3. The Airways
• From trachea, the air passes through 10-
23 generations.
• First 16 generations = CONDUCTING
ZONE, Contain no alveoli, No gas
exchange Anatomic dead space.
• 17th - 19th generation =
TRANSITIONAL ZONE, Alveoli start to
appear, in the respiratory bronchioles.
• 20th - 22nd generations =
RESPIRATORY ZONE, Lined with
alveoli, alveolar ducts and alveolar sacs,
which terminate the tracheobronchial
tree
4. DEFINITION OF PRESSURES AND GRADIENTS IN
THE LUNGS
• Airway opening pressure (Pawo), or 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 (e.g., hyperbaric
chamber) or a negative pressure ventilator (e.g., iron
lung).
• Intrapleural pressure (Ppl) is the pressure in the
potential space between the parietal and visceral
pleurae. Normal Ppl is about -5cm H2O at the end of
exhalation during spontaneous breathing and -10 cm
H2O at the end of inspiration.
5. • Alveolar pressure(PA or Palv): This pressure is
also called intra-pulmonary pressure or lung
pressure. Alveolar pressure normally changes
as the intra-pleural pressure changes. During
inspiration alveolar pressure is about -1cm H2O
and during exhalation it is about +1cm H2O.
7. Four basic pressure gradients are used to describe
normal ventilation:
1. Trans-Airway pressure (PTA): PTA produces air way
movement in the conductive airways. It represents the
pressure caused by resistance to gas flow in the
airways (i.e. airflow resistance).
8. 2. Trans-Thoracic pressure(Pw or Ptt)
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 ), or
Trans-Alveolar pressure : PL maintains alveolar
inflation and is sometimes called the alveolar
distending pressure. All modes of ventilation
increase PL either by decreasing Ppl (negative
pressure ventilators) or increasing PA by
increasing pressure at the upper airway (Positive
pressure ventilators).
9. 4. Trans-respiratiory pressure (PTR ): It is the pressure
required to inflate the lungs and airways during
positive pressure ventilation.
13. GOALS:
Treat hypoxemia
Treat acute respiratory acidosis
Relief of respiratory distress
Prevention or reversal of atelectasis
Resting of ventilatory muscles
14. BASIC PRINCIPLES OF MECHANICAL VENTILATION
Regardless of the disease states when a patient fails to
ventilate or oxygenate adequately the problem lies in 1 of 6
pathophysiological factors
1. Increased airway resistance
2. Change in lung compliance
3. Hypoventilation
4. V/Q mismatch
5. Intrapulmonary shunting
6. Diffusion defects
15. AIRWAY RESISTANCE
Normal airway resistance in adults is 0.6-cm of H2O /l/sec
Resistance increases by following
1. Inside the airway retained secretions
2. In the wall swelling or neoplasm
3. Outside the wall eg. Tumor
16. LUNG COMPLIANCE
Compliance is lung expansion (volume change) per unit pressure
change(work of breathing) V/ P
Abnormal high or low compliance impairs the patient ability to
maintain effective gas exchange
Normal range of compliance in newborn is 1.5-2 ml/cmH2O/kg
Normal range of compliance in adults dynamic= 30-40 ml/cmH2O
Normal range of compliance in adults static= 40-60 ml/cmH2O
17. CLINICAL CONDITIONS THAT DECREASE THE
COMPLIANCE
TYPE OF COMPLIANC
1. STATIC
1. DYNAMIC
CONDITIONS
1. ATELECTASIS
2. ARDS
3. Pneumothorax
4. Obesity
5. Retained secretions
1. Bronchospasm
2. Kinking of ET tube
3. Airway obstruction
19. VENTILATORY FAILURE
5 mechanisms lead to ventilatory failure
1. Hypoventilation
2. Persistent ventilation perfusion mismatch
3. Persistent intrapulmonary shunting
4. Diffusion defect
5. Reduction in PIO2 i.e. inspired oxygen tension
20. HYPOVENTILATION
Caused by depression in CNS
Neuromuscular disease
Airway obstruction
In a clinical setting hypoventilation is characterised by a
reductionof alveolar ventilation and increase in arterial
CO2 tension
21. VENTIATION PERFUSION MISMATCH
Disease process which causes obstruction or atelectasis
result in less oxygen being available leading to low V/Q
Pulmonary embolism is an example that decreases
pulmonary perfusion and high V/Q
22. INTRAPULMONARY SHUNTING
Causes refractory hypoxia
normal shunt is less than 10%
10-20%mild shunt
20-30% significant shunt
>30% critical and severe shunt
eg pneumonia and ARDS
23. DIFFUSION DEFECT
TYPE
1. Decrease in pressure gradient
2. Thickening of A-C membrane
3. Decrease surface areaof A-C
membrane
4. Insufficient time of diffusion
CLINICAL CONDITIONS
1. High altitude, fire combustion
2. Pulmonary edema and retained
secretions
3. Emphysema , pulmonary fibrosis
4. tachycardia
24. Classification
Broadly classified into
Negative pressure ventilatorsaccording to the
manner in which
Positive pressure ventilators they support ventilation
25. Negative pressure ventilators
Exert a negative pressure on the external chest
Decreasing the intrathoracic pressure during
inspiration allows air to flow into the lung, filling its
volume
Physiologically, this type of assissted ventilation is
similar to spontaneous ventilation
It is used mainly in chronic respiratory failure
associated with neuromascular conditions such as
poliomyleitis, muscular dystrophy, a myotrophic
lateral sclerosis, and mysthenia gravis.
