CAPTURE OF XENON FROM ANAESTHETIC GAS AND RE-ADMINISTRATION THEREOF TO THE PATIENT

Abstract

A method for the extraction of xenon gas bound to a filter material using supercritical CO.sub.2 to form a mixture in which both CO.sub.2 and xenon are in a supercritical state.

Claims

1-13. (canceled)

14. A method of reclaiming xenon anaesthetic agent, comprising: i) passing gas including xenon anaesthetic agent from a medical environment through a filter so that xenon anaesthetic agent becomes bound to the filter; ii) subjecting the filter to a supercritical fluid to carry the xenon anaesthetic agent from the filter; and iii) separating the xenon anaesthetic agent from the supercritical fluid.

15. The method as claimed in claim 14, in which at step ii) the supercritical fluid is supercritical carbon dioxide and in which a mixture is formed in which both carbon dioxide and xenon are in a supercritical state.

16. A method as claimed in claim 14, further comprising the step of reintroducing the separated xenon anaesthetic agent to a patient.

17. An apparatus to recover xenon anaesthetic agent from a medical environment, comprising a container including a filter through which medical environment gas can be passed so that xenon anaesthetic agent can become reversibly bound thereto.

18. The apparatus as claimed in claim 17, in which the container is connected or connectable to a source of supercritical carbon dioxide for extraction of the xenon anaesthetic agent from the filter by supercritical carbon dioxide.

19. The apparatus as claimed in claim 18, further comprising a source of supercritical carbon dioxide.

20. The apparatus as claimed in claim 17, in which the container is connected or connectable to the exhaust port of an anaesthetic machine or medical device so that waste gas containing xenon is passed through the filter material in the container to bind the xenon gas from the waste gas stream.

21. The apparatus as claimed in claim 17, in which the container is tolerant of pressures in excess of the critical pressure of carbon dioxide.

22. The apparatus as claimed in claim 17, in which the container is intolerant to the critical pressure of carbon dioxide, the container can be placed in a pressure-tolerant container that is pressure-tolerant above the critical pressure of carbon dioxide.

23. The apparatus as claimed in claim 9, the apparatus further comprising a pressure-tolerant vessel that is pressure-tolerant above the critical pressure of carbon dioxide.

24. The apparatus as claimed in claim 17, in which the filter material comprises one or more of: aerogel, silica gel, zeolites, metal organic frameworks, metal doped silica/zeolite, metal doped aerogel.

25. The apparatus as claimed in claim 17, in which the container comprises a stainless-steel tube.

26. The apparatus as claimed in claim 17, comprising a tube with sealed, floating end caps to contain the filter material.

27. The apparatus as claimed in claim 17, further comprising means for separating xenon from carbon dioxide.

28. The apparatus as claimed in claim 17, further comprising a vortex tube.

29. The apparatus as claimed in claim 17, further comprising means for the chromatographic separation of xenon from contaminants.

30. The apparatus as claimed in claim 29, comprising one or more chromatography columns.

31. The apparatus as claimed in claim 17, further comprising soda lime for absorbing carbon dioxide.

32. The apparatus as claimed in claim 31, further comprising means for removing gaseous contaminants.

33. The apparatus as claimed in claim 17, further comprising means for removing microbiological contaminants.

34. The method of claim 14, comprising removing contaminants.

Description

DETAILED DESCRIPTION

[0061] The present invention is more particularly shown, by way of example, with in the accompanying drawings.

[0062] The example embodiments are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the systems and processes herein described. It is important to understand that embodiments can be provided in many alternate forms and should not be construed as limited to the examples set forth herein.

[0063] Accordingly, while embodiments can be modified in various ways and take on various alternative forms, specific embodiments thereof are shown in the drawings and described in detail below as examples. There is no intent to limit to the particular forms disclosed. On the contrary, all modifications, equivalents, and alternatives falling within the scope of the appended claims should be included. Elements of the example embodiments are consistently denoted by the same reference numerals throughout the drawings and detailed description where appropriate.

[0064] Unless otherwise defined, all terms (including technical and scientific terms) used herein are to be interpreted as is customary in the art. It will be further understood that terms in common usage should also be interpreted as is customary in the relevant art and not in an idealized or overly formal sense unless expressly so defined herein.

[0065] One of ordinary skill in the art will appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention.

[0066] FIG. 1 shows a xenon closed circle breathing system with capture, extraction and re-delivery of xenon into the circuit.

[0067] It is anticipated that although this system described in FIG. 1 is applied to a circle system, the same system can be used to deliver recycled xenon to the gas stream in other anaesthesia systems such as a reflector system or cardiopulmonary bypass machine oxygenator.

[0068] A xenon delivery medical device can be a circle system, reflector or cardiopulmonary bypass machine oxygenator.

