GB2568218A

GB2568218A - Improvements to the capture of anaesthetic agents for remanufacture

Info

Publication number: GB2568218A
Application number: GB1713709.2A
Authority: GB
Inventors: Matthew Brown Sebastian
Original assignee: Sagetech Medical Equipment Ltd
Current assignee: Sagetech Medical Equipment Ltd
Priority date: 2017-08-25
Filing date: 2017-08-25
Publication date: 2019-05-15
Anticipated expiration: 2037-08-25
Also published as: GB201713709D0; GB2568218B

Abstract

An anaesthetic agent capture system for a medical facility, comprising filter material 210 for capturing volatile anaesthetic agents from a gas flow, the system further comprising means 204 for cooling the gas flow carrying the agents whereby to increase the binding capacity of the filter material 210. The means 204 for cooling may be a vortex tube driven by compressed air. Alternatively the cold air is provided by a refrigerant circuit or Peltier cooler. The hot exhaust from the cooling means may be used for additional medical functionality e.g. air blanket.

Description

IMPROVEMENTS TO THE CAPTURE OF ANAESTHETIC AGENTS FOR

REMANUFACTURE

Technical Field

The aim of this invention is to improve the binding efficiency of volatile anaesthetic agents to a filter material, for example by cooling the anaesthetic exhaust stream and/or using pressure-swing absorption. In some embodiments this production of a cold gas stream produces waste heat that is used to warm the patient via different theatre devices. Therefore, the dual objectives of improving anaesthetic agent capture and heating the patient can be achieved in an energy efficient manner. The anaesthetic agent can then be recovered from the adsorbent material by exposing it to supercritical CO₂ in a pressurised system to recover the anaesthetic and leave the filter material intact.

Background

A halocarbon is an organic chemical molecule composed of at least one carbon atom bound covalently with one or more halocarbon atoms. Halocarbons have many uses and are used in several industries as solvents, pesticides, refrigerants, fire-resistant oils, ingredients of elastomers, adhesives and sealants, electrically insulating coatings, plastics and anaesthetics. An alternative term for halocarbons is “halocarbonated fluorocarbons”.

Volatile anaesthetic agents are typically halogenated fluorocarbons, examples of which include desflurane, isoflurane, sevoflurane and halothane. Volatile anaesthetic agents are liquid at room temperature but evaporate easily to produce a vapour for inhalation by a patient to induce anaesthesia. Anaesthetic agents are used extensively in modern healthcare and represent a significant cost. They are also potent greenhouse gases due to their ability to absorb infrared light and their upper atmospheric persistence. Isoflurane and Halothane also contain Chlorine and Bromine groups that contribute to ozone depletion.

Examples of halocarbons which are used as anaesthetic agents typically include desflurane, isoflurane, sevoflurane, halothane and enflurane. These anaesthetics may be referred to as volatile anaesthetic agents because they are liquid at room temperature but evaporate easily to produce a vapour for inhalation by a patient to induce anaesthesia. These agents are administered to patients using the breathing circuit of an anaesthetic machine, also known as a Boyle’s machine. A schematic diagram of part of an anaesthetic machine including its breathing circuit 2 is described below with reference to Figure I. The primary function of the anaesthetic machine is to mix oxygen with volatile anaesthetic agent, at a clinician-specified concentration, for delivery to the patient via the breathing circuit 2.

The anaesthetic machine and breathing circuit 2 comprises a network of piped gas for inhalation by a patient (not shown). Air, oxygen (O₂) and nitrous oxide (N₂O) are supplied respectively to the back bar 15 from an air pipe 3 or an air cylinder pipe 5, an oxygen pipe 7 or an oxygen cylinder pipe 9 and a nitrous oxide pipe I I or a nitrous oxide cylinder pipe 13. Each gas pipe 3,7, II supplies gas at 4 bar. Air and oxygen are supplied by cylinder pipes 5, 9, at 137 bar. Nitrous oxide is supplied by cylinder pipe 13 at 44 bar. To reduce the pressure of the gases supplied by the cylinder pipes 5, 9, 13 to match the pressure of the gases supplied by the gas pipe 3, 7, II each cylinder pipe 5,9, 13 comprises a pressure reducing valve (PRV) 17 which reduces the pressure of gases supplied by the cylinder pipes 5,9, 13 to 4 bar.

Each of the air, oxygen and nitrous oxide is delivered separately to a respective variable flow valve 19, which allows an anaesthetist to mix the air, oxygen and nitrous oxide as required. Each variable flow valve 19 further reduces the pressure of the gases to just over I bar. Figure I shows the gases are delivered to the back bar 15, from left to right, via an air back bar pipe 18, an oxygen back bar pipe 20 and a nitrous oxide back bar pipe 22. It will be immediately apparent to the skilled person that the back bar pipes 18, 20, 22 may be arranged differently. For example, the back bar pipes 18, 20, 22 may be arranged from left to right, in Figure I in the following order: the nitrous oxide back bar pipe 22; the oxygen back bar pipe 20; and the air back bar pipe 18. The back bar 15 comprises a vaporiser 10 and a pressure relief valve 16. The vaporizer 10 contains a vaporisation chamber 2 I in which the agent 12 is housed. The vaporization chamber 21 is arranged so that the agent 12 evaporates to form vapour 14 at the saturated vapour pressure of the agent 12. For example, if the saturated vapour pressure is at too high a concentration to deliver agent 12 to the patient, a variable bypass valve 23 allows the anaesthetist to control the fraction of gases supplied from the back bar 15 20 that pass through the vaporiser 10. Accordingly, the output concentration of volatile agent 12 within the gas flow leaving the back bar 15 is controlled.

The patient inhales gases via a face mask 4 which fits over and forms a seal around the patient’s nose and mouth. The face mask 4 is connected to an inspiratory tube 6 which supplies gases containing an anaesthetic agent 12, and an expiratory tube 8 through which exhaled and unused gases and agent 12 are transported away from the patient. The inspiratory tube 6 and expiratory tube 8 are typically corrugated hoses.

The inspiratory tube 6 comprises a unidirectional inspiratory valve 25 which opens upon inhalation by the patient. When the unidirectional inspiratory valve 25 is in an open state, gas flows through the back bar 15, through the vaporisation chamber 10 where it mixes with vapour 14 from the agent 12. The gas mixed with agent vapour 14 is inhaled by the patient. In use, the breathing circuit 2 dispenses an accurate and continuous supply of anaesthetic agent mixed with oxygen/air/nitrous oxide (N₂O) at a specific concentration to the patient at a safe pressure and flow rate.

The expiratory tube 8 is connected to an expiratory pipe 24 to which is connected a unidirectional expiratory valve 26 through which exhaled and unused gases pass when the unidirectional expiratory valve 26 is open. Gas that passes through the unidirectional expiratory valve 26 flows into a breathing bag 28. An exhaust pipe 30 leads from the breathing bag 28 to a variable pressure-relief valve 32.

A carbon dioxide (CO₂) absorber canister 34 is connected to the expiratory pipe 24 and the inspiratory pipe 15 and arranged to allow gases to flow through the absorber canister 34 from the expiratory pipe 24 to the inspiratory pipe 6. The absorber canister 34 contains soda lime 36 which absorbs carbon dioxide from the gas that flows through the canister 34.

The configuration of the breathing circuit 2 illustrated in Figure I is shown during inhalation of the gas/agent mixture by the patient. The movement of inhaled gases is shown by the solid arrows and the movement of exhaled gases is shown using dashed arrows.

