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P R E S E N T E R : D R . S H A R A T H . K .
M O D E R A T O R : D R . S U J A T H A
Mechanical Ventilation
 History
 Definitions
 Parameters/Variables.
 Modes
 Trouble Shooting
Mechanical Ventilator
 A mechanical ventilator is a machine that
generates a controlled flow of gas into the patient’s
ai...
Classification
 Robert Chatburn:
 Negative Pressure Ventilators.
 Positive Pressure Ventilators.
 (according to the ma...
Negative Pressure Ventilators
 Exert a negative pressure on the external chest
 Decreasing the intrathoracic pressure du...
The Iron Lung
 The iron lung, often referred to in the early days as
the "Drinker respirator", was invented by Phillip
Dr...
Emerson Iron Lung.
Biphasic cuirass ventilation
 Biphasic cuirass ventilation (BCV) is a method
of ventilation which requires the patient to...
Disadvantages
 Complex and Cumbersome
 Difficult for transporting
 Difficult to access the patient in emergency
 Claus...
History
 Andreas Vesalius (1555)
 Vesalius is credited with the first description of positive-
pressure ventilation, but...
Important Terms:
 Peak Inspiratory Pressure
 Total Inspiratory Time
 End Expiratory Pressure
 Mean Airway Pressure
 P...
 Compliance
 Resistance
 Time Constant
 Critical Volume
Important Terms:
 Peak Inspiratory Pressure: Highest pressure during
the inspiratory phase.
 It depends upon:
 Lung- Th...
 Total Inspiratory Time=
Inspiratory time + Inspiratory Pause Time
Inspiratory Time: Time during which Tidal Volume
is de...
 End Expiratory Pressure: Pressure maintained in the
lungs during the Expiratory Phase.
 If allowed to drop to atmospher...
 Peak Airway Pressure: Maximal Airway Pressure
during any time during Inflation.
 Plateau Pressure: Measured when the ti...
 Basic Equation for Gas flow during Positive Pressure
Ventilation:
 Total Pressure Gradient
 =(Elastance x Volume) + (R...
Work of Breathing
 Work is performed whenever an applied force causes
displacement of any mass.
 Work = Mean Pressure x ...
Important Terms:
 Compliance: “Ease of Distension of Alveoli”
 Compliance = Change in Volume
 Change in Pressure
 Elas...
Compliance
 Static Compliance : Tidal Volume
 Plateau Pressure – PEEP
 Value is affected by lung and chest wall complia...
 Static Compliance: measured when the flow of air
has ceased, as during Breath holding or during
Apnoea.
 Static Complia...
 Therefore, a Volume change of 0.2 litres in the
thorax is obtained by a pressure of 1 cm of H20
exerted against the lung...
Resistance:
 It is a measure of opposition to flow, which must be
overcome to move a volume of air through the
patient’s ...
 Time Constant: it is a phenomenon, whereby a given
percentage of a passively exhaled breath of air, will
require a const...
Critical Volume
 The alveolus behaves like an elastic semi sphere and
obeys the Laplace Equation:
 Distending intra alve...
Mechanical Ventilation
 Aims:
 Restore Oxygenation
 Restore Ventilation
 Decrease work of Breathing
 Replace inadequa...
 Power : Mechanical Ventilators are powered either
by electrical energy or potential energy in
compressed air/oxygen.
 O...
Ventilation Parameters:
1) Control Variables
2) Phase Variables
3) Conditional Variables.
Ventilation Parameters:
1. Control Variables:
a) Pressure : regulates the airway pressure to be
maintained during inhalati...
2) Phase Variables:
Control the events taking place in a Ventilatory
Cycle:
a) Initiate Inflation
b) Inflation Phase
c) Cy...
 4 factors can be monitored and controlled during
any of these phases:
 a) Pressure
 b) Flow
 c) Volume
 d) Time
a) Initiate Inflation
 The ventilator can be cycled to the inspiratory phase
by:
 1) Patient Effort: Patient Triggering
...
 A) Patient effort:
 Pressure
 When the patient attempts to inhale, there occurs a
drop in baseline pressure.
 The ven...
 B) Time:
 A timing mechanism decides the changeover, and is
independent of the patient.
 It is used in:
 - Fully cont...
b) Inflation Phase:
 These may be pressure, volume or flow.
 The limit may be reached before inspiration ends
and are us...
C) Stop Inflation(inflation exhalation changeover
 Determines the termination of the inhalation phase,
can be based on:
...
 Volume Cycling: Inspiratory Phase ends when a pre-
set volume is delivered.
 Pressure Cycling: Inspiratory Phase ends w...
D) Exhalation Phase
 The only function of the ventilator in the exhalation
phase is to allow the lungs to empty.
 Exhale...
Positive End Expiratory Pressure(PEEP)
 PEEP increases the end- expiratory or baseline
airway pressure to a value greater...
