1. Mechanical ventilation
Shilanjan Roy
PGT Medicine

2. Objectives

3. Objectives
• Discuss indications and techniques for non
invasive positive pressure ventilation.
• Describe characteristics of different types of
breath and modes of mechanical ventilation.
• Outline basic ventilator settings.
• Interactions between ventilatory parameters
and modifications needed to avoid harmful
effects of mechanical ventilation.
• Initial ventilator management that apply to
specific clinical situations.

4. Indications

5. Indications for Mechanical
Ventilation
• The work of breathing usually accounts for 5% of
oxygen consumption (V02).
•
In the critically ill patient this may rise to 30%.
•
Invasive mechanical ventilation eliminates the
metabolic cost of breathing.

6. Indications for Mechanical
Ventilation
•
Inadequate oxygenation (not corrected by
supplemental O2 by mask).
•
Inadequate ventilation (increased PaCO2).
•
Retention of pulmonary secretions (bronchial
toilet).
•
Airway protection (obtunded patient, depressed
gag reflex).

7. Indications
• Ventilation abnormalities:
•
•
•
•
•
Respiratory muscle fatigue
Chest wall abnormalities
Neuromuscular disease
Increased airway resistance and /or obstruction
Decreased ventilatory drive
• Oxygenation abnormalities:
• Refractory Hypoxaemia
• Excessive work of breathing
• Need for positive end expiratory pressure

8. Other indications
• Need for sedation and / or neuromuscular
blockade.
• Need to decrease systemic / myocardial
oxygen demand.
• Use of hyperventilation to reduce Raised
ICP.
• Facilitation of alveolar recruitment and
prevention of atelectasis.

9. NIPPV ( NON INVASIVE
POSITIVE PRESSURE
VENTILATION)

10. NIV vs. Invasive Mechanical
Ventilation
•NIV is defined as ventilatory support
provided via a tight fitting mask or similar
interface as opposed to invasive support,
which is provided via a laryngeal mask,
endotracheal tube or tracheostomy tube.
• Tight fitting masks deliver can CPAP,
BIPAP or NIV via the mechanical ventilator.

11. Advantages of NPPV
•
•
•
•
Reduced need for sedation
Preservation of airway protective reflexes
Avoidance of upper airway trauma
Decreased incidence of nosocomial sinusitis
and pneumonia
• Improved patient comfort
• Shorter length of ICU and hospital stay
• Improved survival

13. Disadvantages of NPPV
•
•
•
•
•
Claustrophobia
Facial /nasal pressure lesions.
Unprotected airway
Inability to suction deep airway
Gastric distension with use of face mask or
helmet
• Possible upper extremity edema, axillary vein
thrombosis, tympanic dysfunction, and
intrahelmet noise with use of helmet
• Delay in intubation.

14. Contraindications of NPPV
•
•
•
•
•
•
•
•
Cardiac or respiratory arrest.
Haemodynamic instability
Uncooperative.
Inability to protect the airways.
High risk of aspiration.
Active upper GI bleed.
Severe encephalopathy.
Facial trauma, recent surgery &/or burn

15. Conditions likely to respond
to NPPV
• Hypoxaemic respiratory failure:
– Cardiogenic pulmonary edema without
haemodynamic instability
– Respiratory failure in IC patients.
(haematologic malignacies and
transplant patients)
– Patients not candidates for intubation

16. • Hypercapnic respiratory failure:
– AECOPD
– AE bronchial asthma
– Resp failure in patients with cystic
fibrosis
– Patients not candidates for
intubation

17. Initiation of NPPV
• Do not delay intubation if needed.
• Ensure appropriate mask or helmet size.
• Assess patients’ tolerance of the mask by
applying it by hands before securing the
harness.
• Explain the procedure to the patients
• Initial ventilation settings–
–
–
–
–
Mode: spontaneous
Trigger: maximum sensitivity
EPAP : 4-5 cm H2O
IPAP : 10-15 cm H2O
Rate: 6/min

18. Cont…
• Adjust difference between EPAP & IPAP to
achieve effective tidal vol. & CO2 clearance.
• EPAP increments of 2 cm H2O /step to
improve oxygenation by alveolar
recruitment.
• In assist control ventilation begin with VT 6-8
ml/kg.
• Titrate pressure, vol & FiO2 to achieve
appropriate PaO2 & PaCO2 levels.
• Ventilator changes can be made
every 15-30 mins.

