Scope of this talk Revise the anatomy and physiology that you - - PDF document

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Scope of this talk Revise the anatomy and physiology that you - - PDF document

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13/10/2014 Scope of this talk Revise the anatomy and physiology that you learnt in pre-clinical years Respiratory system anatomy and Discuss how we can use measure anatomy physiology in anaesthesia and physiology before, during and

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13/10/2014 1

Respiratory system anatomy and physiology in anaesthesia

Philip Barclay Consultant Anaesthetist Honorary Senior Clinical Lecturer, Imperial College

Scope of this talk

  • Revise the anatomy and physiology that you

learnt in pre-clinical years

  • Discuss how we can use measure anatomy

and physiology before, during and after surgery

  • Show its relevance to the practice of clinical

anaesthesia

The ultimate question

  • What is the main purpose of the anatomical

and physiological systems within our bodies?

The ultimate answer

(to life, the universe and everything)

The ultimate answer

(to life, the universe and everything)

The ultimate answer

(to life, the universe and everything)

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13/10/2014 2

The ultimate answer

(to life, the universe and everything)

The ultimate answer

(to life, the universe and everything)

The ultimate answer

(to life, the universe and everything)

Failure is not an option! Failure is not an option! Failure is not an option!

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13/10/2014 3

Failure is not an option! Failure is not an option!

How do we get oxygen to the brain?

  • Our job for the next 15 minutes

Three groups

  • Anatomists
  • Physiologists
  • “Surgeons”
  • “Anaesthetists”

Anatomists

  • Describe the anatomy of the upper airway
  • Describe the anatomy of lower airways
  • Diagrams
  • Facts and figures

Physiologists

  • Describe how oxygen gets from the air into

the pulmonary vessels

  • Describe how it gets from the circulation into

the brain

  • Diagrams
  • Graphs
  • Facts and figures

Surgeons

  • What type of operations would affect the

patients ability to breathe during surgery

  • Which might cause a problem after surgery
  • Which surgical pathologies may affect

breathing?

  • Which kind of medical conditions that might

affect breathing should I think about before listing a patient for surgery?

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SLIDE 4

13/10/2014 4

Anaesthetists

  • What effect do local anaesthetics have on

breathing during surgery?

  • What effect do general anaesthetics have on

breathing during surgery?

  • How can I monitor the patients breathing

during surgery

  • What happens after surgery?

Anatomy revision

  • Upper Airway above the vocal cords
  • Lower airway – below the vocal cords

– Conducting vs gas exchange- different tissue types

  • Muscles of respiration

Further notes on respiratory physiology and anaesthesia

Airway

  • Airway is Lips/Nose to alveoli
  • Upper Airway: lips/nose to vocal Cords
  • Lower Airway: Vocal Cords down

– Trachea – Conducting Airways – Respiratory Airways – gas exchange with capillaries

  • R heart pulmonary artery

capillaries vein L heart

Pharynx

Lower Airway

  • 23 divisions follow down

from L +R main bronchus bronchi through to terminal bronchi bronchioles respiratory bronchioles alveolar ducts alveolar sacs or ‘alveoli’

1-16 conduction of air 17-23 gas exchange

Anatomy: Muscles of Respiration

  • Upper airway muscles upper airway tone
  • External Intercostals

Inspiration

  • Diaghram

Inspiration

  • Internal Intercostals

Forced Expiration

  • Accessory muscles

Forced Inspiration Neck

  • Accessory muscles

Forced Expiration Abdomen

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SLIDE 5

13/10/2014 5

Physiology revision

  • Spirometry- basic volumes
  • How we breathe spontaneously
  • Compliance / elastance
  • Deadspace and shunt
  • V / Q ratios

0 ml At Rest Inhale Exhale ~2500ml ~6000ml

Physiology: Spirometry 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’

  • ccurs
  • Others

0 ml At Rest Inhale Exhale ~2500ml ~6000ml

Physiology: Closing Capacity

~40+ supine ~60+ standing Normal breath inspirationanimation, 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 H20
  • 5cm H20

Alveolar pressure falls

  • 2cm H20

Lung @ FRC= balance

Physiology: Normal Spontaneous breath

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13/10/2014 6

Normal breath expirationanimation, awake Diaghram relaxes Pleural / Chest volume ↓ Pleural pressure rises

Physiology: Normal Spontaneous breath

Alveolar pressure rises to +1cm H20 Air moves down pressure gradient

  • ut of lungs
  • 5cm H20

+1cm H20

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 together) Lung Elastin fibres in lung - cause recoil = collapse 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: Compliance & Elastance Physiology: Deadspace and shunt Each part of the lung has

