Lecture on MV techniques

1. A.SAMPATH KUMAR
MPT (CARDIOPULMONARY SCIENCES)
ASSISTANT PROFESSOR
DEPT. OF PHYSIOTHERAPY
KMC MANGALORE
MAHE 1

2. Contents
Basic terminology and concepts related to mechanical
ventilator
 Pressures and pressure gradients
 Types of Mechanical Ventilation
 Definition of pressures in PPV
2

4. Introduction
 Function of respiratory system
 Provide oxygen
 Remove carbon dioxide
 Pressure gradients- physiology of a breath

5. What is a ventilator ?
 Simply ,any machine used to push or pull gas
mixture (air and oxygen) into lungs.

6. Normal Mechanics Of Spontaneous
Ventilation
 Spontaneous breathing is movement of air in and out of
the lungs
 VENTILATION: Aim is to bring in fresh air for gas
exchange into lungs and allow exhalation of air that
contains carbon dioxide
 RESPIRATION: Movement of gas molecules across a
membrane
1. External Respiration
2. Internal Respiration
6

7. Pressures and Pressure Gradients
 Air flows from high to low pressure points
 Conductive airway begins at mouth and ends at alveoli
 Gas flows into the lungs:
Pressure in alveoli <Pressure at mouth and vice versa
PRESSURE EQUIVALENTS
1 ATM=760 mm Hg / 1034 cm H2O
1 mmHg = 1.36 cm H2O
1 kilopascal[kPa] = 7.5 mmHg
7

8. Airway Opening Pressure (PAWO)
 Zero (atmospheric) unless positive pressure applied
 Also known as mouth pressure(PM),upper airway
pressure, mask pressure, proximal airway pressure
Pressure at Body Surface (PBS)
 Also equals to zero (atmospheric)
 Pressure exerted on the body by the surrounding air
Definitions of Pressures
8

9.  Alveolar Pressure (P ALV)
 Pressure within alveoli which changes with pressure
changes in the pleura
 Varies during breathing cycle
 Inspiration: -1 cm H2O ; Expiration: +1 cmH2O
 Intrapulmonary pressure
9

10. Intra Pleural Pressure (P PL)
 Pressure between parietal and visceral pleura
 Varies at different levels(normally -5 cm H2O)
 Difficult to measure therefore analysed by measuring
esophageal pressure(PES)
 Intra thoracic Pressure
10

11. 11

12. Pressure Gradients
Trans airway Pressure (PTA)
 Pressure gradients between airway opening and
alveolus
 Also called airway pressure
 Responsible for air movement in conductive airways
 Represents the pressure caused by resistance to gas
flow in the airways
PTA = PAWO- PA
12

13. Transpulmonary Pressure (PL)
 Pressure difference between alveolus and pleural space
 Keeps the alveoli patent
 Also known as Alveolar distending pressure or
Transmural pressure
 All the modes of ventilation increase PL either by
decreasing PPL (NPV) or by increasing the PA(PPV)
PL = PA - PPL
13

14. Transthoracic (PW)
 Pressure difference between alveolus and body surface
 Represents pressure needed for excursion of the lungs
and chest wall
 Also abbreviated as PTT
PW = PA - PBS
14

15. Transrespiratory (PTR)
 Difference between pressures in airway opening and
body surface
 Required to inflate lungs and airways during PPV
 2 components
1. Transthoracic pressure(to overcome elastance)
2. Transairway pressure( to overcome airway flow
resistance)
PTR = PTT + PTA
15

16. Negative pressure ventilation
 Negative pressure ventilation( non invasive )
Iron/tank lungs Chest cuirass or chest shell

18. Positive pressure ventilation
 Positive pressure ventilation
 Invasive
 Non invasive

19. Indication for mechanical
ventilation
 Acute ventilatory failure
 Impending ventilatory failure
 Severe hypoxemia
 Prophylactic ventilatory support

20. Acute respiratory failure
 Paco2 > 50 mm Hg
 pH < 7.30

21. Impending ventilatory failure
 Tidal volume < 3 to 5 ml/kg
 Respiratory rate and pattern > 25 to 35/min
 Minute ventilation > 10 l/min
 Vital capacity < 15 ml/kg
 Maximum inspiratory pressure < -20 cm H2o
 Paco2 ---- increasing to over 50mmHg
 Vital signs----- increased HR,blood pressure

22. Ventilator classification
 Input power
Pneumatically powered ventilator
Electrically powered ventilator
Both

23. Drive mechanism
 Piston drive mechanism
 Bellows drive mechanism
 Reducing valve drive mechanism
 Microprocessor- controlled pneumatic drive
mechanism

24. Control circuit
 Open loop control circuit
 Closed loop control circuit

25. Control variables
 Pressure controller
 Volume controller
 Flow controller
 Time controller

26. Phase variables
 The change from expiration to inspiration
 Inspiration
 The change from inspiration to expiration
 Expiration

27. Trigger variable
 Pressure triggered
 Flow triggered
 Time triggered

28. Limit variable
 Pressure
 Flow
 Volume

29. Cycle variable
 Pressure cycled
 Volume cycled
 Flow cycled
 Time cycled

30. Baseline variable
 PEEP

31. Conditional variable
 Pattern of Variables that are controlled by the
ventilator during the ventilator cycle

32. Out put waveforms
 Pressure wave forms
 Volume wave forms
 Flow wave forms

33. Alarm systems
 Input power Alarms
 Control circuit Alarms
 Out put Alarms

34. Types of breath
 Mandatory
 Assisted
 Supported
 Spontaneous

35. Modes of ventilation
 What initiates the inspiration and how? (Trigger
variable)
 What is the limit for inspiration? (Limit variable)
 When is inspiration ended allowing for expiration to
start? (Cycle variable)

36. Control mandatory ventilation (CMV)
 Volume control ventilation
 Pressure control ventilation

37. Assist control (AC)
 Volume assist control
 Pressure assist control

38. Intermittent mandatory ventilation
(IMV)

39. Synchronized intermittent
mandatory ventilation (SIMV)

40. Pressure support ventilation
 Set inspiratory assist pressure
 No set tidal volume or rate

41. SIMV/PS
 Pressure is delivered by the ventilator whenever the
patient breathes spontaneously

42. Continuous positive airway
pressure (CPAP)

43. Bi-level positive airway pressure
(BiPAP)
 Similar to CPAP, except has different inspiratory and
expiratory pressures.
 The inspiratory pressure is usually higher than the
expiratory pressures.

44. Inverse ratio ventilation (IRV)
 Inspiratory time is longer than expiratory
time.normally expiration is longer.

45. High frequency ventilation
 Delivers a small amount of air (puff) at a high rate.
 Most often seen in infants.
 Rate may vary from 60- 3000 cycles per minute

46. Independent lung ventilation (ILV)
 Each lung is ventilated independently.
 Each lung may have different pressures
 The rate will be the same for both lungs.

47. Advanced Modes Of Ventilation
 Mandatory minute ventilation
 Pressure control ventilation
 Proportional assist ventilation
 Volume assured pressure support (VAPS)
 Pressure Regulated Volume Control
(PRVC)
 Volume Support (VS) mode
 Airway Pressure Release Ventilation
 Adaptive support ventilation (ASV)
 Automode

48. SETTINGS
 Tidal volume – 8-12 ml/kg
 Rate ----- age dependant
 Minute ventilation = TV ×RR
 I:E ratio
 Inspiratory trigger sensitivity
 FiO2
 PEEP
 Flow rate based on limit variable (volume or
pressure)

49. Parameters to be monitored
 Exhaled tidal volume (VTe)
 Exhaled minute ventilation (MVe)
 Rate (f)- spontaneous, machine
 Spontaneous MVe
 Pressure
 Peak
 Plateau
 Mean airway

50.  Compliance
 Static
 Dynamic
 Airway resistance
 PEEP
 Graphics

51. Types Of Ventilators
Negative Pressure Ventilation (NPV)
 Also known as iron lung
 Negative pressure generated around the thoracic area
During inspiration, intrapleural
pressure becomes negative(-5 to -10
cm H2O)
Intra pulmonary pressure also
declines from 0 to -5 cm H2O
This pressure gradient causes
movement of air into lungs
51

52.  NPV resembles normal lung mechanics
 Expiration occurs when negative pressure is removed
and the elastic recoil of lungs passively deflates it
52

53.  Disadvantages
In hypovolemic patients, a normal cardiovascular response
is not present to compensate for the negative pressure on the
abdomen
Significant pooling of blood in the abdomen and reduced
venous return to the heart
53

