Abstract:
An anesthetic filter arrangement for the reflection of unused anesthetic agent in expiration gas back toward a patient has a filter housing having an interior portion arranged to provide an internal gas flow path for an inspiration gas and for an expiration gas passing alternately and in opposite directions through the housing and a filter element disposed in gas communication with the interior portion for adsorption of anesthetic agent from the expiration gas and subsequent desorption of the anesthetic agent into the inspiration gas. The arrangement further. has a thermal regulator operable to reduce thermal energy at the filter element by cooling one or both incoming gas and the filter element, and thereby vary one or both the adsorption and the desorption of the anesthetic agent.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to an anesthetic filter arrangement and in particular to a filter arrangement for the re-use of anesthetics in inhalation anesthesia.  
           [0003]    2. Description of the Prior Art  
           [0004]    Filter arrangements for the re-use of gaseous anesthetics are well known and are described in, for example U.S. Pat. Nos. 5,044,361 and 5,471,979. These filter arrangements (so-called anesthetic reflectors), generally have a filter housing with openings therein delimiting a gas flow path through the interior of the housing. Disposed within the gas flow path is a filter element of an adsorption material for the alternating adsorption and desorption of gaseous anesthetic from and into gas passing along the flow path. These filter elements are placed within gas flow circuit of an anesthetic ventilator system so that anesthetic rich expiration gas, which is exhaled by a patient into the gas flow circuit during an expiration phase, passes through the filter element along the flow path in one flow direction, and so that inspiration gas in the gas flow circuit, which is to be supplied to the patient during an inspiration phase passes through the filter element along the flow path, usually but not necessarily in the opposite flow direction. The filter element adsorbs gaseous anesthetic from the expiration gas then desorbs this adsorbed gaseous anesthetic into the inspiration gas of the succeeding inspiration phase.  
           [0005]    Such filter arrangements exhibit the disadvantage that their retention properties for the gaseous anesthetic are fixed, dependent on the adsorption and desorption characteristics of the filter element material. Adsorption and desorption of gaseous anesthetic to and from the filter element is then largely controlled by varying the flow of gaseous anesthetic, and to a lesser extent the concentration of gaseous anesthetic in gas passing along the gas flow path, through the filter element. Varying these gas flow and concentration parameters, however, may have undesirable effects on the ventilation of a patient who is connected to an anesthetic ventilator system in which the filter arrangement is disposed.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide an anesthetic filter arrangement that avoids, or at least alleviates, the aforementioned disadvantages of known filter arrangements.  
           [0007]    This object is achieved in accordance with the present invention in an anesthetic filter arrangement having a filter housing with an interior portion that provides an internal gas flow path for an inspiration gas and for an expiration gas passing through the housing, a filter element disposed in gaseous communication with the interior portion for adsorption of an anesthetic agent from the expiration gas and subsequent desorption of the anesthetic agent into the inspiration gas, and a thermal regulator operable to decrease thermal energy at the filter arrangement to vary one or both of the absorption and desorption of the anesthetic agent.  
           [0008]    The retention of gaseous anesthetic by the filter element thus is varied by operating the thermal regulator to provide a reduced thermal energy at the element, for example by cooling incoming gas or by directly cooling the element, to thereby vary the adsorption and/or desorption of gaseous anesthetic.  
           [0009]    The thermal regulator may be operable to provide the cooling effect in synchronism with an expiration phase of a patient breathing cycle to thereby increase adsorption of the gaseous anesthetic.  
           [0010]    Additionally, the thermal regulator may be operable to provide an increased thermal energy at the filter element. The retention of gaseous anesthetic by the filter element is thus varied by additionally providing thermal energy at the element, for example by warming incoming gas or by directly warming the element, to thereby vary the adsorption and/or desorption of gaseous anesthetic.  
           [0011]    The thermal regulator may be operable to add the thermal energy in synchronism with an inspiration phase of a patient breathing cycle to thereby increase desorption of the gaseous anesthetic into breathing gas for supply to a patient.  
           [0012]    Preferably, the thermal regulator has one or more thermoelectric (Peltier effect) elements, having a cooling surface located in intimate thermal contact with the filter element or with incoming expiration gas and, optionally, having a heating surface located in intimate thermal contact with the filter element or with incoming inspiration gas. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows an embodiment of a filter arrangement according to the present invention.  
         [0014]    [0014]FIG. 2 a  shows an internal portion of a thermal regulator suitable for use in the arrangement of FIG. 1.  
         [0015]    [0015]FIG. 2 b  shows an external view of the thermal regulator of FIG. 2 a.    
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    As shown in FIG. 1, an anesthetic filter arrangement has a filter housing  2  in which open-ended conduit sections  4 , 6  are formed for leading a gas to and from an interior gas-flow portion  8  of the housing  2 . Contained within the interior portion  8 , and arranged for gas communication with gas therein, is a filter element  10  formed of a suitable sorption material for anesthetic agent. Examples of such material are zeolites of crystalline aluminum silicates that may be pellets or supported on a carrier and an activated carbon filter such as formed from carbon-impregnated material, carbon fiber cloth, or granulated or microporous carbon material. Other known adsorptive and/or absorptive microporous material also can be used.  
         [0017]    A Peltier effect element  12  is provided with a warming surface  12   a  in intimate thermal contact with a first gas flow circuit  14 , 16  using, in the present embodiment, a first known heat exchange unit  18   a , such as may simply be formed by a gas flow conduit having a number of internal ridges, fins or channels to increase the surface area over which heat may be exchanged between gas from the first flow circuit  14 , 16  and the warming surface  12   a . A cooling surface  12   b , opposite the warming surface  12   a  of the Peltier element  12  is arranged in intimate thermal contact with a second gas flow circuit  22 , 24 , here using a second known heat exchange unit  18   b  which together with the first heat exchange unit  18   a  may form a single known heat exchanger.  
         [0018]    The two sections  14 , 16  of the first gas flow circuit are arranged in gas flow communication with the gas conduit  4  of the housing  2 , each on an opposite flow side of a first one-way valve  20  arranged to permit a through flow of gas in a direction from the filter element  10  only.  
         [0019]    The two sections  22 , 24  of the second gas flow circuit are arranged in gas flow communication with the gas conduit  6  of the housing  2 , each on an opposite flow side of a second one-way valve  26  arranged to permit a through flow of gas in a direction from the filter element  10  only.  
         [0020]    As is illustrated in FIG. 1, the one-way valves  20 , 26  may be provided integral with corresponding connector bodies  28 , 30  which are respectively releasably connected to the conduit sections  4 , 6  of the housing  2 . These connector bodies  28 , 30  are intended for releasable coupling with a gas flow circuit of an anesthetic ventilator system in a manner such that, in use, inspiration gas from the ventilator will flow into the housing  2  through the connector body  28  and expiration gas from a patient will flow into the housing  2  through the connector body  30 . This enables the filter element  10  to be easily introduced into and removed from the gas flow circuit.  
         [0021]    Gas ports  32 , 34  are provided at each side of the first one-way valve  20  to provide gas communication between the interior of the connector body  28  and the two conduits  14 , 16  of the first gas flow circuit. Similarly, gas ports  36 , 38  are provided at each side of the second one-way valve  26  to provide gas communication between the interior of the body  30  and the two conduits  22 , 24  of the second gas flow circuit.  
         [0022]    When in use, the exemplary configuration of the anesthetic filter arrangement of FIG. 1 allows gas from a patient (expiration gas) will pass through the filter element  10  in a direction from the conduit  6  to the conduit  4 . Gas to be supplied to a patient (inspiration gas) is allowed to pass through the filter element  10  in an opposite direction, that is, from the conduit  4  to the conduit  6 . The intended directions of gas flow through the filter arrangement are shown by the arrows in FIG. 1.  
         [0023]    In use, the operation and location of the second one-way valve  26  causes expiration gas to flow through the conduit  22  of the second gas flow circuit and to the second heat exchange unit  18   b  where it becomes cooled by the action of the appropriately energized Peltier device  12  using, in a known manner, a power supply unit (not shown). The cooled gas passes from the second heat exchange unit  18   b , through the conduit  24  and into the filter housing  2  through the conduit section  6 . The cooled gas then passes through the filter element  10 , which retains anesthetic agent present in the expiration gas, and out of the filter housing  2  through the conduit  4  and the first one-way valve  20 . The amount of anesthetic agent retained by the filter element  10  is enhanced because of the cooling effect of the gas passing through it.  
         [0024]    As the expiration gas is cooled, water vapor that is normally present in expiration gas will condense. It may be useful to provide a known water trap (not shown) in communication with the cooled expiration gas at a location before it contacts the filter element  10  to collect this condensate. More usefully such a water trap may be provided in communication also with inspiration gas at a location after it contacts the filter element  10  to moisten, in a known manner, the inspiration gas before delivery to a patient.  
         [0025]    The operation and location of the first one-way valve  20  causes inspiration gas to pass through the conduit  14  of the first gas flow circuit and to the first heat exchange unit  18   a  where it becomes heated by the action of the appropriately energized Peltier device  12 . The warmed gas passes from the first heat exchange unit  18   a , through the conduit  16  the filter housing  2  through the conduit section  4 . The warmed gas then passes through the filter element  10 , which releases previously retained anesthetic agent into the inspiration gas, and out of the filter housing  2  through the conduit  6  and the second one-way valve  26 . The release of the anesthetic agent by the element  10  is thus enhanced because of the warming effect of the inspiration gas passing through it.  
         [0026]    Typically, a small amount of carbon dioxide that is present in the expiration gas will be retained by the filter element  10  and will be released into the inspiration gas together with the anesthetic agent. This might be expected to be the detriment of the anesthetic ventilation therapy being provided. It has been discovered by the present inventors, however, that the amount of carbon dioxide which, in use, is re-supplied toward a patient from the filter arrangement according to the present invention is unexpectedly reduced in comparison to the amount re-supplied from a known filter arrangement.  
         [0027]    As described above, the Peltier element  12  and the heat exchange units  18   a ,  18   b  together form a thermal regulating device for varying the temperature of the filter element  10  by varying the temperature of the gases incident on the filter element  10 . The temperature of the incident gases can be controlled by varying the electric current flowing through the Peltier element  12  which, in a known manner, varies the degree of cooling/heating produced by the element  12 .  
         [0028]    It will be appreciated that in the exemplary configuration of FIG. 1 the Peltier device  12  may be appropriately energized so that the warming side becomes  12   a  and the cooling side becomes  12   b . In the use described above expiration gas will now become warmed to thereby diminish the retention by the filter element  10  of gaseous anesthetic present in the expiration gas. The inspiration gas will become cooled to thereby diminish the release of previously retained anesthetic in to the inspiration gas. This may be useful, for example, when trying to wake up a patient.  
         [0029]    Moreover, the Peltier device  12  and heat exchange units  18   a ,  18   b  may be substituted with other active thermal regulation devices, such as refrigerant compression, capable of providing a cooling and optionally a heating effect at the filter element  10 . Also a passive heat exchanger may substitute for the Peltier device  12  and heat exchange units  18   a ,  18   b . In such a passive heat exchanger the heat of the relatively warmer expiration gas is used to warm inspiration gas and itself becomes cooled in the process.  
         [0030]    An example of a Peltier effect thermal regulating device suitable for use in, for example, the anesthetic filter arrangement of FIG. 1 is shown in FIGS. 2 a  and  2   b . Considering now FIG. 2 a , an internal portion of the device is shown in an exploded form to enable components to be more clearly seen. Multiple, here five, Peltier effect elements  12  are arranged in a stack so that, when the elements  12  are suitably energized, warming  12   a  and cooling  12   b  faces of adjacent elements face one another. Between each Peltier element  12  and in intimate thermal contact therewith is a gas flow conduit  40 , 42 . Each gas flow conduit is oriented to provide a direction of gas through-flow (indicated by arrows  44 , 46  in the FIG. 2) selected dependent on which of the faces  12   a  or  12   b  of the adjacent Peltier elements  12  it is in intimate thermal contact with. As illustrated in the present example, all of those gas flow conduits  40  that are arranged in thermal contact with a cooling side  12   b  of Peltier elements  12  are oriented to provide for through flow of gas in a single flow direction  44  that is orthogonal to a single flow direction  46  for gas flowing through those conduits  42  that are arranged in thermal contact with a warming side  12   a  of a Peltier element  12 .  
         [0031]    As is also illustrated in FIG. 2 a , each conduit  40 , 42  is formed, as is preferable, with an increased internal surface area that in the present embodiment is realized by the inner surfaces of channels  48 . The increased surface area increases the efficiency with which thermal energy can communicate between gas within the conduit  40 , 42  and the associated face  12   b ,  12   a  of a Peltier element  12 .  
         [0032]    As shown in FIG. 2 b , a housing  50  is provided to contain the stacked arrangement of FIG. 2 a . An orthogonal arrangement of externally accessible gas flow conduits  52   a ,  52   b ,  54   a ,  54   b  is provided in opposing walls of the housing  50  to define flow paths for gas between external and internal the housing  50  that communicate with respective flow paths  44 , 46  through the associated conduits  40 , 42  of the stack of FIG. 2 a . Thus, referring to FIG. 1, it is intended that the flow conduits  22 , 24  of the second gas flow circuit will be connected with the gas flow conduits  52   a ,  52   b  of the housing  50  and that the flow conduits  14 , 16  of the first gas flow circuit will be connected with the gas flow conduits  54   a ,  54   b  of the housing  50 .  
         [0033]    Usefully, although not essentially, pressure sensors  56   a ,  56   b  may be located within the conduits  54   a ,  54   b  of the housing  50  to provide pressure readings to a differential pressure (ΔP) meter  58  by which gas flow (here inspiration gas flow) through the housing  48  can be calculated in a manner well known in the art. Similar pressure sensors  60   a ,  60   b  may be located within the conduits  52   a ,  52   b  and connected to a differential pressure meter (ΔP)  62  in order to gain a measure of gas flow (here expiration gas flow) through the housing  50 .  
         [0034]    Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.