Mechanical ventilation uses machines called ventilators to generate a controlled flow of gas into a patient's airways to support breathing. There are several basic modes of ventilation including controlled mandatory ventilation (CMV), assist-control ventilation, intermittent mandatory ventilation (IMV), and synchronized intermittent mandatory ventilation (SIMV). CMV controls both the tidal volume and respiratory rate while assist-control adds spontaneous breaths triggered by the patient. IMV and SIMV allow some spontaneous breathing but can cause breath stacking. Pressure support ventilation provides pressure assistance for spontaneous breaths with the patient determining the tidal volume.

1. Mechanical Ventilation
Basic Modes
LOKESH TIWARI
AIIMS PATNA
CME on Mechanical Ventilation: Bench to Bedside
AIIMS RAIPUR: 22nd August 2015

2. What are ventilators ?
▶ A machine that generates a controlled flow of gas into a patient’s airways
▶ Supportive role to buy time

3. Mechanical ventilation
▶ Several models have evolved over time-
▶ Negative pressure ventilation
▶ Positive pressure ventilation
▶ Simple pneumatic system
▶ New generation microprocessor controlled systems.
▶ The basic function and applications remain common.

4. Basic Ventilator Parameters
▶ Tidal volume
▶ Frequency
▶ PIP
▶ Plateau Pressure
▶ PEEP
▶ Inspiratory Time
▶ Expiratory time
▶ I:E Ratio

5. Basic Ventilator Parameters
▶ Mode
▶ Tidal volume
▶ Frequency
▶ PIP
▶ Plateau Pressure
▶ PEEP
▶ Inspiratory Time
▶ Expiratory time
▶ I:E Ratio

6. Starting a ventilator: Mode
▶Mode denotes interplay b/w patient and the
ventilator
▶ Describes the style of breath support based on
relationship between the various possible types of
breath and inspiratory – phase variables

7. Where to Start ?
▶ CPAP, IPAP, EPAP, NIV
▶ Pressure control, Volume control
▶ CMV, Assist Control, IMV, SIMV,
▶ PSV, ASV, MMV,
▶ APRV
▶ PCV, PRVC, PSV, VCIRV, Volume
Support,
▶ Auto Mode,
▶ BiLevel, BiPAP,
▶ HFJV, HFOV

8. Objective From

9. Objective To

10. Objectives
▶ Understand how ventilators control breath delivery, phase and
control variables.
▶ Understand the basic modes of ventilation.
▶ Combinations, tailor-making, mix and match…

11. The ventilator circuit

12. The ventilator circuit
50 psi air
50 psi O2
Blender
Air-O2 mixture
of desired FiO2
at 50 psi
Stepped down
pressure
Flow
regulator
Pressure
regulating
valve
T-piece & ETT
tube
Insp limb
Exp limb

13. Flow regulators / PEEP
Flow in
ventilator
circuit-
constant
Flow in ET & patient
airway-
keeps changing in
magnitude &
direction !!
T-connection
ET
T
Baby’s
airway
Flow
sensor

14. What does flow sensor do?
Flow in
ventilator
circuit-
constant
T-connection
E
T
T
Flow
sensor
Insp flow

RR
= tidal vol
Exp flow
- insp flow
= peri-tube leak

16. Ventilatory Phases
• Inspiration: Inspiratory valve opens and
expiratory valve is closed
• Inspiratory pause: inspiratory valve and
expiratory valve closed
• Expiration: Inspiratory valve closed and
expiratory valve open
• Expiratory pause: Inspiratory valve and
expiratory (or PEEP) valve closed at end
of expiration
Ti T
e
0

17. Phase Variables: Trigger, Limit and Cycling

18. Phase variables
▶Trigger : ventilator (time)- triggered or patient (pressure or flow)
triggered
▶ Limit: flow-limited or pressure-limited
▶ Cycling: volume, time, flow or pressure cycled.

19. Phase variables: Trigger
▶ What causes the breath to begin (signal to open the
inspiratory valve)
▶Machine (controlled): the ventilator will trigger regular breaths at a
frequency which will depend on the set respiratory rate, ie, they will be
ventilator time triggered.
▶Patient (assisted): If the patient does make an effort to breathe and the
ventilator can sense it (by either sensing a negative inspiratory pressure
or an inspiratory flow) and deliver a breath, it will be called a patient-
triggered breath.

20. Phase Variables: Trigger

21. Phase Variables: Trigger

22. Phase variables: Limit
Factor which controls the inspiration inflow
▶ Flow Limited: a fixed flow rate and pattern is set and maintained throughout inspiration.
▶ An adequate tidal volume (Ti dependent)
▶ Pressure will be variable (comp and resistance dependent)
▶ Pressure limited: the pressure is not allowed to go above a preset limit.
▶ The tidal volume will be variable (comp and resistance dependent)

23. Phase variables: Cycling
▶ Signal that stops the inspiration and starts the expiration.
▶ Without inspiratory pause: one signal
▶ With inspiratory pause: two cycling signals (one to close inspiratory valve and
the second to open the expiratory valve)
▶ Volume
▶ Time
▶ Flow
▶ Pressure : back-up form of cycling when the airway pressure reaches the
set high-pressure alarm level

