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Physiology of positive
pressure ventilation
SAMIR EL ANSARY
Global Critical Care
https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512
9555/
Wellcome in our new gro...
Mechanical ventilation –
Supports / replaces the normal ventilatory
pump moving air in & out of the lungs.
Primary indicat...
Goals
 Manipulate gas exchange
↑ lung vol – FRC, end insp / exp lung
inflation
Manipulate work of breathing (WOB)
Mini...
ARTIFICIAL
VENTILATION
- Creates a transairway P
gradient by ↓ alveolar P
to a level below airway
opening P
- Creates – P ...
ventilation without artificial airway
-Nasal , face mask
adv.
1.Avoid intubation / c/c
2.Preserve natural airway defences
...
Ventilatory support
FULL PARTIAL
All energy provided by ventilator
e.g. ACV / full support SIMV ( RR
= 12-26 & TV = 8-10 m...
Understanding physiology of PPV
1) Different P gradients
2) Time constant
3) Airway P ( peak, plateau, mean )
4) PEEP and ...
Pressure gradients
Distending pressure of lungs
Elastance load
Resistance load
Distending
pressure
Flow through the airways is generated by
Transairway pressure (pressure at the airway
opening minus pressure in the lungs)...
Transrespiratory pressure (pressure at the airway
opening minus pressure on the body surface) is the
sum of these two pres...
Trans pulmonary pressure (pressure at airway opening
minus pleural pressure) [= Transrespiratory pressure?]
Transpulmonary...
Pressure, volume, and flow are functions of time
and are called variables. They are all measured
relative to their values ...
Elastance(measure of stiffness) is
the inverse of compliance(measure
of stretchiness)
An increase in elastance implies
tha...
Mean airway pressure Paw = Transrespiratory
pressure
Mean alveolar pressure Palv = Transthoracic
pressure
Transpulmonary pressure is the distending
pressure in a spontaneously(negative)
breathing patient
Transrespiratory pressur...
Airway pressures
Peak insp P (PIP)
• Highest P produced
during insp.
• PRESISTANCE + P INFLATE
ALVEOLI
• Dynamic complianc...
Time constant
• Defined for variables that undergo exponential
decay
• Time for passive inflation / deflation of lung / un...
Why and how to separate dynamic
& static components ?
• Why – to find cause for altered airway
pressures
• How – adding en...
How -End inspiratory hold
• Pendelluft phenomenon
• Visco-elastic properties of lung
End-inspiratory pause
Ppeak < 50 cm H...
At the start of inflation, the airway pressure
immediately rises because of the resistance to gas flow
(A), and at the end...
P2(Pplat) is the static pressure of the respiratory
system, which in the absence of flow equals the
alveolar pressure, whi...
The slow post-occlusion decay from P1 to P2 depends
on the viscoelastic properties of the system and on the
pendulum-like ...
The lung regions that have a low time constant (ie,
rapid zones), where the alveolar pressure rises rapidly,
are emptied i...
The static compliance of the respiratory
system mirrors the elastic features of the respiratory
system, whereas
The dynami...
When the inspiratory pause is shorter than 2 seconds,
P2 does not always reflect the alveolar pressure.
The compliance val...
Ppeak < 50 cm H2O; Pplat
< 35 cm H2O – to avoid
barotrauma
• Pendulum like movement of air between lung units
• Reflects inhomogeneity of lung units
• More in ARDS and COPD
• Can le...
Why
Mean airway P (MAP)
• average P across total cycle time (TCT)
• MAP = 0.5(PIP-PEEP)X Ti/TCT + PEEP
• Decreases as spontane...
PEEP
BENEFITS
1. Restore FRC/
Alveolar recruitment
2. ↓ shunt fraction
3. ↑Lung compliance
4. ↓WOB
5. ↑PaO2 for given FiO2...
How much PEEP to apply?
Lower inflection point – transition from flat to steep part
- ↑compliance
- recruitment begins (pt...
Set PEEP above LIP – Prevent end expiratory airway collapse
Set TV so that total P < UIP – prevent overdistention
Limitati...
