Anesthesia and Vapor Principles
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Questions and Answers

What is the primary function of an anesthesia vaporizer?

  • To measure vapor pressure
  • To convert liquid anesthetic agents into their vapor form (correct)
  • To create a Torricellian vacuum
  • To control the temperature of the patient's breathing circuit

    • What happens to vapor pressure when the temperature is increased?

  • It remains constant
  • It becomes saturated
  • It decreases
  • It increases (correct)

    • What is the term for the maximum vapor pressure at a given temperature when the gas phase is saturated?

  • Saturated vapor pressure (correct)
  • Vapor pressure
  • Critical temperature
  • Liquid-vapor equilibrium

    • What is the principle behind the measurement of atmospheric pressure using a column of mercury?

    <p>Barometer principle</p> Signup and view all the answers

    What occurs when a volatile liquid is introduced into a Torricellian vacuum?

    <p>The liquid evaporates and exerts vapor pressure</p> Signup and view all the answers

    In a closed container, what is the relationship between the liquid and vapor phases of a substance?

    <p>The liquid and vapor phases are in equilibrium</p> Signup and view all the answers

    What is the effect of increasing temperature on the vapor pressure of a substance?

    <p>Vapor pressure increases due to increased evaporation</p> Signup and view all the answers

    What has occured when a liquid volitile agent begins to accumulate above the mercury in a Torricellian

    <p>The vapor pressure reached its maximum</p> Signup and view all the answers

    What is the relationship between temperature and saturated vapor pressure?

    <p>SVP increases with increasing temperature</p> Signup and view all the answers

    As altitude increases, what happens to the boiling point of an anesthetic agent?

    <p>It decreases due to decreased atmospheric pressure</p> Signup and view all the answers

    What is the unit of measurement that directly measures the pressure exerted by the anesthetic vapor itself?

    <p>Millimeters of mercury (mm Hg) or kilopascals (kPa)</p> Signup and view all the answers

    How is the volumes percent of an anesthetic calculated?

    <p>Partial pressure from vapor divided by total ambient pressure, then multiplied by 100%</p> Signup and view all the answers

    What is the characteristic of an anesthetic agent with a higher saturated vapor pressure at room temperature?

    <p>It is more volatile and has a lower boiling point</p> Signup and view all the answers

    Why are both methods of measurement (absolute terms and volume percent) useful in anesthetic practice?

    <p>Because they provide different but complementary information about the anesthetic vapor</p> Signup and view all the answers

    What is the relationship between the saturated vapor pressure of an anesthetic agent and its boiling point?

    <p>The boiling point is the temperature at which the SVP equals atmospheric pressure</p> Signup and view all the answers

    What is the purpose of knowing the SVP of an anesthetic agent?

    <p>To determine its volatility</p> Signup and view all the answers

    What is the primary reason why an anesthetic agent with a higher saturated vapor pressure at room temperature is more volatile?

    <p>It has a lower boiling point at atmospheric pressure.</p> Signup and view all the answers

    If the partial pressure of an anesthetic gas is 80 mmHg and the total pressure is 600 mmHg, what is the volume percentage of the anesthetic gas?

    <p>13.33%</p> Signup and view all the answers

    Why is it important to consider the effects of altitude on the boiling point of an anesthetic agent?

    <p>To adjust the concentration of the anesthetic agent in the gas mixture.</p> Signup and view all the answers

    What is the advantage of using absolute terms (mmHg or kPa) to measure vapor concentration?

    <p>It provides a more accurate measurement of the partial pressure of the anesthetic gas.</p> Signup and view all the answers

    Why is it necessary to consider both absolute terms and volume percentages when measuring vapor concentration?

    <p>To provide a more comprehensive understanding of the anesthetic gas mixture.</p> Signup and view all the answers

    What is the relationship between the saturated vapor pressure of an anesthetic agent and its boiling point at atmospheric pressure?

    <p>The boiling point decreases as the saturated vapor pressure increases.</p> Signup and view all the answers

    What is the primary advantage of expressing anesthetic potency in terms of partial pressure (mmHg) rather than volume percentage?

    <p>It allows for a more direct measurement of the concentration of anesthetic in the central nervous system</p> Signup and view all the answers

    What is the relationship between the MAC and PMAC of an anesthetic agent?

    <p>PMAC is calculated by multiplying MAC by the atmospheric pressure</p> Signup and view all the answers

    Which of the following anesthetic agents has the highest PMAC?

    <p>Desflurane</p> Signup and view all the answers

    What is the MAC of Isoflurane in volume percentage?

    <p>1.15%</p> Signup and view all the answers

    What is the relationship between the boiling point of an anesthetic agent and its saturated vapor pressure?

    <p>They are inversely proportional</p> Signup and view all the answers

    What is the primary reason why an anesthetic agent with a lower boiling point at atm pressure is more volatile?

    <p>It has a lower SVP</p> Signup and view all the answers

    What is the primary advantage of using PMAC over MAC in measuring anesthetic potency?

    <p>It directly reflects the concentration of anesthetic in the central nervous system</p> Signup and view all the answers

    Which of the following anesthetic agents has the highest saturated vapor concentration at room temperature?

    <p>Desflurane</p> Signup and view all the answers

    What is the PMAC of Sevoflurane in mmHg?

    <p>16mmHg</p> Signup and view all the answers

    What is the MAC of Desflurane in volume percentage?

    <p>6-7.25%</p> Signup and view all the answers

    What is the saturated vapor pressure of Isoflurane at room temperature?

    <p>238mmHg</p> Signup and view all the answers

    What is the boiling point of Sevoflurane?

    <p>58.5C</p> Signup and view all the answers

    What is the minimum alveolar concentration (MAC) of Desflurane?

    <p>6-7.25%</p> Signup and view all the answers

    What is the partial pressure of minimum alveolar concentration (PMAC) of Isoflurane?

    <p>8.7mmHg</p> Signup and view all the answers

    What is the relationship between the saturated vapor pressure and boiling point of an anesthetic agent?

    <p>As the boiling point increases, the saturated vapor pressure increases</p> Signup and view all the answers

    What is the approximate saturated vapor pressure of Sevoflurane at room temperature?

    <p>160mmHg</p> Signup and view all the answers

    What is the boiling point of Desflurane?

    <p>22.8C</p> Signup and view all the answers

    Which of the following anesthetic agents has the lowest saturated vapor concentration at room temperature?

    <p>Sevoflurane</p> Signup and view all the answers

    What is the relationship between the boiling point of an anesthetic agent and its volatility?

    <p>Anesthetic agents with a lower boiling point are more volatile</p> Signup and view all the answers

    What is the approximate saturated vapor pressure of Desflurane at room temperature?

    <p>664mmHg</p> Signup and view all the answers

    What is the relationship between the MAC and PMAC of an anesthetic agent?

    <p>PMAC is equal to MAC multiplied by atmospheric pressure</p> Signup and view all the answers

    Which of the following anesthetic agents has the highest saturated vapor concentration at room temperature?

    <p>Desflurane</p> Signup and view all the answers

    What is the approximate boiling point of Isoflurane?

    <p>48.5C</p> Signup and view all the answers

    What is the partial pressure of minimum alveolar concentration (PMAC) of Sevoflurane?

    <p>16mmHg</p> Signup and view all the answers

    Which of the following is a characteristic of an anesthetic agent with a lower boiling point?

    <p>Higher saturated vapor pressure</p> Signup and view all the answers

    What is the relationship between the MAC and PMAC of an anesthetic agent?

    <p>MAC is equal to PMAC divided by atmospheric pressure</p> Signup and view all the answers

    Which of the following anesthetic agents has the highest saturated vapor concentration at room temperature?

    <p>Desflurane</p> Signup and view all the answers

    What is the approximate PMAC of an anesthetic agent with a MAC of 1.5% and atmospheric pressure of 760 mmHg?

    <p>11.7 mmHg</p> Signup and view all the answers

    What is the primary function of materials with high specific heat and thermal conductivity in vaporizer construction?

    <p>To maintain stable temperatures and consistent anesthetic output despite heat loss during vaporization</p> Signup and view all the answers

    What happens to the temperature of the remaining liquid and its surroundings during vaporization?

    <p>It declines</p> Signup and view all the answers

    Why are the saturated vapor concentrations of anesthetic agents at room temperature too potent to be used clinically?

    <p>Because they require dilution by a bypass gas flow to be safe and useful</p> Signup and view all the answers

    What is the purpose of regulating vaporizer output in anesthesia?

    <p>To provide a safe and useful concentration of anesthetic agent to the patient's breathing circuit</p> Signup and view all the answers

    What is the relationship between the latent heat of vaporization and the energy required to convert a unit mass of liquid into vapor?

    <p>The latent heat of vaporization is the energy required to convert a unit mass of liquid into vapor</p> Signup and view all the answers

    Why is copper considered the best material for vaporizer construction?

    <p>Because it has high specific heat and thermal conductivity</p> Signup and view all the answers

    What is the effect of heat loss during vaporization on the output of vapor?

    <p>It decreases the output of vapor unless compensated for</p> Signup and view all the answers

    What is the purpose of the bypass gas flow in regulating vaporizer output?

    <p>To dilute the saturated vapor to a safe and useful concentration</p> Signup and view all the answers

    What is the primary reason why the temperature of the liquid declines during vaporization?

    <p>The heat energy is transferred from the surroundings to the vapor.</p> Signup and view all the answers

    Which of the following materials is the best for constructing a vaporizer due to its high specific heat and thermal conductivity?

    <p>Copper</p> Signup and view all the answers

    What is the purpose of the bypass gas flow in a vaporizer?

    <p>To dilute the saturated vapor to a safe and useful concentration</p> Signup and view all the answers

    What happens to the vapor pressure when the liquid agent is converted to vapor?

    <p>It decreases</p> Signup and view all the answers

    What is the significance of the specific heat of a material in a vaporizer?

    <p>It determines the amount of heat required to raise the temperature of the material</p> Signup and view all the answers

    What is the primary purpose of using materials with high thermal conductivity in a vaporizer?

    <p>To allow for efficient heat transfer from the environment to the vaporizing liquid</p> Signup and view all the answers

    What is the primary function of the bypass gas flow in a vaporizer?

    <p>To dilute the saturated vapor to a safe and useful concentration</p> Signup and view all the answers

    Why are materials with high specific heat and thermal conductivity ideal for vaporizer construction?

    <p>They can efficiently transfer heat from the environment to the vaporizing liquid</p> Signup and view all the answers

    What is the result of the vaporizer creating a saturated vapor in equilibrium with the liquid agent and then diluting it with a bypass gas flow?

    <p>A safe and useful concentration of anesthetic agent</p> Signup and view all the answers

    What is the purpose of the specific heat of a material in a vaporizer?

    <p>To resist temperature changes and act as a thermal buffer</p> Signup and view all the answers

    What is the relationship between the latent heat of vaporization and the temperature of the liquid agent?

    <p>As the temperature of the liquid agent increases, the latent heat of vaporization decreases</p> Signup and view all the answers

    What is the effect of the vaporizer creating a saturated vapor in equilibrium with the liquid agent?

    <p>The vapor concentration becomes too potent to be used clinically</p> Signup and view all the answers

    What is the primary difference between measured flow vaporizers and regulating vaporizer output?

