A brief introduction to mechanical ventilation. contains details on the various variables, modes and settings on the mechanical ventilator. a simple explanation of what seems to be so complicated.

1. BASICS OF MECHANICAL
VENTILATION
Presenter : Dr Anusha M
Moderator : Dr Archana Bhat
Dr Glenn
1

2. INTRODUCTION
-Mechanical ventilation is a therapeutic method that is used to either assist or replace
spontaneous breathing.
-It is indicated in patients who have developed either ventilation failure or oxygenation
failure which may be caused by one of the following pathophysiological mechanisms:
1.Increased airway resistance
2.Changes in lung compliance
3.Hypoventilation
4.V/Q mismatch
5.Intrapulmonary shunting
6.Diffusion defect.
2

3. BASIC PRINCIPLES
Patients requiring mechanical ventilation
Depressed respiratory drive
Excessive ventilatory workload
Failure of ventilatory pump
3

4. VENTILATORY WORK
• The work that the muscles and/or the ventilator must perform is proportional to the
pressure required for inspiration times the tidal volume.
• The pressure required is referred to as the “load” either the muscles or the ventilator
has to work against.
• This is of 2 types- an ELASTIC LOAD (proportional to volume and inversely
proportional to compliance) and a RESISTANCE LOAD (proportional to the airway
resistance).
4

5. TYPES OF MECHANICAL
VENTILATION
Non invasive mechanical ventilation
(NIV)
Conventional mechanical ventilation
(MV)
5

6. NON INVASIVE MECHANICAL
VENTILATION
• Usually provided by using a tight fitting face mask or nasal mask similar to the masks
traditionally used for sleep apnea.
• Very similar to invasive ventilation in that it supports improved gas exchange and
decreased respiratory muscle work.
• The main difference between NIV and MV is that it uses a mask or a helmet interface
rather an endotracheal tube.
• This offers the advantages of being readily taken on and off to facilitate weaning,
maintaining some ability to communicate and also avoids the complications of
sedation and ventilator associated pneumonia.
6

7. • The ideal candidate for NIV:
1. Has a strong cough and minimal secretions
2. Tolerates the interface well
3. Has a quickly reversible condition
• Useful in patients with respiratory failure from acute exacerbations of chronic
obstructive pulmonary disease.
• NIV works on the principle of bilevel positive airway pressure ventilation or pressure
support ventilation.
• It has an End Positive Airway Pressure (EPAP) and an Inspiratory Positive Airway
Pressure (IPAP).
7

8. INITIATING NIV
• The patient requires appropriate acclimatization to the interface before the initiation
• The pressures have to be titrated to the optimal levels.
• One of the strategy recommended is to start by holding the mask on the patient’s face
while talking with them and titrating up the pressures.
• The mask should then be strapped on and adjusted for optimal comfort.
• Most sensitive objective measure of response to NIV- RESPIRATORY RATE.
• All improvements should occur within the first 30-60 minutes of initiating NIV.
8

9. DISADVANTAGES OF NIV
• No direct protection of the airway
• No deep suctioning below the vocal cords
• Limited ability to apply high pressures
• Development of intolerance to the mask over time.
9

10. CONTRAINDICATIONS TO NIV
In patients with
• Restless and agitated patient
• Poor airway protection
• Copious secretions
• Recent esophageal surgery
• Cardiac or respiratory arrest
• Unstable angina and myocardial infarction
• Severe encephalopathy
• Severe GI bleed
• Hemodynamic instability
• Facial trauma or burns
• Upper airway obstruction
10

11. CHOOSING AN INTERFACE
TOTAL FACE MASK
NASAL MASK
HELMET
FULL FACE MASK
11

12. CONVENTIONAL
MECHANICAL VENTILATION
INDICATIONS:
Diseases causing airway obstruction:
•Central: tumor, laryngeal edema, tracheal stenosis
•Peripheral: status asthmaticus, acute exacerbation of COPD
Diseases causing hypoventilation:
•Central : stroke, intracerebral hemorrhage, drug overdose
•Peripheral: neuromuscular weakness due to GB syndrome, amyotrophic lateral
sclerosis
Chest wall disease : Kyphoscoliosis
Alveolar respiratory disease: Pneumonia, Alveolar proteinosis, ARDS
12