Beneficial Effects of PEEP:
 1. Improves Oxygenation.
 2. Improves Lung Compliance.
 3. Reduces Dead Space.
 4. Helps ...
Indications for PEEP
1)Refractory Hypoxemia caused by intra-pulmonary
shunting.
 Refractory Hypoxemia is defined as hypox...
2) Decreased FRC and Lung Compliance.
• A severely decreased FRC and lung compliance can
increase the Alveolar Opening Pre...
Physiology of PEEP
 PEEP reinflates collapsed alveoli and maintains
alveolar inflation during exhalation.
 Once recruitm...
 Normally, the alveolar end-expiratory pressure
equilibrates with atmospheric pressure (zero
pressure)
 The average pleu...
 PEEP
INCREASE IN ALVEOLAR DISTENDING PRESSURE
•
INCREASES FRC BY ALVEOLAR RECRUITMENT

 Improves Ventilation

Increases V/Q
Improves Oxygenation
Decreases work of breathing.
Disadvantages of PEEP:
 1) Barotrauma
 2) Increase in total lung water: Due to increase in
pulmonary venous and lymphati...
Auto PEEP
 The Physiological Manifestation of Hyperinflation
from air trapping is called Intrinsic PEEP.
 IN this condit...
Effects of Auto- PEEP
 Reduced Venous Return:
 (reduced cardiac output, diminished perfusion of
respiratory muscles, and...
C/F of Auto PEEP
 Hypotension
 Tachycardia
 Reduced Breath Sounds.
 Increased work of Breathing.
 ON the Ventilator:
...
 3) Conditional Variables ( Modes of Ventilation)
 This refers to the pattern of interaction between the
patient and the...
Controlling influence:
 Pacing Mechanism: Deciding the Respiratory Rate.
 Powering Mechanism: Determining the tidal
Volu...
Modes of Ventilation
 A ventilator mode can be defined as a set of
operating characteristics that control how the
ventila...
Modes:
 Spontaneous
 Controlled Ventilation
 Pressure Controlled Ventilation
 Assisted Ventilation
 Intermittent Mand...
 Closed Loop Ventilation
 Airway Pressure Release Ventilation
 BiPAP
 DuoPAP and APRV
 Pressure Regulated Volume Cont...
Spontaneous
 Rate and tidal volume are determined by the patient.
 Role of the Ventilator:
1) Provide inspiratory flow t...
Controlled Ventilation (CMV):
 Rate and tidal volume is controlled by the machine.
 Can be given as VOLUME CONTROL or PR...
Pressure Control Ventilation
 In PCV The pressure- controlled breaths are time
triggered by a preset respiratory rate.
 ...
 In pressure support, the plateau pressure is
maintained as long as the patient maintains a
spontaneous inspiratory flow....
Assisted Ventilation
 Rate is controlled by the patient but the tidal volume
is delivered by the machine.
 ASSIST CONTRO...
Intermittent Mandatory Ventilation:
 The patient is allowed to breathe spontaneously with
no machine assistance but the m...
Synchronised intermittent mandatory ventilation
(SIMV)
 Advantages:
 Maintains respiratory muscle strength/ avoids
muscl...
Pressure Support Ventilation
 Pressure Support Ventilation is used to lower the work of
spontaneous breathing and augment...
 PSV is patient triggered, pressure limited and flow
cycled.
 PS is used in SIMV mode in order to wean the
patient by:
1...
PRESSURE CONTROLLED INVERSE RATIO
VENTILATION
 It is a version of pressure controlled – CMV in which all
breaths are pres...
Volume Guaranteed Pressure Support- VSV
 Volume Support Ventilation
 The pressure support is continuously adjusted to
de...
Closed Loop Ventilation
 The Goal is to automatically adjust the ventilator
support according to the patients ventilator ...
Proportional Assist Ventilation (PAV)
 This is a pressure regulated ventilator mode in which
the inspiratory airway press...
 Unlike traditional modes, PAV changes with the
patient’s breathing effort.
 Advantage: It can track changes in breathin...
Neurally Adapted Ventilatory Assistance (NAVA)
 New mode of Mechanical Ventilation that delivers
ventilatory assist in pr...
Knowledge based weaning System (KBW)
 Adjustments are made real time to adjust pressure
support ventilation in order to m...
Adaptive Support Ventilation (ASV)
 Similar to Mandatory Minute Ventilation
(MMV),where a set proportion of the minute
ve...
 ASV always maintains control of ventilation volume
and guarantees:
 A minimum minute ventilation set by the user.
 An ...
Basic Principles of ASV:
 Pressure controlled SIMV is employed, but with
automatically adjusted pressure levels and SIMV ...
 The ventilator uses test breaths to measure the
system compliance, airway resistance, and any
intrinsic PEEP.
 Followin...
Airway Pressure Release Ventilation (APRV)
 In this mode, there are two levels of positive airway
pressure applied for se...
Airway Pressure Release Ventilation(APRV)
 It is similar to CPAP in that the patient is allowed to
breathe spontaneously ...
