SS Gas Analysis - Fall23.pptx
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Gas Analysis Clay Freeman, DNP, CRNA Science in Anesthesia 1 Objectives Readings: Nagelhout: Chap. 15, 18 Davis: Chap. 18,19, 20 • Demonstrate an understanding of various types of oxygen, CO2 and gas analysis • Compare/contrast various methods of analyzing gases • Understand the components of t...
Gas Analysis Clay Freeman, DNP, CRNA Science in Anesthesia 1 Objectives Readings: Nagelhout: Chap. 15, 18 Davis: Chap. 18,19, 20 • Demonstrate an understanding of various types of oxygen, CO2 and gas analysis • Compare/contrast various methods of analyzing gases • Understand the components of the Beer-Lambert Law and applications within anesthesia practice • Analyze capnographs and associated disorders or malfunctions 2 Principles of Gas Analysis Oxygen, Carbon dioxide, and Inhalation agents are matter which we are particularly focused on in anesthesia practice (-) (+) Electromagnetic radiation is independent of matter but interacts with it via Reflection, Refraction, Diffraction or Absorption The interaction between electromagnetic radiation and these gases is measured to perform gas analysis 3 Principles of Gas Analysis Remember: gas molecules will exert a pressure which increases or decreases in relation to volume Dalton’s Law of partial pressures is used to determine the mixture of gases Measurements are created from theories of either Partial Pressure or Volumes Percent 4 Oxygen Analysis Electrogalvan ic Cell (Fuel Cell) Polarographic Electrode (Clark Electrode) Paramagnetic Oxygen Analyzer Fluorescence -Quenching 5 Galvanic Sensor Galvanic (fuel cell) sensor Oxygen passes through a semipermeable membrane. 1) O2 then dissolves into an electrolyte solution (Potassium Hydroxide) 2) At the Cathode (noble metal), oxygen molecules are reduced to hydroxyl ions. 3) Then, the hydroxyl ions oxidize at the Anode (lead or zinc). The electrical potential between the anode and cathode is measured via a Voltmeter • Voltage is directly proportional to the partial pressure of oxygen. A Thermistor compensates for temperature irregularities 6 Galvanic Sensor 7 Galvanic Sensor 8 Calibration & Consumption Results of oxidative-reductive reactions Continual consumption = Limited shelf life 9 Polarographic (Clark) Electrode Clark Electrode Consists of a voltage source connected to cathode and anode electrodes which are immersed in an electrolyte (KCl) solution • A semipermeable (Teflon) membrane covers the cell A polarizing voltage is applied oxygen is reduced to hydroxyl ions at the cathode & Oxidation occurs at the anode The voltmeter measures the current produced between the electrodes created by the reactions. No Passive Consumption Current flows in proportion to the partial pressure of oxygen 10 Clark Electrode 11 Paramagnetic Analyzers Paramagnetic Oxygen Transducer Principle: O2 has 2 electrons in unpaired orbits which make it paramagnetic. Most other gases are weakly diamagnetic 1) Dual-channel tubing: A sample of oxygen passes through one channel and a reference gas through another 2) Rapidly altering electromagnetic fields creates pressure gradient changes which can be measured across a transducer This pressure difference is directly proportional to the concentration difference between the samples Accurate and rapid measurements 12 Paramagnetic Analyzers 13 Fluorescence Quenching Fluorescence Quenching Fluorescence: Electron chemically or electrically excited to a higher energy level Excited electron releases a light photon Emitte d Absorbe d Higher energy level Oxygen has the ability to absorb photons which prevents this energy from being emitted as light Therefore, O2 concentration can be analyzed by determining the amount of emitted photons Fluorescence quenching is directly Lower energ y level Schematic of electron orbit 14 Carbon Dioxide Analysis Severinghaus PCO2 electrode & Colorimetric Sensor 15 Colorimetric Sensor Utilizes the Fluorescence Quenching principle CO2 dissolves into a solution CO2 alters pH of the solution by liberating H+ ions A pH-sensitive dye is activated The fluorescent dye changes color 16 Colorimetric Sensor Filter paper is permeated with pHsensitive dyes Hydrophobic filter prevents moisture contamination Detects CO2 but NOT the concentration Newer devices have calibrated responses to CO2 changes 17 CO2 Measurement Severinghaus PCO2 electrode pH sensitive glass electrode is immersed in a bicarbonate solution with a semipermeable membrane covering the cell surface. 