54. Positive Pressure Ventilation(PPV)
 Air is forced into patients lungs through endotracheal
tube or mask
 Paw= +15 cm H2O ; PA= 0 cm H2O
PTA= Paw – PA = +15 cmH2O
 Inflating Pressure is the sum of pressure to overcome
compliance and pressure to overcome airway
resistance
54

55. During inspiration,
alveolar pressure
becomes positive
Alveolar pressure is
transmitted &
intrapleural
pressure becomes
positive
At end of
inspiration, mouth
pressure becomes
zero & air flows out
55

56. Pressures In PPV
Baseline Pressures:
 When baseline pressure is zero it indicates that no
additional pressure is applied at airway opening during
inspiration or expiration
 Sometimes baseline pressure is higher than zero when
higher pressure is applied during expiration(PEEP)
56

57. Positive End Expiratory Pressure(PEEP)
 PEEP is the application of constant positive pressure in
airways at end of expiration so that the pressure is not
allowed to return to atmospheric pressure
57

58.  Effects:
Recruits atelectatic alveoli
Internally splints and distends already patent alveoli
Counteracts alveolar and small airway closure
Reduces intra pulmonary shunting
Improves FRC and compliance
Improves oxygenation
58

59. Intrinsic/ Auto PEEP
 It is spontaneous development of PEEP as a result of
insufficient expiratory time
 Inadequate expiratory time causes air trapping which
creates positive pressure in thorax
 High auto PEEP can lead to barotrauma &
hemodynamic compromise
59

60.  Causes:
High RR
High Minute Ventilatory(MV) demands
Air flow obstruction
Inverse I:E ratios
60

61. Peak Pressure(PPeak)
 Highest pressure recorded at end of inspiration
 Also known as peak inspiratory pressure(PIP) or peak
airway pressure
 Sum of pressure required to force the gas through
resistance of airways & to fill the alveoli
 PIP= PTA + PA
61

62. Plateau Pressure
 It is measured after the breath has been delivered to
the patient and before exhalation begins
 Exhalation is controlled by the ventilator for a brief
moment by “inspiratory pause”
 Reflects the effect of elastic recoil on the gas volume in
alveoli and pressure exerted by the volume in the
ventilator circuit that is acted upon by the recoil of the
plastic circuit
62

63. 63

64. Mechanism:
 Plateau Pressure measurement is like holding the
breath at the end of inspiration
 At the point of breath holding, the pressures inside the
alveoli and mouth are equal
 However, the relaxation of the respiratory muscles and
elastic recoil of the lung tissues are exerting force on
the inflated lungs
 This creates a positive pressure
64

65. How is a breath delivered??
65

66. Factors Controlled by Ventilator
 The primary variable the ventilator adjusts to achieve
inspiration is called control variable
 Ventilator can control only one of the following
variables at a time
1. Pressure
2. Volume
3. Flow
4. Time
Commonly used
66

67. Pressure Controlled Ventilation
 Ventilator maintains same pressure waveforms in a
specific pattern
 These waveforms are unaffected by changes in lung
characteristics
 Also called pressure limited or pressure targeted
67

68. Volume Controlled Ventilation
 Ventilator maintains volume waveform in a specific
pattern
 Volume & flow waveforms remain unchanged but the
pressure waveforms will vary with changes in lung
characteristics
 Also called as volume limited or volume targeted
68

69. Flow Controlled Ventilation
 When the ventilator controls the flow, the flow and
volume waveforms remain unchanged, but the
pressure waveform changes with alterations in lung
characteristics
 Any breath that has a set flow waveform will also have
a set volume waveform and vice versa
 When flow waveform is selected, the volume waveform
is automatically established
 Volume = flow x time
69

70. Time Controlled Ventilation
 When both the pressure and the volume waveforms
are affected by changes in lung characteristics, the
ventilator delivers a breath that is time controlled
 High frequency jet ventilators and oscillators are time
controlled
 Used less often
70

71. Phases of Breath & Phase Variables
 The 4 phases of a breath are:
1. Change from exhalation to inspiration
2. Inspiration
3. Change from inspiration to exhalation
4. Exhalation
 The variables which control each phase are called
phase variables
71

72. 72

73.  3 phase variables are:
1. Trigger Variable: is the variable that initiates
inspiration
2. Limit Variable: represents the parameters chosen to
be controlled during inspiration.
3. Cycle Variable: is the variable which causes
inspiration to end
73

74. 74

75. Trigger Variable
 The mechanism the ventilator uses to end exhalation
and begin inspiration is the triggering mechanism
 Trigger can be of 2 types:
1. Time trigger- Ventilator triggers itself
2. Patient trigger- based on pressure, flow or volume
changes
75

76. Time Triggering
 Breath begins when the ventilator has measured the
elapsed amount of time
 The rate of breathing is controlled by the ventilator
hence this is also called controlled ventilation
 The breath given is the mandatory breath because the
ventilator starts it
 The operator sets the rate control(frequency)
76

77. Patient Triggering
 When the patient attempts to breathe spontaneously,
the machine will sense the effort ( pressure, flow or
volume)
 For the machine to sense this effort, the operator must
specify the sensitivity i.e. patient effort control
 The lower the pressure or flow change, the more the
sensitivity of the machine
 Eg: - 5 cm H2O is more sensitive than – 1 cm H2O
77

78.  Pressure Triggering
When pressure is trigger, a decrease in pressure is
required to initiate inspiration
This setting reflects amount of pressure drop required
to be generated by the patient to initiate a breath
 Usually – 0.5 to – 2 cm H2O
78

79. High sensitivity will decrease patients effort but with
higher sensitivity settings the machine can trigger
without patients effort(auto cycling)
If we want patients to actively make efforts to breathe
and wean him off then the sensitivity is much less
79

80.  Flow Triggering
The ventilator detects a drop in flow in the patient
circuit during exhalation
Requires less work of breathing than pressure
triggered breath
80

81.  Volume Triggering
Ventilator detects small drop in volume in patient
circuit during exhalation
The machine senses this drop as patient effort and
begins inspiration
81

82. Limit Variables
 The limit variable for inspiration is a preset target
value for pressure, volume or flow that cannot be
exceeded.
 It defines the maximum value that a variable can attain
 This variable limits the variables during inspiration
but does not end inspiratory phase.
82

83.  Pressure Limiting
As the ventilator pushes the gas into the lungs the
pressure rises
This variable allows pressure to rise to a certain value
but not exceed it
To control the excessive or sudden rise in pressure in
turn preventing barotrauma, pressure limit is set
 Eg: pressure support & pressure control modes
83

84.  Volume Limiting
Volume is preset and the waveform doesn’t change
breath to breath
Flow of gas in a time specific interval is assessed by an
electronic valve
A piston operated ventilator is example of volume
limiting
Volume is limited to amount in the piston cylinder
Eg: SIMV, Assist/control mode
84

85.  Flow Limiting
If ventilator flow to the patient reaches but does not
exceed a maximum value before the end of inspiration,
the ventilator is flow limited
That is only certain amount of flow can be provided
85

86. Maximum Safety Pressure
 Ventilators have maximum pressure limit control used
to prevent excessive pressure from reaching a patient’s
lungs
 This control sets the maximum safety pressure
 Normally 10 cm H2O above the average PIP
 Reaching the maximum high pressure limit ends the
inspiratory phase
86

87. Cycle Variable
 The variable the ventilator measures to determine the
end of inspiration is called cycle variable
 The cycle variable can be pressure, volume, flow or
time.
 Only one variable can be controlled(independent
variable) whereas the others can vary and need to be
monitored
87

88.  Volume Cycled
Breathing cycle is terminated when a set volume has
been delivered
Volume remains constant with lung characteristics but
pressure required to deliver that volume can change
according to lung characteristics
88

89. As compliance reduces ,PIP increases because the
ventilator is committed to deliver a preset volume
When inspiratory pause is set, it will increase the
inspiratory time not the inspiratory flow
89

90.  Set Volume VS Delivered Volume
The volume that leaves the ventilator’s outlet is not the
volume that enters the patient’s lungs
In most adult ventilator circuits, about 2 to 3mL gas is
lost to tubing compressibility for every 1cm H2O
90

91.  The actual volume delivered to the patient can be
evaluated by measuring the exhaled volume at the
endotracheal or tracheostomy tube
 To determine the delivered volume, the volume
compressed in the ventilator circuit must be
subtracted from the volume measured at the
exhalation valve
91