19. Invasive mechanical
ventilation

20. Intubation

21. Bare Essentials for Intubation
ALSOBLEED
Airway: oral Guedel airway to lift tongue off
posterior pharynx to facilitate mask ventilation
during pre-intubation phase.
2 Liquids: stop feed and aspirate ng tube.
3 Suction: extremely important to avoid pulmonary
aspiration.
4 Oxygen: preoxygenate patient and ensure a
source of O2 with a delivery mechanism
(ambu-bag and mask) is available

22. Bare Essentials for Intubation
ALSOBLEED
5 Bougie: to facilitate tube insertion in more difficult
airway.
6 Laryngoscope: have a long and short blade
available.
7 Endotracheal tube: for average adult, cuffed oral
endotracheal tube 7.0 for women and 8.0 for men.
8 End tidal CO2: to confirm correct position of tube.
9 Drugs: an induction agent, muscle relaxant,
sedative are usually required.

23. Principles of Mechanical
Ventilation

24. Principles of Mechanical
Ventilation
•
Positive pressure ventilation involves delivering
a mechanically generated ‘breath’ to get O2 in and
CO2 out.
•
Gas is pumped in during inspiration (Ti) and the
patient passively expires during expiration (Te).
•
The sum of Ti and Te is the respiratory cycle or
‘breath’.

25. Basic mechanics
Each mechanical ventilatory cycle can be
divided into 2 phases:
• Inspiration is the point at which exhalation
valve closes and fresh gas enters the chest.
• The amount of gas delivered during
inspiration is limited by 3 parameters that
can be set in the ventilator:
• Volume
• Pressure and/or
• Flow

26. • Cycling :
• Changeover from the end of inspiration to
the second phase , expiration.
• Cycling can occur in response to elapsed
time , delivered volume or a decrease in
flow rates.
• Expiration begins when the gas flow from
the ventilator is stopped and exhalation
circuit is opened to allow gas to escape from
the lungs.

27. • Triggering :
• Changeover from expiration to inspiration.
• All ventilators require some signal from the
patient to determine when inspiration should
begin.
• Triggering signal results when patients
inspiratory effort produces a drop in airway
pressure or diversion of a constant gas flow
in ventilator circuitry.

28. CYCLING
TRIGGERING

29. • In the absence of patients interaction with
the ventilator, breaths are delivered based
on elapsed time.
• This is called UNASSISTED OR
MANDATORY BREATH.
• Based on this definitions two ventilator
breath types are possible:
• Mandatory/ UnAssisted breath
• Assisted breath

30. Principles of Mechanical
Ventilation
•
In the fully ventilated patient, positive pressure
breaths are delivered either as preset volume or
pressure continuous mandatory breaths (CMV)
breaths.
•
The mechanical ventilator triggers the breath
and switches from inspiration to expiration when
the preset volume, pressure (or time) is
achieved/delivered.
•
During CMV the patient takes no spontaneous
breaths.
•
CMV is usually used in theatre and in very unwell
ICU patients.

31. Types of ventilator breaths
• A. volume cycled (control) breath
• Ensures delivery of a preset tidal
volume( unless the peak pressure limit is exceeded)
• On some ventilators setting of peak
inspiratory flow rate and choice of inspiratory
flow waveform( sine, square, decelerating)
determine length of inspiration.
• with volume cycled breaths, worsening
airway resistance or lung compliance results
in increase in peak inspiratory pressure.

32. B.Time cycled breath
• Often called pressure cycled( controlled)
breath, applies a constant pressure over
preset time.
• Produces a decelerating inspiratory flow
waveform as the pressure gradient between
the ventilator( constant pressure) patient(
pressure rises as lung fills) falls.
• In this setting , changes in the airway
resistance or lung compliance will alter the
tidal volume.

33. C. Flow cycled breath
• usually pressure support breath.
• Similar to a time cycled breath.
• However, pressure support is terminated
when the flow rate decreases to a
predetermined percentage of initial flow rate
e.g 25%.

