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

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

14. What does flow sensor do?
Flow in ventilator circuit- constant
T-connection
Flow sensor
ETT
Insp flow
Exp flow  RR
= tidal vol
- 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 Te
Inspiration: the change from expiration to 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

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)
When the inspiratory valve is opened, gas from the compressor will rush into the lung (at a compressed pressure of 60 lb/in2) unless limited by some ventilator mechanism. The term 'limit' denotes the factor which controls the inspiration inflow. It implies that the set limit cannot be overcome and yet, on reaching this The ventilator can either deliver gas at a fixedflow rate and pattern or at a fixed
pressure during inspiration. In flow-limited breathing, a fixed inspiratory flow rate
and pattern is set by the clinician and maintained throughout inspiration. As the
flow is assured, the patient will receive an adequate tidal volume for a given
inspiratory time. However, the airway pressure will rise to whatever level is
required to deliver the flow and there is therefore an increased likelihood of

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 PIP PEEP Ti Te 0.65 sec 0.35 sec
1 resp cycle= Ti + Te

25. Breath type: Spontaneous vs Mechanical vs assisted
Time (sec)
Spontaneous
Paw
(cm H2O)
Inspiration
Expiration
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
Preset Peak Flow
Flow
Dependent on
Cl & Raw
Pressure
Preset Vt
Volume
Time (sec)

28. Pressure Control Ventilation
Flow
Set PC level
Pressure Cl Cl
Volume
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
The ventilator delivers the preset tidal volume at a time triggered (preset) respiratory rate. As the ventilator controls both tidal volume and respiratory rate, the ventilator “controls” the patients minute volume. The patient can not change the ventilator respiratory rate or breath spontaneously. Thus this mode should be applied only when patient has no breathing efforts either due to disease or under heavy sedation and muscle relaxants otherwise it will lead to asynchrony and increased work of breathing.

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

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

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

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

38. Assist 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.
Control ventilation (CMV)
Assist / control ventilation
Pressure

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
Tidal volume (VT) of each delivered breath is the same, whether it is patient triggered (assist) or ventilator triggered (control)
If the patient does not initiate a breath before a requisite period of time determined by the set respiratory rate (RR), the ventilator will deliver the set VT
Regardless of whether the breath is patient-triggered or time-triggered, the exhalation valve closes and the ventilator generates inspiratory flow at a set rate and pattern (flow limited). Inspiratory flow lasts until the set VT is delivered at which time the breath is cycled-off (volume-cycled).
Thus, the AC mode is patient- or time-triggered, flow-limited, and volume-cycled. The airway pressures generated by chosen ventilator settings are determined by the compliance of the respiratory system and the resistance of the airways.

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

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

42. Assist Control Ventilation (Volume)
Patient / Time triggered, Flow limited, Volume cycled Ventilation
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 supported and tidal volume is guaranteed.
Hyperventilation
Respiratory alkalosis.
Natural breaths are not allowed
Breath stacking
High volumes and pressures
Control ventilation (CMV)
Assist / control ventilation
Pressure
tachypnea could lead to hyperventilation and respiratory alkalosis. Breath stacking can occur when the patient initiates a second breath before exhaling the first. The results are high volumes and pressures in the system.

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:
Cons:
Freedom for natural spontaneous breaths even on machine
Lesser chances of hyperventilation
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
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
Pressure
Patient trigerred synchronized breath
Time trigerred mandatory breath

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

56. SIMV
if patient does not make an inspiratory effort then ventilator will deliver a time triggered mandatory breath.
Pressure
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:
Patient initiated assisted ventilation,
Ventilator generated controlled ventilation,
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. Control ventilation (CMV) Assist / control ventilation
Time (sec)
Control ventilation (CMV)
Assist / control ventilation
Pressure
Control Control Assisted
Pressure
Pressure

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