Mechanical Ventilation - PowerPoint - PowerPoint by Z406HEKi

VIEWS: 248 PAGES: 62

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




                 UCL
the centre for
 Anaesthesia
                       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 competitive
       Suxamethonium

Competitive
      Others eg Atracurium

Different properties
Different length of action
Paralyse Respiratory muscles
Apnoea – ie no breathing
Need 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
           IRV
                  VC




TV                           TLC




     FRC

                       ERV




                 RV
0
                        Review 3: Normal breath
            Normal breath inspiration animation, awake

 Lung @ FRC= balance
                                                         Diaghram contracts
                    -2cm H20



Chest volume


Pressure difference                                         Pleural pressure
from lips to alveolus
drives air into lungs
                                                              -7cm H20
ie air moves down
pressure gradient
to fill lungs                                                 Alveolar
                                                              pressure falls
                                                              -2cm H20
                     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
        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
                    -2 cm H20




 lung pressure                                            Air moves down
                                                           pressure gradient
                                                           to fill lungs




                                                              +5 to+10 cm H20
   Pleural
  pressure
                     Ventilator breath expiration animation
                     Similar to spontaneous…ie passive

  Ventilator stops
                                                          Pressure gradient
  blowing air in
                                                          Alveolus-trachea




Air moves out
Down 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….’
                         Details: Inspiration
                          Pressure or Volume?
Pressure cm H20




                  Time
Pressure cm H20




                  Time
                         Details: Expiration
Pressure cm H20




                                   PEEP
                  Time                Positive End Expiratory Pressure
Pressure cm H20




                                   PEEP
                  Time
    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
Details: compliance changes
                  Normal ventilating lungs
Details: compliance changes
                   Abormal ventilating lungs:
                   Eg Left pneumothorax
      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 lung
         ‘over-distended’ alveoli
                                                  Compliance=

                                                  Volume
                                                   Pressure
Volume




                                    energy needed to open alveoli
                                    ?damaged during open/closing
                 Pressure
                                        - abnormal forces
    Regional ventilation: PEEP
         Spontaneous, standing, healthy

                                          Static Compliance=

                                          Volume
                                           Pressure
Volume




                Pressure
     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 lung
         ‘over-distended’ alveoli
                                                  Compliance=

                                                  Volume
                                                   Pressure
Volume




                                    energy needed to open alveoli
                                    ?damaged during open/closing
                 Pressure
                                        - abnormal forces
Effects of PEEP: whole lung
                                            Compliance=

                                            Volume
                                             Pressure
Volume




                             PEEP: start inspiration from a higher
                             pressure
         Pressure            ↓?damage during open/closing

             Raised ‘PEEP’
                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/u1
  211_01.htm

Practicalities in the Critically ill
• http://www.nda.ox.ac.uk/wfsa/html/u16/u1
  609_01.htm
Effects of induction in eg asthma
Effects of position- supine/obese
           IRV
                            VC




TV                                     TLC




     FRC         Closing
                 Capacity
                                 ERV




                        RV
0
           IRV
                        VC




TV                                 TLC




     FRC         Closing
                 Capacity
                             ERV




                      RV
0
Effects of pathology eg PTx

								
To top