Controlled ventilation 1

1. Convential
Mechanical ventilation
SAMIR EL ANSARY
ICU PROFESSOR
AIN SHAMS
CAIRO

2. Global Critical Care
https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512
9555/
Wellcome in our new group ..... Dr.SAMIR EL ANSARY

3. Mechanical ventilation
Supports / replaces the normal
ventilatory pump moving air in &
out of the lungs.

4. Primary indications
apnea
Ac. ventilation failure
Impending ventilation failure
Severe oxygenation failure

5. Goals
Manipulate gas exchange
↑ lung vol – FRC, end insp / exp lung
inflation
Manipulate work of breathing (WOB)
Minimize CVS effects

6. 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

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

8. 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)

9. Understanding physiology of PPV
Different P gradients
Time constant
Airway P ( peak, plateau, mean )
PEEP and Auto PEEP
Types of waveforms

10. Pressure gradients

12. Distending pressure of lungs
Elastance load
Resistance load
Distending
pressure

13. 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

14. 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

15. 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

16. 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

17. • 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

18. Why

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. 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

26. Inadequate expiratory time - Air trapping
iPEEP
Flow curve FV loop
1. Allow more time for expiration
2. Increase inspiratory flow rate
3. Provide ePEEP

27. 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

28. Cardiovascular effects of PPV
Spontaneous ventilation PPV

29. 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

30. 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

31. 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

32. 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

33. Effect on other body systems

34. 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

35. What is a ‘ mode of ventilation’ ?
A ventilator mode is delivery a sequence of
breath types & timing of breath

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

37. 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

38. 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

39. 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

40. Breath types
Spontaneous
Both triggered and
cycled by the patient
Control/Mandatory
Machine triggered
and machine cycled
Assisted
Patient triggered but
machine cycled

41. Waveforms
1. Volume -time
2. Flow - time
3. Pressure - time

42. a) Volume – time graphs
1. Air leaks
2. Calibrate flow transducers

43. b) Flow waveforms
1. Inspiratory flow waveforms

44. 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

45. Inspiratory and expiratory flow waveforms

46. 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)

47. 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)

48. 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

50. 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

51. 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 ↑

52. 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)

53. 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

54. 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

55. 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

56. 4.Synchronized Intermittent Mandatory
Ventilation (SIMV)
• Breath –
SPONTANEOUS
ASSISTED
MANDATORY
• Trigger – PATIENT
TIME
• Limit - VOLUME
• Cycle – VOLUME/ TIME

57. • 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’

58. 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

59. 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

60. 7.Continuous positive airway pressure (CPAP)
Breath –
SPONTANEOUS
CPAP is actually PEEP applied
to spontaneously breathing
patients.
But CPAP is described a mode
of ventilation without
additional inspiratory support
while PEEP is not regarded as
a stand-alone mode

61. Newer modes of ventilation
1. Volume assured pressure support (VAPS)
2. Volume support (VS)
3. Pressure regulated volume controlled (PRVC)
4. Automode
5. Automatic Tube Compensation (ATC)
6. Airway pressure release ventilation (APRV)
7. Proportional Assist Ventilation (PAV)
8. Biphasic positive airway pressure (BiPAP)
9. Neurally Adjusted Ventilatory Assist (NAVA)

62. Newer modes of ventilation
• Recent modes allow ventilators to control one
variable or the other based on a feedback loop
Volume
controlled
Pressure
controlled
Feedback loop
Is the Airway P
exceeding set P
limit ?
Has the
desired/ set
TV been
delivered ?

63. 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

64. 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

65. 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

66. Dual control – breath to breath
P limited +
FLOW cycled
Vol support /
variable P
support
P limited +
TIME cycled
PRVC

67. 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

68. Limitations –
a) MV is fixed , pt may be stuck at that level of
support even if pt demand exceeds MV
chosen by clinician
b) If tachypnoea occurs – ventilator senses it as
↑ MV and ↓ses P support which is exactly
OPPOSITE of what is required

69. Pressure regulated volume controlled (PRVC)
• Autoflow / variable P control
• Similar to VS except that it is a modification of
PCV rather than PSV

70. Had it been
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

71. Automode
 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)
Pitfalls :
 During the switch from time-cycled to flow cycled ventilation
↓
Mean airway pressure ↓
↓
hypoxemia may occur

72. Automatic Tube Compensation
 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

73. 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 d/t ETT
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.

74. 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

75. 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

76. 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

77. Advantages
1. Preservation of spontaneous breathing and
comfort with most spontaneous breathing
occurring at high CPAP
2. breathing occurring at high CPAP
3. ↓WOB
4. ↓Barotrauma
5. ↓Circulatory compromise
6. Better V/Q matching

78. Proportional Assist Ventilation
• Targets fixed portion of patient’s work
during “spontaneous” breaths
• Automatically adjusts flow, volume and
pressure needed each breath

79. 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)

80. Limitations
1. Elastance (E) & resistance (R) cannot be
measured accurately.
2. E & R vary frequently esp in ICU patients.
3. Curves to measure E ( P-V curve) & R (P-F curve )
are not linear as assumed by ventilator.

81. 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

82. .
Can provide total / partial ventilatory support
1. BiPAP – PCV – if pt not breathing
2. BiPAP – SIMV- spontaneous breathing at lower CPAP + mandatory
breaths by switching between 2 CPAP levels
3. CPAP – both CPAP levels are identical in spontaneously breathing
patient
4. BiPAP – P support – additional P support at lower CPAP
5. Bi- vent – additional P support at both levels of CPAP

83. BiPAP
Bi- vent

84. 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

85. Neurally Adjusted Ventilatory Assist (NAVA)
 Electrical activity of respiratory muscles used as
input Eadi (electrical activity of diaphragm)
 Cycling on, cycling off: determined by Eadi
 Synchrony between neural & mechanical
inspiratory time is guaranteed
 Patient comfort

86. Global Critical Care
https://www.facebook.com/groups/1451610115129555/#!/groups/145161011512
9555/
Wellcome in our new group ..... Dr.SAMIR EL ANSARY

87. GOOD LUCK
SAMIR EL ANSARY
ICU PROFESSOR
AIN SHAMS
CAIRO
elansarysamir@yahoo.com