RESPIRATORY PHYSIOLOGY, PHYSICS AND

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1 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: English City: Lahore Country: Pakistan Speaker: Dr. Mohammad Hamid

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3 Respiratory monitoring Clinical monitoring Monitoring equipment

4 Limitations Clinical monitoring Difficult to detect Late sign Affected by anaesthetics e.g. use of muscle relaxants

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6 Monitoring techniques Pulse oximetry Capnography (End tidal CO2) Respiratory rate monitor Arterial blood gases Other imaging techniques Monitors for function of the respiratory system e.g. airway pressure, flow, volumes Different techniques to measure Compliance, Resistance

7 Pulse oximetry Simple Non invasive Measure arterial blood oxygenation Two basic physical principles Detect pulsatile blood flow Detect oxy and reduced Hb Beer Lambert law Concentration of an unknown solute in a solvent can be determined by light absorption

8 Light emitting diodes (LED) Red LED Infra red LED Light turns ON & OFF several hundred times per second ON period Light switches from red to infrared OFF period ( both LED off) Detect and compensate for extraneous light

9 Oxygenated Hb absorb more infra red light (940 nm) Deoxygenated Hb absorb more red light (660 nm) From the difference of absorption of red and infrared light, the ratio between oxy and deoxy Hb can be calculated

10 Photodiode A light sensing equipment Produces an electric signal that is directly proportional to the amount of light hitting at the active surface area Signals are amplified, processed and displayed on the monitor

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14 No calibration required Accuracy ranges between % Advantages Values may differ from one pulse ox to other Software containing calibration curves may vary between manufacturers Some errors in wavelengths of light by LED SpO2 and HR values are averages Averaging period can be adjusted in some oximeters Pitch of the audible tone changes with saturation

15 Reflectance Pulse oximetry Light source and sensor are situated next to each other Tissues must be well perused Signals are weaker Photodiode area is large

16 Functional & Fractional SaO2 Functional SaO2 = O2 Hb x 100 (%) / O2Hb + Hb Fractional SaO2 ( Oxy Hb percentage, OxyHb fraction O2 Hb x 100(%)/ O2Hb + Hb + MetHb + COHb Fractional SaO2 determined by clark electrode At low dyshaemoglobin levels difference between functional and fractional SaO2 is negligible.

17 Absorption characteristics falsely account for a low sat in the patient with Hgb-Met Hgb-CO & Hgb-O 2 have similar absorbance at 666nm so Hgb-CO will be falsely interpreted as Hgb-O2 (high sat)

18 Transthoracic Impedance plethysmography

19 Transthoracic Impedance plethysmography Three lead system (TTI) Two electrodes on opposite side of lower chest Low voltage current pass between electrodes Impedance increases with inspiration and decreases with expiration Converted into a waveform Useful in sleep apnoea Neonatal apnoea

20 Acoustic respiratory rate monitor

21 Carbon dioxide (Capnography)

22 Measurement Techniques Infrared analyzer Photo acoustic spectrometer Raman spectrometer Mass spectrometer

23 Infrared Absorption A beam of infrared light energy is passed through a gas sample containing CO 2 CO 2 molecules absorb specific wavelengths of infrared light energy. Light absorption increases directly with CO2 concentration Photo detector measures the amount of infrared light absorbed Monitor converts this data to a CO2 value and a corresponding waveform (capnogram)

24 Measurement site Mainstream (Flow-through, non diverting or In-line) Sensor placed in the breathing circuit Infra red light absorption used

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26 Main stream (advantages) Fast response time No gas is removed from the airway No sample line occlusion or wave form distortion Less chances of sample contamination Water and secretions are seldom a problem Fewer disposable items used

27 Expensive Main stream (Disadvantages) Can measure only oxygen and CO2 Increase dead space Adds bulk to the breathing system Leaks, disconnections possible CO2 sensor must be cleaned and disinfected between uses Thermal burns reported Electronics are vulnerable to mechanical damage

28 Sidestream Analyzer (aspiration, diverting) Aspirate gas and transport the sample to a remote CO2 analyzer Aspirate 50 to 500ml/min of gas from breathing circuit (commonly ml/min) Analyze multiple gases Accuracy decreases with high respiratory rate Potential for disconnect or leak giving false readings A water trap is usually interposed between the sample line and analyzer to protect optical equipment

29 ETT with monitoring lumen

30 Calorimetric method

31 Volume, Pressure & Flow measurements Volume measurement Spirometer or respirometer Wright s spirometer, Spiromed Pressure measurement Mechanical pressure gauge Airway pressure Vs time wave form

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33 Flow and pressure sensors D-Lite Heated wire anemometer Ultrasonic flow sensor Novometrics side streamsensor Variable orifice flow sensor Fixed orifice flow sensor

34 D-Lite sensor Attached between Y -piece and HME filter Two pressure tubes & one gas sample port Two tubes facing in opposite direction Resistance to gas flow Pressure drop conducted by pressure tubes to a sensor in the monitor which transduced and displayed as wave form A software is used to draw P-V & F-V loops

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37 Measure D Lite sensor Flow rate, Peak flow Peak and static pressure Tidal volume Calculate compliance and resistance Flow and pressure volume loops displayed

38 Pressure volume loop Good compliance 45 degree or less with volume scale More vertical Decrease compliance Represented by more horizontal loop Effective dynamic compliance Ventilator driven TV/ Peak Paw PEEP Not a measure of true thoracic compliance

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43 Flow volume loop Expiratory phase plotted above the horizontal axis Diminished expiratory flow Increase resistance Severe COPD Increase expiratory flow Bronchial intubation Decrease compliance Helps in identification of fixed intra and extra thoracic obstruction

44 Arterial blood gas ph Sanz electrode PaCO2 Severinghaus electrode PaO2 Clark electrode Platinium cathode & Silver anode Determine PaO2 amperometrically Common errors Air bubbles Excessive or inadequate anticoagulant Delayed analysis Non arterial sample

45 THANK YOU