Mechanical Ventilation Dr Rob Stephens [email protected] .
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Transcript of Mechanical Ventilation Dr Rob Stephens [email protected] .
Mechanical Ventilation
Dr Rob [email protected]
www.ucl.ac.uk/anaesthesia/people/stephens
the centre forAnaesthesia UCL
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?
• 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
Several ways to ..connect the machine to Pt is Airway
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 so reflexes
• Others eg – need neuro-muscular paralysis to allow surgery– want to reduce work of breathing – cardiovascular reasons
Anaesthesia Drugs
• Hypnosis = Unconsciousness– Gas eg Halothane, Sevoflurane– Intravenous eg Propofol, Thiopentone
• Analgesia = Pain Relief– Different types: ‘ladder’, systemic vs other
• Neuromuscular paralysis– Nicotinic Acetylcholine Receptor Antagonist
Neuromuscular Paralysis
Nicotinic AcetylCholine Channel
Non competitiveSuxamethonium
CompetitiveOthers eg Atracurium
Different propertiesDifferent length of actionParalyse Respiratory musclesApnoea – ie no breathingNeed to ‘Ventilate’
Review some basics
• 1 What’s 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
TLC
IRV
0RV
FRC
TV
ERV
VC
Normal breath inspiration animation, awake
Diaghram contracts
Chest volume
Pleural pressurePressure difference from lips to alveolusdrives air into lungs
ie air moves down pressure gradientto fill lungs
-2cm H20
-7cm H20
Alveolarpressure falls -2cm H20
Review 3: Normal breath
Lung @ FRC= balance
Normal breath expiration animation, awake
Diaghram relaxes
Pleural / Chest volume
Pleural pressure rises
Review 3: Normal breath
Alveolarpressure rises
Air moves down pressure gradientout of lungs
-7cm H20
+1-2cm H20
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
Ventilator breath inspiration animation
Air blown in
lung pressure Air moves down pressure gradientto fill lungs
Pleuralpressure
-2 cm H20
+5 to+10 cm H20
Ventilator breath expiration animationSimilar to spontaneous…ie passive
Ventilator stops blowing air in
Pressure gradientAlveolus-trachea
Air moves outDown gradient Lung volume
Details: IPPV
• Inspiration– Pressure or Volume?– Machine or Patient initiated?
’control or support’
– Fi02
– Tidal Volume / Respiratory Rate
• Expiration– PEEP? Or no PEEP (‘ZEEP’)
Details: Inspiration Pressure or Volume?
• Do you push in..– A gas at a set pressure? = ‘pressure…..’– A set volume of gas? = ‘volume….’
Time
Pre
ssur
e cm
H20
Time
Pre
ssur
e cm
H20Details: Inspiration
Pressure or Volume?
Time
Pre
ssur
e cm
H20
Time
Pre
ssur
e cm
H20
Details: Expiration
PEEP
PEEP
Positive End Expiratory Pressure
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
Details: Cardiovascular effects
IPPV + PEEP can create a shunt !
Details: Cardiovascular effects
Normal blood flow
Details: Cardiovascular effects
Blood flow: Lung airway pressures
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
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
Normal ventilating lungs
Details: compliance changes
Abormal ventilating lungs: Eg Left pneumothorax
Details: compliance changes
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
Effects of PEEP: whole lungV
olum
e
Pressure
Compliance=
Volume Pressure
energy needed to open alveoli
?damaged during open/closing
- abnormal forces
‘over-distended’ alveoli
Regional ventilation: PEEPV
olum
e
Pressure
Static Compliance=
Volume Pressure
Spontaneous, standing, healthy
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
Effects of PEEP: whole lungV
olum
e
Pressure
Compliance=
Volume Pressure
energy needed to open alveoli
?damaged during open/closing
- abnormal forces
‘over-distended’ alveoli
Effects of PEEP: whole lungV
olum
e
Pressure
Compliance=
Volume Pressure
Raised ‘PEEP’
PEEP: start inspiration from a higher pressure
↓?damage during open/closing
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)
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
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
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
Effects of induction in eg asthma
Effects of position- supine/obese
TLC
IRV
0RV
FRC
TV
ERV
VC
Closing Capacity
TLC
IRV
0RV
FRC
TV
ERV
VC
Closing Capacity
Effects of pathology eg PTx