Auto-PEEP or Intrinsic PEEP
• What is Auto-PEEP?
– Normally, at end expiration, the lung volume is
equal to the FRC
– When...
Auto-PEEP or Intrinsic PEEP
• Why does hyperinflation occur?
– Airflow limitation because of dynamic collapse
– No time to...
Auto-PEEP or Intrinsic PEEP
• Auto-PEEP is measured in a relaxed pt with an
end-expiratory hold maneuver on a mechanical
v...
Inadequate expiratory time - Air trapping
iPEEP
Flow curve FV loop
1. Allow more time for expiration
2. Increase inspirato...
Disadv
1. Barotrauma / volutrauma
2. ↑WOB a) lung overstretching ↓contractility of diaphragm
b) alters effective trigger s...
Cardiovascular effects of PPV
Spontaneous ventilation PPV
Determinants of hemodynamic effects
due to – change in ITP, lung volumes, pericardial
P
severity – lung compliance, chest ...
Low lung compliance – more P spent in lung expansion & less change in ITP
less hemodynamic effects (DAMPNING EFFECT OF LUN...
Effect on CO ( preload , afterload )
Decreased PRELOAD
1.compression of intrathoracic veins (↓ CVP, RA
filling P)
2.Increa...
PPV
↓ preload,
ventricular filling
↓ afterload ,
↑ventricular
emptying
CO –
1. INCREASE
2. DECREASE
1. Intravascular fluid...
Effect on other body systems
Overview
1. Mode of ventilation – definition
2. Breath – characteristics
3. Breath types
4. Waveforms – pressure- time, vo...
What is a ‘ mode of ventilation’ ?
A ventilator mode is delivery a sequence of
breath types & timing of breath
Breath characteristics
A= what initiates a breath -
TRIGGER
B = what controls / limits it –
LIMIT
C= What ends a breath -
...
TRIGGER
What the ventilator
senses to initiate a
breath
Patient
• Pressure
• Flow
Machine
• Time based
Recently – EMG moni...
CONTROL/ LIMIT
Variable not allowed to
rise above a preset
value
Does not terminate a
breath
 Pressure
 Volume
 Pressur...
CYCLING VARIABLE
Determines the end of
inspiration and the
switch to expiration
 Machine cycling
• Time
• Pressure
• Volu...
Breath types
Spontaneous
Both triggered and
cycled by the patient
Control/Mandatory
Machine triggered
and machine cycled
A...
Waveforms
1. Volume -time
2. Flow - time
3. Pressure - time
a) Volume – time graphs
1. Air leaks
2. Calibrate flow transducers
b) Flow waveforms
1. Inspiratory flow waveforms
Sine
Square
Decelerating
• Resembles normal
inspiration
• More physiological
• Maintains constant flow
• high flow with ↓ ...
Inspiratory and expiratory flow waveforms
2. Expiratory flow waveform
 Expiratory flow is not driven by ventilator and is passive
 Is negative by convention
 Sim...
c) Pressure waveform
1. Spontaneous/ mandatory breaths
2. Patient ventilator synchrony
3. Calculation of compliance & resi...
Classification of modes of ventilation
Volume controlled Pressure controlled
TV & inspiratory flow are
preset
Airway P is ...
Volume controlled Pressure controlled
Trigger - patient /
machine
Patient / machine
Limit Flow Pressure
Cycle Volume / tim...
Volume controlled Pressure controlled
Advantages
1. Guaranteed TV
2. Less atelectasis
3. TV increases linearly with MV
Adv...
Conventional modes of ventilation
1. Control mandatory ventilation (CMV / VCV)
2. Assist Control Mandatory Ventilation (AC...
1. Control mandatory ventilation (CMV / VCV)
• Breath - MANDATORY
• Trigger – TIME
• Limit - VOLUME
• Cycle – VOL / TIME
•...
2. Assist Control Mandatory Ventilation
(ACMV)
• Patient has partial control over his respiration – Better Pt ventilator s...