Inhalation by the patient causes the expiratory valve 26 to close and the inspiratory valve 25 to open. This allows recirculated gas to flow from the breathing bag 28, through the absorption canister 34 which absorbs CO₂ in the gas, and into the inspiratory pipe 6. The gas passes through the vaporisation chamber 10 where it mixes with the agent vapour 14. The resultant gas/agent mixture is administered to the patient via the unidirectional inspiratory valve 25 and inspiratory limb 6 of the breathing circuit 2 and the breathing mask 4. The patient breathes the gas/agent mixture into their lungs which dissolve some of the agent vapour 14 into the patient’s blood. This leads to a reversible state of anaesthesia.

Upon exhalation by the patient, the expiratory valve 26 opens and the inspiratory valve 25 closes. The gases exhaled by the patient, including the portion of the agent vapour 14 that is not absorbed by the patient, flow back into the breathing circuit 2 via the expiratory tube 8. The exhaled gases flow into the breathing bag 28 and excess waste gas 38 is vented via the pressure-relief valve 32. A waste pipe 40 guides the vented waste gas 38 from the breathing circuit 2.

The vented waste gas 38 will contain at least trace amounts of unused anaesthetic agent vapour 14. Even trace amounts of anaesthetic in the air in a medical environment will have an effect on medical staff, continued exposure to which will cause adverse health conditions, such as headache, increased incidence of spontaneous abortion, congenital anomalies in babies and haematological malignancy. Accordingly, governmental agencies have set limits on the level of volatile anaesthetic agent that hospital staff may be exposed to. In the USA the level of volatile anaesthetic agent in the air of an operating theatre should not exceed 2 parts per million (ppm), and the level of N₂O should not exceed 25ppm. The limit set for volatile agent in the UK is 50ppm, and for N₂O the limit is set at lOOppm.

In order to ensure that the environment within operating theatres and other medical environments stay within the above limits, the waste gas 38 which contains volatile anaesthetic agent vapour 14 is prevented from entering the atmosphere of medical environments.

To prevent the release of anaesthetic gases into the atmosphere of an operating theatre, in most developed countries, the waste gas 38 is “scavenged”. In hospitals and large veterinary practices, operating theatre suites are provided with a negative pressure circuit. The negative pressure circuit is connected to the exhaust pipe 40 of the anaesthetic machine. The negative pressure circuit extracts the waste gas 38 to the atmosphere via an output pipe at the top of the building. Anaesthetic users of smaller practices extract waste gas 38 from the exhaust pipe 40 using the circuit pressure following the variable pressure release valve 32, which is at a pressure lower than the breathing circuit, to pass waste gases 38 from the exhaust pipe 40 through activated charcoal canisters. Such charcoal canisters are typically able to absorb twelve hours of 25 waste gas 38. However, a problem with charcoal canisters is that once they have been used they cannot be recycled and must be disposed of, which is costly.

Furthermore, unused volatile agent captured by the activated charcoal canisters may be slowly released after disposal. Volatile anaesthetic agents are halogenated fluorocarbons, and therefore their release directly into the atmosphere is particularly undesirable. Halocarbons containing bromine and chlorine groups, collectively referred to as chloroflouorocarbons (CFCs), exert a damaging effect on the ozone layer. Indeed, the release of CFCs from any industry is damaging to the ozone layer. In the stratosphere, light at higher wavelength breaks down the C-CI/Br bond of CFCs which releases highly reactive free radical groups that break down ozone (O₃), depleting the earth’s UV protective barrier. Isoflurane and halothane are both CFCs. Each agent has a different reactivity due to the amount of free radical each agent releases, and the ease with which the carbon-halide group is broken.

Halothane is the most reactive, due to the relative ease with which the Br group may be removed from the molecule, followed by isoflurane. Nitrous oxide (N₂O) also has some ozone depleting potential.

In addition, N₂O and all agents, including sevoflurane and desflurane, are potent greenhouse gases due to their ability to absorb infrared light. Desflurane is the most potent due to its long atmospheric half-life. One kilo of Desflurane is equivalent to approximately 2000-3500kg of CO₂.

The use of CFCs was curbed by the Montreal agreement in 1987 (and subsequent amendments). As a result, the use of CFCs in refrigeration and aerosols was banned and all CFC use not deemed ‘essential’ was monitored. Medical uses of CFCs are deemed ‘essential’ and are therefore unmonitored.

With the banning of the use of CFCs in refrigeration and aerosols, the proportion of halocarbons released into the atmosphere due to medical use has increased and is likely to increase further. Currently, forty million anaesthetics are delivered per year in the US, and five million are delivered per year in the UK. The majority of these anaesthetics are delivered under the influence of volatile agents. In addition, it is estimated that medical use of N₂O contributes 3% of US N₂O emissions.

An alternative way to capture the agent vapour 14 from the waste gas 38 of the breathing circuit 2 is to subject the waste gas 38 to extreme cold using liquid oxygen. Halocarbons will crystallise at around -I I8°C. However, due to safety issues surrounding the use of liquid oxygen and the practicalities of removing and separating crystalline volatile agents from super-cold oxygen pipework, this is not a viable option for most medical establishments.

Another prior art system to capture volatile anaesthetic agent from the waste gas 38 is to pass the waste gas 38 over silicon dioxide (SiO₂), also known as “silica” for extraction by steam. An example of this type of prior art system is described in International Patent Application Publication No. WO 201 1/026230 Al.

Similarly to the charcoal method described above, the waste gas 38 is captured from the exhaust pipe 40 and passed through canisters that contain granular SiO₂ to which the agent 12 binds. Once the SiO₂ is saturated with agent 12, the SiO₂ canisters are removed for processing. During processing the SiO2 is subjected to a steam purge gas at high pressure and high temperature to separate the agent 12 from the SiO₂. Collected anaesthetic agent must be purified to remove water and then separated by fractional distillation.

Detailed description

According to an aspect of the present invention there is provided an anaesthetic agent capture system for a medical facility, comprising filter material for capturing volatile anaesthetic agents from a gas flow, the system further comprising means for cooling the gas flow carrying the agents whereby to increase the binding capacity of the filter material.

A further aspect provides an anaesthetic agent capture system for a medical facility, comprising a canister containing filter material for capturing volatile anaesthetic agents from a gas flow, the system further comprising means for cooling the canister and/or filter material and/or gas flow carrying the agents whereby to increase the binding capacity of the filter material.

The means for cooling may be a vortex tube, Peltier cooler, refrigeration circuit or the like.

A vortex tube based system may be driven by compressed air, for example the compressed air already provided in an operating theatre.

Hot exhaust from the cooling means may be used for additional medical functionality, for example one or more of: warming a thermal mattress; providing an air blanket; warming patient intravenous fluids.

A gas-to-liquid heat exchanger may be used to transfer heat from the hot exhaust.

A further aspect provides an anaesthetic agent capture system, comprising a vortex tube used for the dual function of providing cooling to the air flow that passes through an anaesthetic agent capture canister and also for providing a heat source for the anaesthetist to use in theatre for the warming of a patient.

Gas from the outlet of a capture canister, where provided, may be intermittently sampled.

Systems of the present invention may comprise a negative feedback loop formed from a temperature sensitive measurement device for the regulation of cooled airflow in or outside a canister as produced by the vortex tube to achieve a setpoint.

