Art of ventilation

Dr/Sami Eldahdouh
Assistant Prof. of Pulmonary
Medicine
ART OF
MECHANICAL VENTILATION

Introduction
• Cornerstone for intensive care medicine
• Ventilate is derived from Latin word “ventus”
meaning wind.
• Ventilation is movement of air into and outside
the body
• The ventilators must overcome the pressure
generated by the elastic recoil of the lung at
end inspiration plus the resistance to flow at
the airway.
• Ventilators provide infusion of a blend of air
or oxygen into the circuit.

VENTILATION:
 Ventilation is the movement of air in and out of
the lungs. Movement of air is dependent on
pressure differences between the atmosphere
and the spaces in the lung ( alveolar lumen).
 Exhalation is a passive process, ventilators
expend energy only during inhalation
Flow = (P1 - P2)/R
P1 = atmospheric pressure ( Patm )
P2 = intra-alveolar pressure ( Palv )
R = Resistance

VENTILATION
 When the air pressure inside the lungs(
Palv ) is less than the atmospheric pressure
( Patm ) air will flow into the lungs.
Inhalation = Patm > Palv .
 When the alveolar pressure exceeds the
atmospheric pressure, the air will flow out of
the lungs.
Exhalation = Patm < Palv.

VENTILATION
• Resistance (R) in the respiratory system is
primarily a factor of the radius of the
bronchial passages.
• As the radius decreases, the resistance
increases and flow decreases.
• The radius of the bronchial system can be
modified by the smooth muscle surrounding
the passages or by mucous collecting inside
the bronchioles.

VENTILATION
The changes in pressure and drive of gas during the
ventilation process is dependent on one of the gas laws
- Boyle’s law.
Boyle‟s law states " when the temperature is
constant and a chamber’s volume is increased, the
pressure in the chamber decreases and vice versa "
.
Increased volume = decreased pressure
Decreased volume = increased pressure

VENTILATION
When the lungs are expanded during
inhalation, Palv decreases below Patm and
air flow into the lungs.
When the lungs are compressed during
exhalation, Palv is increased to greater than
Patm and air flows out of the lungs

Objectives of Mechanical Ventilation:
Improves oxygenation and ventilation (pulmonary
gas exchange):
Reverse hypoxemia.
Relieve acute respiratory acidosis.
Decrease the work of breathing:
Decrease oxygen cost of breathing.
Reverse respiratory muscle fatigue.
Affect pressure-volume relationship:
Prevent or reverse atelectasis.
Improve lung compliance.
Prevent further lung injury.
Permit lung and airway healing.

O2CO2
Objectives of Mechanical
Ventilation

INDICATIONS
• CLINICAL CRITERIA.
• LABORATORY CRITERIA.
• OTHER CRITERIA.

Patient not breathing (apnea)
Patient breathing but not
enough(hypoventilation)
Patient breathing enough, but pt
hypoxemic / hypercapneic.(ABG)
Patient breathing with normal gas
exchange, but working hard.(WOB)
Airway protection

LABORATORY CRITERIA
 Blood gases:
 PaO2 < 55 mm Hg
 PaCo2 > 50 mm Hg
 PH < 7.32
 PFT :
 Vital Capacity < 10 ml/Kg
 - ve inspiratory force <25cm H20
 FEV 1 < 60%

OTHER CRITERIA
Controlled hyperventilation eg. head injury.
Severe circulatory shock.
THERE IS NO ABSOLUTE
CONTRAINDICATION FOR
MECHANICAL VENTILATION

ARTIFICIAL VENTILATION
Creates a transairway P
gradient by ↓ alveolar P
to a level below airway
opening P
- Creates – P around
thorax
e.g. iron lung
chest cuirass / shell
Achieved by applying +
P at airway opening
producing a transairway
P gradient
Negative pressure
ventilation
Positive pressure
ventilation

Negative Pressure Ventilation (NPV)
• Negative pressure ventilators apply a negative
pressure intermittently around the patient’s body or
chest wall
• The patient’s head (upper airway) is exposed to
room air
• An example of an NPV is the iron lung or tank
ventilator

Cardiovascular effects of PPV
Spontaneous ventilation PPV

Physiological effect of MV
• The greatest effect positive pressure
ventilation has on the cardiovascular
system is in decreasing venous return,
which in turn decreases CO.
• The reduced venous return and CO sets
into motion compensatory mechanisms.
These include the retention of water and
sodium through hormonal mediators as
ANP .

• Another mechanism includes the
stimulation of the sympathetic nervous
system in an attempt to increase CO and
conserve renal perfusion through
vasoconstriction.

Blood flow to the brain and liver are
impaired or decreased, owing to a decrease
in venous return.
Decreases in venous return are reflected in
elevations in the ICP and decreased HBF.
Perfusion of these two organs is of concern
if impairment exists concomitant with the
requirement for artificial ventilation.

Infections are common in the ventilated
patient and increase proportionally with
the length of time mechanical ventilation is
employed.
Major infection sources are contributed to
repeated breaks in the ventilator circuit
and aspiration of gastric contents.
 There appears to be a positive correlation
with enteral feeding frequency and the use
of antacids and H2 blockers.

MECHANICAL VENTILATOR
• Ventilators are specially designed
pumps that can support the ventilatory
function of the respiratory system and
improve oxygenation through application
of high oxygen content gas and positive
pressure.

