1. Mechanical Ventilation
Dr Rob Stephens

2. Contents Introduction: definition Introduction: review some basics
Basics: Inspiration + expiration
Details
inspiration pressure/volume
expiration
Cardiovascular effects
Compliance changes
PEEP
Some Practicalities

3. 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

7. 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

8. Several ways to ..connect the machine to Pt
Oro-tracheal Intubation
Tracheostomy
Non-Invasive
Ventilation

9. Several ways to ..connect the machine to Pt is Airway

11. 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
of drugs needed to tolerate it
of IPPV itself
route for infection
of airway insertion (teeth damage / bleeding etc

12. Why do it?- indications Hypoxaemia: low blood O2
Hypercarbia: high blood CO2
Need to intubate eg patient unconscious so cough reflexes -so may aspirate to lungs
Others eg
need neuro-muscular paralysis to allow surgery
want to reduce work of breathing
cardiovascular reasons

13. Anaesthesia Drugs Hypnosis = Unconsciousness Analgesia = Pain Relief
Gas eg Halothane, Sevoflurane
Intravenous eg Propofol, Thiopentone
Analgesia = Pain Relief
Different types: ‘ladder’, systemic vs other
Neuromuscular paralysis
Nicotinic Acetylcholine Receptor Antagonist
to relax vocal cords

14. Neuromuscular Paralysis Nicotinic AcetylCholine Channel
Non competitive
Suxamethonium
Competitive
Others eg Atracurium
Different properties
Different length of action
Paralyse Respiratory muscles
Apnoea – ie no breathing
Need to ‘Ventilate’

16. Review some basics 1 What’s the point of ventilation?
2 Vitalograph, lets breathe
3 Normal pressures

17. 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

18. Review 2: Vitalograph

19. IRV VC
TLC TV
FRC
ERV RV

20. Review 3: Normal breath Normal breath inspiration animation, awake
FRC= balance
Diaghram contracts
At FRC/rest -2cm H20
Chest volume
Pressure difference from lips to alveolus
drives air into lungs
ie air moves down
pressure gradient
to fill lungs
Pleural pressure
After inspiration
-5-7cm H20
Alveolar
pressure falls
2 -4 cm H20
during inspiration

21. Review 3: Normal breath Normal breath expiration animation, awake
Starts at -5-7cm H20
Diaghram relaxes
Pleural /
Chest volume 
Pleural pressure
rises
End at-1-2cm H20
Alveolar
pressure rises
Air moves down
pressure gradient
out of lungs

22. The basics: Inspiration
Comparing with spontaneous
IPPV: Air blown into lungs via airway
2 different ways to do this
Set a pressure / or set a volume
Air flows down pressure gdt
Lungs expand
Compresses
pleural cavity (inside chest)
abdominal cavity
pulmonary vessels

23. IPPV: Ventilator breath inspiration animation
Air blown in
-2 cm H20
 lung pressure
Air moves down
pressure gradient
to fill lungs
+5 to+10 cm H20
 Pleural
pressure

24. IPPV: 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

25. Details: IPPV Intermittant Positive Pressure Ventilation
Inspiration
Pressure or Volume?
Machine or Patient initiated?
’control’ = machine or ‘support’ = patient
Fi02 %
How much tidal Volume / Respiratory Rate?
Expiration - passive
PEEP? Or no PEEP (‘ZEEP’)

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

27. Details: Inspiration Pressure or Volume?
Pressure cm H20
Pressure Controlled
Time
Volume Controlled
Pressure cm H20
Time

28. Details: Expiration Pressure cm H20 PEEP Time
Positive End Expiratory Pressure
Pressure cm H20
PEEP
Time

29. Details: Cardiovascular effects
Compresses Pulmonary vessels
Reduced RV inflow
Reduced RV outflow
Reduced LV inflow
Think of R vs L heart pressures
RV 28/5mmHg
LV 120/70mmHg
~10 cmH20 =~ 7 mmHg =~1KPa