26.
27. The iron lung, often referred to in
the early days as the "Drinker
respirator", was invented
by Phillip Drinker(1894 – 1972)
and Louis Agassiz Shaw
Junior, professors of industrial
hygiene at the Harvard School of
Public Health .
The machine was powered by an
electric motor with air pumps from
two vacuum cleaners. The air
pumps changed the pressure
inside a rectangular, airtight metal
box, pulling air in and out of the
lungs
28.
29. Positive pressure ventilators
Inflate the lungs by exerting positive pressure
on the airway, similar to a bellows mechanism,
forcing the alveoli to expand during inspiration
Expiration occurs passively.
modern ventilators are mainly PPV s and are
classified based on related features, principles
and engineering.
31. Components of a Ventilator
1.Power source or input power (electrical or gas source)
a. Electrically powered ventilators
b. Pneumatically powered ventilators
c. Combined power ventilators
2.Positive or negative pressure generator
3.Control systems and circuits
a. Open and closed loop systems to control ventilator
function
b. Control panel (user interface)
c. Pneumatic circuit
4. Power transmission and conversion system
a. Volume displacement, pneumatic designs
b. Flow control valves
5.Output (pressure, volume, and flow waveforms)
32.
33.
34. These essential parts are aided by other
components, which are added to the circuit to
optimize gas delivery and ventilator function.
35. Ventilator Settings & their Significance
FiO2
PIP
PEEP
Rate
Ti , Te , Ti : Te ratio
Gas Flow
TV
36. FiO2
• Increased FiO2 Increases PaO2 & thus oxygenation
• Very high FiO2 directly toxic to Retina, Lungs, Brain, Gut (free radical
injury)
a) For pts with severe hypoxemia/ abnormal cardiopulmonary status: initial
FiO2 is 80-100%, can be decreased to 50%
• Both FiO2 & MAP determine oxygenation
• Parameter which are more likely to be effective and less damaging
should be used to increase PaO2
• E.g.– if FiO2 is > 0.6-0.7, increase MAP
if FiO2 is < 0.3-0.4, decrease MAP
b) For pts with mild hypoxemia/Normal Cardiopulmonary status: Initial FiO2
may be set 40-50%, change as per ABG
37. PIP
• PIP in part determines TV & Minute Ventilation
• Initial PIP: based on Chest movement & Breath
sounds
• Normal neonatal lungs 12-14 cm H2O
• Mild to moderate lung disease 16-20
• Severe lung disease 20-25
• Increase in PIP Increases TV, Increases CO2 elimination,
Decreases PaCO2, Increases PaO2
• Inappropriately high PIP Increased risk of Air
leaks,barotrauma.
• Inappropriately low PIP Lung collapse & insufficient
ventilation Increased PaCO2, Decreased PaO2, Atelectasis
38. PEEP
Alveolar distending pressure is 5 cmH2O (Alveolar-Pleural)
• This distending pressure is sufficient to maintain a normal
end expiratory alveolar volume to overcome the elastic
recoil of alveolar wall.
• If decreased compliance Inward elastic recoil of alveoli is
increased alveolar collapse Intrapulmonary shunting.
• PEEP increases the alveolar end expiratory pressure
Increases alveolar distending pressure Re-expansion/
Recruitment of collapsed alveoli Improves ventilation
• Thus, PEEP leads to increased V/Q ratio, improves
oxygenation, decreased work of breathing
39. Rate
• Rate in part determines Minute volume thus CO2
eliminatiion
40. Ti & Te
• Ti : Te Ratio should be kept as physiological as
possible = Close to 1:2
• Insufficient Ti Inadequate TV delivery, CO2
retention
• Insufficient Te Air trapping
41. Gas Flow Rate
• A minimum gas flow as required by the machine
should be used (5-7 Lt/min.)
