This document discusses various modes of mechanical ventilation. It begins by defining what a ventilation mode is, noting that a mode describes the control, phase, and conditional variables in mandatory, spontaneous, or combined breaths. It then discusses different control variables like pressure, volume, and flow. It explains phase variables that initiate, sustain, and end inspiration. Limit and cycle variables that determine the magnitude and end of inspiration are also covered. Common modes like pressure control, volume control, and their advantages and disadvantages are summarized. The document provides details on interpreting pressure waveforms and calculating plateau pressure.

1. Dr. Maninder Dhaliwal
Consultant Pediatric Intensivist
Medanta – The Medicity
Modes Of Ventilation
Exams - Summary
All the best

2. Question 1.
• What is a mode of ventilator?
• Which mode will you use & why?
• Pressure vs Volume ?
• Newer mode?
• PRVC, VAPS, APRV, BPAP
• NAVA
• NIV & HFO

3. What is a mode?
• CMV
• Assit Control
• SIMV
• CPAP
• Pressure
• Volume

6. The word ‘‘control’’ – What it means?
• ‘‘Controlled ventilation’’
• ‘‘Assist/Control’’
• ‘‘Dual control’’
• “Control Variable”

7. What is a mode?
• A “mode” is a predetermined pattern of interaction
between the ventilator and the patient.
• A well defined mode must describe
– control,
– phase and
– conditional variables & is defined for
• Mandatory
• Spontaneous
• Combined Breaths
Respir Care 2013;58(2):348 –366.

10. How a Breath is Delivered
• CONTROL VARIABLES aka Independent Variable
– The primary variable that the ventilator decides how to to
achieve inspiration
–Pressure : APRV, PCV, NAVA
–Volume : Volume control, assist control
–Flow: Volume
–Time: HFO

11. How a Breath is Delivered
• Pressure Controller

12. How a Breath is Delivered
• Volume Controller
– The ventilator maintains the volume waveform in a
specific pattern, the delivered breath is volume
controlled (volume limited, volume targeted)

13. How a Breath is Delivered
• PHASE VARIABLES
– Ventilator-supported breath may be divided into
three distinct phases
1. The initiation of inspiration
2. Inspiration itself
3. Expiration
– To understand a breath cycle, you must know how the
ventilator starts, sustains, and stops inspiration and you must
know what occurs between breaths

14. How a Breath is Delivered
• PHASE VARIABLES
– The phase variable is a variable that is measured
and used by the ventilator to initiate some phase of
the breath cycle
• Trigger variable – causes a breath to begin
• Limit variable – limits the magnitude of any parameter
(pressure, flow, volume) during inspiration
• Cycle variable – causes the end of inspiration

15. How a Breath is Delivered
• Limit Variable
– A limit variable is the maximum value a variable
(pressure, flow, volume) can attain. This limits the
variable during inspiration but does not end the
inspiratory phase.
• Do not confuse this with cycle variable, which always ends
inspiration

16. How a Breath is Delivered
• Maximum Safety Pressure:
Pressure Limiting vs. Pressure Cycling
– All ventilators have a maximum pressure limit control, which
is used to prevent excessive pressure from reaching a
patient’s lungs – reaching the maximum high pressure limit
ends the inspiratory phase
• AKA
– High pressure limit
– Upper pressure limit
– Pressure limit

17. How a Breath is Delivered
• Cycle Variable
– The variable a ventilator measures to determine the
end of inspiration is called the cycling mechanism –
once cycling occurs, expiratory gas flow begins
• Cycle variables
– Pressure
– Volume
– Flow
– time

18. How a Breath is Delivered
• Pressure Cycled
– Ventilator will deliver flow until a present pressure
is reached, at which point inspiration ends and
expiratory flow begins
• The most common application of pressure-cycling is for
alarm setting (e.g., high pressure alarm) and IPPB

19. How a Breath is Delivered
• Flow Cycled
– Ventilator will deliver flow until a present level is
met, at which point flow stops and expiration begins
• The most frequent application of flow cycling is pressure
support mode ventilation (to be discussed in a future
module)

20. How a Breath is Delivered
• Time Cycled
– Expiratory flow starts because a present time
interval has elapsed

21. How a Breath is Delivered
• Limit Variable
This figure illustrates the
importance of distinguishing
between the terms limit and
cycle. A, Inspiration is pressure
limited and time cycled. B,
Inspiration is flow limited and
volume cycled. C, Inspiration is
both flow limited and volume
limited (because flow and volume
reach preset values before
inspiratory time ends) and time
cycled (after the preset
inspiratory hold time).
A B C

22. How a Breath is Delivered
TYPES of Breaths
Machine Cycled
Mandatory breath T,L,C by ventilator
Assisted breath L,C by ventilator
Trigger either patient or time
Patient Cycled
Supported T,C by patient L by ventilator
Spontaneous T,L,C by patient

23. How a Breath is Delivered
• BASELINE VARIABLE
– The variable that is controlled during the expiratory
phase
Note: Most commonly, pressure is controlled during the
expiratory phase
» PEEP

25. [Respir Care 2013;58(2):348 –366.