Classification
1. ICU Ventilators The condition of lung is poor
2. Anaesthetic ventilators The condition of lung is good
3. Transport ventilator
• The ventilator is compact and used for transportation of
victim/patients from one site to other
4. Other/special
(a) High frequency ventilator
(i) High frequency positive pressure ventilator
(ii) High frequency jet ventilator
(iii) High frequency oscilitation ventilator

ICU ventilator
A. Positive pressure ventilation (PPV)
(a) Non invasive PPV
(i) Nasal mask
(ii) Facial mask
These has less complications and as effective as
invasive ventilators
(b) Invasive PPV
(i) Nasotracheal tube
(ii) Oro tracheal tube
(iii) Tracheostomy

ventilation without artificial airway
-Nasal , face mask
adv.
1.Avoid intubation / c/c
2.Preserve natural airway defences
3.Comfort
4.Speech/ swallowing +
5.Less sedation needed
6.Intermittent use
Disadv
1.Cooperation
2.Mask discomfort
3.Air leaks
4.Facial ulcers, eye irritation, dry nose
5.Aerophagia
6.Limited P support
e.g. BiPAP, CPAP
Noninvasive

Modes of standalone NIV:
Both CPAP and BPAP have different modes:
Fixed pressure CPAP: The same pressure from breath
to breath. A change in the pressure should be done
manually.
CPAP with Expiratory release pressure.
Automatic CPAP also called Auto CPAP,
Auto PAP or APAP: automatically changes or titrates, the
amount of pressure delivered to the patient from breath to
breath to the minimum required to maintain an open airway
by measuring the resistance in the patient's breathing, So
giving the patient the precise pressure required at a given
moment (pressure changes from breath to another
according to the patient's needs)

Fixed pressure BPAP: both IPAP and EPAP are fixed.
The schedule of shift between IPAP and EPAP may be:
 S (Spontaneous):the device gives IPAP when flow
sensors detect spontaneous inspiratory effort and then
returns to EPAP.
 T(Timed): the shift between IPAP and EPAP is after a
fixed time period to give a fixed respiratory rate
(regardless the patient effort)
 S/T(Spontaneous/Timed): A "backup“ rate is set to
ensure that the patient receive a minimum number of
breaths per minute if he fails to breathe spontaneously
i.e. Like spontaneous mode, the device gives IPAP on
patient inspiratory effort. But if the patient can't initiate a
breath in a certain period of time after last expiration, the
device shifts to IPAP.

 Automatic BPAP (Auto BPAP):
automatically changes the amount of pressure
delivered according to the patient's needs on a
breath by breath ,
The clinician sets EPAP minimum and PS
maximum and the machine changes EPAP and
IPAP within these limits. It differs from ASV in the
algorithm used and the pressure ranges.

 N.B:
NIV should be used with extreme caution in patients
with pulmonary pathology (e.g. pneumonia, collapse,
effusion) that affect only one side of the lungs. In
such cases, NIV primarily ventilates the good lung,
producing increased pressure and compressing
intrapulmonary blood vessels on that side, which
leads to decreased blood flow to the healthy lung
and increased pulmonary blood flow to the affected
lung, or area of lower pressure This can lead to V/Q
mismatch
.

Ventilator Settings Terminology
•A/C: Assist-Control
•IMV: Intermittent Mandatory Ventilation
•SIMV: Synchronized Intermittent
Mandatory Ventilation
•Bi-level/Biphasic: Non-inversed Pressure
Ventilation with Pressure Support
(consists of 2 levels of pressure)

•PRVC: Pressure Regulated Volume
Control
•PEEP: Positive End Expiratory Pressure
•CPAP: Continuous Positive Airway
Pressure
•PSV: Pressure Support Ventilation
•NIPPV: Non-Invasive Positive Pressure
Ventilation

Terminology
Tidal volume (VT).
Respiratory rate/frequency
Minute ventilation (VE): The product of VT
and respiratory frequency (VT • f). It is
usually expressed in liters/minute.
Peak airway pressure (Paw): The pressure
that is required to deliver the VT to the
patient. It has a unit of centimeters of
water (cm H2O).

Plateau pressure (Pplat): The pressure that is
needed to distend the lung. This pressure
can only be obtained by applying an end
inspiratory pause. It also has a unit of cm
H2O.
Peak inspiratory flow: The highest flow that is
used to deliver VT to the patient during
inspiratory phase. It is usually measured in
liters/minute.
Mean airway pressure: The time-weighted
average pressure during the respiratory
cycle. It is expressed in cm H2O.

Inspiratory time: The amount of time (in
seconds) it takes to deliver VT.
Positive end-expiratory pressure (PEEP): The
amount of positive pressure that is
maintained at end-expiration. It is
expressed in cm H2O.
Fraction of inspired oxygen (FiO2): The
concentration of O2 in the inspired gas,
usually between 0.21 (room air) and 1.0
(100% O2).

Ventilatory support
FULL PARTIAL
All energy provided by ventilator
e.g. ACV / full support SIMV ( RR
= 12-26 & TV = 8-10 ml/kg)
Pt provides a portion of energy
needed for effective ventilation
e.g. SIMV (RR < 10)
Used for weaning
WOB total = WOB ventilator (forces gas into lungs)+ WOB patient (msls draw
gas into lungs)

Mechanical ventilation is produced through
the interaction of only 5 variables
1.Time
2.Volume
3.Pressure
4. inspiratory: expiratory (I:E) ratio
5.Flow

Breath characteristics
A= what initiates a breath -
TRIGGER
B = what controls / limits it –
LIMIT
C= What ends a breath -
CYCLING

Trigger
• How does the vent know when to give a
breath? - “Trigger”
–patient effort
–elapsed time
• The patient‟s effort can be “sensed” as a
change in pressure or a change in flow (in
the circuit)

Trigger
(1) Machine timer, in which breaths are initiated by a
timer in the machine set by the clinician.
(2) Pressure change (pressure trigger), in which
patient effort pulls the airway/circuit pressure
negative, and machine breaths are initiated when
this pressure drop exceeds the set negative
pressure threshold (pressure sensitivity).
(3) Flow change (flow trigger), in which patient effort
draws flow from the circuit, and machine breaths
are initiated when flow into the patient exceeds the
set flow threshold (flow sensitivity).