The present invention also provides a capture canister for use in capturing volatile anaesthetic agents, the canister being formed from aluminium.

The aluminium may be coated internally with a polymer, for example Polytetrafluoroethylene (PTFE) or Polyethylene Napthalate (PEN).

A further aspect provides a vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius, most preferably -20 degrees Celsius, to mix with the anaesthetic exhaust from an anaesthetic machine to increase the binding capacity of a filter material for anaesthetic agent.

A further aspect provides a vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius to the outside of a canister, that contains a filter material to capture anaesthetic agent from the anaesthetic exhaust, when the anaesthetic machine is not in operation.

A further aspect provides a vortex tube to provide hot air, as a by-product of the cold air stream required to increase the binding capacity of a filter material to anaesthetic agent, for the heating of a patient in theatre by a warming blanket, intravenous fluid warmer or mattress warmer.

A further aspect provides a method of increasing the amount of volatile anaesthetic agent captured onto a filter material, the method comprising the step of cooling gas carrying the agent over the filter.

The method may further comprise the step of removing agent captured on the filter material using supercritical fluid extraction.

A further aspect provides the use of pressure-swing absorption to increase the binding capacity of a filter material for volatile anaesthetic agent.

A further aspect provides a method of capturing Desflurane, comprising the step of providing filter material, providing a gas flow containing Desflurane, and cooling the gas flow and/or the filter material.

In an embodiment of this invention, a vortex tube is used for the dual function of providing cooling to the air flow that passes through an anaesthetic agent capture canister and also for providing a heat source for the anaesthetist to use in theatre for the warming of the patient. A vortex tube is a device that separates a compressed gas input into hot and cold streams. There are no moving parts and is often made of stainless steel with very low maintenance requirements. The basic design can be altered but generally, the compressed gas is injected tangentially into the primary swirl chamber and accelerates to a high rotatory frequency. The end conical nozzle only allows hot gas to escape, cold gas is then forced to return down the centre of the vortex tube to an outlet past the swirl chamber. Vortex tubes can generate negative temperatures of -60°C with positive temperatures of up to 200°C.

In some aspects and embodiments of the invention, the vortex chamber uses pressurised medical air from the medical facility supply. This is provided at 6 or 8 bar in the United Kingdom, although other supply pressures may be used in other countries. The cooled gas stream is passed into an inlet to the canister to act as a venturi, drawing in the anaesthetic exhaust. When the anaesthetic machine is operating and gases are flowing into breathing circuit and into the exhaust, the cooled air (at +10 to -50°C) enters the canister mixed with the anaesthetic exhaust.

The capture canister contains a filter material. The filter material can, for example, be silica, zeolite, a silica aerogel with or without functionalisation by halocarbons or other material familiar to those skilled in the art. The filter material reversibly binds the anaesthetic agent. Some other contaminants present in exhaled breath naturally or from breakdown of the anaesthetic agent (e.g. Hexafluoroisopropanol, compound A, compound B etc in the case of Sevoflurane) may also bind. Other gases present such as oxygen, carbon dioxide and some other compounds present in exhaled breath do not bind significantly to the filter material. The anaesthetic agent vapour pressure is reduced by reducing the temperature and this increases binding to the filter material. Therefore, by cooling the incoming airflow, the vortex tube increases the binding of the anaesthetic agent to the filter material. This is referred to as capture efficiency in this document and its effect is to increase the capture capacity of the filter material. This is especially important in the case of Desflurane, a volatile anaesthetic agent that has a boiling point of 23°C. The cooled air and anaesthetic agent pass into the canister and the anaesthetic agent is bound by the filter material. The cool air and any other gases from the anaesthetic exhaust not bound by the filter material pass out of the capture canister and into a charcoal canister. This charcoal canister absorbs any remaining anaesthetic agent or halocarbon/hydrocarbon contaminant that would not be desirable in theatre air before the gases pass out of the charcoal canister and back into the local environment. Alternatively, the exhaust gases may pass into a negative pressure Anaesthetic Gas Scavenging System (AGSS).

In one aspect of the invention, the cold outlet of the vortex tube directly enters the capture canister with the anaesthetic exhaust and the outside of the canister is not cooled. A thermal jacket is placed around the capture canister to conserve the temperature gradient. In another aspect of the invention, when the anaesthetic machine is not operational, the gas enters a chamber surrounding the capture canister, cooling the outside of the canister. This second configuration maintains the temperature of the canister, and the binding capacity of the filter material when the machine is not in use. It is beneficial to not pass any gas through the canister when the machine is not operational as there is no anaesthetic agent in the gas when the machine is not in operation and the gas may remove a trace amount of anaesthetic from the filter material, which can be substantial over a long period of time (e.g. weekend). The flow of cold air can be controlled by a negative feedback loop operating from a temperature feed at the outlet of the canister. In both circumstances, the canister is contained within an envelope that prevents splashed theatre material from contaminating the surface of the canister and insulates the canister to reduce the work needed for cooling.

A cooled air supply of +10 to -50°C that is passed, with waste volatile anaesthetic gases, through a canister containing filter material for the capture of anaesthetic agents when the anaesthetic machine is in operation and passed around the outside of the canister when the anaesthetic machine is not in operation to maintain the low temperature of the filter material.

The control of the temperature of the filter material by a negative feedback loop with thermal input from a temperature sensitive measurement device at the outlet of the canister containing the filter material.

The thermal insulation of a canister containing a filter material for the capture of anaesthetic agent so that the canister can be efficiently cooled to increase the binding capacity of the filter material for volatile anaesthetic agents.

Air entering the vortex tube comes from the compressed medical air supplied in the hospital or from a bottle. A filter can be used before the air enters the vortex tube to remove particulates and specially to remove any hydrocarbon/halocarbon contaminants that are present in the compressed air supply. The air supply should be dry, but the vortex tube will also act to dry the cooled air stream as moisture preferentially remains in the hot gas stream.

The waste product of the vortex tube is a hot air stream. However, localised heating is required in anaesthesia. When the patient is anaesthetised, their core body heat is re-distributed peripherally. The patient can cool very significantly if thermal losses are not controlled. A theatre environment is temperature controlled to maintain staff comfort to 19-21 °C unless in special circumstances. This temperature, combined with the 14 air changes per hour in theatre, can lead to significant patient cooling that can cause problems during anaesthesia (for example with impaired coagulation), in recovery (shivering on waking, slow emergence) and in the post-operative period (reduced wound healing). Therefore, specific measures are put in place to provide localised heating to the patient. This can be from a thermally controlled mattress or air blanket that covers parts not exposed during the operation.

The hot exhaust from the vortex tube can be used to provide a heat source to warm patient fluids and the patient directly via the mattress or heating blanket. The hospital air supply is filtered and clean so will not contaminate the theatre environment. The air inlet can be used as part of the fresh-air inlet for the theatre in the ventilation calculations.

The blankets can be heated by mixing the vortex outlet with theatre air to provide a safe temperature, that can be adjusted by the anaesthetist depending on patient core temperature. The mattress is usually heated by a separate liquid or resistance wire circuit. A gas-to-liquid heat exchanger can be used to transfer heat from the vortex tube outlet to the mattress heating circuit. A similar gas-to-liquid heat exchanger can be used to heat patient intravenous fluids. The liquid intravenous (IV) fluid circuit is often contained within a disposable plastic envelope to prevent contamination. Either this system, or a contained coil of IV tubing can be used within an enclosure surrounded by the hot vortex gas output.