34. Principles of Mechanical Ventilation
Volume cycled/ Control
Breath
Flow
Pressure
Pressure cycled/Control
Breath
Ti
Te
Ti
Te

35. Why is the peak airway pressure
(PAP) important?
• Ventilator Induced Lung Injury (VILI).
•
Mechanical ventilation is injurious to the lung.
•
Aim PAP< 35 cm H20.( platue pressure < 30 cm
water)
• HIGH PAP may cause barotruma(pneumothorax),
• Volutruma( lung parenchymal injury)
Don’t forget that the peak airway
pressure will also include the PEEP that
is added

36. Principles of Mechanical Ventilation
Volume Breath
Pressure Breath
Flow
Pressure
35 cm H20
Ti
Te
Ti
Te

37. Pneumothorax- Example of
ventilator induced barotruma

38. MODES AND SETTINGS
OF MECHANICAL
VENTILATION

39. Overview of topics
1. Settings
2. Modes
3. Advantages and disadvantages between
modes
4. Guidelines in the initiation of mechanical
ventilation
5. Common trouble shooting examples with
mechanical ventilation

40. Settings
1.
2.
3.
4.
5.
6.
7.
Trigger mode and sensitivity
Respiratory rate
Tidal Volume
Positive end-expiratory pressure (PEEP)
Flow rate
Inspiratory time
Fraction of inspired oxygen

41. Trigger
 There are two ways to initiate a ventilator-delivered breath:
pressure triggering or flow-by triggering
 When pressure triggering is used, a ventilatordelivered breath is initiated if the demand
valve senses a negative airway pressure
deflection (generated by the patient trying to
initiate a breath) greater than the trigger
sensitivity.
 When flow-by triggering is used, a continuous
flow of gas through the ventilator circuit is
monitored. A ventilator-delivered breath is
initiated when the return flow is less than the
delivered flow, a consequence of the patient's
effort to initiate a breath

42. Tidal Volume
• The tidal volume is the amount of air
delivered with each breath. The
appropriate initial tidal volume
depends on numerous factors, most
notably the disease for which the
patient requires mechanical
ventilation.

43. Respiratory Rate
• An optimal method for setting the
respiratory rate has not been
established. For most patients, an
initial respiratory rate between 12 and
16 breaths per minute is reasonable

44. Positive End-Expiratory
Pressure (PEEP)
• Mechanically ventilated patients usually
receive positive end-expiratory pressure
(PEEP), to overcome the loss of
physiological PEEP provided by the
larynx and vocal cords.
• Applied PEEP is generally added to mitigate
end-expiratory alveolar collapse.

45. PEEP
• PEEP is delivered throughout the respiratory
cycle and is synonymous to CPAP, but in the
intubated patient.
A typical initial applied PEEP is 5 cmH2O. However, up
to 20 cmH2O may be used in patients undergoing
low tidal volume ventilation for acute respiratory
distress syndrome (ARDS)

46. Flow Rate
• The peak flow rate is the maximum flow
delivered by the ventilator during inspiration.
Peak flow rates of 60 L per minute may be
sufficient, although higher rates are
frequently necessary.
• An insufficient peak flow rate is
characterized by dyspnea, spuriously low
peak inspiratory pressures, and scalloping
of the inspiratory pressure tracing

47. Inspiratory Time: Expiratory
Time Relationship (I:E Ratio)
• During spontaneous breathing, the
normal I:E ratio is 1:2, indicating that
for normal patients the exhalation time
is about twice as long as inhalation
time.
• If exhalation time is too short “breath
stacking” occurs resulting in an
increase in end-expiratory pressure
also called auto-PEEP.
• Depending on the disease
process, such as in ARDS, the I:E
ratio can be changed to improve
ventilation

48. Fraction of Inspired Oxygen
• The lowest possible fraction of inspired
oxygen (FiO2) necessary to meet
oxygenation goals should be used.
• This will decrease the likelihood that
adverse consequences of supplemental
oxygen will develop, such as absorption
atelectasis, accentuation of hypercapnia,
airway injury, and parenchymal injury

49. Modes of Ventilation: The
Basics
•
•
•
•
Assist-Control Ventilation :Volume Control
Assist-Control Ventilation: Pressure Control
Pressure Support Ventilation
Synchronized Intermittent Mandatory
Ventilation :Volume Control
• Synchronized Intermittent Mandatory
Ventilation :Pressure Control

50. Assist Control Ventilation
• A set tidal volume (if set to volume control)
or a set pressure and time (if set to pressure
control) is delivered at a minimum rate
• Additional ventilator breaths are given if
triggered by the patient.

51. • Once stabilised on CMV, the level of ventilatory
support may be reduced (weaning).
•
This can be done by providing a mixture of
synchronised intermittent mandatory breaths
(SIMV) and spontaneously triggered pressure
supported breaths (PSV).