92.  System leaks
This is another method to assess why the delivered
volume may be less than that of set volume
The ventilator may be unable to recognize or
compensate for leaks
A leak can be detected by using an exhaled volume
monitor
If the measured volume from the patient is less than
that of delivered by the ventilator, a leak is present
92

93.  Time Cycled
Inspiratory phase ends when a predetermined time has
elapsed
With gas flow constant and interval fixed, the tidal
volume can be predicted
Tidal Volume = Flow x Inspiratory Time
93

94.  Time Cycled Volume Ventilation: Flow pattern and
volume delivery is unaffected by airway resistance and
compliance but pressure adjustments are made by the
ventilator
 Time Cycled Pressure Ventilation: volumes and flow
vary as per airway resistance and compliance.
Pressures are constant/ controlled. Also known as
Pressure Control Ventilation(PCV)
94

95.  Flow Cycled
The ventilator cycles into expiratory phase once the
flow has decreased to a predetermined value during
inspiration.
Volume, time and pressure will vary according to lung
characteristics
Most commonly used cycling mechanism in pressure
support mode
95

96.  Pressure Cycled
When a preset pressure threshold is reached, the
ventilator will end inspiration
The volume delivered depends upon flow, duration of
inspiration & lung characteristics
Disadvantage:
 Lower tidal volumes delivered
Advantage:
 Limits high peak pressures
96

97.  Inspiratory Pause
Inspired volume is delivered but expiratory valve
remains closed
Plateau Pressure used to calculate static compliance
Helps to improve peripheral distribution of gases and
oxygenation
97

98. Expiratory Phase
 History : Negative End Expiratory Pressure(NEEP)
 Baseline Pressure: pressure level from which a
ventilator breath begins
 ZEEP
 PEEP
98

99.  Expiratory Pause
A maneuver performed at the end of exhalation
Patient is allowed to exhale completely and then
ventilator pauses the breath before delivering the next
breath
Both the inspiratory and expiratory valve will be closed
Purpose: To measure the pressure associated with air
trapped in the lungs(auto PEEP)
99

100.  Expiratory Retard
Used in patients with disease that leads to early airway
closure.
Normally pursed lib breathing would create a back
pressure to prevent this early airway closure.
In mechanically ventilated patient , this effect is
created by ventilatory circuits, bacterial filters and
expiratory valves as they will resist the flow of air
100

101. Types of Breaths
 Machine cycled breaths: Mandatory Breath
Assisted Breath
 Patient cycled breaths: Spontaneous breath
Supported Breath
101

102. Mandatory Breath
 Triggered, limited and cycled by the ventilator
 Ventilator controls the timing(time triggering) or tidal
volume or both
102

103. Assisted Breath
 Triggered by Patient
Limited by Machine
Cycled by Machine
 Patient initiates all or some of the breaths
 Ventilator gives variable amount of support
throughout the cycle
103

104. Supported Breath
 Triggered by the patient
Limited by the machine
Cycled by the patient
 Same as spontaneous breath with an inspiratory
pressure greater than baseline
104

105. Spontaneous breath
 Triggered, limited and cycle by the patient
 Tidal volume is determined by patient
 The volume or pressure delivered is based on patient
demand and patient’s lung characteristics rather than
the set value
105

106. Effects of PPV
Effects on Cardiovascular System
Thoracic Pump Mechanism
Increased Pulmonary Vascular Resistance
Effects on Diaphragm
Effects on intra cranial pressure
Effects on Renal System
Liver & GIT
106

107. Reduced Cardiac
Output
Renal Effects
Neurological
Effects
Liver & GIT
107

108. • During inspiration, increased airway pressure is
transmitted to intrapleural space and great vessels
• Intra thoracic pressure rises which compresses the
blood vessels and raises CVP
• The increased CVP reduces the pressure gradient
between systemic veins and right heart
• This reduces the venous return to right heart and right
ventricular filling(preload)
• Right ventricular stroke volume decreases
108

109. Increase in PVR & alteration in RV
function
• At high PEEP, the capillaries around alveoli get stretched and narrowed
• Resistance in Pulmonary circulation increases
• Right ventricular after load increases (PVR rises)
• Right ventricle cannot overcome the increase in PVR
• Overdistension of right ventricle
• Reduction in right ventricular output
109

110. Coronary Blood Flow
• Reduction in venous return and alteration in
ventricular function
• Reduced coronary aretery perfusion pressure
gradient
• Reduced cardiac output
• Myocardial dysfunction and myocardial ischemia
110

111. Effects on Diaphragm
 Prolonged mechanical ventilation promotes
diaphragmatic atrophy & contractile dysfunction
 Diaphragmatic atrophy is due to increased protein
breakdown & reduced synthesis
 Calpain caspase 3 & ubiquitin proteasome system are
main contributors to MV induced diaphragmatic
proteolysis
111
Critical Care Medicine 2009

112.  Increased reactive oxygen species (ROS) production
and a diminished antioxidant capacity in the
diaphragm
 12 to 18 hours of MV results in significant fiber atrophy
& reduced cross sectional area in slow and fast muscle
fibers
 Prolonged MV increases cytoplasmic lipid vacuoles
which act as secondary lysosomes involved in
autophagic process
112
Critical Care Medicine 2009

113.  Promotes time-dependent and progressive decrease in
diaphragmatic specific force production at both
submaximal and maximal stimulation frequencies
 Diaphragmatic atrophy is associated with diverse areas
of abnormal sarcomere structure and irregular Z-line
structure
 Muscle biopsy showed generalised fibre atrophy,
myofibril necrosis and disorganisation with loss of
thick myosin filaments
113
Critical Care Medicine 2009

114. Intracranial Pressure
• Reduced Venous return
• Increased CVP & Reduced cardiac output
• Lower Cerebral Perfusion Pressure(ICP – MSBP)
• Cerebral Hypoxemia
• Raised ICP & cerebral oedema
117

115. Renal Effects
• Reduced cardiac output
• Reduced renal blood flow
• Renal arterial blood pressure reduces below 75 mm Hg
• Reduced GRF
• Reduced urine output
118

116. Liver & GIT
 PPV increases serum bilirubin (>2.5 mg/100ml) which
leads to liver malfunction
 Reduced cardiac output will reduce portal venous
pressure
 Splanchnic resistance increases
 Ischemia of liver and gastric mucosa
 Further causes gastric ulceration and bleeding
119

117. Minimising Ill Effects of PPV
 Reduce Mean Airway Pressure
 Inspiratory flow
 I:E Ratio
 PEEP
 Peak Plateau pressure < 30 cm H2O
120

118. Complications of PPV
Problems related to positive pressure
 Ventilator Induced Lung Injury
Barotrauma
Volutrauma
Atelectrauma
Biotrauma
Oxygen Toxicity
121

119.  Systemic Complications:
Reduced cardiac output
Alteration in renal function
Positive fluid balance( fluid retention)
Impaired hepatic function
Increased ICP
122

120. Problems related to artificial airway:
 Infection(VAP)
 Patient anxiety & stress
 Sedation & analgesia
 Communication
Gastric Distress:
 Abdominal distention
 Ulcers & gastritis
123

121. Need for Mechanical Ventilation
Physiological Objectives
 Support or manipulate pulmonary gas exchange
Alveolar ventilation
Alveolar oxygenation: maintain oxygen delivery
124

122.  Increasing Lung Volume
Prevent or treat atelectasis with adequate end
inspiratory lung inflation
Restore and maintain an adequate FRC
 Reduce work of breathing
125

123. Clinical Objectives
 Reverse acute respiratory failure
 Reverse respiratory distress
 Reverse hypoxemia
 Prevent or reverse atelectasis and maintain FRC
 Reverse respiratory muscle fatigue
 Permit sedation or paralysis or both
 Reduce systemic or myocardial oxygen consumption
126

124. Indications
Acute Respiratory Failure (ARF)
 Purpose of ventilation is to maintain normal
respiratory balance(homeostasis)
 In ARF, respiratory activity is absent or insufficient to
maintain adequate oxygen uptake and carbon dioxide
clearance
127

125.  Clinical definition: inability to maintain arterial PO2,
PCO2 & pH at acceptable levels
PO2 below predicted normal range for patients age
PCO2 over 50mm Hg
pH of 7.25 or lower
 2 forms: lung failure with hypoxemia
pump failure with hypercapnia
128

126. Type 1 Respiratory Failure
 Hypoxic lung failure
 Acute life threatening or vital organ threatening tissue
hypoxia
 Results from severe V/Q mismatching
 Diffusion defects
 Right to left shunting
129

127. Type 2 Respiratory Failure
 Hyercapnic Respiratory Failure/ Pump failure
 Inability of the body to maintain normal PCO2
 3 types of disorders can lead to pump failure
CNS disorders
Neuromuscular disorders
Disorders that increase work of breathing
130

128. CNS
 Reduced drive to breathe
Depressant drugs
Brain or brainstem lesions
Sleep apnoea
 Increased drive to breathe
Metabolic acidosis
Anxiety
131

129. Neuromuscular Disorders
 Paralytic disorders: GBS, MG, muscular dystrophies
 Paralytic drugs: curarae, insecticides
 Drugs that affect NM transmission
 Impaired muscle function: electrolyte imbalance,
fatigue, malnutrition and chronic pulmonary diseases
reducing diaphragm contraction capacity
132

130. Increased WOB
 Pleura occupying lesions
 Chest wall deformities
 Increased airway resistance
 Lung tissue involvement
 Pulmonary vascular problems
 Post operative pulmonary complications
 Dynamic hyperinflation
133

131. Type 3 Respiratory Failure
 Considered as a subtype of type 1 failure
 Common in the post-operative period with atelectasis
 Causes of post-operative atelectasis include:
Decreased FRC
Supine/ obese/ ascites
Anesthesia residual effects
Upper abdominal incision
Airway secretions
134
Critical Care Medicine

132. Type 4 Respiratory Failure
 Secondary to shock
 Hypoperfusion can lead to respiratory failure
 Therapy is directed to minimise ill effects of limited
cardiac output by the overworking respiratory muscles
until the etiology of the hypoperfusion state is
identified and corrected.
 Shock can be cardiogenic, hypovolemic or septic
135
Critical Care Medicine

133. Criteria for Mechanical Ventilation
 Apnea or absence of breathing
 Acute respiratory failure
 Impending respiratory failure
 Refractory hypoxic respiratory failure with increase in
WOB
136

134. Goals for Mechanical Ventilation
 Support the pulmonary system
 Reduce the work of breathing
 Restore arterial and acid base balances if possible
 Increase oxygen delivery to the body tissues
 Prevent complications associated with mechanical
ventilation
137

135. Indications for Invasive MV
 Apnea or impending respiratory arrest
 Acute exacerbation of COPD with dyspnea, tachypnea
and acute respiratory acidosis & 1 of the following:
Acute cardiovascular instability
Altered mental status or persistent un co-operativeness
Inability to protect the lower airway
Copious secretions
Abnormalities of the face or upper airway that would
prevent effective NIV
138

136.  Acute ventilatory insufficiency in cases of NM disease
accompanied by any of the following:
 Acute respiratory acidosis
 Progressive decline in vital capacity to below 10 to 15
mL/Kg
 Progressive decline in max inspiratory pressure
below -20 to -30 cm H2O
139

137.  Acute hypoxemic respiratory failure with tachypnea,
respiratory distress and persistent hypoxemia despite
of high FiO2 delivery and presence of following
 Acute cardiovascular instability
 Altered mental status or persistent un
cooperativeness
 Inability to protect the lower airway
140

138. Modes
 The mode is determined by
Type of breath
Control variable(Volume or Pressure)
Timing of breath delivery (CMV/SIMV/Spont)
142

139. Full & Partial Ventilatory Support
 Tells the extent of mechanical ventilation provided
 Full ventilatory support: invasive mechanical
ventilation
 Partial Ventilatory Support: invasive or non invasive
mechanical ventilation
143

140. Full Ventilatory Support
 The ventilator provides all the energy to maintain
effective alveolar ventilation
 FVS is provided when a rate of 8 breaths/ min or more
is provided with a tidal volume of 6 – 12 ml/kg of body
weight
 FVS ensures that patient is not required to perform
any work of breathing
 Mode that gives set volume or pressure is selected
144

141. Partial Ventilatory Support
 Set machine rates are lower than 6 breaths/min
 Patient participates in WOB to maintain alveolar
ventilation
 Modes: SIMV, PSV, volume support (VS), Proportional
assist ventilation and Mandatory Minute
Ventilation(MMV)
145

142. Targeting Volume as Control Variable
 Volume will be constant
 Specified volume is delivered regardless of changes in
lung compliance and resistance or patient effort.
 Set parameters: tidal volume, inspiratory flow rate, RR
 Used when the goal is to maintain a certain level of
PaCO2.
146

143.  Disadvantage:
Peak and alveolar pressures can rise and lead to over
distension
The flow set on the machine may not match the patient
demand
Sensitivity may not be set appropriately further
increasing the WOB & lead to patient ventilator
dyssynchrony
147

144. Targeting Pressure as Control
Variable
 The pressure remains constant, whereas volume delivery
changes as lung characteristics change.
 Advantages:
Reduces risk of over-distention of lungs by limiting the
pressure on the lungs: ‘lung protective strategy’
More comfortable for patients who breath
spontaneously
148

145.  Disadvantage:
 Tidal volume decreases when lung characteristics
deteriorate.
 Volume delivery will vary
149

146. Continuous Mandatory Ventilation
 All breaths are mandatory
 Breaths are volume or pressure targeted
 Patient receives preset number of breaths per minute
of preset tidal volume
 Time triggered breath in CMV mode: control mode
 Patients makes no spontaneous effort
150

147. Controlled Ventilation:
 Patient takes no effort to breathe and ventilation is
completely controlled
 “Locking out” is making the machine completely
insensitive to patients effort
 Patients need to be sedated with medications to
suppress their spontaneous effort
 Used to hyperventilate neurological patients with raised
ICP
151

148. 152

149.  Indications:
Patients who are obtunded due to drugs, cerebral
malfunction
Spinal cord or phrenic nerve injury
Motor nerve paralysis
During anesthesia
153

150.  Disadvantages:
Patient ventilator asynchrony
Respiratory muscle weakness and disuse atrophy if
used for longer period
Acid base balance should be monitored since it is
completely controlled by clinician
Adverse hemodynamic effects as each breath is
delivered under positive pressure
154

151.  Assist/Control Ventilation :
 Patient triggered or time triggered CMV mode
 Operator sets minimum rate, sensitivity level and type of
breath(Volume or Pressure)
 Patient can trigger breath at a faster rate than the set
minimum, but only the set volume or pressure is delivered
with each breath.
155

152.  Pressure triggering occurs because the ventilator is
sensitive to pressure or flow changes that occur as the
patient attempts to take a breath.
 When ventilator senses slightly negative pressure or in
drop in flow, the inspiratory cycle begins.
 Minimum breath rate is set to deliver minimum tidal
volume, allowing the patient to take additional breaths
156

153. 157

154.  Advantages:
Allows patients to control rate of breathing yet delivers
preset volume
Allows some work to be done by respiratory muscles
Asynchrony is minimised
 Disadvantages:
Respiratory Alkalosis: patient hyperventilates
Auto cycling/triggering
Auto PEEP : if patient hyperventilates
158

155. Intermittent Mandatory Ventilation
 Periodic volume or pressure controlled breath occur at
set intervals (time triggered)
 Between Mandatory breaths, patient can breath
spontaneously without receiving a mandatory breath
159

156.  The spontaneous baseline pressure can be set at
ambient pressure or higher positive baseline
pressures(PEEP)
 Some ventilators can provide pressure support for
spontaneous breaths
160

157.  Advantages
Allows spontaneous breaths in the cycle
Respiratory muscle strength is maintained and
prevents atrophy
 Disadvantages
Breath Stacking – patient’s inspiration and machine’s
inspiration simultaneously
Asynchrony
161

158. Synchronized Intermittent
Mandatory Ventilation (SIMV)
 Same as IMV except that mandatory breaths are
patient triggered rather than time triggered
 The patient can breathe spontaneously between
mandatory breaths
 At a predetermined interval (preset RR) the ventilator
waits for the patient’s next inspiratory effort
162

159.  When it senses the effort, the ventilator assists the
patient by synchronously delivering a mandatory
breath
 After mandatory breath, ventilator allows the patient
to breath spontaneously without receiving mandatory
breath until the next mandatory breath is due
 Operator sets target volume or pressure, maximum
mandatory breath rate & sensitivity level
163

160.  If the patient fails to initiate ventilation within that
time interval(Assist Window), then the ventilator will
provide a mandatory breath at the end of time period
 Spontaneous breath can be supported with Pressure
support with PSV to reduce the work of breathing for
spontaneous breath
 Used to wean patients and reduce dependency
164

161. 165

162.  Advantages
Guaranteed minute ventilation with low pressures
Fewer cardiovascular side effects
Synchrony
Less atrophy of muscles
No breath Stacking
No sedation required
 Disadvantage
The WOB associated with triggering
166

163. 167

164. Mandatory Minute Ventilation
 Patient breathes spontaneously yet a constant minute
ventilation is guaranteed
 If patient’s spontaneous ventilation does not match
the target VE, the ventilator provides whatever part of
the VE the patient does not achieve
168

165.  In V-MMV, if VE is not achieved, the ventilator
responds by delivering mandatory volume breaths by
increasing rates
 The assisted breaths are patient triggered, machine
controlled and machine cycled
 The mandatory breaths are triggered, limited and
cycled by the machine
169

166.  In P-MMV, the ventilator increases the level of PS
when the target VE is not achieved
 Patient triggered, Pressure Limited and patient cycled
 There are no mandatory breaths in P-MMV and if VE
is achieved then no PS adjustments
170

167.  If used for weaning:
VE should be set to target a PaCO2 sufficient to
stimulate spontaneous breathing
A VE that is 80% to 90% of patient’s VE requirements
is usually acceptable
 Indications:
As a weaning tool
Unstable ventilatory drive with a desire of spontaneous
breathing
171

168.  Advantage:
 Prevents hypoventilation and resultant hypercapnia and
respiratory acidosis
 Smoother transition from MV to spontaneous ventilation
 Disadvantage
 Does not monitor the quality of spontaneous breaths
 Rapid, shallow breathing can achieve the target VE without
adequate alveolar ventilation & lead to atelectasis
 When the VE demand increases because of fever, activity
the target VE is not adjusted and patient’s demand wont be
met
172

169. Spontaneous Modes
 3 modes for continuous spontaneous breathing:
1. Spontaneous breathing
2. CPAP
3. PSV
173

170. Spontaneous Breathing
 Patients can breathe spontaneously
 Also called T piece method
 Mimics having the patients ET tube connected to
Briggs adaptor & humidified oxygen source via large
bore tubing
174

171.  Spontaneous breaths are:
Patient triggered
Tidal volumes vary with the patients inspiratory flow
demand
Inspiration lasts as long as the patient actively inspires
Inspiration is terminated when patient’s inspiratory
flow demand decreases to a preset minimal value
175

172.  Advantage:
Ventilator can monitor the patient’s breathing and can
activate alarm if undesirable circumstances arise
 Disadvantage:
Considerable patient effort is required to breath
through the circuit and to open inspiratory valves for
gas flow
176

173.  Spontaneous Breath Trial(SBT)
Used to evaluate readiness to wean from the MV
During the trial , ventilator support is reduced and the
patient is allowed to breathe spontaneously for brief
period (15 – 30 mins)
Vital signs, SPO2 and appearance are monitored
177

174. Pressure Support Ventilation
 Patients spontaneous respiratory activity is augmented
by the delivery of a preset amount of inspiratory
positive pressure
 When the patient triggers(onset of inspiration),the
preselected PS is delivered throughout inspiration,
promoting flow of gas into the lungs
178

175.  VT is variable determined by patients effort, amount of
PS, compliance & resistance in the system
 Gas flow is delivered with decelerating flow wave
pattern in which flow rate naturally decays when the
lungs fill during inspiration
 PS is a flow cycled mode because inspiration ends on
the basis of flow crieteria
179

176.  Components of PS breath:
Trigger: breaths can be triggered but detection of
change in pressure or flow
Rise Time: amount of time taken to reach a set
pressure
 Short rise time: immediate attainment of peak flow
and inspiratory demands are met
 Long rise time: increased work of breathing
180

177.  Indications:
Weaning from MV
Augments inspiratory flow & reduces WOB
Used with NIV to augment spontaneous inspiratory
volumes
181

178.  Advantages:
May be used to overcome resistance of artificial airway
and circuit
Improves patient ventilator synchrony(patient has
control)
Allows operator to augment inadequate spontaneous
VT thereby reducing WOB
Amount of work can be titrated hence as a weaning
tool(used till VT becomes 10 – 15 ml/kg & RR –
25breaths/ min or less)
Improves endurance of respiratory muscles(high
volumes, low pressures)
182

179.  Disadvantages:
Variable VT so no guarantee of alveolar ventilation
The ventilator may fail to cycle to expiration if an extensive
air leak occurs either around airway or in the circuit
because flow rate that cycles inspiration wont be reached
& will prolong inspiratory cycle under positive pressure
The increased flow created by inline nebulizer may be
detected as patient’s VT & may result in failure to detect
apnea
183

180. Continuous Positive Airway
Pressure
 Positive pressure is applied throughout the respiratory
cycle
 Patient must have a reliable ventilatory drive &
adequate tidal volume because no mandatory breaths
are provided
 Patient does all the WOB
184

181.  CPAP provides positive pressure at end of exhalation
thus preventing alveolar collapse, improves FRC &
enhances oxygenation
 Indications:
SBT during weaning
In conditions with adequate ventilation but
incompetent oxygenation (atelectasis)
Dynamic hyperinflation & auto PEEP
185

182.  Advantages
Increases the FRC and reduces intra pulmonary
shunting
Promotes respiratory muscle strengthening since no
mandatory breaths given
Weaning with CPAP is good because of alarms and
delivery of mandatory breaths in backup mode
 Disadvantages
Decrease cardiac output, increased ICP and
pulmonary barotrauma
186

183. 187

184. Bilevel Positive Airway Pressure
 Ventilation of the lungs involves two forces. The
ventilator generates a positive pressure & the
inspiratory muscles produce a negative pressure. The
two forces combine to produce a change of volume in
the lungs.
 Operator sets two pressure levels
 Inspiratory positive pressure(IPAP)
 Expiratory positive pressure (EPAP)
188

185.  Inspiration is commonly patient trigger but sometime
time triggered also.
 BiPAP allows for adjustment of the flow and pressure
to assist in inhalation or exhalation through the
administration at two distinct levels of positive
pressure
 IPAP: similar to PCV
 EPAP: similar to PEEP
189

186.  IPPV-BIPAP: no spontaneous activity on the part of the
patient. Ventilation is pressure-controlled and time-cycled.
All ventilation activity is carried out by the ventilator.
 SIMV-BIPAP: spontaneous breathing on the lower pressure
level only. Increased pressure at the upper level delivers a
machine-generated flow.
 Genuine BIPAP: patient breathes spontaneously at both the
upper and the lower pressure levels. Mechanical ventilation
is superimposed on the spontaneous breathing as a result
of step changes in pressure, but spontaneous breathing is
not impeded.
190

187.  Indication
Acute respiratory failure
Hyercapnic exacerbation of COPD
191

188.  Advantages:
Spontaneous breathing during mechanical ventilation
allows additional volumes to be ventilated.
Less stressful for patients to be able to breathe
spontaneously at any time
Less sedation required
192

189. Advanced Modes
193

190. Airway Pressure Release
Ventilation(APRV)
 Designed to provide two levels of positive pressure
and to allow spontaneous breathing at both levels
when spontaneous effort is present.
 Both pressure are time triggered and time cycled.
 Newer ventilators allow patient triggering & cycling
which allows synchronisation with patient effort
194
Cleveland Clinic Journal of Medicine 2011

191.  The curve has 2 inflection points between which the
slope is steep indicating maximum compliance
 Below the lower inflection point , the alveoli may
collapse
 Above the upper inflection point the alveoli will
overdistend
 Generally a PEEP of 2 cm H2O above lower inflection
is used
195
Cleveland Clinic Journal of Medicine 2011

192. 196
Cleveland Clinic Journal of Medicine 2011

193. • A baseline high pressure is set(P High)
• Mandatory breaths are achieved by releasing baseline high
pressure for a brief period ,usually 0 cm H2O(P Low)
• Lungs partially deflate & quickly resume high pressure before
unstable alveoli can collapse
• The release time should be very short
• Residual volume of air creates auto PEEP (intentional)
• Recruitment of alveoli
197
Cleveland Clinic Journal of Medicine 2011

194. Settings
 P high: If P plat is lower than 30 cm H2O use this as
initial P high
 P low: 0 cm H2O
 T high: 4 sec
 T Low: 0.6 – 0.8 sec
 Titrate sedation so spontaneous breathing is atleast
10% of total minute ventilation
198
Cleveland Clinic Journal of Medicine 2011

195. 199

196.  Indications
Partial to full ventilatory support
Patients with ALI/ARDS
Patients with refractory hypoxemia due to collapsed
alveoli
Patients with massive atelectasis
200