A vortex tube may be provided, operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius, most preferably -20 degrees Celsius, to mix with the anaesthetic exhaust from an anaesthetic machine to increase the binding capacity of the filter material for anaesthetic agent.

A vortex tube may be provided, operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50°C to the outside of a canister, that contains a filter material to capture anaesthetic agent from the anaesthetic exhaust, when the anaesthetic machine is not in operation.

A negative feedback loop may be provided, formed from a temperature sensitive measurement device (e.g. thermocouple or thermistor) for the regulation of cooled airflow in or outside the canister as produced by the vortex tube to achieve a setpoint.

A vortex tube to provide hot air, as a by-product of the cold air stream required to increase the binding capacity of a filter material to anaesthetic agent, for the heating of the patient in theatre by a warming blanket, intravenous fluid warmer or mattress warmer.

Other methods of providing cooling to the capture canister/gas/ flow/filter material could be used, such as the conventional refrigeration circuit or Peltier cooling. This would require heat exchange within the anaesthetic machine gas exhaust, which would cause condensation of anaesthetic. Therefore, the passage of filtered air over the cooled surface of the Peltier cooler or evaporator could be used to deliver a cold air stream to mix with the anaesthetic exhaust. Both refrigeration circuits and Peltier coolers produce a waste warm air stream that can be used to warm the patient as described previously. It is important to deliver cooling at a variable flow rate as the anaesthetic circuit output has variable flow- from 0.2 litres/minute during maintenance anaesthesia to 30 litres/minute during induction and emergence. Most anaesthetic is exhausted during induction and emergence when oxygen/air gas flows are high. However, although the vortex tube is a preferable device, both the refrigeration circuit and Peltier cooling systems can be used to provide both a source of cooling and a warm air stream for patient warming to achieve the same goals as the vortex tube.

The use of Peltier cooling or the refrigeration circuit for the cooling of anaesthetic gases to increase binding capacity of the filter material for volatile anaesthetic agent and the provision of waste warm air to warm the patient.

The use of the waste warm air streams from the cooling of anaesthetic gases to increase the binding capacity of the filter material for volatile anaesthetic agent, to warm the patient in theatre by a warming blanket, intravenous fluid warmer or mattress warmer.

Suitable features of the vortex tube are that is provides hot and cold air streams instantly. Unlike a refrigeration circuit that takes time to get down to temperature. The flow or pressure drop through the tube can vary the temperatures or flow of cold gas delivered. This means that when the patient is connected to the circuit, the cold air flow can be started instantly and adjusted to the temperature of the device and air flow of the exhaust. Equally, this is when the warm air is required for the blanket/mattress/IV fluids.

It is not the intention of this invention to liquify the anaesthetic as is provided for in patent US I 1432152 by exposure to the cryogenic oxygen system. This invention aims to increase binding of the anaesthetic agents by the filter material. Our experiments have shown that anaesthetic agents are stable on the filter material under clinical conditions. The canister and filter material may then be subjected to supercritical CO₂. Under these conditions, the anaesthetic agent is released from the filter material, separated from the CO₂ and may be purified by supercritical fluid chromatography in order to be resupplied. Simple liquification of the anaesthetic exhaust as in patent US I 1432152 does not provide the selection given by supercritical fluid extraction. Anaesthetic agent captured from a clinical environment in normal use and extracted using supercritical CO₂ is over 99.5% pure, with the most significant contaminants often halocarbon breakdown products of the parent compound and very low water content. Therefore, there are significant advantages to absorption and extraction using supercritical CO₂ rather than simple liquification in that this step provides a purification step.

It would be possible to use cooling to liquify the anaesthetic agent directly from the exhaust. However, it is difficult to cool the exhaust to such an extent at high flow rates, with low concentrations of anaesthetic and provide a surface for condensation. The energy provided by absorption replaces the energy required in cooling the entire gas flow to temperatures at which the anaesthetic has no vapour pressure, and provides a surface which is not present in a gas flow to enable rapid removal from the gas flow. Furthermore, the capture and extraction of anaesthetic by supercritical CO₂selectively desorbs non-polar compounds (such as the anaesthetic agents) and leaves behind almost all water and polar contaminants. Finally, the capture and desorption by supercritical CO₂ provides selection against contamination by infectious material that could otherwise be transmitted.

In some embodiments the present invention uses supercritical CO₂ to remove the anaesthetic agent from the filter material; this is for several reasons:

• Volatile anaesthetic agents are highly soluble in supercritical CO₂ without modifier (such as ethanol/methanol) • Extraction efficiencies are high, so the process time is reduced • Temperatures are low, preventing anaesthetic breakdown • The high pressures mean that equipment is small and economically viable for small installations • The CO₂can be used in a circular process that is highly efficient • The CO₂ is selective for non-polar compounds, leading to high purity after extraction • The CO₂ can be used to drive chromatographic purification leading to a product that can be re-delivered to the user having passed pharmaceutical quality assessment.

• The process does not use any solvents or produce any toxic chemicals.

•

The combination of these reasons offers a significant improvement over alternative methods described in the prior art.

According to another aspect of this invention, gas from the outlet of the capture canister can be intermittently sampled by the anaesthetic monitoring system when the patient is not connected (between cases, at the beginning and end of theatre or for several seconds during a case). The outlet of the canister is before the charcoal canister. Therefore, any breakthrough of anaesthetic through the capture compound can be detected and trigger an alert to the anaesthetist to change the capture canister when convenient.

Anaesthetic gas detection is usually provided by means of infra-red systems, although other methods can be used by those familiar with anaesthesia including but not limited to raman spectroscopy, acoustic measurement, refractive index, mass spectrometry.

Broadband infrared light is transmitted through a sample of gas (either in-line or removed from the anaesthetic circuit by vacuum). In one method for example, infrared light passes through a series of different wavelength filters onto different thermopiles. The ratio of different absorbances by each filter area determines what anaesthetic agent is being used and what concentration it is at.

Intermittent sampling can be achieved by diverting the vacuum that pulls air from the anaesthetic breathing circuit to the capture canister output. Sampling only needs to occur for several seconds. Intermittent breaks in sampling occur anyway during normal anaesthesia for re-calibration of the IR detector (also measures CO₂concentration). Therefore, this would not be expected to cause an impact on safety. This sample would be discarded after detection into the charcoal canister rather than put back into the patient circuit as happens to gas taken from the patient circuit.

By this method, the technology in this invention can easily be applied to the current anaesthetic machine with minimal cost.

The sampling of the output of a canister containing a filter material for the capture of volatile anaesthetic gases by a low-flow rate gas stream drawn from the canister outlet and intermittently passed through the anaesthetic gas detection system already used for anaesthesia so as not to interfere significantly with clinical anaesthesia and to detect significant breakthrough of anaesthetic agent through a saturated filter material.

In another embodiment of this invention, an intermittent pressure can be applied to the contents of the capture canister to increase binding further by the process of pressure-swing absorption. The pressure is provided by the vortex tube air flow against a closed capture canister outlet valve. In order to prevent reverse pressure on the anaesthetic machine exhaust, a disc one-way valve is placed on the inlet to the canister where the anaesthetic exhaust enters the canister. Between this valve and the anaesthetic machine exhaust is an elastic storage bag with perforated plastic core to prevent total collapse of the bag. When the valve is closed, the bag accepts the anaesthetic exhaust. When the valve is open, the venturi effect from the entrainment of the vortex tube air draws excess air from the bag, rapidly clearing the exhaust air that has accumulated. This bag can have a volume of 50ml_ to 5 Litres or, more preferably, 2 Litres. The canister outlet valve only closes for a short duration that does not cause the bag to exceed its capacity. A pressure relief valve is present near the anaesthetic exhaust and also in the canister inlet to prevent over-pressurisation of the canister.