52. Synchronized Intermittent
Mandatory Ventilation
 Breaths are given are given at a set minimal rate,
however if the patient chooses to breath over the
set rate no additional support is given
 One advantage of SIMV is that it allows patients to
assume a portion of their ventilatory drive
 SIMV is usually associated with greater work of
breathing than AC ventilation and therefore is less
frequently used as the initial ventilator mode
 Like AC, SIMV can deliver set tidal volumes
(volume control) or a set pressure and time
(pressure control)
 Negative inspiratory pressure generated by
spontaneous breathing leads to increased venous
return, which theoretically may help cardiac output
and function

53. SIMV and Pressure Support
Ventilation
• In SIMV mode the ventilator allows two kinds of
breath.
• The first is delivered according to the preset
waveform and is the “mandatory breath”. The timing
of the start of this breath may be triggered by the
patient’s respiratory effort but, if the patient is not
making sufficient respiratory effort, is determined by
the ventilator. The second is a spontaneous breath. If
SIMV is combined with pressure support then the
ventilator facilitates this second breath by providing
pressure support. This second type of breath is
entirely dependent on patient effort.
• The graphs illustrate the changes in pressure and
flow that occur with first a mandatory breath and then
a pressure-supported breath

54. SIMV and Pressure Support Ventilation
Ventilator
Patient

55. SIMV and Pressure Support
Ventilation
• Ventilator assisted breaths are synchronized with
the patient’s breathing to prevent the possibility
of a mechanical breath on top of a spontaneous
breath.
•
However, the patient’s attempt at a breath would
not be enough to generate an adequate tidal
volume on its own, hence the term ‘pressure
support’.

56. Pressure Support
Ventilation
• The patient controls the respiratory rate
and exerts a major influence on the
duration of inspiration, inspiratory flow rate
and tidal volume
• The model 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.

57. PSV
•
As patients improve, mandatory breaths are
withdrawn and receive pressure-supported breaths
alone.
•
Finally, as tidal volumes improve, the level of
pressure support is reduced and then withdrawn
so patients breathe spontaneously with PEEP
alone.
•
Extubation can now be contemplated.
•
Spontaneous modes of breathing should always
be encouraged as respiratory muscle function is
maintained

58. Pressure Support Ventilation
Patient
Patient

59. • PSV augments the patients own
respiratory effort and best adjusted by
observing changes in patients resp
rate, vt and comfort.
• Pressure support is only delivered during
inspiration and the patient’s attempt at breathing
triggers the breath rather than the ventilator.
•
A standard level of pressure support delivered in
inspiration is 20 cm H20

60. Airway pressure & flow tracings for commonly used modes of mechanical
ventilation

61. Advantages of Each Mode
Mode
Advantages
Assist Control Ventilation (AC)
Reduced work of breathing compared
to spontaneous breathing
AC Volume Ventilation
Guarantees delivery of set tidal
volume
AC Pressure Control Ventilation
Allows limitation of peak inspiratory
pressures
Pressure Support Ventilation (PSV)
Patient comfort, improved patient
ventilator interaction
Synchronized Intermittent Mandatory
Ventilation (SIMV)
Less interference with normal
cardiovascular function

62. Disadvantages of Each
Mode
Mode
Disadvantages
Assist Control Ventilation (AC)
Potential adverse hemodynamic
effects, may lead to inappropriate
hyperventilation
AC Volume Ventilation
May lead to excessive inspiratory
pressures
AC Pressure Control Ventilation
Potential hyper- or hypoventilation with
lung resistance/compliance changes
Pressure Support Ventilation (PSV)
Apnea alarm is only back-up, variable
patient tolerance
Synchronized Intermittent Mandatory
Ventilation (SIMV)
Increased work of breathing compared
to AC

63. Successful Weaning and Extubation
• To succeed, the initiating cause of respiratory failure,
sepsis, fluid and electrolyte imbalance and nutritional
status should all be treated or optimised.
• Failure to wean is associated with:
• Ongoing high V02.
• Muscle fatigue.
• Inadequate drive.
• Inadequate cardiac reserve.

64. Successful Weaning and
Extubation
•
Weaning screens exist to help select patients for
extubation.
•
In the unsupported patient, if f/Vt is >100,
extubation is likely to be unsuccessful.
•
There is some evidence to support extubation to
NIV, particularly in patients with COPD.

