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Questions and Answers
What is a key requirement of the Joint Commission regarding scavenging systems?
Which component is NOT part of a scavenging system?
What type of pressure relief valves do closed scavenging systems require?
How do active scavenging systems prevent contamination of the operating room environment?
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Which statement is true regarding open and closed scavenging systems?
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What characterizes an active scavenger system?
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Which statement correctly describes vapor pressure in relation to anesthesia?
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What is the primary function of a modern vaporizer in relation to anesthetic gases?
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Which of the following best describes Dalton’s Law as applied to vapor pressure?
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What impact does saturation vapor pressure (SVP) have on the use of sevoflurane in anesthesia?
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Which of these factors does NOT affect vaporization in anesthesia vaporizers?
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What is a consequence of too much suction in a scavenger system?
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What differentiates a concentration calibrated vaporizer from a measured flow vaporizer?
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What leads to the formation of saturated vapor pressure (SVP) in a closed container?
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How does increasing the temperature affect the saturated vapor pressure of a volatile anesthetic agent?
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What role do carrier gases like N2O and O2 play in the process of vaporization of anesthetic agents?
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What happens to the vapor output of a vaporizer when carrier gas is introduced?
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Which of the following anesthetics has the highest saturated vapor pressure (SVP)?
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In a closed container achieving vapor equilibrium, which statement is true at constant temperature?
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What must be continuously supplied to maintain constant temperature inside a vaporizer?
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If the vapor pressure of an anesthetic agent is increased, which effect can generally be expected?
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Study Notes
Vaporizers
- Convert liquid anesthetic into a volatile inhalation agent
- Should be calibrated for accuracy of delivered concentration
- Based on laws of physics
- You must memorize the chemical properties of the volatile agents
Vaporizer Pressure
- Saturated vapor pressures are too high
- SVP of Sevoflurane 160 mmHg
- Divide by atmospheric pressure of 760 mmHg
- 160/760 (100) = 21% (The MAC of Sevo is 2.1%)
- Need to dilute to a concentration that is not lethal
Vaporizer Types
- Measured Flow
- The flow through the liquid is measured
- It is then diluted
- Needs to be calculated
- Example: The copper Kettle, Vernitrol
- Concentration Calibrated (Most Are Variable Bypass)
- Deliver a set concentration based on the dial setting
Basic Vaporizer Design
- Gas enters Vaporizer
- Flow is split (Variable Bypass)
- Majority is bypassed
- Some enters the vaporizing chamber
- Saturated gas leaves chamber
- Diluted by bypass gas
- Delivered to patient
Applied Physics
- Vapor Pressure
- Dalton's Law (The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases)
- Based on characteristics of agent
- Varies with Temperature
- Boiling Point
- Vapor pressure equals atmospheric pressure, all liquid is in the vapor phase
- Latent Heat of Vaporization
- Heat required to change liquid into a vapor
- Comes from liquid and environment
- Vapor Pressure - Pressure exerted on walls of a container by molecules that broke away from the liquid surface. Equilibrium will be achieved if temperature remains constant. All volatile anesthetics have a specific vapor pressure. The concentration can be calculated from the vapor pressure above the liquid.
- Volumes Percent (Vol%) - The number of units of volume of gas in relation to a total of 100 units of volume for the total gas volume.
Vaporization
- Vapor: Gas phase of a substance that is liquid at room temperature and atmospheric pressure
- Vaporization: Conversion of liquid to gas (inside Vaporizer)
- Vaporization depends on:
- Vapor pressure of agent
- Temperature of environment
- Amount of carrier gas (N2O & O2) used
Saturated Vapor Pressure
- Liquid inside a closed container
- Molecules of liquid break away and enter space above to form a vapor
- At constant temp:
-
molecules entering and leaving liquid are equal
-
molecules in vapor phase stays constant
- Pressure created when molecules bombard the walls of the container Saturated Vapor Pressure (SVP)
-
- Volatile Anesthetic Agent (VAA): Liquid that has a tendency to change to a vapor at standard temp & press. Higher volatility = stronger tendency to change to vapor = higher SVP
SVP
- Methoxyflurane: 23 mmHg
- Sevoflurane: 160 mmHg *
- Enflurane: 175 mmHg
- Isoflurane: 238 mmHg *
- Halothane: 243 mmHg
- Desflurane: 660 mmHg *
- *These are generally considered the most common agents used in modern practice
SVP and Temperature Changes
- Heat increases SVP
- More molecules enter gas phase
- Less molecules re-enter liquid phase
- Cooling decreases SVP
- Less molecules enter gas phase
- More molecules re-enter liquid phase
Carrier Gas (N2O, O2)
- Passing of carrier gas over the liquid decreases SVP
- Heat is needed continuously to vaporize anesthetic agents and maintain constant SVP
- When practitioner turns on vaporizer, carrier gas enters the vaporizer to pick up and deliver VAA to patient SVP decreases
- The liquid agent (e.g. Isoflurane) generates more vapor as an inherent attempt to keep SVP constant heat is lost decreased vaporizer output
Temperature Compensation
- Heat must be supplied to the liquid anesthetic inside vaporizer to maintain constant temperature constant SVP
Vaporizer Classification
- Method of Regulating Output Concentration
- Concentration Calibrated (Variable-Bypass)
Scavenging Systems
- Active - Require suction
- Passive - Rely on passive flow
- Joint Commission requires an active system
- You may find passive systems in some smaller institutions
Scavenging Systems Properties
- Not affect dynamics of breathing
- Not affect oxygenation of the patient
Scavenging Systems Components
- Relief Valve
- Conducting tubing
- Interface
- Disposal Line
- Remember: The Joint Commission requires active scavenging systems. This means that the system must use a vacuum to remove excess anesthetic gas.
Types of Scavenging Systems
- Open - Vent directly to the outside and require no valves
- Closed - Closed to the outside and therefore require negative and positive pressure relief valves to protect the patient
- Active - Connected to the hospital vacuum line.
- Passive - Vent the gases far away enough to prevent contamination of the OR environment.
Scavenging Systems Summary
- Interface – Open (newer models), Closed (older models)
- Active – Passive suction vs. atmospheric venting
- Must have positive and negative pressure relief valves to prevent patient harm from too much pressure or vacuum
Scavenging Systems Components
- Gas Collection System, APL Valve - Ventilator Relief Valve. 19 or 30 mm. (Different than ventilator)
- Scavenging Interface
- Gas Disposal tubing
- Gas Disposal Assembly
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Description
Dive into the world of anesthesia vaporizers, exploring how liquid anesthetics are transformed into volatile inhalation agents. Understand the calibration requirements, types of vaporizers, and basic design principles. Prepare yourself to memorize essential chemical properties critical for safe and effective anesthesia.