1) CO2 diffuses into the cell & reacts with water, producing carbonic acid 2) Voltmeter measures electrical charge created by H+ ion concentration Current measured is proportional to CO2 concentration 18 Severinghaus 19 Organic & Inorganic Gas Gases; organic (volatile anesthetics) and inorganic gases (N2O) Absorption of electromagnetic wave measurements are based on the Beer-Lambert Law • Absorption determined by the thickness and absorbing properties of the substance 20 Beer-Lambert Law Itrans= Iin · e-DC Itrans = The transmitted light Iin = The incident light D = The distance through the medium C = Concentration of the solute = The extinction coefficient of the solute li ltrans n D e 21 Beer-Lambert Law 22 Gas Analysis Mass Spectrometry Infrared Analysis Raman Scattering Analysis 23 Mass Spectrometry Basic Components: Ionizer, mass analyzer, detector A sample is ionized and passed through a curved tube in a magnetic field. The ionized gas molecules become deflected by the magnetic/electric field Ions produce electrical currents at the collectors which can be processed Separates all gases in a mass-to-charge (m/z) ratio Measurement given is a Volumes Percent of the sample gas mixture 24 Mass Spectrometry 25 Pros / Cons Advantages: • central unit ease of maintenance • lower operating costs • complete, multiple gas analysis • can detect mixtures of volatile anesthetics Disadvantages: • slow lag time 2-10 minutes • not continuous readings • measures only preprogrammed gases • malfunction ends all gas monitoring • Bulky equipment • Required inline sampling 26 Infrared Analysis Molecules absorb Infrared light if they are polyatomic and asymmetric A gas sample is sent through a band of infrared radiation (IR) to observe this interaction The fraction of radiation absorbed is measured within a gas mixture • Partial pressure of individual gases is then determined 27 Infrared Analysis IR beam emitted (via heated radiator) IR beam filtered IR beam passes through gas sample Detector receives IR and converts to electrical signal to be processed Detector usually consists of temperature regulated solid-state material, flexible wall diaphragm, & a crystal 28 Infrared Analysis Every gas absorbs radiation at a distinct wavelength Spectrophotometric Analysis Collision Broadening 29 Infrared Analysis Advantages: • • • • • Accurate real time multiple gas analysis Portable newer models can detect mixtures of [multiple] volatile anesthetics Disadvantages: • oxygen, nitrogen, helium not measured • Gases may have overlapping absorption bands • anesthetic gas measurement interference by water vapor (asymmetric) 30 Ramen Spectroscopy High-intensity electromagnetic beam (laser) interacts with gas molecules which results in alterations to wavelength frequency Detectors observe for these unique characteristics of scattered electromagnetic radiation Disadvantages: • Unable to measure monatomic gases (helium, xenon) • Require frequent calibration • Require higher volumes of sampling gas 31 Piezoelectric Gas Analysis Piezoelectric Crystals oscillate from application of an electrical current. Henry’s Law is applied by coating the crystal by surrounding it in a liquid layer Gas dissolves into the liquid The resonant frequency of the crystal is altered in proportion to the liquid saturation Unable to identify the gas sample 32 Capnography Standard anaesthesia practice requires the measurement of both Ventilation & Oxygenation Alveola CO2 is a byproduct of physiologic metabolism r arterial Exhaled CO2 reflects