Monitoring. Suzie Ward March 2013

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1 Monitoring Suzie Ward March 2013

2 Monitoring 1 Oximetry Capnography Oxygen Vapours

5 FRCA Primary Pulse oximetry; how does it work? Is it fast or slow? What are its problems? Graph of light absorption of Hb and HbO2 Capnography: sidestream main-stream, advantages / disadvantages. Waveforms Picture of anaesthetic machine and monitor - what gases are being monitored?mechanism of gas monitoring. Monitoring Equipment: photo of Fi Iso, Nitrous, O2. Qs about how gas is monitored. Physical principles of the capnograph Capnography - how does it work, infra red, what can

7 Monitor Observe and check the progress or quality of (something) over a period of time; keep under systematic review

9 Minimum standards SECTION V:MONITORING THE PATIENT The following monitoring devices are essential to the safe conduct of anaesthesia. Induction and Maintenance of Anaesthesia 1. Pulse oximeter 2. NIBP monitor 3. Electrocardiograph 4. Airway gases: oxygen, carbon dioxide

10 Pulse oximeter

11 Pulse oximeter Principles Sources of error Limitations

12 Principles Displays the percentage of arterial hb in the oxyhb configuration Light absorbance of oxyhb is different from deoxyhb at wavelengths used red (660nm) and infrared (940nm) so the ratio of oxy/deoxy hb can be calculated frpm the ratio of the absorption of red and ir light Absorbance of both wavelengths has pulsatile component arterial pulsation

14 What actually happens? 1.2 LEDs operate in sequence 30 x/sec with a photodetector on the other side At 660 (red light) Hb absorbs about 10x that of Hb02. Reverse happens at 940 The high freq of the LED decreases the noise (movement effect) on the signal

15 2.Microprocessor selects out and analyses DC (constant) and AC (pulsatile) components at 660 and 940 nm. 3.Saturation of Hb calculated from absorption at the 2 wavelengths (Beer- Lambert)

16 4.Pulsatile changes in light absorption analysed, absorption by venous blood/tissue deducted, arterial sats measured 5.Measurements plotted against standard calibration curve Direct measurements of arterial oxygen sats volunteers with induced hypoxia 6.Number displayed on screen

17 Oxygen saturation estimated by measuring transmission of light Beers law Lamberts law Relationship between light absorbed and concentration of solute ( diff hb s) in the solution Relation between the absorption of light and thickness of the absorbing layer

18 Limitations?

19 Limitations Only accurate > 70% Does not measure oxygen delivery Time lag- average secs so cannot detect acute desaturation Pressure sores with continuous use No info about adequacy of ventilation just oxygenation

20 Sources of error?

21 Sources of error Dyshaemoglobinaemia methb,cohb, iv methylene blue Light Nail varnish Irregular rhythms Hypoperfusion Movement Vasoconstriction Electrical interference

22 Capnography

23 Capnography Continuous monitoring of expired C02 tension in the airway to allow monitoring of end tidal CO2 tension

24 Side stream CO 2 sensor in main unit away from airway Continuous sample drawn at 150mls/min from patient Sample contains anaesthetic gases and is routed to gas scavenger/ returned to system. Water trap

25 Analysing cell interposed in breathing system Mainstream Gas analysed in circuit

26 Pros and cons?

27 Mainstream Pros No sampling tube so no obstruction No effect due to pressure drop/ changes in water vapor pressure No pollution No delay Paediatrics Cons Bulky/ heavy at patient end Can become hot/ burn Sensor windows may clog with secretions Difficult in unusual patient positions eg prone No other vapours

28 Sidestream Pros Cons Easy to connect No problems with sterilization Used awake and with 02 delivery Easy in unusual positions Other vapours analysed from sample Delay in recording due to movement of gases from the ET to unit -transit/rise time Sampling tube obstruction Water vapor pressure changes affect CO 2

29 Draw a capnogram

31 Expiratory segment Phase I CO 2 -free gas from airway (anatomical and apparatus dead space) Phase II S-shaped upswing (mixing of dead space and alveolar gas) Phase III Plateau representing CO 2 -rich gas from alveoli. Mostly has positive slope due to steady excretion of C02 into alveoli, late emptying of alveoli with lower v/q ratios and so higher paco2