26. Major VILI – lung protective strategies
Barotrauma Volutrauma BiotraumaAtelectotrauma (R/D)
High Lung Volume Ventilator-Induced Lung Injury
Ventilator-Induced Lung Injury at Low Lung Volumes
Biotrauma, Inflammation, and Multiorgan Failure from Ventilator-
Induced Lung Injury
Low TV PEEP
ARDS net ALVEOLI

29. How do you normally breath??
Imagine this to be your flow of air in lungs
This is your inspiration only………….

30. Expiration is passive
So graph is mostly similar
Volume Ventilation Pressure Ventilation
Flow Time Scalar
Flow LPM
Time
Seconds
Constant Flow
Decelerating
Flow

31. Understand Volume Mode
• Must
• Easy
• More Informative
• P Plat – calculation

32. ventilator
Diaphragm
Ppeak
Pres
RET tube
Rairways
Pres
Pplat
Understanding the pressure-time waveform
using a ‘square wave’ flow pattern
time
pressure
The pressure-time waveform is a reflection
of the pressures generated within the
airways during each phase of the
ventilatory cycle.
At the beginning of the inspiratory cycle,
he ventilator has to generate a pressure Pres
to overcome the airway resistance.
Note: No volume is delivered at this time.
fter this, the pressure rises in a linear fashion
o finally reach Ppeak. Again at end inspiration,
air flow is zero and the pressure drops by an
amount equal to Pres to reach the plateau
pressure Pplat. The pressure returns to
baseline during passive expiration.
Pres

33. C
P peak
Where
is
P plat?

34. P peak
P plat
Inspiratory Pause

35. Pressure Mode
PIP
Decelerating
Flow
No
P plat

36. Normal variations – Pressure wave form
Paw
Pressure VentilationVolume Ventilation
1 2 3 4 5 6
Sec
1
SEC
Expiration
Flow
1 2 3 4 5 6
VT
Liters
Constant
Flow
Decelerating
Flow
Square
Wave
Shark Fin

38. Pressure Control
• Pressure under my control – airway pressure under my control, not
transpulmonary – so relative control only as heterogenous lung, false sense of
security
• Faster tidal volume delivery – high peak flows – early filling of alveoli – but more
shear forces
• Variable peak inspiratory flows – better adaptation to flow hunger / inspiratory
effort of patient – better synchrony in spontaneous mode
• Decelerating flow
• Favorable gas distribution – like dropping a glass of water on floor & the water
trickles into every nook & corner – better in ARDS – Improves oxygenation
• Favorable in leak – although volume is lost through leak – the ventilator will
continue to pressurize the airway for the duration of Ti – if leak is big – it
sometimes mimic constant flow
Advantages

39. Pressure Control
• Many clinicians prefer PCV, because it is easy to control
peak airway pressure and keep peak inspiratory
pressure below critical limits, thus possibly reducing
volutrauma
• It have demonstrated an improvement in oxygenation
and pulmonary mechanics in ARDS patients who were
switched from VCV to PCV while VT, inspiratory time
and PEEP were held constant. The finding was thought
to reflect an increase in mean airway pressure.
Davis K, Branson RD, Campbell RS, et al. Comparison of volume control and pressure control
ventilation: is flow waveform the difference? J Trauma

40. • The only study - ARDS comparing VCV and PCV
within the context of a lung-protecting
ventilation strategy showed pressure control
to afford safe maintenance of the ventilation
parameters and pH levels.
• This same study also recorded a decrease in
the incidence of multiorgan failure over time.
• But no affect on mortality
Prospective randomized trial comparing pressure controlled ventilation and volume-
controlled ventilation in ARDS. For the Spanish Lung Failure Collaborative Group. Chest.
2000;117:1690---6.

41. PC - Disadvantage
• The major disadvantage of PCV is that in a patient with
unstable or changing lung mechanics, any significant
fluctuation in the lung compliance or airway resistance
will directly affect the delivered tidal volumes.
• Tidal volumes can vary substantially with changes in
compliance or resistance, producing undesirable changes
in minute ventilation

42. PC – Disadvantage: New Proof
• The high peak inspiratory flow of PCV may
aggravate lung injury because of greater shear
forces in PC mode than the lower peak
inspiratory flow of VCV
Effects of peak inspiratory flow on development of ventilator-induced lung injury
in rabbits. Anesthesiology 2004

43. • For early management of patients with acute
lung injury (ALI) or acute respiratory distress
syndrome (ARDS), in ARDS network centers,
volume assist control was the most commonly
selected mode of ventilation (56% overall),
and volume-targeted ventilation was used in
most patients (82%).

