What is vaporizer?
is designed to add a controlled amount of an inhalational agent, after changing it from liquid to vapor, to the FGF. This is normally expressed as a percentage of saturated vapor added to the gas flow.
What is Characteristics of the ideal vaporizer?
1. Its performance is not affected by changes in FGF, volume of the liquid agent, ambient temperature and pressure, decrease in temperature due to vaporization and pressure fluctuation due to the mode of respiration. 2. Low resistance to flow.
2. Light weight with small liquid requirement.
3. Economy and safety in use with minimal servicing requirements.
4. Corrosion- and solvent-resistant construction.
What is the classification of vaporizers by location?
1. Inside the breathing system. Gases pass through a very low resistance, draw-over vaporizer due to the patient’s respiratory efforts (e.g. Goldman, Oxford Miniature Vaporizer [OMV]).
2. Outside the breathing system. Gases are driven a plenum (high resistance, unidirectional) vaporizer due to gas pressure.
What is Components of vaporizer?
1. The case with the filling level indicator and a port for
2. the filling device.
3. Percentage control dial on top of the case.
4. The bypass channel and the vaporization chamber.
5. Bimetallic strip.
6. The vaporizers are mounted on the back bar using the interlocking Selecta Tec system.
What is type of vaporizer?
• Plenum: is driven by positive pressure from the anesthetic machine, and is usually mounted on the machine.
• Draw over: is driven by negative pressure developed by the patient, and must therefore have a low resistance to gas
What is Mechanism of action?
1. The calibration of each vaporizer is agent-specific.
2. FGF is split into two streams on entering the vaporizer. One stream flows through the bypass channel and the other, smaller stream (typically less than 20% of total), flows through the vaporizing chamber. The two gas streams reunite as the gas leaves the vaporizer.
3. The vaporization chamber is designed so that the gas leaving it is always fully saturated with vapor before it rejoins the bypass gas stream. This should be achieved despite changes in the FGF.
4. Full saturation with vapor is achieved by increasing the surface area of contact between the carrier gas and the anesthetic agent. This is achieved by having wicks saturated by the inhalational agent, a series of baffles or by bubbling the gas through the liquid.
5. The desired concentration is obtained by adjusting the percentage control dial. This alters the amount of gas flowing through the bypass channel to that flowing through the vaporization chamber.
6. In the modern designs, the vapor concentration supplied by the vaporizer is virtually independent of the FGFs between 0.25 and 15 L/min.
7. During vaporization, cooling occurs due to the loss of latent heat of vaporization.
8. The amount of vapor carried by the FGF is a function of both the saturated vapor pressure (SVP) of the agent and the atmospheric pressure.
What is Problems in practice and safety features?
1. In modern vaporizers (Tec Mk 5), the liquid anesthetic agent does not enter the bypass channel even if the vaporizer is tipped upside down due to internal valves acting as an antispill mechanism. In earlier designs, dangerously high concentrations of anesthetic agent could be delivered to the patient in cases of agent spillage into the bypass channel.
2. The Selecta Tec system increases the potential for leaks. This is due to the risk of accidental removal of the O-rings with changes of vaporizers
3. Minute volume divider ventilators exert back pressure of oxygen and the inhalational agent within the vaporizing chamber (Tec Mk 2).
4. Preservatives, such as thymol in halothane, accumulate on the wicks of vaporizers with time. Large quantities may interfere with the function of the vaporizer. Thymol can also cause the bimetallic strip in the Tec Mk 2 to stick. Enflurane and isoflurane do not contain preservative.5. A pressure relief valve downstream of the vaporizer opens at about 35 kPa. This prevents damage to flowmeters or vaporizers if the common gas outlet is blocked.
6. The bimetallic strip has been situated in the bypass channel since the Tec Mk 3.
7. The vaporizer needs regular servicing to ensure accurate calibration.
8. Despite its temperature-compensation properties, the vaporizer can deliver unreliable inhalational agent concentrations in extreme ambient temperatures.
What is Advantages of vaporizer?
1. Easy to use and reliable.
1. 2. Properly calibrated modern variable bypass vaporizers are accurate to +/- 15% of the dial
2. setting for all flows between 200 ml.min-1 and 15 l.min-1 at 21°C.
3. This type of vaporizer does not require a power source.
What is Disadvantages of vaporizer?
1. High internal resistance so must be used ‘out of circle’.
2. The heat sink makes the vaporizer heavy – another reason why this type of vaporizer is not suitable for use in the field.
3. There are no alarms to indicate that the level of liquid anesthetic inside the vaporizer is low.
4. Temperature compensation only works within a reasonable range of ambient temperatures. If the vaporizer is used in an extremely hot or cold environment it will deliver anesthetic unreliably.
How to filling vaporizer devices?
These are agent-specific being geometrically coded (keyed) to fit the safety filling port of the correct vaporizer and anesthetic agent supply bottle . They prevent the risk of adding the wrong agent to the wrong vaporizer and decrease the extent of spillage. The safety filling system, in addition, ensures that the vaporizer cannot overflow. Fillers used fordesflurane and sevoflurane have valves that are only opened when fully inserted into their ports. This prevents spillage.
By: B.M.T. Montadher Talib