2. What are ventilators ?
A machine that
generates a
controlled flow
of gas into a
patient’s airways
2
3. Basic Ventilator Parameters
Tidal volume
Frequency
PIP
Plateau Pressure
PEEP
Inspiratory Time
Expiratory time
I : E Ratio
3
4. Basic Ventilator Parameters
Mode
Tidal volume
Frequency
PIP
Plateau Pressure
PEEP
Inspiratory Time
Expiratory time
I : E Ratio
4
5. Starting a ventilator : Mode
Mode denotes interplay between patient and the
ventilator
Describes the style of breath support based on
relationship between the various possible types of
breath and inspiratory – phase variables
5
6. 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
6
10. 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
10
13. Basic Modes of Ventilation
Controlled Mandatory Ventilation
Assist Control Ventilation
Intermittent Mandatory Ventilation
Synchronized Intermittent Mandatory Ventilation
Pressure Support
Combinations
13
14. 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
14
18. 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
18
19. 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
19
21. Time (sec)
Control ventilation (CMV) Assist / control ventilation
Pressure
Control Control Assisted
Assist Control Ventilation 21
22. 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.
22
23. 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
23
25. 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) 25
26. Patient / Time triggered, Flow limited, Volume cycled Ventilation
Assist Control Ventilation (Volume)
Time (sec)
Flow
Pressure
Volume
Preset VT
Volume Cycling
26
27. 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
27
28. 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
28
30. 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)
30
34. 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
34
36. 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.
36
37. Synchronization window
Pressure
Time interval just prior to time triggering in which the ventilator
is responsive to the patient’s inspiratory effort.
Time (sec)
Time trigerring
37
38. SIMV
Pressure
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
38
40. SIMV
Pressure
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.
40
43. 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
43
44. 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
44
45. 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.
45
46. 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.
46
47. 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
47
53. 53
Ventilation modality types
Pressure Volume
Controlled breath Assist/Controlled breath Spontaneous breath
+ Sedation -
Patient trigger and cycle the breath
Patient trigger the breath
Ventilator cycle the breath
Ti Te
Editor's Notes
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.