Anesthesia and Vapor Principles

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.