TRIGGER
What the ventilator
senses to initiate a
breath
Patient
• Pressure
• Flow
Machine
• Time based
Recently – EMG monitoring of phrenic
Nerve via esophageal transducer
Pressure triggering
-1 to -3 cm H2O
Flow triggering
-1 to -3 L/min

Flow delivery phase
• Once the breath is triggered, the inspiratory
valve in the ventilator opens, and the flow is
delivered.
• The flow delivery is governed by a target or
limit set by the clinician for the ventilator
during inspiration.

CONTROL/ LIMIT
 Pressure Controlled
• Pressure targeted, pressure
limited – P peak set
• Volume Variable
 Volume Controlled
• Volume targeted, volume
limited - VT set
• Pressure Variable
 Dual Controlled
• volume targeted
(guaranteed) and pressure
limited

CYCLING VARIABLE
Determines the end
of inspiration and
the switch to
expiration
 Machine cycling
• Time
• Pressure
• Volume
 Patient cycling
• Flow

End of Insp…cycle mechanisms
• The cycle phase, during which the machine
terminates a breath by any of four commonly
used cycle-off criteria:
(1) Volume, in which a breath is terminated
when a target volume is achieved;
(2) Time, in which a breath is terminated when
a set inspiratory time is achieved;

End of Insp…cycle mechanisms
• The cycle phase, during which the machine
terminates a breath by any of four commonly
used cycle-off criteria:
(3) Flow, in which a breath is terminated when
inspiratory flow has fallen to a set level; and
(4) Pressure, in which a breath is terminated
when a set inspiratory pressure is achieved.

The Control Variable-
Inspiratory Breath Delivery
• Volume controlled
–Pressure may vary
• Pressure controlled
–Flow and volume may vary
• Time controlled (HFOV)
–pressure, flow, volume may vary

Pressure vs. Volume
• Pressure Limited
1. Control FiO2 and mAP
(oxygenation)
2. Still can influence
ventilation somewhat
(respiratory rate, PAP)
3. Decelerating flow pattern
(lower PIP for same TV)
4. If ETT is obstructed acutely,
delivered tidal volume will
decrease
5. Adjust PIP or PAP
• Volume Limited
1. Control minute
ventilation
2. Still can influence
oxygenation somewhat
(FiO2, PEEP, I-time)
3. Square wave flow
pattern
4. Square wave (constant)
flow pattern results in
higher PIP for same tidal
volume
5. Adjust Tidal Volume

Breath types
Spontaneous
Both triggered and
cycled by the
patient
Control/Mandato
ry
Machine triggered
and machine
cycled
Assisted
Patient triggered but
machine cycled

Time
Pressure
Assisted Controlled
Mechanical breath:
• starts by machine or patient
• ends by machine

Time (sec)
Pressure
(cm H2O)
Set PS level
Patient Triggered, Flow Cycled,
Pressure limited
Starts & ends by patient

Supported breath…
Time (sec)
Pressure
(cm H2O)
Set PS level
Patient Triggered, Flow Cycled,
Pressure limited
Starts & ends by patient

Types of Breaths
•M=machine, P=patient
Limit (control)
End
(cycle)
Start
(trigger)
Breath
Volume or pressureMMControlled
Mechanical
Volume or pressureMPAssisted  V

Types of Breaths
•M=machine, P=patient
Limit (control)
End
(cycle)
Start
(trigger)
Breath
Volume or pressureMMControlled
Mechanical
Volume or pressureMPAssisted
-PPSpontaneous
Spontaneous
PressurePPSupported
 V

Waveforms
 Volume -time
 Flow - time
 Pressure - time

b) Flow waveforms
1. Inspiratory flow waveforms

Sine
Square
Decelerating
• Resembles normal
inspiration
• More physiological
• Maintains constant flow
• high flow with ↓ Ti &
improved I:E
• Flow slows down as
alveolar pressure
increases
• meets high initial flow
demand in spont breathing
patient - ↓WOB
Accelerating • Produces highest PIP as
airflow is highest towards
end of inflation when
alveoli are less compliant
Square-
volume
limited modes
Decelerating
– pressure
limited modes
Not used

Inspiratory and expiratory flow waveforms

. Expiratory flow waveform2
• Expiratory flow is not driven by ventilator and is
passive
• Is negative by convention
• Similar in all modes
• Determined by Airway resistance & exp time (Te)
Use
1.Airtrapping & generation of AutoPEEP
2.Exp flow resistance (↓PEFR + short Te) & response
bronchodilators (↑PEFR)

Pr due to resistance
Pr due to elastance
Peak insp pr = Total pr
P
Plat pr
EEP
Ti Te
Pressure-time diagram

Time
Pressure
Assisted Controlled
Pressure waveform
Pressure controlled “ACV”

waveform………
Pressure controlled
Zero flow
Inspiration
Expiration
Time
Flow
PIF
PEF
What is flow?? How related to volume??
TI
TE
Volume controlled
Decelerating flowConstant flow

waveform ……….
Inspiration Expiration
Time
Volume
Inspiratory Tidal Volume
TI TE
Pressure controlled
Volume controlled

