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
10. Objectives
Understand how ventilators control breath delivery, phase and
control variables.
Understand the basic modes of ventilation.
Combinations, tailor-making, mix and match…
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
PEEP
PIP
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
15.
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
0
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.
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
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
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
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
37. Time (sec)
Control ventilation (CMV) Assist / control ventilation
Pressure
Control Control Assisted
Assist Control Ventilation
38. Control ventilation (CMV)
Assist / control ventilation
Pressure
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.
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
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
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
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
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)
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
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 windowPressure
Time interval just prior to time triggering in which the ventilator
is responsive to the patient’s inspiratory effort.
Time (sec)
Time trigerring
54. SIMVPressure
Patient trigerred
synchronized breath
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
Time trigerred
mandatory breath
56. SIMVPressure
Patient trigerred
synchronized breath
if patient does not make an inspiratory effort then ventilator will deliver a
time triggered mandatory 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.
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 VentilationPressure
Spontaneous breath with PS
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
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
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.
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.
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.