3. Intermittent mandatory ventilation (IMV)
Breath stacking
Spontaneous breath immediately after a
controlled breath witho...
4.Synchronized Intermittent Mandatory
Ventilation (SIMV)
• Breath –
SPONTANEOUS
ASSISTED
MANDATORY
• Trigger – PATIENT
TIM...
• Basically, ACMV with spontaneous breaths (which
may be pressure supported) allowed in between
• Synchronisation window –...
5.Pressure controlled ventilation (PCV)
• Breath – MANDATORY
• Trigger – TIME
• Limit - PRESSURE
• Cycle – TIME/ FLOW
Rise...
6.Pressure support ventilation (PSV)
• Breath – SPONTANEOUS
• Trigger – PATIENT
• Limit - PRESSURE
• Cycle – FLOW
( 5-25% ...
Newer modes of ventilation
Dual modes of ventilation
Devised to overcome the limitations of both V &
P controlled modes
Dual control within a
breath
...
Dual control within a breath
Combined adv –
1. High & variable initial flow rate of P controlled
breath ( thereby - ↑ pt –...
1. Breath triggered (pt/ time) –
2. P support level reached quickly –
3. ventilator compares delivered and desired/ set TV...
Dual control – breath to breath
P limited +
FLOW cycled
Vol support /
variable P
support
P limited +
TIME cycled
PRVC
Volume support
Allows automatic weaning of P support as
compliance alters.
OPERATION –
C = V
P
changes during
weaning & gu...
Pressure regulated volume controlled
(PRVC)
• Autoflow / variable P control
• Similar to VS except that it is a
modificati...
1. Conventional V controlled mode – very high P would have resulted in an
attempt to deliver set TV -------- BAROTRAUMA
2....
Shifts between P support (flow cycled)& P
control (time cycled) mode with pt efforts
Combines VS & PRVC
If no efforts : P...
Pitfalls :
During the switch from time-cycled
to flow cycled ventilation
Mean airway pressure
hypoxemia may occur
Automode
 Compensates for the resistance of ETT
 Facilitates “ electronic weaning “ i.e pt during ATC mimic their
breathing patte...
Static condition
Single P support level can eliminate ETT
resistance
Dynamic condition
Variable flow e.g. tachypnoea & in ...
1. Feed resistive coef
of ETT
2. Feed %
compensation
desired
3. Measures
instantaneous flow
Calculates P support
proportio...
Airway pressure release ventilation
(APRV)
• High level of CPAP with brief intermittent
releases to a lower level
Conventi...
Higher plateau P – improves oxygenation
Release phase – alveolar ventilation & removal of CO2
Active patient – spontaneous...
Settings
1.Phigh (15 – 30 cmH2O )
2.Plow (3-10 cmH2O ) == PEEP
3. F = 8-15 / min
4. Thigh /Tlow = 8:1 to 10:1
If ↑ PaCO2 -...
Proportional Assist Ventilation
• Targets fixed portion of patient’s
work during “spontaneous”
breaths
• Automatically adj...
WOB
Ventilator measures – elastance & resistance
Clinician sets -“Vol. assist %” reduces work of elastance
“Flow assist%” ...
Biphasic positive airway pressure
(BiPAP)
PCV & a variant of APRV
Time cycled alteration between 2 levels of CPAP
BiPAP ...
BiPAP
Bi- vent
Advantages
1. Allows unrestricted spontaneous breathing
2. Continuous weaning without need to change
ventilatory mode – un...
Neurally Adjusted Ventilatory Assist
(NAVA)
Global Critical Care
https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512
9555/
Wellcome in our new gro...
