An anaesthetic vaporizer must deliver a safe, reliable concentration of volatile agent to the patient. Anaesthetists should understand the basic principles of. Vaporizers are an integral part of modern-day anaesthesia, allowing the delivery of safe concentrations of volatile anaesthetic agent. Over time, vaporizer design. Anaesthesia vaporizers for inhalational anaesthetic agents. Principal, classification, types, hazards.

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Vapor pressure Molecules escape from a volatile liquid to the vapor phase, creating a “saturated vapor pressure” at equilibrium.

Vapor pressure VP increases with temperature. VP is independent of atmospheric pressure, it depends only on the physical characteristics of the liquid, and its temperature. So, even although evaporation proceeds at a rate governed by liquid temperature and is independent of altitude barometric pressureindividual vaporizer types may or may not function the same at altitude.

Latent heat of vaporization is the number of calories needed to convert 1 g of liquid to vapor, without temperature change in the remaining liquid. Thus, the temperature of the remaining liquid will drop as vaporization proceeds, lowering VP, unless this is prevented. Specific heat is the number of calories needed to increase the temperature of 1 g of a substance by 1 degree C. Manufacturers select materials for vaporizer construction with high specific heats to minimize temperature changes associated with vaporization.

Thermal conductivity – a measure of how fast a substance transmits heat. High thermal conductivity is desirable in vaporizer construction. The copper kettle and Vernitrol probably strictly museum pieces at this point are measured-flow, bubble-through, non-temperature compensated, multiple agent, and out of circuit.

The Tec 6 desflurane vaporizer is not a variable bypass vaporizer, it is a gas-vapor blender. These two flows rejoin at the vaporizer outlet.

The splitting ratio of these two flows depends on the ratio of resistances to their flow, which is controlled by the concentration control dial, and the automatic temperature compensation valve.

Vaporizers | Anesthesia Equipment Simplified | AccessAnesthesiology | McGraw-Hill Medical

Effect of flow rate: Clinically this is relatively unimportant, since we titrate to effect end tidal agent concentration and use overpressure. Effect of ambient temperature: The output of modern vaporizers is linear from degrees C, due to. Effect of intermittent back pressure transmitted from breathing circuit: The pumping effect is due to positive pressure ventilation or use of the oxygen flush valve. It can increase vaporizer output.

Modern vaporizers are vapoorizers immune older vaporizers were certainly not immune due to check valves between the vaporizer outlet and the common gas outlet, smaller vaporizing chambers, or tortuous inlet chambers. Any of these design vaporizrs prevent gas which has left the vaporizers from re-entering it.


The effect of altitude on vaporizer performance is controversial. Dorsch and Dorsch Understanding Anesthesia Equipment 5th ed. Some sources state that variable bypass types need not be adjusted for moderate changes in barometric pressure, but the Tec 6 must be dialed up vaporizere the desired dose at higher altitudes.

For either funnel or keyed filler types, vaporizrs the vaporizer only to the top etched line within the sight glass. Do not hold the bottle up on a keyed filler until it stops bubbling this will overfill the chamber, particularly if the concentration control dial is “on”, or if leaks are present.

The only current vaporizer which can be filled while it is operating is the Tec 6 Desflurane but even that vaporizer is safer to fill in the “off” position. Ehrenwerth and Eisenkraft give the formula: Typically, 1 mL of liquid volatile agent yields about mL vapor. This is why tipping is so hazardous- it discharges liquid agent into the control mechanisms, or distal to the outlet. And minute amounts of liquid agent discharged distal to the vaporizer outlet result in a large bolus of saturated vapor delivered to the patient instantaneously.

Click on the thumbnail, or on the underlined text, to see the larger version 68 KB. The Vapor is one of two tippable vaporizers Aisys cassettes are the other. The dial must first be rotated to a “T” setting “transport” or “tip” which is beyond zero clockwise.

Click on the thumbnail, or on the underlined text, to see the larger version. The Vapor is also tippable. Click on the thumbnail, or on the underlined text, to see the larger version KB. Aladin vaporizer Aisys, ADU Cassettes containing each volatile liquid anesthetic are inserted into a port containing the central electronic control mechanism, which recognizes the contents of the cassette and dispenses agent into the stream of fresh gas flow.

Because each cassette is only a liquid sump without control mechanisms, they can be tipped in any orientation without danger, and they are maintenance free. The cassette and the control mechanisms vapodizers checked as part of the electronic equipment checklist daily. The Aladin will not deliver volatile agent without mains power or battery backup, and adequate oxygen or air pressure.

Modern Anaesthesia Vapourisers

The output of older vaporizers varies slightly with changes in fresh gas mixture, whereas the Aladin compensates for this automatically.

The Aisys has low agent alarms on all vaporizers. The cassettes are extremely light, and may be removed with one hand. For a study of this vaporizer’s performance, see Anesth Analg ; Tec 6 desflurane vaporizer: Because of the volatility of this agent, new systems were designed to contain, transfer, and vaporize it.

This means that desflurane is nearly boiling at room temperature. Note that not all desflurane vaporizers are Tec 6 type.


The Aladin cassette Aisys, Avance is a variable bypass vaporizer. Classification from Anesth Analg ; Heats agent to 39 degrees C, which produces a vapor pressure of around mm Hg. Electronic controls inject pure vapor into the fresh gas flow from the flowmeters, controlled by the concentration control dial, and a transducer which senses the fresh gas flow rate, and adjusts the vapor output accordingly. Requires electrical power it shuts off in power failures!

In use it is similar to variable bypass vaporizers: The operator’s manual states that it may be filled during use but it is safer to turn it off when filling. A mark on a liquid crystal display indicates when the liquid level is one bottle low mL. The user must replace a battery which powers the alarms periodically. There is an alarm for low liquid level. The unit requires a warm-up period. Tec 6 alarm panel. Ohmeda Tec 4, 5 With the center vaporizer removed if three are mounted side by sideone can activate both outer vaporizers simultaneously in machines manufactured afterthis fault is corrected.

Vaporizer outlet has check valve. Sevotec 5 vaporizer right. Click on the thumbnail, or on the underlined text, to see the larger version 25 KB. The Sevotec 5 is used in a similar fashion to the other Tec 5 vaporizers. Penlon Sigma Delta sevoflurane vaporizer right.

Click on the thumbnail, or on the underlined text, to see the larger version 15 KB. There is no outlet check valve- the tortuous inlet arrangement protects from the pumping effect. Return to the top of this page. Return to Table of Contents. Go to the vaporizes page. Flow-over including the Aladin for desflurane, which does not require added heat like the Tec anaestthesia.

Filling a keyed vaporizer. Click on the thumbnail, or on the underlined text, to see the larger version 35 KB. Filling a funnel-type vaporizer. Click on the thumbnail, or on the underlined text, to see the larger version 28 KB. Tec 6 operating principles. Click on the thumbnail, or on the underlined text, to see the larger version 57 KB. Press and hold the mute button until all lights and alarms activated. A “No Output” alarm should ring within seconds. This tests battery power for the alarms.

This step is crucial in relation to the quick emergence characteristics of this agent- any interruption in its supply must be noted and responded to at once.