24. The ventilatory cycle
Ti
PIP
PEEP
0.35 sec
T
e
0.65 sec
1 resp cycle= Ti + Te

25. Mechanical
Time (sec)
Spontaneous
Paw
(cm H2O)
Inspiration
Expiration
Expiration
Inspiration
Breath type: Spontaneous vs
Mechanical vs assisted
Assisted

26. Control variables
▶ Pressure: Pressure signal is the feedback signal (Pressure Preset)
▶ Volume: Volume signal is the feedback signal. usually measure the flow
and turn it into volume signal electronically. (volume preset)
▶ Time
▶ Flow
▶ Combinations

27. Volume Control Ventilation
Pressure
Volume
Flow
Preset Peak Flow
Preset Vt
Dependent on
Cl & Raw
Time (sec)

28. Pressure Control Ventilation
Flow
Pressure
Volume
Cl
Cl
Set PC level
Time (sec)

29. Basic Modes of Ventilation
▶ Controlled Mechanical Ventilation
▶ Assist Control Ventilation
▶ Intermittent Mandatory Ventilation
▶ Synchronized Intermittent Mandatory Ventilation
▶ Pressure Support
▶ Combinations

30. Controlled mandatory ventilation
(CMV)
The ventilator delivers
▶ Preset tidal volume (or pressure) at a time triggered (preset) respiratory
rate.
▶ As the ventilator controls both tidal volume (pressure) and respiratory rate,
the ventilator “controls” the patients minute volume.
Pressure

31. Controlled mandatory ventilation
(CMV)
Volume controlled Pressure controlled

32. Preset VT
Volume Cycling
Dependent on
CL & Raw
Time (sec)
Flow
(L/m)
Pressure
(cm H2O)
Volume
(mL)
Preset Peak Flow
Time triggered, Flow limited, Volume cycled Ventilation
Controlled mandatory ventilation (Volume-
T
argeted)

33. Flow
(L/min)
Pressure
(cm H2O)
Volume
(ml)
Time (sec)
Time-Cycled
Set PC level
Time Triggered, Pressure Limited, Time Cycled Ventilation
Controlled mandatory ventilation (Pressure-
Targeted)

34. Controlled mandatory ventilation
(CMV)
▶ Patient can not breath spontaneously
▶ Patient can not change the ventilator respiratory rate
▶ Suitable only when patient has no breathing efforts
▶ Disease or
▶ Under heavy sedation and muscle relaxants

35. Controlled mandatory ventilation
(CMV)
▶ Asynchrony and increased work of breathing.
▶ Not suitable for patient who is awake or has own respiratory efforts
▶ Can not be used during weaning

36. Assist Control Ventilation

37. Time (sec)
Control ventilation (CMV) Assist / control ventilation
Pressure
Control Control Assisted
Assist Control Ventilation

38. Control ventilation (CMV)
Assist / control ventilation
PressureAssist Control Ventilation
▶ A set tidal volume (volume control) or a set pressure and time (pressure
control) is delivered at a minimum rate
▶ Additional ventilator breaths are given if triggered by the patient
▶ Mandatory breaths: Ventilator delivers preset volume and preset flow rate
at a set back-up rate
▶ Spontaneous breaths: Additional cycles can be triggered by the patient but
otherwise are identical to the mandatory breath.

39. Assist Control Ventilation
▶ Tidal volume (VT) of each delivered breath is the same, whether it is
assisted breath or controlled breath
▶ Minimum breath rate is guaranteed (controlled breaths with set VT)
Control ventilation (CMV)
Assist / control ventilation
Pressure

40. Assist Control Ventilation
(volume) Assist Control
Ventilation
(Pressure) Assist Control
Ventilation

41. Time (sec)
Patient / TimeTriggered, Pressure Limited, Time Cycled Ventilation
Pressure
Flow
Volume
Set PC level
Time-Cycled
Pt triggered Time triggered
Assist Control Ventilation (Pressure)

42. Patient / Time triggered, Flow limited, Volume cycled Ventilation
Assist Control Ventilation (Volume)
Time (sec)
Flow
Pressure
Volume
Preset VT
Volume Cycling

43. Assist Control Ventilation
▶ Asynchrony taken care of to some extent
▶ Low work of breathing, as every breath is
▶ Hyperventilation
▶ Respiratory alkalosis.
supported and tidal volume is guaranteed.
▶ Natural breaths are not allowed
▶ Breath stacking
▶ High volumes and pressures
Control ventilation (CMV)
Assist / control ventilation
Pressure

44. Assist Control Ventilation
🞄Hyperventilation and breath stacking can usually be
overcome by choosing optimal ventilator settings and
appropriate sedation.
Control ventilation (CMV)
Assist / control ventilation
Pressure

45. Intermittent Mandatory Ventilation
(IMV)
Pressure
🞄Machine breaths are delivered at a set rate (volume or pressure
limit)
Time (sec)

46. Intermittent Mandatory Ventilation
(IMV)
Pressure
🞄Machine breaths are delivered at a set rate (volume or pressure
limit)
🞄Patient is allowed to breath spontaneously from either a
demand valve or a continuous flow of gases but not offering
any inspiratory assistance.
Time (sec)

47. Intermittent Mandatory Ventilation
(IMV)
Pressure
🞄Patient’s capability determines Tidal volume of spontaneously
breaths
🞄Some freedom to breath naturally even on mechanical ventilator
Time (sec)

48. Intermittent Mandatory Ventilation
(IMV)
Pressure
🞄Random chance of breath stacking and asynchrony: Increased
WOB
🞄Uncomfortable feeling
Time (sec)

49. Intermittent Mandatory Ventilation
(IMV)
Pressure controlled IMV Volume controlled IMV

50. Intermittent Mandatory Ventilation
(IMV)
Pros:
▶ Freedom for natural spontaneous
breaths even on machine
▶ Lesser chances of hyperventilation
Cons:
▶ Asynchrony
▶ Random chance of breath stacking.
▶ Increase work of breathing
▶ Random high airway pressure
(barotrauma) and lung volume
(volutrauma)
Setting appropriate pressure limit is important to reduce the risk of barotrauma

51. Can we synchronize
it?

52. Synchronized Intermittent Mandatory
Ventilation
▶ Ventilator delivers either patient triggered assisted breaths or time
triggered mandatory breath in a synchronized fashion so as to avoid
breath stacking
▶ If the patient breathes between mandatory breaths, the ventilator will
allow the patient to breathe a normal breath by opening the demand
(inspiratory) valve but not offering any inspiratory assistance.

53. Synchronization window
Pressure
🞄Time interval just prior to time triggering in which the ventilator
is responsive to the patient’s inspiratory effort.
Time trigerring
Time (sec)

54. SIMV
Pressure
If the patient makes a spontaneous inspiratory effort that falls in sync window,
the ventilator is patient triggered to deliver an assisted breath and will count it
as mandatory breath
Patient trigerred
synchronized breath
Time trigerred
mandatory breath

55. SIMV
Pressure
if patient does not make an inspiratory effort then ventilator will deliver a
time triggered mandatory breath.
Patient trigerred
synchronized breath
Time trigerred
mandatory breath

56. SIMV
Pressure
if patient does not make an inspiratory effort then ventilator will deliver a
time triggered mandatory breath.
Patient trigerred
synchronized breath
Time trigerred
mandatory breath
If the pt triggers outside this window, vent will allow this spontaneous breath to occur by opening the
demand (inspiratory) valve but does not offer any inspiratory assistance.

57. Synchronized Intermittent Mandatory
Ventilation
Pressure
3 types of breathing:
1. Patient initiated assisted ventilation,
2. Ventilator generated controlled ventilation,
3. Unassisted spontaneous breath.

58. Synchronized Intermittent Mandatory
Ventilation
P-SIMV V-SIMV

59. Synchronized Intermittent Mandatory
Ventilation (SIMV)
⚫It allows patients to assume a portion of their ventilatory drive:
Weaning is possible
⚫Greater work of breathing than AC ventilation and therefore some
may not consider it as the initial ventilator mode
⚫Friendly cardiopulmonary interaction: Negative inspiratory
pressure generated by spontaneous breathing leads to increased
venous return, which theoretically may help cardiac output and
function

60. Pressure Support Ventilation
▶ Pressure (or Pressure above PEEP) is the setting variable
▶ No mandatory breaths
▶ Applicable on Spontaneous breaths: a preset pressure assist,
▶Flow cycling: terminates when flow drops to a specified fraction
(typically 25%) of its maximum.
▶ Patient effort determines size of breath and flow rate.

61. Pressure Support Ventilation
▶ Pressure (or Pressure above PEEP) is the setting variable
▶ No mandatory breaths
▶ Applicable on Spontaneous breaths: a preset pressure assist,
▶ Flow cycling: terminates when flow drops to a specified fraction (typically
25%) of its maximum.
▶ Patient effort determines size of breath and flow rate

62. Pressure Support Ventilation
▶ Pressure (or Pressure above PEEP) is the setting variable
▶ No mandatory breaths
▶ Applicable on Spontaneous breaths: a preset pressure assist,
▶ Flow cycling: terminates when flow drops to a specified fraction (typically
25%) of its maximum.
▶ Patient effort determines size of breath and flow rate.

63. Pressure Support Ventilation
▶ It augments spontaneous VT decreases spontaneous rates and WOB
▶ Used in conjunction with spontaneous breaths in any mode of ventilation.
▶ No guarantee of tidal volume with changing respiratory mechanics,
▶ No back up ventilation in the event of apnea.

64. Pressure Support Ventilation
▶ Provides pressure support to overcome the increased work of breathing
imposed by the disease process, the endotracheal tube, the inspiratory
valves and other mechanical aspects of ventilatory support
▶ Allows for titration of patient effort during weaning.
▶ Helpful in assessing extubation readiness

65. SIMV + PS Ventilation
Pressure
Spontaneous breath with PS

66. Summary

67. Time (sec)
Control ventilation (CMV)
Pressure
Control
Assist / control ventilation
Control Assisted
Pressure
Pressure

68. Thank you!! You have done it!!!