13. Cardiovascular disease : CHF, cardiac arrest, severe shock of any etiology
Others: pneumothorax, trauma, pulmonary embolism
Post operative management: for patients who are not able to be safely extubated
following the surgical procedure, either due to an underlying condition, the nature of
the surgery or complications of the surgery. Examples : Patients with
•Morbid obesity
•Post operative hypothermia
•Pre existing lung disease
•Cardiac surgery
•Gross abdominal distension
13

14. CLINICAL PARAMETERS
Obtundation or coma
Restless or agitated patient
Inability to clear secretions
Respiratory rate of >35/ minute
Rising PaCO2 (>50 mmHg) on the ABG, despite interventions
Severe hypoxemia (PaO2 <40mmHg, SaO2 <75%)
Progressive acidosis (pH < 7.30)
Hypotension
14

15. CONTROL VARIABLES
When providing ventilatory support, the mechanical ventilator can control 4 primary
variables:
PRESSURE
VOLUME
FLOW
TIME
15

16. VOLUME CONTROLLER: uses volume change as a feedback signal to control the
volume delivered. It measures volume by the displacement of the piston or bellows
that serve as the ventilator’s drive mechanism.
FLOW CONTROLLER: allows pressure to vary with changes in the patient’s
compliance and resistance while directly measuring and controlling flow. Flow may be
measured by vortex sensors, heated wire grids, Venturi pneumotachometers, strain
gauge flow sensors and other devices.
TIME CONTROLLERS: are ventilators that measure and control inspiratory and
expiratory time.
16

17. PRESSURE CONTROLLER
When the ventilator controls the trans respiratory system pressure (airway
pressure minus body surface pressure).
It can be further classified as a POSITIVE PRESSURE VENTILATOR when it
applies pressure inside the chest to expand it and once the pressure is stopped,
the patient exhales passively through the recoil of the lungs and chest wall. This
type of ventilator requires the use of a tight fitting mask or an airway.
17

18. Regardless of the type of pressure applied, the lungs expand as a result of positive
TRANS RESPIRATORY SYSTEM PRESSURE which will determine the depth and
volume of inspiration. Hence, a typical pressure controller is unaffected by changes in
the patient’s compliance or resistance.
18

19. PHASE VARIABLE
A ventilator supported breath may be
divided into four distinct phases:
I. The change from expiration to
inspiration
II.Inspiration
III.The change from inspiration to
expiration
IV.Expiration
19

20. TRIGGER VARIABLE
The variable that determines the start of inspiration in a ventilator.
Any of the four control variables may be used by the ventilator to initiate inspiration.
Time triggered breath: initiated and delivered by the ventilator when a preset time
interval has elapsed. This is determined by the respiratory rate which has been set
on the ventilator.
EX: If the ventilator respiratory rate is set at 12 breaths per minute, the time triggering
interval for each complete breath is 5 seconds and the ventilator automatically delivers
one mechanical breath every 5 seconds without regard to the patient’s breathing effort.
20

21. 21

22. PRESSURE TRIGGERED
BREATH
It is initiated and delivered by the ventilator when it senses the patient’s spontaneous
(negative pressure) inspiratory effort.
Pressure triggering uses the drop in airway pressure that occurs at the beginning of a
spontaneous inspiratory effort to signal the ventilator to begin inspiration.
The amount of negative pressure below the patient’s baseline airway pressure (or
end expiratory pressure) a patient must generate to trigger the ventilator into
inspiration is the sensitivity level. The range of acceptable sensitivity levels is -1 to -
5cm of H20 below the patient’s baseline pressure.
22