    <p>The requirement of complex calculations</p> Signup and view all the answers

    In a variable bypass vaporizer, what is the purpose of the bypass pathway?

    <p>To direct the remaining gas flow that isn't sent through the vaporizer.</p> Signup and view all the answers

    What is the purpose of the wicks and baffles in a flow-over vaporizer?

    <p>To increase the surface area for vaporization</p> Signup and view all the answers

    What is the primary difference between flow-over vaporizers and bubble-through vaporizers?

    <p>The method of vaporization</p> Signup and view all the answers

    What is the primary advantage of using a variable bypass vaporizer

    <p>Increased accuracy of anesthetic concentration</p> Signup and view all the answers

    What is the purpose of a large surface area in a vaporizing chamber?

    <p>To allow for efficient vaporization</p> Signup and view all the answers

    which is not a difference between flow-over and bubble-through vaporizers?

    <p>The design of the vaporizing chamber</p> Signup and view all the answers

    What is the purpose of the bypass pathway in a variable bypass vaporizer?

    <p>To facilitate the mixing of saturated vapor and bypass gas</p> Signup and view all the answers

    What is the primary advantage of variable bypass vaporizers over measured flow vaporizers?

    <p>They do not require calculations to determine anesthetic concentration</p> Signup and view all the answers

    If the SVP concentration is 30% and the carrier gas percentage is 70%, what is the proportion of the chamber's atmosphere occupied by the anesthetic vapor?

    <p>30%</p> Signup and view all the answers

    What percentage of the chamber's atmosphere is occupied by the carrier gas for Sevoflurane at standard conditions?

    <p>21%</p> Signup and view all the answers

    What is the volume of anesthetic vapor that needs to be evolved per minute to deliver 1% Isoflurane to the breathing circuit at a total gas flow rate of 5 L/min?

    <p>50 mL/min</p> Signup and view all the answers

    What is the total flow rate that must be delivered to create a 1% Isoflurane mixture?

    <p>5,161 mL/min</p> Signup and view all the answers

    What is a major problem associated with Measured Flow Vaporizers?

    <p>All of the above</p> Signup and view all the answers

    Why is it necessary to have an anesthetic agent analyzer with high- and low-concentration alarms when using Measured Flow Vaporizers?

    <p>To prevent overdose</p> Signup and view all the answers

    What happens if fresh gas is not turned on with the measured flow to the vaporizer?

    <p>The patient will receive a lethal dose of the anesthetic agent</p> Signup and view all the answers

    What is the percentage of Isoflurane in the vaporizing chamber?

    <p>31%</p> Signup and view all the answers

    What is the volume of carrier gas required to deliver 1% Isoflurane to the breathing circuit at a total gas flow rate of 5 L/min?

    <p>111 mL/min</p> Signup and view all the answers

    If 50 mL of Isoflurane represents 31% of the ATM, what is the total volume emerging from the vaporizer?

    <p>161 mL/min</p> Signup and view all the answers

    What is the minimum additional flow required to create a 1% Isoflurane mixture at a total gas flow rate of 5 L/min?

    <p>4,839 mL/min</p> Signup and view all the answers

    What is the percentage of the chamber's atmosphere occupied by the carrier gas for Sevoflurane at standard conditions?

    <p>79%</p> Signup and view all the answers

    What is the formula to calculate the volume of exiting anesthetic vapor in a measured flow vaporizer?

    <p>Total volume/carrier gas % X SVP concentration %</p> Signup and view all the answers

    What is the primary purpose of a measured flow vaporizer?

    <p>To deliver a precise concentration of anesthetic vapor</p> Signup and view all the answers

    What is a significant disadvantage of Measured Flow Vaporizers?

    <p>They require inconvenient calculations and are prone to user error</p> Signup and view all the answers

    What is the primary purpose of the bypass in a Variable Bypass vaporizer?

    <p>To divide the total gas flow into two parts</p> Signup and view all the answers

    How is the total flow exiting a vaporizer calculated?

    <p>Volume of anesthetic gas / Saturated vapor concentration</p> Signup and view all the answers

    What is the required Carrier Gas Volume in a vaporizer?

    <p>Total exiting gas volume - anesthetic volume</p> Signup and view all the answers

    What is the inflow splitting ratio in the example of a Sevoflurane vaporizer set to deliver 1% Sevo with 2000ml bypass gas?

    <p>25:1</p> Signup and view all the answers

    What is the result of a 1% Sevo concentration with an inflow splitting ratio of 25:1?

    <p>100 mL gas exits, with 21 mL Sevo and 79 mL carrier gas</p> Signup and view all the answers

    What is the formula for calculating the volume of agent in a vaporizer?

    <p>FGF rate x Desired concentration of anesthetic gas</p> Signup and view all the answers

    What is the purpose of the anesthetic agent analyzer with high- and low-concentration alarms in Measured Flow Vaporizers?

    <p>To monitor the anesthetic agent concentration</p> Signup and view all the answers

    What is the inflow gas splitting ratio for 2% Sevoflurane?

    <p>12:1</p> Signup and view all the answers

    What is the outflow gas splitting ratio for 3% Isoflurane?

    <p>9.33:1</p> Signup and view all the answers

    What is the inflow gas splitting ratio for 1% Isoflurane?

    <p>44:1</p> Signup and view all the answers

    What is the outflow gas splitting ratio for 4% Sevoflurane?

    <p>4.25:1</p> Signup and view all the answers

    What is the inflow gas splitting ratio for 3% Sevoflurane?

    <p>7:1</p> Signup and view all the answers

    What is the outflow gas splitting ratio for 2% Sevoflurane?

    <p>9.5:1</p> Signup and view all the answers

    What is the inflow gas splitting ratio for 3% Isoflurane?

    <p>14:1</p> Signup and view all the answers

    What is the outflow gas splitting ratio for 1% Isoflurane?

    <p>30:1</p> Signup and view all the answers

    What is the inflow gas splitting ratio for 2% Sevoflurane?

    <p>12:1</p> Signup and view all the answers

    What is the outflow gas splitting ratio for 4% Isoflurane?

    <p>6.75:1</p> Signup and view all the answers

    What happens when a low SVP vaporizer is filled with a high SVP agent?

    <p>The output concentration will be higher than indicated on the dial.</p> Signup and view all the answers

    What is not a limitation of temperature compensation in contemporary variable bypass vaporizers?

    <p>The output concentration accuracy is limited to a specific temperature range.</p> Signup and view all the answers

    What is the purpose of a thermometer in measured flow vaporizers?

    <p>To measure the liquid agent temperature and reference vapor pressure curves.</p> Signup and view all the answers

    Why is it essential to use agent-specific filling mechanisms in vaporizers?

    <p>To prevent misfilling and ensure accurate output concentrations.</p> Signup and view all the answers

    What is a primary advantage of contemporary variable bypass vaporizers?

    <p>They automatically adjust for changes in temperature.</p> Signup and view all the answers

    What occurs when a high SVP vaporizer is filled with a low SVP agent?

    <p>The output concentration will be lower than indicated on the dial.</p> Signup and view all the answers

    Why do modern vaporizers take time to adjust for temperature changes?

    <p>Because the compensation times are dependent on the temperature-sensitive valves.</p> Signup and view all the answers

    What is the likely outcome if a halothane vaporizer is filled with isoflurane?

    <p>The total MAC output will be close to the intended value.</p> Signup and view all the answers

    What is the correct formula to calculate the concentration for a misfilled vaporizer?

    <p>C' = C * (SVP_B / SVP_A)</p> Signup and view all the answers

    What is the consequence of mixing halothane, enflurane, and isoflurane in a vaporizer?

    <p>The agents will affect each other's vaporization, but not react chemically.</p> Signup and view all the answers

    What should be done if a vaporizer is suspected to be misfilled?

    <p>Empty the vaporizer, remove it from service, label it as misfilled, and return it to the manufacturer.</p> Signup and view all the answers

    What is the effect of halothane on the vaporization of enflurane and isoflurane?

    <p>Halothane makes enflurane and isoflurane vaporize more easily.</p> Signup and view all the answers

    What is the clinical impact of mixing anesthetic agents in a vaporizer?

    <p>The clinical impact depends on the potencies and delivered concentrations of the agents.</p> Signup and view all the answers

    What is the consequence of mixing halothane with enflurane in a vaporizer?

    <p>Halothane increases the vaporization of enflurane</p> Signup and view all the answers

    What is the consequence of filling an enflurane vaporizer with halothane?

    <p>The total MAC output is more than three times higher than intended</p> Signup and view all the answers

    What is the clinical impact of mixed agents?

    <p>It is unpredictable and can lead to errors in delivered vapor concentration</p> Signup and view all the answers

    What is the reason for the difficulty in predicting vaporizer output when mixing agents?

    <p>The agents affect each other's vaporization</p> Signup and view all the answers

    What is the primary reason for avoiding overfilling of vaporizers?

    <p>To prevent liquid agent from entering the gas delivery system</p> Signup and view all the answers

    What is the recommended procedure if a vaporizer is tilted?

    <p>Purge the vaporizer with high oxygen flow from the anesthesia machine's flowmeter</p> Signup and view all the answers

    What is the approximate volume of vapor produced by 1 mL of liquid agent?

    <p>200 mL</p> Signup and view all the answers

    Why is it important to confirm the efficacy of the flush before returning a vaporizer to clinical use?

    <p>To ensure the vaporizer is free of any residual anesthesia agent</p> Signup and view all the answers

    What should be done if a vaporizer is found to be contaminated with liquid agent?

    <p>Withdraw the workstation from use until authorized service personnel deem it safe</p> Signup and view all the answers

    What happens to the vapor output when nitrous oxide is introduced in a vaporizer?

    <p>It initially decreases</p> Signup and view all the answers

    How are Measured Flow Vaporizers affected by carrier gas composition?

    <p>They are not affected at all</p> Signup and view all the answers

    What happens to the vapor output when nitrous oxide is discontinued?

    <p>It temporarily increases</p> Signup and view all the answers

    What is the primary reason why the MAC of sevoflurane remains essentially unchanged despite the increase in volume percentage under hypobaric conditions?

    <p>Because the potency of sevoflurane is determined by its partial pressure, not volume percent.</p> Signup and view all the answers

    What happens to the volume percentage of sevoflurane when used under hypobaric conditions, compared to sea level?

    <p>It increases.</p> Signup and view all the answers

    What is the primary advantage of quantifying anesthetic potency in terms of partial pressure (mmHg) rather than volume percentage?

    <p>It is more accurate in hypobaric conditions.</p> Signup and view all the answers

    Why is it important to consider the effects of altitude on the vaporizer output concentration?

    <p>Because the volume percentage of anesthetic agents changes with altitude.</p> Signup and view all the answers

    What is the relationship between the volume percentage and partial pressure of an anesthetic agent in hypobaric conditions?

    <p>The volume percentage increases, while the partial pressure remains the same.</p> Signup and view all the answers

    What is the primary reason why sevoflurane vaporizers can be used in hypobaric conditions?

    <p>Because the vaporizer output concentration is independent of the barometric pressure.</p> Signup and view all the answers

    What is the primary function of an interlock device in an anesthesia manifold?