Volume ModesPressure Modes
Types of Waveforms……SummeryPressureFlowVolume
Time

Basic Ventilator Modes
• “Control” modes
– Volume control (Assist control): VC (AC)
– Pressure control: PC
• Mixed
– Synchronized Intermittent Mandatory
Ventilation (SIMV) with support (controlled
and spontaneous)
• “Spontaneous” Modes
– Pressure Support (PS)
– CPAP
– T-Piece

Conventional modes of ventilation
1. Control mandatory ventilation (CMV / VCV)
2. Assist Control Mandatory Ventilation (ACMV)
3. Intermittent mandatory ventilation (IMV)
4. Synchronized Intermittent Mandatory
Ventilation (SIMV)
5. Pressure controlled ventilation (PCV)
6. Pressure support ventilation (PSV)
7. Continuous positive airway pressure (CPAP)

. Control mandatory ventilation (CMV /1
VCV)
• Breath - MANDATORY
• Trigger – TIME
• Limit - VOLUME
• Cycle – VOL / TIME
• Patient has no
control over
respiration
• Requires sedation
and paralysis of
patient

. Assist Control Mandatory Ventilation2
ACMV)(
• Patient has partial control over his respiration – Better Pt ventilator synchrony
• Ventilator rate determined by patient or backup rate (whichever is higher) – risk
of respiratory alkalosis if tachypnoea
• PASSIVE Pt – acts like CMV
• ACTIVE pt – ALL spontaneous breaths assisted to preset volume
• Breath – MANDATORY
ASSISTED
• Trigger – PATIENT
TIME
• Limit - VOLUME
• Cycle – VOLUME / TIME
Once patient initiates the
breath the ventilator takes
over the WOB
If he fails to initiate,
then the ventilator
does the entire WOB

Basic Modes of Ventilation
• Volume Assist-Control Mode
• Breath can be initiated by the machine timer
(control mode) or by the patient (assist mode) .
• The VT is then delivered by a flow targeted
mechanism (i.e., a fixed flow set by the clinician)
until a preset VT is reached.
• The ventilator terminates the breath (volume
cycle-off) and allows expiration to proceed.

• Volume Assist-Control Mode
• We sets RR, VT, PIFR, FiO2 and PEEP
• The dependent variables are pressures (Paw and
Plat).
• The inspiratory time (Ti) is determined by the
ratio of VT and inspiratory flow (Ti = VT/flow
rate).

. Intermittent mandatory ventilation3
(IMV)
Breath stacking
Spontaneous breath immediately after
a controlled breath without allowing
time for expiration ( SUPERIMPOSED
BREATHS)
 Basically CMV which allows
spontaneous breaths in
between
 Disadvantage
 In tachypnea can lead to
breath stacking - leading
to dynamic hyperinflation
 Not used now – has been
replaced by SIMV
• Breath – MANDATORY
SPONTANEOUS
VENTILATOR
• Limit - VOLUME
• Cycle - VOLUME

.Synchronized Intermittent Mandatory4
SIMV)Ventilation (
• Breath –
SPONTANEOUS
ASSISTED
MANDATORY
TIME
• Limit - VOLUME
• Cycle – VOLUME/
TIME

• Basically, ACMV with spontaneous breaths (which
may be pressure supported) allowed in between
• Synchronization window – Time interval from
the previous mandatory breath to just prior to the
next time triggering, during which ventilator is
responsive to patients spontaneous inspiratory
effort
• Weaning
Adv
 Allows patients to exercise their respiratory muscles in
between – avoids atrophy
 Avoids breath stacking – „Synchronization window‟

.Pressure controlled ventilation (PCV)5
• Breath –
MANDATORY
• Trigger – TIME
• Limit - PRESSURE
• Cycle – TIME/ FLOW
Rise time
Time taken for airway
pressure to rise from
baseline to maximum

• Pressure Assist-Control Mode
• Breath can be initiated by the machine timer
(control mode) or by the patient (assist mode) .
• The VT is delivered by a pressure-targeted
mechanism (i.e., an inspiratory pressure set by the
clinician).
• The ventilator continues to deliver the breath
until a preset Ti is reached (time cycle-off).
• The breath is then terminated, and expiration
follows.

• The clinician sets RR, inspiratory pressure, and Ti,
in addition to FiO2 and PEEP.
• The flow waveform is always decelerating in the
PAC mode because the flow slows as it reaches
the pressure limit.
• The magnitude of VT, however, depends on the
resistance and compliance of the respiratory
system and, sometimes, on Ti .

• Delivers VT that is machine or patient triggered,
pressure targeted, and at a frequency that at least
equals the preset rate; each breath is terminated
by a preset Ti (time cycle-off ).

• Advantages
• Pressure limiting
• Patient comfort
• Disadvantages
• No guaranteed VT or VE

.Pressure support ventilation (PSV)6
• Breath – SPONTANEOUS
• Limit - PRESSURE
• Cycle – FLOW
( 5-25% OF PIFR)
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

• Pressure Support Ventilation Mode
• In the PSV mode, all breaths are initiated by the
patient.
• The VT is delivered by a pressure-targeted
mechanism (i.e., an inspiratory pressure set by the
clinician).

• The ventilator continues to deliver the breath
until the inspiratory flow has decreased to a
specific level (e.g., at 25% of the peak inspiratory
flow) (flow cycle-off).

• Because each breath on the PSV mode is initiated
by the patient, it is very important to ensure that
the patient has reliable breathing effort before
being placed on the PSV mode. Otherwise,
hypoventilation or apnea may occur.

• The magnitude of VT delivered may differ from
breath to breath, depending on lung mechanics
and the patient’s respiratory drive.