23. 23

24. FLOW TRIGGERED
When the patient’s inspiratory flow reaches a specific value, a ventilator supported
breath is delivered.
It is more sensitive and responsive to to a patient’s efforts
Here, a continuous flow passes through the ventilator circuit and returns to the
ventilator (delivered flow= returned flow).
As the patient initiates a breath, part of the delivered flow goes to the patient and the
return flow to the ventilator is therefore reduced. The ventilator senses this flow
differential and instantly supplies enough flow to satisfy the mechanical or
spontaneous tidal volume.
CMV, SIMV and PSV can all be flow triggered.
24

25. 25
RETURNED FLOW=DELIVERED FLOW RETURNED FLOW< DELIVERED FLOW

26. LIMIT VARIABLE: The variable which is not allowed to rise above a preset value
during the inspiratory time.
CYCLE VARIABLE: Inspiration ends when a specific cycle variable is reached which
will be measured by the ventilator and used as a feedback signal to end the
inspiratory flow delivery which then allows the exhalation to begin.
26

27. MODES OF MECHANICAL
VENTILATION
A ventilator mode is a set of operating characteristics that control how the ventilator
functions.
(1)Positive End Expiratory Pressure (PEEP)
(2)Continuous Positive Airway Pressure (CPAP)
(3)Bi level Positive Airway Pressure (BiPAP)
(4)Controlled Mandatory Ventilation (CMV)
(5)Assist Control (AC)
(6)Intermittent Mandatory Ventilation (IMV)
(7)Synchronised Intermittent Mandatory Ventilation (SIMV)
(8)Mandatory Minute Ventilation (MMV)
(9)Pressure Support Ventilation (PSV)
(10)Pressure Control Ventilation (PCV)
(11)Airway Pressure Release Ventilation (APRV)
(12)Inverse Ratio Ventilation (IRV)
27

28. CLASSIFICATION OF
VENTILATOR MODES
28
CONTROL MODES SUPPORT MODES
Pressure controlled Volume controlled
PSV
CPAP
PEEP
BiPAP
IMV
SIMV
Assist Control

29. 29
CHARACTERISTI
CS
VOLUME TARGETED
MODES
PRESSURE TARGETED
MODES
EXAMPLES CMV, A/C, SIMV PSV, PCV
VOLUME
Constant
Guarantees volume at expense of
letting airway pressure vary
Variable
Guarantees pressure at expense
of letting tidal volume vary
INSPIRATION
Terminates when the preset tidal
volume is delivered
Terminates when preset
pressure is reached
PEAK AIRWAY
PRESSURE
Variable
It increases as needed to deliver
prescribed tidal volume
Fixed
Volume delivered will decrease
with increased airway resistance
or decreased lung compliance
INSPIRATORY
FLOW RATE
Fixed
If patient breathes faster, work of
breathing increases
Variable
If patient inspires faster, variable flow
rate may match change in inspiratory
demand or may be insufficient.

30. 30

31. PEEP
It increases the baseline airway pressure
or the end expiratory pressure to a value
greater than atmospheric pressure.
Indications: (a) Increased intrapulmonary
shunt (b) Decreased lung compliance (c)
refractory hypoxemia (when the patient’s
PaO2 is 60mmHg or less at an FiO2 of
50% or more)
31

32. 32
Basic principle is that PEEP
reinflates the collapsed alveoli and
maintains alveolar inflation during
exhalation. Once “recruitment” is
over, PEEP lower the alveolar
distending pressure and facilitates
gas diffusion and oxygenation.
Disadvantages: (a) decreased
venous return (b) Barotrauma (c)
Increased ICP (d) alteration in the
renal function

33. CPAP
33
PEEP applied to the airway of a
patient who is breathing
spontaneously.
When EPAP is same as IPAP,
CPAP results.

34. BIPAP
34
•Applies positive pressures to both inspiration
and expiration
•IPAP provides positive pressure breaths
which improves hypoxemia and/or
hypercapnia.
•EPAP is in essence CPAP which improves
the recruitment of the alveoli.
•Indications: chronic respiratory failure.
•It may be used in one of the following modes:
a)Spontaneous
b)Spontaneous /time (S/T)
c)Timed
•EPAP can never be increased to more than
IPAP.