GOOD LUCK
SAMIR EL ANSARY
ICU PROFESSOR
AIN SHAMS
CAIRO
elansarysamir@yahoo.com
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
Conv. ventilation physi
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  1. 1. Physiology of positive pressure ventilation SAMIR EL ANSARY
  2. 2. Global Critical Care https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512 9555/ Wellcome in our new group ..... Dr.SAMIR EL ANSARY
  3. 3. Mechanical ventilation – Supports / replaces the normal ventilatory pump moving air in & out of the lungs. Primary indications – a.apnea b.Ac. ventilation failure c. Impending ventilation failure d.Severe oxygenation failure
  4. 4. Goals  Manipulate gas exchange ↑ lung vol – FRC, end insp / exp lung inflation Manipulate work of breathing (WOB) Minimize CVS effects
  5. 5. 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
  6. 6. 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 Noninvasive 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
  7. 7. 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)
  8. 8. Understanding physiology of PPV 1) Different P gradients 2) Time constant 3) Airway P ( peak, plateau, mean ) 4) PEEP and Auto PEEP 5) Types of waveforms
  9. 9. Pressure gradients
  10. 10. Distending pressure of lungs Elastance load Resistance load Distending pressure
  11. 11. Flow through the airways is generated by Transairway pressure (pressure at the airway opening minus pressure in the lungs). Expansion of the elastic chamber is generated by Transthoracic pressure (pressure in the lungs minus pressure on the body surface).
  12. 12. Transrespiratory pressure (pressure at the airway opening minus pressure on the body surface) is the sum of these two pressures and is the total pressure required to generate inspiration. Transrespiratory pressure can have two components, one secondary to the ventilator (pvent) and one secondary to the respiratory muscles (Pmusc)
  13. 13. Trans pulmonary pressure (pressure at airway opening minus pleural pressure) [= Transrespiratory pressure?] Transpulmonary pressure is the distending force of the lung The airway-pressure gauge on a positive-pressure ventilator displays transrespiratory pressure
  14. 14. Pressure, volume, and flow are functions of time and are called variables. They are all measured relative to their values at end expiration. Elastance and resistance are assumed to remain constant and are called parameters.
  15. 15. Elastance(measure of stiffness) is the inverse of compliance(measure of stretchiness) An increase in elastance implies that the system is becoming stiffer.
  16. 16. Mean airway pressure Paw = Transrespiratory pressure Mean alveolar pressure Palv = Transthoracic pressure
  17. 17. Transpulmonary pressure is the distending pressure in a spontaneously(negative) breathing patient Transrespiratory pressure is the distending pressure in positive pressure ventilation
  18. 18. Airway pressures Peak insp P (PIP) • Highest P produced during insp. • PRESISTANCE + P INFLATE ALVEOLI • Dynamic compliance • Barotrauma Plateau P • Observed during end insp pause •P INFLATE ALVEOLI •Static compliance •Effect of flow resistance negated
  19. 19. Time constant • Defined for variables that undergo exponential decay • Time for passive inflation / deflation of lung / unit t = compliance X resistance = VT . peak exp flow Normal lung C = 0.1 L/cm H2O R = 1cm H2O/L/s COAD – resistance to exp increases → time constant increases → exp time to be increased lest incomplete exp ( auto PEEP generates). ARDS - inhomogenous time constants
  20. 20. Why and how to separate dynamic & static components ? • Why – to find cause for altered airway pressures • How – adding end insp pause - no airflow, lung expanded, no expiration
  21. 21. How -End inspiratory hold • Pendelluft phenomenon • Visco-elastic properties of lung End-inspiratory pause Ppeak < 50 cm H2O Pplat < 30 cm H2O Ppeak = Pplat + Paw
  22. 22. At the start of inflation, the airway pressure immediately rises because of the resistance to gas flow (A), and at the end of inspiratory gas flow the airway pressure immediately falls by the same pressure (A) to an inflexion point. Thereafter, the airway pressure more gradually declines to the plateau pressure. The loss of airway pressure after the inflexion (B) is due to gas redistribution (Pendelluft) and the visco- plasto-elastic lung and thorax behaviour
  23. 23. P2(Pplat) is the static pressure of the respiratory system, which in the absence of flow equals the alveolar pressure, which reflects the elastic retraction of the entire respiratory system. The pressure drop from PIP to P1 represents the pressure required to move the inspiratory flow along the airways without alveolar interference, thus representing the pressure dissipated by the flow- dependent resistances(airway resistance).