BiPAP
 Of value in preventing intubation of the end stage
COPD patient.
 Other indications:
 Patients with restrictive ...
BiPAP
 If the patient is breathing spontaneously, the IPAP
and EPAP may be set at 8 cm H20 and 4 cm H2o
respectively.
 S...
 The spontaneous breaths are triggered, limited,
controlled and cycled by pressure.
 Mandatory breathes are pressure con...
DuoPAP and APRV
 Two modes of pressure ventilation.
 These modes support spontaneous breathing at two
operator selected ...
 In DuoPAP, the switchover between the two levels
depends on the set respiratory rate and the time
setting for T(high). T...
Pressure Regulated Volume Controlled
 This mode is a form of closed loop ventilation
 Combines features of volume & pres...
 Increased Airflow resistance (non elastic/elastic)=
Increased PIP/ Flow
 Increased Airflow resistance (non elastic/elas...
Mandatory Minute Ventilation (MMV)
 A.k.a Minimum minute ventilation.
 Provides a predetermined minute ventilation when
...
Volume Assured Pressure Support (VAPS)
 Incorporates inspiratory pressure support
ventilation (PSV) with conventional vol...
 The delivered volume is then compared with the
preset volume for further action by the ventilator.
Setting the Ventilator:
 A) Does the patient need Full Ventilatory Support
(FVS) or Partial Ventilatory Support (PVS)
 B...
 C) Adjust settings for PaCO2- pH.
 Tidal Volume of about 6-7 ml/kg and adjust to keep:
 PaCO2 30-50 mm Hg.
 PaCO2 28-...
 IN the ARDS Network Study on Low Tidal Volume,
the Tidal Volume was calculated on the basis of a
predicted body weight b...
 D) Respiratory Rate: Depending on Patient’s age.
 E) Mode Of Ventilation.
 Commonly used mode is SIMV with pressure
su...
Approach to High Airway Pressures:
 A) Ventilator and Pneumatic Circuit.
 High Tidal Volumes.
 High Flow, Low Inspirato...
 B) Airway: ETT/ Tracheostomy Tube.
 Displaced tube- Bronchial intubation.
 Kinked ET tube.
 Obstructed Tube- Clot, mu...
 C) Patient:
 Biting ET tube.
 Cough
 Dysynchrony
 Pathology in airway (bronchospasm), Parenchyma
(reduced compliance...
Monitoring the ventilated Patient.
 Mandatory
 Continuous rhythm with ECG
 Continuous BP with arterial line
 Venous pr...
Troubleshooting.
References:
 Clinical Application of Mechanical Ventilation. 3rd
edition. David W. Chang.
 Critical Care Manual. Christi...
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
Mechanical ventilation sharath
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  1. 1. P R E S E N T E R : D R . S H A R A T H . K . M O D E R A T O R : D R . S U J A T H A Mechanical Ventilation
  2. 2.  History  Definitions  Parameters/Variables.  Modes  Trouble Shooting
  3. 3. Mechanical Ventilator  A mechanical ventilator is a machine that generates a controlled flow of gas into the patient’s airway, to support the ventilatory function of the respiratory system and improves oxygenation, through application of high oxygen content and a positive pressure.
  4. 4. Classification  Robert Chatburn:  Negative Pressure Ventilators.  Positive Pressure Ventilators.  (according to the manner in which they support ventilation)
  5. 5. 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 assisted ventilation is similar to spontaneous ventilation  It is used mainly in chronic respiratory failure associated with neuromascular conditions such as poliomyleitis, muscular dystrophy, amyotrophic lateral sclerosis, and mysthenia gravis.
  6. 6. The Iron Lung  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
  7. 7. Emerson Iron Lung.
  8. 8. Biphasic cuirass ventilation  Biphasic cuirass ventilation (BCV) is a method of ventilation which requires the patient to wear an upper body shell or cuirass, so named after the body armour worn by medieval soldiers.  The ventilation is biphasic because the cuirass is attached to a pump which actively controls both the inspiratory and expiratory phases of the respiratory cycle .
  9. 9. Disadvantages  Complex and Cumbersome  Difficult for transporting  Difficult to access the patient in emergency  Claustrophobic
  10. 10. History  Andreas Vesalius (1555)  Vesalius is credited with the first description of positive- pressure ventilation, but it took 400 years to apply his concept to patient care. The occasion was the polio epidemic of 1955, when the demand for assisted ventilation outgrew the supply of negative-pressure tank ventilators (known as iron lungs).  In Sweden, all medical schools shut down and medical students worked in 8-hour shifts as human ventilators, manually inflating the lungs of afflicted patients.  Invasive ventilation first used at Massachusetts General Hospital in 1955.  Thus began the era of positive-pressure mechanical ventilation (and the era of intensive care medicine).