197.  Advantages
Allows inverse ratio ventilation (IRV) with or without
spontaneous breathing (less need for sedation or
paralysis)
Improves patient-ventilator synchrony if spontaneous
breathing is present
Improves mean airway pressure
Improves oxygenation by stabilizing collapsed alveoli
Allows patients to breath spontaneously while
continuing lung recruitment
201

198.  Disadvantages
Variable VT
Could be harmful to patients with high expiratory
resistance (i.e., COPD or asthma)
Auto-PEEP is usually present
Caution should be used with hemo dynamically
unstable patients
Asynchrony can occur is spontaneous breaths are out
of sync with release time
202

199. Pressure Regulated Volume Control
(PRVC)
 Control: Volume
 Trigger: Patient or Time
 Limit: Pressure
 Target: Lowest pressure for set volume
 Cycle: Time
 Pressure-limited Time-cycled Ventilation
203

200. • Inspiratory pressure is increased to deliver set volume
• Maximum available pressure is maintained
• Breath is delivered at preset VE, rate and during preset
inspiratory time
• When VT corresponds to set value, pressure remains
constant
• If preset volume increases, pressure decreases; the ventilator
continually monitors and adapts to the patient’s needs
204

201.  Indications
Patient who require the lowest possible pressure and a
guaranteed consistent VT
ALI/ARDS
Patient with the possibility of compliance or Raw
changes
205

202.  Advantages:
Maintains a minimum PIP
Guaranteed VT
Patient has very little WOB requirement
Allows patient control of respiratory rate
Breath by breath analysis
206

203.  Disadvantages:
Varying mean airway pressure
May cause or worsen auto-PEEP
When patient demand is increased, pressure level may
diminish when support is needed
A sudden increase in respiratory rate and demand may
result in a decrease in ventilator support
207

204. ADAPTIVE SUPPORT VENTILATION
 A dual control mode that uses pressure ventilation (PC
& PSV) to maintain a set minimum VE (volume target)
using the least required settings for minimal WOB
depending on the patient’s condition and effort
 It automatically adapts to patient demand by
increasing or decreasing support, depending on the
patient’s elastic and resistive loads
208

205.  The clinician enters the patient’s ideal body weight,
which allows the ventilator’s algorithm to choose a
required VE.
 The ventilator then delivers 100 mL/min/kg.
 A series of test breaths measures the system
compliance, resistance & auto PEEP
 If no spontaneous effort occurs, the ventilator
determines the appropriate respiratory rate, VT and
pressure limit delivered for the mandatory breaths
209

206.  I:E ratio and TI of the mandatory breaths are
continually being “optimized” by the ventilator to
prevent auto-PEEP
 If the patient begins having spontaneous breaths, the
number of mandatory breaths decrease and the
ventilator switches to PS at the same pressure level
 Pressure limits for both mandatory and spontaneous
breaths are always being automatically adjusted to
meet the VE target
210

207. 211

208.  Indications
Full or partial ventilatory support
Patients requiring a lowest possible PIP and a
guaranteed VT
ALI/ARDS
Patients not breathing spontaneously and not
triggering the ventilator
Patient with the possibility of work load changes (CL
and Raw)
Facilitates weaning
212

209.  Advantages
Guaranteed VT and RR
Minimal patient WOB
Ventilator adapts to the patient
Weaning is done automatically and continuously
Decelerating flow waveform for improved gas
distribution
Breath by breath analysis
213

210.  Disadvantages
Inability to recognize and adjust to changes in alveolar
dead space
Possible respiratory muscle atrophy
Varying mean airway pressure
In patients with COPD, a longer TE may be required
A sudden increase in respiratory rate and demand may
result in a decrease in ventilator support
214

211. Proportional Assist Ventilation
(PAV)
 Control: Pressure
 Trigger: Patient
 Limit: Pressure
 Cycle: Flow
 Target: Volume
 Pressure Limited Flow Cycled Ventilation
215

212.  Regulates the pressure output of the ventilator
moment by moment in accord with the patient’s
demands for flow and volume.
 If the clinician has set PAV at 60%, the ventilator
would provide 60% of the calculated pressure, the
remaining pressure being left to the patient to
generate.
 The pressure applied by the respiratory muscles
(Pmus) to the system is used to overcome the elastic
(E) and resistive (R) opposing forces.
216

213.  The pressure delivered varies from breath to breath,
due to changes in elastance, resistance and flow
demand.
 Pressure applied by respiratory muscles is
proportional to the volume (V) displacement
 Elastic (E) & resistive (R) forces are proportional to the
airflow rate (ARF)
 Pmus = E x V + R x AFR
217

214. 218

215. How it differ from Pressure Ventilation?
 In pressure ventilation, flow will decelerate when
airway pressure meets the target level.
 In PAV there is no pressure target; pressure will
increase, as will flow, as patient demand increases.
 Compared to conventional modes in PAV patient
has generate more force to trigger the ventilator.
219

216. Neurally adjusted ventilator assist
(NAVA)
 NAVA is an assist mode of MV that delivers a pressure
proportional to the electrical activity of the diaphragm
 NAVA is proportional to the neural output of the
patients central respiratory command
 Ventilator is triggered & cycled off based on the
electrical activity of the diaphragm value
220
Critical Care 2012

217.  The placement of a specifically designed nasogastric
tube that has a series of EMG electrodes near its distal
end, positioned across the diaphragm.
 As EMG activity increases, pressure is applied during
the inspiratory phase, and as the diaphragm relaxes,
airway pressure decreases.
 Inspiration ends at a specific percentage of the peak
EMG activity.
221
Critical Care 2012

218. 222

219.  Advantages:
NAVA greatly improves triggering, since gas delivery
begins when the diaphragm is simulated, not as a
result of flow in the airway.
Thus, even in the presence of severe air trapping or
large system leaks, triggering is not compromised.
223
Critical Care 2012

220. High Frequency Ventilation
 Uses above normal ventilating rates with below
normal ventilating volumes
 3 basic modes of HFV
1. High Frequency Positive Pressure Ventilation
(HFPPV)
2. High Frequency Jet Ventilation (HFJV)
3. High Frequency Oscillatory ventilation (HFOV)
224

221.  High Frequency Positive Pressure Ventilation
(HFPPV)
 Uses respiratory rates of about 60 to 100 breaths/min
 Uses conventional positive pressure ventilator set at
high rates with lower than normal tidal volumes
225

222. High Frequency Jet Ventilation (HFJV)
 HFJV uses rates into the thousands up to 4000
breaths/min
 Uses a nozzle or an injector
 Small diameter tube creates high velocity jet of air that
is directed into the lungs
 Exhalation is passive
226

223. High Frequency Oscillatory ventilation (HFOV)
 Use a small piston device to deliver gas in a “to-and-
fro” motion pushing gas in during inspiration and
drawing gas out during exhalation
 HFOV has been used in infants with Respiratory
distress and in adults or infants with open air leaks
such as broncho pleural fistula
227

224. 228

225. HFOV in ARDS
 Characterized by the rapid delivery of small tidal
volumes of gas and the application of high mean
airway pressures
 High mean airway pressures prevent cyclical
derecruitment of the lung and the small tidal volumes
limit alveolar overdistention
 Respiratory rate ranges from 180 to 600 breaths/min
and inspiratory bias flow of 30 to 60 L/min
229
Chest 2007

226.  Gas transport improves due to bulk flow of gas to
alveolar units close to the proximal airways &
asymmetric velocity profiles
 Asynchronous filling of adjacent alveolar spaces called
pendelluft
 This occurs due to due to:
Different alveolar-emptying times
Collateral ventilation through non airway connections
between neighboring alveoli
230
Chest 2007

227. 231
Chest 2007

228. Non Invasive Ventilation
 Treatment of choice for acute on chronic respiratory
failure unless cardiovascular stability is a factor
 Reduces need & complications of intubation, reduces
hospital stay & hospital mortality rates
 Beneficial for patients with COPD & chronic
ventilatory failure in patients with musculoskeletal
problems
233

229. Indications
At least 2 of these factors should be present:
 RR > 25 breaths/min
 Moderate to severe acidosis: pH 7.30 to 7.35, PaCO2 :
45-60 mm Hg
 Moderate to severe dyspnea with use of accessory
muscles and paradoxical breathing
234

230. Contraindications
 Absolute
Respiratory arrest
Cardiac arrest
Non-respiratory organ failure
Upper airway obstruction
Inability to protect the airway or high risk of aspiration
or both
Inability to clear secretions
Facial or head surgery or trauma
235

