Slide 1 - UCL by G86WSI

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									 Anaesthesia & Respiratory System


                Dr Rob Stephens
Consultant in Anaesthesia UCLH        Thanks to Dr Roger Cordery
Hon. Senior Lecturer UCL

www.ucl.ac.uk/anaesthesia/people/stephens
  Google UCL Stephens
  talk on webpage above & supporting material
  robcmstephens@googlemail.com
‘Lethal injection drug production
ends in the US’
                         Contents
• Anatomy + Physiology revision
• What is Anaesthesia?
• Anaesthesia effects…
   –   airway
   –   ‘respiratory depression’
   –   FRC
   –   Hypoxaemia
   –   after Anaesthesia
• Tips on the essay
               Introduction

• Why learn?- intellectually interesting
• Practical – understand – prevent problems
• Practical – find new solutions
             Anatomy revision
• Upper Airway above the vocal cords
• Lower airway – below the vocal cords
  – Conducting vs gas exchange-
• Muscles of respiration
                     Airway
• Airway is Lips to alveoli
• Upper Airway: lips to vocal Cords
                                               Pharynx
• Lower Airway: Vocal Cords down
  – Trachea
  – Conducting Airways
  – Respiratory Airways – gas exchange
  – pulmonary artery – capillaries – vein – heart
                   Lower Airway

• 23 divisions follow down                 1-16 conduction of air


     from L +R main bronchus
     bronchi through to terminal bronchi
     bronchioles
                                            17-23 gas exchange
     respiratory bronchioles
     alveolar ducts
     alveolar sacs or ‘alveoli’
                  Anatomy
• Alveolus in detail – pulmonary capillary


                           Bronchiole
     Alveolus
            Anatomy: Muscles
• External Intercostals   Inspiration
• Diaghram                Inspiration
• Internal Intercostals   Forced Expiration
• Accessory muscles       Forced Inspiration
      Neck
• Accessory muscles       Forced Expiration
      Abdomen
            Physiology revision
•   Spirometry- basic volumes
•   How we breathe spontaneously
•   Compliance / elastance
•   Deadspace and shunt
•   V / Q ratios
          Physiology: Spirometry
                                   ~6000ml



Inhale




At Rest                            ~2500ml




Exhale



                                       0 ml
            Physiology: Volumes
• Tidal Volume, TV
• Functional Residual Capacity, FRC
   Volume in lungs at end Expiration
   not a fixed volume - conditions change FRC
• Residual Volume, RV
      Volume at end of a forced expiration
• Closing Volume, CV
      Volume in expiration when alveolar closure ‘collapse’
       occurs
• Others
          Physiology: Closing Capacity
                                     ~6000ml



Inhale




At Rest                              ~2500ml


                                ~40+ supine
                                ~60+ standing
Exhale



                                          0 ml
            Physiology: Normal Spontaneous breath
              Normal breath inspiration animation, awake

  Lung @ FRC= balance
                                                           Diaghram contracts
                        -2cm H20



 Chest volume


                                                              Pleural pressure
Pressure difference
from lips to alveolus
drives air into lungs                                           -5cm H20

ie air moves down
pressure gradient                                                Alveolar
to fill lungs                                                    pressure falls
                                                                 -2cm H20
          Physiology: Normal Spontaneous breath
            Normal breath expiration animation, awake


                       -5cm H20
   Diaghram relaxes

                                                        Pleural /
                                                        Chest volume 

  Pleural pressure
  rises
           +1cm H20                                     Alveolar
                                                        pressure rises
                                                        to +1cm H20
Air moves down
pressure gradient
out of lungs
        Physiology: Compliance & Elastance
Compliance = the volume Δ for a given pressure Δ
  A measure of ease of expansion
  ΔV / ΔP
  Normally ~ 200ml / 1 cm H2O for the chest
  2 types: static & dynamic

Elastance = the pressure Δ for a given volume Δ
   = the opposite of compliance
   The tendency to recoil to its original dimensions
   A measure of difficulty of expansion
   ΔP / ΔV
   eg blowing a very tight balloon
      Physiology: Compliance & Elastance

Chest, Lung, Thorax (both)

Lung
   Elastin fibres in lung - cause recoil
   Alveolar surface tension - cause recoil
   Alveolar surface tension reduced by surfactant

For the chest as a whole, it depends on
      Lungs and Chest Wall
      Diseases affect separately
          eg lung fibrosis, chest wall joint disease
         Physiology: Deadspace and shunt

Each part of the lung has
   Gas flow, V               Ratio V/Q
   Blood flow, Q             Perfect V/Q =1
   V/Q mismatching

