
apnea and hypoxia.
• Pt receives a set number of breaths
and cannot breathe between
• Similar to Pressure Control
• Pt initiates all breaths, but
ventilator cycles in at initiation to
give a preset tidal volume
• Pt controls rate but always receives
a full machine breath
• Assist mode unless pt’s respiratory
rate falls below preset value
• Ventilator then switches to control
• Rapidly breathing pts can overventilate
and induce severe respiratory alkalosis
and hyperinflation (auto-PEEP)
Ventilator delivers a fixed volume
Guarantee minute ventilation allows control over RR
In a trachypneic patient > lead to over ventilaton and severe
respiratory alkalosis>> Hyperinflation .
INTERMITENT MANDATORY VENTILATION (IMV)
•Allows patient to breathe spontaneously through ventilator
• In between the mandated breaths, the patient is free to
breath at his desired respiratory rate.
1. Between the mandatory breaths the patient is free to
choose his own respiratory rate, tidal volume and flow rate.
2. The mandatory breath is delivered in synchrony with
patient effort, making for comfortable breathing.
3. The patients’ respiratory muscles are active and so disuse
atrophy is less common.
1. Hypoventilation is possible if the mandatory breath rate is
not set high enough.
2. Work of breathing may be high, if trigger-sensitivity and
flow rate are inappropriate to patients needs.
3. Excessive work of breathing may occur during the
spontaneous breaths unless an adequate level of pressure
support is added.
•Normal respiratory drive but respiratory muscles unable to
perform all WOB
•In maintaining normal PaCO2
•Weaning from mechanical ventilation
The ventilator attempts to synchronize the set number mandatory
breaths with the patients respiratory efforts
The ventilator waits for a patient effort during a sensitive peroid
before every breath.
INDICATION: -In weaning
- Initially after full ventilatory support to partial
- Heavy sedation & paralysis
CONTRAINDICATION- Respiratory muscles fatigue
• Prevention of respiratory muscles atrophy
• Decreased requirement of sedation
• Lower mean airway pressure
• Respiratory muscles fatigue
• Increased risk of CO2 rentation
• Increased WOB
MANDATORY MINUTE VENTILATION (MMV)
•It is a mode where the patient breathe spontaneously, yet a
constant minute ventilation (VE) is guaranteed.
•If the patient’s spontaneous ventilation does not match the
target VE , the ventilator provides whatever part of the VE the
patient does not achieve.
To prevent hypercapnia
To prevent hypoventilation & respiratory acidosis
Better patient – ventilator interaction
Less hemodynamic effects
Higher work of breathing than CMV, AC
Risk of lung injury due to high peak airway pressures
PRESSURE SUPPORT VENTILATION
The pressure support ventilation is patient-triggered, flow cycled,
pressure supported mode where each inspiratory effort of the patient
is augmented by the ventilator at a preset level of inspiratory
Pressure support may be used independently as a ventilator mode or
used in conjunction with CPAP or SIMV.
1. Maximizing patient control of respiration, thereby enhancing
patient comfort on the ventilator.
2. Increase the patient’s spontaneous tidal volume
3. Decrease the patient’s spontaneous respiratory rate
4. Decrease work of breathing
5. Providing alternative mode of weaning from mechanical
1. PSV is not used as a sole ventilator support during acute respiratory
failure because of the risk of hypoventilation.
2. Not suitable for the management of patient with central apnea.
3. Developed of atelactasis due to smaller tidal volume in patients with
brief inspiratory times and high respiratory impedance.
4.Requires spontaneous respiratory effort
5.Delivered volumes affected by changes incompliance
Patient who don’t have sufficient capacity (i.e. SIMV mode)
To faciliatate weaning
If patient needs mandatory breaths
PRESSURE CONTROL VENTILATION(PCV)
Pressure - controlled breaths are time triggered , pressure
limited, time cycled
Can minimize the peak inspiratory pressure while still
maintaining adequate PaO2 & PaCO2.
Decreased mean airway pressure
Requires sedation or paralysis
Ventilation does not change in response to clinical
ADAPTIVE SUPPORT VENTILATION(ASV)
A mode of ventilation that changes the number of mandatory
breaths and pressure support level according to the patient’s
•Designed to reduce episodes of central apnea in CHF:
Improvement in sleep quality, decreased daytime sleepiness
•Can be used for patients who are at risk for central apnea like
those with Brain damage.
PROPORTIONAL ASSIST VENTILATION (PAV)
PAV , there is no target flow, volume, or pressure during
•The pressure used to provide the pressure support is
variable and is in proportion to the patient’s pulmonary
Characterstics and demand.
•Has the ability to track changes in breathing effort over
Where the elastance / airflow resistance shows sudden
improvement , the pressure PAV may be too high . This
may lead to overdistension , increased air trapping , and
All clinical situations characterized by high ventilatory output
uncoupled with ventilatory requirements (i.e. respiratory
alkalosis) may be potentially worsened by PAV
Hypercapnic respiratory failure in COPD
Adaptability of ventilator to changing patients ventilatory
Increases sleep efficiency
Non- invasive use of PAV in COPD &Kyphoscoliotic
patients:delivered through nasal mask; improves dyspnea
VOLUME – ASSURED PESSURE
SUPPORT ( VAPS)
A mode of ventilation that assures a stable tidal volume by
incorporating inspiratory PSV with conventional volume- assistd
o VAPS incorporates pressure support ventilation with
conventional volume- assisted cycles to provide stable tidal volume
in patient with irregular breathing patterns
o VAPS may prolong the inspiratory time.
o Patients with airflow obstruction should be monitored closely in
order to prevent air trapping.
Pressure – Regulated Volume control ( PRVC)
It provides volume support with the lowest pressure
possible by changing the flow and inspiratory time
Decelerating inspiratory flow pattern
Pressure automatically adjusted for changes in compliance
and resistance within a set range
– Tidal volume guaranteed
– Prevents hypoventilation
Pressure delivered is dependent on tidal volume achieved
on last breath
– Intermittent patient effort → variable tidal Volumes
Asynchrony with variable patient effort
VOLUME VENTILATION PLUS ( VV+)
An option that combines volume control plus and volume
Volume control Plus (VC+)
•It is used to deliver mandatory breaths during AC and
SIMV modes of ventilation
•VC+ is intented to provide a higher level of synchrony
than standarad volume control ventilation
•In VC + , the clinician sets the target tidal volume
Volume Support ( VS)
•It is intended to provide a control tidal volume and
increased patient comfort
Indicated in – weaning from anesthesia
AIRWAY PRESSURE RELEASE
APRV- A mode of ventilation in which the spontaneous breaths are
at an elevated basline(i.e.CPAP).This elevated baseline is periodically “
released” to facilitate expiration.
•Preservation of spontaneous breathing and comfort with most
spontaneous breathing occurring at high CPAP
•Better V/Q matching
Disadvantage of APRV
•Volumes change with alteration in lung compliance and
•Limited access to technology capable of delivering APRV
•An adequately designed and powered study to demonstrate
reduction in mortality or ventilator days compared with optimal
lung protective conventional ventilation
•May be less comfortable than the PSV and SIMV modes ,
and synchonization with mechanical breaths may also be a
In patient with ARDS ( decreased lung compilance)
Inverse Ratio Ventilation (IRV)
IRV Improves Oxygenation by-
1)Decrease intrapulmonary shunting
2)Increasing V/Q matching
3) Decrease dead space ventilation
• Exacerbation of hemodynamic instability
•Requires deep sedation and paralysis
•Changes in lung compliance result in changes in
1.I:E ratio is greater than 1, in which inspiration is longer than
2. Used in patients with acute severe hypoxemic respiratory failure.
3. Used with heavily sedated patients
4. Used in ARDS and acute lung injury
AUTOMATIC TUBE COMPENSATION(ATC)
A mode of ventilation that offsets and compensates for he
air - flow resistance imposed by the arificial airway.
It allows the patient to have a breathing pattern as if
breathing Spontaneously without an artificial airway.
With ATC, the pressure delivered by the ventilator to
compensate for the airflow resistance is acitve during
inspiration and expiration.
It is dependent on the airflow characteristics and the
flow demand of the patient.
Unnecessary delays in this discontinuation process can
increase the complication rate the ventilation(pneumonia ,
airway trauma) as well as cost.
Prematuration discontinuation carries its own set of
problem, including difficulty in reestabilishing airtificial
airways and compromised gas exchange.
ESSENTIAL TO BEGIN WEANING
Awake, alter & co-operative
No effect of sedation / neuromuscular blockade
Nutritional status good
Spontaneous TV > 5-8 ml/Kg
VC > 10- 15 ml/kg
PEEP requriment <5mm of H2O
Static complaince > 30 ml/mm of H2O
MV < 10 L
PaCO2 < 50 mm of Hg with normal PH
PaO2 > 60 @ FiO2 0.4 / less
SaO2 > 90% @ FiO2 0.4 / less
PaO2 / FiO2 > 200
CONVENTIONAL MODES NEWER MODES
MODES OF WEANING
1. Clinical application of mechanical ventilation by
David W. Chang
2. Management of the mechanically ventilated patient
by Lynelle N. B. Pierce
3. Internet refrences