• Low Flow Rate (0.5-3 l/min): may cause
hypercapnia, may not be enough to produce
required PIP at high rates (Short Ti)
• High Flow Rate (4-10 l/min): necessary to attain
high PIP at high rates, But may cause Barotrauma
& Airleaks
42. Tidal Volume
• TV in health= 8-10 ml/kg body wt
• During Ventilation, Initial TV = 10-12 ml/kg
• Lower TV (5-7 ml/kg) can be used (permissive
hypercapnia) in ARDS/ HMD to minimize the airway
pressures and risk of barotrauma.
• But Lower TV may lead to Acute hypercapnia,
increased work of breathing, severe acidosis &
collapse.
43. Working of a Ventilator
Control variables
Phase
Trigger
Limit
Cycle
44. Control Variables
The mechanical ventilator can control 4 primary
variables during inspiration—
Pressure, Volume, Flow and Time
1.Pressure controlled ventilator ventilator controls
trans respiratory system pressure i.e. airway pressure-
body surface pressure.
Means that pressure level that is delivered to the pt
will not vary in spite of changes in compliance or
resistance.
Further classified as PPV & NPV
45. 2. Volume controlled ventilator:
• Volume delivery remains constant with changes in
compliance & resistance, while the pressure varies.
3.Flow controlled ventilator:
• Allows the pressure to vary with changes in compliance
& resistance while directly measuring and controlling
flow
4. Time controlled ventilator:
• Measure and control inspiratory & expiratory time
• Allows pressure and volume to vary with changes in
compliance & resistance
46. PRESSURE V/S VOLUME VENTILATION
PRESSURE VENTILATION VOLUME VENTILATION
Parameters set
by the operator
• PIP, PEEP, Rate, FIO2, Ti • TV, PEEP, Rate, FIO2, Ti
Parameters
determined by
the ventilator
• TV, Te • PIP, Te
Advantages • Higher MAP with the same PIP
• Lung protective for noncompliant
lungs
• Guaranteed minute ventilation
Disadvantages • Does not accommodate for rapid
changes in pulmonary compliance
• Not optimal for patients with an
endotracheal tube with large
leaks
• Minute ventilation not guaranteed • PIP May reach dangerous level
if compliance is worsening
47.
48. Volumetargeted ventilation
The selection of using volume or pressure ventilation is
based on whether
consistency of tidal volume delivery is important
or the limiting of pressure is important.
Advantage : it guarantees a specific volume delivery and
VE, regardless of changes in lung compliance and
resistance or patient effort. Volume ventilation is used
when the goal is to maintain a certain level of PaCO2
disadvantage : when the lung condition worsens. This can
cause the peak and alveolar pressures to rise, leading
to alveolar over distention.
Volume ventilation is commonly chosen as the
initial form of ventilation in adults.
49. Pressure ventilation (PV)
Advantage :
reduces the risk of overdistention of the lungs by limiting the pressure
put on the lung.
the ventilator delivers a descending flow pattern during PV. The
proposed advantage of PV is that limiting the pressure spares more
normal areas of the lungs from overinflation ; this is considered a
component of lung protective strategies. It also may be more
comfortable for patients who can breathe spontaneously.
Disadvantages
Volume delivery varies.
VT and VE decrease when lung characteristics deteriorate.
PV and VV are equally beneficial in patients who are not
spontaneously breathing when a descending flow pattern is used. On
the other hand, in spontaneously breathing patients, PV may lower
the WOB and improve patient comfort to a greater extent than VV,
thereby reducing the need for sedatives and neuromuscular blocking
50. Phase variables
A ventilator supported breath is divided into 4 distinct
phases: 1) Change from expiration to inspiration 2)
Inspiration 3) Change from inspiration to expiration 4)
Expiration.
51. Trigger Variable
What determines the start of inspiration?
1. Time triggered: Breath is initiated and delivered when a
preset time interval has elapsed.
2. Pressure triggered: Beginning of spontaneous inspiratory
effort by pt Drop in airway pressure Sensed by
ventilator as a signal to initiate and deliver a breath.
3. Flow triggered: More sensitive & responsive to pt’s effort
Continuous flow is given(delivered=returned)pt effort part of flow
goes to pt returned flow< delivered flow sensed by ventilator to
initiate breath
52. Limit Variable
• What is set to its upper limit during inspiration?