  24. 24. The slow post-occlusion decay from P1 to P2 depends on the viscoelastic properties of the system and on the pendulum-like movement of the air (pendelluft). During the post-inspiratory occlusion period there is a dynamic elastic rearrangement of lung volume, which allows the different pressures in alveoli at different time constants to equalize, and depends on the inhomogeneity of the lung parenchyma.
  25. 25. The lung regions that have a low time constant (ie, rapid zones), where the alveolar pressure rises rapidly, are emptied in the lung regions that have higher time constants (ie, slow zones), where the pressure rises more slowly because of higher resistance or lower compliance
  26. 26. The static compliance of the respiratory system mirrors the elastic features of the respiratory system, whereas The dynamic compliance also includes the resistive (flow-dependent) component of the airways and the endotracheal tube
  27. 27. When the inspiratory pause is shorter than 2 seconds, P2 does not always reflect the alveolar pressure. The compliance value thus measured is called quasi- static compliance. In healthy subjects the difference between static compliance and quasi-static compliance is minimal, whereas it is markedly higher in patients who have acute respiratory distress syndrome or chronic obstructive pulmonary disease
  28. 28. Ppeak < 50 cm H2O; Pplat < 35 cm H2O – to avoid barotrauma
  29. 29. • Pendulum like movement of air between lung units • Reflects inhomogeneity of lung units • More in ARDS and COPD • Can lead to falsely measured high Pplat if the end- inspiratory occlusion duration is not long enough
  30. 30. Why
  31. 31. Mean airway P (MAP) • average P across total cycle time (TCT) • MAP = 0.5(PIP-PEEP)X Ti/TCT + PEEP • Decreases as spontaneous breaths increase • MAPSIMV < MAPACV • Hemodynamic consequences Factors 1. Mandatory breath modes 2. ↑insp time , ↓ exp time 3. ↑ PEEP 4. ↑ Resistance, ↓compliance 5. Insp flow pattern
  32. 32. PEEP BENEFITS 1. Restore FRC/ Alveolar recruitment 2. ↓ shunt fraction 3. ↑Lung compliance 4. ↓WOB 5. ↑PaO2 for given FiO2 DETRIMENTAL EFFECTS 1. Barotrauma 2. ↓ VR/ CO 3. ↑ WOB (if overdistention) 4. ↑ PVR 5. ↑ MAP 6. ↓ Renal / portal bld flow PEEP prevents complete collapse of the alveoli and keep them partially inflated and thus provide protection against the development of shear forces during mechanical inflation
  33. 33. How much PEEP to apply? Lower inflection point – transition from flat to steep part - ↑compliance - recruitment begins (pt. above closing vol) Upper inflection point – transition from steep to flat part - ↓compliance - over distension
  34. 34. Set PEEP above LIP – Prevent end expiratory airway collapse Set TV so that total P < UIP – prevent overdistention Limitation – lung is inhomogenous - LIP / UIP differ for different lung units
  35. 35. Auto-PEEP or Intrinsic PEEP • What is Auto-PEEP? – Normally, at end expiration, the lung volume is equal to the FRC – When PEEPi occurs, the lung volume at end expiration is greater then the FRC
  36. 36. Auto-PEEP or Intrinsic PEEP • Why does hyperinflation occur? – Airflow limitation because of dynamic collapse – No time to expire all the lung volume (high RR or Vt) – Lesions that increase expiratory resistance Function of- Ventilator settings – TV, Exp time Lung func – resistance, compliance
  37. 37. Auto-PEEP or Intrinsic PEEP • Auto-PEEP is measured in a relaxed pt with an end-expiratory hold maneuver on a mechanical ventilator immediately before the onset of the next breath
  38. 38. Inadequate expiratory time - Air trapping iPEEP Flow curve FV loop 1. Allow more time for expiration 2. Increase inspiratory flow rate 3. Provide ePEEP
  39. 39. Disadv 1. Barotrauma / volutrauma 2. ↑WOB a) lung overstretching ↓contractility of diaphragm b) alters effective trigger sensitivity as autoPEEP must be overcome before P falls enough to trigger breath 3. ↑ MAP – CVS side effects 4. May ↑ PVR Minimising Auto PEEP 1. ↓airflow res – secretion management, bronchodilation, large ETT 2. ↓Insp time ( ↑insp flow, sq flow waveform, low TV) 3. ↑ exp time (low resp rate ) 4. Apply PEEP to balance AutoPEEP