[0069] Oxygen 1 is delivered to the anaesthetic circuit through a servo valve under electronic control 2. Xenon gas 3 is delivered to the circuit though a solenoid or piezo injection valve 4 under electronic control. Electronic control (not shown) of a negative feedback loop with a target concentration set by medical personnel is determined by pressure 5 and gas monitoring 6 systems. The oxygen/xenon gas mixture passes down the inspiratory limb of the circuit through the inspiratory one-way valve 7. The gas monitoring system detects the concentration of xenon, carbon dioxide and Oxygen at the patient end of the circuit. This is performed by a negative pressure system removing a constant stream of gas from the patient y-piece. Most of this gas is returned to the patient circuit (not shown). Expiratory gases pass down the expiratory limb to the expiratory one-way valve 8 and pressure transducer 5. This reading is used to set the back pressure of the exhaust valve 9. A pressure relief valve 10 protects the circuit from overpressure. Some of the expiratory gases are vented through the exhaust valve (adjustable pressure limiting valve) 9 and the remainder pass through the carbon dioxide absorber 11 and to the ventilator/bag assembly where either mechanical (ventilator) or manual (bag) means are used to pressurize the circle during the ventilation cycle to produce inspiration and expiration. These recirculated gases then circulate back to the inspiratory limb via the gas injectors, where further gas can be added to regulate the system volume (and therefore pressure) and gas concentrations.

[0070] Exhaust gas from the exhaust valve 9 passes down the exhaust limb to one of two collection chambers 12a 12b tolerant of supercritical carbon dioxide pressure above 73 bar. In one preferred embodiment the working pressure of the chamber is 100 bar and the vessel is manufactured from 316 stainless steel. Each collection chamber is controlled by two selection valves 13a 13b and two section valves 14a 14b. These selection valves ensure that each chamber is either set to receive gas from the exhaust valve 9 and ventilate it to air, the suction or Anaesthetic Gas Scavenging System (AGSS) or to receive supercritical carbon dioxide from the pump 15 and heater 16 and pass it to the back-pressure regulator 17. The chambers 12a 12b can have a single input and output through which both exhaust and supercritical fluid can pass or can have separate inputs for the exhaust and supercritical fluid. In a preferred embodiment, separate inputs and outputs are used for the supercritical fluid and exhaust due to the different pressures and flow-rates required for exhaust and supercritical fluid. The selection valves 13a 13b 14a 14b ensure that each chamber 12a 12b is only open to either the exhaust or the supercritical fluid and that one chamber 12a or 12b is exposed to the exhaust while the other chamber 12b or 12a is exposed to the supercritical fluid. The control of the valves is under electronic control (not shown). The flow of exhaust gas and supercritical fluid can be in the same direction or in a preferred embodiment, in different directions as shown in FIG. 1. This improves the rate of desorption of the xenon by the supercritical fluid and increases the absorption capacity.

[0071] The use of a chamber for the capture of xenon onto a filter material that is capable of withstanding pressures above the critical pressure of carbon dioxide.

[0072] The use of two chambers, such that one is exposed to the exhaust of the xenon delivery medical device and the other is exposed supercritical carbon dioxide for extraction.

[0073] The use of a single opening at either end of the chamber for the passage of both the exhaust from the xenon delivery medical device and supercritical carbon dioxide for extraction of xenon from the filter material contained within the chamber.

[0074] The use of separate openings at either end of the chamber, one for the passage of the exhaust from the xenon delivery medical device and the other for the passage of supercritical carbon dioxide for extraction of xenon from the filter material contained within the chamber.

[0075] The chambers 12a 12b are filled with a filter material 17a 17b that absorbs xenon gas. The chambers may be cooled, and the exhaust gas cooled to temperatures from room temperature down to 50 degrees Celsius (not shown) to improve binding. The filter material may include but is not limited to silica gel, zeolites, metal organic frameworks, or metal doped silica/zeolite, most preferably a metal (silver or lithium) doped aerogel. The filter material binds the xenon gas reversibly from the exhaust gases from the exhaust valve 9 when the chamber is connected to the exhaust and releases the xenon gas when exposed to the flow of supercritical carbon dioxide.

[0076] Carbon dioxide is provided by a pressurized cylinder 18 and powered valve 19 and one-way valve 20a to a pump 15 that pressurizes the carbon dioxide above 73 bar, although lower pressures can be used for liquid carbon dioxide extraction. The liquid is then heated above the critical temperature by a heater 16 to form a supercritical fluid. The supercritical fluid is exposed to the filter material 13a or 13b in pressure-tolerant chamber 12a or 12b, dissolving the xenon to form a supercritical solution. Any non-polar contaminants from the patient or breathing systems may also be absorbed by the filter material and desorbed by the supercritical solution. The supercritical solution passes to the back-pressure regulator 17 and is depressurized into a volume buffer vessel 21 with pressure monitoring 22. The supercritical solution is depressurized further through a pressure reducing valve 23 to enter the vortex tube gas separator through an inlet throttle restriction in the vortex tube 24. The tangential entry and depressurization at the throttle restriction combined with the gas reflection at the throttle valve at the xenon outlet end 25 cause separation of the gas streams into a xenon-rich gas stream at one end 25 and the xenon-depleted carbon dioxide stream at the other end 26. The xenon-depleted gas stream passes through the one-way valve 20b to the pump 15 for recirculation. The volume of the system is controlled negative feedback from the pressure of the buffer vessel 21 acting on the carbon dioxide inlet valve 19.