The use of pressure-swing absorption to increase the binding capacity of a filter material for volatile anaesthetic agent.

The use of pressure-swing absorption to increase the binding capacity of a filter material for volatile anaesthetic agent for subsequent extraction by supercritical fluid.

At the end of the operation, the supply of anaesthetic is discontinued but the patient can still be under varying degrees of anaesthesia with or without airway devices present. They may be fully woken in recovery areas away from main theatres. Anaesthetic agent administered during the operation is absorbed by different degrees into the various pharmacokinetic compartments of the body depending on many factors such as the anaesthetic agent used, the age/composition of the patient and the concentration of anaesthetic agent used during the operation. This anaesthetic agent must be excreted by exhalation to achieve a brain concentration low enough to render the patient awake. This ‘load’ of anaesthetic agent can be significant and is essentially discharged into the environment in recovery. Recovery areas are known to often exceed nationally recommended limits for exposure to anaesthetic agent as these environments often have lower air change frequencies than theatres.

In a further use of this invention, waste volatile anaesthetic agent can be recovered from the patients’ breath following the end of anaesthesia when the patient is in recovery areas. This has the advantage of capturing this anaesthetic agent that would otherwise be lost and also of reducing the pollution of recovery areas by volatile anaesthetic agents. In recovery areas, the patient is administered oxygen through a tight-fitting mask or airway device already present, connected to two hoses via a Ypiece. At the end of each hose, is a one-way valve that ensures uni-directional flow of gas. The inspiratory limb has an oxygen supply delivered at a clinician specified concentration, and the exhaust end feeds into the canister containing a filter material for the capture of volatile anaesthetic agents as previously described. The hoses are made of wide-bore, flexible, non-outgassing plastic. This Y-piece and two plastic hoses are a common component of the circle anaesthetic system and could stay with the patient following the end of the case along with the filter and t-piece that connect them to the patient (airway device or mask), or alternatively, just the filter and t-piece could remain with the patient to be connected to a y-piece and hosing present in recovery.

Recovery areas contain oxygen and compressed air supplies that can be used to supply the patient with air/oxygen and also power vortex tube cooling systems to increase capture efficiency as required. The patient often still needs warming in recovery areas, as patients being cold delays their emergence from anaesthesia and discharge from recovery. Therefore, the waste hot air stream from the vortex tube can equally be used to drive warming blankets, IV fluid warmers and mattress warmers.

The capture of waste volatile anaesthetic agent from the patient following the end of anaesthesia onto a filter material in a canister in recovery areas.

The use of a cooled air stream, preferably from a vortex tube, to cool the exhaled patient gas stream during use or to cool the outside of the canister when not in use to increase the binding capacity of the filter material for volatile anaesthetic agent when recovering such agents following the end of anaesthesia.

The use of the waste warm air stream from the cooling device, most preferably a vortex tube, to drive warming devices such as a blanket, mattress or IV fluid warmer to maintain patient temperature after the end of anaesthesia.

The canisters are removed for processing and the anaesthetic agent removed from the canister by the process of supercritical fluid or liquid CO₂ extraction perhaps followed by purification by supercritical fluid chromatography as described in these patents.

It is anticipated that canisters may be different. They could share a common inlet/outlet for exhaust gases and supercritical fluid or separate inlet/outlets could be used for the anaesthetic exhaust and the extraction fluid. Furthermore, the canister may be tolerant of the pressures and temperatures required for supercritical fluid extraction in CO₂ (73 bar and 3 I degrees Celsius) or may be pressure intolerant, with the pressure maintained by extracting anaesthetic by placing the canister in a pressure vessel and allowing pressurised CO2 to pass around the outside and through the inside of the canister.

In a preferred version, the same port is used for the passage of anaesthetic exhaust gases and also for the supercritical fluid. The canister consists of a pressure tolerant tube with floating end caps. The canister is placed inside a pressure vessel with ends that are moulded to fit the canister end caps. Upon pressurisation, the end caps of the canister move outwards, and the loads are retained by the ends of the pressure vessel. The tube of the canister can have a reduced factor of safety as it is retained within the pressure vessel and can be made thin as no welding is required. The end caps can be made of medical grade plastic (e.g. Nylon-66, Ertalyte, Polyether Ether Ketone [PEEK]) or fluoropolymer (e.g. PTFE) or a combination of plastic and filler (e.g. PTFE with carbon). The end caps are sealed to the canister tube using a compatible seal such as medical grade PTFE. This allows a small movement of the end caps within the canister tube leading to engagement with the ends of the pressure vessel upon pressurisation. The benefit of the floating end cap is to create a flow that is retained within the canister and does not go outside the canister (as would happen if the canister was completely pressure intolerant) as it is difficult to control for contamination of the outside of the canister. However, the canisters must be easy to handle and as lightweight as possible. This is achieved by avoiding welded points in the canister that would be liable to failure under pressure and containing the tube in the pressure vessel for safety. Therefore, the tube walls can be made thin- either of stainless steel or aluminium coated with a polymer to protect sevoflurane from breakdown or other material familiar to those skilled in the art.

The use of a polymer coating on the internal surface of a canister containing a filter material for the capture of volatile anaesthetic agents to prevent the breakdown of the volatile anaesthetic agent by exposure to ions on the metal surface.

The pressure vessel is a pressure-tolerant tube with a base at one end and a lid at the other. The lid can be attached to the tube by screw, clip or bayonet fitting. In a preferred embodiment, a bayonet fitting is used to provide a definitive end-stop to closing the lid. The base and lid of the pressure vessel contain a moulded PTFE fitting that fits the shape of the end caps of the canister. Different end caps can be used for veterinary and human product or where different anaesthetic agents are captured, so that veterinary canisters only fit into the veterinary pressure vessel. This is advantageous as the medicines regulatory agency may require the separation of human and veterinary production lines.

Moulded ends of the pressure vessel that fit the end caps of the canister so that the mobile end caps of the canister can move on their seals when pressurised and be retained by the ends of the pressure vessel, thus keeping the flow of supercritical CO₂inside the canister and not exposing the outside of the canister to flow that may incorporate unknown contaminants.

Different canister end caps and moulded-ends for the pressure vessel that are unique for each anaesthetic agent or for human and veterinary capture of anaesthetic exhaust so that single anaesthetic agents can be extracted from a source that uses a single agent or to ensure the process separation of human and veterinary lines for the purposes of regulatory compliance.

The use of liquid CO₂ for the extraction of anaesthetic agent captured onto a filter material.

The use of aluminium coated internally with a polymer such as PTFE or PEN (Poly Ethylene Napthalate) to form the canister.

