This document provides an overview of basic ventilator mechanics including: 1) Definitions of mechanical ventilation, the types of mechanical ventilation including invasive positive and negative pressure ventilation, and the indications for mechanical ventilation. 2) Basic ventilator terminology including lung compliance, elasticity, tidal volume, minute ventilation, inspiratory-expiratory ratio, and more. 3) The criteria for initiation of invasive mechanical ventilation, types of breaths and modes of ventilation including controlled, assist-control, SIMV, and spontaneous/pressure support modes. 4) Initial ventilator settings and adjustments including factors like FiO2, tidal volume, respiratory rate, PEEP, and how to troubleshoot issues

1. Basic Ventilator Mechanics
Nasreen Rafiq
(MScN,BScN)

2. Objectives
• Definition of mechanical ventilation
• Indication and types of mechanical ventilation
• Basic ventilation terminologies
• Criteria of mechanical ventilation
• Variable for ventilatory breaths
• Types of breaths and Modes of ventilation
• Basic ventilator settings
• Ethical consideration

3. Invasive Mechanical Ventilation
Artificial ventilation of lungs through endo-tracheal or tracheostomy
tubes using ventilators.
Advantages
▪ Protects airway
Disadvantages
▪ High cost and patients’ discomfort
▪ Improves ventilation & tissue
oxygenation
▪ Ventilator associated injuries and
infections
▪ Decreases the work of breathing
(Chang, 2014; Wunsch, 2010)

4. Indications
1. Neurological Impairment CNS Involvement (Drug overdose, brain
Role of Nurses
injury/lesion)
2. Neuromuscular abnormalities (Myasthenia Gravis, GBS)
• Identify the
indication of
3. Primary respiratory impairments (respiratory failures, pneumonia, ARDS,
mechanical
COPD, pulmonary edema, atelectasis, fibrosis)
ventilation
4. Post surgery (General anesthesia)
5. Post cardiac arrest
6. Trauma (chest wall trauma)

5. (Iqbal et al., 2015)
Types of Invasive Mechanical Ventilation
Positive-pressure Ventilation
Mechanical Ventilation

6. Negative-pressure Ventilation
(Kacmarek, 2011)
Basic Terminologies
o Lung Compliance (Distensibility): Change in
volume per unit change in pressure. V/ P
o Lung Elastance (Elasticity): Change in
pressure required to elicit a unit change in

7. volume (reciprocal of compliance). 🡪 intrinsic
tendency to deflate following inflation
(Papandrinopoulou, Tzouda, & Tsoukalas, 2012)
Pressure Volume Curve for Lung Compliance and Elasticity
Increased
Compliance and
decreased
Elasticity
Normal Compliance
and Elasticity
Over-Distention Barotrauma Dynamic

8. hyperinflation
X mL e
m
u
Decreased
Compliance and
Increased elasticity
l
o
V
g
n
u
L
5 cmH 2O
Pleural Pressure
10 cmH 2O
20 cmH 2O

9. Terms and Definitions
o Tidal Volume (Vt): Amount of air passes in and out of lungs with each cycle.
(volume delivered with each preset breath)
o Minute Ventilation (VE): Volume of gas exchanged per minute [RR x TV]
o Inspiratory:Expiratory (I:E) Ratio: the ratio of inspiratory to expiratory
time determined by the speed of gas flow (1:2)
o Vital Capacity (VC): Maximum air expelled from lungs after a maximum
inhalation

10. o Flow: Speed of gas flow delivered during inspiration.
Flow Volume Curve for Lung Ventilation Inc. flow 🡪 Faster

11. speed of gas 🡪 shorter Inspiratory time (Ti)
FRC: volume
of air left in
the lungs
after a
normal
expiration
Terms and Definitions

12. oPeak Inspiratory Pressure (PIP): Highest proximal (upper) airway pressure
reached during inspiration.
oPlateau Pressure (Pplat): the pressure on small airways and alveoli at the end
of inspiration (inspiratory pause; goal<30 cmH2O).
oPositive End Expiratory Pressure (PEEP): The positive pressure that
remains in the alveoli at the end of expiration to restore FRC.
oAuto-PEEP Unintentional intrapulmonary PEEP (Positive pressure) due to
unwanted air trapping.
Chang, 2014

