Abstract:
A nasal cannula for delivering respiratory gases to a neonatal infant comprising a manifold including a chamber, a gases inlet to the chamber and a gases outlet a low resistance path for gases through the chamber from its inlet to its outlet and a pair of nasal prongs in fluid communication with the chamber with each prong substantial equidistant the inlet, and directly in the low resistance path to deadspace eliminate.

Description:
FIELD OF INVENTION  
         [0001]    This invention relates to Nasal Cannulae particularly though not solely to nasal cannulae for delivering Continuous Positive Airway Pressure (CPAP) to neonates.  
         BACKGROUND  
         [0002]    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 apnoea and to provide a high flow system to stimulate the patients 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.  
           [0003]    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.  
           [0004]    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.  
           [0005]    “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 apnoea, 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.  
           [0006]    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.  
           [0007]    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 .  
           [0008]    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.  
           [0009]    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.  
           [0010]    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.  
           [0011]    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  
         [0012]    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.  
           [0013]    Accordingly in a first aspect the present invention maybe broadly said to consist in nasal cannula for delivering respiratory gases to a neonatal infant comprising:  
           [0014]    a manifold including a chamber, a gases inlet to said chamber and a gases outlet to said chamber, and a low resistance path for said gases through said chamber from said inlet to said outlet  
           [0015]    a pair of nasal prongs in fluid communication with said chamber substantial equidistant said inlet, said prongs juxtaposed directly in said path.  
           [0016]    Preferably said cannula includes securement means to hold said prongs in place in the nares of said neonate.  
           [0017]    Preferably said securement means including a strap adapted to pass around the back of the neck of said neonate and engage with said cannula and thereby hold said prongs in place in the nares of said neonate.  
           [0018]    Preferably said strap includes a low resistance portion, said low resistance portion adapted to engage with said cannula in a sliding fashion to allow said strap substantial lateral (iguanian axial) movement relative to said cannula.  
           [0019]    Preferably said low resistance portion comprises a thin plastic strand or strip.  
           [0020]    Preferably the remainder of said strap includes an adjustable attachment to said low resistance portion to in use adjust the tension of said strap.  
           [0021]    Preferably said securement means including an infant bonnet comprising head cover means adapted to at least partially cover the head of an infant and including at least a cuff of elastic property to securely locate said cover means on said infant head, and medical tube securing means connected with said cover means on the outer surface thereof, said medical tubes adapted to in use connect to said cannula, said securing means operable to hold medical tubes passing over said cover means against at least lateral (iguanian axial) movement.  
           [0022]    Preferably said head cover means is formed of a knit fabric in a tubular configuration and open at both ends, said securing means is connected with said outer surface adjacent one said open end and end closing means are connected with said outer surface adjacent the other said open end, said end closing means being operable to hold the said knit fabric of its respective said end in a closed, bunched together, condition.  
           [0023]    Preferably either or both of said tube securing means and said end closing means arc or include a lace or tie stitched to said head cover means.  
           [0024]    Preferably said lace or tieing is secured at its centre to said head cover means to provide two alms, said arms passing through a tightening toggle slidable on said arms.  
           [0025]    Preferably said tightening toggle is operable between at least two conditions, being biased to a pinch off condition in which said arms of said lace or tie are clamped within their passage through said toggle and manipulable to a free configuration in which said toggle may slide a long said arms of said lace or tie.  
           [0026]    In a second aspect the present invention may be broadly said to consist in a system for delivering respiratory gases in a neonatal infant comprising  
           [0027]    a source of pressurised gases,  
           [0028]    an inhalatory conduit in fluid communication with said source of gases and adapted to convey gases,  
           [0029]    a nasal cannula in fluid communication with said inhalatory conduit and adapted to deliver gases to the nasal passages of said infant,  
           [0030]    an exhalatory conduit in fluid communication with said delivery means and adapted to convey gases from said delivery means, and  
           [0031]    a pressure regulating device disposed within or in fluid communication with said exhalatory gases transport means and adapted to achieve a predetermined mean pressure of gases delivered to the nasal passages of said infant by regulating the flow of gases through said pressure regulating device.  
           [0032]    Preferably pressure regulating device comprising:  
           [0033]    a container adapted to house a body of liquid,  
           [0034]    terminal conduit means including proximate and distal ends, said proximate end adapted for connection to said exhalatory conduit, and said distal end adapted for submergence in said body of liquid,  
           [0035]    such that in use the mean pressure of gases delivered to the nasal passages of said infant is determined by the level to which said distal end is submerged in said body of liquid.  
           [0036]    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.  