35. CMV
35
The preset tidal volume is delivered at a set
time interval (time triggered respiratory rate)
Hence, the ventilator is controlling both the
tidal volume and the respiratory rate I.e it is
controlling the minute ventilation
Requires sedation
Used when the patient “fights” the ventilator
in the initial stages of ventilatory support.
Their spontaneous respiratory efforts
become asynchronous with the ventilator’s
ability to to provide adequate inspiratory
flow.

36. ASSIST CONTROL
36
The patient is allowed to increase
the ventilatory respiratory rate (i.e
assist) in addition to preset
mechanical ventilatory respiratory
rate.
Cycling mechanism: Inspiration
is terminated when a preset tidal
volume is delivered and the
ventilator is cycled to expiration.
It does not allow the patient to
take spontaneous breaths but both
the ventilatory breath and the
assist breath have the same
preset tidal volume.

37. Indications: Used as an initial setting in patients with stable respiratory drive
(spontaneous inspiratory efforts of at least 10-12/ minute)
Advantages : Patient’s work of breathing is very small when the triggering sensitivity
(pressure or flow) is set appropriately. It allows the patient to control the respiratory
rate and therefore the minute ventilation to normalize the PaCO2.
Disadvantages : Alveolar hyperventilation.
37

38. IMV
38
A mode in which the ventilator delivers the
mandatory breath and also allows the
patient breathe spontaneously at any tidal
volume the patient is capable of in
between the mandatory breaths.

39. 39
Disadvantage : BREATH STACKING- when the patient takes a
spontaneous breath while the mandatory breath is being delivered
and thus increasing the lung volume and airway pressure
significantly.

40. SIMV
40
•A mode in which the ventilator delivers the
mandatory breaths to the patient at or
near the time of a spontaneous breath.
Hence, the mandatory breaths are
synchronized with the spontaneous
breaths.
•Patient triggering might be based on
either pressure or flow.
•During the time interval just before the
mandatory breath is being delivered, the
ventilator is responsive to the patient’s
spontaneous inspiratory efforts and is
called as the SYNCHRONISATION
WINDOW.

41. In between the mandatory breaths, the patient is allowed to breathe spontaneously to
any tidal volume the patient desires. The gas source is supplied by a demand valve
which is always patient triggered and is either pressure or flow dependent.
Indications: To provide partial ventilatory support.
Advantages : (a) avoids muscle atrophy (b) reduces ventilation to perfusion
mismatch (c) facilitates weaning.
41

42. MMV
An additional function of the SIMV mode where a predetermined minute ventilation is
delivered to the patient when there is an apnea episode. Then, there will be an
automatic increase in the mandatory breath rate, thereby increasing the minute
ventilation.
42

43. PSV
43
A preset pressure is applied to the
patient’s airway for the duration of a
spontaneous breath.
It lowers the work of spontaneous
breathing and augments the tidal
volume of a spontaneous breath.
It may be used along with SIMV mode
to facilitate weaning in a difficult to
wean patient.

44. PCV
44
The pressure controlled breaths are time triggered by a preset respiratory rate and hence req
Indicated in severe ARDS.

45. SUMMARY
45
MODE FUNCTION CLINICAL USE
CONTROL
VENTILATION
Delivers preset volume or
pressure regardless of patient’s
own inspiratory efforts
Usually used for apneic patients
ASSIST
VENTILATION
Delivers breath in response to
patient efforts
Used for spontaneously
breathing patients with
weakened respiratory muscles
SIMV
Breaths are synchronized with
patient’s respiratory efforts
Used for weaning patients
PRESSURE
SUPPORT
VENTILATION
Preset pressure that augments
the patient’s inspiratory efforts
Often used with SIMV during
weaning

46. 46
MODE FUNCTION CLINICAL USE
PEEP
Positive pressure applied at the
end of expiration
Used along with A/C, CV and
SIMV to improve oxygenation by
recruitment
CPAP
Similar to PEEP but used only
spontaneously breathing
patients
Maintains constant positive
pressure in airways

