Mechanical Ventilation Dr Rob Stephens robcmstephens@googlemail.com www.ucl.ac.uk/anaesthesia/people/stephens

  • View
    212

  • Download
    0

Embed Size (px)

Text of Mechanical Ventilation Dr Rob Stephens robcmstephens@googlemail.com...

  • Slide 1
  • Mechanical Ventilation Dr Rob Stephens robcmstephens@googlemail.com www.ucl.ac.uk/anaesthesia/people/stephens
  • Slide 2
  • Contents Introduction: definition Introduction: review some basics Basics: Inspiration + expiration Details inspiration pressure/volume expiration Cardiovascular effects Compliance changes PEEP Some Practicalities
  • Slide 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
  • Slide 4
  • Slide 5
  • Slide 6
  • Slide 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
  • Slide 8
  • Several ways to..connect the machine to Pt Oro-tracheal Intubation Tracheostomy Non-Invasive Ventilation
  • Slide 9
  • Several ways to..connect the machine to Pt is Airway
  • Slide 10
  • Slide 11
  • Slide 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
  • Slide 13
  • Why do it?- indications Hypoxaemia: low blood O 2 Hypercarbia: high blood CO 2 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
  • Slide 14
  • 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
  • Slide 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
  • Slide 16
  • Slide 17
  • Review some basics 1 Whats the point of ventilation? 2 Vitalograph, lets breathe 3 Normal pressures
  • Slide 18
  • Review 1 Whats the point of ventilation? Deliver O 2 to alveoli Hb binds O 2 (small amount dissolved) CVS transports to tissues to make ATP - do work Remove CO 2 from pulmonary vessels from tissues metabolism
  • Slide 19
  • Review 2: Vitalograph
  • Slide 20
  • TLC IRV 0 RV FRC TV ERV VC
  • Slide 21
  • Normal breath inspiration animation, awake Diaghram contracts Chest volume Pleural pressure Pressure difference from lips to alveolus drives air into lungs ie air moves down pressure gradient to fill lungs -2cm H 2 0 -7cm H 2 0 Alveolar pressure falls -2cm H 2 0 Review 3: Normal breath Lung @ FRC= balance
  • Slide 22
  • Normal breath expiration animation, awake Diaghram relaxes Pleural / Chest volume Pleural pressure rises Review 3: Normal breath Alveolar pressure rises Air moves down pressure gradient out of lungs -7cm H20 +1-2cm H 2 0
  • Slide 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
  • Slide 24
  • Ventilator breath inspiration animation Air blown in lung pressure Air moves down pressure gradient to fill lungs Pleural pressure -2 cm H 2 0 +5 to+10 cm H 2 0
  • Slide 25
  • Ventilator breath expiration animation Similar to spontaneousie passive Ventilator stops blowing air in Pressure gradient Alveolus-trachea Air moves out Down gradient Lung volume
  • Slide 26
  • Details: IPPV Inspiration Pressure or Volume? Machine or Patient initiated? control or support Fi0 2 Tidal Volume / Respiratory Rate Expiration PEEP? Or no PEEP (ZEEP)
  • Slide 27
  • Details: Inspiration Pressure or Volume? Do you push in.. A gas at a set pressure? = pressure.. A set volume of gas? = volume.
  • Slide 28
  • TimePressure cm H 2 0 TimePressure cm H 2 0 Details: Inspiration Pressure or Volume?
  • Slide 29
  • TimePressure cm H 2 0 TimePressure cm H 2 0 Details: Expiration PEEP Positive End Expiratory Pressure
  • Slide 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
  • Slide 31
  • Details: Cardiovascular effects IPPV + PEEP can create a shunt !
  • Slide 32
  • Details: Cardiovascular effects Normal blood flow
  • Slide 33
  • Details: Cardiovascular effects Blood flow: Lung airway pressures
  • Slide 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
  • Slide 35
  • Details: Cardiovascular effects Compresses Pulmonary vessels Inspiration + Expiration More pressure, effects on cardiovascular If low blood volume vessels more compressible effects
  • Slide 36
  • Details: compliance changes If you push in.. A gas at a set pressure? = pressure.. Tidal Volume compliance Compliance = volume / 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
  • Slide 37
  • Normal ventilating lungs Details: compliance changes
  • Slide 38
  • Abormal ventilating lungs: Eg Left pneumothorax Details: compliance changes
  • Slide 39
  • Slide 40
  • Slide 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
  • Slide 42
  • Effects of PEEP: whole lung Volume Pressure Compliance= Volume Pressure energy needed to open alveoli ?damaged during open/closing - abnormal forces over-distended alveoli
  • Slide 43
  • Regional ventilation: PEEP Volume Pressure Static Compliance= Volume Pressure Spontaneous, standing, healthy
  • Slide 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
  • Slide 45
  • Effects of PEEP: whole lung Volume Pressure Compliance= Volume Pressure energy needed to open alveoli ?damaged during open/closing - abnormal forces over-distended alveoli
  • Slide 46
  • Effects of PEEP: whole lung Volume Pressure Compliance= Volume Pressure Raised PEEP PEEP: start inspiration from a higher pressure ?damage during open/closing
  • Slide 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)
  • Slide 48
  • Practicalities Ventilation: which route? Intubation vs others Correct placement? Ventilator settings: spontaneous vs control Pressure vs volume PEEP? How much Oxygen to give (Fi0 2 ) Monitoring adequacy of ventilation (pCO 2, pO 2 ) Ventilation: drugs to make it possible Ventilation: drug side effects Other issues
  • Slide 49
  • Slide 50
  • Practicalities Ventilation: which route? Intubation vs others Correct placement? Ventilator settings: spontaneous vs control Pressure vs volume PEEP? How much Oxygen to give (Fi0 2 ) Monitoring adequacy of ventilation (pCO 2, pO 2 ) Ventilation: drugs to make it possible Ventilation: drug side effects
  • Slide 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
  • Slide 52
  • Slide 53
  • Other reading http://www.nda.ox.ac.uk/wfsa/html/u12/u1 211_01.htm Practicalities in the Critically ill http://www.nda.ox.ac.uk/wfsa/html/u16/u1 609_01.htm
  • Slide 54
  • Slide 55
  • Slide 56