  40. 40. Cardiovascular effects of PPV Spontaneous ventilation PPV
  41. 41. Determinants of hemodynamic effects due to – change in ITP, lung volumes, pericardial P severity – lung compliance, chest wall compliance, rate & type of ventilation, airway resistance
  42. 42. Low lung compliance – more P spent in lung expansion & less change in ITP less hemodynamic effects (DAMPNING EFFECT OF LUNG) Low chest wall compliance – higher change in ITP needed for effective ventilation more hemodynamic effects
  43. 43. Effect on CO ( preload , afterload ) Decreased PRELOAD 1.compression of intrathoracic veins (↓ CVP, RA filling P) 2.Increased PVR due to compression by alveolar vol (decreased RV preload) 3.Interventricular dependence - ↑ RV vol pushes septum to left & ↓ LV vol & LV output Decreased afterload 1. emptying of thoracic aorta during insp 2. Compression of heart by + P during systole 3. ↓ transmural P across LV during systole
  44. 44. PPV ↓ preload, ventricular filling ↓ afterload , ↑ventricular emptying CO – 1. INCREASE 2. DECREASE 1. Intravascular fluid status 2. Compensation – HR, vasoconstriction 3. Sepsis, 4. PEEP, MAP 5. LV function
  45. 45. Effect on other body systems
  46. 46. Overview 1. Mode of ventilation – definition 2. Breath – characteristics 3. Breath types 4. Waveforms – pressure- time, volume –time, flow- time 5. Modes - Volume & pressure limited 6. Conventional modes of ventilation 7. Newer modes of ventilation
  47. 47. What is a ‘ mode of ventilation’ ? A ventilator mode is delivery a sequence of breath types & timing of breath
  48. 48. Breath characteristics A= what initiates a breath - TRIGGER B = what controls / limits it – LIMIT C= What ends a breath - CYCLING
  49. 49. 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
  50. 50. CONTROL/ LIMIT Variable not allowed to rise above a preset value Does not terminate a breath  Pressure  Volume  Pressure Controlled • Pressure targeted, pressure limited - Ppeak set • Volume Variable  Volume Controlled • Volume targeted, volume limited - VT set • Pressure Variable  Dual Controlled • volume targeted (guaranteed) and pressure limited
  51. 51. CYCLING VARIABLE Determines the end of inspiration and the switch to expiration  Machine cycling • Time • Pressure • Volume  Patient cycling • Flow May be multiple but activated in hierarchy as per preset algorithm
  52. 52. Breath types Spontaneous Both triggered and cycled by the patient Control/Mandatory Machine triggered and machine cycled Assisted Patient triggered but machine cycled
  53. 53. Waveforms 1. Volume -time 2. Flow - time 3. Pressure - time
  54. 54. a) Volume – time graphs 1. Air leaks 2. Calibrate flow transducers
  55. 55. b) Flow waveforms 1. Inspiratory flow waveforms
  56. 56. 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
  57. 57. Inspiratory and expiratory flow waveforms
  58. 58. 2. Expiratory flow waveform  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)
  59. 59. c) Pressure waveform 1. Spontaneous/ mandatory breaths 2. Patient ventilator synchrony 3. Calculation of compliance & resistance 4. Work done against elastic and resistive forces 5. AutoPEEP ( by adding end exp pause)
  60. 60. Classification of modes of ventilation Volume controlled Pressure controlled TV & inspiratory flow are preset Airway P is preset Airway P depends on above & lung elastance & compliance TV & insp flow depend on above & lung elastance & compliance
  61. 61. Volume controlled Pressure controlled Trigger - patient / machine Patient / machine Limit Flow Pressure Cycle Volume / time time / flow TV Constant variable Peak P Variable constant Modes ACV, SIMV PCV, PSV
  62. 62. Volume controlled Pressure controlled Advantages 1. Guaranteed TV 2. Less atelectasis 3. TV increases linearly with MV Advantages 1. Limits excessive airway P 2. ↑ MAP by constant insp P – better oxygenation 3. Better gas distribution – high insp flow ↓Ti & ↑Te ,thereby, preventing airtrapping 4. Lower WOB – high initial flow rates meet high initial flow demands 5. Lower PIP – as flow rates higher when lung compliance high i.e early insp. phase Disadvantages 1. Limited flow may not meet patients desired insp flow rate- flow hunger 2. May cause high Paw ( Disadvantages 1. Variable TV ↑TV as compliance ↑ ↓TV as resistance ↑