• Advantages
• Patient comfort
• Better patient ventilator synchrony
• Disadvantages
• No guaranteed VE.
• Inadequate for patients with unreliable
respiratory drive

PSV initiation
• Patient should be able to initiate an
inspiratory effort, detected by pressure
or flow trigger
• Pressure triggering : pressure sensitivity
-2 cm H20 to 0,5 cm H20
• Flow triggering : flow sensitivity 1-5
l/mn

Rise time
• Time required for the ventilator to reach the
PS setting at the onset of inspiration
• Should be adjusted to patient comfort, to
decrease the work of breathing
• Allows to adjust the flow at the onset of the
inspiratory phase

Problems faced during PSV
• Apneas
• Patient – ventilator dyssynchrony :
– COPD patients :
– AutoPEEP :
» Increases the effort required to trigger the ventilator
» Decreases the delivered Vt
– Inspiratory flow decreases slowly  flow cycle criteria not
reached at the end of neural inspiration  active exhalation to
pressure cycle the breath
– High minute ventilation : insufficient inspiratory flow

Which level of PS ?
• PS + PEP  30 cm H2O (barotrauma)
• Unloading of respiratory muscle :
– Should encourage reconditioning and prevention of
atrophy
– While avoiding fatigue
• Objectives : Vt 8-10 ml / kg, RR < 30-35/mn
and no SCM muscle contractions

Other parameters settings
• Triggers set at their higher sensitivity, decreased if
auto-cycling
• Rise time titration
• PEEP according to auto-PEEP and gas exchange
• FiO2 according to gas exchange

For which patients ?
• COPD
• ALI
• Patient not synchronized with the ventilator on
Flow AC MV
• Weaning
• NIV

.Continuous positive airway pressure7
(CPAP)
Breath –
SPONTANEOUS
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

BiPAP
• Allows one to apply IPAP and EPAP
• IPAP provides positive pressure breaths
and it improves hypoxemia and/or
hypercapnia
• EPAP (essentially PEEP) improves
oxygenation by increasing the FRC and
enhancing alveolar recruitment

• Indications for BiPAP:
1. preventing intubation of end-stage COPD
patient
2. supporting patients with chronic ventilatory
failure
3. patient‟s with restrictive chest wall disease
4. neuromuscular disease
5. nocturnal hypoventilation

Alternative Modes Of
Mechanical Ventilation
• Dual-control ventilation modes were
designed to combine the advantages of
volume-control ventilation with pressure-
control ventilation
• These dual-control modes attempt to
increase the safety and comfort of
mechanical ventilation

pressure-regulated volume-
control (PRVC)
• a desired tidal volume is preset and the
ventilator delivers a pressure-limited
(controlled) breath until that preset tidal
volume is achieved
• ↑ Vt ↓ PIP & ↓ Vt ↑ PIP
• provides the opportunity to deliver minimum
minute ventilation at the lowest peak airway
pressures possible

volume support ventilation
(VSV)
• The patient triggers every breath, controlling
his own respiratory frequency and inspiratory
time but the machine can guarantee minute
ventilation
• The pressure support is automatically
adjusted up or down according to patient's
lung compliance and/or resistance to deliver
a preset tidal volume
• This mode cannot be used in a patient who
lacks spontaneous breathing effort
• This mode is considered as a self-weaning
mode

Auto mode
PRVC
VSV
• designed for automatic weaning from
pressure control to pressure support
depending on the patient's effort.

Automatic tube
compensation (ATC)
Designed to overcome the resistance
of the endotracheal tube by means of
continuous calculations.

Proportional assist
ventilation (PAV)
• This mode adjusts airway pressure in
proportion to the patient's effort
• If patient's effort and/or demand are
increased, the ventilator support is
increased, and vice versa, to always give
a set proportion of the breath

High-frequency
ventilation (HFV)
• HFV is time-cycled positive pressure
ventilation that delivers a high frequency (60–
120 breathes per min) of small tidal volumes
(1.5 mL/kg) that are usually less than the
anatomic dead space
• 3 different modes: high-frequency positive-
pressure ventilation (HFPPV), high-
frequency jet ventilation (HFJV), and high-
frequency oscillatory ventilation (HFOV)

APRV (airway pressure
release ventilation)
• Is similar to CPAP in that the pt. is allowed
to breathe spont. without restriction

• Combines two separate levels of CPAP and
the pt. may breathe spont. from both levels
• Periodically, pressure is dropped to the
lower level, reducing mean airway press.
• During spont. expir. the CPAP is dropped
(released) to a lower level which simulates
an effective expiration

Mode: Combination of breaths
ModeBreath
Controlled
Assisted
Spontaneous
Supported

ModeBreath
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assisted
Spontaneous
Supported

ModeBreath
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assist
(Volume or pressure
assist)
Assisted
Spontaneous
Supported

ModeBreath
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assist
(Volume or pressure
assist)
Assisted
Spontaneous
Supported

ModeBreath
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assist
(Volume or pressure
assist)
Assisted
CPAPSpontaneous
Supported

ModeBreath
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assist
(Volume or pressure
assist)
Assisted
CPAPSpontaneous
PSVSupported

ModeBreath
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
Assist
(Volume or pressure
assist)
Assisted
CPAPSpontaneous
PSVSupported

ModeBreath
SIMV/PS
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
AssistAssisted
CPAPSpontaneous
PSVSupported

ModeBreath
BiPAPSIMV/PS
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
AssistAssisted
CPAPSpontaneous
PSVSupported

Control Modes
ModeBreath
BiPAP
SIMV/PS
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
AssistAssisted
CPAPSpontaneous
PSVSupported

Spontaneous Modes
ModeBreath
BiPAP
SIMV/PS
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
AssistAssisted
CPAPSpontaneous
PSVSupported