231.  Relative
Cardiovascular instability
Uncooperative patient
Copious or viscous secretions
Fixed nasopharyngeal abnormalities
Extreme obesity
236

232. Intubation Without Ventilation
 Some patients are intubated because of airway
obstruction, protect the airway & facilitate removal of
secretions
 If no indications of ventilatory support & 7 mm ET
tube is used it is reasonable to conclude that PPV isn’t
needed
237

233. NIV to IPPV
 Respiratory arrest
 Respiratory rate > 35 breaths/ min
 Severe dyspnea, use of accessory muscle & paradoxical
breathing
 Life threatening hypoxemia: PaO2 < 40 mm Hg or
PaO2/FiO2 <200
 Severe acidosis and hypercapnia
 Impaired mental status
 CV complications
 Other circumstances like pneumonia, pulmonary
embolism, massive pleural effusion, sepsis
238

234. Weaning
 The process of liberating patients from mechanical
ventilatory support is referred as weaning
 Synonyms: Discontinuation, Gradual withdrawal,
Liberation
 Weaning should be done at the earliest to prevent VAP,
VILI, airway trauma & unnecessary sedation
 Pre mature weaning can lead to early fatigue of ventilatory
muscles, compromised gas exchange & loss of airway
protection
239

235.  Short term mechanical ventilator (STMV):
 Less than 3 consecutive days
 No consecutive illness
 Long term mechanical ventilator (LTMV):
 Beyond 3 days
 More chances of consecutive illness and
complications
240

236. Stages of Weaning
 4 stages (AACN weaning continuum model, 1998)
1. Acute
2. Pre-wean
3. Wean
4. Outcome stages
241

237. Acute stage
 24-72 hours
 The patient is initially placed on a ventilator and
unstable
 Some patients may progress rapidly & are extubated
 High level ventilatory & hemodynamic support
 Weaning is not expected & ventilatory parameters are
adjusted to protect the lung
 Focus on correction of condition
242

238. Pre-wean stage
 Patient is stable yet may require a high level of care
 High level cardiopulmonary support is not be necessary
 Modes used are SIMV, PSV
 Lower levels of oxygen and PEEP
 Regular assessing and testing of weaning ability
 Clinical interventions aim to restore & improve baseline
status
243

239. Weaning stage
 Short with rapid progress over consecutive days
 Marked by physiologic stability & attempts to withdraw
ventilatory support with aggressive weaning trials
 CPAP and PSV are used as trial modes
 Goal is to determine duration of spontaneous breathing
without evidence of intolerance
244

240.  Once the goal is achieved a decision is made to
extubate in case of ET tube
 In case of tracheostomy, attempt prolonged trials of
spontaneous breathing (24 hours)
 Specific techniques: capping of tracheostomy, use of
speaking valves and tube downsizing
245

241. Outcome stage
 It is the final stage
 Consists of
Complete weaning with removal of artificial airway
Complete weaning with an artificial airway
Incomplete weaning with partial ventilatory support
Full ventilatory support
Death
246

242.  Weaning Success : It is defined as absence of
ventilatory support 48 hours following extubation
 Weaning in progress : it is an intermittent category
for patients who extubated but continue to receive
ventilatory support by non invasive ventilation
 Weaning failure : Either failure of spontaneous
breathing trial (SBT) or need for reintubation within
48 hours following extubation
247

243.  Weaning failure exhibits as tachypnea, tachycardia,
hypertension, hypotension, hypoxia, acidosis or
arrhythmias & increased work of breathing
 Causes of weaning failure:
Inadequate ventilatory drive
Respiratory muscle weakness
Respiratory muscle fatigue
Increased work of breathing
Cardiac failure
248
Clinics in Chest Medicine 1988

244. Traditional Weaning Modes
SIMV PSV T- Piece
249

245. Pressure support versus T-tube for weaning from
mechanical ventilation in adults (Review)
 Objective : To evaluate the effectiveness and safety of
two strategies, a T-tube and pressure support
ventilation, for weaning adult patients with respiratory
failure that required invasive mechanical ventilation
for at least 24 hours
 Study included 9 RCTs with 1208 patients; 622 patients
were randomized to a PS spontaneous breathing trial
(SBT) and 586 to a T piece SBT
250
Cochrane database 2014

246.  Pressure support ventilation (PSV) and a T-tube were used
directly as SBTs in four studies (844 patients,69.9% of the
sample).
 In 186 patients (15.4%) both interventions were used along
with gradual weaning from mechanical ventilation; the PS
was gradually decreased, twice a day, until it was minimal
and periods with a T-tube were gradually increased to two
and eight hours for patients with difficult and prolonged
weaning.
 In two studies (14.7% of patients) the PS was lowered to 2
to 4 cm H2O and 3 to 5 cm H2O based on ventilatory
parameters until the minimal PS levels were reached. PS
was then compared to the trial with the T-tube (TT).
251
Cochrane database 2014

247.  Primary outcome : weaning success (absence of the
requirement for ventilatory support within 48 hours after
extubation)
 Secondary outcomes:
 ICU mortality
 Time of weaning from MV or weaning duration
 Reintubation.
 Intensive care unit (ICU) and hospital length of stay (LOS)
 Proportion with VAP.
 Physiologic parameters, including:
1. Respiratory rate (RR),
2. Tidal volume (VT ),
3. Rapid and shallow breathing index (RSBI or RR/VT )
252
Cochrane database 2014

248.  Weaning success: found a larger but not statistically
significant proportion of patients assigned to PS were
successfully extubated from invasive MV compared
with patients assigned to T-tube
 There was no statistically significant difference in ICU
mortality, reintubation, ICU and hospital length of
stay ,pneumonia and rapid shallow breathing index in
both the groups
253
Cochrane database 2014

249.  Successful SBT ( 2 hours) revealed a statistically
significant difference in the proportion of patients in
the PS group compared with the patients in the T piece
group
 Evaluated tidal volume and respiratory rates showed a
statistically significant difference in the PS group.
254
Cochrane database 2014

250. Assessing Readiness to Wean
 Clinical assessment
 Objective measurements
255

251. Clinical assessment
 Adequate cough
 Absence of excessive tracheobronchial secretion
 Resolution of disease acute phase for which the
patient was intubated
256

252. Objective Measurements
 Clinical stability
Stable cardiovascular status (i.e. HR<140 beats/min,
no or minimal vasopressors)
Stable metabolic status
257

253.  Adequate oxygenation
SpO2 >90% on FIO2< 0.4 (or PaO2/FIO2 >150 mmHg)
PEEP <8 cmH2O
 Adequate mentation
No sedation or adequate mentation on sedation (or
stable neurologic patient)
258

254.  Adequate pulmonary function
RR ≤ 35 breaths/min
MIP ≥ -20 to -25 cmH2O
VT > 5 mL/kg
VC >10 mL/kg
Rapid Shallow Breathing Index (RSBI) RR/VT < 105
breaths/min/L
No significant respiratory acidosis
259

255. Patients Ventilatory Muscle
Strength
 Measured by:
Vital capacity
Tidal volume
Respiratory rate
Rapid shallow breathing Index (RSBI)
260

256. Vital capacity
 Patient takes maximum inspiration followed by
maximum exhalation
 VC is good indicator of pulmonary reserve.
 Normally : three times that of tidal volume.
 Minimum value for weaning is 10 to 15 ml/kg.
261

257. Tidal volume
 A spirometer is used & patient is taken off the
ventilator for measurements
 Patient is assessed at zero CPAP while connected to
ventilator.
 Patient is asked to breathe normally for 1 minute and
average tidal volume is calculated
 Good predictor of respiratory muscle endurance.
 5 ml/kg or more is expected.
262

258. Rapid shallow breathing index
 RR : VT index
 Describes a pattern of breathing consistent with an
increases workload and potential for fatigue
 Can be measure at off or on ventilator
 Success when index ≤105
 Failure when index >105
263

259. Maximum Inspiratory
Pressure(PImax)
 PImax is measured using a Bourdon gauge pressure
manometer while therapist occludes the airway
 The procedure should be stopped if oxygen
desaturation or arrhythmias occur
 MIP is normally -50 to -100cm H2O
 An MIP of 0 to -20 is inadequate for creating a VT
large enough to produce a good cough
266

260. 267

261. Drive to Breathe
 Established by measurement of airway occlusion
pressure
 To obtain P 0.1, the airway is occluded during the first
100 msec of inspiration and the pressure at the upper
airway is measured
 This value reflects both the drive to breath and
ventilatory muscle strength
268