30. Details: Cardiovascular effects
IPPV + PEEP can create deadspace !
ie reduce blood flow

31. Details: Cardiovascular effects
Normal blood flow

32. Details: Cardiovascular effects
Blood flow:  Lung airway pressures

33. Details: Cardiovascular effects
Compresses Pulmonary capilary vessels
Reduced LV inflow
 Cardiac Output: Stroke Volume
Blood Pressure = CO x resistance –
 Blood Pressure
Neurohormonal: Renin-angiotensin activated
Reduced RV outflow- backtracks to body
Reduced RA inflow
Head-  Intracranial Pressure
Others -  venous pressure eg liver
Strain: if RV poorly contracting

34. Details: Cardiovascular effects
Compresses Pulmonary vessels
Inspiration + Expiration
More pressure,  effects on cardiovascular
If low blood volume eg bleeding
vessels more compressible
 effects

35. 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
Airway pressure will change

36. Details: compliance changes
Normal ventilating lungs

37. Details: compliance changes
Abormal ventilating lungs:
Eg Left pneumothorax

40. Regional ventilation; PEEP
Normal, awake spontaneous
Ventilation increases as you go down lung
as ‘top’ ` (non-dependant) alveoli larger already
so their potential to increase size reduced
non-dependant alveoli start higher up
compliance curve

41. Effects of PEEP: whole lung
‘over-distended’ alveoli
Compliance=
Volume
 Pressure
Volume
energy needed to open alveoli
?damaged during open/closing
- abnormal forces
Pressure

42. Regional ventilation: PEEP
Spontaneous, standing, healthy
Static Compliance=
Volume
 Pressure
Volume
Pressure

43. Regional ventilation; PEEP
Lying down, age, general anaesthesia
Lungs smaller, compressed
Pushes everything ‘down’ compliance curve
PEEP pushes things back up again
Reduces the open/closeing of alveoli
By keeping them open/less damage
Best PEEP = best average improvement

44. Effects of PEEP: whole lung
‘over-distended’ alveoli
Compliance=
Volume
 Pressure
Volume
energy needed to open alveoli
?damaged during open/closing
- abnormal forces
Pressure

45. Effects of PEEP: whole lung
Compliance=
Volume
 Pressure
Volume
PEEP: start inspiration from a higher pressure
↓?damage during open/closing
Pressure
Raised ‘PEEP’

46. Effects of PEEP Normal, Awake
in expiration alveoli do not close (closing capacity)
change size
Lying down / GA/ 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 ie increases FRC
Danger: but applied to all alveoli
Start at higher point on ‘compliance curve’
CVS effects (Exaggerates IPPV effects)

47. Practicalities Ventilation: which route? Ventilator settings:
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

49. Practicalities Ventilation: which route? Ventilator settings:
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)
How much ventilation- Futier NEJM ;
Ventilation: drugs to make it possible
Ventilation: drug side effects

50. Clinical studies: How to ventilate
Surgery: 2013 NEJM Futier
Lower TV, PEEP, Recruitment is better
ICU: NEJM 2000 ARDSNet ‘ARMA’
Lower TV is better
ICU: NEJM 2004 ARDSNet ‘ALVEOLI’
Lower FiO2 & more PEEP is better

51. Summary IPPV: definition Usually needs anaesthesia- triad of drugs
Needs a tube to connect person to ventilator
Modes of ventilation
Pressures larger + positive ; IPPV vs spontaneous
CVS effects
PEEP opens aveoli, CVS effects

52. Stuff to know Why use IPPV/definition
Airway- connecting to the machine
Modes: inspiration Pressure/volume; control/support
Expiration: PEEP
Pressures in the cycle vs spontaneous
CVS effects IPPV vs spontaneous
General Anaesthesia – see previous lecture
Drugs- triad

53. Thank you
Any questions
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