ventilation, pulmonary vasculature status, & aerobic metabolism 33 Capnography Time-based Capnograph: The graphic display that shows CO2 pressures over time Most commonly measured via Infrared Analysis Allows for interpretation of ventilation, Correct placement of airway device {Gold Standard}, anesthetic management, & patients aerobic state 34 Standard of Care Standard 6: Equipment Adhere to manufacturer’s operating instructions and other safety precautions to complete a daily anesthesia equipment check. Verify function of anesthesia equipment prior to each anesthetic. Operate equipment to minimize the risk of fire, explosion, electrical shock, and equipment malfunction. Standard 9: Monitoring & Alarms Monitor - evaluate, and document the patient’s physiologic condition as appropriate for the procedure and anesthetic technique. When a physiological monitoring device is used, variable pitch and threshold alarms are turned on and audible. Document blood pressure, heart rate, and respiration at least every five minutes for all anesthetics. a. Oxygenation - Continuously monitor oxygenation by clinical observation and pulse oximetry. The surgical or procedure team communicates and collaborates to mitigate the risk of fire. b. Ventilation - Continuously monitor ventilation by clinical observation and confirmation of continuous expired carbon dioxide during moderate sedation, deep sedation or general anesthesia. Verify intubation of the trachea or placement of other artificial airway device by auscultation, chest excursion, and confirmation of expired carbon dioxide. Use ventilatory monitors as indicated. 35 Gas Sampling Sidestream • Fixed volume of gas continuously sampled from circuit • Poor measurement if sampling rate exceeds expiratory flow rate • Remote from patient • Slower total response time Mainstream • Sensor in circuit • Close to ETT • Subject to interference • Adds weight to the circuit • Require frequent calibration • Increases dead space 36 Principles of Gas Analysis Measurement Timing 37 Arterial-Alveolar Gradient EtCO2 is used to infer PaCO2 • EtCO2 underestimates PaCO2 by 25mmHg due to presence of dead space • General anesthesia: underestimates 510mmHg Arterial-alveolar gradient • Factors that increase dead space will increase the gradient Decreased cardiac output Decreased perfusion of lung apices Smoking COPD Advanced age Pulmonary embolism 38 Waveform Analysis Phase 0 • Inspiratory phase Phase 1 • Exhalation of Dead space • Minimal to no CO2 Phase II • Mixture of alveolar and dead space gas • Expired CO2 is from the upper airways Phase III • Alveolar plateau • Corresponds to alveolar-pCO2 *Phase IV • End-tidal CO2 typically measured at this point 39 Waveform Analysis Phase 0 • Inspiratory phase Phase 1 • Exhalation of Dead space • Minimal to no CO2 Phase II • Mixture of alveolar and dead space gas • Expired CO2 is from the upper airways Phase III • Alveolar plateau • Corresponds to alveolar-pCO2 *Phase IV • End-tidal CO2 typically measured at this point 40 Waveform interpretation Increases EtCO2 Decreases EtCO2 Hypoventilation Hyperventilation Malignant hyperthermia Hypothermia Sepsis Low cardiac output Rebreathing CO2 Pulmonary embolism Administration of bicarbonate Accidental disconnect or tracheal extubation Insufflation of carbon dioxide during laparoscopy Cardiac arrest 41 Waveform interpretation 42 Waveform interpretation x2 43 EtCO2 Waveforms Norm al CO2 mmHg 35-40 ~ 25mm/secon d 44 Prolonged Expiratory Upstroke Asthma, Bronchospasm, COPD, partially obstructed ETT/circuit 45 Curare Cleft 46 Elevated Baseline incompetent expiratory valve, exhausted CO2 absorbent, insufficient gas flow 47 Clinical Applications 48 Additional Resources • Anesthesia Equipment: Principles and Applications. 3rd ed. Ehrenwerth, Eisenkraft, Berry. Chap 8. • Miller’s Anesthesia. 9th ed. Gropper, et al. Chap 41. • Narrative Review Article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3821265/ • Albuterol Explained: https://www.youtube.com/watch?v=a8tZUt54YAU 49