    <p>To prevent concurrent use of multiple vaporizers</p> Signup and view all the answers

    What is the effect of high concentrations and flows on the output of a contemporary vaporizer?

    <p>The output is slightly lower than the dial setting</p> Signup and view all the answers

    What is the approximate formula for liquid agent consumption per hour?

    <p>3 x Dial setting (vol%) x FGF (L/min)</p> Signup and view all the answers

    What is the primary factor that affects the liquid agent consumption per hour?

    <p>Vaporizer dial setting</p> Signup and view all the answers

    What is the purpose of knowing the relationship between the fresh gas flow rate and the vaporizer output?

    <p>To calculate the liquid agent consumption</p> Signup and view all the answers

    What is the primary purpose of an interlock device in an anesthesia manifold?

    <p>To prevent contamination of multiple vaporizers</p> Signup and view all the answers

    What is the effect of high concentrations and flows on vaporizer output?

    <p>Output may be slightly lower than the dial setting</p> Signup and view all the answers

    What is the pumping effect due to in older vaporizers?

    <p>Increased output due to pressurization and subsequent pressure drop</p> Signup and view all the answers

    How do modern vaporizers mitigate the pumping effect?

    <p>Design features that minimize the pumping effect</p> Signup and view all the answers

    What is the effect of fluctuating back pressure on vaporizer output?

    <p>Output increases due to the pumping effect</p> Signup and view all the answers

    What is the relationship between fresh gas flow rate and vaporizer output in contemporary vaporizers?

    <p>Output is independent of the flow rate within normal clinical range</p> Signup and view all the answers

    What is the key takeaway regarding vaporizer output in high concentrations and flows?

    <p>Output may be slightly lower than the dial setting due to incomplete evaporation</p> Signup and view all the answers

    What is the primary function of an interlock device in anesthesia?

    <p>To prevent contamination of multiple vaporizers</p> Signup and view all the answers

    What affects the liquid agent consumption in vaporizers?

    <p>Both the fresh gas flow rate and vaporizer dial setting</p> Signup and view all the answers

    What can occur in older vaporizers due to fluctuating back pressure?

    <p>Increased output</p> Signup and view all the answers

    What is a key takeaway regarding vaporizer output?

    <p>Output is generally stable, but may be slightly lower at high concentrations and flows</p> Signup and view all the answers

    What is a contributing factor to the pumping effect in older vaporizers?

    <p>Low flow rates</p> Signup and view all the answers

    How do modern vaporizers mitigate the pumping effect?

    <p>Through design features that minimize the effect</p> Signup and view all the answers

    What is a feature of the Dräger Vapor 19.n that prevents the pumping effect?

    <p>Spiraled intake tube in the vapor chamber</p> Signup and view all the answers

    What is not affected by the Dräger Vapor 19.n?

    <p>Barometric pressure</p> Signup and view all the answers

    What does the Dräger Vapor 19.n include for temperature regulation?

    <p>A temperature compensating device</p> Signup and view all the answers

    What is the purpose of the spiraled intake tube in the Dräger Vapor 19.n?

    <p>To prevent the pumping effect</p> Signup and view all the answers

    What is a feature of the Dräger Vapor 2000 that allows for easy removal and transportation?

    <p>Transport mode that isolates the sump from the rest of the vaporizer</p> Signup and view all the answers

    What is a difference between the Dräger Vapor 2000 and 3000?

    <p>The Vapor 3000 has integrated illumination for control dial and agent level indicators</p> Signup and view all the answers

    What is a benefit of the spill-proof design of the Dräger Vapor 2000?

    <p>It prevents liquid anesthetic from entering control elements</p> Signup and view all the answers

    What is a compatibility feature of the Dräger Vapor 2000?

    <p>It is compatible with both Dräger and GE Select-a-Tec mounting systems</p> Signup and view all the answers

    What is an environmental condition that the Dräger Vapor 2000 is designed to operate in?

    <p>Extended temperature range of 15-40°C</p> Signup and view all the answers

    What is required to activate the concentration control dial on a GE-Datex-Ohmeda Tec 5?

    <p>Mounting the vaporizer to the machine</p> Signup and view all the answers

    What is the purpose of the extension rod on a GE-Datex-Ohmeda Tec 5?

    <p>To prevent the activation of multiple vaporizers simultaneously</p> Signup and view all the answers

    What is a characteristic of the keyed filler port on a GE-Datex-Ohmeda Tec 5?

    <p>It is only available on newer models</p> Signup and view all the answers

    How often is factory servicing required for a GE-Datex-Ohmeda Tec 5?

    <p>Every three years</p> Signup and view all the answers

    What happens when a vaporizer is turned on a GE-Datex-Ohmeda Tec 5?

    <p>The extension rod is deployed</p> Signup and view all the answers

    What design feature is improved in the GE-Datex-Ohmeda Tec 7 and Tec 850?

    <p>Ergonomic design</p> Signup and view all the answers

    What is a benefit of the GE-Datex-Ohmeda Tec 7 and Tec 850?

    <p>Does not require factory maintenance</p> Signup and view all the answers

    What is a safety feature of the GE-Datex-Ohmeda Tec 7 and Tec 850?

    <p>Safety systems in case the vaporizer is tipped or shaken</p> Signup and view all the answers

    What is an advantage of the GE-Datex-Ohmeda Tec 7 and Tec 850 compared to the tec 5

    <p>Improved ergonomic design and safety systems</p> Signup and view all the answers

    How does the design of the GE-Datex-Ohmeda Tec 7 and Tec 850 address user safety?

    <p>By adding safety systems in case the vaporizer is tipped or shaken</p> Signup and view all the answers

    What is the purpose of the heated pressurized sump in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>To heat desflurane to 39°C to maintain a constant vapor pressure</p> Signup and view all the answers

    What is the function of the Variable Pressure Regulation in the Tec 6 vaporizer?

    <p>To sense the fresh gas inflow pressure and match the vapor pressure</p> Signup and view all the answers

    What is the purpose of the Sump Shut-off Valve in the Tec 6 vaporizer?

    <p>To prevent uncontrolled vapor output during warm-up and malfunctions</p> Signup and view all the answers

    What is the advantage of the Tec 6 vaporizer's ability to maintain a constant vapor concentration at varying altitudes?

    <p>It ensures consistent anesthetic delivery regardless of altitude</p> Signup and view all the answers

    What is the purpose of the Concentration Dial in the Tec 6 vaporizer?

    <p>To directly control the amount of desflurane vapor added to the fresh gas flow</p> Signup and view all the answers

    What is the purpose of the Electronics and Display in the Tec 6 vaporizer?

    <p>To provide status information and alert users to malfunctions</p> Signup and view all the answers

    What is the advantage of the Tec 6 vaporizer's agent-specific design?

    <p>It ensures safe filling of desflurane and prevents contamination</p> Signup and view all the answers

    What is the primary purpose of the heated pressurized sump in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>To maintain a constant vapor pressure of 1500 mm Hg</p> Signup and view all the answers

    What prevents fresh gas from entering the desflurane reservoir in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>The fixed restrictor</p> Signup and view all the answers

    What is the purpose of the solenoid locking device in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>To prevent the concentration dial from being activated during warm-up</p> Signup and view all the answers

    What is the advantage of the GE-Datex-Ohmeda Tec 6 vaporizer's ability to refill during use?

    <p>It increases the convenience of use and reduces downtime</p> Signup and view all the answers

    What is the effect of altitude on the GE-Datex-Ohmeda Tec 6 vaporizer's performance?

    <p>It has no effect on the vaporizer's performance</p> Signup and view all the answers

    What is the purpose of the additional heaters in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>To prevent condensation in the rotary valve and pressure transducers</p> Signup and view all the answers

    What is the significance of the sump shut-off valve in the GE-Datex-Ohmeda Tec 6 vaporizer?

    <p>It prevents uncontrolled vapor output during warm-up and malfunction</p> Signup and view all the answers

    What is the advantage of the GE-Datex-Ohmeda Tec 6 vaporizer's agent-specific design?

    <p>It ensures safe filling of the desflurane</p> Signup and view all the answers

    What is a key feature of the Dräger D-Vapor?

    <p>It is significantly lighter in weight</p> Signup and view all the answers

    What happens when the Dräger D-Vapor is in transport setting?

    <p>The vaporizer can be moved in any direction</p> Signup and view all the answers

    How long does the emergency battery back-up last on the Dräger D-Vapor?

    <p>5 minutes</p> Signup and view all the answers

    What is similar about the Dräger D-Vapor and Tec 6?

    <p>Their function</p> Signup and view all the answers

    What is the function of the microprocessor controlled proportional valve in the Penlon Sigma Alpha?

    <p>To dose a precise flow of desflurane vapor into the fresh gas flow</p> Signup and view all the answers

    What happens when the liquid Des is turned on in the Penlon Sigma Alpha?

    <p>It flows into the heater chamber and quickly evaporates</p> Signup and view all the answers

    What is the effect of the liquid desflurane evaporating quickly in the heater chamber?

    <p>It prevents further delivery of liquid desflurane</p> Signup and view all the answers

    What is the purpose of the microprocessor controlled proportional valve in the Penlon Sigma Alpha?

    <p>To dose a precise flow of desflurane vapor into the fresh gas flow</p> Signup and view all the answers

    What is the result of the liquid desflurane evaporating quickly in the heater chamber?

    <p>The pressure of the reservoir chamber is maintained</p> Signup and view all the answers

    What is the primary advantage of integrating the concentration control hardware and software into the anesthesia machine?

    <p>increased accuracy of concentration control</p> Signup and view all the answers

    How does the GE Aladin Vaporizing System maintain the optimal vaporization of anesthetic agents?

    <p>by keeping the gas at its saturated vapor pressure (SVP) within the cassette</p> Signup and view all the answers

    What is the primary benefit of using agent-specific vaporization in the GE Aladin Vaporizing System?

    <p>increased precision in concentration control</p> Signup and view all the answers

    What is integrated into the anesthesia machine itself in the GE Aladin Vaporizing System?

    <p>Concentration control hardware</p> Signup and view all the answers

    What is the purpose of the sump in the GE Aladin Vaporizing System?

    <p>To store the anesthetic agent</p> Signup and view all the answers

    What is the characteristic of the GE Aladin Vaporizing System that ensures precise control of the anesthetic agent?

    <p>Advanced computerized control</p> Signup and view all the answers

    How does an flow i vaporizer apply principles of vapor concentration?

    <p>By measuring the liquid volume and correlating it to a known vapor volume</p> Signup and view all the answers

    how is the amount of vapor injected into the fresh gas flow determined for the FLOW-i?

    <p>The desired concentration and fresh gas flow rate</p> Signup and view all the answers

    What happens to the liquid agent in the vaporizer chamber?

    <p>It is pulsed into the chamber for vaporization</p> Signup and view all the answers

    What is the purpose of the heated chamber in the vaporizer?

    <p>To vaporize the liquid agent</p> Signup and view all the answers

    Study Notes

    General Principles

    General Principles

    Saturated Vapor Pressure (SVP)

    • SVP is the maximum pressure exerted by the vapor of a liquid at a specific temperature
    • SVP is a physical property that depends on the agent and temperature

    Boiling Point

    • Boiling point is the temperature at which SVP equals atmospheric pressure, causing the liquid to change entirely into gas
    • Example: Water boils at 100°C at 1 atm (760 mm Hg) because its SVP at that temperature equals atmospheric pressure

    Volatility

    • Agents with higher SVPs at room temperature are more volatile and have lower boiling points
    • Example: Desflurane is a highly volatile anesthetic agent, boiling at 22.9°C at 1 atm

    Altitude Effects

    • Boiling points decrease with decreasing atmospheric pressure
    • As altitude increases, atmospheric pressure decreases

    Units of Vapor Concentration

    Absolute Terms

    • Units: Millimeters of mercury (mm Hg) or kilopascals (kPa)
    • Meaning: Directly measures the pressure exerted by the anesthetic vapor itself
    • Alternative unit: Milligrams per liter (mg/L)

    Volumes Percent (Vol%)

    • Meaning: Represents the proportion of anesthetic vapor in the total gas mixture being inhaled
    • Calculation: Dalton's Law of Partial Pressures helps calculate Vol% by dividing the partial pressure of the anesthetic by the total pressure, then multiplying by 100%
    • Example: Isoflurane (anesthetic) with a partial pressure of 60 mmHg, total ambient pressure of 760 mmHg would be Vol% = (60/760) x 100% = 7.9%

    Importance of Both Methods

    • Absolute Terms: useful for understanding the physical properties of the vapor itself, such as how it behaves under different temperatures and pressures
    • Volumes Percent: relevant for clinical practice, tells the anesthesia provider how much anesthetic the patient is receiving relative to the other gases

    Saturated Vapor Pressure and Anesthetic Agents

    • Saturated vapor pressure (SVP) is the maximum pressure exerted by the vapor of a liquid at a specific temperature, depending on the agent and temperature.
    • Boiling point is the temperature at which SVP equals atmospheric pressure, causing the liquid to change entirely into gas.
    • Volatility is higher in agents with higher SVPs at room temperature, resulting in lower boiling points.

    Boiling Point and Volatility

    • Water boils at 100°C at 1 atm (760 mm Hg) because its SVP at that temperature equals atmospheric pressure.
    • Desflurane, a highly volatile anesthetic agent, boils at 22.9°C at 1 atm.

    Altitude Effects

    • Boiling points decrease with decreasing atmospheric pressure.
    • As altitude increases, atmospheric pressure decreases, affecting boiling points.

    Units of Vapor Concentration

    • Absolute terms: units are millimeters of mercury (mm Hg) or kilopascals (kPa), measuring the pressure exerted by the anesthetic vapor itself.
    • Alternative unit: milligrams per liter (mg/L).
    • Volumes percent (Vol%): represents the proportion of anesthetic vapor in the total gas mixture being inhaled.

    Calculating Volumes Percent

    • Dalton's Law of Partial Pressures helps calculate Vol%: the total pressure of a gas mixture is the sum of the pressures of each individual gas.
    • Vol% = partial pressure of anesthetic vapor / total pressure x 100%.

    Example Calculation

    • Given partial pressures: Oxygen (O2) = 500 mmHg, Nitrous Oxide (N2O) = 200 mmHg, Isoflurane (anesthetic) = 60 mmHg.
    • Vol% of Isoflurane = 60 mmHg / (500 mmHg + 200 mmHg + 60 mmHg) x 100% = 6% of the gas mixture.

    Importance of Measurement Units

    • Absolute terms are useful for understanding the physical properties of the vapor itself, such as behavior under different temperatures and pressures.
    • Volumes percent are relevant for clinical practice, indicating the amount of anesthetic the patient is receiving relative to other gases.

    Minimum Alveolar Concentration (MAC)

    • MAC is a traditional measure of anesthetic potency, defined as the alveolar concentration that prevents movement in 50% of patients during a standard surgical stimulus.
    • MAC is commonly expressed as a volume percentage (vol%) at sea level (760 mmHg).

    Partial Pressure of Anesthetic (PMAC)

    • PMAC is a more precise way to understand anesthetic potency, representing the partial pressure (mmHg) of the anesthetic in the alveoli that corresponds to 1 MAC.
    • PMAC directly reflects the concentration of anesthetic in the central nervous system, determining the depth of anesthesia.

    Anesthetic Properties

    Isoflurane

    • Boiling point: 48.5°C
    • Saturated Vapor Pressure: 238 mmHg
    • Saturated Vapor Concentration: 31%
    • MAC: 1.15% (vol%)
    • PMAC: 8.7 mmHg

    Sevoflurane

    • Boiling point: 58.5°C
    • Saturated Vapor Pressure: 160 mmHg
    • Saturated Vapor Concentration: 21%
    • MAC: 2.1% (vol%)
    • PMAC: 16 mmHg

    Desflurane

    • Boiling point: 22.8°C
    • Saturated Vapor Pressure: 664 mmHg
    • Saturated Vapor Concentration: 87%
    • MAC: 6-7.25% (vol%)
    • PMAC: 46-55 mmHg

    Minimum Alveolar Concentration (MAC)

    • MAC is a traditional measure of anesthetic potency, defined as the alveolar concentration that prevents movement in 50% of patients during a standard surgical stimulus.
    • MAC is commonly expressed as a volume percentage (vol%) at sea level (760 mmHg).

    Partial Pressure of Anesthetic (PMAC)

    • PMAC is a more precise way to understand anesthetic potency, representing the partial pressure (mmHg) of the anesthetic in the alveoli that corresponds to 1 MAC.
    • PMAC directly reflects the concentration of anesthetic in the central nervous system, determining the depth of anesthesia.

    Anesthetic Properties

    Isoflurane

    • Boiling point: 48.5°C
    • Saturated Vapor Pressure: 238 mmHg
    • Saturated Vapor Concentration: 31%
    • MAC: 1.15% (vol%)
    • PMAC: 8.7 mmHg

    Sevoflurane

    • Boiling point: 58.5°C
    • Saturated Vapor Pressure: 160 mmHg
    • Saturated Vapor Concentration: 21%
    • MAC: 2.1% (vol%)
    • PMAC: 16 mmHg

    Desflurane

    • Boiling point: 22.8°C
    • Saturated Vapor Pressure: 664 mmHg
    • Saturated Vapor Concentration: 87%
    • MAC: 6-7.25% (vol%)
    • PMAC: 46-55 mmHg

    Anesthetic Gases

    • Isoflurane:

    • MAC (minimum alveolar concentration): 1.15% (vol%)

    • PMAC (partial minimum alveolar concentration): 8.7 mmHg

    • Boiling point: 48.5°C

    • Saturated vapor pressure: 238 mmHg

    • Saturated vapor concentration: 31%

    • Sevoflurane:

    • MAC: 2.1% (vol%)

    • PMAC: 16 mmHg

    • Boiling point: 58.5°C

    • Saturated vapor pressure: 160 mmHg

    • Saturated vapor concentration: 21%

    • Desflurane:

    • MAC: 6-7.25% (vol%)

    • PMAC: 46-55 mmHg

    • Boiling point: 22.8°C

    • Saturated vapor pressure: 664 mmHg

    • Saturated vapor concentration: 87%

    Anesthetic Gases

    • Isoflurane:

    • MAC (minimum alveolar concentration): 1.15% (vol%)

    • PMAC (partial minimum alveolar concentration): 8.7 mmHg

    • Boiling point: 48.5°C

    • Saturated vapor pressure: 238 mmHg

    • Saturated vapor concentration: 31%

    • Sevoflurane:

    • MAC: 2.1% (vol%)

    • PMAC: 16 mmHg

    • Boiling point: 58.5°C

    • Saturated vapor pressure: 160 mmHg

    • Saturated vapor concentration: 21%

    • Desflurane:

    • MAC: 6-7.25% (vol%)

    • PMAC: 46-55 mmHg

    • Boiling point: 22.8°C

    • Saturated vapor pressure: 664 mmHg

    • Saturated vapor concentration: 87%

    Anesthetic Gases

    • Isoflurane:

    • MAC (minimum alveolar concentration): 1.15% (vol%)

    • PMAC (partial minimum alveolar concentration): 8.7 mmHg

    • Boiling point: 48.5°C

    • Saturated vapor pressure: 238 mmHg

    • Saturated vapor concentration: 31%

    • Sevoflurane:

    • MAC: 2.1% (vol%)

    • PMAC: 16 mmHg

    • Boiling point: 58.5°C

    • Saturated vapor pressure: 160 mmHg

    • Saturated vapor concentration: 21%

    • Desflurane:

    • MAC: 6-7.25% (vol%)

    • PMAC: 46-55 mmHg

    • Boiling point: 22.8°C

    • Saturated vapor pressure: 664 mmHg

    • Saturated vapor concentration: 87%

    Anesthetic Gases

    • Isoflurane:

    • MAC (minimum alveolar concentration): 1.15% (vol%)

    • PMAC (partial minimum alveolar concentration): 8.7 mmHg

    • Boiling point: 48.5°C

    • Saturated vapor pressure: 238 mmHg

    • Saturated vapor concentration: 31%

    • Sevoflurane:

    • MAC: 2.1% (vol%)

    • PMAC: 16 mmHg

    • Boiling point: 58.5°C

    • Saturated vapor pressure: 160 mmHg

    • Saturated vapor concentration: 21%

    • Desflurane:

    • MAC: 6-7.25% (vol%)

    • PMAC: 46-55 mmHg

    • Boiling point: 22.8°C

    • Saturated vapor pressure: 664 mmHg

    • Saturated vapor concentration: 87%

    Anesthetic Gases

    • Isoflurane:

    • MAC (minimum alveolar concentration): 1.15% (vol%)

    • PMAC (partial minimum alveolar concentration): 8.7 mmHg

    • Boiling point: 48.5°C

    • Saturated vapor pressure: 238 mmHg

    • Saturated vapor concentration: 31%

    • Sevoflurane:

    • MAC: 2.1% (vol%)

    • PMAC: 16 mmHg

    • Boiling point: 58.5°C

    • Saturated vapor pressure: 160 mmHg

    • Saturated vapor concentration: 21%

    • Desflurane:

    • MAC: 6-7.25% (vol%)

    • PMAC: 46-55 mmHg

    • Boiling point: 22.8°C

    • Saturated vapor pressure: 664 mmHg

    • Saturated vapor concentration: 87%

    Latent Heat of Vaporization

    • The energy required to convert a unit mass of liquid into vapor, measured in calories per gram
    • This energy is taken from the remaining liquid and its surroundings, causing a decline in temperature and vapor pressure
    • As a result, the output of vapor is reduced unless compensated for

    Specific Heat

    • The amount of heat required to raise the temperature of 1 gram of a substance by 1°C
    • High specific heat materials resist temperature changes, acting as a thermal buffer

    Thermal Conductivity

    • The rate at which heat is transferred through a substance
    • High thermal conductivity allows for efficient heat transfer from the environment to the vaporizing liquid

    Vaporizer Construction

    • Ideal materials for vaporizers have high specific heat (holds onto heat) and thermal conductivity (ability to absorb and retain environmental heat)
    • These materials help maintain stable temperatures and consistent anesthetic output despite heat loss during vaporization
    • Copper is the best material, followed by bronze and stainless steel

    Regulating Vaporizer Output

    • Measured flow of vaporizer output is achieved through a two-step process
    • Step 1: The vaporizer creates a saturated vapor in equilibrium with the liquid agent
    • Step 2: The saturated vapor is diluted by a bypass gas flow, resulting in a safe and useful concentration flowing to the patient's breathing circuit

    Vapor Pressure and Concentration at Room Temperature

    • Halothane: SVP 243 mmHg, saturated vapor concentration 32%
    • Sevoflurane: SVP 160 mmHg, saturated vapor concentration 21%
    • Isoflurane: SVP 241 mmHg, saturated vapor concentration 31%
    • These concentrations are too potent to be used clinically, requiring dilution with a bypass gas flow.

    Latent Heat of Vaporization

    • The energy required to convert a unit mass of liquid into vapor, measured in calories per gram
    • This energy is taken from the remaining liquid and its surroundings, causing a decline in temperature and vapor pressure
    • As a result, the output of vapor is reduced unless compensated for

    Specific Heat

    • The amount of heat required to raise the temperature of 1 gram of a substance by 1°C
    • High specific heat materials resist temperature changes, acting as a thermal buffer

    Thermal Conductivity

    • The rate at which heat is transferred through a substance
    • High thermal conductivity allows for efficient heat transfer from the environment to the vaporizing liquid

    Vaporizer Construction

    • Ideal materials for vaporizers have high specific heat (holds onto heat) and thermal conductivity (ability to absorb and retain environmental heat)
    • These materials help maintain stable temperatures and consistent anesthetic output despite heat loss during vaporization
    • Copper is the best material, followed by bronze and stainless steel

    Regulating Vaporizer Output

    • Measured flow of vaporizer output is achieved through a two-step process
    • Step 1: The vaporizer creates a saturated vapor in equilibrium with the liquid agent
    • Step 2: The saturated vapor is diluted by a bypass gas flow, resulting in a safe and useful concentration flowing to the patient's breathing circuit

    Vapor Pressure and Concentration at Room Temperature

    • Halothane: SVP 243 mmHg, saturated vapor concentration 32%
    • Sevoflurane: SVP 160 mmHg, saturated vapor concentration 21%
    • Isoflurane: SVP 241 mmHg, saturated vapor concentration 31%
    • These concentrations are too potent to be used clinically, requiring dilution with a bypass gas flow.

    Latent Heat of Vaporization

    • The energy required to convert a unit mass of liquid into vapor, measured in calories per gram.
    • This energy is taken from the remaining liquid and its surroundings, causing the temperature to decline and vapor pressure to drop.
    • As a result, the output of vapor decreases unless compensated for.

    Specific Heat

    • The amount of heat needed to raise the temperature of 1 gram of a substance by 1°C.
    • High specific heat materials resist temperature changes, acting as a thermal buffer.

    Thermal Conductivity

    • The rate at which heat is transferred through a substance.
    • High thermal conductivity allows for efficient heat transfer from the environment to the vaporizing liquid.

    Vaporizer Construction

    • Materials with high specific heat and thermal conductivity are ideal for vaporizers.
    • Copper is the best material, followed by bronze and stainless steel, as it helps maintain stable temperatures and consistent anesthetic output.

    Regulating Vaporizer Output

    • Measured flow vaporizers create a saturated vapor in equilibrium with the liquid agent, which is then diluted by a bypass gas flow to achieve a safe and useful concentration.
    • SVP and vapor concentrations at room temperature:
      • Halothane: SVP 243 mmHg, saturated vapor concentration 32%
      • Sevoflurane: SVP 160 mmHg, saturated vapor concentration 21%
      • Isoflurane: SVP 241 mmHg, saturated vapor concentration 31%

    Measured Flow Vaporizers

    • Measured flow vaporizers (obsolete) required calculations to determine anesthetic concentration.
    • Measured flow of oxygen entered the vaporizer and mixed with bypass gases.

    Variable Bypass Vaporizers

    • Total fresh gas flow enters the vaporizer, and the flow is split between the vaporizing chamber and the bypass pathway.
    • Desired concentration is created by mixing saturated vapor and bypass gas.

    Vaporizing Chamber

    • A large surface area is required for efficient vaporization.
    • Flow-over vaporizers use wicks and baffles, while bubble-through vaporizers (obsolete) passed oxygen through a sintered bronze disc.

    Measured Flow Vaporizers

    • Obsolete measured flow vaporizers required calculations to determine anesthetic concentration.
    • In obsolete systems, a measured flow of oxygen entered the vaporizer and mixed with bypass gases.

    Regulating Vaporizer Output

    • Measured flow vaporizers (contemporary) work by having total fresh gas flow enter the vaporizer.
    • The flow is split between the vaporizing chamber and the bypass pathway.
    • The desired concentration is created by mixing saturated vapor and bypass gas.

    Vaporizing Chamber

    • A large surface area is required for efficient vaporization.
    • Flow-over vaporizers use wicks and baffles to achieve this.
    • Bubble-through vaporizers (now obsolete) passed oxygen through a sintered bronze disc to achieve vaporization.

    ###Measured Flow Vaporizers (Obsolete)

    • Required calculations to determine anesthetic concentration
    • Measured flow of oxygen entered vaporizer and mixed with bypass gases

    ###Variable Bypass Vaporizers (Contemporary)

    • Total fresh gas flow enters vaporizer
    • Flow is split between vaporizing chamber and bypass pathway
    • Desired concentration created by mixing saturated vapor and bypass gas

    ###Vaporizing Chamber

    • Large surface area required for efficient vaporization
    • Flow-over vaporizers use wicks and baffles for efficient vaporization
    • Bubble-through vaporizers (obsolete) passed oxygen through sintered bronze disc

    Calculation of Vaporizer Output

    • The volume of carrier gas entering and exiting the vaporizing chamber is equal.
    • The total exit volume is larger due to the addition of anesthetic vapor.
    • Anesthetic vapor at its Saturated Vapor Pressure (SVP) occupies a fixed percentage of the chamber's atmosphere.

    SVP Concentration

    • For example, sevoflurane at standard conditions occupies 21% of the chamber's atmosphere.
    • The remaining percentage of the chamber's atmosphere is occupied by the carrier gas (e.g., 79% for sevoflurane at standard conditions).

    Calculating Exiting Anesthetic Vapor

    • The volume of exiting anesthetic vapor can be calculated using proportions.
    • Formula: Volume of exiting anesthetic vapor = (Total volume / carrier gas %) X SVP concentration %.

    Calculation of Vaporizer Output

    • The volume of carrier gas entering and exiting the vaporizing chamber is equal, but the total exit volume is larger due to added anesthetic vapor.
    • Anesthetic vapor at its SVP occupies a fixed percentage of the chamber's atmosphere, and the remaining percentage is occupied by the carrier gas.

    Measured Flow Vaporizers

    • Measured Flow Vaporizers include Copper Kettle and Verni-Trol.
    • To deliver 1% Isoflurane to the breathing circuit, the vaporizer must evolve 50 ml of Isoflurane per minute at a total gas flow rate of 5 L/min.
    • Isoflurane represents 31% of the ATM, so the carrier gas represents 69%.
    • 50 ml of Isoflurane mixed with 111 ml of carrier gas results in 161 ml/min emerging.

    Problems with Measured Flow Vaporizers

    • Inconvenient calculations are required to operate the vaporizer.
    • User error can result in serious overdose.
    • Lethal exposure to SVP can occur if fresh gas is not turned on with the measured flow to the vaporizer.
    • An anesthetic agent analyzer with high- and low-concentration alarms is required.
    • End concentrations and flows are not precise, leading to more or less than the desired concentration.

    Calculation of Vaporizer Output

    • The volume of carrier gas entering and exiting the vaporizing chamber is equal, but the total exit volume is larger due to added anesthetic vapor.
    • Anesthetic vapor at its SVP occupies a fixed percentage of the chamber's atmosphere (e.g., 21% for sevoflurane at standard conditions).
    • The remaining percentage of the chamber's atmosphere is occupied by the carrier gas (e.g., 79% for sevoflurane at standard conditions).

    Measured Flow Vaporizers (Copper Kettle, Verni-Trol)

    • Measured flow vapor volume can be calculated using proportions: Measured flow vapor volume = (Total volume/carrier gas %) X SVP concentration %.
    • Example: to deliver 1% Isoflurane to the breathing circuit at a total gas flow rate of 5 L/min, the vaporizer needs to evolve 50 ml of Isoflurane per minute.
    • Isoflurane represents 31% of the ATM, and the carrier gas represents 69%.
    • Therefore, 111 mL/min oxygen is bubbling through liquid Isoflurane, and 161 mL/min emerges (50 iso and 111 carrier).

    Problems with Measured Flow Vaporizers

    • Inconvenient calculations are required.
    • Prone to user error resulting in serious overdose.
    • Lethal exposure to SVP if fresh gas is not turned on with the measured flow to the vaporizer.
    • Requires an anesthetic agent analyzer with high- and low-concentration alarms.
    • End concentrations and flows are not precise.

    Variable Bypass Vaporizers

    • Splitting ratio: the total gas flow is divided between a bypass and the vaporizing chamber, depending on the anesthetic agent, temperature, and desired concentration.
    • Example: Sevoflurane vaporizer set to deliver 1% Sevo, with a gas flow of 2079 mL/min split into 79 mL entering the vaporizing chamber and 2000 mL entering the bypass.
    • The exiting gas mixture is 21mL Sevoflurane, 79 mL carrier gas, and 2000 mL bypass gas, resulting in a 1% Sevo concentration with a splitting ratio of 25:1.
    • Volume of agent calculation: FGF rate x Desired concentration of anesthetic gas.
    • Total flow exiting vaporizer = Volume of anesthetic gas/Saturated vapor concentration.
    • Required carrier gas volume = Total exiting gas volume - anesthetic volume.

    Dial Settings for Isoflurane and Sevoflurane

    Inflow Gas Splitting

    • 1% dial setting: Isoflurane has a 44:1 ratio, Sevoflurane has a 25:1 ratio
    • 2% dial setting: Isoflurane has a 21:1 ratio, Sevoflurane has a 12:1 ratio
    • 3% dial setting: Isoflurane has a 14:1 ratio, Sevoflurane has a 7:1 ratio

    Outflow Gas Splitting

    • 1% dial setting: Isoflurane has a 30:1 ratio, Sevoflurane has a 20:1 ratio
    • 2% dial setting: Isoflurane has a 14.5:1 ratio, Sevoflurane has a 9.5:1 ratio
    • 3% dial setting: Isoflurane has a 9.33:1 ratio, Sevoflurane has a 6:1 ratio
    • 4% dial setting: Isoflurane has a 6.75:1 ratio, Sevoflurane has a 4.25:1 ratio

    Dial Settings for Isoflurane and Sevoflurane

    Inflow Gas Splitting

    • 1% dial setting: Isoflurane has a 44:1 ratio, Sevoflurane has a 25:1 ratio
    • 2% dial setting: Isoflurane has a 21:1 ratio, Sevoflurane has a 12:1 ratio
    • 3% dial setting: Isoflurane has a 14:1 ratio, Sevoflurane has a 7:1 ratio

    Outflow Gas Splitting

    • 1% dial setting: Isoflurane has a 30:1 ratio, Sevoflurane has a 20:1 ratio
    • 2% dial setting: Isoflurane has a 14.5:1 ratio, Sevoflurane has a 9.5:1 ratio
    • 3% dial setting: Isoflurane has a 9.33:1 ratio, Sevoflurane has a 6:1 ratio
    • 4% dial setting: Isoflurane has a 6.75:1 ratio, Sevoflurane has a 4.25:1 ratio

    Temperature Compensation in Vaporizers

    • As temperature falls, SVP decreases, leading to less anesthetic vapor delivery in uncompensated vaporizers.
    • Temperature compensation methods include:
      • Manual (e.g., Copper Kettle)
      • Automatic (e.g., contemporary variable bypass vaporizers)
      • Measured Flow Vaporizers (outdated)

    Measured Flow Vaporizers

    • Use a thermometer to measure liquid agent temperature and reference vapor pressure curves for manual adjustment.