  11. 11. Important Terms:  Peak Inspiratory Pressure  Total Inspiratory Time  End Expiratory Pressure  Mean Airway Pressure  Peak Airway Pressure  Plateau Pressure  Basic Equation for Gas Flow
  12. 12.  Compliance  Resistance  Time Constant  Critical Volume
  13. 13. Important Terms:  Peak Inspiratory Pressure: Highest pressure during the inspiratory phase.  It depends upon:  Lung- Thoracic wall compliance.  Airway Resistance.  Delivered Tidal Volume  Inspiratory Flow Rate  End Expiratory Pressure (PEEP)  Work of Breathing
  14. 14.  Total Inspiratory Time= Inspiratory time + Inspiratory Pause Time Inspiratory Time: Time during which Tidal Volume is delivered. Inspiratory Pause time: Time during which Gas is allowed to distribute from Upper to Lower Airways.
  15. 15.  End Expiratory Pressure: Pressure maintained in the lungs during the Expiratory Phase.  If allowed to drop to atmospheric pressure: it is known as ZEEP (Zero End Expiratory Pressure)  Negative: NEEP ( Not used any more)  Positive: PEEP ( Used Commonly)  Mean Airway Pressure: Pressure during one Respiratory Cycle.
  16. 16.  Peak Airway Pressure: Maximal Airway Pressure during any time during Inflation.  Plateau Pressure: Measured when the tidal inflation volume is held in the lungs after the end of inflation, preventing the lungs from deflating.  End expiratory Pressure is set by the presence or absence of special devices.
  17. 17.  Basic Equation for Gas flow during Positive Pressure Ventilation:  Total Pressure Gradient  =(Elastance x Volume) + (Resistance x Flow)  = (Positive Pressure Generated by the Ventilator) – (Negative pleural Pressure generated by inspiratory muscles)
  18. 18. Work of Breathing  Work is performed whenever an applied force causes displacement of any mass.  Work = Mean Pressure x Volume Change (Area under the Pressure-Volume curve) Work is done by overcoming:  Compliance of Lung and Thoracic Cage.  Resistance of airways.  Frictional Resistance of Tissues  Inertia.
  19. 19. Important Terms:  Compliance: “Ease of Distension of Alveoli”  Compliance = Change in Volume  Change in Pressure  Elastance: Ability of the lung parenchyma to return to its original form after being stretched.  Elastance = Change in Pressure  Change in Volume
  20. 20. Compliance  Static Compliance : Tidal Volume  Plateau Pressure – PEEP  Value is affected by lung and chest wall compliance.  Dynamic Compliance : Tidal Volume  Peak Pressure – PEEP  Value is affected by Airway Resistance and Static Compliance.
  21. 21.  Static Compliance: measured when the flow of air has ceased, as during Breath holding or during Apnoea.  Static Compliance= ∆Volume in Litres ∆ Pressure in cm of H20 (kPascals)  Compliance of lungs: 0.2 litres/cm of H20 (2.0 L/kPa)  Compliance of Thoracic Wall: 0.2 Litres/cm of H20.
  22. 22.  Therefore, a Volume change of 0.2 litres in the thorax is obtained by a pressure of 1 cm of H20 exerted against the lungs in conjunction with a pressure of 1 cm of H20 against the Thoracic wall, giving a total Thoracic Compliance of 0.1 litre/cm of H20.  = 0.2 = 0.1 litre/cm of H20  1+1
  23. 23. Resistance:  It is a measure of opposition to flow, which must be overcome to move a volume of air through the patient’s conducting airways in a unit of time.  Flow Rate = Tidal Volume ( L/sec)  Inspiratory time  Resistance = P Peak – P Plateau (cmH20/L/sec) Flow Rate Normal: 0.6-2.4 cm H2o/L/sec.
  24. 24.  Time Constant: it is a phenomenon, whereby a given percentage of a passively exhaled breath of air, will require a constant amount of time, to be exhaled, regardless of the starting volume. (with constant lung mechanics)  Time Constant = Resistance x Compliance
  25. 25. Critical Volume  The alveolus behaves like an elastic semi sphere and obeys the Laplace Equation:  Distending intra alveolar pressure =  2 x Surface tension of air liquid interface  Radius of alveolus
  26. 26. Mechanical Ventilation  Aims:  Restore Oxygenation  Restore Ventilation  Decrease work of Breathing  Replace inadequate respiratory drive due to central nervous system dysfunction.
  27. 27.  Power : Mechanical Ventilators are powered either by electrical energy or potential energy in compressed air/oxygen.  Oxygen Blender: Oxygen blenders need an input of air and oxygen to blend it to deliver the mixture at the set FiO2.
  28. 28. Ventilation Parameters: 1) Control Variables 2) Phase Variables 3) Conditional Variables.
  29. 29. Ventilation Parameters: 1. Control Variables: a) Pressure : regulates the airway pressure to be maintained during inhalation.  b) Volume and Flow:  Volume= Flow x Inspiratory time  c) Time.  Used to control set pressure for a prescribed time.
  30. 30. 2) Phase Variables: Control the events taking place in a Ventilatory Cycle: a) Initiate Inflation b) Inflation Phase c) Cycle to Exhalation d) Exhalation.
  31. 31.  4 factors can be monitored and controlled during any of these phases:  a) Pressure  b) Flow  c) Volume  d) Time
  32. 32. a) Initiate Inflation  The ventilator can be cycled to the inspiratory phase by:  1) Patient Effort: Patient Triggering  2) After a predetermined time: Time Triggering.  3) Manually : Manual Triggering.
  33. 33.  A) Patient effort:  Pressure  When the patient attempts to inhale, there occurs a drop in baseline pressure.  The ventilator senses the drop in pressure.  Flow:  The patient’s inspiratory effort causes a decrease in the baseline flow through the circuit.
  34. 34.  B) Time:  A timing mechanism decides the changeover, and is independent of the patient.  It is used in:  - Fully controlled ventilation  - back up safety system in case the patient fails to trigger inspiration.
  35. 35. b) Inflation Phase:  These may be pressure, volume or flow.  The limit may be reached before inspiration ends and are used as limiting variables.  The time period between the end of inspiration and the start of exhalation is the inspiratory pause time.
  36. 36. C) Stop Inflation(inflation exhalation changeover  Determines the termination of the inhalation phase, can be based on:  Volume  Pressure  Time  Flow.
  37. 37.  Volume Cycling: Inspiratory Phase ends when a pre- set volume is delivered.  Pressure Cycling: Inspiratory Phase ends when the pressure reaches a pre-set value.  Time Cycling: Cycling occurs when the Pre-set inspiratory time is completed.
  38. 38. D) Exhalation Phase  The only function of the ventilator in the exhalation phase is to allow the lungs to empty.  Exhaled volumes may be measured by the lungs during this phase.  Exhalation can be to:  - Atmospheric Pressure ( ZEEP)  - Sub Atmospheric Pressure (NEEP)  - Above Atmospheric Pressure (PEEP)
  39. 39. Positive End Expiratory Pressure(PEEP)  PEEP increases the end- expiratory or baseline airway pressure to a value greater than atmospheric (0 cm H2o on the ventilatory manometer)  It is often used to improve the patient’s oxygenation status, especially in hypoxemia that is refractory to high level of Fio2.
  40. 40. Beneficial Effects of PEEP:  1. Improves Oxygenation.  2. Improves Lung Compliance.  3. Reduces Dead Space.  4. Helps to keep alveoli open in those with High Closing volumes.  5. Decreases Work of Breathing.  6. Effect on Cardiovascular Function.
  41. 41. Indications for PEEP 1)Refractory Hypoxemia caused by intra-pulmonary shunting.  Refractory Hypoxemia is defined as hypoxemia that responds poorly to moderate to high levels of oxygen.  May be caused by reduction of Functional Residual Capacity, Atelectasis, or Low V/Q mismatch.
  42. 42. 2) Decreased FRC and Lung Compliance. • A severely decreased FRC and lung compliance can increase the Alveolar Opening Pressure. • This increases the work of breathing, and can lead to fatigue of respiratory muscles. • PEEP increases the FRC.
  43. 43. Physiology of PEEP  PEEP reinflates collapsed alveoli and maintains alveolar inflation during exhalation.  Once recruitment of these alveoli occcurs, PEEP lowers the alveolar distending pressure and facilitates gas diffusion and oxygenation.
  44. 44.  Normally, the alveolar end-expiratory pressure equilibrates with atmospheric pressure (zero pressure)  The average pleural pressure is approximately -5 cm of H20.  The alveolar distending pressure is 5 cm of H20.  This distending pressure is sufficient to maintain a normal end-expiratory alveolar volume to overcome the elastic recoil of the alveolar wall.
  45. 45.  PEEP INCREASE IN ALVEOLAR DISTENDING PRESSURE • INCREASES FRC BY ALVEOLAR RECRUITMENT
  46. 46.   Improves Ventilation  Increases V/Q Improves Oxygenation Decreases work of breathing.
  47. 47. Disadvantages of PEEP:  1) Barotrauma  2) Increase in total lung water: Due to increase in pulmonary venous and lymphatic pressures.  3) Reduction in Cardiac Output and O2 Delivery: Due to reduced Venous Return, Raised Pulmonary Vascular Resistance and RV dilatation.  4) Organ Perfusion:  PEEP increases Cerebral Venous Pressures: Increases ICP  Renal: ADH levels increase. Reduced Urine Output.  Hepatic: Elevated Intra thoracic pressure, can lead to decreased Hepatic Venous return > Hepatic Congestion.
  48. 48. Auto PEEP  The Physiological Manifestation of Hyperinflation from air trapping is called Intrinsic PEEP.  IN this condition, the end expiratory pressure remains positive even in the absence of external PEEP.  It can occur due to:  Abnormal respiratory mechanics of the patient.  Inappropriate ventilatory settings.
  49. 49. Effects of Auto- PEEP  Reduced Venous Return:  (reduced cardiac output, diminished perfusion of respiratory muscles, and respiratory muscle fatigue)  Increases the work of breathing  Incorrect interpretation of CVP and Wedge Pressures.
  50. 50. C/F of Auto PEEP  Hypotension  Tachycardia  Reduced Breath Sounds.  Increased work of Breathing.  ON the Ventilator:  High Peak- Plateau Difference of Airway Pressure.  Increasing Plateau Pressure.
  51. 51.  3) Conditional Variables ( Modes of Ventilation)  This refers to the pattern of interaction between the patient and the machine.  Terms:  Spontaneous Breath: one which is initiated and terminated by the patient.  Mandatory Breath: one in which the ventilator determines the start or end of inspiration  A mandatory breath which is patient triggered is called Assisted Breath.
  52. 52. Controlling influence:  Pacing Mechanism: Deciding the Respiratory Rate.  Powering Mechanism: Determining the tidal Volume.  Spontaneous Ventilation: Both rate and tidal volume are controlled by the patient.  CPAP: Spontaneous Ventilation with the addition of PEEP.
  53. 53. Modes of Ventilation  A ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions.
  54. 54. Modes:  Spontaneous  Controlled Ventilation  Pressure Controlled Ventilation  Assisted Ventilation  Intermittent Mandatory Ventilation.  Synchronised Intermittent Mandatory Ventilation  Pressure Support Ventilation  Pressure Controlled Inverse Ratio Ventilation  Volume Guaranteed Pressure Support Ventilation
  55. 55.  Closed Loop Ventilation  Airway Pressure Release Ventilation  BiPAP  DuoPAP and APRV  Pressure Regulated Volume Control.  Mandatory Minute Ventilation.  Volume Assured Pressure Support
  56. 56. Spontaneous  Rate and tidal volume are determined by the patient.  Role of the Ventilator: 1) Provide inspiratory flow to the patient in a timely manner. 2) Provide flow adequate to fulfill a patient’s inspiratory demand (tidal volume or inspiratory flow) 3) Provide adjunctive modes such as PEEP to complement a patient’s spontaneous breathing effort.
  57. 57. Controlled Ventilation (CMV):  Rate and tidal volume is controlled by the machine.  Can be given as VOLUME CONTROL or PRESSURE CONTROL.  Continuous positive airway pressure (CPAP) refers to the addition of a fixed amount of positive airway pressure to spontaneous respirations, in the presence or absence of an endotracheal tube.
  58. 58. Pressure Control Ventilation  In PCV The pressure- controlled breaths are time triggered by a preset respiratory rate.  Once inspiration begins, a pressure plateau is created and maintained for a preset inspiratory time.  Pressure-controlled breaths are therefore time triggered, pressure limited and time cycled.
  59. 59.  In pressure support, the plateau pressure is maintained as long as the patient maintains a spontaneous inspiratory flow.  In pressure control, the pressure plateau is maintained for a preset inspiratory time.  PC, is usually indicated for patients with severe ARDS who require extremely high peak inspiratory pressures during mechanical ventilation in a volume cycled mode.  They have a higher incidence of barotrauma.
  60. 60. Assisted Ventilation  Rate is controlled by the patient but the tidal volume is delivered by the machine.  ASSIST CONTROL VENTILATION: The patient can breathe at his own rate assisted by the machine but in addition the machine delivers a minimum set number of controlled breaths at the rate set on the machines.
  61. 61. Intermittent Mandatory Ventilation:  The patient is allowed to breathe spontaneously with no machine assistance but the machine delivers a minimum set rate and tidal volume. Breath Stacking occurs.  SIMV: Similar to IMV, but breath stacking is avoided by synchronising the mandatory breath delivered by the machine to the patient’s inspiratory effort. i.e. the mandatory breath is triggered by the patient.
  62. 62. Synchronised intermittent mandatory ventilation (SIMV)  Advantages:  Maintains respiratory muscle strength/ avoids muscle atrophy.  Reduces ventilation to perfusion mismatch.  Decreases mean airway pressure.  Facilitates weaning.
  63. 63. Pressure Support Ventilation  Pressure Support Ventilation is used to lower the work of spontaneous breathing and augment a patient’s spontaneous tidal volume.  PSV applies a preset pressure plateau to the patient’s airway for the duration of a spontaneous breath.  PSV is considered spontaneous because: 1) They are patient triggered. 2) The tidal volume varies with the patient’s inspiratory flow demand. 3) Inspiration lasts only for as long as the patient actively inspires. 4) Inspiration is terminated when the patient’s inspiratory flow demand decreases to a preset minimum value.
  64. 64.  PSV is patient triggered, pressure limited and flow cycled.  PS is used in SIMV mode in order to wean the patient by: 1) Increasing the patient’s spontaneous tidal volume. 2) Decreases the patients spontaneous respiratory rate. 3) Decreases the work of breathing.
  65. 65. PRESSURE CONTROLLED INVERSE RATIO VENTILATION  It is a version of pressure controlled – CMV in which all breaths are pressure limited and time cycled and the patient cannot trigger a breath.  Net effects of inverse I:E ratio are: 1. Increase in Mean airway pressure (MAP) without increasing peak pressure despite a constant tidal volume and PEEP. 2. Improved ventilation of alveoli which have longer time constants for expansion. 3. Build up of intrinsic PEEP, as the tidal volume cannot be exhaled before the inspiration begins thus avoiding end expiratory collapse of the alveoli with long time constants.
  66. 66. Volume Guaranteed Pressure Support- VSV  Volume Support Ventilation  The pressure support is continuously adjusted to deliver a preset tidal volume.
  67. 67. Closed Loop Ventilation  The Goal is to automatically adjust the ventilator support according to the patients ventilator demand and changes in respiratory mechanics.  This is done by utilizing appropriate software.  The following closed loop systems are commercially available: 1) Proportional Assist Ventilation (PAV) 2) Neurally Adapted Ventilatory Assistance (NAVA) 3) Knowledge based weaning systems (KBW) 4) Adaptive Support Ventilation (ASV)
  68. 68. Proportional Assist Ventilation (PAV)  This is a pressure regulated ventilator mode in which the inspiratory airway pressure with each breath is titrated by the ventilator in proportion to the patient’s inspiratory airflow.  In PAV, there is no target flow, volume or pressure during mechanical ventilation.  The pressure used to provide the pressure support is variable and is in proportion to the patient’s pulmonary characteristics (elastance and airflow resistance) and demand (volume or flow)
  69. 69.  Unlike traditional modes, PAV changes with the patient’s breathing effort.  Advantage: It can track changes in breathing effort over time.  By varying the pressure to augment flow and volume, a more uniform breathing pattern becomes possible.  When PAV is used with CPAP, reduction of inspiratory work occurs and reaches values close to those in normal subjects.
  70. 70. Neurally Adapted Ventilatory Assistance (NAVA)  New mode of Mechanical Ventilation that delivers ventilatory assist in proportion to the electrical activity of the diaphragm.  An Oesophageal catheter is inserted to obtain a diaphragmatic EMG in order to achieve better patient-ventilator synchrony.
  71. 71. Knowledge based weaning System (KBW)  Adjustments are made real time to adjust pressure support ventilation in order to maintain  respiratory rate,  tidal volume and  end tidal CO2 within a predefined range.  At a minimal level of pressure support, a trial of spontaneous breathing is analysed and if successful, a suggestion is made to discontinue ventilation.
  72. 72. Adaptive Support Ventilation (ASV)  Similar to Mandatory Minute Ventilation (MMV),where a set proportion of the minute ventilation is delivered by the machine and the rest is by the patient.  It switches automatically from a PCV-like behaviour to an SIMV-like or PSV like behaviour, according to the patient’s status.
  73. 73.  ASV always maintains control of ventilation volume and guarantees:  A minimum minute ventilation set by the user.  An effective tidal volume, well above the theoretical dead space of the patient.  A minimal breath rate.
  74. 74. Basic Principles of ASV:  Pressure controlled SIMV is employed, but with automatically adjusted pressure levels and SIMV rate based on measured lung mechanics. Adjustments are made with each breath. User sets: 1. Ideal body weight (IBW) 2. Minimum Minute Ventilation 3. FiO2 4. PEEP 5. Trigger sensitivity.
  75. 75.  The ventilator uses test breaths to measure the system compliance, airway resistance, and any intrinsic PEEP.  Following determination of these variables, the ventilator selects and provides the frequency, inspiratory time, I:E ratio, and high pressure limit for mandatory and spontaneous breaths.
  76. 76. Airway Pressure Release Ventilation (APRV)  In this mode, there are two levels of positive airway pressure applied for set time periods and spontaneous breathing is possible at both levels.  Mandatory breaths can be set and occurs when the pressure increases from the lower to the higher pressure.  It can be conceptualized as two levels of CPAP.  Also called BiPAP.
  77. 77. Airway Pressure Release Ventilation(APRV)  It is similar to CPAP in that the patient is allowed to breathe spontaneously without restriction.  During spontaneous exhalation, the PEEP is dropped.(released) to a lower level and this action simulates an effective exhalation manouvre.
  78. 78. BiPAP  Of value in preventing intubation of the end stage COPD patient.  Other indications:  Patients with restrictive chest wall disease.  Neuromuscular disease.  Nocturnal hypoventilation.
  79. 79. BiPAP  If the patient is breathing spontaneously, the IPAP and EPAP may be set at 8 cm H20 and 4 cm H2o respectively.  Spontaneous/Timed mode: Breaths per min. is set 2- 5 breaths below the patient’s spontaneous rate.  Timed mode: BPM is set slightly higher than the patient’s spontaneous rate.
  80. 80.  The spontaneous breaths are triggered, limited, controlled and cycled by pressure.  Mandatory breathes are pressure controlled and pressure limited but time triggered and time cycled.
  81. 81. DuoPAP and APRV  Two modes of pressure ventilation.  These modes support spontaneous breathing at two operator selected levels of positive airway pressure.  They can combine spontaneous and mandatory breaths.  The spontaneous breaths can be pressure supported.  Cycling between the two levels can be triggered by time or patient effort.  The two modes differ in the operator settings determining the pattern of breaths.
  82. 82.  In DuoPAP, the switchover between the two levels depends on the set respiratory rate and the time setting for T(high). The two pressure levels are set by P(high) and PEEP.  The baseline pressure is the PEEP pressure.  In APRV, the switchover is decided by the time settings T(high) and T(low) and pressure settings by the P(high) and P(low).  The Baseline pressure is P(low) pressure.
  83. 83. Pressure Regulated Volume Controlled  This mode is a form of closed loop ventilation  Combines features of volume & pressure ventilation  It is used primarily to achieve volume support while keeping the peak inspiratory pressure (PIP) at lowest level possible.  This is achieved by altering the peak flow and inspiratory time in response to changing airway or compliance characteristics.  First test breath is delivered to calculate compliance
  84. 84.  Increased Airflow resistance (non elastic/elastic)= Increased PIP/ Flow  Increased Airflow resistance (non elastic/elastic)= PIP/ Decresed Flow.
  85. 85. Mandatory Minute Ventilation (MMV)  A.k.a Minimum minute ventilation.  Provides a predetermined minute ventilation when the patient’s spontaneous breathing effort becomes inadequate.  For eg.: an apnoea episode may cause the actual minute ventilation to fall below a preset level.  When this occurs, the mandatory rate is increased automatically to compensate for the decrease in minute ventilation caused by the apnoea.
  86. 86. Volume Assured Pressure Support (VAPS)  Incorporates inspiratory pressure support ventilation (PSV) with conventional volume-assisted cycles.  In VAPS, the therapist must preset the desired minimum tidal volume and the pressure support level.  During VAPS, the mechanical breaths may be patient or time triggered.  Once a breath is triggered, the ventilator tries to reach the pressure support level as soon as possible.
  87. 87.  The delivered volume is then compared with the preset volume for further action by the ventilator.
  88. 88. Setting the Ventilator:  A) Does the patient need Full Ventilatory Support (FVS) or Partial Ventilatory Support (PVS)  B) Adjust settings for PaO2.  FiO2, start at 100% O2 and reduce to maintain PaO2 >60 mm Hg.  PEEP, start at 5 cm H2O and adjust.
  89. 89.  C) Adjust settings for PaCO2- pH.  Tidal Volume of about 6-7 ml/kg and adjust to keep:  PaCO2 30-50 mm Hg.  PaCO2 28-32 mm Hg on those with raised intracranial pressure.
  90. 90.  IN the ARDS Network Study on Low Tidal Volume, the Tidal Volume was calculated on the basis of a predicted body weight based on the fact that normal lung volumes depend on the height and weight of the patient. The formula used were:  Men: Predicted Weight: 50 + 0.91( Ht- 152.4)  Women: Predicted Weight: 45.5 + 0.91( Ht- 152.4)
  91. 91.  D) Respiratory Rate: Depending on Patient’s age.  E) Mode Of Ventilation.  Commonly used mode is SIMV with pressure support.  F) Alarm Settings:  Settings for High Pressure, Low Pressure (Disconnection), Apnoea and other alarms must be set.  Too many alarms cause “Alarm Fatigue” in ICU personnel.
  92. 92. Approach to High Airway Pressures:  A) Ventilator and Pneumatic Circuit.  High Tidal Volumes.  High Flow, Low Inspiratory Time, Inverse I:E Ratio.  Fluid in Circuit/Filter, Blocked FIlter, Kinked Circuit.
  93. 93.  B) Airway: ETT/ Tracheostomy Tube.  Displaced tube- Bronchial intubation.  Kinked ET tube.  Obstructed Tube- Clot, mucus, foreign body  Cuff Herniation
  94. 94.  C) Patient:  Biting ET tube.  Cough  Dysynchrony  Pathology in airway (bronchospasm), Parenchyma (reduced compliance)  Pleura (air/fluid)  Ascites, elevated intra abdominal pressure.  Increased muscle tension- tetanus, seizures.
  95. 95. Monitoring the ventilated Patient.  Mandatory  Continuous rhythm with ECG  Continuous BP with arterial line  Venous pressure with CVP line  Hourly u/o & daily fluid balance  12 hourly ABG  Daily X ray chest  Daily haematology & biochemistry
  96. 96. Troubleshooting.
  97. 97. References:  Clinical Application of Mechanical Ventilation. 3rd edition. David W. Chang.  Critical Care Manual. Christian Medical College, Vellore.  Wylie and Churchill-Davidson’s: A practice of Anaesthesia. 5th Edition  Wikipaedia. (world wide web)
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