47. NEGATIVE PRESSURE
VENTILATION
NEGATIVE PRESSURE VENTILATORS apply sub atmospheric pressure outside the
chest wall, which causes the chest wall to expand, and the pressure difference
between the lungs and the atmosphere causes air to flow into the lungs. Once
negative pressure is no longer applied, the patient is allowed to exhale passively to
ambient pressure.
Unless an airway obstruction is present, this type of ventilation doesn’t require an
artificial airway.
47

48. IRON LUNGS
It encloses the patient’s body except for the head and neck in a tank and the air in it
is evacuated to produce a negative pressure around the chest cage.
The tidal volume delivered is directly proportional to the negative pressure applied to
the chest wall.
Since this type of ventilation does not require intubation, it has been extensively used
to support chronic respiratory failure.
The disadvantages include poor patient access, decreased cardiac output, known as
“tank shock”
48

49. 49

50. CHEST SHELL/ CUIRASS
Designed to alleviate disadvantages associated with iron lungs where only the
patient’s chest is covered and leaves the arms and lower body exposed. Best suited
for home care settings.
50

51. MECHANICAL VENTILATION
IN COPD
NIV is the first line of treatment for these patients
MV is required in patients who have a more severe form of the disease.
Indications:
• MAJOR: (any one of the following):
A. Respiratory arrest
B. Loss of consciousness
C. Psychomotor agitation requiring sedation
D. Hemodynamic instability with systolic BP <70 or >180 mmHg
E. Heart rate <50 BPM
F. Gasping for air
51

52. MINOR (any two of the following):
A. Respiratory rate >35 breath/ min
B. Worsening acidaemia or pH <7.25
C. PaO2 <40 mmHg or PaO2/ FiO2 <200mmHg despite oxygen
D. Decreased alertness
52

53. NIH NHLBI ARDS CLINICAL NETWORK
MECHANICAL VENTILATION PROTOCOL
SUMMARY
INCLUSION CRITERIA:
1. PaO2/ FiO2 < 300 (corrected for altitude)
2. Bilateral patchy, diffuse, or homogenous infiltrates consistent with pulmonary
edema
3. No clinical evidence of left atrial hypertension.
VENTILATOR SETUP AND ADJUSTMENT :
• Calculate predicted body weight- 50 (female- 45.5) + 2.3 [height-60]
53

54. • Select any ventilator mode
• Set ventilator settings to achieve an initial tidal volume of 8ml/ kg PBW
• Reduce tidal volume by 1ml/kg at intervals <2 hours until Vt= 6ml/ kg PBW
• Set initial rate to approximate baseline minute ventilation (<35 /minute)
• Adjust the Vt and RR to achieve pH and plateau pressure goals below.
54

55. WEANING:
• Criteria for conducting SPONTANEOUS BREATHING TRIAL:
1. FiO2 <0.40 and PEEP <8
2. FiO2 and PEEP values lesser than the previous day
3. SBP >90mmHg without vasopressor support
4. No neuromuscular blocking agents being used.
55

56. SPONTANEOUS BREATHING TRIAL:
If all above criteria are met and subject has been in the study for at least 12 hours,
initiate a trial of up to 120 minutes Spontaneous Breathing with FiO2 <0.5 and PEEP <5
If tolerated for at least 30 minutes, consider extubation.
If not tolerated, presume pre weaning settings.
56

57. REFERENCES
1.David WC. Clinical Application of Mechanical Ventilation 2nd edition, Delmar
Thomson Learning Inc. 2001
2. Harrison T, Kasper D. Harrison's principles of internal medicine. New York: McGraw-
Hill Medical Publ. Division; 2017.
3.Tintinalli, J. E., Stapczynski, J. S., Ma, O. J., Yealy, D. M., Meckler, G. D., & Cline, D.
(2016). Tintinalli's emergency medicine: A comprehensive study guide (Eighth
edition.). New York: McGraw-Hill Education.
4.McConachie I. Handbook of ICU Therapy. 3rd ed. Leiden: Cambridge University
Press; 2006.
57

58. Thank you
58