Gent 1998
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Gent 1998 |
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THE PRODUCTION AND AVAILABILITY OF XENON
MR M E GARRETT, Bsc, CChem, CEng, FRSC, FIChemE, FRSA, MICIWEM
Director Innovation, BOC
Xenon is the Greek word for stranger (when krypton was first distilled from liquid air a strange residue was left, this was identified as a new gas and it was named xenon) . The gas is present in the atmosphere, which is the major source, but at a concentration of only 0.09 vpm, it becomes a liquid at -108C and freezes at -111'C it also has a critical temperature of 16.6C and a critical pressure of 58.2 atma.
The gas is quite heavy with a molecular weight of 131 and is colourless, odourless and without taste. The low concentration in air means the recovery of xenon is only practical on very large air separation plants, typically those capable of separating 1000 tonnes per day of oxygen or more. The xenon is tapped from the upper distillation column four distillation trays below the normal oxygen product off-take location and this section operates at close to total reflux. The xenon and krypton concentrate in the liquid stream allowing enhancement of the combined gases to a concentration of 0.4% (xenon = 0.03%). Although the concentration of xenon at this point seems quite low it is necessary because methane can be present in similar concentrations and must be kept below its flammability limit.
The second stage of xenon preparation involves the separation of krypton and xenon from the oxygen, argon and hydro-carbons, this is achieved by catalytic destruction of the hydro-carbon and oxygen followed by drying and distillation to produce the krypton/xenon concentrate at about 98%.
The final stages of purification are laboratory scale, because even a 1000 /day plant will only produce about 4m3/day of the mixed gases which represents a 70% recovery. Final purification involves the adsorption of xenon at low temperature followed by further cooling to freeze out the krypton. Reheating and selective recycling will produce purities of 99.995%. At normal temperatures the gas is supercritical but when the ambient temperature falls below 16.6C the gas will condense in the cylinder as a liquid. The low concentration of initial recovered gas and the small quantity captured daily indicates that recycling of recovered gas from operating theatres is likely to be an attractive process. The cost of the material is a function of supply and demand as well as the processing costs and recovered gas from hospitals could provide a significant reduction in cost. Currently the cost is such that it is economic to recover xenon and neon from flat computer arrays when they are being scrapped.
Xenon because of its rarity is normally measured in litres of gas at STP rather than as the tonnage unit used for the major industrial gases. Current world production is about 6 million litres with BOC accounting for nearly 20% of the world's supply. There are about 13 other suppliers, the largest of which is L'Air Liquide with nearly 30% of the world's supply. Currently xenon is used for a variety of applications which includes high intensity lamps, flash bulbs for cameras, medical uses, flat panel displays, lasers, x-ray tubes and even some for anaesthesia, proportionately lighting accounts for 39% and anaesthesia 10% which is a similar amount as for other medical uses. Lasers use about 20%.
It is interesting to compare these figures with those predicted for the year 2001. World production is then estimated to be over 9 million litres with anaesthesia rising to 15% and lighting accounting for 24%, there is however a new application, aerospace which accounts for 30%. In some ways this is sad because the aerospace use is for a xenon ion engine used to manoeuvre satellites and this will mean that much of the xenon taken into space will be lost to the world forever whereas today every scrap is recycled. An alternative gas for this application would be krypton of which there is a very much greater supply and were this to be adopted xenon supplies and costs in 2001 will be much more favourable.
Xenon was once a part of the inert gas group (helium neon, radon, xenon, krypton, argon) but because of the discovery of xenon compounds the group was later renamed the noble gases. Compounds include clathrates and also fluorides, chloride fluorides, chlorides, oxides, oxyfluorides, xenates, fluoroxenates, perxenates and complex salts. Enzymatic reactions have also been observed, although the xenon compounds are of great interest many are explosively unstable. However, the cost has limited its use but hopefully greater use will influence this to make it more widely available than before.
Xenon - Technical solutions to administer Xenon
by Dr. M. Th.A. Teeling - Physio b. v., Haarlem, The Netherlands
The lecture was given by Mr B. Wederkamp
It is essential for a technician, at the start of a new project, to know the properties of the substance he is dealing with. We all know Xenon is a noble gas. Xenon is a large molecule, with a weight of 131.30 g.mol-1. Being a noble gas, Xenon cannot be measured using a chemical method, only methods based on physical properties can be applied.
The different methods available are based on:
* weight (mass spectrometry)
* light absorption (UV)
* heat conductivity
* gas chromatography
Almost all experiments so far are carried out using the mass spectrometer to verify the inspiratory Xenon concentration. This equipment, however, is expensive and must be accurately calibrated. The sample used for the measurement is wasted.