13. (Gattinoni, 2016)
Criteria for Initiation of Invasive Ventilator Support
Parameters Normal
Ranges
Ventilator
Indication
Respiratory rate
(breaths/min)
10-20 bpm >35
Tidal Volume (ml/kg
of IBW)
5-8ml/kg <3
Vital Capacity 50-60ml/kg <10-15
(Chang, 2014)

14. Criteria for Initiation of Invasive Ventilator SupportRole of Nurses
Parameters
• Monitor vital si
Normal
ABGs, chest
X-ray.Ranges
Ventilator
Indication
• Encourage deep breathing,
ABGs
coughing suctioning,
nebulization.
PH •
7.35-7.45
BIPAP trial.
< 7.25

15. PaO2 • 70-100
Identify th
need and
indicatio
of invasi
< 60
PCO2
• 35-45
mech
ventilation.
Monit
the work
> 50
(Chang, 2014)
breathing
Ventilator Variables

16. Control Variables
Time
Flow
Volume
Pressure
Phase Variables
Sensitivity Trigger
Independent & fixed during every breaths
Control initiation of inspiratory phase in the
ventilator cycle
Time
Flow
Drop 🡪 begins the
inspiration.
Identifies patients’
respiratory effort
Initiates

17. response to that
effort
Pressure
PVA due to ineffective trier settin occurred in 93% Mellot et al. 2014
Triggers

19. Variables
Role of Nurses
• Determine correct
Cycle Variable • Determines the termination of the
Inspiration is terminated after
trigger
and
Inspiration is terminated after
a preset pressure has been
inspiration
a preset tidal volume has been
Pressure
Flow sensitivity.
• Breath gets terminated once the pre
Volume
set value is reached Time
delivered by the ventilator delivered by the ventilator

20. • Set correct values
and achieved by the patient. for
control
and achieved by the patient
Inspiration is terminated after a preset
variables.
inspiratory time (Ti) is achieved.
• Determine the

21. patient required
Inspiration is terminated when
cycle variable.
a preset air flow is delivered
in the preset inspiratory time.
(Chang, 2014)
Types of Breaths
Breath Types

22. Mandatory Spontaneous
(Kim & Doyle, 2012)
Modes of Ventilator
Control Mode Ventilation

23. Assist control Mode Ventilation
Synchronized Intermittent Mandatory Ventilation
Spontaneous/pressure Support Mode Ventilation
(Kim & Doyle, 2012)
Controlled Mode Ventilation (CMV)

24. Type of breaths: Mandatory breaths mechanically delivered. Trigger and
cycle: Ventilator controlled (Breaths are initiated and terminated by the
ventilator).

25. Assist-control (AC) Mode Ventilation
Volume Controlled
Modes
Pressure Controlled

26. Mandatory Breath
Types
Controlled Breaths
Assisted Breaths
Volume Versus Pressure Control in (AC) Mode Ventilation
• Volume Control
• Delivers a particular volume
of air with each breath
• Vt and MV remain constant
• Pressure varies and depends
upon:
⮚ Patient’s lung compliance

27. Pressure Control
• Delivers a selected gas
pressure with each breath
• PIP and pPlat remain constant
• Tidal volumes vary and
depend upon:
⮚ Patient’s lung compliance
Controlled Versus Assisted Breaths in (AC) Mode Role of an
Nurses
• Calculate IBW to set effective

28. Vt.
Advantages
•
Patient controlled trigge
• Decreases patients’ workup of
ventilation.
breathing.
•
Disadvantages
fy the need of PC or VC
BUT Ventilator
controlled
• Alveolar hyperventilation
cycle
R and VC/PC, flow, Ti,
FiO2
ventilator BUT • Supports
patient’s own
ABG interpreta
respiratory drive
•
ths can be initiated by
atient and PEEP on the
basis of
• Respiratory alkalosis
lways terminated by a

29. ventilator.
or MV and modulate the
RR and Vt.
• Look for patient triggering.
• Assess for sedation
Synchronized Intermittent Mandatory Ventilation
Role of an Nurses

30. • Monitor ABGS and V/S.
Delievers a preset Vt at a preset Rate (RR)
• Monitor the Vt of the
Spontaneous breaths between mandatory breaths are:
• patient triggered spontaneous breaths.
• Set backup Vt,
flow,
• Supported by the
patient’s strength
and lung
mechanics
sensitivity, Ti,
FiO2,
PEEP.