Combined Modes
ModeBreath
BiPAP
SIMV/PS
SIMV
(VC-SIMV)
(PC-SIMV)
ACM
(VC-ACM)
(PC-ACM)
CMV
(VC-CMV)
(PC-CMV)
Controlled
AssistAssisted
CPAPSpontaneous
PSVSupported

MODE OF VENTILATION
• Tailored to need of the patient
• SIMV / A/C modes for initial settings
• In pts with good resp drive & mild – mod resp
failure – PSV

• For Paralyzed pts : CMV or A/C mode
• For Non paralyzed pts : SIMV mode
• Pts with normal resp effort
mild resp failure : PSV mode

SETTING UP THE VENTILATOR MODE
FOR THE PATIENT

SETTING UP THE VENTILATOR MODE
FOR THE PATIENT
1. What are the objectives for mechanical
ventilation?
2. Does the patient have a reliable central
respiratory drive?
3. What are the patient’s acute disease
processes and comorbid conditions?
4. How does the patient’s underlying
disease respond to treatment?

TIDAL VOLUME
• Initial TV : 4 – 10 ml/Kg of ideal bd wt
• Lowest values are recommended in presence of
Obstructive airway ds & ARDS
• Goal : to adjust TV so that plateau pressures are less than
30 cm H20.
• With lower values the following can occur:
– Hypoventilation,
– Hypoxemia,
– Atelectasis.
• With higher values the following can occur:
– Barotrauma,
– Respiratory alkalosis
– Decreased cardiac output can occur.

 If there is a significant decrease in the measured VT
compared with the set VT, one needs to check for
leaks in the ventilator circuit, including the cuff and
tubing.
 Patients with a chest tube may also have lower
measured VT if there is a lung leak and a portion of
the VT is lost through the chest tube (e.g., in
bronchopleural fistula).

IBW is calculated as 50 kg + 2.3 kg for
each inch above 60 inches (152.5cm) in
men.
IBW is calculated as 45.5 kg + 2.3 kg for
each inch above 60 inches (152.5cm) in
women.

RESPIRATORY RATE
• With lower values the following can occur:
– Hypoventilation,
– Hypoxemia,
– Patient discomfort owing to increased work of
breathing
• With higher values the following can occur:
– Barotrauma,
– Respiratory alkalosis
– Auto PEEP because the expiratory time shortens.

SUPPLEMENTAL O2 THERAPY
• Lowest FiO2 that produces an
Sp02 > 90 %
PaO2 > 60 mm Hg
is recommended

INSPIRATION : EXPIRATION RATIO
• Normal I:E ratio to start is 1:2
• Reduced to 1:3 or 1:4 in presence of
obstructive airway disease in order to air
trapping
• Inverse I:E – in ARDS

INSPIRATORY FLOW RATE
• 60 L/min is typically used
• Increased to 100 L/min : to deliver TVs
quickly and allow for prolonged expiration
in presence of obstructive airway ds

POSITIVE END EXPIRATORY
PRESSURE ( PEEP )
• Titrated according to PEEP and BP
• High PEEP ( > 10 H20 ) – pneumonia,
ARDS
PEEP – reduces risk of atelectasis
- increase no of open alveoli
( decrease V/Q mismatch )
- in CHF : decrease venous return
• Physiological PEEP ( 3-5 cm H20):to
prevent decrease in FRC in normal lungs

SENSITIVITY ( TRIGGER )
• To determine when an assisted breath must be
delivered, the ventilator must sense inspiratory
effort by detecting a threshold drop in the airway
pressure.
• The sensitivity of the trigger is based upon the
magnitude of the dropped pressure .
• Ventilator trigger sensitivity is usually set at -0.5 to -
1.5 cm H2O.
• High sensitivity values result in self-cycling; in
contrast to insensitive values results in increased
work of breathing .

• Triggering of the ventilator is more difficult in
patients with airflow limitations and dynamic
hyperinflation, where the end-expiratory lung
volume exceeds the relaxation volume of the
respiratory system.
• In this case the patient must generate sufficient
pressure to offset;
– The elastic recoil associated with hyperinflation and
then
– Overcome the sensitivity threshold.
• So, decreasing the sensitivity threshold put the
patient in the better position to trigger the
ventilator with least effort .

Inspiratory flow profile
• Many flow profiles are available for selection at initial
ventilator setting:
• Constant,
• Decelerating,
• Accelerating,
• Sinusoidal.
• No significant differences exist with these flow profiles in
terms of gas exchange or work of breathing. However,
from a practical standpoint, a decelerating pattern may
be beneficial in:
– Obstructive airway disease
– Early diffuse ARDS.
• If lobar atelectasis or other conditions with low
compliance exist, a constant flow may results in better
distribution of tidal ventilation .

Vent settings to improve oxygenation
•FIO2
•Simplest maneuver to quickly increase PaO2
•Long-term toxicity at >60%
•Free radical damage
•Inadequate oxygenation despite 100% FiO2 usually due to
pulmonary shunting
•Collapse – Atelectasis
•Pus-filled alveoli – Pneumonia
•Water/Protein – ARDS
•Water – CHF
•Blood – Hemorrhage.
PEEP and FiO2 are adjusted in tandem

Vent settings to improve oxygenation
•PEEP
• Increases FRC
• Prevents progressive atelectasis and
intrapulmonary shunting
• Prevents repetitive opening/closing (injury)
• Recruits collapsed alveoli and improves
V/Q matching
• Resolves intrapulmonary shunting
• Improves compliance
• Enables maintenance of adequate PaO2
at a safe FiO2 level
• Disadvantages
• Increases intrathoracic pressure (may
require pulmonary a. catheter)
• May lead to ARDS
• Rupture: PTX, pulmonary edema
PEEP and FiO2 are adjusted in tandem
Oxygen delivery (DO2), not PaO2, should be
used to assess optimal PEEP.