• If one variable (volume/pressure/flow) is not allowed
to rise above a preset value during the inspiratory
time, is termed as Limit Variable
• Pressure limited/ Volume limited/ Flow limited
53. Cycle Variable
• What ends inspiration?
• This variable is measured and used as feedback signal by
ventilator to end inspiratory flow delivery, which then allows
exhalation to begin
• Most newer ventilators are Flow controlled, Time cycled
54. Continuous Positive Airway Pressure and PEEP
Two methods of applying continuous pressure to the
airways have been developed to improve oxygenation in
patients with refractory hypoxemia: continuous positive
airway pressure (CPAP) and PEEP.
CPAP is the application of pressures above ambient to
improve oxygenation in a spontaneously breathing patient.
55.
56. Like CPAP, PEEP provides a positive pressure to the
airway, therefore the pressure in the airway remains
above ambient even at the end of expiration. The term
PEEP is defined as positive pressure at the end of
exhalation .Use of the term commonly implies that the
patient is also receiving mandatory breaths from a
ventilator.
57. PEEP becomes the baseline variable during
mechanical ventilation.PEEP theoretically helps prevent
early airway closure and alveolar collapse at the end of
expiration by increasing (and normalising) the functional
residual capacity (FRC) of the lungs; this in turn allows for
better oxygenation.
58. Bi-PAP: Bi-level Positive Airway Pressure
• Independent positive airway pressures to both inspiration and expiration
(IPAP & EPAP)
• IPAP provides positive pressure breaths and improves ventilation &
hypoxemia d/t hypoventilation.
• EPAP is in essence CPAP which increases FRC, improves alveolar
recruitment Improves PaO2
• Used in cases of Advanced COPD, Chronic ventilatory failure,
Neuromuscular dis., Restrictive chest wall dis.
• Bi-PAP device can be used as CPAP
• Initiate with IPAP=8, EPAP=4, then gradual increments of 2cmH2O in both
61. Operating Modes
11)Adaptive Support Ventilation (ASV)
12)Proportional Assist Ventilation (PAV)
13)Volume Assured Pressure Support (VAPS)
14)Pressure Regulated Volume Control (PRVC)
15)Volume Ventilation Plus (VV+)
16)Pressure Control Ventilation (PCV)
17)Airway Pressure Release Ventilation (APRV)
18)Inverse Ratio Ventilation (IRV)
19)Automatic Tube Compensation (ATC)
62. Modes of Ventilation
Basically there are three breath delivery techniques
used with invasive positive pressure ventilation
Spontaneous modes
SIMV – synchronized
CMV – controlled mode ventilation
63. Spontaneous Modes
Three basic means of providing support for continuous
spontaneous breathing during mechanical ventilation
Spontaneous breathing
CPAP
Bi-PAP
64. Spontaneous Modes
• Patients can breathe spontaneously through a ventilator circuit;
sometimes called T-Piece Method because it mimics having the patient
ET tube connected to a Briggs adapter (T-piece)
• Role of ventilator in this mode is to provide:
1. Inspiratory flow in a timely manner
2. Adequate flow to meet pt’s inspiratory demand (TV & inspiratory
flow)
3. Provide adjunctive mode as PEEP to complement pt’s spontaneous
breath
– Disadvantage-May increase patient’s WOB with older ventilators
65.
66. Controlled Mandatory Ventilation (CMV)
Ventilator delivers preset TV/Pressure at a Time triggered rate
Ventilator controls both the pt’s TV & RR, So ventilator controls the pt’s Minute
Volume
Pt can not change RR or breath spontaneously, so only used when pt is on sedation/
respiratory depressants/ NM blockers.
Indications of CMV:
1. Severely distressed pt, vigorously struggling Rapid inspiratory efforts Asynchrony/
Fighting in the initial stages CMV
2. Tetanus/ status epilepticus Interrupts ventilation delivery
3. Crushed chest injuries d/t Paradoxical chest movements
67. Assist Control (ACMV)
Every breath delivers a preset mechanical TV (Volume Cycled) either assisted or
controlled
If Pressure/Flow triggered by Pt’s spontaneous effort = ASSIST
If Time triggered by ventilator = CONTROL (Safety Net)
Adv.: 1) Work of breathing is handled by ventilator,
2) Pt himself can control RR & therefore minute ventilation to normalize PaCO2
Disadv.: Pt with inappropriately high respiratory drive* High assist rate despite low
PaCO2 Hypocapnia & Respiratory alkalosis
Indi.= Mostly used for a pt. with stable respiratory drive to provide full ventilatory
support when pt. first placed on ventilator.