262.  Normal range : 0 to -2
 Higher value(0): strong respiratory muscles and
vigorous respiratory drive
 Lower value (-6): weak drive or muscle weakness
high drive to breath/weaning failure
269

263. Signs of Increased WOB
 Use of accessory muscles
 Asynchronous breathing
 Nasal flaring
 Diaphoresis
 Anxiety
 Tachypnea
 Sub sternal and intercostal retractions
 Patient asynchronous with ventilator
270

264.  Oxygen consumption > 15% of total oxygen production
 Increased metabolic rate: high CO2 production
(Capnography)
 High ratio of dead space to tidal volume (VD/VT) >0.6
 High airway resistance
 Low compliance
271

265.  CROP Index
Evaluates compliance, resistance, respiratory rate,
oxygenation and inspiratory pressure
Provides good assessment of respiratory muscle
overload and fatigue
CROP= (Cd x Pimax [PaO2/PAO2]) / f
CROP values above 13 indicate the likely hood of
successful ventilator weaning
272

266. Predicting Success in weaning from mechanical
ventilation
 Predictors of Success in SBT
273
Chest 2001
Predictor Sensitivity Specificity
Minute Ventilation 0.60 0.41
RR 0.97 0.53
Tidal volume 0.74 0.58
RSBI 0.97 0.42
Pimax 0.90 0.32

267. Predictor Sensitivity Specificity
Minute Ventilation 0.63 0.52
RR 0.77 0.51
Tidal volume 0.85 0.73
RSBI 0.84 0.44
CROP index 0.77 0.71
Pimax 0.90 0.27
274
Predictors of Successful Extubation
Chest 2001

268. Adequacy of Oxygenation
PaO2 >60 mm Hg
PEEP < 5 to 8 cm H2O
PaO2/FiO2 >250 mm Hg
PaO2/PAO2 >0.47
P(A-a)O2 <350 mm Hg (FiO2=1)
%QS/QT < 20% to 30%
275

269. Assessment of SBT
 Typically conducted when basic findings suggest that
the patient is ready to be weaned but the clinician is
uncertain about the patient’s ability to tolerate
breathing spontaneously
 The patient is allowed to breath spontaneously for a
few minutes to determine the patient’s ability to
perform an extended SBT
276

270.  SBT determines patients ability to tolerate
unsupported ventilation determines by patients
respiratory pattern, hemodynamic stability adequacy
of gas exchange & subjective comfort
 A patient is considered fit for extubation if he can
tolerate SBT for 30 to 120 mins
277

271. Monitoring:
 RR > 30 – 35 breaths
Increase of > 10 breaths or decrease below 8 breaths
 VT < 250 to 300 mL
 BP
A drop of 20 mm Hg systolic
A rise of 30 mm Hg systolic
Systolic values>180 mm Hg
A change of 10 mm Hg diastolic
278

272.  HR – increasing more than 20% or exceeds 140
beats/min
 Sudden onset of frequent premature ventricular
contractions (>4-6/min)
 Diaphoresis
 Clinical signs that indicate deterioration of the
patient’s condition or that demonstrate the patient is
anxious, not ready for weaning – ABG and oxygen
saturation
279

273.  Post extubation difficulties:
Hoarseness
Sore throat
Cough
Subglottic edema
Increased WOB from secretions
Laryngospasm
Risk of aspiration
280

274. Troubleshooting
 It is the identification and resolution of technical
malfunctions in patient ventilator system .
1. Patient Related Problems
2. Ventilator Related Problems
281

275. Patient Related Problems
 Airway Problems
 Bronchospasm
 Secretions
 Pulmonary edema
 Dynamic Hyperinflation / Auto PEEP
 Change in body position
 Drug induced distress
 Abdominal distension
282

276. Ventilator Related Problems
 Leaks
 Inadequate oxygenation
 Inadequate ventilatory support
 Trigger sensitivity
 Inadequate flow settings
 Dyssynchrony
283

277. Alarms
High Pressure Alarms:
Causes Assessment and management
Increase resistance to gas flow Air flow obstruction by kinks, biting,
secretions, migration of airway in right
bronchus, bronchospasm, herniation of
cuff over tube end, spontaneous
breathing efforts, malfunctioning of
sensors
Evaluate: PIP and Pplat
Decrease pulmonary compliance Stiff lungs, pneumonia, ARDS,
pneumothorax
Treatment: attend underlying cause,
PEEP, mobilisation of secretions,
suctioning, enhance ventilation
Patient gagging or coughing or
attempting to talk
Correct the cause and check cuff
pressure if patient is attempting to talk
284

278.  Low Pressure Alarms: 5 – 10 cm H2O below PIP
 Low oxygen pressure
 Low PEEP/CPAP
Patient ventilator
disconnection
Determine cause of leak, loose
connection, cuff leak
Loss of oxygen source Accidental disconnection of oxygen
inlet
If O2 source problem is being corrected
start MHI with portable O2 source
Leak in circuit Check for leaks in entire ventilator
circuit
Machine not sensitive to detect
inspiratory effort
285

279. Volume Alarms
 Low exhaled tidal volume or Minute Ventilation
Causes Assessment & Management
Patient disconnected or leak Leak in circuit(adaptors, humidifier), check for
signs of hypoxemia and hypercapnia
If leak not detected increase VT to compensate
for volume loss
In PC mode with compliance &
high airway resistance
Treat the underlying cause of reduced
compliance
Provide additional ventilatory support by
shifting to VC mode & increasing inspiratory
pressure assistance to achieve VT, increase
number of mandatory breaths
286

280. Causes Assessment & Management
High pressure alarm is reached which
causes ventilator to dump rest of VT
Correct the high pressures
Insufficient gas flow Assess and correct I:E ratio
Increase flow rate
287

281.  High exhaled tidal volumes & Minute ventilation
Causes Assessment & Management
Increased RR or VT Raised VE can be due to anxiety,
pain, metabolic acidosis or
hypoxemia
Check if the cause of raised RR is
respiratory alkalosis
Inappropriate ventilator setting Too high VT or RR
Check for trigger sensitivity
288

282.  Apnea: no exhalation for approximately 20 sec
Cause Assessment & Management
No detectable spontaneous
respiratory effort
Cause: lethargy, heavy sedation,
respiratory arrest.
Stimulate lethargic patients &
discontinue weaning if apneic periods
are frequent
If respiratory arrest: MHI
If pulseless: CPR
If patient is fine: check for sensitivity
of mandatory breaths
Loose connection to exhalation flow
sensor
Secure the connection
289

283.  Low PaO2: considered less than 60 – 70 mm Hg
291
Causes Assessment & Management
Change in lung function Assess for hypoxemia, collection of
secretions or bronchospasm evident by
elevated PIP
Increase FiO2 or PEEP
Improve lung function with chest PT &
removal of secretion
Check for hemoglobin
Air leak/ Loss of PEEP Check & correct air leak.
Check for cuff pressure

284.  High PaO2: considered more than 100 mm Hg
292
Causes Assessment & Management
Improvement in lung function Decrease PEEP or FiO2
FiO2 should be reduced till non toxic
levels(<0.5)

285.  Respiratory Alkalosis
293
Causes Assessment & Management
Factors that increase RR( anxiety,
pain, CNS abnormality)
Sedation
Inappropriate ventilator settings (Vt,
RR)
Mandatory: 8 – 10 ml/kg
Spontaneous : 5 ml/kg
Reduce Vt in SIMV mode
Reduce inspiratory pressure in PS & PC
mode
Reduce SIMV rate if RR is high
Ventilator Self Cycling Happens when sensitivity is too high
Adjust sensitivity to 2 cm H2O below
baseline

286.  Respiratory Acidosis
294
Causes Assessment & management
Inadequate RR Seen due to over sedation or acute neurologic
event
Increase rate of mandatory breaths
Inadequate VT If difference in EVT & set VT is > 50 ml then
check for leaks
If EVT is not 8 – 10 ml/kg for mandatory
breaths & 5 ml/kg then increase the set VT in
volume cycled modes & inspiratory pressure in
pressure & flow cycled modes
Excess glucose loads Eliminate over feeding
Increased physiologic dead
space
Check for hyperinflation
Reduce Vt and PEEP if possible
Increased mechanical dead
space
Remove dead space tubing if present

287. References
 Mechanical ventilation by Susan Pilbeam
 Management of mechanically ventilated patients by
N.B. Pierce
 Clinical Application of Mechanical Ventilation by
David Chang
295

288. Thank You
296