In a separate aspect of this invention, in the purification of anaesthetic agents using supercritical chromatography, plain silica can be used as the stationary phase for the separation of contaminants. This can be achieved in a single separation step that removes ethanol and acetone and many other respiratory contaminants and also removes HFIP and other breakdown products of sevoflurane. Furthermore, liquid carbon dioxide (below its critical temperature of 3 I °C) can be used as the mobile phase in chromatography to separate the anaesthetic agent from contaminants instead of supercritical carbon dioxide (i.e. carbon dioxide above its critical temperature). This offers some improvements over supercritical carbon dioxide, especially when using modifiers such as methanol or ethanol, to improve chromatography resolution. This is due to the presence of the modifier increasing the effective critical temperature of the mobile phase (CO₂ and modifier). However, due to the low viscosity of liquid CO₂ near its critical temperature, the change from supercritical CO₂ to liquid CO₂

ΊΊ may offer some chromatography reproducibility benefits without significantly increasing the pressure drop across the column or causing localised heating within the column stationary phase.

The use of plain silica as the stationary phase in supercritical chromatography for the separation of volatile anaesthetic agents from each other if mixed or from contaminants such as breakdown products or commonly exhaled compounds.

The use of liquid CO₂ as the mobile phase instead of supercritical CO₂ for the purification of volatile anaesthetic agents from breakdown products or commonly exhaled compounds, or for the separation of different volatile anaesthetic agents from each other in the presence or absence of modifier.

In a final aspect regarding the separation of anaesthetic agent from carbon dioxide. Some embodiments use a gas liquid separator (GLS) at 10-20 bar at -20°C to separate out liquid anaesthetic from the carbon dioxide gas, which is then recycled. The low temperature is required to fully remove anaesthetic from the CO₂ gas as the vapour pressure of the gas is temperature dependent. In a further embodiment of this invention, the pressure of the anaesthetic/CO₂ mixture entering the gas liquid separator is reduced to 40 bar initially, with the temperature of the Gas Liquid Separator held above 5°C. At this temperature, the CO₂ will still be gaseous and the majority of the anaesthetic agent will be in a liquid state, so that separation can proceed. A small amount of anaesthetic will remain in the gas flow at its saturated vapour pressure at the selected temperature. When all of the extraction is complete, the circuit continues to recirculate, but the pressure in the GLS is reduced to 15 bar or atmospheric pressure and the temperature dropped to -20°C so that the last of the remaining anaesthetic agent is removed from the gas stream and the collected anaesthetic is fully depressurised, leading to release of the CO₂ dissolved in the liquid anaesthetic. This has the advantage that recirculating CO₂ can be passed through a condenser after passing through the GLS and liquified before being pumped again. This means that a gas booster system is not required to increase the pressure of the CO₂until the final stage and a much higher flow rate of CO₂ can be achieved with a reduced energy input by pumping liquid rather than gas.

The initial depressurisation of CO₂ liquid or supercritical fluid containing waste volatile anaesthetic agent following extraction from a filter material or chromatography to a pressure of 20 to 60 bar at temperatures that ensure CO₂ is in a gaseous phase, most preferably 40 bar and 5 degrees Celsius, for the purposes of using cooling to re-liquify the gaseous CO₂ for subsequent re-use in extraction or chromatography.

The later depressurisation of CO₂ liquid or supercritical fluid containing waste volatile anaesthetic agent following extraction from a filter material or chromatography to a pressure of I to 20 bar and cryogenic temperatures that ensure the CO₂ is in a gaseous phase but that the saturated vapour pressure of the volatile anaesthetic agent is close to zero.

Different aspects and embodiments of the invention may be used separately or together.

Further particular and preferred aspects of the present invention are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with the features of the independent claims as appropriate, and in combination other than those explicitly set out in the claims.

The present invention will now be more particularly described, by way of example.

Example embodiments are described below 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.

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.

The terminology used herein to describe embodiments is not intended to limit the scope. The articles “a,” “an,” and “the” are singular in that they have a single referent, however the use of the singular form in the present document should not preclude the presence of more than one referent. In other words, elements referred to in the singular can number one or more, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used herein, specify the presence of stated features, items, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, items, steps, operations, elements, components, and/or groups thereof.

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.

Index of Drawings

Figure I - Diagram of anaesthetic machine and breathing circuit

Figure 2- Diagram of anaesthetic capture system with cold air input

Figure 3- Diagram of anaesthetic capture system with cold air input to canister and to sleeve

Figure 4- Flow chart of heat flows

Figure 5- Diagram of pressure-swing absorption system and waste gas reservoir bag that integrates with the capture systems in figures 2 and 3.

Figure 6- Diagram showing the integration of figures 2,3,5 with the AGSS system Figures 7a and 7b- Diagrams showing how cooling and pressure can be used to improve capture efficiency when gas is collected for multiple theatres as the final part of an AGSS system.

Detailed Description of Drawings

Figure I is described in the background.

Figure 2 shows the anaesthetic waste capture system with a cold air input. Exhaust gases 38 from the anaesthetic machine X enter the capture canister through a negative pressure prevention and one-way valve unit 202 into a venture pipe 203. The cold air inlet 204 from the vortex tube (not shown) enters the venture pipe 203 through injection nozzles 205 that accelerate the air flow and reduce the pressure at the outlet, drawing in air from the anaesthetic machine exhaust 38 and also from general theatre air 206. The one-way valve unit 202 prevents the application of positive pressure on the anaesthetic machine exhaust and reverse flow into the breathing circuit. If there is no gas coming from the anaesthetic machine exhaust, then the cold air feed 204 will only entrain theatre air 206. Entrained air passes into the canister 208 through the end cap 207. The canister is insulated 209 to keep the temperature of the canister contents low. The canister contains a filter material 210 that binds the volatile anaesthetic agent. This filter material may be silica, halocarbon-modified silica, an aerogel, a halocarbon modified aerogel, zeolite, carbon or other materials known to those skilled in the art. Methods of joining the canister to the inlet include but are not limited to a bayonet fitting, tapered push fit connection or screw fitting. The mixture of gases passes through the canister 208, the anaesthetic agent is absorbed onto the filter material 210 and the remaining gases exit the canister through the exit pipe 2 I I. The canister is connected to the exit pipe 211 by a similar mechanism to the canister’s connection to the inlet as described. The canister can be removed from the insulated fitting by detaching the exit pipe, opening the clip on the side of the insulation casing

212 and then removing the canister from the inlet. Another canister can then be placed into the insulated housing and connected to the inlet and outlet fittings.

The filter material has a specific capacity for binding anaesthetic. For example, I litre of plain silica can reversibly bind 100- I25ml_ of volatile anaesthetic agent before breakthrough at room temperature. This capacity is increased by cooling the exhaust gases as described above. The anaesthetic machine uses infrared spectrophotometry to detect the presence and concentration of anaesthetic agents as part of routine anaesthesia. A sample line connected to the sampling port 213 pulls a small sample of gas intermittently during and after the anaesthetic case to test for breakthrough of anaesthetic agent through the filter material 210. If anaesthetic agent is detected above a set threshold as determined by the user, then the canister can be changed. Any anaesthetic agent that breaks through the filter material is bound by a charcoal filter 214 placed just distal to the canister.

It is anticipated that two canisters could be joined together by a simple push-fit, bayonet, screw off or other connector. Then breakthrough anaesthetic agent gases from the first filter would enter the second canister. Upon changing canisters, the first canister would be removed and the second canister placed first, with a new canister, empty of anaesthetic, placed second. This has the benefit of fully filling a canister to its capacity without leading to excessive breakthrough of anaesthetic agent through the filter material.

Figure 3 shows an altered configuration of the anaesthetic exhaust capture system in figure 2 by using the cold air stream to maintain the low temperature of the filter material when the anaesthetic machine is not in use.

During operation of the anaesthetic machine, waste anaesthetic agent from the anaesthetic machine 38 enters the inlet venturi 203 via a one-way valve 202 under the negative pressure produced by the cold air stream 204a introduced through the venturi nozzles 205. Negative pressure on the anaesthetic circuit is prevented by allowing theatre air 206 to enter the inlet when exhaust volumes are low. The waste gases 38 pass into the canister 208 in an insulated sleeve 209 and anaesthetic agent binds to a filter material 210. The scrubbed gas stream exits the canister through the outlet 21 I with detection of any anaesthetic breakthrough by a vacuum port 213. In case of breakthrough, gases pass through activated charcoal 214 before returning to the theatre environment.

When the anaesthetic machine is not in operation, the cold air stream is diverted into the insulated sleeve around the outside of the canister 208 to cool the canister and maintain the temperature of the filter material 210.

The cold air flow is regulated by a thermistor or thermocouple 303 in the exit pipe 311. This acts as an input to a controller 301 that regulates the production of cold air from the vortex tube, Peltier cooler or refrigeration circuit (not shown). The controller also receives input from the anaesthetic exhaust (not shown) to inform the controller that the anaesthetic machine is in operation, at which point the controller influences the position of a 3 port, 2 position valve 302 that directs the flow of cold air from around the outside of the canister via port 204b to passing through the canister and filter material via port 204a.

Figure 4 shows a flowchart that details the flow of cold and hot air from the vortex tube to provide a cold airstream for the improvement of anaesthetic capture by the filter material and also uses the waste hot air stream to provide heating for the patient via three different methods.

Figure 5 shows how pressures-swing absorption can be used to improve capture efficiency. Anaesthetic waste gases 38 pass via a one-way valve 202a into a perforated plastic pipe 502 and bag 501 that contains the gas, through a second one-way valve 202b into the capture systems as described in Figure 2 or 3. Gas then proceeds from the exit pipe 21 I of the canister 208 (figure 2 or 3) and instead of going directly into the activated charcoal absorber 214, they pass through a solenoid valve 503 under the control of a controller 504. Intermittent closure of the solenoid valve leads to a pressure accumulation in the capture canister 208 containing the filter material 210 following closure of the one-way valve 202b. The anaesthetic from the waste gas 38 binds more efficiently under the increased pressure to the filter material 210. The solenoid valve 503 then releases and the canister 208 depressurises. The release of anaesthetic from the capture material 210 proceeds more slowly than the absorption, and therefore, due to the cycling of pressure, more anaesthetic agent is bound to the filter material 210 in the collection canister 208 than at atmospheric pressure. While the solenoid valve 503 is closed, the anaesthetic machine may still be producing gas, and therefore this gas is collected in the bag 501 between the two one-way valves

202a and 202b. A pressure relief valve 505 protects the anaesthetic circuit from overpressure and is filtered by a connection to the charcoal canister 214.

Figure 6 shows how the capture systems shown in the figures 2,3 and 5 are incorporated into an AGSS system. This is a system familiar to those skilled in the art of anaesthesia. Waste gases, scrubbed of anaesthetic agent 38 enter the exit pipe 21 I and any breakthrough anaesthetic is detected by the vacuum feed 213 to the gas detector (not shown). The exit pipe 21 I enters a chamber 604 with a large internal volume 605 that exceeds the maximum vital capacity of the patient (this may be used in veterinary practices, so this can be significantly larger than the 5 Litres common for humans). Any large vital capacity output from the exhaust fills the chamber 605. The AGSS system is a negative pressure circuit that draws air at a rate much greater than the maximum ventilatory flow of the patient (usually 100 litres/min). This negative pressure circuit is connected to the top of the chamber 604 by an outlet 601 to which is connected a negative pressure prevention valve 602 that contains a weighted disc 602. During normal operation, a mixture of anaesthetic waste gases and theatre air is formed inside the chamber 605 and passes through the valve 603 into the outlet 601 and to the AGSS system 607. If the inlet 606 was occluded, then a negative pressure would result that pulls the weighted disc 602 upwards to occlude the outlet 601. The AGSS is therefore prevented from exerting a negative pressure on the anaesthetic exhaust. Various flowmeters can be used to indicate proper function of the unit (not shown) familiar to those skilled in the art.

Figure 7a shows how the process of cooling can be used to improve the capture efficiency of anaesthetic agents when capturing from multiple theatres. Figure 7b complements figure 7a by showing the detail of the capture chamber design.

With reference to 7a and 7b, waste anaesthetic 38 enters a compressor that increases the pressure to 2-80 bar, most preferably 20 bar. The gas then passes through valve 704a. 704a is a pneumatic valve that has one position open. In this case, 704a is open to the passage of anaesthetic waste gas 38. This gas passes into the capture chamber 701a and binds to the filter material 210 inside the inner pressure-tolerant envelope 721. The temperature is maintained by a thermal jacket 716 that contains a coolant fluid circulated through intakes 717a and 717b and outlets 718a and 718b and insulated 715. The scrubbed gas then exits through pneumatic valve 705a and through a backpressure regulator 707 to maintain pressure in the capture chamber 701a. The gas is then vented to the atmosphere. During the time that chamber 701a is capturing anaesthetic, chamber 701 b is using supercritical CO2 to remove the anaesthetic agent, condense it and leave the filter material intact. Carbon dioxide is stored in a cylinder 723 and delivered to the circuit via a pneumatic valve 722 and check valve 724 into a compressor 703 which increases pressure to 73-150 bar, most preferably 80 bar. Pressurised CO₂ is heated to 3 I to l00°C by a heater 726 under negative feedback control (not shown). The critical temperature of CO₂ is 3 I °C and the critical pressure is 73 bar. Therefore, the resultant fluid is a supercritical fluid. This passes into the chamber via valve 704b, which is open to supercritical fluid, but closed to the waste anaesthetic from the compressor 702. The chamber is heated to 31-100°C, most preferably 50°C by the thermal jacket 716 and heat maintained by the insulation 716. The envelope 721 is capable of tolerating pressures of up to 100 bar or more with an appropriate margin of safety. The supercritical CO₂ dissolves the anaesthetic agent and flushes it from the filter material 210, leaving the filter material unchanged.

The mixture of supercritical CO₂ and anaesthetic passes through valve 705b and back pressure regulator 708 into a buffer tank 709 under the control of the pressure or level gauge 710. This gauge controls the opening of the CO₂ inlet valve 722, regulating system CO2 volume. Pressure reducing valve 71 I reduces the pressure of CO2 to 15 bar and the mixture enters the cyclonic separator, cooled to -20°C 712. The CO₂ is gaseous, but the anaesthetic is liquid and collects at the bottom of the collector, passing through valve 713 to near atmospheric pressure and into collection tank 714. The anaesthetic agent may be a mixture of agents and may contain contaminants, breakdown products or respiratory products that are soluble in supercritical CO₂. It also contains a trace of water required to keep Sevoflurane stable. The collection tank may be lined by a polymer to prevent any lewis acid breakdown of sevoflurane, such as Polyethylene Napthalate or PTFE. The clean CO₂ gas exits the cyclonic separator (Gas Liquid Separator - GLS) 712 and passes back to the compressor 703 via a checkvalve 725 to pass through the tank again.

At the end of extraction, the CO2 is scrubbed by passing through activated charcoal and re-pressurised to fill the CO2 cylinder 723 and the vessel 701b is reduced to atmospheric pressure, ready for collection. This process is not shown but would be familiar to someone skilled in fluid processes.

