Abstract:
An anesthetic reflector has a housing internally containing two externally accessible gas channels and a filter of a material for releasable sorption of gas-borne anesthetic agent. The filter is movable between the gas channels to expose the same portion of the filter to the interior of each channel in turn.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an anesthetic reflector of the type allowing re-use of exhaled anesthetic agents in inhalation anesthesia.  
           [0003]    2. Description of the Prior Art  
           [0004]    Anesthetic reflectors for the re-use of gas-borne anesthetic agents are well known and are described in, for example, U.S. Pat. Nos. 5,044,361 and 5,471,979. These reflectors generally have a housing in which there is provided openings that delimit a common gas flow channel through the interior of the housing. Retained within the housing and disposed internally the gas flow channel is a filter for the alternating sorption and desorption of anesthetic agent from and into gas passing along the common flow channel. In use, these anesthetic reflectors are located within pneumatic circuits of anesthetic ventilator systems so that anesthetic-rich expiration gas, which is exhaled by a patient into the pneumatic circuit during an expiration phase of a patient breathing cycle, passes along the common flow channel and through the filter in one flow direction and so that inspiration gas in the pneumatic circuit, which is to be supplied to the patient during a subsequent inspiration phase of the patient breathing cycle, passes along the common flow channel, usually but not necessarily in the opposite flow direction, and through the filter. The filter acts to retain anesthetic agent borne by the expiration gas and then to release this retained anesthetic agent into the inspiration gas for re-supply (reflection) to the patient.  
           [0005]    One problem with these known reflectors is that the common flow channel constitutes a “dead-space” in which carbon dioxide (CO 2 ), that is also exhaled by the patient, remains after an expiration phase, and therefore may be undesirably re-supplied to the patient with the inspiration gas.  
           [0006]    In order to overcome this problem it is known to provide an additional filter for retaining CO 2  in inspiration gas passing from the anesthetic gas reflector. Such a CO 2  filter may be integral with the reflector or may be a separate unit.  
           [0007]    A further problem with the known reflectors is that in order to be able to quickly reduce the anesthetic concentration in the inspiration gas that otherwise would pass through the reflector, an additional gas flow line and associated flow controller are required by which the anesthetic sorption filter may be selectively by-passed. It is further known to realize this by-pass line as a separate flow channel within the housing of the reflector.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide an anesthetic reflector, and an inhalation anesthesia system employing such an anesthetic reflector, wherein the above-discussed problems associated with known anesthesia reflectors are at least alleviated.  
           [0009]    This object is achieved in accordance with the principles of the present invention in an anesthetic reflector having a housing with two externally accessible gas channels formed therein, and containing a filter for releasable sorption of gas-borne anesthetic agent, wherein the filter is movable between the gas channels to expose the same portion of the filter to the interior of each channel, in alternation.  
           [0010]    The above object also is achieved in an inhalation anesthesia system employing such an anesthetic reflector.  
           [0011]    By arranging for the filter to be movable, either by rotation or translation, between the two gas flow channels in turn, then at least the problem of the re-supply of the dead-space CO 2  may be alleviated.  
           [0012]    Moreover, the inventive anesthetic reflector has the further advantage that by selectively halting the movement of the filter during the provision of inhalation anesthesia, the concentration of anesthetic in the inspiration gas for delivery to a patient may be relatively quickly reduced without the need for a separate by-pass conduit. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a first embodiment of an anesthetic reflector according to the invention.  
         [0014]    [0014]FIG. 2A shows a filter usable in the reflector of FIG. 1.  
         [0015]    [0015]FIG. 2B shows an example of the common wall portion of the reflector of FIG. 1 usable with the filter of FIG. 2.  
         [0016]    [0016]FIG. 3 shows a second embodiment of an anesthetic reflector according to the invention.  
         [0017]    [0017]FIG. 4 shows an inhalation anesthesia system incorporating an anesthetic reflector according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The anesthetic reflector illustrated in FIG. 1, has a housing  2 , that in the present example is of a cylindrical form, containing a first gas channel  4  and a second gas channel  6 , here separated by a common wall portion  8 . Two gas ports  10 , 12  are provided in the housing  2  to connect the first gas channel  4  externally of the housing  2  in a flow-through configuration. One of the two gas ports  10 , 12  (in this embodiment the port  12 ) is provided with a one-way valve  14  so that flow-through within the first gas chamber  4  is in one direction only. Similarly, two gas ports  16 , 18  are provided in the housing  2  to connect the second gas channel  6  externally of the housing  2 , also in a flow-through configuration. One of the two gas ports  16 , 18  (in this embodiment the port  18 ) is provided with a one-way valve  20  so that flow-through is in one direction only. The two one-way valves  14 , 20  are mutually orientated such that flow through is in opposite directions in the gas channels  4 , 6 . In this manner the first gas channel  4 , for example, can be connected to an inspiration gas line of a pneumatic circuit of an inhalation anesthesia system (not shown) and the second gas channel  6  can then be connected to an expiration line of the pneumatic circuit.  
         [0019]    The present embodiment of the anesthetic reflector may be connected to a gas conditioning unit  22  (shown with broken lines) that is provided in the inspiration line preferably immediately upstream of the gas port  10 , by which inspiration gas will enter the first gas channel  4 . The unit  22  is configured to at least warm the incoming inspiration gas. In this manner the desorption of sorbed anesthetic gas will be enhanced. Indeed thermal energy may be supplied to enhance desorption in a number of ways apparent to those skilled in the art. The unit  22  also may be adapted to humidify the incoming inspiration gas.  
         [0020]    A disc-shaped filter  24  has a suitable anesthetic sorption material, for example activated carbon cloth or granules, and is preferably removably retained within the housing  2  and arranged to pass through an opening  26  (shown exaggerated for clarity) in the common wall portion  8 , which may be formed of two separate sections  8   a ,  8   b . In the present embodiment a section  24   a  of the sorbing material of the filter  24  extends into and essentially divides the first gas channel  4  and a section  24   b  extends into and essentially divides the second gas channel  6 . The filter  24  is provided with a through-hole  28  for removable engagement with a rotatable shaft  30  by which the filter  24  can be rotated. In the present embodiment a motor  32  is connectable to the shaft  30  and is operable to rotate it.  
         [0021]    A projection  34  also may be provided around the inner surface of each gas channel  4 , 6  against which a peripheral portion of a surface  36  of the filter  24  can seal. In this manner the amount of gas in each of the gas channels  4 , 6  that passes through the filter  24  may be increased and so the reflection properties of the reflector enhanced.  
         [0022]    A suitable configuration of the filter  24  is illustrated in FIG. 2A with cooperating sections  8   a ,  8   b  of the common wall portion  8  illustrated in FIG. 2B. The sorbing material of the filter  24  is divided into a number of identical segments, indicated generally at  38 , using dividing members that are in the present example shown as compressible ribs (indicated generally at  40 ). These ribs  40  protrude from each of the opposing surfaces, for example the surface  36 , of the filter  24  and in use form a gas-tight seal against a cooperating facing surface,  44  say, of the common wall portion  8 . To further minimize leakage of gas between the two gas channels  4 , 6  the surfaces of the common wall section  8  that face opposite surfaces of the filter  24  are shaped to conform to the shape of the segments  38 . An example of this is illustrated in FIG. 2B. Cooperating sections  8   a ,  8   b  that constitute the common wall section  8  are each provided with a surface  42 , 44  respectively that in use faces an opposing surface,  36  for example, of the filter  24 . Each surface  42 , 44  of the sections  81 , 8   b  is formed to conform substantially to the shape of an opposing pair of segments  38  of the filter  24 . It is intended that in use the ribs  40  that delimit this opposing pair of segments  38  contact and are compressed against a corresponding surface  42 , 44  to inhibit transport of gas between the channels  4 , 6 .  
         [0023]    A further embodiment of the anesthetic reflector according to the present invention is illustrated in FIG. 3. A housing  46  has an internal arrangement of a first gas channel  48  and a second gas channel  50  that are externally accessible by means of a pair of gas ports  52 , 54  that arranged at opposite ends of the housing  46  to provide a common flow path for the first  48  and the second  50  gas channels. It will be appreciated that these gas ports  52 , 54  may be fixedly or removably attached to the housing  46 . A one-way valve  56 , 58  is associated with respectively the first  48  and the second  50  gas channel and cooperate to permit gas flow in an opposite direction in each channel  48 , 50 . In the present example these valves  56 , 58  are both located in a respective branch of one  52  or preferably both  52 , 54  (only one  52  shown) gas ports but may of course be located in their respective gas channel  48 , 50  internal the housing  46 .  
         [0024]    An opening  60  is provided in the housing  46  into which a filter holder  62  is removably received. A slot  64  is formed in each of the channels  48 , 50  (only one shown) in an opposing arrangement and located beneath the opening  60 . A corresponding slot  66  is provided through the body of the filter holder  62  which cooperates with the slots  64  in each of the channels  48 , 50  to form a conduit through which an anesthetic sorption filter  68  can slide in a reciprocating movement between internal each of the channels  48 , 50  in turn. A rod  70  is also provided to releasably attach to the filter  68  when the filter  68  is located within the housing  46  and is sized to be externally accessible when the filter  68  is in either channel  48 , 50 . In the present example, the rod  70  is devised for a push fit connection to the filter  68 . For this purpose, a releasable detent  72  is integrated in the filter holder  62  and may be actuated to move in to and out of contact with a peripheral portion of the filter  68  when located within the slot  66  to hold the filter  68  within the filter holder  62  as the rod  70  is attached or detached.  
         [0025]    An inhalation anesthesia system is shown in FIG. 4 and has a known anesthesia ventilator  74  for the metering and controlled delivery of an anesthetic containing breathing gas and a conventional pneumatic circuit  76  for guiding the flow of gases between the ventilator  74  and the airways of a patient (not shown). The pneumatic circuit  76  in the present example has an inspiration line  78 , through which gas will flow towards the patient, an expiration line  80 , through which gas will flow from the patient and a patient line  82 , providing a common gas flowpath to and from the patient and in gas connection to both the inspiration line  78  and the expiration line  80 . An anesthetic concentration sensor  84  may be placed in the patient line to sense the concentration of anesthetic in both the inspiration and the expiration gas and to provide a measure of the same as a control parameter to the ventilator  74 . An anesthetic reflector according to the present invention such as is, for example, described above with respect to FIG. 1 is also provided as a part of the system. The housing  2  of the reflector is connected in line with the inspiration line  78  and with the expiration line  80  and is orientated such that the one-way valves  14 , 20  (not shown in FIG. 4) permit gas flow within the inspiration line  78  through only the first gas channel  4  and gas flow within the expiration line  80  through only the second gas channel  6 , as indicated, in the present example, by the arrows  86  that are visible on an outer surface of the housing  2  for user orientation purposes.  
         [0026]    It will be apparent to those skilled in the art that when a reflector according to the present invention, such as is for example described above in respect to FIG. 3, is employed having only one pair of gas ports  52 , 54  then the reflector housing  46  may be connected in-line to the common gas flow path that is provided by the patient line  82  of the anesthesia system.  
         [0027]    The motor  32  is coupled to rotate the disc shaped filter  24  of FIG. 1 and is operably connected to a control unit  88  which controls the motor  32  in order to achieve a desired rotation of the filter  24  between the two gas channels  4 , 6 . The desired rotation is preferably selected in order to avoid saturation of the filter  24  with exhaled anesthetic and to minimize CO 2  re-breathing and is dependent on one or more parameters that is typically either controlled or monitored by the ventilator  74 , such as the frequency of breathing, the minute volume and the concentration of anesthetic. The control unit  88  is therefore operably connected to the ventilator  74  to receive an indication of the one or more parameters.  
         [0028]    For example, assuming that the gas-holding volume of the disc shaped filter  24  is 80 ml then 40 ml will lie in the expiration side  6  and contains therefore about 5 vol % CO 2  (that is about 2 ml CO 2 ). If an acceptable level of re-breathing is 0.4 ml, which would be the case for even for small tidal volumes (a tidal volume of 200 ml would then have 0.2 vol % of CO 2 ), then a suitable rotational speed would be one tenth of a revolution per breath since this would mean that one fifth of the amount of expired CO 2  will appear in the inspiration side  4 .  
         [0029]    It will be appreciated by those skilled in the art that the control unit  88  may control the motor  32  to provide an intermittent rotation of the disc  24  or provide an oscillation of the disc  24  provided that the portion, for example  24   b , of the filter  24  that, during an exhalation phase of a patient breathing cycle, was located within the second channel  6  to retain anesthetic present in the exhalation gas is moved to be located within the first channel  4  to release the retained anesthetic into the inspiration gas flowing through the first channel  4  during an inspiration phase of a patient breathing cycle.  
         [0030]    Additionally, the control unit  88  may be configured to halt the rotation of the disc filter  24  for one or more breathing cycles, for example in response to a manually input signal. This permits a relatively rapid reduction in the amount of anesthetic released from the filter  24  into the inspiration gas flowing in the inspiration line  78 . Additionally or alternatively a bias flow of anesthetic free gas through the gas channel  6  connected to the expiration line  80  may be provided during an expiration phase to flush anesthetic from the portion  24   b  of the filter  24  in that channel  6 .  
         [0031]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventor to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of his contribution to the art.