Physio has looked into the cheapest measurement principle; thermo-conductivity. This method is fairly simple to calibrate when used in combination with the PhysioFlex. The Xenon sample is not wasted as it is fed back into the system. The disadvantage, unfortunately, is that almost every gas has an effect. Within the possible mixtures found in the PhysioFlex, the sensor is far more sensitive for Xenon than for the other gases. The concentrations of the other gases are also known, therefore their effects can be eliminated.
Xenon has a high viscosity, this means that the dosage system must have a larger capacity to allow the required flow and also has to be calibrated accordingly. During wash-in or flush relatively high flows are required, after wash-in uptake is extremely low, this means that the dosage system needs high accuracy over a wide range.
Being that expensive the waste of Xenon must be minimised. Drager started a research project using its Cicero, a traditional semi-dosed system capable for use for minimal flow condition. Traditional systems, even minimal flow, require a constant surplus of fresh gas and have relatively large system volumes. A Xenon recycling system could reduce the amount wasted, however this equipment also involves additional costs.
The Physio company, being the expert within Drager for Quantitative Anaesthesia, looked into the problem. The PhysioFlex system is in these respects much more favourable:
a small system volume < 4 1.
FGF = patient uptake
all gases influencing the thermo-conductivity analyser are measured
the sample is fed back into the system.
In the PhysioFlex oxygen concentration is feedback controlled and therefore very constant. The dosage of Xenon in the system is based on the volume loss due to uptake or loss (for example flush). The concentration of Xenon is observed by the user, however if the amount of "foreign" gas exceeds 10% a flush is advised ((FI02 + FIXe) < 90%). One flush procedure (one minute) uses approximately 5 1, so around 3 - 4 litres of Xenon are wasted.
Another advantage is the simplicity. Just by a key stroke the use of Xenon can be selected. No adjustment to the equipment has to be made by the user. All parameters are stored in memory, so after several cases, up to 75 hours of anaesthesia, the user can download the data with the Flexcom program and analyse the gas usage.
References
1. Lawrence JH, Loomis WF, et al.
Preliminary Observations on the Narcotic Effect of Xenon with a Review of Values for Solubilities of Gases in Water and Oils.
J Physiol 1946;105:197-204
2. Cullen SC, Gross EG.
Anesthetic Properties of Xenon in animals and Human Beings, with Additional Observations on Krypton
Science 1951; 113:580-582.
3. Pittinger CB, Moyers J, et al.
Clinico Pathologic Studies Associated with Xenon Anesthesia
Anesthesiology 1953;14:10-17.
4. Lachmann B, Armbruster S, Schairer W, Landstra M, Trouwborst A, Van Daai FJ, Kusuma A, Erdmann W.
Safety and efficacy of Xenon in routine use as an inhalation anaesthetic
The Lancet 1990;335:1413-1415.
5. Luttropp HH, Tomasson R, et al.
Clinical Experience with Minimal Flow Xenon Anesthesia Acta-anesthesiologica Scand 1994;38:121-125.
6. Giunta F, Natale G, Del Turco M, Del Tacca M.
Xenon: a review of its anaesthetic and pharmacological properties
Applied Cardiopulmonary Pathophysiology 1996;6:95-103.
XENON APPLICATION
T. Marx, M. Georgieff, G. Froba
University Clinic for Anesthesiology, Ulm, Germany
Pollution of anesthesia work areas and environment occurs during general anesthesia. Volatile anesthetics represent toxic hazards to operating personnel, have ozone-depleting potential and contribute to the greenhouse effect. Since 1951 Xenon has been known to have anesthetic potency at atmospheric pressure. The high price of xenon makes low-flow technologies and recycling of the substance necessary. In the first step of our project, we constructed a recycling system for xenon.
Recycling system
We used a thermodynamic procedure to purity xenon during anesthesia.
Our purification process is based on the favourable circumstances of a partial liquefaction of a 70% xenon mixture at a pressure exceeding 60 bars and a temperature of 20 degrees below zero. Because of their critical parameters, oxygen and nitrogen stay gaseous during this process. The compressor takes the gas out of the pressureless reservoirs and compresses it in a cooled-condenser-container. If the pressure increases to 60 bar and the temperature decreases to 20 degrees below zero, the xenon-share in the gas mixture begins to liquefy. The xenon gas, stored in the reservoir can now be reused in the anesthesia device.
Experimental animal study
After consent of the local animal care commission, 28 pigs were randomly assigned to group 1, 2, 3, or 4:
Group 1: Total intravenous anesthesia TIVA,
Group 2: Anesthesia with inspiratory xenon concentrations of 30%,
Group 3: 50% xenon and Group 4: 70% xenon.
The median body weights (25.-75. percentile) in groups 1, 2, 3 and 4 were 41.5 (34.5-42.9) kg, 40.5 (40.0-41.9) kg, 41.0 (39.3-41.9) kg and 37.5 (35.9-41.1) kg, respectively.