Although illustrative embodiments of the invention have been disclosed in detail herein, 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 as defined by the appended claims and their equivalents.

Claims

1. An anaesthetic agent capture system for a medical facility, comprising filter material for capturing volatile anaesthetic agents from a gas flow, the system further comprising means for cooling the gas flow carrying the agents whereby to increase the binding capacity of the filter material.

2. An anaesthetic agent capture system for a medical facility, comprising a canister containing filter material for capturing volatile anaesthetic agents from a gas flow, the system further comprising means for cooling the canister and/or filter material and/or gas flow carrying the agents whereby to increase the binding capacity of the filter material.

3. A system as claimed in claim I or claim 2, in which the means for cooling is a vortex tube.

4. A system as claimed in claim 3, in which the vortex tube is driven by compressed air.

5. A system that uses a vortex tube to provide a cold air stream that is mixed with the anaesthetic machine exhaust to reduce the vapour pressure of the volatile anaesthetic agent and thus increase absorption to a filter material contained in a removable canister, increasing the capacity of the filter material for volatile anaesthetic agent with or without using the waste heat stream to warm the patient during surgery.

6. A system as claimed in any preceding claim, in which cold air is provided from passing air over a refrigerant circuit or Peltier cooler with or without diverting waste heat to warm the patient.

7. A system as claimed in any preceding claim, where a cold air stream is diverted around a removable canister when the system is not in operation to maintain the low temperature of filter material without passing gas not containing volatile anaesthetic agent through the canister.

8. A system as claimed in any preceding claim, in which hot exhaust from the cooling means is used for additional medical functionality.

9. A system as claimed in any preceding claim, comprising a negative feedback loop formed from a temperature sensitive measurement device for the regulation of cooled airflow in or 35 outside a canister as produced by the vortex tube to achieve a setpoint.

28 08 18

IO. A system as claimed in any preceding claim, in which gas from the outlet of a capture canister is intermittently sampled to determine the amount of anaesthetic agent that is not captured by the filter material.

5 I I. A system as claimed in any preceding claim, comprising a vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at + IO to -50 degrees Celsius, most preferably -20 degrees Celsius, to mix with the anaesthetic exhaust from an anaesthetic machine to increase the binding capacity of a filter material for anaesthetic agent.

10 12. A system as claimed in any preceding claim, comprising a vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius to the outside of a canister, that contains a filter material to capture anaesthetic agent from the anaesthetic exhaust, when the anaesthetic machine is not in operation.

15 13. A system as claimed in any preceding claim, where a compressor pressurises gas collected from a central anaesthetic agent collection system into a cooled chamber containing a filter material for the reversible absorption of volatile anaesthetic agent, whereby the anaesthetic agent is removed from the filter material by the use of supercritical fluids in a subsequent step.

9. A system as claimed in claim 8, in which the hot exhaust is used for one or more of: warming a thermal mattress; providing an air blanket; warming patient intravenous fluids.

10. A system as claimed in claim 8 or claim 9, in which a gas-to-liquid heat exchanger is used to transfer heat from the hot exhaust.

11. A system as claimed in any preceding claim, comprising a negative feedback loop formed from a temperature sensitive measurement device for the regulation of cooled airflow in or outside a canister as produced by the vortex tube to achieve a setpoint.

12. An anaesthetic agent capture system, comprising a vortex tube used for the dual function of providing cooling to the air flow that passes through an anaesthetic agent capture canister and also for providing a heat source for the anaesthetist to use in theatre for the warming of a patient.

13. A system as claimed in any preceding claim, in which gas from the outlet of a capture canister is intermittently sampled to determine the amount of anaesthetic agent that is not captured by the filter material.

I I. A capture canister for use in capturing volatile anaesthetic agents, the canister being formed from aluminium.

12. A canister as claimed in claim I I, in which the aluminium is coated internally with a polymer.

13. A canister as claimed in claim 12, in which the polymer is PTFE or PEN.

14. A vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius, most preferably -20 degrees Celsius, to mix with the anaesthetic exhaust from an anaesthetic machine to increase the binding capacity of a filter material for anaesthetic agent.

15. A vortex tube operating from a compressed air or nitrogen supply that supplies cooled air at +10 to -50 degrees Celsius to the outside of a canister, that contains a filter material to capture anaesthetic agent from the anaesthetic exhaust, when the anaesthetic machine is not in operation.

16. A vortex tube to provide hot air, as a by-product of the cold air stream required to increase the binding capacity of a filter material to anaesthetic agent, for the heating of a patient in theatre by a warming blanket, intravenous fluid warmer or mattress warmer.

17. A system where a compressor pressurises gas collected from a central anaesthetic agent collection system into a cooled chamber containing a filter material for the reversible absorption of volatile anaesthetic agent, whereby the anaesthetic agent is removed from the filter material by the use of supercritical fluids in a subsequent step.

18. A method of increasing the amount of volatile anaesthetic agent captured onto a filter material, the method comprising the step of cooling gas carrying the agent over the filter.

19. A method as claimed in claim 18, further comprising the step of removing agent captured on the filter material using supercritical fluid extraction.

20. The use of pressure-swing absorption to increase the binding capacity of a filter material for volatile anaesthetic agent.

21. The use of liquid carbon dioxide as the mobile phase for the chromatographic separation of volatile anaesthetic agents from contaminants such as breakdown products or commonly exhaled products.

5

22. The use of liquid carbon dioxide as the mobile phase for the chromatographic separation of volatile anaesthetic agents from each other.

23. A capture canister for use in capturing volatile anaesthetic agent, the coating of the internal surface of the removable canister containing the filter material with

10 Polytetrafluoroethylene (PTFE) or Polyethylene Napthalate (PEN).

24. A method of capturing desflurane, comprising the step of providing filter material, providing a gas flow containing desflurane, and cooling the gas flow and/or the filter material to improve the propensity of desflurane to bind to the filter.

28 08 18

Amendments to the claims have been filed as follows

1. An anaesthetic agent capture system for a medical facility, comprising filter material for capturing volatile anaesthetic agents from a gas flow, the system further comprising a vortex

5 tube for cooling the gas flow carrying the agents whereby to increase the binding capacity of the filter material.

2. A system as claimed in claim I, comprising a canister containing the filter material for capturing volatile anaesthetic agents from a gas flow.

3. A system as claimed in claim 2, in which the vortex tube is driven by compressed air.

4. A system as claimed in any preceding claim that uses the vortex tube to provide a cold air stream that is mixed with an anaesthetic machine exhaust to reduce the vapour pressure of

15 the volatile anaesthetic agent and thus increase absorption to a filter material contained in a removable canister, increasing the capacity of the filter material for volatile anaesthetic agent with or without using the waste heat stream to warm a patient during surgery.

5. A system as claimed in any preceding claim, where a cold air stream is diverted around a 20 removable canister when the system is not in operation to maintain the low temperature of filter material without passing gas not containing volatile anaesthetic agent through the canister.

6. A system as claimed in any preceding claim, in which hot exhaust from the vortex tube 25 is used for additional medical functionality.

7. A system as claimed in claim 6, in which the hot exhaust is used for one or more of: warming a thermal mattress; providing an air blanket; warming patient intravenous fluids.

30 8. A system as claimed in claim 6 or claim 7, in which a gas-to-liquid heat exchanger is used to transfer heat from the hot exhaust.