Gas flow, V Blood flow, Q 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% Ratio V/Q Perfect V/Q =1

Normal ‘Shunt’

Shunt

% Blood not going through ventilated alveoli

  • r blood going through unventilated alveoli
  • Normal- 1-2%
  • Pulmonary eg alveolar collapse, pus, secretions
  • Cardiac eg ASD/VSD ‘hole in the heart’

(but mostly left to right…. due to L pressure> R pressures)

Normal ‘Shunt’

Air enters Alveolus Pulmonary capilary ‘Shunted’ blood 1-2% Blood in contact with ventilated alveolus

Venous Arterial V Q

‘venous admixture’

Sv0275% Sa02~100%

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13/10/2014 7

Increased Pulmonary Shunt

Not much air enters Alveolus Pulmonary capilary ‘Shunted’ blood 1-2% Blood in contact with unventilated alveolus

Venous Arterial V low V/Q = low Q normal

Alveolus filled with pus

  • r collapsed…..

Sv0275% Sa0275%

Pulmonary Hypoxic Vasoconstriction

Less air enters Inflammatory exudate eg pus or fluid

Arterial Venous

Blood diverted away from hypoxic alveoli

V low Q less V/Q =

towards normal

A method of normalising

the V/Q ratio

Deadspace

  • That part of tidal volume that does not come into

contact with perfused alveoli

  • Tidal volume

= anatomical

  • Pathological

Alveolar volume ~400ml Deadspace volume ~ 200ml Conducting airways ie trachea and 1- 16= Anatomical deadspace

Deadspace

Air enters Alveolus Pulmonary capilary ‘Shunted’ blood 1-2% Blood in contact with ventilated alveolus

Venous Arterial V Q

Deadspace

Air enters Alveolus Pulmonary capillary low flow eg bleeding or blocked ‘Shunted’ blood 1-2% Blood in contact with ventilated alveolus

Venous Arterial V Q

V/ Q = Hi

Classic anatomical = trachea!

Deadspace- Anatomical

Trachea from L +R main bronchus bronchi through to terminal bronchi bronchioles respiratory bronchioles alveolar ducts alveolar sacs or ‘alveoli’

conduction of air Deadspace volume gas exchange Alveolar volume

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13/10/2014 8

Physiology: V/Q in lung

Both V and Q increase down lung Q increases more than V down lung Another way to think about Q/V is ‘west zones’ V/Q ratios change down lung If patient supine (on back) V/Q changes front to back

Physiology: V/Q in lung Respiratory effects of Anaesthesia

  • airway
  • ‘respiratory depression’
  • Functional Residual Capacity, FRC
  • Hypoxaemia

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- above vs below cords

–Supraglottic: Guedel, iGel –Infraglottic: endo-tracheal tube

Supraglottic Airway Device

The iGel

Respiratory effects of Anaesthesia

  • airway
  • ‘

‘ ‘ ‘respiratory depression’

  • Functional Residual Capacity, FRC
  • Hypoxaemia
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SLIDE 9

13/10/2014 9 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 iGel

V L/min Arterial CO2 kPa

Increasing concentration of volatile Awake

Volatiles response to CO2

Anaesthesia ‘respiratory depression’

5.3 9 7

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

PaO2 kPa

Awake High concentration Low concentration 8 13 5

Anaesthesia ‘respiratory depression’

V L/min

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

Respiratory effects of Anaesthesia

  • airway
  • ‘respiratory depression’
  • Functional Residual Capacity, FRC
  • Hypoxaemia
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SLIDE 10

13/10/2014 10

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!

0 ml At Rest Inhale Exhale ~2500ml ~6000ml

Physiology: Closing Volume

0 ml At Rest Inhale Exhale ~2500ml ~6000ml

Physiology: Closing Volume

What causes these changes?

  • 1. Cephalad (to brain) movement of the diaphragm
  • 2. Loss of inspiratory muscle tone
  • 3. Reduced cross sectional rib cage area
  • 4. Gas trapping behind closed airways

Anaesthesia FRC Respiratory effects of Anaesthesia

  • airway
  • ‘respiratory depression’
  • FRC
  • Hypoxaemia

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 by volatiles

– increases V/Q mismatch

  • No cough/ yawn ?-collapse/secretions
  • Apnoea/Airway obstruction- no 02 in no CO2 out!
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13/10/2014 11

Hypoxaemia: Atelectasis

Atelectasis = the lack of gas exchange within alveoli, due to alveolar collapse or fluid consolidation

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 mis-smatch – PHVC (reduces V/Q mismatch)

  • Some new changes happen

– Wound pain causing hypoventilation – Drug overdose causing hypoventilation – Pneumonia, cough supression, PE, LVF etc

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