32 Inspiratory segment Phase 0/4 After phase III capnogram rapidly descends Inspiratory - fresh gases (CO 2 free) are inhaled and CO 2 falls rapidly to zero The segment of CO 2 trace from start of inspiration to start of expiration is phase 0

33 Clinical application 5 characteristics to note when analysing 1. Frequency 2. Rhythm 3. Height ( value)- 5.3kpa (40 mmhg) 4. Baseline 5. Shape of waveform

34 Changes in ETC02 value C02 production Pulmonary perfusion Alveolar ventilation Machine fault

35 Waveforms

36 Measurement of C02-gas Spectroscopy- infrared/ photoacoustic. Vapours. Raman scattering Mass spectrometer Piezoelectric absorption

37 Spectroscopy- infrared Depends on the ability of gases containing different atoms to absorb IR light -not 02/N Absorb a specific wavelength (C µm) Amount absorbed is proportional to amount of gas present ( Beers Law)

38 Generated IR radiation is focused through chopper wheel with filters with diff wavelengths Sample and reference chambers. Remaining light passes to photodetector, pressure/ temperature integrated and signal processed and amplified

39 IR emitted by hot wire Chopper/filter-alternating signal ( easier to amplify) Sapphire windows

40 Problems At wavelengths used other molecules can interfere with absorption peaks Falsely high readings Collision broadening

41 Photoacoustic If initial radiation pulsed subsequent vibration of molecules detected with a microphone as sound at wavelengths specific for molecule

44 Raman Absorption and immediate emission of light by gases in a pattern specific to individual molecules

45 Sevringhaus electrode- blood C02 partial pressure measured as a result of change in ph of a soln Based on : C02 +H20< > H2C03-<>H+ +HC03- Slow response time(2-3 mins) Maintain 37

46 H+ ion sensitive glass with electrodes either side C02 diffuses thru membrane to electrolyte soln NaHC03 and produces H+ Change in ph measured by glass electrode

47 STAND UP, HANDS IN THE AIR, JUMP UP AND DOWN,TURN AROUND, SIT DOWN

48 FRCA- it s why you are here measurement of 02 and diff reactions capnography vivas IR and measurement of co2 and volatiles diff ways of 02 measurement capnography osce and pulse oximeter viva

49 Oxygen measurement Paramagnetic- mainly used in theatre Polarographic (Clark/Oxygen)- blood gases Fuel cell

50 Paramagnetic 2 chambers separated by pressure transducer Sample and reference gas introduced into the chambers 02 is attracted to the magnetic field (paramagnetism) because it has unpaired electrons in the outer shell Electromagnet pulsed creating a magnetic field

51 Paramagnetic O2 molecules are attracted into the field which is transmitted across the transducer as a change in pressure The magnitude of change is a measure of oxygen partial pressure in the gas Accurate, sensitive, rapid. Long life

52 . Schematic drawing of a Paramagnetic sensor; oxygen is drawn towards the magnet and will create a pressure difference between the limbs if the concentration is different.

53 Polarographic Measures partial pressure of oxygen in blood/gas Platinum cathode and Ag/Agcl anode in KCl 0.6mV applied In the electrolyte: KCl + OH = KOH + Cl At the anode: Ag + Cl = AgCl + e At the cathode: O2 + 2H2O + 4e = 4OH

54 More 02 available more e- taken up at cathode and greater current flow Cathode separated from blood by membrane to prevent protein deposits Temp 37 3 year shelf life Blood sample taken anaerobically/ heparinised/ bubble free/ no delay

56 Fuel cell Battery requiring 02 for current flow Cathode gold but same reaction occurs 02 +2H20 +4e-=4OH- Anode is lead and provides e- Pb +2OH-> PbO + H20 + 2e- The voltage produced is proportional to 02 conc

58 Summary Monitoring is an essential component of anaesthesia Exam favorite - capnography/oximeter Physics- simple concepts, finite amount of knowledge for easy points so worth the time THANKYOU FOR LISTENING

RESPIRATORY PHYSIOLOGY, PHYSICS AND

Course n : Course 3 Title: RESPIRATORY PHYSIOLOGY, PHYSICS AND PATHOLOGY IN RELATION TO ANAESTHESIA AND INTENSIVE CARE Sub-category: Techniques Topic: Respiratory monitoring Date: May 05-07, 2016 Language: