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

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 after surgery Philip Barclay • Show its relevance to the practice of clinical Consultant Anaesthetist anaesthesia Honorary Senior Clinical Lecturer, Imperial College The ultimate question The ultimate answer (to life, the universe and everything) • What is the main purpose of the anatomical and physiological systems within our bodies? The ultimate answer The ultimate answer (to life, the universe and everything) (to life, the universe and everything) 1

13/10/2014 The ultimate answer The ultimate answer (to life, the universe and everything) (to life, the universe and everything) The ultimate answer Failure is not an option! (to life, the universe and everything) Failure is not an option! Failure is not an option! 2

13/10/2014 Failure is not an option! Failure is not an option! How do we get oxygen to the brain? Anatomists • Our job for the next 15 minutes • Describe the anatomy of the upper airway • Describe the anatomy of lower airways Three groups • Anatomists • Physiologists • Diagrams • “Surgeons” • Facts and figures • “Anaesthetists” Physiologists Surgeons • Describe how oxygen gets from the air into • What type of operations would affect the the pulmonary vessels patients ability to breathe during surgery • Describe how it gets from the circulation into • Which might cause a problem after surgery the brain • Which surgical pathologies may affect breathing? • Diagrams • Which kind of medical conditions that might affect breathing should I think about before • Graphs listing a patient for surgery? • Facts and figures 3

13/10/2014 Anaesthetists Anatomy revision • Upper Airway above the vocal cords • What effect do local anaesthetics have on breathing during surgery? • Lower airway – below the vocal cords • What effect do general anaesthetics have on breathing during surgery? – Conducting vs gas exchange- different tissue types • How can I monitor the patients breathing during surgery • Muscles of respiration • What happens after surgery? Further notes on respiratory Airway physiology and anaesthesia • Airway is Lips/Nose to alveoli • Upper Airway: lips/nose to vocal Cords Pharynx • Lower Airway: Vocal Cords down – Trachea – Conducting Airways – Respiratory Airways – gas exchange with capillaries • R heart pulmonary artery capillaries vein L heart Anatomy: Muscles of Respiration Lower Airway • Upper airway muscles upper airway tone • 23 divisions follow down 1-16 conduction of air • External Intercostals Inspiration • Diaghram Inspiration from L +R main bronchus • Internal Intercostals Forced Expiration bronchi through to terminal bronchi • Accessory muscles Forced Inspiration bronchioles Neck 17-23 gas exchange respiratory bronchioles • Accessory muscles Forced Expiration alveolar ducts Abdomen alveolar sacs or ‘ alveoli ’ 4

13/10/2014 Physiology revision • Spirometry- basic volumes • How we breathe spontaneously • Compliance / elastance • Deadspace and shunt • V / Q ratios Physiology: Spirometry Physiology: Volumes ~6000ml • Tidal Volume, TV Inhale • Functional Residual Capacity, FRC Volume in lungs at end Expiration not a fixed volume - conditions change FRC At Rest • Residual Volume, RV ~2500ml Volume at end of a forced expiration • Closing Volume, CV Volume in expiration when alveolar closure ‘ collapse ’ Exhale occurs • Others 0 ml Physiology: Normal Spontaneous breath Physiology: Closing Capacity Normal breath inspiration animation, awake ~6000ml Lung @ FRC= balance Diaghram contracts -2cm H 2 0 Inhale ↑ Chest volume At Rest ↓ Pleural pressure ~2500ml Pressure difference from lips to alveolus -5cm H 2 0 drives air into lungs ~40+ supine ~60+ standing ie air moves down pressure gradient Exhale Alveolar to fill lungs pressure falls -2cm H 2 0 0 ml 5

13/10/2014 Physiology: Normal Spontaneous breath Physiology: Compliance & Elastance Normal breath expiration animation, awake Compliance = the volume Δ for a given pressure Δ A measure of ease of expansion -5cm H20 ΔV / ΔP Diaghram relaxes Normally ~ 200ml / 1 cm H 2 O for the chest Pleural / Chest volume ↓ 2 types: static & dynamic Pleural pressure rises Elastance = the pressure Δ for a given volume Δ +1cm H 2 0 Alveolar = the opposite of compliance pressure rises to +1cm H 2 0 The tendency to recoil to its original dimensions Air moves down A measure of difficulty of expansion pressure gradient out of lungs ΔP / ΔV eg blowing a very tight balloon Physiology: Deadspace and shunt Physiology: Compliance & Elastance Each part of the lung has Chest, Lung, Thorax (= both together) Gas flow, V Ratio V/Q Blood flow, Q Perfect V/Q =1 Lung V/Q mismatching Elastin fibres in lung - cause recoil = collapse Alveolar surface tension - cause recoil Deadspace = Ratio: V Normal/ Low Q Alveolar surface tension reduced by surfactant That part of tidal volume that does not come into contact with perfused alveoli For the chest as a whole, it depends on Shunt = Ratio: V low/ Normal Q Lungs and Chest Wall That % of cardiac output bypasses ventilated alveoli Diseases affect separately Normally = 1-2% eg lung fibrosis, chest wall joint disease Normal ‘ Shunt ’ Normal ‘ Shunt ’ Shunt V Air enters Alveolus % Blood not going through ventilated alveoli or blood going through unventilated alveoli Pulmonary capilary •Normal- 1-2% Blood in contact Sa0 2 ~100% Q •Pulmonary eg alveolar collapse, pus, secretions with ventilated alveolus •Cardiac eg ASD/VSD ‘ hole in the heart ’ Sv0 2 75% (but mostly left to right…. due to L pressure> R pressures) ‘ Shunted ’ blood 1-2% Arterial Venous ‘ venous admixture ’ 6