Deadspace = Ratio: V Normal/ Low Q
That part of tidal volume that does not come into contact
with perfused alveoli

Shunt =         Ratio: V low/ Normal Q
That % of cardiac output bypasses ventilated alveoli
Normally = 1-2%
                      Normal ‘Shunt’
                                            Air enters Alveolus   V



Pulmonary capilary
                                Blood in contact
                            with ventilated alveolus   Q

                     ‘Shunted’ blood 1-2%

  Venous                                                          Arterial
                                 ‘venous admixture’
                       Increased Shunt
                                      Not much air enters Alveolus
                                                                V low
  Alveolus filled with pus
  or collapsed…..

                                                                V/Q = low
Pulmonary capilary
                                  Blood in contact
                             with unventilated alveolus
                                 Q normal

                       ‘Shunted’ blood 1-2%

  Venous                                                        Arterial
 Pulmonary Hypoxic Vasoconstriction
 A method of normalising
          the V/Q ratio                   Less air enters   V low
 Inflammatory exudate
      eg pus or fluid                                       V/Q =
                                                            towards normal


                              Q less
                        Blood diverted away
                        from hypoxic alveoli


Venous                                                        Arterial
                   Deadspace

• That part of tidal volume that does not come into
  contact with perfused alveoli


                         Deadspace volume ~ 200ml
                         Conducting airways ie trachea and 1-16
• Tidal volume
                         Alveolar volume ~500ml
                              Normal
                                            Air enters Alveolus   V



Pulmonary capilary
                                Blood in contact
                            with ventilated alveolus   Q

                     ‘Shunted’ blood 1-2%

  Venous                                                          Arterial
                               Deadspace
                                                                 Classic = trachea!

                                                Air enters Alveolus   V

Pulmonary capillary low flow
eg bleeding or blocked

                                                                           V/  Q
                                  Blood in contact
                                with ventilated alveolus   Q

                         ‘Shunted’ blood 1-2%

     Venous                                                           Arterial
                   Deadspace
                                      conduction of air
                                      Deadspace volume
Trachea
from L +R main bronchus
bronchi through to terminal bronchi
bronchioles
respiratory bronchioles                gas exchange
                                       Alveolar volume
alveolar ducts
alveolar sacs or ‘alveoli’
Physiology: V/Q
          What is Anaesthesia?
• Reversable drug induced unconsciousness
• ‘Triad’
   – Hypnosis, Analgesia, Neuromuscular Paralysis
• Induction, Maintainence, Emergence, (Recovery)
• Spontaneous vs Positive Pressure Ventilation
           Anaesthesia Timeline
•   Preoperative
•   Induction: Analgesia & IV hypnotic
•   Maintain: Analgesia & Volatile Hypnotic
•   Emergence: Analgesia Only
•   Recovery

• Patient can be paralysed vs not=
       • Needs ventilation vs spontaneously breathing
                    Anaesthesia
• 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
  Anaesthetic
   Machine
Delivers Precise
Volatile Anaesthetic Agents
Carrier Gas

Other stuff
   Hypnosis
Volatile or Inhalational
Anaesthetic Agents

Eg Sevoflurane
-A halogenated ether
-with a carrier gas
-ie air/N20
Intravenous
Analgesia = Pain relief
                     Systemic:
                     not limited to one
                     part of the body
        by unknown
           Analgesia = Pain relief
   Systemic: not limited to one part of the body

•Simple
      eg Paracetamol
•Non Steroidal Anti-Inflammatory Drugs
      eg Ibuprofen
•Opiods
      weak eg Codeine
      strong eg Morphine, Fentanyl
•Others
      Ketamine, N2O, gabapentin…..
         Analgesia = Pain relief
Regional: limited to one part of the body
                Neuromuscular
                Paralysis

             Nicotinic AcetylCholine Channel
             @ NMJ


Drug Image
             Non-competitive
                Suxamethonium

             Competitive
                All Others eg Atracurium

             Different properties
             Different length of action
             Paralyse Respiratory muscles
             Apnoea – ie no breathing
             Need to ‘Ventilate’
    Respiratory effects of Anaesthesia
•   airway
•   ‘respiratory depression’
•   FRC
•   Hypoxaemia
          Anaesthesia Airway
• Upper: loss of muscular tone eg oropharynx
• Upper: tongue falls posteriorly ie back
            Anaesthesia Airway
•   Upper: loss of muscular tone eg oropharynx
•   Upper: tongue falls posteriorly ie back
•   Need to keep it open to allow airflow!
•   “Airway obstruction’ = no airflow
•   Keep Airway open:
     – Airway manoeuvres (chin lift etc)
     – Airway devices
           –Into trachea = intubation
           –Other devices
Laryngeal Mask Airway
   Anaesthesia ‘respiratory depression’
• CO2 and O2 response curves of volatiles
• Opioids
• Respiratory depression
     …..is opposed by surgical stimulation
• No cough – good and bad
  – Caused by all 3 types of drug
  – Forced expiration: expands lungs, clears secretions
  – Allows pt to tolerate airway tubes…eg LMA
        Anaesthesia ‘respiratory depression’
         Volatiles  response to CO2

