What Is Anesthetic Vaporizers?
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Anesthetic Vaporizers - Types and Techniques

Published on Aug 23, 2023 and last reviewed on Nov 10, 2023   -  5 min read


Anesthetic vaporizers are crucial components of anesthesia equipment that vaporize a liquid anesthetic drug and administer a precise dosage to the patient.


Anesthetic vaporizers, used to provide volatile anesthetics, have progressed from essential masks used for open ether anesthesia to the latest electronically controlled vaporizers capable of delivering modern and sophisticated inhalation anesthetic drugs. The development of powerful inhalational anesthetics with distinct properties impacts the advancement of vaporizers. Anesthetic vaporizers must administer a safe and predictable concentration of volatile drugs to the patient and reduce the barometric pressure and temperature during the evaporation process, enabling anesthetists to work more effectively.

The electronic vaporizers have been designed to be highly safe, with several priority indicators to alert the operator if there is a problem. Furthermore, with the use of highly effective volatile agents and agents with low boiling points, recent vaporizers can manage the vapor output with great precision even when the anesthetic machine fresh gas flows (FGF) are modified to vary the anesthetic depth quickly.

Modern vaporizers are microprocessor-controlled systems that can securely add an exact and controllable vapor concentration to fresh gas flow. They are agent-specific and can provide a consistent drug concentration irrespective of temperature or flow through the vaporizer. In addition, vaporizers have been developed to accommodate the qualities of new inhalational anesthetic drugs.

What Is the Basic Physiology of the Anesthetic Vaporiser?

  • A substance in its gaseous phase is referred to as vapor. To enter this phase, a material should attain a temperature lower than its critical temperature, which varies from drug to drug.

  • The ideal gas law, which says that the pressure exerted by the gas mostly on container walls is precisely proportional to the number of gas molecules (n) and the temperature within the container given in degrees Kelvin, explains the gas behavior in a sealed container (K). Nevertheless, it is inversely related to the container's volume (v).

  • In other words, the gas molecules within the container act as objects in space, colliding with one another and the container walls, causing pressure to build up.

What Are the Physical Properties of the Vaporizer?

  • A vapor is composed of a high-kinetic-energy molecule that has broken the links between their counterparts and left the surface of a liquid.

  • The molecules leave and return to the liquid randomly, gradually equilibrating and at what point the vapor is entirely saturated.

  • At equilibrium, these molecules put a lot of pressure on the surrounding, known as saturated vapor pressure (SVP).

  • The greater the temperature, the more and more energy is present in the molecules; as a result, more molecules depart the liquid, and SVP rises.

  • The liquid boils when SVP equals atmospheric pressure. As molecules escape from the liquid, the energy in the liquid is decreased (the latent heat of vaporization), lowering the liquid's temperature.

How Are Modern Vaporizers Classified?

Modern vaporizers are classified into two types. They are:

  1. Measured flow vaporizers:

    1. Desflurane vaporizer.

    2. Direct injection of volatile anesthetic vaporizer (for the anesthetics Desflurane, Enflurane, Isoflurane, Sevoflurane, and Halothane).

  2. Variable bypass vaporizers:

    1. Plenum vaporizers (for Halothane, Enflurane, Isoflurane, Sevoflurane except Desflurane).

    2. Plenum vaporizers with electronic control (for the anesthetics Desflurane, Enflurane, Isoflurane, Sevoflurane, and Halothane).

What Are the Indications for Anesthetic Vaporiser?

Every procedure requiring general anesthesia using an inhalation anesthetic approach should employ an anesthetic vaporizer.

What Are the Contraindications for the Anesthetic Vaporiser?

If the vaporizer is suspected of malfunctioning, it should be taken apart and replaced with the new one. In individuals predisposed to severe reactions to some anesthetic drugs (malignant hyperthermia), the vaporizers on the anesthetic machine should be disconnected, and intravenous anesthetic is the best alternative.

What Are Various Equipment for the Anesthetic Vaporisers?

Variable Bypass Vaporizers:

  • Two types of variable bypass vaporizers are drawn over and plenum (with or without an electronic operator). The gas mixture is pulled into the vaporization chamber in the draw-over vaporizers, passing it over anesthetic liquid.

  • Negative pressure (sub-atmospheric pressure) is generated directly by the patient's respiration, drawing anesthetic gas from the vaporizer to the patient.

  • Plenum vaporizers have a pressurized vaporization container that produces higher internal resistance (above atmospheric pressure) for the new gas to flow.

  • This type of vaporizer is now the most popular and is distinguished by its precision in the gas mixture delivered to the patient.

Mode of Operation:

  • The fresh gas is separated into two streams after exiting the flowmeter and entering the vaporizer. A single stream flow feeds the bypassing circuits and the temperature-regulating equipment.

  • The other stream runs down through the pressure-regulating labyrinth into the vaporizing chamber, which combines it with the vapor of the liquid anesthetic medication. It is then combined with the new gas flow as it travels throughout the concentration cone.

  • The temperature-regulating component modifies the bypass flow ratio to the vaporization chamber to compensate for variations in anesthetic vapor pressure due to temperature fluctuations.

Main Characteristics of Variable Bypass Vaporizers:

  • The release of the dial can be utilized to regulate the interlock mechanism when pushed inward toward the dial when the vaporizer bar is closed. The interlock mechanism permits the manifold's port valves to open and the vaporizer to function.

  • The interlock system also stops neighboring vaporizers from being turned on. These vaporizers are set at eight percent Sevoflurane concentration and other anesthetic agents at a five percent concentration.

  • These could be packed with 300 ml of dry wicks, 75 ml of which should be kept as the standard threshold of filling in the wicks unit.

Cassette Type Vaporizer:

  • This vaporizer is compatible with Halothane, Isoflurane, Enflurane, Sevoflurane, and Desflurane anesthetic equipment. The unit is divided into two sections.

  • The first component is permanently installed in the anesthetic machine, while the second is a replaceable cassette that stores the liquid anesthetic drug and serves as a vaporization chamber.

  • It is crucial to remember that this vaporizer is managed by a microprocessor that obtains data regarding the gas composition from flowmeters, temperature and pressure sensors within the vaporization compartment, and from the output of the vaporization compartment to deliver a precise concentration of anesthetic gas.

  • This vaporizer also has a single valve that prohibits backward flow to the variable flow chamber. The cassette vaporizer also incorporates automatic control of oxygen concentration, ensuring that an oxygen concentration of less than 25 percent is never administered to the patient, regardless of the anesthetic gas concentration.

  • If the pressure inside the cassette surpasses 2.5 bars (1899 mmHg), the pressure release valve on this vaporizer will activate, eliminating this pressure from being passed to the breathing circuit. Finally, this vaporizer is peculiar in that tipping is not an issue with this device.

What Are the Complications of Using Anesthetic Vaporizers?

  1. Vaporizer safety characteristics and risks.

  2. Incomplete filling of the agent.

  3. Tipping.

  4. Administration of multiple vapors at the same time.

  5. Vaporizer overfilling.

  6. Vapor escapes into the fresh gas line.

  7. Leaks in the equipment.


The mechanism of vaporizers is complicated and necessitates a thorough grasp of thermodynamics, gasses, and physics. To reduce the risk, anesthetists must be knowledgeable about the appropriate function of anesthetic devices and be able to spot apparatus malfunctions.

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Last reviewed at:
10 Nov 2023  -  5 min read




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