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Mechanical Ventilation. Rob Stephens. Contents. 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?.

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contents
Contents
  • 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
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 it5
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
Several ways to ..connect the machine to Pt
  • Oro-tracheal Intubation
  • Tracheostomy
  • Non-Invasive

Ventilation

definition what is it7
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
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
Review some basics
  • 1 Whats the point of ventilation?
  • 2 Vitalograph, lets breathe
  • 3 Normal pressures
review 1
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
slide12

IRV

VC

TLC

TV

FRC

ERV

RV

0

slide13

Review 3: Normal breath

Normal breath inspiration animation, awake

Lung @ FRC= balance

Diaghram contracts

-2cm H20

Chest volume

Pleural pressure

-7cm H20

Alveolar

pressure falls

Air moves down

pressure gradient

to fill lungs

slide14

Review 3: Normal breath

Normal breath expiration animation, awake

-7cm H20

Diaghram relaxes

Pleural /

Chest volume 

Pleural pressure

rises

-2cm H20

Alveolar

pressure rises

Air moves down

pressure gradient

out of lungs

the basics inspiration
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
slide16

Ventilator breath inspiration animation

Air blown in

0 cm H20

 lung pressure

Air moves down

pressure gradient

to fill lungs

+5 to+10 cm H20

 Pleural

pressure

slide17

Ventilator breath expiration animation

Similar to spontaneous…ie passive

Ventilator stops

blowing air in

Pressure gradient

Alveolus-trachea

Air moves out

Down gradient

 Lung volume

details inspiration pressure or volume
Details: Inspiration Pressure or Volume?
  • Do you push in..
    • A gas at a set pressure? = ‘pressure…..’
    • A set volume of gas? = ‘volume….’
slide19

Details: Inspiration Pressure or Volume?

Pressure cm H20

Time

Pressure cm H20

Time

slide20

Details: Expiration

Pressure cm H20

PEEP

Time

Positive End Expiratory Pressure

Pressure cm H20

PEEP

Time

details cardiovascular effects
Details: Cardiovascular effects
  • Compresses Pulmonary vessels
  • Reduced RV outflow
  • Reduced LV inflow
details cardiovascular effects25
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 effects26
Details: Cardiovascular effects
  • Compresses Pulmonary vessels
  • Inspiration + Expiration
    • More pressure,  effects on cardiovascular
    • If low blood volume
      • vessels more compressible
      •  effects
details compliance changes
Details: compliance changes
  • If you push in..
    • A gas at a set pressure? = ‘pressure…..’
      • Tidal Volume  compliance
      • Compliance = Δvolume / Δpressure
      • 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
slide28

Details: compliance changes

Normal ventilating lungs

slide29

Details: compliance changes

Abormal ventilating lungs:

Eg Left pneumothorax

effects of peep
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 peep33
Effects of PEEP

‘over-distended’ alveoli

Compliance=

Volume

 Pressure

Volume

  • energy needed to open alveoli
  • ?damaged during open/closing
    • - abnormal forces

Pressure

effects of peep34
Effects of PEEP

Compliance=

Volume

 Pressure

Volume

PEEP: start inspiration from a higher pressure

↓?damage during open/closing

Pressure

Raised ‘PEEP’

slide35

IRV

VC

TLC

TV

FRC

Closing

Capacity

ERV

RV

0

slide36

IRV

VC

TLC

TV

FRC

Closing

Capacity

ERV

RV

0

regional ventilation peep
Regional ventilation: PEEP

Spontaneous, standing

‘over-distended’ alveoli

Compliance=

Volume

 Pressure

Volume

Pressure

regional ventilation peep38
Regional ventilation: PEEP

Mechanical Ventilation

Compliance=

Volume

 Pressure

Volume

Pressure

practicalities
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
practicalities41
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
Other reading
  • http://www.nda.ox.ac.uk/wfsa/html/u12/u1211_01.htm

Practicalities in the Critically ill

  • http://www.nda.ox.ac.uk/wfsa/html/u16/u1609_01.htm