Basics of Mechanical Ventilation

Mechanical Ventilation: Part –I(Basics and Modes)
Presenter:
Dr. Tirtha Raj Bhandari
Anesthesiologist
Dadeldhura Hospital, Dadeldhura
5/28/2021
Department of Anesthesiology and intensive care, Dadeldhura
Hospital
1

Objectives
• Basic physiology and physics of lung and ventilator
• To discuss indication of mechanical ventilation
• To discuss different modes for mechanical ventilation
• To discuss Troubleshooting during mechanical ventilation
• To discuss Weaning
5/28/2021
Hospital
2

CLASSIFICATION
MECHANICAL VENTILATION
3
• Airway pressure
1. Negative pressure ventilation
2. Positive pressure ventilation
• Invasiveness
1. Invasive Ventilation
2. Non-invasive mechanical ventilation

CLASSIFICATION
MECHANICAL VENTILATION
4
1. Negative Pressure Ventilators (Extrathoracic)
 Applied to the outside of the chest which causes chest to rise and expand
(inspiration).
 Indicated for intermittent use, home care and patients with
neuromuscular pathologies.
Examples:
a. lron Lung (Body Tank).
b. Chest Cuirass
2. Positive Pressure Ventilators (lntrapulmonary Pressure)
 Creates a positive pressure that will push air into the patient's lungs and
increase intrapulmonary pressure

AIRWAY RESISTANCE
5
• Occurs as a result of the friction between the air molecules and the walls of
the tracheobronchial tree, and to some extent, as a result of the friction
between the air molecules themselves
• Poiseuille’s law states that the resistance (Raw) to the flow of fluids through a
long and narrow tube is:
►Proportional to the length of the tube (l) and the viscosity of the
fluid (η)
► Inversely proportional to the fourth power of the radius (r).
• This means small changes in the radius can have inordinate effects on airway
resistance

AIRWAY RESISTANCE
6
• Normal Raw ranges from 0.6 to 2.4 cm H2O/L/s. With an endotracheal tube in situ
• The driving pressure across a tube in ventilated patient is a function of the difference
between the pressures at its ends
• In a patient who is not being given positive pressure breaths is dependent upon the
difference between the atmospheric pressure (Patm) and the alveolar pressure (PALV)
(Raw) in a Spontaneous breathing
Patient

AIRWAY RESISTANCE
7
Clinical conditions that increase airway resistance are:

AIRWAY RESISTANCE
8
• The airflow resistance of a patient-ventilator system may be monitored using the pressure-
volume (P-V) loop
• An increased bowing of the P-V
loop suggests an overall increase
in airflow resistance
• When the inspiratory flow exceeds
a patient’s tidal volume and
inspiratory time requirement,
bowing of the inspiratory limb may
result (line A2)
• When the expiratory airflow resistance is increased (e.g., bronchospasm), bowing of the
expiratory limb (line B2) may occur

LUNG COMPLIANCE
9
• Measure of distensibility of Lung and calculated by:
If a large change in volume is achieved by applying a relatively small
amount of airway pressure, the lung is easily distensible and is said to be
highly compliant
• A stiff and poorly compliant lung resists expansion and only a small
change in volume occurs with a relatively large change in pressure
• Compliance has two components
A) static B) Dynamic
C = ∆V/∆P

STATIC LUNG COMPLIANCE
10
• Static compliance is the true measure of distensibility of the respiratory
system (lung + chest wall)
• Static compliance can be measured on the ventilator as follows:
where
Vt = Tidal Volume
Ppl = Plateau pressure
PEEP = Positive end-expiratory pressure
• Measured when the flow is momentarily stopped
Cstat = Vt
(Ppl – PEEP)

STATIC LUNG COMPLIANCE
11
• In mechanically ventilated patient with an essentially normal chest wall
and lungs, the static compliance of the respiratory system is usually in the
range of 70–100 mL/cm H2O

DYNAMIC LUNG COMPLIANCE
12
• It is measured while air is still flowing through the bronchial tree
• It reflects not only the lung and chest wall stiffness, but also the airway resistance, against which
distending forces have to act
• It measure of both static compliance and airflow resistance and can be regarded as a measure of
impedance
• Dynamic compliance falls when either lung stiffness or airway resistance increases
• Dynamic compliance can be measured as:
Vt = tidal volume,
P Pk = peak airway pressure,
PEEP = positive end-expiratory pressure.
Cdyn = Vt
(Ppk – PEEP)

LUNG COMPLIANCE
14
• Static and dynamic compliance in various lung conditions

Alveolar Ventilation & Dead-Space
• The total surface area of the alveolar epithelium is about 72–80 m2
• Approximately 85–95% (about 70 m2) of this is in contact with pulmonary
capillaries: this constitutes the alveolocapillary interface
• The part of the inspired gas that does not come into contact with the
pulmonary capillary bed is termed the dead-space
• Dead space can be: 1)Anatomical
2)Alveolar
3) Physiological

• Minute ventilation is the product of
the tidal volume times the respiratory
rate
• It is inversely proportional to the
PaCO2.
• It also affects the PaO2 in a nonlinear
fashion; however, manipulating the
minute volume for the change in PaO2
is undesirable, as only
• small changes in PaO2 can be brought
about by large alterations in minute
ventilation.
• Such large changes in minute
ventilation can have a profound and
unwanted effect on PaCO2.

EXAMPLE:
• A set tidal volume of 500 mL and a RR of 10 breaths/min results in a minute ventilation of 500
× 10 = 5,000 mL/min
• The same minute ventilation can be produced by a tidal volume of 250 mL delivered at a RR of 20
breaths/min 250 × 20 = 5,000 mL/min
• When dead-space 150ML is taken the alveolar ventilation
In the first example would be (500 – 150) × 10 = 3,500,
In the second example would be (250 – 150) × 20 = 2,000
• The alveolar ventilation in the first instance would vastly exceed the alveolar ventilation in the second
example
• The PaCO2 is inversely proportional not to all of the minute ventilation, but to that part of the ventilation
that is independent of dead-space

Peak Inspiratory Pressure (Ppeak)
• During a ventilator-driven tidal breath, the
airway pressure rises rapidly to a peak which is
called as Peak Inspiratory Pressure
• It is influenced both by airway resistance and
compliance
• It can be high either on account of narrowed
airways or stiff lung
• It is used to deliver the tidal volume by
overcoming non-elastic (airways) and elastic(lung
parenchyma) resistance

Plateau Pressure (Pplateau)
• At the end of inspiration, the airway
pressure falls to a plateau as the air
diffuses out to the periphery of
tracheobronchial tree
• This pressure within the airway during
no airflow period is called the pause
pressure or the plateau pressure
• It is a reflection of the static compliance
• Any condition that stiffens the lung will
increase the pause pressure.

POSITIVE END-EXPIRATORY
PRESSURE (PEEP)
• PEEP is alveolar pressure above atmospheric pressure that exist at the end of
expiration
• Types of PEEP:
A)Extrinsic PEEP
►PEEP provided by mechanical ventilator
B)Intrinsic PEEP
• Secondary to incomplete expiration
• Also known as auto PEEP

Baseline Pressure PEEP/CPAP
• Physiological effects of positive end-expiratory pressure (PEEP)

Mean Airway Pressure(Pmean)
►Average pressure within the airway over the entire respiratory cycle
►Is significantly affected by:
 PEEP
 Inspiratory time (TI)
►Is affected to a lesser degree by:
 Peak pressure
►Has significant affect on oxygenation

• Pressure, volume and flow relationship is described by equation of motion
for the respiratory system. (stems from Newton’s third law of motion)
PTR = PE+PR
PTR Transrespiratory pressure(P at the airway opening minus pressure at
the body surface)
PE pressure caused by elastic resistance,
PR Resistance due to airflow
29
Physics

Volume
Compliance
A (PAW)
Flow x resistance +
Physics
PEEP
Compliance
Volume
Resistance
Flow
(Paw)
pressure
Airway 



Only possible to set one of:
Pressure
Flow
Volume
Other variables become a dependent variable
+PEEP

Indications
1) Can not oxygenate (low PaO2/SpO2)- Hypoxemic respiratory failure
2) Can not ventilate (high PCO2)- Hypercarbic Respiratory failure
3) Both
4) Can not protect airway/ secure airway( Low GCS)
5) When clinician/ physician confused, either patient need or not,
needs mechanical ventilation
6) Elective ventilation for GA
5/28/2021
Hospital
31

Goals/Principles of mechanical Ventilation
1) To provide adequate ventilation and oxygenation
2) To achieve adequate lung volume and recruitment
3) To improve lung compliance
4) To reduce work of breathing
5) To limit lung injury
5/28/2021
Hospital
32

Assessment for MV
We should know
1)History and physical examination
2) Laboratory and radiological finding of patient
3) Anatomical size and structure of airway and lungs
4) Disease severity
5/28/2021
Hospital
33

Classification
Both on inferior airway invasion
1) Non- invasive : No inferior airway invasion
2) Invasive: Invasion by endotracheal tube
Based on modes
1) Controlled Mechanical Ventilation: PCV, VCV, PRVC, HFV, CMV, IMV
2) Supported spontaneous breathing: PSV, VSV
3)Mixed Respiratory Support: SIMV/ or +PS
4) Assisted spontaneous breathing: CPAP, APRV
5/28/2021
Hospital
34

VCV
Volume is independent variable
Pressure varies with compliance of lung
Expiration is passive not affected by ventilator mode, rather affected
by compliance and resistance
Not a weaning mode
Peak airway Pressure= R*F+ Vt/compliance+ PEEP
Plateau Pressure= Vt/compliance+ PEEP
5/28/2021
Hospital
35

VCV
What do we set??
Vt and RR for Minute Ventilation For PaCO2 Management
PEEP and FiO2 For Pao2 Management
Flow/ I:E ratio- for both
5/28/2021
Hospital
36

PCV
Pressure is independent variable
Volume is dependent variable Depends on: level of pressure, I-time
also it is the function of compliance and airway resistance. That’s why
volume deliver can vary breath to breath.
Ventilator adjust flow to maintain pressure.
Flow decreases throughout the inspiratory cycle.
Good mode to use if patient has large air leak, the ventilator will
increase the flow to compensate it.
Not a weaning mode
5/28/2021
Hospital
37

PCV
What do we set??
Pressure limit, T-Insp, RR,FIO2,PEEP
P and RR for Minute ventilation PaCO2 management
FiO2 and PEEP for PaO2 management
5/28/2021
Hospital
38

VCV and PCV
5/28/2021
Hospital
39

Pressure Support=PS
Supports each spontaneous breath with supplemental flow to
achieve preset pressure
All breath are triggered by patient
Preset value  PIP, PEEP, FiO2
Patient determine Rate, Ti, I/E ratio, TV
5/28/2021
Hospital
40

PS
Needs intact respiratory drive
Helps to overcome airway resistance/ tube resistance, so that
spontaneous breathing will be easier
Can not be use in patient not having spontaneous breathing(i.e.
muscle relaxant)
5/28/2021
Hospital
41

SIMV= Synchronized intermittent mandatory
ventilation
Preset mechanical breath delivered within interval acc to preset and
wait for spontaneous in between, which it will use as a trigger to
deliver full breath.
If not sensed it will automatically give a breath
Vt on spontaneous breaths depends entirely upon the patient effort
and lung mechanics, can be pressure or volume controlled.
5/28/2021
Hospital
42

SIMV
Tb(time for breathing) = Tm(mandatory)+Ts(spontaneous)
If patient tries to breath during Tm, ventilator gives a fully assisted
breath
If Patient tries to breath during Ts, the ventilator will allow the
patient to take breath
5/28/2021
Hospital
43

5/28/2021
Hospital
44

5/28/2021
Hospital
45

5/28/2021
Hospital
46

SIMV+PS
SIMV+PS= provides assistance for spontaneous breath to overcome tube resistance
5/28/2021
Hospital
47

CPAP
Provides continuous positive pressure throughout the respiratory
cycle
So gives supports to inspiration and resistance to expiration
Can be use both in invasive and non-invasive form.
Very similar to PEEP
5/28/2021
Hospital
48

PEEP
PEEP is a residual pressure above atmospheric pressure maintained
at the end of expiration.
PEEP can be added to any mode
PEEP helps to recruit alveoli, increase FRC , Redistribute pulmonary
edema, Decrease intrapulmonary shunt, Increase PaO2.(GOOD)
PEEP , decreases venous return/CO, increase ICP/intensify cerebral
ischemia/ risk of barotrauma(Bad)
5/28/2021
Hospital
49

CPAP
5/28/2021 Dadeldhura Hospital Dadeldhura 50

CPAP

BiPAP

CPAP Vs BiPAP

IPAP/EPAP

NASAL CPAP FOR NEONATE/INFANT
Nasal prong/Nasopharyngral tube/ET tube can be use for nasal cpap
5/28/2021
Hospital
69

Indication
Disease condition;
1)Retained lung fluid
2)Post-extubation (if risk of airway collapse)
3)Atelectasis
4)Respiratory distress syndrome
5) For administration of controlled concentration of nitric oxide
5/28/2021
Hospital
70

CONTD
Physical findings:
1)Increase WOB ,indicated by increase RR by 30-40%
2)Sub-sternal/suprasternal retraction
3)Grunting and nasal flaring
4)Pale or cyanotic skin color
5)Agitation
5/28/2021
Hospital
71

Contraindication/ Should 'Not Try
C/I:
Choanal atresia
Untreated diaphragmatic hernia
Cleft palate
TEF
Should 'not try:
Cardiovascular instability
Severe ventilatory impairment
Severe hypoxemia
Frequent apnea
High level of sedation
5/28/2021
Hospital
72

How it Helps??
Reduces grunting and tachypnea
Increases FRC and PaO2
Decreases intrapulmonary shunting
Improves lung compliance
Aids in stabilization of floppy infant chest wall
5/28/2021
Hospital
73

CONTD
Improves distribution of ventilation
Reduce WOB
Reduces central and obstructive sleep apnea by mechanically
splinting the upper airway.
Better recruitment and oxygenation
Stimulation of infant/neonate for breathing
5/28/2021
Hospital
74

Mechanical Ventilation:
Part-II(Troubleshooting and Weaning)
Presenter:
Dr.Tirtha Raj Bhandari
Anesthesiologist
Dadeldhura Hospital,dadeldhura
5/28/2021
Hospital
75

Troubleshooting and Weaning
5/28/2021
Hospital
76

Common Troubleshooting
1) Ventilator alarms
2) Hypoxia(Desaturation)
3) Hypotension
4) Patient ventilator dysynchrony
77

Assessment
• Is the chest moving and is it moving symmetrically?
• Is the patient cyanosed?
• What is the arterial saturation?
• Is the patient haemo-dynamically stable?
-Do not forget to observe respiratory pattern and feature of respiratory
distress
78

High Airway Pressure
Why does this matter??
-Risk of barotrauma
-Hypoventilation(premature termination by high airway pressure)
79

Causes of high airway pressure;
80

CONTD
• Ventilator malfunction/setting
• circuits problems
• Endotracheal tube obstruction
• Increase airway resistance
• Decrease compliance of lung
81

Dynamic Compliance Static compliance(lung)
Bronchospasm Obesity
Kinking of tubes Atelectasis, ARDS
Airway obstruction(mucus, secretions) Pneumothorax
Retained secretion
82

Static Compliance Both PIP and PLAT
84

Low Airway Pressure/volume
Why it is important??
-Risk of hypoventilation hypoxia and hypercarbia(Lactic and
respiratory acidosis)  Deasaturation Bradycardia Cardiac Arrest
85

Causes of Auto-peep formation
• Inadequate time for expiration, either by flow limitation or
development of resistance in airway or endotracheal tube
• More time for inspiration
• Obstructive airway disease
• High minute ventilation( High Tidal Volume, High Frequency)
• Dysynchrony
88

Pathophysiological Consequences of air
trapping
• Air-trappingDynamic hyperinflation Autopeep
leads following consequences,
1) Increase intra-thoracic pressure
2) Increase work of breathing
3) Decrease preload  Hypotension
4) Worsened V/Q mismatch
5) Increase risk of barotrauma
89

Management of Auto-PEEP
• Depends upon cause
-decrease MV
-allow sufficient time for expiration
-bronchodilator
-use higher size tube
-remove obstruction in airway
-increase sedation
93

Desaturation(Hypoxia)
• Ventilatory Malfunction
• ET tube disconnection(circuit malfunction), cuff leak
• Oxygen failure
• Any causes of hypoxic respiratory failure
• Special consideration: endobronchial intubation,
pneumothorax, collapse of part of lung, pulmonary
edema, bronchospasm and pulmonary embolism
94

