Abstract:
An HME for a tracheostomy tube has a flexible outer housing of a gas-permeable material containing an HME element of discrete particles, granules or the like of a hygroscopic material. The particles are contained between the outer housing and an inner wall of a foam. The inner wall has a ciliated surface facing the end of the tube, which acts to distribute gas over the surface of the HME element. The HME is attached to a flange on an inner cannula by means of a removable adhesive. The HME may include a suction port through a self-closing aperture, which makes a wiping seal with a suction catheter inserted in the tube.

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to gas-treatment devices. 
   The invention is more particularly concerned with heat and moisture exchangers (HMEs) or the like for use with tracheostomy tubes. 
   In normal breathing, inhaled air passes through the nose where it is warmed and moistened before passing to the trachea and bronchial passages. Where a patient breathes via a tracheal tube or laryngeal mask, gas is supplied directly to the trachea, by-passing the nose. The gas is, therefore, preferably warmed and moistened to prevent discomfort and damage to the lining of the trachea. This is often achieved by a heat and moisture exchange device or HME connected to the tracheal tube to receive both exhaled and inhaled gases. The HME has a moisture-absorbing element, such as of a treated paper or foam, that absorbs moisture in exhaled gases and transfers a major part of this to the inhaled gases. The element also warms inhaled gas in the same way. HMEs are sold by Portex Limited of Hythe, England under the trade mark Thermovent. Examples of HMEs are described in: GB 2303307; GB 2321600; GB 2277689; GB 2268496; GB2267840; GB 2233904; EP 535016; EP 533644; EP 387220; EP 265163; EP 413127; U.S. Pat. No. 4,516,573; U.S. Pat. No. 4,090,513; U.S. Pat. No. 4,771,770; U.S. Pat. No. 4,200,094; and U.S. Pat. No. 4,048,993. The HME may also include a filter for removing particles, bacteria and viruses from gas supplied to or from the patient. 
   Conventional HMEs have an exchange element within a rigid housing that is coupled to the machine end of the tracheal tube. This can be relatively bulky and is a particular problem where the patient is breathing unaided via a tracheostomy tube since it is preferable for this to be as unobtrusive as possible. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an alternative gas-treatment device and assembly. 
   According to one aspect of the present invention there is provided a gas-treatment device for connection to the machine end of a patient breathing tube, the device being conformable. 
   The device preferably includes a flexible outer housing and a gas-treatment element that is substantially conformable to the shape of the outer housing. The outer housing is preferably of a gas-permeable material, such as a fabric. The device preferably includes an HME element. The HME element may include a discrete material, such as in the form of particles, granules or small balls. The HME element may include a zeolite. The device may include a flexible outer housing, a conformable gas-treatment element within the housing and gas-dispersion means within the housing arranged to disperse gas over the gas-treatment element. The gas-dispersion means may include a ciliated surface. The patient breathing tube is preferably a tracheostomy tube. The gas-treatment device may be supported on a flange of the tube and is preferably removably attached with the flange, such as by means of an adhesive. The breathing tube preferably has a coupling extending within the gas-treatment device, the coupling having at least one side port. The gas-treatment device may include a self-sealing port arranged to be aligned with the machine end of the breathing tube such as to enable an elongate member to be inserted through the port and the device, into the tube. The port is preferably arranged to make a wiping seal with the elongate member. 
   According to another aspect of the present invention there is provided a gas-treatment device including a port for connection to a patient breathing tube and a gas-treatment element, the device including an outer wall of gas-permeable material such that gas passes to and from the patient breathing tube via the port, the gas-treatment element and through the outer wall. 
   The wall may be of a fabric and the gas-treatment element may be an HME element. The HME element may include a discrete material, such as in the form of particles, granules or small balls. 
   According to a further aspect of the present invention there is provided an assembly of a breathing tube and a gas-treatment device according to the above one or other aspect of the invention. 
   The breathing tube preferably includes an outer tube and a removable inner cannula inserted within the outer tube, the gas-treatment device being mounted at the machine end of the inner cannula. 
   A tracheostomy tube assembly including an HME, in accordance with the present invention, will now be described, by way of example, with reference to the accompanying drawing. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a perspective view of the assembly; 
       FIG. 2  is a partly cross-sectional view of a part of the assembly showing the HME; and 
       FIG. 3  is a partly cross-sectional view of a part of an alternative assembly having a modified HME. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference first to  FIGS. 1 and 2 , the assembly comprises an outer, tracheostomy tube  1 , a removable inner cannula or liner  2  and an HME gas-treatment device  3  connected to the machine end of the cannula. When inserted, the inner cannula  2  is considered to form a part of the tracheostomy tube  1 . 
   The tracheostomy tube  1  is conventional having a shaft  10  curved to the anatomy of the patient so that, in use, its patient end  11  is directed caudally within the trachea. The machine end  12  of the tube  1  terminates flush with a laterally-extending flange  13  shaped to lie flat on the patient&#39;s skin to either side of the tracheostomy. 
   The cannula  2  has a shaft  20  curved to the same shape as the tracheostomy tube  1  and its external diameter is such that it is a close sliding fit within the tracheostomy tube. The cannula  2  also has a flange  23  at its machine end  22  of the same shape as the flange  13  of the tracheostomy tube so that the two flanges lie close to one another when assembled. A short cylindrical coupling  24  projects from the rear, machine side of the flange  23 . The coupling  24  has a tapered female bore adapted to receive a 15 mm male coupling and it also has a number of side ports  25  equally spaced around its circumference. The side ports  25  are arranged so that they will be occluded when a male coupling or 15 mm connector is inserted. 
   The HME  3  is fitted over the coupling  24  and is attached to the flange  23 . The HME  3  has an outer wall or housing  30  of a bonded-fibre fabric or other gas-permeable flexible material, such as a perforated material. The housing  30  has a generally rectangular shape, when viewed along the axis of the cannula  2 , that follows approximately the outline of the flange  23 . Alternatively, the housing could be oval or elliptical viewed along the axis of the cannula. In section, as shown in  FIG. 2 , the housing  30  is oval. Centrally in one side of the housing  30  there is a circular aperture  31  the diameter of which is approximately equal to the external diameter of the coupling  24 . A region  32  on the outside of the housing  30  around the aperture  31  has a low-tack adhesive, which forms a secure, gas-tight seal with the machine side of the flange  23 . The HME could be attached to the cannula in other ways, such as by a mechanical clasp or by hook-and-loop fabric. The coupling  24  projects through the aperture  31  into a central cavity  33  within the housing  30 . The cavity  33  is enclosed by a porous foam sponge wall or insert  35  having multiple fingers  36  projecting inwardly towards the aperture  31  to provide a ciliated surface  37  to the cavity. 
   The HME  3  is completed by an HME element  38  located between the wall  30  and the foam insert  35 . The element  38  extends along the machine-end face  39  of the housing  30  and the edges  40  but not along the major part of the patient-end face  41  in the region  32  because contact with the flange  23  in this region prevents passage of gas. The HME element  38  is of a discrete material, that is, it is formed of separate discrete pieces so that it can conform freely to the shape of the housing  30 . In particular, the element  38  is formed from particles  42  of zeolites, which act as molecular sieves, or small balls of foam or paper treated with a hygroscopic material of the kind commonly used in HME paper elements. 
   The HME  3 , therefore, has a soft, conformable nature of the same kind as a bean bag and can be laid substantially flat over the machine side of the flange  23 . 
   In use, the cannula  2  is inserted in the tracheostomy tube  1  of a patient who is breathing spontaneously. The two flanges  13  and  23  are secured together to hold the cannula  2  in position. When the patient exhales, air flows along the bore of the inner cannula  2 , through the coupling  24 , via its open end and the side ports  25 , into the cavity  33  within the HME  3 . The fingers  36  of the sponge element  35  distribute the air over the entire surface of the HME element  38  for maximum efficiency so that the major part of the heat and moisture in the exhaled breath is transferred to the element. The foam member  35  also takes some part in absorbing the heat and moisture. The gas then flows out through the wall  30  of the HME  3  over a relatively large area. When the patient inhales, air flows in through the wall  30 , through the element  38  and the foam  35  taking up the major part of the heat and moisture absorbed in these parts. The warmed and moistened air then flows through the coupling  24  along the tracheostomy tube  1 , via the inner cannula  2 , to the patient. 
   The arrangement of the present invention enables a low profile HME to be provided, which is inconspicuous, does not interfere with bedding and clothing and produces less leverage on the tube to which it is connected. The HME presents a conformable external surface, which also makes it comfortable where it comes into contact with the skin. The porous nature of the wall acts as a coarse filter preventing inhalation of larger particles and insects etc. Because the air flows in and out over a large area there is a reduced risk of occlusion. 
   The inner cannula with the HME is removed and replaced periodically when secretions start to collect. It will be appreciated, however, that the HME could be attached directly to the flange of the tracheostomy tube where an inner cannula is not used, the HME being removed and replaced as necessary. If access is needed to the coupling  24 , such as to connect the patient to a ventilator or resuscitator, the HME can be readily removed by pulling apart the adhesive join at the region  32 . 
   The HME could be modified to allow use of a suction catheter, endoscope or other elongate member, as shown in  FIG. 3  where similar components have been given the same reference number with the addition of  100 . The housing  130  is of a similar shape to the housing  30  shown in  FIG. 2  but it has a second aperture  151  located directly opposite the aperture  131  in which the coupling  124  is received. The second aperture  151  differs from the first in that it is normally closed, being formed by a passage through the foam member  135 , which is extended to the wall  130  around the aperture. The aperture  151  is closed resiliently by the nature of the foam but can be opened when it is necessary to insert a suction catheter  200  or the like along the tracheostomy tube simply by pushing the catheter through the aperture. The foam member  135  around the aperture  151  contacts the catheter  200  around its circumference to provide a wiping seal that restricts the escape of gas through the aperture around the outside of the catheter. 
   The invention, in some of its aspects, is not confined to HMEs but could be used with other gas-treatment devices such as filters.