Alternative Modes
• I:E inverse ratio ventilation (IRV)
• ARDS and severe hypoxemia
• Prolonged inspiratory time (3:1) leads to
better gas distribution with lower PIP
• Elevated pressure improves alveolar
recruitment
• No statistical advantage over PEEP, and
does not prevent repetitive collapse and
reinflation
• Prone positioning
• Addresses dependent atelectasis
• Improved recruitment and FRC, relief of
diaphragmatic pressure from abdominal
viscera, improved drainage of secretions
• Logistically difficult
• No mortality benefit demonstrated
• ECHMO
• Airway Pressure Release (APR)
• High-Frequency Oscillatory
Ventilation (HFOV)
• High-frequency, low amplitude
ventilation superimposed over
elevated Paw
• Avoids repetitive alveolar open and
closing that occur with low airway
pressures
• Avoids overdistension that occurs
at high airway pressures
• Well tolerated, consistent
improvements in oxygenation, but
unclear mortality benefits
• Disadvantages
• Potential hemodynamic compromise
• Pneumothorax
• Neuromuscular blocking agents

Vent settings to improve ventilation
•Respiratory rate
• Max RR at 35 breaths/min
• Efficiency of ventilation decreases
with increasing RR
• Decreased time for alveolar emptying
•TV
• Goal of 10 ml/kg
• Risk of volutrauma
•Other means to decrease PaCO2
• Reduce muscular activity/seizures
• Minimizing exogenous carb load
• Controlling hypermetabolic states
•Permissive hypercapnea
•Preferable to dangerously high RR
and TV, as long as pH > 7.15
RR and TV are adjusted to maintain VE and PaCO2
•I:E ratio (IRV)
• Increasing inspiration time will
increase TV, but may lead to
auto-PEEP
•PIP
• Elevated PIP suggests need for
switch from volume-cycled to
pressure-cycled mode
• Maintained at <45cm H2O to
minimize barotrauma
•Plateau pressures
• Pressure measured at the end
of inspiratory phase
• Maintained at <30-35cm H2O to
minimize barotrauma

Different diseases
ventilation

ASTHMA & COPD
• TV 6-8ml per kg,
• Increase Expiratory Flow Time to max: to
prevent increase intrinsic PEEP (100L per min)
• I : E : increased 1:2
• PEEP: 5

Minimize
DH
Decrease
minute
ventilation
Increase
expiratory
time
Decrease
resistance to
Expiratory
flows
Add extrinsic
PEEP

1. Initial setting of minute ventilation (VE):
 Tidal volume (VT) is set to 6 - 8 ml/kg of IBW.
Start with 8 and decrease to 6 if Peak pressure
increased.
 RR is set to 8 -10 breath/min. Start with 10 and
decrease to 8 if airway resistance is high and
need longer expiratory time.

2. Increase expiratory time :
 Increase peak flow (60-80L/min).
 Avoid end-inspiratory pause: the use of end
inspiratory pause increased DH not only by
decreasing expiratory time but also by decreasing
isovolume expiratory flow because of the reduction of
elastic energy stored at viscoelastic elements of
respiratory system.
 Use square wave form.

Changing Flow Waveform in Volume Ventilation:
Effect on Inspiratory Time
1 2 3 4 5 6
SEC
120
-120
V
.
LPM

Increased Peak Flow: Decreased Inspiratory Time
1 2 3 4 5 6
SEC
120
-120
V
.
LPM

3. Maximize trigger sensitivity:
 The threshold for triggering should be set to its
maximum possible level, such that auto cycling
does not occur.
 Decreasing the resistance of the inspiratory
ventilator line and using a large bore
endotracheal tube are of particular concern in
flow triggering.

ARDS
• A/C mode
• Tidal Volume : 4-6 ml/Kg
• PEEP : 5-15
• Ventilatory rate : 12 UP to 25
titrated to maintain Ph > 7.25

Scenario
 A 40-year-old man sustained multiple lacerations
from a motor vehicle crash.
 Admission to the emergency department for
evaluation revealed a fractured left femur, a
deep laceration of the right arm, an open
pneumothorax on the right side of the chest,
abdominal bruising.

 A chest tube with pleural drainage was inserted
for the pneumothorax.
 The patient developed a fever of 39.5° C and
severe refractory hypoxemia 4 days after
surgery.
 A chest radiograph showed resolution of the
pneumothorax and the presence of bilateral
fluffy infiltrates.

 ABGs on a nonrebreathing mask at the time were pH
= 7.29; PaCO2 = 51 mm Hg; PaO2 = 76 mm Hg;
HCO3 − = 24.8 mEq/L.
 Vital signs were blood pressure = 148/90 mm Hg; heart
rate = 152 beats/min; RR = 42 breaths/min and
labored.
 The patient was restless and anxious. Mask CPAP at
12 cm H2O was initiated with FIO2 = 100%. The
CPAP is intolerated.

 The patient, who was 72 inch and weighed 117 kg, was
sedated, paralyzed, orally intubated, and placed on
ventilatory support.
1. What were the indications for ventilation of this
patient?
2. What clinical information suggests that this patient may
have developed ARDS?
3. What would be appropriate initial ventilator settings for
this patient?

1.The initial indications for ventilation in this patient are
increased WOB, respiratory failure, refractory
hypoxemia, and inability to tolerate mask CPAP.
2. In terms of precipitating factors, he sustained a
fracture of the left femur, which may cause fat emboli,
and chest injuries that resulted in a pneumothorax.
Bilateral fluffy infiltrates are present on a chest
radiograph, and PaO2/ FIO2<100 i.e severe ARDS.