Management
• Increase Fio2 to 1.0
• Check whether the chest is moving or not
• Briefly examine chest to determine the cause of desaturation
• If cause is not obvious manually ventilate the patient with
100% oxygen to exclude ventilator malfunction as the cause
• Treat underlying cause
• Alter ventilator settings to improve oxygenation
• Chest x-ray
95

Hypotension
Immediately after the initiation of mechanical ventilation
hypotension can occur:
Causes:
• Relative Hypovolaemia: reduction in venous return exacerbated
by positive intra-thoracic pressure.
• Drug induced vasodilation and myocardial depression: all
induction agents have some short lived vaso-dilatory myocardial
depressant effects.
• Tension pneumothorax
• Gas trapping ( dyanamic hyperinflation)
Delayed cause may be due to pathological process going on in
patient’s body.
98

Management
• Depends upon causes
-fluid therapy
-decrease positive pressure/peep
-treat air trapping
-chest tube(if pneumothorax)
99

Dysynchrony
According to its relationship to specific phases of the delivered breath:
• breath initiation/trigger,
• flow delivery and
• breath cycling/termination.
*Asynchrony/dysynchrony index
101

Ineffective trigger
Causes: improper setting of sensitivity, weak patient
effort, auto-peep 103

Auto-trigger
Causes: low trigger sensitivity, circuit leak, water in the circuit, cardiac oscillation. 104

Double trigger
Causes: unusually high ventilatory demand, low PaO2/FiO2, longer/too short inspiratory time of patient
105

Flow Dysynchrony
Causes: High respiratory drive, insufficient flow setting 106

Premature cycling
Causes: Increase neural inspiratory time, earlier termination of inspiration by ventilator
107

Management
• Select the appropriate mode
• Proper trigger setting
• Adjust adequate flow
• Adjust proper cycling
• Clear airway
• Treat auto-peep
• Sedation
• Neuromuscular blockade
109

WEANING
• Weaning is the process of withdrawing mechanical
ventilatory support and transferring the work of
breathing from the ventilator to the patient.
• In most cases, weaning may be accomplished rapidly
from full ventilator support to unassisted spontaneous
breathing.
110

Formula
• RSBI= RR(f)/Tidal Volume(L)
• P/F ratio: PO2/FiO2:,FiO2=1=100%
5/28/2021
Hospital
113

Formula
5/28/2021
Hospital
114

Formula
5/28/2021
Hospital
115

Weaning success
• Weaning success is defined as absence of ventilatory
support 48 hours following the extubation.
• The spontaneous breaths are unassisted by mechanical
ventilation,
• Supplemental oxygen, bronchodilators, pressure
support ventilation, or continuous positive airway
pressure may be used to support and maintain adequate
spontaneous ventilation and oxygenation.
117

Weaning In Progress
• Weaning in progress is an intermediate category (between weaning
success and weaning failure) for patients who are extubated but
continue to receive ventilatory support by noninvasive ventilation
(NIV)
118

Weaning Failure
• Weaning failure is defined as either the failure of
spontaneous breathing trial (SBT) or for reintubation
within 48 hours following extubation.
• Patients who fail the SBT often exhibit the following
clinical signs: tachypnea, tachycardia, hypertension,
hypotension, hypoxemia, acidosis, or arrhythmias.
• Physical signs of SBT failure may include agitation,
distress, diminished mental status, diaphoresis, and
increased work of breathing
119

CONTD
• Causes of failure are
1)Increase airway resistance
2)Decrease in compliance of lungs
3)Respiratory muscle fatigue
121

Spontaneous Breathing Trail
• The patient may be discontinued from full ventilatory support
and placed on a spontaneous breathing mode via the ventilator
or T-tube (Brigg’s adaptor) for up to 30 minutes.
• Oxygen and low level pressure support may be used to
supplement oxygenation and augment spontaneous breathing.
• The criteria for passing an SBT include normal respiratory pattern
(i.e., absence of rapid shallow breathing), adequate gas
exchange, and hemodynamic stability.
122

Rapid Shallow Breathing Index(RSBI)
124
<100=success of weaning
>100=failure of weaning

5/28/2021
Hospital
126

Basics of Mechanical Ventilation

More Related Content

What's hot

Similar to Basics of Mechanical Ventilation

More from Tirtha Raj Bhandari,MD

Recently uploaded

Basics of Mechanical Ventilation

Editor's Notes