31. • Ensure back-up PS to help
spontaneous breaths.
(Donn & Sinha, 2012)
Spontaneous Mode OR Pressure Support Ventilation
Role of Nurses
• Set backup pressure
support to facilitate dead
space ventilation.
Type of breath: Spontaneous
• Ensure Apnea backup
Trigger and cycle: Patient

32. controlled
• Monitor ABGs
• Breaths are initiated and terminated by the patient.
• Monitor for work of
breathing
• prepare for extubation
after a SBT
(Pilbeam, 2015)
Summarizing the Modes

33. Variables Controlle
d mode
Ventilation
Assist
control
mode
Ventilation
SIMV
Mode
Spontaneou
s mode
Ventilation
Trigger Ventilator
controlled
Patient
controlled
Patient
controlled
Patient
controlled
Cycle Ventilator
controlled
Ventilator
controlled
Patient/
Ventilator
controlled
Patient
controlled
Initial Ventilator Settings - Trouble

34. ShootingRole of Nurses
(Chang, 2014)
• Monitor ABGS, Chest X
Parameters
• Assess for
compliance and Mode
elasticity.
Assist
FiO2
• Monitor Vt, PIP, 100 %
Vt
•
avoid asynchron
es for the
ion to 5-
RR • Monitor hemodyn
s
10-12

35. Inspiratory Flow
ventila
0L/min
PEEP accordingly.
5 cmH
Subsequent Adjustments - Trouble Shooting Hypoxia
Hypercapnia
Role of Nurses
• Monitor and interpret ABGS
Role of an Nurses
Goal: PaO2: 55-80 Goal: PCO2: 35-45

36. correctly to opt for relevant
interventions.
• Ensure and monitor regular
chest X-ray.
• Titrate PEEP/FiO2 according
to the protocol.
• Monitor for arrhythmias.
• Simultaneous pharmacological and non
pharmacological
management
(Aga Khan University Hospital, 2018, Chang, 2014)
• Monitor ABGs. • Increase MV • Increase flow • Monitor chest x
ray for dynamic hyperinflation

37. Inspiratory (Ti) and Expiratory (TE) Times- Trouble Shooting
• Total cycle time (TCT):
• Inspiratory time + Expiratory time
• RR 20 breaths/min 🡪3 seconds (TCT)
Inspiratory time (Ti): 1 second (if)
Vt: 1000ml and Inspiratory flow: 60L/min

38. I:E: (1:2)
1 lit Vt delivered in 60L/min: 1 lit/sec
3sec – 1 sec = 2 sec for expiration
Role of Nurses
• Air entry at
least per sift
• Set required
RR,Vt, Flow.
• Ensure I:E
ratio 1:2

39. • Monitor for auto-PEEP
(expiratory hold maneuver)
o Prolong expiratory time, Increase
flow, Decrease RR
• Monitor for signs of
pneumothorax.
• Check plateau pressure q4H.
• Monitor vital signs.
Compliance and Resistance - Trouble Shooting (Chang,

40. 2014)

41. Compliance and Resistance - Trouble
Shooting Protective Lung Ventilation
o Ventilate with low tidal volumes
(4- 8ml/kg).
Plateau pressure Goals: < 30 cm
H2O
RCT: Patients given smaller ventilator breaths had significantly
higher
o Volumes based on predicted body
survival than patients with conventional treatment. use of large
weight, PH & plateau pressure.
breaths resulted in ongoing inflammation (Bein et.al, 2013) o If
Pplat > 30 cmH2O: decrease Vt by 1ml/kg steps (minimum 4ml/kg)

42. o If Pplat < 25 cmH2O and Vt < 6ml/kg, increase Vt by 1ml/kg until
Pplat> 25 cmH2O or Vt =6ml/kg
(Aga Khan University Hospital, 2018)
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48. Acknowledgements
• Ms Ambreen Gowani
• Dr. Rubina Barolia
• Dr. Naveed Haroon
• Mr. Usman (Respiratory
Therapist)
• Dr. Sadaf Hanif
• Dr. Faheem Sheikh

49. • Anaiz Khowaja