The physiologic hallmark of ARDS is hypoxaemia,
which is typically corrected with with oxygen and PEEP.
Limiting atelectrauma (lung injury from repetitive
opening and closing of alveoli) by PEEP, and barotrauma
(lung injury from overdistention of alveoli) by low tidal
volume about 6 ml/kg of IBW may prevent vetilator
associated lung injury.
This is called Lung protective strategy (LPS).

3. The appropriate initial ventilator settings are:
He is 72 inch tall and weighs 117 kg.
BSA = HT in cm x Wt in Kg /3600 = 2.42 m2
 Initial VE = (4 × BSA) = 9.68 L/min.

Pressure-controlled ventilation can be used instead of
volume-controlled ventilation. It would be helpful to start
with VC-CMV to measure plateau pressure and
compliance.
PC-SIMV + PSV and PC-CMV are equally acceptable.
An initial PEEP of 10 cm H2O and an FIO2 of 100%
should be set.

IBW is calculated as 50 kg + 2.3 kg for each inch above
60 inches (152.5cm) in men.
 IBW is calculated as 45.5 kg + 2.3 kg for each inch
above 60 inches (152.5cm) in women.
The tidal volume set at 6 ml/kg IBW and then
decreased by 1ml/kg IBW as necessary to maintain a
plateau pressure < 30 cmH2O. The minimum tidal
volume is 4 ml/kg IBW.

IBW = 77.6 Kg. So start wit VT = 6x 77.6= 465 ml.
 RR = VE /VT = 9.68/0.465 = 20 breaths/min.
A descending ramp waveform should be used.

CHF
• Respond well to positive pressure ventilation
(opens alveoli, reduces preload)
• Many benefit from trial of
noninvasive CPAP / BiPAP
• Intubated pts usually manage to oxygenate well
• But PEEP can be increased to improve
oxygenation and reduce preload.

Low Expired Minute Volume Alarm
• A low expired minute volume usually means that
there is a leak in the system

Low Expired Minute Volume Alarm
• A low expired minute volume usually means that
there is a leak in the system
• Disconnection from the ventilator
• Leak in connections:
• Y-connector
• Humidifier circuit
• Cuff deflation, leak or rupture
• Upward migration of endotracheal tube out of the
larynx
• Hypoventilation
• Large bronchopleural fistula with chest drain in-situ
• Ventilator malfunction

High Expired Minute Volume Alarm
• Hyperventilation by the patient due to any
reason can trigger the alarm for high expired
minute volume.

High Expired Minute Volume Alarm
• Hyperventilation by the patient due to any
reason can trigger the alarm for high expired
minute volume.
• Pain
• Anxiety
• Hypoxemia
• Metabolic acidosis
• Excessive CO2 production
• Fever
• Hypercatabolic states (excessive CO2 production)
• Calorie loading (excessive CO2 production)
• Ventilator malfunction

Upper Airway Pressure Limit Alarm
• When the alarm is triggered, the ventilator
immediately cycles to expiration,
terminating the inspiration.
• The upper airway pressure limit is typically
set at 10–15 cm H2 O above the observed
peak inspiratory pressure.

 Coughing
 Endotracheal/tracheostomy tube obstruction
 Kinking of endotracheal tube
 Biting of endotracheal tube
 Increased airway secretions

 Excessive condensation (“raining out”) into the
ventilator circuit
 Downward migration of endotracheal tube into a
mainstem bronchus
 Herniation of the endotracheal tube cuff
 Bronchospasm
 „Clashing‟ with the ventilator
 Low lung compliance (pulmonary edema,
pneumothorax, collapse of a lobe or lung,
consolidation)
 Inspiratory/expiratory valve malfunction

Low Airway Pressure Limit Alarm
• The low airway pressure limit is typically set
at 10–15 cm H2O below the observed peak
inspiratory pressure.
• The alarm is activated if the airway pressure
falls, such as in leaks or disconnections

Disconnection
Upward migration of ET
Circuit leak at connection points
HME
 Humidifier
Water trap
Closed suction catheter
Temperature sensors
In-line nebulizers
Exhalation valve

ET Cuff
Inadequately inflated ET cuff
ET cuff deliberately under- inflated to provide a
“minimal leak”
Bronchopleural fistula with chest drain in
situ

Apnea Alarm
• The apnea alarm should be set such that it is
activated if the patient makes no attempt to
breathe for at least 15–20 s, on a
spontaneous mode of breathing.
• Many ventilators automatically switch over
to a backup mode that ensures full
mechanical support until spontaneous
breaths are resumed.

Apnea Alarm
Drugs (sedatives, paralyzing agents)
CNS injury or disease
Hyperoxic hyperventilation
Hypocapnia

Apnea Alarm
Metabolic alkalosis
CSA (lack of triggering during sleep)
Uremia
Hypothermia
Respiratory muscle weakness

TROUBLESHOOTING
• Anxious Patient
– Can be due to a malfunction of the ventilator
– Patient may need to be suctioned
– Frequently the patient needs medication for
anxiety or sedation to help them relax

Low Pressure Alarm
• Usually due to a leak in the circuit.
– Attempt to quickly find the problem

High Pressure Alarm
• Usually caused by:
– A blockage in the circuit (water
condensation)
– Patient biting his ETT
– Mucus plug in the ETT
– You can attempt to quickly fix the
problem

Low Minute Volume
Alarm
• Usually caused by:
– Apnea of your patient .
– Disconnection of the patient from
the ventilator
– You can attempt to quickly fix the
problem

Art of ventilation

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