Gas Analysis Technologies

Gas Analysis

• Gas analysis technologies employ various methods to quantify both organic and inorganic gases.
• Infrared Absorption Analysis relies on the ability of each volatile agent to absorb specific frequencies of electromagnetic radiation within the infrared spectrum.
• The amount of infrared absorption determines concentration.
• Raman Scattering Analysis uses a monochromatic laser beam through a polyatomic gas mixture to raise the vibration frequency of the excited gas molecules which can then be absorbed or experience a scattered-frequency change.
• Mass Spectrometry, a historically dominant technology, identifies gases based on the amount of deflection after ionizing gas molecules and passing them through a magnetic field.
• Piezoelectric Gas Analysis utilizes the piezoelectric effect and Henry's law to determine gas concentrations.
• A piezoelectric crystal vibrates at a specific frequency when current is applied.
• As gas dissolves into the liquid, in proportion to the liquid gas interphase concentration above the liquid the resonant frequency of the crystal is modified, but the agent is not identified.

Photoacoustic Gas Analysis

• A gas sample is exposed to a filtered, pulsating infrared light beam within a closed chamber.
• The pulsating beam increases and decreases the gas molecules, causing changes in temperature and chamber pressure based on Gay-Lussac's law.
• Microphones measure the resulting pressure wave.

Oxygen Analysis

• Electro-galvanic cell (fuel cell)
• Polarographic electrode (Clark electrode)
• Paramagnetic oxygen sensor
• Fluorescence quenching
• pH optode

Carbon Dioxide Analysis

• Infrared absorption analysis
• Severinghaus PCO2 electrode
• Fluorescence quenching
• pH optode

Oxygen Analysis Standards

• An oxygen analyzer should be placed in the breathing circuit, continuously monitoring the oxygen concentration the patient is receiving.
• Required as a standard of care.
• Devices are capable of detecting oxygen pipeline crossover and should trigger a high-priority alarm within 30 seconds if O2 falls below 18%.
• The three main types of oxygen analyzers are galvanic (fuel cell), polarographic (Clark), and paramagnetic, which is self-calibrating with a fast response time.

Oxygen Analysis: Fuel Cell

• Also called an electrogalvanic cell because the reaction creates its own electric current by consuming its “fuel”, calibrated daily.
• The electrogalvanic sensor has a gas permeable membrane but not liquid.
• At the anode electrons are liberated in an oxidative reaction.
• The current produced by the electrons consumed in the reaction at the cathode is measured by the meter.
• Electron flow between the anode and cathode is directly proportional to the partial pressure of oxygen in the sample gas.
• Electrogalvanic cells longevity is affected by the concentration and duration of oxygen exposures.

Oxygen Analysis: Clark Electrode

• Consists of a voltage source (battery) and a current meter connected between a platinum cathode and a silver anode, immersed in a potassium chloride electrolyte cell.
• A membrane permeable to oxygen, but not electrolyte covers one surface of the cell.
• A polarizing voltage is applied between the electrodes.
• At the silver anode, electrons are liberated by the oxidative reaction of silver with the chloride electrolyte.
• The consumption of electrons at the platinum cathode measures the current with the meter.
• Current flows in proportion to oxygen concentration.
• No electrode consumption occurs if no voltage is applied.

Oxygen Analysis: Paramagnetic

• The paramagnetic oxygen sensor uses oxygen molecules' unique attraction into magnetic fields.
• It has two nitrogen-filled bulbs attached together by a stem which resembles a dumbbell.
• Oxygen introduction into the sensor displaces the dumbbell apparatus out of the magnetic field as oxygen is attracted into the field, with the amount of displacement directly proportional to the concentration of oxygen.
• The sensors contain a small optical mirror reflecting a projected light beam.
• The light beam is reflected onto a photocell generating a small voltage that counteracts the dumbbell apparatus displacement.
• Increased oxygen concentration increases the displacement of the dumbbell apparatus, which in turn directs a greater amount of reflected light onto the photocell.

Oxygen Analysis: Paramagnetic Transducer

• A type of oxygen analyzer that shares the same unique attraction of oxygen molecules to a magnetic field.
• A transducer measures the pressure difference between a known gas and a sample gas.
• Variations measure pressure or flow alterations relative to the magnetic attraction of oxygen concentrations.