Anesthesia
After premedication and induction of anesthesia, controlled ventilation was performed using room air. lntermittent positive pressure ventilation was carried out in a partial rebreathing system (Draeger Cicero, Draegerwerk Lubeck, Germany), which was calibrated for xenon anesthesia by the manufacturer. The fresh gas flow was set to 1 l/min. The ventilation volume was adjusted to achieve normocapnia according to expiratory CO2 concentrations. Xenon was added now to the inspiratory gas mixture according to the randomisation. To compensate the higher uptake of xenon immediately after application, the flow was increased to 6 l/min during the first five minutes. In the average the duration of xenon anesthesia amount to 4h.
Xenon was supplied in a purity of 99,9999 % by Messer-Griesheim, Krefeld, Germany. Monitoring In- and expiratory oxygen and carbon dioxide concentrations were measured simultaneously by infrared absorption (Draeger Cicero, Draegerwerk Lubeck, Germany) and by mass spectrometry (Fisons Gaslab300, Fisons Instruments, Weesp, Netherlands). In- and expiratory xenon concentrations were measured on-line by mass spectrometry alone.
Results
The measured output of recovered xenon was 67 percent with a purity of 89%, determined in the animal study by difference weighing the bottles.
The liquid xenon contained 7.2% of oxygen and 3.8% of nitrogen. Organic impurities were not detected.
The results of our experiments seemed to be so optimistic, that the process of legal approval for xenon as anaesthetic agent was started in Europe in 1996. New technologies are supposed to increase the recycling effectivity.
Closed system anesthesia
In a recently finished experiment, inert Xe 131 was traced with radioactive Xe133 to investigate the organ distribution under conditions of anesthesia. Another subject of the investigation was the advancement of the closed anesthesia system.
Main accumulation of xenon after 4 hours of anesthesia occurred in the bowels. No further accumulation of xenon was seen in other organ systems. Half life times of organ specific wash-in and wash-out curves are presently calculated. Using the advanced closed system, a mean amount of 8 liters of xenon was needed for four hours of anesthesia, 4.5 liters dead space of the system are already included in that finding. Using the closed system, gas concentrations were held easily at the required values (Fig.2).
Conclusion
Xenon still must be regarded to be the ideal inhalation agent. Further steps to its routine use must include the advancement of dosed system anesthesia and new aspects of recycling systems. As a negative aspect the price of xenon increased from US $ 5 to US $ 10 in the last year. The reason is a satellite program by the NASA, using xenon as satellite fuel.
On the other hand, Berkley Labs in Californa and other institutions are searching for the so-called "missing xenon". Based on the assumption, that the relative distribution of all elements is roughly the same on all objects in the solar system, the fact is known, that the earth's atmosphere contains 2000 times less xenon than all other known planets.
It is commonly assumed that that amount of xenon still is present on our planet. So our hope may be directed to that search. On the other hand, it is clearly obvious that the development of the price of xenon is dependent on many factors and is hardly predictable in the close future.
XENON IN THE PhysioFlex: THE FIRST CLINICAL EXPERIENCE
R. Tenbrinck K Leendertse W Erdmann
Dept Anesthsiology, University Hospital Dijkzigt, DR. Molenwaterplein 40, 3015 GD Rotterdam, The Netherlands
The year 1998 is an important one for Xenon; one century after its discovery, 50 years after its first use in anaesthesia and ten years after the first very successful trial in our hospital [1] we are able to show the first clinical results with the use of the Rotterdam developed Drager PhysioFlex.
This PhysioFlex is a standard type; the only modifications are an extra inlet for the Xenon gas and an adapted infrared sensor for measuring the Xenon concentrations. The software is updated so that the concentration, flow and the total consumption of Xenon are indicated on the screen. The first group of 15 patients consisted of ASA 1-2 aged 20 - 70 for minor surgical interference. Benzodiazepines of other sedatives were avoided in the premedication.
Induction was performed with propofol 2mg/kg, fentanyl 2-3.mcg/kg and atracurium 0.5 mg/kg. After preoxygenation the patient was intubated and connected to the PhysioFlex. Xenon / Oxygen mixture (FIO2 0.25) was flushed in. Mean wash-in time was 2.5 minutes before achieving a Xenon concentration of 65-72%
This procedure costs about 9 - 11 l of Xenon. There was no additional volatile or intravenous anesthetic. Hemodynamics and ventilation were stable as reported before [1]. After the operation the extubation is as soon as possible as soon as the Xenon concentration dropped below 8%. 70% of patients are able to recollect their name and operating date immediately after extubation. There was no evidence of awareness during the whole procedure.
Conclusion:
Xenon can be used safely and success in the PhysioFlex; its superior anesthetic aspects are clearly shown by the hemodynamic and ventilatory values during the operation and the cerebral performance immediately after extubation. There was no awareness in the Xenon group during the operation.
1. Lancet 1990; 335 1413-5
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