44. Volume Mode
Advantages
• Minute ventilation is guaranteed
• The set tidal volume is guaranteed
• Inspiratory Pause :
– to improve Tidal volume distribution
– to reduce PaCO2 & to enlarge PaO2, (due to
involving a large part of lungs into gaseous
exchange)
– to refine V/Q ratio (ventilation/perfusion ratio)
– Pendelluft effect

45. Volume Mode

46. Volume mode
Hess DR, Dillman C, Kacmarek RM. In vitro evaluation
of aerosol bronchodilator delivery during mechanical
ventilation: pressure-control vs. volume control
ventilation. Intensive Care Med. Jul 2003;29(7):1145-
1150.

47. Volume Mode
• Calculate P Peak & P Plat
– Resistance (Difference between P plat - Ppeak
– Targeted P Plat in both Asthma & ARDS

48. Volume Mode
• A major limitation of volume control is the fact that
administration of the inspiratory flow in each
respiration is fixed in its values, and if the patient is
active, he or she may have a variable inspiratory
demand, generating ‘‘dyssynchrony due to
inadequate inspiratory flow’’ or also a ‘‘double
trigger’’ effect in requiring a volume larger than the
programmed volume

49. • Volume can more easily be directed toward
areas of lesser resistance or increased
compliance, thereby producing ‘overdistended
areas’ – VILI
Limited flow may not meet patients desired insp
flow rate- flow hunger
May cause high Paw ( barotrauma)

50. SIMV + PS Mode
• How many types of breath present?
Controlled mandatory
Assisted Synchronized
Spontaneous supported

52. SIMV
• Guaranted minimum vol with assist breath
• Respiratory alkalosis less as compared to
assist mode as it has a window for
spontaneous breaths
• Less atrophy of muscles – active participation
by patients
• All advantages of spontaneous breaths.

53. SIMV
• Initial mode of choice or is it weaning mode?
• Or is it falling out of favour ?
• Not preferred by many presently, but still the
most popular mode in pediatrics.
• With newer modes – this mode will soon
become historical

54. CPAP vs PEEP
CPAP
• Is a mode & it usually
means without additional
inspiratory support
• Always in spontaneously
inspiration
PEEP
• Baseline variable
• Always in conjunction with
positive pressure ventilation
as a additional support to
some mode – PS, Assist
control, SIMV
Wrongly called – CPAP + PS, but it is PSV
Pressure support is usually above PEEP, so no need to say PS + PEEP
Anesth Int Care 1986

55. Pressure Support
• Reducing the load on respiratory muscles
• Improving synchrony between patient and ventilator
without excessive sedation
• Easing the weaning process

56. Equation of motion
in pressure support ventilation
• Pressure = pressure applied by the
ventilator on the airway + pressure
generated by respiratory muscles
• Pmus is determined by respiratory drive
and respiratory muscle strenght
Paw + Pmus = Vt/C + VxR + PEP

57. Increase in PS level will not affect flow and Vt if there
is subsequent decrease in respiratory drive (lower
Pmus) or unloading of the respiratory muscles.

58. Determinant factors of
inspiratory flow in PSV
• Pressure support setting
• Pmus (inspiratory effort)
• Airway resistance
• Respiratory system compliance
• Vt directly depends on inspiratory flow, but also
on auto-PEEP (decreases the driving pressure
gradient)

59. Auto-cycling
• Leaks
• Patient movement
• Water in the ventilator circuit
• Cardiac signals
→ Signal noise trigerring the vent especially when
settings sensitive
→ Respiratory alkalosis, lung hyperinflation

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

62. Pressure Support termination
(cycling)
Goal : cycling to expiration at the end of neural
inspiratory time
• Flow : Fixed absolute flow or % of peak
inspiratory flow ± elapsed inspiratory time

64. Drawbacks of a high inspiratory
flow at the onset of inspiration
• Inspiratory phase may be prematurely terminated
if ventilator cycles at a flow that is a fraction of
peak inspiratory flow
• Flow-related inspiratory terminating reflex →
shortening of neural inspiration → shallow
inspiratory efforts
• Individual patient titration of rise time is
necessary in adddition to proper setting of PS to
optimize the efficacy of PSV

68. Problems faced during PSV
• Apneas
• Vt variable – alveolar ventilation not guaranteed
• If Resistance increases – secretions/compliance
• If obstruction increases – asthma
• Vt decreases
• AutoPEEP :
» Increases the effort required to trigger the ventilator
» Decreases the delivered Vt
» Inspiratory flow decreases slowly → flow cycle criteria not reached
at the end of neural inspiration → active exhalation to pressure cycle
the breath
• If leak +, than flow rate to cycle may never be achieved
Also autotriggering – but now managed in new ventilators
• Be careful while using in line nebulisers

69. Which level of PS ?
• Unloading of respiratory muscle :
– Should encourage reconditioning and prevention of
atrophy
– While avoiding fatigue
• Objectives : Vt 6 -10 ml / kg, RR < 30-35/mn and
no SCM muscle contractions

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

71. Pressure Support
Regardless of the goal for pressure support, the simplest
method of determining what PS level to
use is to use the PS level providing the lowest RR with
adequate oxygenation.

73. So Many knobs – So Many Modes
Student brain running : want to excel ------- want to pass
Examiners want it simple – believe me try to keep it simple