  63. 63. 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)
  64. 64. 1. Control mandatory ventilation (CMV / VCV) • Breath - MANDATORY • Trigger – TIME • Limit - VOLUME • Cycle – VOL / TIME • Patient has no control over respiration • Requires sedation and paralysis of patient
  65. 65. 2. Assist Control Mandatory Ventilation (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
  66. 66. 3. Intermittent mandatory ventilation (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 • Trigger – PATIENT VENTILATOR • Limit - VOLUME • Cycle - VOLUME
  67. 67. 4.Synchronized Intermittent Mandatory Ventilation (SIMV) • Breath – SPONTANEOUS ASSISTED MANDATORY • Trigger – PATIENT TIME • Limit - VOLUME • Cycle – VOLUME/ TIME
  68. 68. • Basically, ACMV with spontaneous breaths (which may be pressure supported) allowed in between • Synchronisation 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 – ‘Synchronisation window’
  69. 69. 5.Pressure controlled ventilation (PCV) • Breath – MANDATORY • Trigger – TIME • Limit - PRESSURE • Cycle – TIME/ FLOW Rise time Time taken for airway pressure to rise from baseline to maximum
  70. 70. 6.Pressure support ventilation (PSV) • Breath – SPONTANEOUS • Trigger – PATIENT • 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
  71. 71. Newer modes of ventilation
  72. 72. Dual modes of ventilation Devised to overcome the limitations of both V & P controlled modes Dual control within a breath Switches from P to V control during the same breath e.g. VAPS PA Dual control from breath to breath P limit ↑ or ↓ to maintain a clinician set TV ANALOGOUS to a resp therapist who ↑ or ↓ P limit of each breath based on TV delivered in last breath
  73. 73. Dual control within a breath Combined adv – 1. High & variable initial flow rate of P controlled breath ( thereby - ↑ pt – vent synchrony, ↓WOB, ↓sense of breathlessness) 2. Assured TV & MV as in V controlled breaths Starts as P limited breaths but change over to V limited breath by converting decelerating flow to constant flow if minimum preset TV not delivered
  74. 74. 1. Breath triggered (pt/ time) – 2. P support level reached quickly – 3. ventilator compares delivered and desired/ set TV 4. Delivered = set TV -------- Breath is FLOW cycled as in P controlled modes 5. Delivered < set TV -------- Changeover from P to V limited ( flow kept constant + Ti ↑) P rises above set P support level till set TV delivered
  75. 75. Dual control – breath to breath P limited + FLOW cycled Vol support / variable P support P limited + TIME cycled PRVC
  76. 76. Volume support Allows automatic weaning of P support as compliance alters. OPERATION – C = V P changes during weaning & guides P support level Preset & constant P support dependent on C compliance ↑ - P support ↓ ↓ - P support ↑ By 3 cm H2O / breath Deliver desired TV
  77. 77. Pressure regulated volume controlled (PRVC) • Autoflow / variable P control • Similar to VS except that it is a modification of PCV rather than PSV
  78. 78. 1. Conventional V controlled mode – very high P would have resulted in an attempt to deliver set TV -------- BAROTRAUMA 2. Conventional P controlled mode – inadequate TV would have been delivered
  79. 79. Shifts between P support (flow cycled)& P control (time cycled) mode with pt efforts Combines VS & PRVC If no efforts : PRVC (time cycled) As spontaneous breathing begins : VS (flow cycled) Automode
  80. 80. Pitfalls : During the switch from time-cycled to flow cycled ventilation Mean airway pressure hypoxemia may occur Automode
  81. 81.  Compensates for the resistance of ETT  Facilitates “ electronic weaning “ i.e pt during ATC mimic their breathing pattern as if extubated ( provided upper airway contorl provided)  Operation As the flow ↑ / ETT dia ↓, the P support needs to be ↑to ↓WOB ∆P (P support) α (L / r4 ) α flow α WOB Automatic Tube Compensation
  82. 82. Static condition Single P support level can eliminate ETT resistance Dynamic condition Variable flow e.g. tachypnoea & in different phases of resp. P.support needs to be continously altered to eliminate dynamically changing WOB.