68. Intermittent Mandatory Ventilation (IMV)
Ventilator delivers control/mandatory breaths at a set time interval independent of
pt’s spontaneous respiratory rate.
Allows the pt. to breath spontaneously at any TV in b/w control breaths
Was the first widely used mode that allowed partial ventilatory support.
Disadv.: Ventilator Asynchrony, Breath Staking.
Not used nowadays
Gave birth to SIMV
69. Synchronized IMV (SIMV)
Mandatory breaths are synchronized with pt’s spontaneous breathing efforts to avoid
asynchrony.
Ventilator delivers a mandatory breath at or near the time of a spontaneous breath.
The time interval (just prior to time triggered ventilator breath) in which ventilator is
responsive to pt’s spontaneous breath is= “Synchronization Window”, usual
window is 0.5 sec*
SIMV permits the pt. to breath spontaneously to any tidal volume the pt’ desires.
The gas source for spont. breathing is supplied by “demand valve” always pt.
triggered
Spontaneous breaths taken by the pt. are TRULY SPONTANEOUS Rate & TV are
dependent on pt, humidified gas at selected FiO2 is given by ventilator.
70.
71. Synchronized IMV (SIMV)
• SIMV allows patients with an intact respiratory drive to exercise inspiratory
muscles between assisted breaths, making it useful for both supporting
and weaning intubated patients
• Indication: To provide partial ventilatory support.
• When a pt placed on ventilator Full ventilatory support is appropriate for
initial 24 hrs Then Trial of partial ventilatory support on SIMV (pt is
actively involved in providing part of minute volume) Gradually decrease
the mandatory rate as tolerated by the pt.
• Adv:
1. Maintains respiratory muscle strength/ avoids muscle atrophy
2. Reduces V/Q mismatch
3. Decreases MAP
4. FACILITATES WEANING ( Using small decrements* in
mandatory rate)
72. Mandatory Minute Ventilation (MMV)
An additional safety function of SIMV mode, that
provides a predetermined minute ventilation when
pt’s spontaneous breathing effort becomes
inadequate.
E.g. Apnea mandatory rate increased automatically to
compensate for decrease in minute ventilation caused
by apnea.
74. Artificial airways as a connection to the ventilator
Face mask : In resuscitation and for minor procedures under
anaesthesia
Tracheal intubation : often performed for mechanical ventilation of hours
to weeks duration
Supraglottic airway : a supraglottic airway (SGA) is any airway device
that is seated above and outside the trachea, as an alternative to
endotracheal intubation.
Cricothyrotomy : Patients requiring emergency airway management, in
whom tracheal intubation has been unsuccessful, may require an airway
inserted through a surgical opening in the cricothyroid membrane.
Tracheostomy : When patients require mechanical ventilation for several
weeks
Mouthpiece : Less common interface, does not provide protection
against aspiration
75. Noninvasive Positive Pressure Ventilation In Adults
INDICATIONS
At least two of the following factors should be present:
Respiratory rate >25 breaths/min
Moderate to severe acidosis: pH, 7.30 to 7.35; PaC02, 45
to 60 mm Hg
Moderate to severe dyspnea with use of accessory
muscles and paradoxical breathing pattern
76. Circumstances in Which Noninvasive Positive Pressure
Ventilation Should Be Changed to Invasive Ventilation
Respiratory arrest
Respiratory rate >35 breaths/min
Severe dyspnea with use of accessory muscles and
possibly paradoxical breathing
Life-threatening hypoxemia: Pa02 <40 mm Hg or PaO/FI02
<200
Severe acidosis (pH <7.25) and hypercapnia (PaC02 >60
mm Hg)
Somnolence, Impaired mental status
Cardiovascular complications (hypotension, shock, heart
failure)
Failure of noninvasive positive pressure ventilation
Other circumstances (e.g., metabolic abnormalities, sepsis,
pneumonia, pulmonary embolism, barotrauma, massive
pleural effusion)
77. INDICATIONS OF ACUTE RESPIRATORY FAILURE AND THE NEED FOR MECHANICAL SUPPORT IN ADULTS
CRITERIA NORMAL CRITICAL
VALUES VALUES
VENTILATION
• pH 7.35 to 7.45 <7.25
• PaCO2 (mm Hg) 35 to 45 >55 and rising
• Dead space to tidal volume 0.3 to 0.4 >0.6
ratio (VD/VT)
OXYGENATION
• PaO2 80 to 100 <70 on O2 >0.6
• Alveolar to arterial O2 3 to 30 >450 on O2
difference P(A-a)O2
• Ratio of arterial to alveolar PO2 0.75 <0.15
(PaO2/PAO2)
• PaO2/FIO2 475 <200
79. Purpose of Graphics
Graphics are waveforms that reflect the patient-ventilator
system and their interaction.
Purpose of monitoring graphics includes:
• Allows user to interpret, evaluate, and troubleshoot the
ventilator and the patient’s response to ventilator.
• Monitors the patient’s disease status (C and Raw).
• Assesses patient’s response to therapy.
• Monitors ventilator function
• Allows fine tuning of ventilator to decrease WOB, optimize
ventilation, and maximize patient comfort.
80. Types of Waveforms
Scalars: plot pressure/volume/flow against time…time is
the x axis
Loops: plot pressure/volume/flow against each
other…there is no time component
Six basic waveforms:
• Square: AKA rectangular or constant wave
• Ascending Ramp: AKA accelerating ramp
• Descending Ramp: AKA decelerating ramp
• Sinusoidal: AKA sine wave
• Exponential rising
• Exponential decaying
•Generally, the ascending/descending ramps are considered the same as the
exponential ramps.
82. Pressure/Time Scalar
•The baseline for the pressure waveform increases when PEEP is added.
•There will be a negative deflection just before the waveform with patient
triggered breaths.
5
15
No patient effort Patient effort
PEEP +5
83. Pressure/Time Scalar
•Air trapping (auto-PEEP)
•Airway Obstruction
•Bronchodilator Response
•Respiratory Mechanics (C/Raw)
•Active Exhalation
•Breath Type (Pressure vs. Volume)
•PIP, Pplat
•CPAP, PEEP
•Asynchrony
•Triggering Effort
Can be used to assess:
86. Volume/Time Scalar
The Volume waveform will generally have a “mountain
peak” appearance at the top. It may also have a plateau, or
“flattened” area at the peak of the waveform.
•There will also be a plateau if an inspiratory pause set or inspiratory hold maneuver is
applied to the breath.
88. Volume/Time Scalar
Air-Trapping or Leak
•If the exhalation side of the waveform doesn’t return to baseline, it could be from
air-trapping or there could be a leak (ETT, vent circuit, chest tube, etc.)
Loss of volume
89. Flow/Time Scalar
Auto-Peep (air trapping)
•If expiratory flow doesn’t return to baseline before the next breath starts, there’s auto-
PEEP (air trapping) present , e.g. emphysema.
Start of next breath
Expiratory flow
doesn’t return to
baseline
= Normal
90. Flow/Time Scalar
In Volume modes, the
shape of the waveform will
be square or rectangular.
This means that flow
remains constant
throughout the breath
cycle.
In Pressure modes,
(PC, PS, PRVC, VS)
the shape of the
waveform will have a
decelerating ramp flow
pattern.
91. Flow/Time Scalar
•Air trapping (auto-PEEP)
•Airway Obstruction
•Bronchodilator Response
•Active Exhalation
•Breath Type (Pressure vs. Volume)
•Flow Waveform Shape
•Inspiratory Flow
•Asynchrony
•Triggering Effort
Can be used to assess:
92. Air Trapping (auto-PEEP)
Causes:
• Insufficient expiratory time
• Early collapse of unstable alveoli/airways during exhalation
How to Identify it on the graphics
• Pressure wave: while performing an expiratory hold, the waveform rises
above baseline.
• Flow wave: the expiratory flow doesn’t return to baseline before the next
breath begins.
• Volume wave: the expiratory portion doesn’t return to baseline.
• Flow/Volume Loop: the loop doesn’t meet at the baseline
• Pressure/Volume Loop: the loop doesn’t meet at the baseline
94. Pressure/Volume Loops
Volume is plotted on the y-axis, Pressure on the x-
axis.
Inspiratory curve is upward, Expiratory curve is
downward.
Spontaneous breaths go clockwise and positive
pressure breaths go counterclockwise.
The bottom of the loop will be at the set PEEP level.
It will be at 0 if there’s no PEEP set.
If an imaginary line is drawn down the middle of
the loop, the area to the right represents inspiratory
resistance and the area to the left represents
expiratory resistance.
95. 15 305
Dynamic
Compliance
A
A = Inspiratory
Resistance/
Resistive WOB
B
Pressure/Volume Loops
(Cdyn)
•The top part of the P/V loop represents Dynamic compliance (Cdyn).
• Cdyn = Δvolume/Δpressure
500
250
B = Exp.
Resistance/
Elastic WOB
98. Pressure/Volume Loops
15 305
Airway Resistance
•As airway resistance increases, the loop will become wider.
•An increase in expiratory resistance is more commonly seen. Increased inspiratory
resistance is usually from a kinked ETT or patient biting.
500
250
102. Flow/Volume Loops
Flow is plotted on the y axis and volume on the x axis
Flow volume loops used for ventilator graphics are the same as
ones used for Pulmonary Function Testing, (usually upside
down).
Inspiration is above the horizontal line and expiration is below.
The shape of the inspiratory curve will match what’s set on the
ventilator.
The shape of the exp flow curve represents passive
exhalation…it’s long and more drawn out in patients with less
recoil.
Can be used to determine the PIF, PEF, and Vt
104. Flow/Volume Loops
•Air trapping
•Airway Obstruction
•Airway Resistance
•Bronchodilator Response
•Insp/Exp Flow
•Flow Starvation
•Leaks
•Water or Secretion accumulation
•Asynchrony
Can be used to assess:
105. 0 0
Flow/Volume Loops
•The shape of the inspiratory curve will match the flow setting on the ventilator.
106. Flow/Volume Loops
0
200 400 600
20
40
60
-20
-40
-60
Expiratory portion
of loop does not
return to starting
point, indicating a
leak.
A Leak
•If there is a leak, the loop will not meet at the starting point where inhalation starts and
exhalation ends. It can also occur with air-trapping.
= Normal
107. 0 0
Reduced
PEF“scooping”
Flow/Volume Loops
•The F-V loop appears “upside down” on most ventilators.
•The expiratory curve “scoops” with diseases with small airway obstruction (high
expiratory resistance). e.g. asthma, emphysema.
Airway Obstruction
110. Is the patient gas trapping?
expiratory flow does not return to baseline before
inspiration commences (i.e. gas is trapped in the
airways at end-expiration).
111. COMPLICATIONS OF MECHANICAL VENTILATION:
Aspiration
Tracheal stenosis, laryngeal edema
Infection
Barotrauma
Decreased cardiac output, especially with PEEP
Fluid retention
Immobility
Stress ulcer, paralytic ileus
Inadequate nutrition
113. Weaning refers to gradual reduction of ventilatory
support from a patient whose condition is improving.
114. Weaning criteria
The following criteria are recommended :
• Evidence of some reversal of the underlying cause of respiratory failure.
• Adequate oxygenation: arterial partial pressure of oxygen (Pa02) ≥ 60
mm Hg with fractional inspired oxygen (FI 02)≥ 0.4 ;
• ratio of arterial partial pressure of oxygen to fractional inspired oxygen
(Pa 02F/I02)≥ 150 to 200 mm Hg ;
• required positive end expiratory pressure (PEEP)≥ 5 to 8 cm H20 ;
• FI 02≥ 0.4 to 0.5 ;
• hydrogen ion concentration (pH)≥ 7.25.
• Hemodynamic stability ;that is, no clinically important hypotension and
no requirement for vasopressors or a requirement only for low-dose
vasopressor therapy (e.g., dopamine or dobutamine < 5μg /kg/min).
• Patient capable of initiating an inspiratory effort.
115. SPONTANEOUS BREATHING TRIAL
The best approach to determining a patient's
readiness to wean is a carefully supervised SBT. An SBT
typically is conducted when the basic assessment findings
suggest that the patient is ready to be weaned but the
clinician nonetheless is uncertain about the patient's ability
to sustain breathing without mechanical support.
116. Clinical Signs and Symptoms Indicating Problems during a
Spontaneous Breathing Trial
• Respiratory rate exceeding 30 to 35 breaths/min (clinicians
also should watch for increases of more than 10 breaths/min
or decreasing below 8 breaths/min).
• Tidal volume (VT) decreasing below 250 to 300 mL.
• Blood pressure changing significantly, as demonstrated by
-A drop of 20 mm Hg systolic or
-A rise of 30 mm Hg systolic or
-Systolic values >180 mm Hg or
-A change of 10 mm Hg diastolic (e.g., rise >90 mm Hg)
• Heart rate increasing more than 20% or exceeds 140
beats/min.
• Sudden onset of frequent premature ventricular contractions
(more than 4 to 6 per minute).
• Diaphoresis occurring.
117. Methods Of Titrating Ventilator Support During Weaning
Three approaches commonly have been used to reduce
ventilatory support :
Synchronised intermittent mandatory ventilation,
Pressure support ventilation
T-piece weaning.
118. Pressure Support Ventilation
With pressure support ventilation (PSV), the patient
controls the rate, timing, and depth of each breath i.e. PSV
is patient triggered, pressure limited, and flow cycled.
119. T-Piece Weaning
The original T-piece trial followed a schedule that
progressively increased the length of time the patient was
removed from ventilatory support.
120. When T-piece weaning is accomplished through the ventilaor,
the ventilator mode is set to spontaneous/continuous positive
airway pressure (CPAP) ; that is, the mandatory rate is
turned off. The advantage of using the ventilator is the
availability of alarms; the disadvantage is that the patient's
efforts to breathe through the ventilator system may result in
an increased workload.
122. Once the SBT is tolerated, the ability to clear secretions,
a decreasing secretion burden, and a patent upper
airway are other criteria that should be met to increase
extubation success.
Patients should be assessed daily for their readiness to
be weaned from mechanical ventilation by withdrawing
sedation and performing a spontaneous breathing trial.
123.
124. Thank you for your
patient
listening…………………
…………………………
……………….
125. Manipulations to Increase Oxygenation
Advantage Disadvantage
↑ Fio2 Minimizes barotrauma Fails to affect V/Q matching
Direct toxicity, especially >0.6
↑ PI Improves V/Q matching Barotrauma: Air leak, BPD
↑
PEEP
Maintains FRC, prevents collapse Obstructs venous return
Increases expiratory work and CO2
↑ TI Critical opening time Necessitates slower rates,
↑
Flow
maximizes MAP Greater shear force, more
barotrauma
Greater resistance at greater flows
126. Manipulations to Increase Ventilation
Advantage Disadvantage
↑ Rate Easy to titrate
Minimizes barotrauma
Maintains same dead space/TV
↑ PI
Better bulk flow (improved dead
space/TV)
More barotrauma
↓ PEEP Decreases dead space
Decreases expiratory load
Decreases MAP
Decreases oxygenation (alveolar
collapse)
Stops splinting obstructed /closed
airways
↑ Flow Permits shorter TI, longer TE More barotrauma
↑ TE
Allows longer time for passive
expiration
Shortens TI
Decreases MAP
Decreases oxygenation
127. Pressure Regulated Volume Control (PRVC)
PRVC provides volume support with the lowest possible PIP by
changing the Peak Flow & Ti
PRVC is a Dual control mode: Both TV & PIP can be controlled at
same time
Airflow resistance = PIP / Flow
At a constant flow, increased airflow resistance requires higher PIP.
PRVC lowers the flow to reduce PIP.
At a constant PIP, increased airflow resistance lowers flow. PRVC
prolongs Ti to deliver the target TV.
Works with CMV or SIMV mode
Volume cycled, Time / Pt triggered
128. Volume Ventilation Plus (VV+)
• VV+ is an option that combines two different dual mode volume
targeted breath types: VC+ and VS
a) VOLUME CONTROL PLUS (VC+):
• VC+ is used to deliver mandatory breaths during AC and SIMV
modes
• Intended to provide a higher level of synchrony than standard
volume control ventilation.
• Target TV & Ti is set Ventilator delivers a single test breath
using standard volume & flow to determine compliance Then
Target pressures for subsequent breaths are adjusted accordingly
to compensate for any TV differences
129. Volume Ventilation Plus (VV+)
b) VOLUME SUPPORT (VS):
Target TV is set and ventilator uses variable pressure support
levels to provide the target TV.
Only target TV is set (not the Ti or Mandatory Rate) ventilator
delivers a single spontaneous pressure support breath and
then uses variable pressure support levels to provide target TV.
Mandatory Rate and minute ventilation is determined by
triggering effort of the patient.
Used during “Awakening from anesthesia”
130. Airway Pressure Release Ventilation (APRV)
• Like half Filled air balloon
• Pt. is allowed to breath spontaneously at an elevated baseline (i.e. CPAP).
This elevated baseline is released periodically to facilitate expiration.
• Newer mode, indicated in patients with lower compliance e.g. ARDS in which
conventional volume controlled ventilation requires very high PIP
• APRV can provide effective partial ventilatory support with a lower PIP in
these pts.
131. High Frequency Ventilation (HFV)
• Delivers small Tidal volumes at very high rates, reduces the risk of
barotrauma.
• Limited to the situations in which conventional ventilation has failed
• Categorized by rate and the method used to deliver the TV
Type of HFV Rate per min.
HFPPV (HF Positive Pressure
Ventilation)
60 - 150
HFJV (HF Jet Ventilation) 240 - 660
HFOV (HF Oscillatory Ventilation) 480 - 1800