                      Awake



                                  Increasing concentration of volatile
V
L/min




                    5.3       7           9
                          Arterial CO2
                          kPa
 Anaesthesia ‘respiratory depression’

 Volatiles reduce minute ventilation

• Unstimulated volatiles
  – Reduce Vtidal and therefore V minute

  – Make you less responsive to the effects of CO2
  – ie slope is more flat
      = the normal increase in ventilation that occurs
        when CO2 rises is reduced
  Anaesthesia ‘respiratory depression’
        Volatiles response to hypoxaemia




V
L/min
                                   Awake
                                   Low concentration

                                   High concentration



                   5      8        13
                       PaO2 kPa
                  Opioids
• Opioids = a drug acting on Opioid receptor
• Morphine, Fentanyl
• Act in CNS, PNS, GI
• Reduced respiratory rate, increase tidal
  volume, but still increase PaCO2
• Suppress cough
Opioids
              Anaesthesia FRC
Why important?- closing Volume and O2 store
Why would it change?
FRC is decreased by 16-20% by Anaesthesia
  – Falls rapidly (seconds to minutes).
  – FRC remains low for 1-2 days
• Weak but significant correlation with age
• Less FRC reduction if patient is in the sitting
  position
    but most operations aren’t done sitting!
          Physiology: Closing Volume
                                  ~6000ml



Inhale




At Rest                           ~2500ml




Exhale



                                       0 ml
          Physiology: Closing Volume
                                  ~6000ml



Inhale




At Rest                           ~2500ml




Exhale



                                       0 ml
               Anaesthesia FRC
What causes these changes?
  1.   Cephalad movement of the diaphragm
  2.   Loss of inspiratory muscle tone
  3.   Reduced cross sectional rib cage area
  4.   Gas trapping behind closed airways
       Anaesthesia Hypoxaemia
Hypoxaemia – Low blood oxygen level
• FRC changes- Closing Vol,
   collapse/atelectasis and shunt
• Position also effects eg legs/laparoscopy/head down
  - Tidal volume
• Hypovolaemia/vasodilation increases deadspace,
   – V/low Q areas ….mismatch
• PHVC reduced volatiles
   – increases V/Q mismatch
• No cough/ yawn?
                    Atelectasis
Atelectasis = the lack of gas exchange within alveoli,
due to alveolar collapse or fluid consolidation
 CT scan of Diaphragm during
awake spontaneous breathing
CT scan of Diaphragm during
  anaesthesia: Atelectasis
            After Anaesthesia
• Some changes persist
  – Collapse/Atelectasis abnormal 1-2 days
  – FRC abnormal 1-2 days
  – CO2 and O2 responses normal in hours
  – V/Q missmatch
  – PHVC (reduces V/Q mismatch)


• Some new changes happen
  – Wound pain causing hypoventilation
  – Drug overdose causing hypoventilation
                  Summary 1
• Airway – conducting and respiratory
• Physiology
     • V/Q different as you go down lung
     • Extreme – no blood flow (Deadspace)
     • Extreme – no ventilation (Shunt)
• Anaesthesia
  – Hypnosis, Analgesia, Paralysis
                 Summary 2
Anaesthesia effects due to drugs!
  – Upper airway obstruction
  – Respiratory ‘depression’
  – Hypoxaemia
      – collapse (FRC/Closing volume) = ‘shunt’
      -  pulmonary blood flow - deadspace
     - PHVC drugs
                 Further reading
• Pulmonary physiology‪Michael G. Levitzky
  ‪
• http://en.wikipedia.org/wiki/Respiratory_physiology

• Several articles on my webpage
• Pulmonary Physiology and Pathophysiology: an integrated,
  case-based approach John West mostly free on google books
             Writing the essay
•   Break the answer down into parts
•   Lots of space
•   Graphs and diagrams, labelled
•   Underline important parts
•    Headline each paragraph with a statement?

• Don’t just write dense text

								
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