Apparatus for recovering an anaesthetic agent

0001The present invention relates to an apparatus for recovering an anaesthetic agent and relates particularly, but not exclusively, to such an apparatus for recovering anaesthetic agent exhaled by a patient. The invention also relates to a method of recovering anaesthetic agent exhaled by a patient.

0002Many anaesthetic agents used to anaesthetise patients during invasive surgery are exhaled by the patients into the atmosphere immediately surrounding him and can therefore be inhaled by the operating staff immediately adjacent thereto. Such quantities of anaesthetic agent whilst being comparatively small, nevertheless present an uncertain long term effect on operating personnel. Consequently, there exists a requirement for a method of separating the anaesthetic gas remaining in a patients exhalation and preventing it from being inhaled by the operating personnel.

0003Accordingly, the present invention provides an apparatus for recovering an anaesthetic agent exhaled from a patient, the apparatus comprising a buffer vessel, for receiving a patients exhalation and for temporarily storing the same; a compressor, downstream of the buffer and operably connected thereto for receiving and compressing exhaled gas; separation means, for receiving compresses exhaled gas and for separating said anaesthetic agent therefrom, said separation means comprising a membrane separation apparatus operably connected to receive compressed exhaled gas to its tube side and being configured for allowing said anaesthetic agent to pass through the membrane to the shell side thereof, said separation means further including a first outlet for receiving pressurised gas depleted in anaesthetic agent and a second outlet for receiving said separated anaesthetic agent and for directing it to a region other than the atmosphere surrounding the patient.

0004Preferably, the region comprises an anaesthetic supply means for supplying anaesthetic to the patient, thereby to provide for recycling of said separated anaesthetic agent.

0005Advantageously, the apparatus further includes disposal means operably connected to the first outlet of the separation means or directing pressurised gas depleted the anaesthetic agent for release to atmosphere at a point remote from the atmosphere surrounding the patient.

0006Preferably, the apparatus includes pressure sensor means for monitoring the pressure within the buffer and for causing operation of the compressor only upon detection of a pressure above about atmospheric pressure.

0007Conveniently, the apparatus further includes control means for receiving a signal from said pressure monitor and for initiating control over the operation of the compressor as and when necessary. Preferably, the compressor is operable to compress the exhaled gas to a pressure equal to or greater than 1 atmosphere gauge.

0008Advantageously, the apparatus includes a gas analyser operably connected to monitor the purity of separated anaesthetic agent and being operably connected to an anaesthetic supply apparatus such as to enable recycled anaesthetic agent to be re mixed with make-up oxygen and fresh anaesthetic agent for supply to the patient.

0009Conveniently, the buffer vessel comprises a collapsible/expandable bag buffer.

0010In one particular arrangement, the anaesthetic agent comprises nitrous oxide.

0011The present invention will now be more particularly described by way of example only with reference to and as illustrated in figure 1 attached hereto which is a schematic representation of the present invention.

0012From figure 1 it will be seen that an anaesthetic supply apparatus 10 supplies oxygen 12 and anaesthetic agent 14 to control valves 16 and 18 before these components are mixed and directed along supply line 20 to a patients breathing mask 22. During sedation, the patients exhalation is withdrawn via line 24 and directed to a buffer vessel 26 in the form of, for example, a collapsible/expandable bag buffer. A pressure sensor 28 acts to a monitor the pressure within the buffer 26 and provides a signal to a pump controller 30 via line 32. A pump 34 situated downstream of buffer 26 is operably linked to pump controller 30 which initiates control and operation of the pump only upon detection of a pressure within the buffer equal to or greater than 1 atmosphere gauge. Line 36 is provided for withdrawing exhalation from buffer 26 and directing it to pump 34. Once compressed, the exhalation is directed via line 38 to a separation apparatus shown generally at 40. The separation apparatus 40 comprises a membrane separation apparatus operably connected to receive compressed exhaled gas to its tube side 42 and being configured for allowing said anaesthetic agent to pass through the membrane 44 to the shell side 46 thereof from which it may be withdrawn in a manner to be described later herein. A first outlet 48 is provided for receiving pressurised gas depleted in anaesthetic agent and for directing it to line 50 for subsequent disposal. A second outlet 52 is provided for receiving separated anaesthetic agent and for directing it to line 54 which conducts the separated anaesthetic agent to a region other than the atmosphere surrounding the patient. Whilst it will be appreciated that this region might be any area other than that in which the operating staff are situated, it will conveniently comprise the anaesthetic supply apparatus itself in which case the recycled anaesthetic agent may be used once again. In this arrangement, it will be necessary to provide a gas analyser purity monitor 56 and control apparatus 58 which initiates control over the introduction of recycled anaesthetic via valve 60 and modifies the flow rate of new anaesthetic agent via control valve 18. If necessary, control may also be initiated over oxygen supply valve 16. For the purposes for this control, line 62 is provided for supplying a signal to controller 58 from monitor 56 and lines 64 to 68 are provided for initiating control over valves 16, 18 and 60. Once remixed with fresh anaesthetic agents and oxygen, the recycled anaesthetic is once again supplied to the patient via line 20. Whilst it will be appreciated that little if any anaesthetic agent will remain in the gas supplied to first outlet 48, and that it will therefore not present a major hazard to the operating staff, this gas stream is conveniently discharged to atmosphere in a region other than the atmosphere surrounding the patient. A control valve 70 may be provided in outlet line 50.

0013If necessary, pump 34 may be operated to pressurise the exhaled gas to a pressure somewhat greater than that described above thereby facilitating the provision of compressed recycled anaesthetic agent to anaesthetic supply apparatus 10. A further advantage of the present invention resides in the fact that items such as dust and bacteria will be retained within the membrane rather than past pack to the anaesthetic supply. Such a membrane may therefore be used on a number of patients without presenting a biological hazard. Alternatively, such separation apparatus are comparatively inexpensive to produce and hence a fresh unit may be provided for each and every patient.

0014Whilst it will be appreciated that the present invention may be employed with any one a number of anaesthetic agents, it has been found to be particularly suitable for use with nitrous oxide.

0015Although described above with particular reference to an apparatus, it will be appreciated that the invention also relates to a method of recovering an anaesthetic agent from a patient's exhalation, and that many of the apparatus features described above are equally directly applicable to said method.