    Contemporary Variable Bypass Vaporizers

    • Use temperature-sensitive valves in the bypass flow for automatic compensation.
    • Temperature-sensitive valve designs include:
      • Gas-filled bellows linked to bypass valve (older models)
      • Bimetallic strip in a flap valve (GE Tec series)
      • Expansion element controlling bypass and chamber flows (Dräger Vapor)

    Limitations of Temperature Compensation

    • Vapor pressure varies nonlinearly with temperature.
    • Output concentration accuracy is limited to a specific temperature range.
    • The boiling point of the anesthetic agent must never be reached.
    • Temperature compensation times:
      • Modern vaporizers take time to adjust for temperature changes (e.g., Dräger 19.n takes 6 minutes for each 1°C change).

    Vaporizer Calibration and Misfilling

    • Modern vaporizers are calibrated for specific anesthetic agents.
    • Using the wrong agent in a vaporizer leads to inaccurate output concentrations.
    • High SVP vs. Low SVP:
      • If a low SVP vaporizer is filled with a high SVP agent, the output concentration will be higher than indicated.
      • If a high SVP vaporizer is filled with a low SVP agent, the output concentration will be lower than indicated.
    • Potency considerations:
      • Misfilling can lead to significant changes in delivered anesthetic potency (MAC equivalent).

    Prevention of Misfilling

    • Careful attention to the agent and vaporizer during filling.
    • Use of agent-specific filling mechanisms, such as:
      • Color-coded collars
      • Keyed filling devices

    Vaporization of Mixed Anesthetic Agents

    • Mixing agents in vaporizers can lead to unpredictable vaporizer output and large errors in delivered vapor concentration due to partial filling with the correct agent and topping it off with the wrong one.

    Chemical Interactions

    • Mixed agents (halothane, enflurane, isoflurane) do not react chemically with each other.
    • Halothane affects enflurane and isoflurane, making them vaporize more easily.

    Clinical Consequences

    • The clinical impact of mixed agents depends on their potencies and delivered concentrations.
    • Mixed agents can lead to unpredictable clinical outcomes due to varying MAC outputs.

    Examples of Misfilled Vaporizers

    • Halothane vaporizer filled with isoflurane: Total MAC output is close to the intended value.
    • Enflurane vaporizer filled with halothane: Total MAC output is more than three times higher than intended.

    Actions to Take if Misfilling is Suspected

    • Empty the vaporizer.
    • Remove it from service.
    • Label it as misfilled.
    • Return it to the manufacturer.

    Calculating Concentration for a Misfilled Vaporizer

    • C' = C * (SVP_B / SVP_A)
    • C' = Output concentration of the incorrectly filled agent (agent B).
    • C = Concentration set on the vaporizer dial for the intended agent (agent A).
    • SVP_B = Saturation vapor pressure of the incorrectly filled agent (agent B).
    • SVP_A = Saturation vapor pressure of the intended agent (vaporizer) (agent A).

    Vaporization of Mixed Anesthetic Agents

    • Mixing agents in vaporizers can lead to unpredictable vaporizer output and large errors in delivered vapor concentration due to partial filling with the correct agent and topping it off with the wrong one.

    Chemical Interactions

    • Mixed agents (halothane, enflurane, isoflurane) do not react chemically with each other.
    • Halothane affects enflurane and isoflurane, making them vaporize more easily.

    Clinical Consequences

    • The clinical impact of mixed agents depends on their potencies and delivered concentrations.
    • Mixed agents can lead to unpredictable clinical outcomes due to varying MAC outputs.

    Examples of Misfilled Vaporizers

    • Halothane vaporizer filled with isoflurane: Total MAC output is close to the intended value.
    • Enflurane vaporizer filled with halothane: Total MAC output is more than three times higher than intended.

    Actions to Take if Misfilling is Suspected

    • Empty the vaporizer.
    • Remove it from service.
    • Label it as misfilled.
    • Return it to the manufacturer.

    Calculating Concentration for a Misfilled Vaporizer

    • C' = C * (SVP_B / SVP_A)
    • C' = Output concentration of the incorrectly filled agent (agent B).
    • C = Concentration set on the vaporizer dial for the intended agent (agent A).
    • SVP_B = Saturation vapor pressure of the incorrectly filled agent (agent B).
    • SVP_A = Saturation vapor pressure of the intended agent (vaporizer) (agent A).

    Filling of Vaporizers

    • Follow the manufacturer's instructions to ensure safe and proper filling of vaporizers.
    • Avoid overfilling or tilting the vaporizer, as it can lead to lethal consequences.
    • Liquid agent in the gas delivery system can be lethal, so caution is necessary.
    • If the vaporizer is tilted, purge it with high oxygen flow from the anesthesia machine's flowmeter.
    • Use a calibrated agent analyzer to confirm the efficacy of the flush before returning to clinical use.
    • A small amount of liquid agent (1 mL) can produce a large amount of vapor (~200 mL), leading to high concentrations.
    • If an issue arises, it is prudent to withdraw the workstation from use until authorized service personnel deem it safe.

    Effect of Carrier Gas Composition on Vaporizer Output

    • Changing the carrier gas composition (e.g., nitrous oxide/oxygen vs. nitrogen/oxygen) affects vaporizer output concentration.
    • Nitrous oxide dissolves in liquid anesthetic agents, initially decreasing vapor output when introduced.
    • When nitrous oxide is discontinued, dissolved nitrous oxide comes out of solution, temporarily increasing vapor output.

    Measured Flow Vaporizers

    • Unaffected by carrier gas composition because they only use oxygen.

    Dräger Vaporizers

    • Calibrated with air; using 100% oxygen or nitrous oxide/oxygen mixtures slightly alters output concentrations.

    GE Tec Vaporizers

    • Calibrated with oxygen; using air or nitrous oxide decreases output concentration.
    • However, this reduction is not clinically significant due to nitrous oxide's contribution to MAC (minimum alveolar concentration).

    Effects of Changes in Barometric Pressure on Vaporizers

    • Vaporizers are typically used at sea level pressure (760 mmHg) but can be used in hypobaric conditions (low pressure, high altitudes) with contemporary designs having proportioning control downstream of the vaporizing chamber.

    Hypobaric Conditions and Anesthetic Potency

    • At 760 mmHg (sea level), a sevoflurane vaporizer set to 2% delivers 0.95 MAC (Minimum Alveolar Concentration).
    • At 500 mmHg (12,000 ft altitude), the same 2% setting delivers 3% sevoflurane by volume, but still 0.94 MAC, due to potency being determined by partial pressure, not volume percent.
    • Although volume percent increases under hypobaric conditions, partial pressure and MAC remain essentially the same.
    • Quantifying in mg/L also demonstrates consistent potency despite changes in volume percent.

    Key Takeaways

    • Under hypobaric conditions, variable bypass vaporizer output concentration (vol%) is lower than the dial setting.
    • However, potency (MAC) remains essentially unchanged despite changes in volume percent.

    Anesthesia Manifold Safety

    • An interlock device is used to prevent contamination of multiple vaporizers attached to an anesthesia manifold.
    • The interlock device allows only one vaporizer to be in use at a time, preventing simultaneous use of multiple vaporizers.

    Liquid Agent Consumption

    • The amount of liquid agent used per hour depends on the vaporizer dial setting and the fresh gas flow rate.
    • Approximate formula for liquid agent consumption: 3 x Dial setting (vol%) x FGF (L/min).

    Contemporary Vaporizers

    • Output concentration is mostly independent of fresh gas flow rate within the normal clinical range.
    • At high concentrations and flows, output may be slightly lower than the dial setting due to incomplete evaporation and temperature drop in the vaporizing chamber.
    • Key takeaway: High concentrations and flows can slightly decrease the output compared to the set value due to incomplete evaporation and cooling within the chamber.

    Anesthesia Manifold and Vaporizers

    • An interlock device is used to prevent contamination of multiple vaporizers attached to an anesthesia manifold, allowing only one vaporizer to be in use at a time.

    Fresh Gas Flow Rate and Liquid Agent Consumption

    • The amount of liquid agent used per hour depends on the vaporizer dial setting and the fresh gas flow rate.
    • The approximate formula to calculate liquid agent consumption is: 3 x Dial setting (vol%) x FGF (L/min).
    • In contemporary vaporizers, the output concentration is mostly independent of fresh gas flow rate within the normal clinical range.
    • However, high concentrations and flows can slightly decrease the output compared to the set value due to incomplete evaporation and cooling within the chamber.

    Fluctuating Back Pressure and Vaporizer Output

    • Fluctuating back pressure (from IPPV or oxygen flush) can alter gas flow and increase vaporizer output in older models.
    • Factors contributing to this issue include low flow rates, low concentration settings, small liquid agent volume, and large, rapid pressure changes.
    • Pressurization compresses gas in the vaporizer, and when pressure drops, vapor exits both normally and through the inlet, increasing bypass flow and overall output.
    • Modern vaporizers have design features to minimize the pumping effect, and some older models used check valves to limit pressure transmission, but these are no longer used in the newest models.
    • The pumping effect was a significant issue in older vaporizers, leading to increased output under certain conditions, but modern designs have largely mitigated this problem.

    Anesthesia Manifold and Vaporizers

    • An interlock device is used to prevent contamination of multiple vaporizers attached to an anesthesia manifold, allowing only one vaporizer to be in use at a time.

    Fresh Gas Flow Rate and Liquid Agent Consumption

    • The amount of liquid agent used per hour depends on the vaporizer dial setting and the fresh gas flow rate.
    • The approximate formula to calculate liquid agent consumption is: 3 x Dial setting (vol%) x FGF (L/min).
    • In contemporary vaporizers, the output concentration is mostly independent of fresh gas flow rate within the normal clinical range.
    • However, high concentrations and flows can slightly decrease the output compared to the set value due to incomplete evaporation and cooling within the chamber.

    Fluctuating Back Pressure and Vaporizer Output

    • Fluctuating back pressure (from IPPV or oxygen flush) can alter gas flow and increase vaporizer output in older models.
    • Factors contributing to this issue include low flow rates, low concentration settings, small liquid agent volume, and large, rapid pressure changes.
    • Pressurization compresses gas in the vaporizer, and when pressure drops, vapor exits both normally and through the inlet, increasing bypass flow and overall output.
    • Modern vaporizers have design features to minimize the pumping effect, and some older models used check valves to limit pressure transmission, but these are no longer used in the newest models.
    • The pumping effect was a significant issue in older vaporizers, leading to increased output under certain conditions, but modern designs have largely mitigated this problem.

    Vaporization

    • Vapor: the gaseous form of a substance that can also exist as a liquid or solid at temperatures below its critical temperature
    • Critical Temperature: the temperature above which a gas cannot be liquefied by pressure alone

    Anesthesia Vaporizers

    • Devices that convert liquid anesthetic agents into their vapor form and deliver a controlled amount to the patient's breathing circuit

    Vapor, Evaporation, and Vapor Pressure

    • Liquid-Vapor Equilibrium: in a closed container, an equilibrium is established between liquid and vapor phases of a substance
    • Vapor Pressure: the pressure exerted by the vapor molecules on the container walls
    • Temperature Effect: increasing temperature increases vapor pressure due to increased evaporation
    • Saturated Vapor Pressure (SVP): the maximum vapor pressure at a given temperature when the gas phase is saturated

    Measurement of Vapor Pressure and SVP

    • Barometer Principle: measures atmospheric pressure using a column of mercury
    • Torricellian Vacuum: the vacuum created above the mercury column in a barometer
    • Introducing Vapor: adding a volatile liquid to the vacuum allows it to evaporate and exert vapor pressure
    • Saturation: when excess liquid remains unevaporated, the vapor pressure reaches its maximum (SVP) at that temperature

    Saturated Vapor Pressure and Anesthetic Agents

    • SVP depends on the agent and temperature
    • Boiling Point: the temperature at which SVP equals atmospheric pressure, causing the liquid to change entirely into gas
    • Volatility: agents with higher SVPs at room temperature are more volatile and have lower boiling points
    • Example: water boils at 100°C at 1 atm (760 mm Hg) because its SVP at that temperature equals atmospheric pressure

    Units of Vapor Concentration

    • Absolute Terms: units of mm Hg or kPa, directly measuring the pressure exerted by the anesthetic vapor itself
    • Alternative Unit: milligrams per liter (mg/L)
    • Volumes Percent (Vol%): represents the proportion of anesthetic vapor in the total gas mixture being inhaled
    • Calculation: uses Dalton's Law of Partial Pressures

    Minimum Alveolar Concentration

    • MAC (Minimum Alveolar Concentration): the traditional measure of anesthetic potency, defined as the alveolar concentration (vol%) that prevents movement in 50% of patients during a standard surgical stimulus
    • PMAC (Minimum Alveolar Pressure): a more precise way to understand anesthetic potency, represents the partial pressure (mmHg) of the anesthetic in the alveoli that corresponds to 1 MAC

    Examples of Anesthetic Agents

    • Isoflurane: boiling point 48.5°C, SVP 238 mmHg, saturated vapor concentration 31%, MAC 1.15%, PMAC 8.7 mmHg
    • Sevoflurane: boiling point 58.5°C, SVP 160 mmHg, saturated vapor concentration 21%, MAC 2.1%, PMAC 16 mmHg
    • Desflurane: boiling point 22.8°C, SVP 664 mmHg, saturated vapor concentration 87%, MAC 6-7.25%, PMAC 46-55 mmHg

    Latent Heat of Vaporization

    • The energy (in calories) needed to convert a unit mass of liquid into vapor
    • This energy is taken from the remaining liquid and its surroundings, reducing the output of vapor unless compensated for

    Specific Heat and Thermal Conductivity

    • Specific Heat: the amount of heat needed to raise the temperature of 1 gram of a substance by 1°C
    • Thermal Conductivity: the rate at which heat is transferred through a substance
    • Ideal materials for vaporizer construction have high specific heat and thermal conductivity, such as copper, bronze, and stainless steel

    Regulating Vaporizer Output

    • Measured Flow: SVP and vapor concentrations at room temperature are too potent to be used clinically, so the vaporizer creates a saturated vapor in equilibrium with the liquid agent, which is then diluted by a bypass gas flow
    • First, the vaporizer creates a saturated vapor in equilibrium with the liquid agent
    • Second, the saturated vapor is diluted by a bypass gas flow
    • Result: safe and useful concentration flowing to the patient's breathing circuit

    Vaporizer Construction

    • Materials with high specific heat and thermal conductivity are ideal
    • Copper is the best, followed by bronze and stainless steel

    Regulating Vaporizer Output (continued)

    • Measured Flow Vaporizers (Obsolete): required calculations to determine anesthetic concentration
    • Variable Bypass Vaporizers (Contemporary): total fresh gas flow enters the vaporizer, and the flow is split between the vaporizing chamber and the bypass pathway
    • Desired concentration is created by mixing saturated vapor and bypass gas

    Vaporizing Chamber

    • Large surface area is required for efficient vaporization
    • Flow-over vaporizers use wicks and baffles
    • Bubble-through vaporizers (obsolete) passed oxygen through a sintered bronze disc### Anesthesia Vaporizers
    • There are two types of vaporizers: Measured Flow Vaporizers (Copper Kettle, Verni-Trol) and Variable Bypass Vaporizers.
    • Measured Flow Vaporizers require inconvenient calculations and are prone to user error, which can result in serious overdose.
    • Lethal exposure to SVP can occur if fresh gas is not turned on with the measured flow to the vaporizer.
    • Required anesthetic agent analyzer with high- and low-concentration alarms.

    Volume of Exiting Anesthetic Vapor

    • (Total volume/carrier gas %) X SVP concentration %
    • SVP at standard conditions: 21% for sevoflurane, 31% for isoflurane
    • Carrier gas percentage: 79% for sevoflurane, 69% for isoflurane

    Inflow Gas Splitting

    • 1%: Isoflurane- 44:1, Sevoflurane- 25:1
    • 2%: Isoflurane- 21:1, Sevoflurane- 12:1
    • 3%: Isoflurane- 14:1, Sevoflurane- 7:1

    Outflow Gas Splitting

    • 1%: Isoflurane- 30:1, Sevoflurane- 20:1
    • 2%: Isoflurane- 14.5:1, Sevoflurane- 9.5:1
    • 3%: Isoflurane- 9.33:1, Sevoflurane- 6:1
    • 4%: Isoflurane- 6.75:1, Sevoflurane- 4.25:1

    Calculation of Vaporizer Output

    • Volume of carrier gas entering and exiting the vaporizing chamber is equal.
    • Total exit volume is larger due to added anesthetic vapor.
    • Anesthetic vapor at SVP occupies a fixed percentage of the chamber's atmosphere.

    Variable Bypass Vaporizers

    • Splitting Ratio: Total gas flow is divided between bypass and vaporizing chamber.
    • Example: Sevoflurane vaporizer set to deliver 1% Sevo, a gas flow of 2079 mL/min is split into 79 mL entering the vaporizing chamber and 2000 mL entering the bypass.

    Temperature Compensation

    • As temperature falls, SVP also falls, leading to less anesthetic vapor delivery in uncompensated vaporizers.
    • Temperature compensation methods: manual (e.g., Copper Kettle), automatic (e.g., contemporary variable bypass vaporizers).
    • Limitations of temperature compensation: vapor pressure varies nonlinearly with temperature, output concentration accuracy is limited to a specific temperature range.

    Misfilling of Vaporizers

    • Misfilling can lead to significant changes in delivered anesthetic potency (MAC equivalent).
    • Prevention of misfilling: careful attention to the agent and vaporizer during filling, use of agent-specific filling mechanisms (e.g., color-coded collars, keyed filling devices).
    • Effect of misfilling: clinical consequences depend on potencies and delivered concentrations of mixed agents.

    Filling of Vaporizers

    • Follow manufacturer's instructions.
    • Avoid overfilling or tilting the vaporizer.
    • Liquid agent in the gas delivery system can be lethal.
    • Use a calibrated agent analyzer to confirm the efficacy of the flush before returning to clinical use.

    Effects of Changes in Fresh Gas Composition

    • Carrier gas change affects output concentration.
    • Nitrous oxide solubility: nitrous oxide dissolves in liquid anesthetic agents, initially decreasing vapor output, then increasing it when discontinued.

    Effects of Changes in Barometric Pressure

    • Vaporizers are usually used at sea level pressure (760 mmHg).
    • Hypobaric conditions (low pressure, high altitudes) can alter output concentration.
    • Output concentration (vol%) is lower than the dial setting, but potency (MAC) remains essentially unchanged.

    Dräger Vapor 2000

    • Improved version of Vapor 19.1 with increased sump capacity of 300 mL.
    • Designed for easy removal and transportation without draining.
    • Features a spill-proof design that prevents liquid anesthetic from entering control elements.
    • Transport mode isolates the sump from the rest of the vaporizer.
    • Operates within an extended temperature range of 15–40°C.
    • Compatible with Dräger and GE Select-a-Tec mounting systems.

    Dräger Vapor 3000

    • Operates on the same principles as the Vapor 2000.
    • Adds integrated illumination for the control dial and agent level indicators.

    GE-Datex-Ohmeda Tec 5

    • Must be mounted to the machine to enable concentration control dial functionality
    • Features an extension rod that deploys when a vaporizer is turned on, preventing simultaneous activation of other vaporizers
    • Equipped with a keyed filler port (except for earlier models)
    • Requires mandatory factory servicing every three years

    Vaporization

    • Vapor: the gaseous form of a substance that can also exist as a liquid or solid at temperatures below its critical temperature
    • Critical Temperature: the temperature above which a gas cannot be liquefied by pressure alone

    Anesthesia Vaporizers

    • Devices that convert liquid anesthetic agents into their vapor form and deliver a controlled amount to the patient's breathing circuit

    Vapor, Evaporation, and Vapor Pressure

    • Liquid-Vapor Equilibrium: in a closed container, an equilibrium is established between liquid and vapor phases of a substance
    • Vapor Pressure: the pressure exerted by the vapor molecules on the container walls
    • Temperature Effect: increasing temperature increases vapor pressure due to increased evaporation
    • Saturated Vapor Pressure (SVP): the maximum vapor pressure at a given temperature when the gas phase is saturated

    Measurement of Vapor Pressure and SVP

    • Barometer Principle: measures atmospheric pressure using a column of mercury
    • Torricellian Vacuum: the vacuum created above the mercury column in a barometer
    • Introducing Vapor: adding a volatile liquid to the vacuum allows it to evaporate and exert vapor pressure
    • Saturation: when excess liquid remains unevaporated, the vapor pressure reaches its maximum (SVP) at that temperature

    Saturated Vapor Pressure and Anesthetic Agents

    • SVP depends on the agent and temperature
    • Boiling Point: the temperature at which SVP equals atmospheric pressure, causing the liquid to change entirely into gas
    • Volatility: agents with higher SVPs at room temperature are more volatile and have lower boiling points
    • Example: water boils at 100°C at 1 atm (760 mm Hg) because its SVP at that temperature equals atmospheric pressure

    Units of Vapor Concentration

    • Absolute Terms: units of mm Hg or kPa, directly measuring the pressure exerted by the anesthetic vapor itself
    • Alternative Unit: milligrams per liter (mg/L)
    • Volumes Percent (Vol%): represents the proportion of anesthetic vapor in the total gas mixture being inhaled
    • Calculation: uses Dalton's Law of Partial Pressures

    Minimum Alveolar Concentration

    • MAC (Minimum Alveolar Concentration): the traditional measure of anesthetic potency, defined as the alveolar concentration (vol%) that prevents movement in 50% of patients during a standard surgical stimulus
    • PMAC (Minimum Alveolar Pressure): a more precise way to understand anesthetic potency, represents the partial pressure (mmHg) of the anesthetic in the alveoli that corresponds to 1 MAC

    Examples of Anesthetic Agents

    • Isoflurane: boiling point 48.5°C, SVP 238 mmHg, saturated vapor concentration 31%, MAC 1.15%, PMAC 8.7 mmHg
    • Sevoflurane: boiling point 58.5°C, SVP 160 mmHg, saturated vapor concentration 21%, MAC 2.1%, PMAC 16 mmHg
    • Desflurane: boiling point 22.8°C, SVP 664 mmHg, saturated vapor concentration 87%, MAC 6-7.25%, PMAC 46-55 mmHg

    Latent Heat of Vaporization

    • The energy (in calories) needed to convert a unit mass of liquid into vapor
    • This energy is taken from the remaining liquid and its surroundings, reducing the output of vapor unless compensated for

    Specific Heat and Thermal Conductivity

    • Specific Heat: the amount of heat needed to raise the temperature of 1 gram of a substance by 1°C
    • Thermal Conductivity: the rate at which heat is transferred through a substance
    • Ideal materials for vaporizer construction have high specific heat and thermal conductivity, such as copper, bronze, and stainless steel

    Regulating Vaporizer Output

    • Measured Flow: SVP and vapor concentrations at room temperature are too potent to be used clinically, so the vaporizer creates a saturated vapor in equilibrium with the liquid agent, which is then diluted by a bypass gas flow
    • First, the vaporizer creates a saturated vapor in equilibrium with the liquid agent
    • Second, the saturated vapor is diluted by a bypass gas flow
    • Result: safe and useful concentration flowing to the patient's breathing circuit

    Vaporizer Construction

    • Materials with high specific heat and thermal conductivity are ideal
    • Copper is the best, followed by bronze and stainless steel

    Regulating Vaporizer Output (continued)

    • Measured Flow Vaporizers (Obsolete): required calculations to determine anesthetic concentration
    • Variable Bypass Vaporizers (Contemporary): total fresh gas flow enters the vaporizer, and the flow is split between the vaporizing chamber and the bypass pathway
    • Desired concentration is created by mixing saturated vapor and bypass gas

    Vaporizing Chamber

    • Large surface area is required for efficient vaporization
    • Flow-over vaporizers use wicks and baffles
    • Bubble-through vaporizers (obsolete) passed oxygen through a sintered bronze disc### Calculating Vaporizer Output
    • The volume of carrier gas entering and exiting the vaporizing chamber is equal
    • The total exit volume is larger due to added anesthetic vapor
    • Anesthetic vapor at its SVP occupies a fixed percentage of the chamber's atmosphere
    • The remaining percentage of the chamber's atmosphere is occupied by the carrier gas
    • The volume of exiting anesthetic vapor can be calculated using proportions: (Total volume/carrier gas %) X SVP concentration %

    Measured Flow Vaporizers (Copper Kettle, Verni-Trol)

    • Problems:
      • Inconvenient calculations required
      • Prone to user error resulting in serious overdose
      • Lethal exposure to SVP if fresh gas not turned on with the measured flow to the vaporizer
      • Required anesthetic agent analyzer with high- and low-concentration alarms
      • End concentrations and flows were not precise

    Variable Bypass Vaporizers

    • The total gas flow is divided between a bypass and the vaporizing chamber, the ratio depending on the anesthetic agent, temperature, and desired concentration
    • Example: Sevoflurane vaporizer set to deliver 1% Sevo, a gas flow of 2079 mL/min is split into:
      • 79 mL entering the vaporizing chamber
      • 2000 mL entering the bypass
      • The exiting gas mixture: 21mL Sevoflurane, 79 mL carrier gas, 2000 mL bypass gas
      • Result is a 1% Sevo concentration with a splitting ratio of 25:1

    Volume of Agent Calculation

    • Formula: FGF rate x Desired concentration of anesthetic gas
    • Total flow exiting Vaporizer = Volume of anesthetic gas / Saturated vapor concentration
    • Required Carrier Gas Volume = Total exiting gas volume - anesthetic volume

    Temperature Compensation

    • Methods:
      • Manual (e.g., Copper Kettle)
      • Automatic (e.g., contemporary variable bypass vaporizers)
    • Temperature-Sensitive Valve Designs:
      • Older models: Gas-filled bellows linked to bypass valve
      • GE Tec series: Bimetallic strip in a flap valve
      • Dräger Vapor: Expansion element controlling bypass and chamber flows
    • Limitations of Temperature Compensation:
      • Vapor pressure varies nonlinearly with temperature
      • Output concentration accuracy is limited to a specific temperature range
      • The boiling point of the anesthetic agent must never be reached

    Misfilling and Mixing Anesthetic Agents

    • Prevention of Misfilling:
      • Careful attention to the agent and vaporizer during filling
      • Use of agent-specific filling mechanisms (e.g., color-coded collars, keyed filling devices)
    • Clinical Consequences:
      • The clinical impact of mixed agents depends on their potencies and delivered concentrations
    • Examples of Misfilled Vaporizers:
      • Halothane vaporizer filled with isoflurane: Total MAC output is close to the intended value
      • Enflurane vaporizer filled with halothane: Total MAC output is more than three times higher than intended
    • Calculate the Concentration for a Misfilled Vaporizer:
      • C' = C * (SVP_B / SVP_A)

    Filling of Vaporizers

    • Follow manufacturer's instructions
    • Avoid overfilling or tilting the vaporizer
    • Liquid agent in the gas delivery system can be lethal
    • If tilted, purge the vaporizer with high oxygen flow from the anesthesia machine's flowmeter
    • Use a calibrated agent analyzer to confirm the efficacy of the flush before returning to clinical use

    GE-Datex-Ohmeda Tec 6 (Desflurane)

    Design and Features

    • Specifically designed for the highly volatile anesthetic desflurane
    • Requires a heated pressurized sump
    • Heated vaporizer heats desflurane to 39°C to maintain a constant vapor pressure (1500 mm Hg)

    Vapor Pressure Regulation

    • Variable pressure regulation controls vapor pressure entering the concentration dial to match the fresh gas inflow pressure
    • Concentration dial directly controls the amount of desflurane vapor added to the fresh gas flow

    Sump and Liquid Management

    • Sump holds 450 mL of desflurane and is electronically monitored with liquid level displayed on LCD
    • Heater maintains desflurane at 39°C to generate vapor under pressure
    • Sump shut-off valve closes during warm-up and malfunctions to prevent uncontrolled vapor output

    Safety Features

    • Solenoid locking device prevents concentration dial activation until warm-up is complete
    • Additional heaters located in rotary valve and pressure transducers prevent condensation
    • No fresh gas enters the desflurane sump
    • Electronics and display provide status information and alarms alert users to malfunctions
    • Alarms automatically close the sump shut-off valve

    Operation and Adjustments

    • Agent-specific patented system ensures safe filling of desflurane
    • Can be refilled during use
    • Effects of altitude: maintains dialed-in concentration even at varying altitudes
    • Potency adjustment required for high or low altitude situations:
      • Higher dial settings needed at higher altitudes to compensate for decreased partial pressure
      • Lower dial settings needed at lower altitudes
    • If tipped, an alarm sounds, and the control electronics enables the sump shut-off valve

    GE-Datex-Ohmeda Tec 6 (Desflurane)

    Design and Features

    • Specifically designed for the highly volatile anesthetic desflurane
    • Requires a heated pressurized sump
    • Heated vaporizer heats desflurane to 39°C to maintain a constant vapor pressure (1500 mm Hg)

    Vapor Pressure Regulation

    • Variable pressure regulation controls vapor pressure entering the concentration dial to match the fresh gas inflow pressure
    • Concentration dial directly controls the amount of desflurane vapor added to the fresh gas flow

    Sump and Liquid Management

    • Sump holds 450 mL of desflurane and is electronically monitored with liquid level displayed on LCD
    • Heater maintains desflurane at 39°C to generate vapor under pressure
    • Sump shut-off valve closes during warm-up and malfunctions to prevent uncontrolled vapor output

    Safety Features

    • Solenoid locking device prevents concentration dial activation until warm-up is complete
    • Additional heaters located in rotary valve and pressure transducers prevent condensation
    • No fresh gas enters the desflurane sump
    • Electronics and display provide status information and alarms alert users to malfunctions
    • Alarms automatically close the sump shut-off valve

    Operation and Adjustments

    • Agent-specific patented system ensures safe filling of desflurane
    • Can be refilled during use
    • Effects of altitude: maintains dialed-in concentration even at varying altitudes
    • Potency adjustment required for high or low altitude situations:
      • Higher dial settings needed at higher altitudes to compensate for decreased partial pressure
      • Lower dial settings needed at lower altitudes
    • If tipped, an alarm sounds, and the control electronics enables the sump shut-off valve

    Dräger D-Vapor (Desflurane)

    • Operates similarly to Tec 6, indicating a similar functionality and mechanism
    • Designed for transport settings, allowing the vaporizer to be moved in any direction, ensuring flexibility and ease of use
    • Equipped with a 5-minute emergency battery back-up, providing a safety net in case of power failure
    • Significantly lighter in weight, making it easier to transport and handle

    Penlon Sigma Alpha Anesthesia Machine

    • Delivers a precise flow of desflurane vapor into the fresh gas flow
    • Utilizes a microprocessor-controlled proportional valve to regulate the flow
    • Liquid desflurane flows into the heater chamber when the machine is turned on
    • The liquid desflurane rapidly evaporates in the heater chamber
    • The evaporation process matches the pressure of the reservoir chamber
    • This pressure equilibrium prevents further delivery of liquid desflurane into the heater chamber

    GE Aladin Vaporizing System

    • Advanced computerized vaporizer specifically designed for GE Datex Ohmeda machines
    • Involves the sump with a keyed filling system
    • Features concentration control hardware and software integrated into the anesthesia machine
    • Agent-specific, ensuring the gas maintains its Saturated Vapor Pressure (SVP) within the cassette

    GE Aladin Vaporizing System

    • Advanced computerized vaporizer specifically designed for GE Datex Ohmeda machines
    • Involves the sump with a keyed filling system
    • Features concentration control hardware and software integrated into the anesthesia machine
    • Agent-specific, ensuring the gas maintains its Saturated Vapor Pressure (SVP) within the cassette

    Vapor Concentration Generation

    • Agent-specific cartridges are used in conjunction with electronic injection to generate vapor concentrations.
    • The process applies principles that involve converting measured liquid volume to known vapor volume to create standard vapor concentrations.
    • Pressurized liquid agent is pulsed into a heated chamber to facilitate vaporization.
    • Fresh gas flows through the chamber, where it picks up the vaporized agent.
    • The amount of agent injected is dependent on the desired concentration and the flow rate of the fresh gas.

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    Description

    Explore the properties of vapor, including its relation to temperature and pressure, and its application in anesthesia vaporizers. Learn about liquid-vapor equilibrium and more.

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