1. Review of Mechanical Ventilation
In The Name of GOD
Review of Mechanical Ventilation
Mohsen Savaie MD, CCM
Anesthesiologist, Intensivist
Assistant Professor

2. Mechanical Ventilation
Support Gas Exchange
Manage Work of Breathing
Ventilation goals are
Avoid Lung Injury
2/28

3. Abbreviations
VT : Volume of each respiration FiO2 : Fraction of inspiratory O2 (%)
RR : Respiratory Rate Ti : Inspiratory Time
MV : Volume that is inhaled or exhaled per min Te : Expiratory Time
PEEP : Positive End-Expiratory Pressure I:E Ratio : Ti/Te
CPAP : Continuous Positive Airway Pressure PIP : Peak Inspiratory Pressure
IPPV : Intermittent Positive Pressure Ventilation Flow : Inspiratory Flow Rate (Lit/Min)
Trigger : Factor that Start Inspiration (T, P, Flow)
3/28

4. Pressure Graph of Mechanical Ventilation
Peak Pressure
Plattue Pressure
PEEP t t
4/28

5. Timing of Mechanical Ventilation
Respiratory cycle time
Inspiratory time
Expiratory time
Inspiratory pause time
Volume
The time from the end of one inspiration to the beginning of the next is called the expiratory time
Inspiratory flow time
Time
5/28

6. Timing of Mechanical Ventilation
3 secs
2 secs
1 sec
 Respiratory rate without changing Inspiratory time or inspiratory flow
0.5 s
Flow
Volume
If the respiratory rate is increased the respiratory cycle shortens. If the inspiratory time is kept constant this will result in a change in I:E ratio. As the inspiratory flow has not been changed the inspiratory flow and pause times have not changed.
Set: RR, Insp Time, Flow rate
Time
6/28

7. Timing of Mechanical Ventilation
3 secs
1 sec
2 sec
0.5 s
Volume
So we also need to decrease the set inspiratory time
Time
Set: RR, Insp Time, Flow rate
7/28

8. Modes of Mechanical Ventilation
Volume Controlled
(A)CMV : (Assisted) Controlled Mechanical Ventilation
(S)IMV : (Synchronized) Intermittent Mandatory Ventilation
MMV : Mandatory Minute Ventilation
Pressure Controlled
PCV : Pressure Controlled Ventilation
(P) SIMV : Pressure SIMV
Spontaneous
PSV (ASB) : Pressure Support Ventilation (Assisted Spontaneous Breathing)
Other Modes
APRV, PRVC, BIPAP, NAVA, Smart, NIV, VAPS, ASV, PAV, HFPPV, HFJV, HFOV
8/28

9. Control Mandatory Ventilation (CMV)P
Tidal Volume
Respiratory Rate
Flow : lit/min
Peak Pressure t
9/28

10. Assist Control Mechanical Ventilation (ACMV)
Volume Control (Maquet)
IPPV (Drager)
S-CMV (Hamilton) P
Tidal Volume
Respiratory Rate
Trigger : 1-5
Flow : lit/min
Peak Pressure t
10/28

11. SIMV
Mandatory breath
Mandatory breath
Pressure support breath
Pressure
PEEP
Time
Flow
Time
Trig
Trig
Trig
Trig
Setting : TV, RR, Trigger : 1-5, Flow : lit/min, Peak Pressure, Pressure Support, PEEP, T insp (I/E)
11/28

12. PRVC (Pressure Regulated Volume Control)
(Auto flow Ventilation)
PRVC (Pressure Regulated Volume Control) P
Deliver a set TV at the minimum pressure level necessary, according to the airways/lung/thorax mechanics.
Constant pressure during the entire inspiration. 60 t P aw
cmH 2
SEC 1 2 3 4 5 6
-20
120
12/28

13. Pressure Control Ventilation (PCV)
Fio2
Peak Insp Pressure
Respiratory Rate
PEEP
PC above PEEP
Pressure
PEEP
Time
Flow
Time
A constant pressure is applied to the airway during inspiration. This results in a high initial flow which falls to zero or close to zero by the end of inspiration. As a result of this flow pattern oxygenation may be improved.
Volume
13/28
Time

14. Note that the pressure is applied to the proximal end of the ETT and is not the pressure in the alveoli as some of the pressure will be dissipated across the ETT and the major airways.
14/28

15. Pressure Support Ventilation (PSV) =Assisted Spont Breathing (ASB)
Fio2
Trigger : 1-5
Pressure Support 6-20
PEEP
VSV ?
Pressure
PS above PEEP
PEEP
Set % of max inspiratory flow
Constant preset airway pressure supplied during inspiration.
The patient is able to able to control the respiratory rate and the inspiratory time. By varying respiratory effort he is also able, to some extent, to control the tidal volume. As a result the tidal volume, inspiratory flow and inspiratory time may all vary from breath to breath
[Click on slide now to zoom in on flow waveform] Cycling from inspiration to expiration occurs when inspiratory flow decreases to a set percentage of the maximum inspiratory flow. This percentage is set using the inspiratory cycle-off control
Flow
Volume
15/28

16. BIPAP Bi-Level Positive Airway Pressure
Allows Spontaneous Breathing during the Mandatory Breaths
Spontaneous Breathing
BIPAP
The standard Mandatory Ventilation modes used in every ICU are IPPV and PCV (very seldom). Both Ventilation Modes guarantee the Patients Ventilation: IPPV, guarantees a Minute Volume, PCV guarantees that the pressure will never pass a previously set Pmax level. But both modes interact poorly with the patient, as you can see in the drawings.
The Ventilator will start fighting the patient, because the vent is only able to do what it was instructed to do, give mandatory strokes one after the other regardless of the patients efforts. Other events like coughing will also interrupt ventilation, creating high airway pressures.
The consequences are well known: alarms and sedation of the patient. So the patient won't suffer anymore from an inconsiderate ventilator that does not allow him to breath spontaneneously (by the way the patient will be very quiet and unable to do anything).
The patient's spontaneous breathing is surpressed...
(The blue part of our lung drawing is inactive, there is no creation of negative pressures by expansion of the diaphragm of the lung, only the red part the positive pressure generated by the mandatory strokes is still there)
PCV
16/28

17. BIPAP Bi-Level Positive Airway Pressure
Pinsp
Rise Time
The time it takes to achieve Pinsp
PEEP
The standard Mandatory Ventilation modes used in every ICU are IPPV and PCV (very seldom). Both Ventilation Modes guarantee the Patients Ventilation: IPPV, guarantees a Minute Volume, PCV guarantees that the pressure will never pass a previously set Pmax level. But both modes interact poorly with the patient, as you can see in the drawings.
The Ventilator will start fighting the patient, because the vent is only able to do what it was instructed to do, give mandatory strokes one after the other regardless of the patients efforts. Other events like coughing will also interrupt ventilation, creating high airway pressures.
The consequences are well known: alarms and sedation of the patient. So the patient won't suffer anymore from an inconsiderate ventilator that does not allow him to breath spontaneneously (by the way the patient will be very quiet and unable to do anything).
The patient's spontaneous breathing is surpressed...
(The blue part of our lung drawing is inactive, there is no creation of negative pressures by expansion of the diaphragm of the lung, only the red part the positive pressure generated by the mandatory strokes is still there) Ti
Ti - Inspiratory phase
lungs are maintained distended at set Pinsp Te
Te – Expiratory phase
Lungs are prevented from complete collapse by set PEEP
17/28

18. BIPAP and Synchronisation with Spontaneous Breathing
BIPAP Bi-Level Positive Airway Pressure
BIPAP and Synchronisation with Spontaneous Breathing P
Exp. Trigger t
Insp. Trigger
The standard Mandatory Ventilation modes used in every ICU are IPPV and PCV (very seldom). Both Ventilation Modes guarantee the Patients Ventilation: IPPV, guarantees a Minute Volume, PCV guarantees that the pressure will never pass a previously set Pmax level. But both modes interact poorly with the patient, as you can see in the drawings.
The Ventilator will start fighting the patient, because the vent is only able to do what it was instructed to do, give mandatory strokes one after the other regardless of the patients efforts. Other events like coughing will also interrupt ventilation, creating high airway pressures.
The consequences are well known: alarms and sedation of the patient. So the patient won't suffer anymore from an inconsiderate ventilator that does not allow him to breath spontaneneously (by the way the patient will be very quiet and unable to do anything).
The patient's spontaneous breathing is surpressed...
(The blue part of our lung drawing is inactive, there is no creation of negative pressures by expansion of the diaphragm of the lung, only the red part the positive pressure generated by the mandatory strokes is still there)
Exp.Trig. Window
Insp.Trig. Window
Dual PAP Ventilation (BIPAP+PS)
18/28

19. Oxygenation Failure Ventilatory Failure
Increase PEEP and Pinsp
Increase delta Pinsp – Peep ( Increase TV)
Change Tinsp or RR
Increase frequency (RR)
The Evita will always be synchronised with the Patient's Breathing so that there are less mismatches. The Ventilator always waits to give the mandatory stroke the moment when the patient is making and inspiratory effort or no effort at all (Flow is zero).
For the exhalation the vent also waits until the patient is exhaling or there is no further flow at all.
If this is not case, i.e. the patient is exhaling when there should the inspiratory phase, Evita waits until the patient has finished her/his exhalation, and then gives the mandatory stroke. (For the exhalation phase it is the same as inspiration but the other way around).
So Evita has smooth synchronization with the patient, and the flexible trigger window adapts the valve's behaviour to the patient's requirements, avoiding mismatches.
19/28

20. Airway Pressure Release Ventilation (APRV)
Continuous positive airway pressure (Inspiration) with regular, brief, intermittent releases in airway pressure (Expiration).
Positive pressure drives oxygenation.
The timed releases of pressure aid in CO2 clearance.
It is the primary mode of choice for patients with ARDS.
20/28

21. Airway Pressure Release Ventilation (APRV)
In diseased lung they become important
21/28

22. APRV Setting 22/28 P High : = Plattue Pressure P Low (Release) : = 0
T High : = seconds (0.5-2 each times)
T Low : = 0.5–0.8 seconds
Frequency should always be less than 12
Patient must be encouraged to breathe spontaneously during APRV
22/28

23. Adaptive Support Ventilation (ASV)
Very easy mode presented by Hamilton corporation.
You set only the patients weight or height and percent of calculated minute volume that must be delivered by machine, then lventilator automatically set best RR and TV to provide minute ventilation.
23/28

24. Volume vs Pressure Modes ?
Volume Modes
TV is constant
Inspiratory pressure varies
Inspiratory flow is constant
Pressure Modes
TV varies
Inspiratory pressure is constant
Inspiratory flow varies
24/28

25. Which Mode is Better ? Apnoeic patient :
Control of minute ventilation important → → Volume Assist Control
Control of peak pressure important → → Pressure Assist Control
Intermittent spontaneous breaths → → SIMV
Regular spontaneous breaths and improving condition → → PS
25/28

26. Problem Solving Low O2 Saturation High PCo2 Other Problems ? 26/28
Increase FiO2
Check Patient and Circuit
Increase PEEP
Increase Inspiration Time
High PCo2
Check Patient and Circuit
Increase TV
Increase RR
Other Problems ?
26/28

27. Clinical Pearls
Ventilator kills your patient unless you prevent it from doing so!
The best mode is the most suitable and comfortable mode for patients (not for you).
Patient fight with your mistakes not with the ventilator!
Calm your patient with opioids & Hypnotics, not relaxants.
‌Nebulizers & Humidifiers are your guardian angels.
Use lab. tests to conform diagnosis not to diagnose.
Plan and order nutrition professionally.
Plan for and manage the stress of ETT & IPPV.
27/28

28. Thanks for your attention