  83. 83. 1. Feed resistive coef of ETT 2. Feed % compensation desired 3. Measures instantaneous flow Calculates P support proportional to resistance throughout respiratory cycle Limitation Resistive coef changes in vivo ( kinks, temp,molding, secretions) Under/ overcompensation may result.
  84. 84. Airway pressure release ventilation (APRV) • High level of CPAP with brief intermittent releases to a lower level Conventional modes – begin at low P & elevate P to accomplish TV APRV – commences at elevated P & releases P to accomplish TV
  85. 85. Higher plateau P – improves oxygenation Release phase – alveolar ventilation & removal of CO2 Active patient – spontaneous breathing at both P levels Passive patient – complete ventilation by P release
  86. 86. Settings 1.Phigh (15 – 30 cmH2O ) 2.Plow (3-10 cmH2O ) == PEEP 3. F = 8-15 / min 4. Thigh /Tlow = 8:1 to 10:1 If ↑ PaCO2 -↑ Phigh or ↓ Plow - ↑ f If ↓ PaO2 - ↑ Plow or FiO2
  87. 87. Proportional Assist Ventilation • Targets fixed portion of patient’s work during “spontaneous” breaths • Automatically adjusts flow, volume and pressure needed each breath
  88. 88. WOB Ventilator measures – elastance & resistance Clinician sets -“Vol. assist %” reduces work of elastance “Flow assist%” reduces work of resistance's Increased patient effort (WOB) causes increased applied pressure (and flow & volume) ELASTANCE (TV) RESISTANCE (Flow)
  89. 89. Biphasic positive airway pressure (BiPAP) PCV & a variant of APRV Time cycled alteration between 2 levels of CPAP BiPAP – P support for spontaneous level only at low CPAP level Bi-vent - P support for spontaneous level at both low & high CPAP  Spontaneous breathing at both levels  Changeover between 2 levels of CPAP synchronized with exp & insp
  90. 90. BiPAP Bi- vent
  91. 91. Advantages 1. Allows unrestricted spontaneous breathing 2. Continuous weaning without need to change ventilatory mode – universal ventilatory mode 3. Synchronization with pt’s breathing from exp. to insp. P level & vice versa 4. Less sedation needed
  92. 92. Neurally Adjusted Ventilatory Assist (NAVA)
  93. 93. Global Critical Care https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512 9555/ Wellcome in our new group ..... Dr.SAMIR EL ANSARY
  94. 94. GOOD LUCK SAMIR EL ANSARY ICU PROFESSOR AIN SHAMS CAIRO elansarysamir@yahoo.com
  • AbdulahadMohammed

    Oct. 31, 2019
  • mehdimoosavian

    Aug. 6, 2018
  • drsamgeorge

    May. 13, 2018
  • ShangRenWang

    Jan. 11, 2017

Conv. ventilation physi

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