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

12. 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

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

14. 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

15. 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’

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

18. 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

19. Review 2: Vitalograph

20. IRV VC
TLC TV
FRC
ERV RV

21. Review 3: Normal breath Normal breath inspiration animation, awake
FRC= balance
Diaghram contracts
-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
-7cm H20
Alveolar
pressure falls
-2cm H20

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

23. The basics: Inspiration
Comparing with spontaneous
Air blown into lungs
2 different ways to do this (pressure / volume)
Air flows down pressure gdt
Lungs expand
Compresses
pleural cavity
abdominal cavity
pulmonary vessels

24. 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

25. 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

26. Details: IPPV Inspiration Expiration Pressure or Volume?
Machine or Patient initiated?
’control or support’
Fi02
Tidal Volume / Respiratory Rate
Expiration
PEEP? Or no PEEP (‘ZEEP’)

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

28. Details: Inspiration Pressure or Volume?
Pressure cm H20
Time
Pressure cm H20
Time

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

30. Details: Cardiovascular effects
Compresses Pulmonary vessels
Reduced RV inflow
Reduced RV outflow
Reduced LV inflow
Think of R vs L heart pressures
RV 28/5
LV 120/70

31. Details: Cardiovascular effects
IPPV + PEEP can create a shunt !

32. Details: Cardiovascular effects
Normal blood flow

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

34. 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

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

36. 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

37. Details: compliance changes
Normal ventilating lungs

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

41. 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

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

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

44. Regional ventilation; PEEP
Lying down, age, general anaesthesia
Lungs smaller, compressed
Pushes everything ‘down’ compliance curve
PEEP pushes things back up again
Best PEEP = best average improvement

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

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

47. 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)

48. 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

50. 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

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

53. Other reading http://www.nda.ox.ac.uk/wfsa/html/u12/u1211_01.htm
Practicalities in the Critically ill

58. Effects of induction in eg asthma

59. Effects of position- supine/obese

60. IRV VC
TLC TV
FRC
Closing
Capacity
ERV RV

61. IRV VC
TLC TV
FRC
Closing
Capacity
ERV RV

62. Effects of pathology eg PTx