Download Mechanical Ventilation

Mechanical Ventilation
Rob Stephens
the centre for
Anaesthesia
UCL
Contents
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•
•
•
Introduction: definition
Introduction: review some basics
Basics: Inspiration + expiration
Details
–
–
–
–
–
inspiration pressure/volume
expiration
Cardiovascular effects
Compliance changes
PEEP
• Some Practicalities
Definition: What is it?
• Mechanical Ventilation
=Machine to ventilate lungs = move air in (+ out)
– Several ways to..move air in (IPPV vs others)
Intermittent Positive Pressure Ventilation
Definition: What is it?
• Mechanical Ventilation
=Machine to ventilate lungs = move air in (+ out)
– Several ways to..move air in (IPPV vs others)
Intermittent Positive Pressure Ventilation
– Several ways to ..connect the ventilator to
the patient
Several ways to ..connect the
machine to Pt
• Oro-tracheal Intubation
• Tracheostomy
• Non-Invasive
Ventilation
Definition: What is it?
• Mechanical Ventilation
=Machine to ventilate lungs = move air in (+ out)
– Several ways to..move air in (IPPV vs others)
Intermittent Positive Pressure Ventilation
– Several ways to ..connect the machine to Pt
– Unnatural- not spontaneous
• consequences
Why do it?- indications
• Hypoxaemia: low blood O2
• Hypercarbia: high blood CO2
• Need to intubate eg patient unconscious
• Others eg
– need neuro-muscular paralysis to allow surgery
– want to reduce work of breathing
– cardiovascular reasons
Review some basics
• 1 Whats the point of ventilation?
• 2 Vitalograph, lets breathe
• 3 Normal pressures
Review 1
What’s the point of ventilation?
– Deliver O2 to alveoli
• Hb binds O2 (small amount dissolved)
• CVS transports to tissues to make ATP - do work
– Remove CO2 from pulmonary vessels
• from tissues - metabolism
Review 2: Vitalograph
IRV
VC
TLC
TV
FRC
ERV
RV
0
Review 3: Normal breath
Normal breath inspiration animation, awake
Lung @ FRC= balance
-2cm H20
Diaghram contracts
Chest volume
Pleural pressure
-7cm H20
Air moves down
pressure gradient
to fill lungs
Alveolar
pressure falls
Review 3: Normal breath
Normal breath expiration animation, awake
-7cm H20
Diaghram relaxes
Pleural /
Chest volume 
Pleural pressure
rises
-2cm H20
Air moves down
pressure gradient
out of lungs
Alveolar
pressure rises
The basics: Inspiration
Comparing with Spontaneous
• Air blown into lungs
– Different ways to do this
– Air flows down pressure gdt
– Lungs expand
– Compresses
– pleural cavity
– abdominal cavity
– pulmonary vessels
Ventilator breath inspiration animation
0 cm H20
 lung pressure
Air blown in
Air moves down
pressure gradient
to fill lungs
+5 to+10 cm H20
 Pleural
pressure
Ventilator breath expiration animation
Similar to spontaneous…ie passive
Ventilator stops
blowing air in
Air moves out
Down gradient
Pressure gradient
Alveolus-trachea
 Lung volume
Details: Inspiration
Pressure or Volume?
• Do you push in..
– A gas at a set pressure? = ‘pressure…..’
– A set volume of gas? = ‘volume….’
Details: Inspiration
Pressure cm H20
Pressure or Volume?
Pressure cm H20
Time
Time
Pressure cm H20
Details: Expiration
PEEP
Pressure cm H20
Time
Positive End Expiratory Pressure
PEEP
Time
Details: Cardiovascular effects
• Compresses Pulmonary vessels
• Reduced RV outflow
• Reduced LV inflow
Details: Cardiovascular effects
• Compresses Pulmonary vessels
• Reduced LV inflow
–  Cardiac Output: Stroke Volume
– Blood Pressure = CO x resistance –
 Blood Pressure
– Neurohormonal
• Reduced RV outflow- backtracks to body
– Head-  Intracranial Pressure
– Others -  venous pressure
Details: Cardiovascular effects
• Compresses Pulmonary vessels
• Inspiration + Expiration
– More pressure,  effects on cardiovascular
– If low blood volume
• vessels more compressible
•  effects
Details: compliance changes
• If you push in..
– A gas at a set pressure? = ‘pressure…..’
•
•
•
•
Tidal Volume  compliance
Compliance = Δ volume / Δ pressure
If compliance: ‘distensibility stretchiness’ changes
Tidal volume will change
– A set volume of gas? = ‘volume….’
• Pressure 1/ compliance
• If compliance: ‘distensibility stretchiness’ changes
• Airway pressure will change
Details: compliance changes
Normal ventilating lungs
Details: compliance changes
Abormal ventilating lungs:
Eg Left pneumothorax
Effects of PEEP
Normal, Awake
–
–
in expiration alveoli do not close (closing capacity)
change size
Lying down / Paralysis / +- pathology
–
–
–
Lungs smaller, compressed
Harder to distend, starting from a smaller volume
In expiration alveoli close (closing capacity)
PEEP
–
–
–
Keeps alveoli open in expiration
Danger: applied to all alveoli
Start at higher point on ‘compliance curve’
Effects of PEEP
‘over-distended’ alveoli
Compliance=
Volume
Volume
 Pressure
energy needed to open alveoli
?damaged during open/closing
Pressure
- abnormal forces
Effects of PEEP
Compliance=
Volume
Volume
 Pressure
PEEP: start inspiration from a higher
pressure
Pressure
Raised ‘PEEP’
↓?damage during open/closing
IRV
VC
TLC
TV
FRC
Closing
Capacity
ERV
RV
0
IRV
VC
TLC
TV
FRC
Closing
Capacity
ERV
RV
0
Regional ventilation: PEEP
Spontaneous, standing
‘over-distended’ alveoli
Compliance=
Volume
Volume
 Pressure
Pressure
Regional ventilation: PEEP
Mechanical Ventilation
Compliance=
Volume
Volume
 Pressure
Pressure
Practicalities
• Ventilation: which route?
• Intubation vs others
• Correct placement?
• Ventilator settings:
•
•
•
•
•
spontaneous vs ‘control’
Pressure vs volume
PEEP?
How much Oxygen to give (Fi02 )
Monitoring adequacy of ventilation (pCO2,pO2)
• Ventilation: drugs to make it possible
• Ventilation: drug side effects
• Other issues
Practicalities
• Ventilation: which route?
• Intubation vs others
• Correct placement?
• Ventilator settings:
•
•
•
•
•
spontaneous vs ‘control’
Pressure vs volume
PEEP?
How much Oxygen to give (Fi02 )
Monitoring adequacy of ventilation (pCO2,pO2)
• Ventilation: drugs to make it possible
• Ventilation: drug side effects
Other reading
• http://www.nda.ox.ac.uk/wfsa/html/u12/u12
11_01.htm
Practicalities in the Critically ill
• http://www.nda.ox.ac.uk/wfsa/html/u16/u16
09_01.htm
Effects of induction in eg asthma
Effects of position- supine/obese
Effects of pathology eg PTx