65. Guidelines in the Initiation of
Mechanical Ventilation
• Primary goals of mechanical ventilation are
adequate oxygenation/ventilation, reduced
work of breathing, synchrony of vent and
patient, and avoidance of high peak
pressures
• Set initial FIO2 on the high side, you can
always titrate down
• Initial tidal volumes should be 8-10ml/kg,
depending on patient’s body habitus. If
patient is in ARDS consider tidal volumes
between 5-8ml/kg with increase in PEEP

66. Guidelines in the Initiation of
Mechanical Ventilation
• Use PEEP in diffuse lung injury and ARDS
to support oxygenation and reduce FIO2
• Avoid choosing ventilator settings that limit
expiratory time and cause or worsen auto
PEEP(espl in obstructive airway disease)
• When facing poor oxygenation, inadequate
ventilation, or high peak pressures due to
intolerance of ventilator settings consider
sedation, analgesia or neuromuscular
blockage

67. SPECIFIC CASE
SCENARIOS

68. Trouble Shooting the Vent
• If we have a patient with history of COPD/asthma
with worsening oxygen saturation and increasing
hypercapnia differential includes:
– Given the nature of the disease process, patients
have difficultly with expiration (blowing off all the
tidal volume)
– Must be concern with breath stacking or autoPEEP
– Management options include:
Decrease respiratory rate
Decrease tidal volume
Adjust flow rate for quicker
inspiratory rate
Increase sedation
Adjust I:E ratio

69. Trouble Shooting the Vent
• Increase in patient agitation and dis-synchrony on the
ventilator:
– Could be secondary to overall
discomfort
• Increase sedation
– Could be secondary to feelings of
air hunger
– Options include increasing tidal volume,
increasing flow rate, adjusting I:E ratio,
increasing sedation

70. Trouble shooting the vent
• If you are concern for acute respiratory distress
syndrome (ARDS)
– Correlate clinically and radiologic
findings of diffuse patchy infiltrate on
CXR
– Obtain a PaO2/FiO2 ratio (if < 200 likely
ARDS)
– Begin ARDS net protocol:
• Low tidal volumes
• Increase PEEP rather than FiO2
• Consider increasing sedation to promote
synchrony with ventilator

71. ARDS Protocol
• Start with a PEEP of 5 and uptitrate..optimal PEEP is
usually 8-15 cm H2O.
• Start with a Vt of 8 ml/kg then gradually decrease till
Vt of 6 ml/kg is reached.
• P plat should be < 30.
• Ph> 7.15 is acceptable.

72. CM V
PSV
PEE P
S IM V
PSV
M a n d a to ry
O v erla p
S p o n ta n eo u s

73. Standard Ventilator Settings
MORITE
Mode
O2
CMV, Volume Control
0.5 (50% 02)
Respiratory Rate
12/minute
Inspiratory Action
Set Vt at 500 mls
Inspiratory Time
Set I:E ratio 1:2
Expiratory Action
Set PEEP at 5 cm H20
Be Aware
PAP ≤35 cm H2O

74. HYPOTENSION ASSOC WITH
MECHANICAL VENTILATION
• 1)TENSION PNEUMOTHORAX
• 2)CONVERSION FROM NEGATIVE TO POSITIVE
INTRATHORASIC PRESSURES.
• 3)Auto PEEP.
• 4)AMI./ MYOCARDIAL ISCHAEMIA.

75. TAKE HOME MESSAGE
• 1) Goals of NIV and IPPV are to suppport
ventilation and oxygenation, reduce work of
breathing and patient comfort.
• 2)NPPV is best utilized in C/A/C patients
whose resp condition is expected to improve
in 48-72 hrs.
• 3)Guidelines for initiating mechanical
ventilation should be carefully followed.
• 4)Inspiratory plateue pressures should be
maintained <30 cm H2o.

76. TAKE HOME MESSAGE
• 5) During mech ventilation, patient must be carefully
monitored using vent alarm systems, rintermittant
ABG analysis, pulse oximetry , physical assessment,
and chest radiograph as needed.
• 6) Hypotension in ventilated pt should be prompt
evaluated for pneumothorax, auto PEEP, AMI.
• 7)The primary determinants of oxygenation are Fi02
and Mean airway pressure whereas alveolar
ventilation affects CO2 exchange.
• 8) THE Complex interaction of inspiratory pressures,
I:E Ratio, Fio2, and PEEP must be evaluated.