[0077] The throttle at the xenon-rich outlet 25 of the vortex gas separator can be closed until there is sufficient xenon in the gas stream to allow separation and opened proportionally to the amount of xenon in the system. This concentration can be detected by ultrasound, katharometer or refractive index at any point from the selection valve 13a or 13b and the vortex tube 24.

[0078] The xenon-rich gas stream passes through a carbon dioxide absorber 27 and is stored in a vessel 28 ready for re-delivery to the patient circuit via a solenoid or piezo valve 4 under physician target electronic control and negative feedback from the patient gas detector 6 and a carbon dioxide absorber to remove any remaining carbon dioxide 29.

[0079] FIG. 2 shows the purification of xenon by liquid carbon dioxide.

[0080] Carbon dioxide contained in a pressurized cylinder with liquid and vapour phase 18 (approx. 55 bar at room temperature) passes through a powered valve 19 and one-way valve 20a to a condenser 101 to cool the carbon dioxide to 10 degrees Celsius, although other temperatures and pressures to ensure liquid carbon dioxide can be used. The cold liquid carbon dioxide passes to a liquid carbon dioxide pump 102 increasing the pressure to 70 bar although other liquid carbon dioxide pressures can be used. The fluid passes through a heater 103 to increase the temperature above the critical temperature of carbon dioxide, 31 degrees Celsius. In a preferred embodiment the fluid is heated to 50 degrees Celsius. The supercritical carbon dioxide passes to a rotary 6-port injection valve 104. This injection valve links to a fixed volume loop 105 that is filled with extracted xenon with contaminants from the patient or breathing system 106 contained in a pressurized vessel 107 at 70 bar and a temperature below 17 degrees Celsius such that the xenon is a liquid. Other temperatures and pressures to ensure liquid xenon can be used. The liquid xenon is pumped 108 around the loop during the filling setting of the rotary valve 104 and then during the load setting of the rotary valve 104, the valve turns and connects the loop to the flow of supercritical carbon dioxide from the pump 102. This flow takes the bolus of xenon/contaminants 106 into the chromatography column 108 filled with the stationary phase 109. In a preferred embodiment the stationary phase is plain silica although other normal and reverse-phase stationary phases can be used as knows to those skilled in the art.

[0081] The xenon 106 is separated from contaminants during passage through the column 108 by its interaction with the stationary phase 109, driven by the flow of carbon dioxide from the pump 102. The purified xenon, diluted in carbon dioxide, is detected by the detector 110 immediately after leaving the column. The detection method can be mass spectrometry, microthermal (katharometer), x-ray absorption, ultrasound or refractometry although other detection systems know to those familiar with the art can be used. When the bolus of xenon is detected, the electronic controller (not shown), often a Programmable Logic Controller, activates a three-way valve 112 to pass the xenon and carbon dioxide into the collection system. The xenon and carbon dioxide first pass through a back-pressure regulator 111 and then the three-way valve 112 into the collection buffer 113 with pressure sensor 114. When sufficient pressure is in the buffer 113, the xenon/CO.sub.2 mixture passes through a powered valve 115 and pressure-reducing valve 116 into the vortex tube gas separator 117. The vortex tube gas separator separates the xenon from the carbon dioxide by the virtue of density, with the xenon exiting via the throttle valve at one end 118 and the carbon dioxide via the other end 119. The high xenon fraction coming from 118 is passed through soda lime 120 to remove any remaining carbon dioxide a powered valve 121 then a condenser 122 and stored in a vessel 123. This process may require increasing the pressure of the xenon (pump not shown). It is possible to use more than one vortex tube gas separator in series to increase the purity of the xenon fraction before soda lime.

[0082] The carbon dioxide leaves the vortex tube gas separator 119, passing through a one-way valve 124 and an activated carbon 125 filled capture chamber 126 to scrub out any contaminants and then passes through another one-way valve and back to the condenser 101 for recirculation.

[0083] Carbon dioxide exiting the column without xenon is passed through the back-pressure regulator 111, three-way valve 112 and is directed straight to recirculation via a one-way valve 128 and activated charcoal 125 filled capture chamber 126 to remove contaminants.

[0084] Further steps may be taken to remove microbiological contaminants, package and present the Xenon ready for re-supply as a medical gas. These steps are not shown but are familiar to those skilled in the art.

[0085] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiments shown and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention.