Abstract:
A nasal cannula for delivering respiratory gas to a neonatal infant includes a gas inlet configured to engage a respiratory conduit, a gas outlet configured to engage an expiratory conduit, and a pair of nasal prongs. The gases inlet and the gases outlet are in fluid communication via a low resistance path. Each of the nasal prongs is located substantially equidistant from, and in fluid communication with, the gases inlet, and substantially equidistant from and in fluid communication with, the gases outlet. The nasal prongs are juxtaposed directly in the low resistance path.

Description:
FIELD OF INVENTION 
     This invention relates to Nasal Cannulae particularly though not solely to nasal cannulae for delivering Continuous Positive Airway Pressure (CPAP) to neonates. 
     BACKGROUND 
     Certain individuals require a respiratory supplement such as air, oxygen, or other gases. Such gases are freely supplied and/or supplied at controlled pressures. Such gases are also supplied through the patient&#39;s mouth and/or through the patient&#39;s nose. Nasal supply systems provide an advantage in that they are generally more convenient and less intrusive than mouth based or mouth covering devices. Despite their convenience, nasal based devices are deemed uncomfortable in light of securement straps placed across the face and/or around the head and used to secure the device to an individuals breathing cavity. Moreover, conventional cannulas do not provide a proper seal around the nares to inhibit apnea and to provide a high flow system to stimulate the patient&#39;s breathing. Hence, even with such securement straps, these nasal devices often dislodge from the breathing cavity. This is of particular concern with children, infants, or the elderly who do not understand the importance of keeping the nasal breathing device in place, whether it be a nasal CPAP or nasal cannula. 
     It is known to be beneficial and therapeutic to supply an individual with a sufficient amount of respiratory airway pressure in order to maintain a minimum level of air volume in the lungs. If the air volume falls below this minimum level, then the lungs may collapse, which can be extremely dangerous or even deadly to the individual. Moreover, the back pressure can increase oxygen levels in the lungs and decrease carbon dioxide levels. This will also improve PH by removal of carbon dioxide, which is an acid, from the blood. Hence, the application of such sufficient pressure, called continuous positive airway pressure (CPAP), has been found to be advantageous in maintaining a minimum air volume or lung pressure when an individual is spontaneously breathing. CPAP can be supplied through nasal attachment devices such as a nasal cannulae, or through mouth based or endotracheal devices. 
     A number of CPAP devices are known including endotracheal tubes, head chambers, face chambers, face masks, nasal prongs, and nasal cannula. While each type of device has advantages and disadvantages, the nasal cannula provides a comfortable alternative for providing CPAP and/or airflow assistance. Prior art nasal cannulae have been disclosed in many forms with various methods of securing the device to the nasal passageway. One such cannula assembly is disclosed in U.S. Pat. No. 3,513,844 which uses an adjustable strap that encircles an individual&#39;s head. A similar device is disclosed in U.S. Pat. No. 4,106,505 wherein the supply tubes to the cannula are hooked over an individual&#39;s ears and around the head. Even more cumbersome, U.S. Pat. No. 5,477,852 discloses a device with a headband for holding and positioning the nasal inserts and associated supply tubes. Yet another system in U.S. Pat. No. 5,271,391 discloses a cannula which is secured by applying strips of pressure sensitive adhesive tape to the supply tubes leading from each side of the cannula, thereby attaching the supply tubes to the cheeks of an individual with the cannula positioned in between. 
     “Bonnet” type devices are also used to hold the CPAP nasal cannulae in place. However, this method generally puts pressure on an individual&#39;s nose and upper lip thereby causing pressure necrosis in the centre of the nose. A particularly sensitive individual is a young child, infant or baby. The bonnet also fails to adequately keep the nasal prongs in position, particularly with infants who move or roll around in their crib. In a hospital or care facility setting, it is not uncommon for an attendant to discover that the CPAP device has been disconnected from a patient&#39;s nose, which can lead to apnea, desaturations, bradycardia, or hypoxia which is dangerously low oxygen levels in the blood. In practice, the tubing for these bonnet type CPAP&#39;s is draped around both sides of the patient&#39;s cheek which means that the most comfortable lying down position is on the patient&#39;s back. Pressure on the patient&#39;s cheeks caused by the securement device can make other positions uncomfortable. 
     Other prior art anchoring systems include adhesive devices which attach directly to the nose. U.S. Pat. No. 4,823,789 discloses a nose tube anchoring strip which has an adhesive coated sheet shaped to fit over an individual&#39;s nose and an appendage for holding a nasal-gastric tube. A similar system is found in U.S. Pat. No. 5,156,641 which has an anchoring cord adhesively attached to an individual&#39;s nose at one end and attached to hold a naso-gastric catheter at the other end. U.S. Pat. No. 5,513,635 provides a securement device with a body engagement portion which adheres across the nose of an individual with cannula engaging portions extending down therefrom. Similarly, U.S. Pat. No. 5,682,881 discloses the use of an adhesive foam pad secured to the upper lip for positioning of the cannula. 
     In U.S. Pat. No. 3,643,660 a unified nasal cannula comprises a hollow tubular body having an upper flat or plane surface and a pair of spaced and curved elongated tubular extensions, having exterior orifices for directing a gas flow which extensions project upwardly at an angle from the surface. Referring to  FIGS. 2 and 3  we see that because the inlet  400  is from one side the prongs  402 , 404  may see slightly different pressures. There is also the potential for downstream prong  404  to rebreathe the expired CO 2  from upstream prong  402 . 
     In U.S. Pat. No. 5,975,077 a cannula is disclosed including an airway injecting gas in fluid communication with nostrils of a patient and aerodynamically designed passageways for both the ambient air and the injected gas to optimize the fluid flow characteristics during inhalation and exhalation of the patient. 
     In U.S. Pat. No. 4,774,946 a cannula is described attached to an elongated flexible tube. The nasal prongs include bulbous portions that seat and seal the nasal tubes in the nares. 
     In U.S. Pat. No. 5,193,532 a device is disclosed for generating by ejector action a continuous positive airway pressure (CPAP), comprising a breathing-channel which at one end opens into the atmosphere and at another end is adapted to be provided with an attachment device to the nose and/or mouth of the patient as seen in  FIG. 1 . The inlet is situated between a channel open to the atmosphere and open to the prongs in such a manner that the stream of fresh gas is directed mainly co-axially into the channel, producing an ejector action. 
     However, while these prior art systems do provide nasal CPAP they suffer from a number of disadvantages including: insufficiently securement to the patients head, potential for unbalanced pressure in each prong, and potential for rebreathing of expired CO 2 . 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a nasal cannula which goes someway to overcoming the above mentioned disadvantages or which will at least give the public a useful choice. 
     Accordingly in a first aspect the present invention consists in a nasal cannula for delivering respiratory gas to a neonatal infant comprising: 
     a gases inlet configured to engage an inspiratory conduit, 
     a gases outlet configured to engage an expiratory conduit, 
     a hollow manifold chamber, said gases inlet and said gases outlet in fluid communication through said chamber,
         a pair of nasal prongs, each of said prongs substantially equidistant from, and in fluid communication with, said gases inlet through said manifold chamber and substantially equidistant from and in fluid communication with said gases outlet through said manifold chamber,   said hollow manifold chamber providing a low resistance path between said gases inlet and said gases outlet and configured internally to limit the deadspace of said nasal cannula substantially to the volume of said prongs, said prongs juxtaposed directly in said low resistance path.       

     In a further aspect the invention consists in a system for delivering respiratory gas to a patient comprising 
     a source of pressurised gas, 
     an inhalatory conduit in fluid communication with said source of gas and adapted to convey gas, 
     a nasal cannula in fluid communication with said inhalatory conduit and adapted to deliver gas to the nasal passages of an infant, 
     an exhalatory conduit in fluid communication with said cannula and adapted to convey gas from said cannula, 
     a pressure regulating device disposed within or in fluid communication with said exhalatory conduit and adapted to achieve a predetermined mean pressure of gas delivered to the nasal passages of a neonatal infant by regulating the flow of gas through said exhalatory conduit, 
     said nasal cannula including a low resistance path between said inhalatory conduit and said exhalatory conduit. 
     To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. 
     The invention consists in the forgoing and also envisages constructions of which the following gives examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One preferred form of the present invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is a side view of a prior art cannula on an infant, 
         FIG. 2  is a perspective view of a prior art cannula on an infant, 
         FIG. 3  is a cross section of a prior art cannula, 
         FIG. 4  is a perspective view from above of the present invention, 
         FIG. 5  is a section view of the present invention, 
         FIG. 6  is a perspective view of the present invention, 
         FIG. 7  is a side view of the present invention, 
         FIG. 8  is a view or the present invention from below, 
         FIG. 9  is a view of the present invention from above, 
         FIG. 10  is an illustration of the present invention is use on a neonate, 
         FIG. 11  is a block diagram of a CPAP system, in use with the present invention, 
         FIG. 12  is a side view of a bonnet, used to hold the cannula of the present invention in position, and 
         FIG. 13  is an illustration of the bonnet of  FIG. 13  in use on an neonate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 11  in which a typical application is depicted. A humidified Continuous Positive Airway Pressure (CRAP) system is shown in which a patient  19  is receiving humidified and pressurised gases through a nasal cannula  100  connected to a inhalatory conduit  21 . It should be understood that the present invention, however, is not limited to the delivery of CPAP gases but is also applicable to other types of gases delivery systems. Inhalatory conduit  21  is connected to the outlet  12  of a humidification chamber  10  which contains a volume of water  15 . Inspiratory conduit  21  may contain heating means or heater wires  20  which heat the walls of the conduit to ensure a constant humidity profile along the conduit and therefore reduce condensation of humidified gases within the conduit. As the volume of water  15  within humidification chamber  10  is heated, water vapour begins to fill the volume of the chamber above the water&#39;s surface and is passed out of the humidification chamber  10  outlet  12  with the flow of gases (for example air) provided from a gases supply means or blower  18  which enters the chamber  10  through inlet  16 . 
     With reference to  FIGS. 5 and 11 , the humidified gases pass through the inhalatory conduit  21  to the cannula  100 , which is in communication with the nose of a patient  19  through prongs  116 , 118 . The expired gases pass through the prongs  116 , 118  to the output manifold  130 . The excess gases then flow through the exhalatory conduit  230 . It is preferred that exhalatory conduit  230  is connected to a pressure regulator  234 . 
     In the preferred embodiment of the present invention the flow of exhalatory gases is discharged into a chamber  204  containing a column of water  238 , as seen in  FIG. 11 . The gases flowing through the exhalatory conduit  230  are discharged into the body of water  238  from a short conduit  236  which extends from the expiratory conduit into the vessel  204 . This results in a bubbling effect, whereby the gases eventually exit the vessel  204  via the outlet port  252 , which can also be used to initially fill the chamber  204  with water. The outlet port  252  includes shielding to prevents liquid aerosols created by the vigorous bubbling on the surface of the water from being expelled. It will be appreciated that the short conduit  236 , could equally be integrated into the end of the expiratory conduit  230 . It will also be appreciated that by adjusting the level of which the short conduit  236  is submerged in the body of water  238  the mean pressure of supplied gases through the cannula  100  can be controlled. 
     Nasal Cannula 
     Referring now to  FIGS. 4 to 10  the nasal cannula  100  is seen in more detail. The inlet manifold  110 , is connected to an inlet port  112 . Inlet port  112  accepts the gas flow from the humidifier and air/oxygen blender or any other flow source apparatus as would be appropriate. The diameter of the inlet manifold  110  is as large as possible to ensure minimal pressure drop in the gases before delivery to the patient. In fluid communication with the inlet manifold are two nasal prongs  116 ,  118 . The gases are then able to flow from the inlet manifold  110  up through the nasal prongs into the corresponding nares of the patient. The prongs  116 ,  118  themselves are cylindrical with a slight taper narrowing at the top. The diameter is carefully chosen such that it will substantially seal against the interior of the nare, without imparting any substantial pressure thereon. As well as sealing this also provides some level of securement and keeps the cannula  100  in place. 
     An important feature of the present invention is shown in  FIG. 4  The two nasal prongs  116 ,  118  are spaced apart at a distance optimised for the nare spacing for a neonatal infant. However the present invention would be equally applicable for patients of all sizes and the design is easily scalable. It will be appreciated that while the nasal structure of each infant will be somewhat different, almost inevitably the septum will be lower than the fleshy parts on the side of the nose. As mentioned in the discussion of the prior art this may result in irritation and pressure necrosis on the septum. To avoid this, there is a notch  126  or indentation between the two nasal prongs  116 ,  118  as shown in  FIG. 4  and  FIG. 6 . The indentation  126  is designed such that there will be no contact with the septum. 
     Reference is now made to  FIG. 5  which shows a sectional view of the cannula  100 . The inlet manifold  110  is separated from the outlet manifold  130  by a partition  132  running horizontally between the inlet  110  and outlet  130 . The partition  132  terminates approximate to the base  134  of the prongs  116 ,  118 . In this fashion there will always be at least some flow flowing directly from the inlet manifold  110  to the outlet manifold  130  as shown by arrow  170 . As the diameter of inlet manifold  110  is as large as possible and the entrance/exit of the inlet and outlet manifolds  110 ,  130  are located each of the partition  132 , a path exists from the inlet manifold  110  to the outlet manifold  130  that is a low resistance path shown by arrow  170 . This ensures that the dead space or tidal volume is limited to the volume of the prongs  116 , 118 . This configuration results in the minimum build up of expired CO 2  and also reduces any opportunity for condensation in the cannula  100 . 
     The prongs  116 ,  118  are formed as part of a moulded rubber or silicon insert  136  which seals to the hard plastic body  138  of the cannula  100  via an interference or compression fit to the hard plastic body  138  of the cannula  100 . The prongs  116 ,  118  are able to be used as a disposable component, or alternatively they can be easily interchanged for a different size, a nasal mask, mouthpiece or other interface as desired. The inlet port  112  is formed as part of the body  138 , with inlet  110  at the base of the inlet port  112 . Inlet port  112  may be adopted to fit any typical connection configuration for commercially available conduits. Similarly the outlet port  142  is in fluid communication with the outlet manifold  130 . A further sensor port  144  can be provided to measure any parameters of the delivered gases for example pressure, temperature, or humidity. As shown in  FIG. 7 , an inlet/outlet connector  154  can be connected to act as an interface between the nasal cannula  100  and the inhalatory conduit  21  and exhalatory conduit  230 . The connector  154  can be formed from extruded PVC or Silicon or any other suitable material. The sensor port  144  can also be connected to a measurement tube  156  which can be formed as part of the connector  154 . 
     Head Securement 
     As can be seen in  FIGS. 10 to 12  the cannula  100  can be secured to the head of a patient  19  by a bonnet. A preferred form of infant bonnet includes a head covering portion  330  which is preferably formed of a stretchable or elastic material having thermal insulation properties. An example of appropriate material is a synthetic or cotton knit fabric. The head covering  330  is provided in the form of a open ended tube. Where the material used for the covering  330  provides more stretch along one principal axis, then that principal axis is preferably aligned across the longitudinal axis of the tube. 
     As shown in  FIG. 12 , the head covering  330  has one open end  332 . A zone  331  adjacent to this open end  332  stiffer than the surrounding region. The zone  331  may comprise thr example a region of modified knit form, a cuff formed from an alternate material or material configuration or a multi layer hem of the tube. 
     A strap is provided on the outer surface of the covering  330  for supporting a breathing tube or other medical conduits or wiring. 
     The securing means is a strap  333  with which is sewn onto the bonnet. The strap has Velcro® attached at one end. As shown in  FIG. 10 , a foam block  334  with a triangular outside shape, is fitted over the connector  154 . The foam block  334  is positioned on the strap  333 . The strap  333  is then closed around the foam block and secured with the Velcro® The foam block  334  is used to firmly hold the connector  154  in place on the bonnet  330  to prevent displacement of the nasal prongs from the nares. Alternatively, as shown in  FIG. 13 , if inlet/outlet connector  154  is not used, flexible tubes  321  can be attached directly to the head covering  330 . 
     The second open end  347  of the head coveting  330  is preferably formed with a simple hem. The open end  347  is preferably closeable or retainable in a closed position by a closing means  340 . The closing means  340  may comprise a further lace or tie of similar configuration to the securing means  333 . The lace or tie  340  has two arms  342 ,  344 . The arms  342 ,  344  preferably tie together or pass through a toggle. 
     In use the end  347  of head covering  330  is bunched together as an end bunch  341 . The loop of lace or tie  340  is passed over the bunch  341 . The bunch  341  is firmly secured in a closed configuration within the tightened loop of the lace or tie  340 . 
     The closing means  340  thus provides for easy and efficient closing or opening of the infant bonnet should there be a need for access to the top of the head of the infant. Access may for example be required for placement of electrodes or for cranial ultrasounds. Where access is required the closing means  340  may be released and the bunched portion of end  347  opened to provide necessary access. This access is available without disturbing the other end  332  of the head covering  330  or the securing means  333  supporting medical tubes or wires in place. 
     Cannula Securement 
     Ideally the patient  19  should not be mouth breathing. Both inhalation and exhalation should be done through the cannula. In the preferred embodiment the jaw of the patient  19  is held closed to eliminate mouth leak. Mouth leak is undesirable because it causes a lower pressure thus reducing the level of CPAP. 
     Referring now particularly to  FIGS. 8 to 10  we see that the base of the cannula  100  is secured to the head of the patient  19  using strap  150 . Strap  150  passes around the back of the neck of the patient  19  and is connected to the cannula  100  by way of a sliding rod  152 . Rod  152  is secured to body  138  by jaws, or clip  160  as shown in  FIG. 8 . This allows the rod  152  substantial relative lateral and rotational movement with respect to the cannula  100  as the patient  19  twists their head, and exerts forces on the strap  150 . Adequate restraining force is provided directly on the cannula  100  without any twisting of the cannula  100 . The rod  152  can be a plastic, for example acetal material, engaging into the jaw or clip  160  on the underside of the body  138 . The tension in the strap  150  can be adjusted to a comfortable level for the patient  19 . 
     What has been described is an improved nasal cannula of pressure necrosis or irritation that might normally be associated with the use of such a device. The improvement ensures a balanced feed to both prongs, low dead space high flow through the manifold so rebreathing of CO 2  is minimised.