13/10/2014 Increased Pulmonary Shunt Pulmonary Hypoxic Vasoconstriction A method of normalising Not much air enters Alveolus the V/Q ratio V low V low Less air enters Alveolus filled with pus or collapsed….. Inflammatory exudate V/Q = eg pus or fluid V/Q = low towards normal Pulmonary capilary Blood in contact Sa0 2 75% with unventilated alveolus Q less Q normal Sv0 2 75% Blood diverted away from hypoxic alveoli ‘ Shunted ’ blood 1-2% Arterial Venous Venous Arterial Deadspace Deadspace • That part of tidal volume that does not come into V Air enters Alveolus contact with perfused alveoli Deadspace volume ~ 200ml Conducting airways ie trachea and 1- 16= Anatomical deadspace • Tidal volume Pulmonary capilary = anatomical Blood in contact Alveolar volume ~400ml Q with ventilated alveolus • Pathological ‘ Shunted ’ blood 1-2% Arterial Venous Deadspace Deadspace- Anatomical Classic anatomical = trachea! conduction of air V Air enters Alveolus Deadspace volume Trachea from L +R main bronchus Pulmonary capillary low flow V/ � Q = Hi eg bleeding or blocked bronchi through to terminal bronchi bronchioles � Blood in contact Q with ventilated alveolus respiratory bronchioles gas exchange Alveolar volume alveolar ducts ‘ Shunted ’ blood 1-2% alveolar sacs or ‘ alveoli ’ Arterial Venous 7

13/10/2014 Physiology: V/Q in lung Physiology: V/Q in lung Both V and Q increase down lung Q increases more than V down lung V/Q ratios change down lung If patient supine (on back) V/Q changes front to back Another way to think about Q/V is ‘ west zones ’ Respiratory effects of Anaesthesia Anaesthesia Airway • Upper: loss of muscular tone eg oropharynx • airway • Upper: tongue falls posteriorly ie back • ‘ respiratory depression ’ • Need to keep it open to allow airflow! • “Airway obstruction’ = no airflow • Functional Residual Capacity, FRC • Keep Airway open: • Hypoxaemia – Airway manoeuvres (chin lift etc) – Airway devices- above vs below cords – Supraglottic: Guedel, iGel – Infraglottic: endo-tracheal tube S upraglottic A irway D evice Respiratory effects of Anaesthesia The iGel • airway • ‘ ‘ respiratory depression ’ ‘ ‘ • Functional Residual Capacity, FRC • Hypoxaemia 8

13/10/2014 Anaesthesia ‘ respiratory depression ’ Anaesthesia ‘ respiratory depression ’ Volatiles � response to CO 2 • CO 2 and O 2 response curves of volatiles Awake • Opioids • Respiratory depression Increasing concentration of volatile V …..is opposed by surgical stimulation L/min • 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 5.3 7 9 Arterial CO 2 kPa Anaesthesia ‘ respiratory depression ’ Anaesthesia ‘ respiratory depression ’ Volatiles � response to hypoxaemia Volatiles reduce minute ventilation • Unstimulated volatiles – Reduce V tidal and therefore V minute V L/min – Make you less responsive to the effects of CO 2 Awake Low concentration – ie slope is more flat High concentration = the normal increase in ventilation that occurs when CO 2 rises is reduced 8 13 5 PaO 2 kPa Opioids Respiratory effects of Anaesthesia • Opioids = a drug acting on Opioid receptor • airway • Morphine, Fentanyl • ‘ respiratory depression ’ • Act in CNS, PNS, GI • Functional Residual Capacity, FRC • Reduced respiratory rate, increase tidal • Hypoxaemia volume, but still increase PaCO 2 • Suppress cough 9