Oxygen Analysis: Fluorescence Quenching

• Fluorescence is caused by a molecule emitting light (photons) after being energized by an electric current or exposure to Electron Magnetic Resonance.
• Chemically-initiated and electrically initiated fluorescence occurs by energizing an electron to a higher energy level.
• The energized electron returns to its lower resting energy level and releases a photon, or a spontaneous emission, which is observed as light.
• The light’s color emitted represents the photons released frequency.
• Using oxygen's ability to suppress or quench certain molecules prevents them from fluorescing.
• Oxygen, if present, absorbs this photon and prevents its release, proportional to the emitted photons frequency.

Carbon Dioxide Analysis: Flourescence Quenching

• Fluorescence quenching technology can measure carbon dioxide.
• Carbon dioxide causes a pH change, which frees hydrogen ions to react with a quenching agent or a fluorescent dye in the sensor.
• The concentration of carbon dioxide is in proportional to measured change in fluorescence.

Carbon Dioxide Analysis: Colorimetric Carbon Dioxide Sensor

• A dry-state sensor undergoes a color change in the presence of carbon dioxide and is used to differentiate esophageal intubation from endotracheal intubation.
• The paper is impregnated with a fluorescent dye that fluoresces or changes color in the presence of carbon dioxide indicating presence, but not the quantity of carbon dioxide.

Carbon Dioxide Analysis: Severinghaus PCO2 Electrode

• An electrode frequently used in anesthesia for carbon dioxide analysis.
• The electrode uses a gas-permeable membrane and is immersed into a pH-sensitive electrode in a bicarbonate solution.
• Carbon dioxide diffuses into the sensor; it is converted into free hydrogen ions, generating an electric charge proportional to the carbon dioxide concentration.

Transcutaneous Carbon Dioxide Measurement

• Similar to pulse oximetry.
• Measures the Hydrogen ion change at the skin level.
• Helpful when patients have a ventilation-perfusion mismatch or obesity
• Transcutaneous measurements may more accurately estimate arterial Carbon Dioxide when compared to ETCO2.

Carbon Dioxide Absorption

• Carbon dioxide absorption facilitates rebreathing of exhalations and conserves agent, oxygen, nitrous oxide, and tracheal humidity, which prevents respiratory acidosis.
• Fresh gas flow dictates the amount of rebreathing within the circle system.
• Minute ventilation is increased by increasing tidal volume, respiratory rate, or both due to granule exhaustion and may be ineffective with an exhausted absorbent as the patient inspires a gas mixture from which Carbon Dioxide has been inadequately absorbed.
• Desiccated soda lime is devoid of water, and agent degradation can be very dangerous.
• Potassium hydroxide is the biggest offender.
• Soda lime degrades current inhalation agents with sevoflurane degraded most and desflurane least.
• Low flows of fresh gas, high gas concentrations, high absorbent temperatures, and dry absorbents lead to more degradation.
• The presence of compound A causes renal dysfunction.
• The compound A issue is worse with sevoflurane, high concentrations of gas, prolonged usage, and low flows and are more likely to be an issue if used for more than two hours.
• Formation of CO is worse with Desflurane than Isoflurane and is minimized with low flow to preserve humidity.

Carbon Dioxide Absorption Recommendations

• The product insert does not recommend sevoflurane at total fresh gas flows of less than 1 to 2 L/min for more than 2 MAC hours.
• It is recommended that oxygen be turned off at the end of each case, and that absorbents are changed regularly. This is particularly important when fresh gas flow is left on over the weekend or overnight, and low flows used to keep granules moist.
• Amsorb Plus and Litholyme do not degrade inhaled anesthetics.
• Replace when 50-70% of absorbent has changed color.
• If exhausted during the case increase fresh gas flow.
• DO NOT just increase minute ventilation.

Carbon Dioxide Absorption Processes

• lonic reactions occur on the granules surfaces in an aqueous medium.
• A 10%-20% water content is appropriate depending on formulation.
• 1 mole of CO2 absorption produces 13,000 kcal of heat energy.
• Calcium hydroxide is the main component, where 50% of the canister volume is actually air.
• The contents are usually 80% Ca(OH)2; 15% H2O; 4% NaOH; 1% KOH.
• It’s best to limit Sodium Hydroxide and omit Potassium Hydroxide.
• Small amounts of silica increase hardness and reduce dust.
• Granule size should be 4-8 mesh, representing a compromise between absorptive capacity and resistance to air flow.
• Channeling is when gas flows through low resistance pathways causing a bad situation.
• The optimal size provides adequate surface/absorptive capacity and resistance to air flow while minimizing channeling.
• The effectiveness of small granules is dependent on surface area while the effectiveness of large granules is dependent on airflow resistance.

Carbon Dioxide Absorption Features

• The absorbent must neutralize an acid and allow for anesthetic gas conservation including humidity.
• CO can have ionic reactions in Soda Lime with activators like Sodium Hydroxide and Potassium Hydroxide added to increase reaction.
• Activators are also combined with carbonate ions in a reversible reaction which produce water and energy,
• Ethyl violet indicates absorbent pH and changes to blue-purple at a pH of 10.3.

Soda Lime and Amsobr

• Soda Lime contains water, calcium hydroxide, sodium, and potassium hydroxide.
• Fragments are easily produced along with dust which can lead to bronchospasm.
• Silica is used to add hardness to minimize dust formation.
• Alkaline bases are the end products that are corrosive if reaching the skin.
• Absorption for Soda Lime runs 23 liters of CO2 per 100 grams of absorbent.
• Amsorb Plus contains water, calcium hydroxide, and calcium chloride humectant which aids in moisture retention and excludes string bases.
• The addition of calcium sulfate and polyvinylpyrrolidone increases hardness.
• Absorption occurs at a rate of 10.2 liters of CO2 per 100 grams of absorbent.

Alternative Absorbents

• Litholyme is a new generation Co2 absorbent utilizing lithium as a catalyst that is similar to Amsorb Plus.
• Since it lacks a color indicator, it can may only be used with capnography monitoring.
• Spirolith uses Lithium hydroxide rather than Calcium Hydroxide doesn’t degrade volatile agents or desiccation effects.

Impending Exhaustion

• Exhaustion is noted with increased partial pressure of end-tidal carbon dioxide, may be accompanied by an increase in inspired carbon dioxide, and can lead to respiratory acidosis and hyperventilation.
• Signs of sympathetic nervous system activation include a flushed appearance, cardiac irregularities and sweating.
• Late signs include increased then later decreased heart rate, blood pressure and dysrhythmia.

Thermodynamics

• First Law | Law of conservation of energy= Energy cannot be created or destroyed.
  • The increase in the internal energy of a thermodynamic system is equal to the amount of heat energy added to the system minus the work done by the system on the surroundings.
• Second Law | Energy moves toward greater entropy or randomness=
  • The entropy of an isolated system not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.
• Third Law | Absolute zero (0 ° K or – 273.15 °C/-460 ° F) is void of all energy:
  • Absolute zero is theoretical.
• Entropy implies imbalance and moves from high concentrations of energy to low and ends when all energy is equally distributed. Entropy is the universal trend toward equilibration.
  • It drives everything from ice melting to gas expansion and proposes relationships for sleep and general anesthesia.
• Energy can be defined as the exertion of kinetic force or the capacity of potential to do work.
• A joule is the unit of measurement for energy, and a single joule is described as the force of 1 N that moves its point of application one meter.
• Two energy types: potential and kinetic.
• The kinetic molecular theory builds on Newtonian physics and thermodynamics relating to molecular movement/energy and forces between these molecules.

Temperature Metrics & Principles

• Matter may change form when adding heat energy and varies with the measurement of thermal state
• Units for measurement:
  • Celsius to Kelvin: K = C + 273
  • Celsius to Fahrenheit: °F = 1.8(°C) + 32
  • Fahrenheit to Celsius: °C = (°F – 32)/1.8
• Concepts:
  • Heat is thermal energy; temperature the quantitative measurement of that energy - using a standard temperature of 273.15 K (0 °C).
  • All heat loss/energy loss from a system is inherently unidirectional.

Redistribution

• Redistribution of heat loss is driven by vasoconstriction and increased redistribution due to vasodilating anesthetics.
  • A patients core temperature can still drop quickly due to vasodilating actions of anesthetics. Loss of temperature occurs primarily in the first hour, when vasoconstriction has decreased and vasodilation begins after anesthetic is administered.
• General hypothermia occurs when below 36 degrees C or 96.8 degrees.
• Heat loss from a body's surface generally increases:
  • Radiation from electromagnetic wavelength infrared transfer.
  • Convection with currents.
  • Conduction with direct touch to something cold.
  • Evaporation of moisture from patients skin or exhaled gases.

Atmospheric Values

• Atmospheric pressure: the cumulative effect of gravity on atmospheric gases.
• The greater the altitude is equivalent to less atmospheric gasses.
• Standard pressure = 100 kPa/kilopascal - measurement and is gravitational force on gases in a set area.
• Memorize these conversions:
  • 1 torr = 1 mmHg
  • 1 kPa = 10.2 cm H2O = 7.5 mmHg
  • 1 atm (atmosphere) = 760 mmHg = 760 torr = 1 bar = 100 kPa = 1020 cm H2O = 14.7 lb./ in2
• Bourdon gauges are often used in anesthesia to measure high pressures, such as in gas cylinders, and zero referenced to atmospheric pressure.

Vaporization Overview

• Vaporization is the process of converting a liquid to a vapor state.
• Vaporization requires energy and evaporation is the name of the process specific to liquids.
• The volatility of a substance is influenced by its temperature and vapor pressure.
• Vapor pressure and boiling points are inversely related.
  • The temperature of a liquid will not rise above its boiling point.
• Vapor pressures are volatile anesthetics under standard conditions =
  • Isoflurane = 238-240mmHg
  • Sevoflurane = 160-170mmHg
  • Desflurane = 660-669mmHg

Vaporization Principles

• Vaporizers must be calibrated for each specific agent or the patient may not be adequately sedated.
• If a high vapor pressure is in a low calibrated vaporizer, more drug will be dispensed.
• If a high calibrated vaporizer contains a low vapor pressure anesthetic, there will be too much drug.
• Vapor rate: three factors
  • Vapor pressure
  • Partial pressure of vapor
  • Temperature Atmospheric pressure and boiling points are influenced by altitude.

Vapor Pressure as Functional Properties

• The function of temperature and not pressure in a closed space with vapor liquid at the rate of vaporization and condensation meet equilibrium.
• Higher VP means faster evaporation.
• Inverse relationship of intermolecular forces relates to vapor pressure and the energies needed to overcome molecular structure, the lower the pressure of the liquid. Water having a lower vapor pressure represents a liquid state bound more tightly, while the heat of vaporization is equal to the energy needed to change them.
• The latent heat of vaporization represents the number of calories needed to change a gram.
• VP of the liquid determines mole fraction to a max standard:
  • Oxygen and an anesthetic gas will mix in closed space.
  • Composition of the flow is dependent on temperatures and vaporizer.
• Doses depend of oxygen with what is possible in energetics instead of therapeutics. Dalton’s law of partial pressures = Pt = P1 + P2 + P3 etc. times atmospheric % and pressure at sea level.

Humidity Parameters

• Absolute = mass of water vs volume, but relative = ration of max water at saturated vapor.
• 100% equals concentration in water solubility.
  • Solubility increases while temperature remains constant and decreases when saturated vapor changes.
• Breathing is quickly humidified 100% when breathing by nasal passages.
• High fresh gas can bypass upper passageways; dry gases decrease 10% when breathing in room temperatures.
• Boiling point increases with intermolecular forces or the relationship between boiling and altitude increases related to atmospheric level

Important Properties

• Molar enthalpy of fusion (∆Η°fus) needs heat to convert a mole from liquid to normal melt point.
• Molar enthalpy of vaporization (ΔΗ°vap) with heat to normal boiling.
• With higher energy you can now overcome to stick to molecules.
• Water heat of vaporization is much greater from fluid vs H2O fusion/heat transfer is much higher in the system/environment around the container.
• Evaporation causes a cooling while endothermic with cooling absorbed by heat as a steamer.
• Lines equilibrium crossing will alter state, pressure vs temperature with all 3 meeting where solid-liquid point is, with low alteration due to liquid or solids from low pressure.
• Liquid is boiling where all points line to equal atmosphere with limited liquefied temperature of gas but N2O (36.45) and liquid.
• Pressure meets at 750 psi with all gas exhausted (Volume at 400).

Joule & Thompson

• Isothermal alterations of change in volume with temperature will not have an impact if closed.
• Rapid expansion = process adiabatically has no affect.
• Effects = frost, nitrous and flows through.

Vaporizers

• Anesthetic liquids exert vapor pressure and both exist but are cooled with fresh gas and must be compensated:
  • Metals for high temperature, valves or modulated temperature. Desflurane= vapor at atmospheric pressure at 20C and must be heated. at 39 degrees in 2 atm and pure gas through no gas of flow.

Desflurane Considerations

• Desflurane releases gas at altitudes which needs to be dialed at a higher standard.
• Elevation will still affect the body which sevo + iso can compensate.
• Cylinder with gas at N20 releases a liquid and heat with Joule (latently changes).
• Temperature decreases as the gas is moderately on with 1590 cylinder volume; with O2 needs 1.9 L cylinder level in normal heat .
  • But the heat will be lost and pressure flow will decrease as more pressure to O2 usage to maintain what is needed.
• And that O2 is at C with liters contained.
  • Problem of volume and time and when some used it .
    • Volume or low will affect average. -KE is related to temperature in all cases, the faster to heat, it must be the same, M, KE. kinetic are in constant movement. kinetic in the molecule theory fails related to higher rate.