           [0037]    The invention consists in the forgoing and also envisages constructions of which the following gives examples. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0038]    One preferred form of the present invention will now be described with reference to the accompanying drawings in which:  
         [0039]    [0039]FIG. 1 is a side view of a prior art cannula on an infant,  
         [0040]    [0040]FIG. 2 is a perspective view of a prior art cannula on an infant,  
         [0041]    [0041]FIG. 3 is a cross section of a prior art cannula,  
         [0042]    [0042]FIG. 4 is a closeup perspective view from above of the present invention,  
         [0043]    [0043]FIG. 5 is a section view of the present invention,  
         [0044]    [0044]FIG. 6 is a closeup perspective view of the present invention,  
         [0045]    [0045]FIG. 7 is a side view of the present invention,  
         [0046]    [0046]FIG. 8 is a closeup view of the present invention from below,  
         [0047]    [0047]FIG. 9 is a closeup view of the present invention from above,  
         [0048]    [0048]FIG. 10 is an illustration of the present invention is use on an neonate,  
         [0049]    [0049]FIG. 11 is a block diagram of the CPAP system,  
         [0050]    [0050]FIG. 12 is a side view of the bonnet, and  
         [0051]    [0051]FIG. 13 is an illustration of the bonnet is use on an neonate 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0052]    Referring now to FIG. 11 in which a typical application is depicted. A humidified Continuous Positive Airway Pressure (CPAP) system is shown in which a patient  19  is receiving humidified and pressurised gases through a nasal cannula  28  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 .  
         [0053]    The humidified gases pass through the inhalatory conduit  21  to the cannula  100  connected to the patient&#39;s  19  nose 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  to a pressure regulator  234 .  
         [0054]    In the preferred embodiment of the present invention the pressure regulator  234 , takes the form of discharging the flow of exhalatory gases 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 chamber  204 . This results in a bubbling effect, whereby the gases eventually exit the chamber  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.  
         [0055]    Nasal Cannula  
         [0056]    Referring now to FIGS.  4  to  10  the nasal cannula  100  is seen in more detail. The inlet manifold  110 , includes an inlet port  112 . This 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.  
         [0057]    An important feature of the present invention is shown in FIG. 2 and in more detail in FIG. 3. 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 he 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. It can be seen that the inlet manifold  110  has a notch  126  or indentation in its uppermost portion between the two nasal prongs  116 ,  118 . The indentation  126  is designed such that there will be no contact with the septum.  
         [0058]    Referring now particularly to FIG. 5 showing a sectional view of the cannula  100 . The inlet manifold  110  is separated from the outlet manifold  130  by a partition  132  running horizontally the length of both manifolds. 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 . This ensures that the deadspace 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 .  
         [0059]    The prongs  116 ,  118  are made from a moulded rubber or silicon insert  136  which has an interference or compression fit seal to the hard plastic body  138  of the cannula  100 . The prongs are able to be used as a disposable component or alternatively easily interchangeable for different sizes, a nasal mask, mouthpiece or other interface as desired. The inlet port  112  connects directly to inlet manifold  110  and may be provided with 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  is provided to measure any parameters of the delivered gases for example pressure, temperature, humidity. An integral 10mm inlet 10 mm outlet conduit  154  formed from extruded PVC or silicon was found to be suitable for this purpose. The sensor port  144  is connected to a measurement tube  156  which may also form part of the integral inlet outlet tube  154  connected to the cannula  100 .  
         [0060]    Head Securement  
         [0061]    As can be seen in FIGS.  10  to  12  the cannula  100  is secured to the neonates head by a bonnet overs its head. The infant bonnet of the present invention includes a head covering portion  330  which is preferably formed of a stretchable or elastic material having thermal insulation property. 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 of the covering  330  provides more stretch along one principal axis then that principal axis as preferably aligned across the axis of the tube.  
         [0062]    The head covering  330  preferably includes a zone adjacent one open end  332  which is stiffer than the surrounding region. The zone  331  may comprise for 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.  
         [0063]    A securing device is provided on the outer surface of the covering  330  for supporting a breathing tube or other medical conduits or wiring.  
         [0064]    The securing means is a strap  333  with which is sewn onto the bonnet. The strap has Velcro attached at one end. The nasal tubing is fitted with a foam block  334  with a triangular outside shape. 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 nasal tubing  321  in place on the bonnet  330  to prevent displacement of the nasal prongs from the nares.  
         [0065]    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.  
         [0066]    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 .  
         [0067]    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.  
         [0068]    Cannula Securement  
         [0069]    Ideally the neonate should not be breathing out of its mouth. Both inhalation and exhalation should be done through the cannula. In the preferred embodiment the neonates jaw is strapped shut to eliminate mouth leak. Mouth leak is undesirable because it causes a lower pressure thus reducing the level of CPAP.  
         [0070]    Referring now particularly to FIGS.  8  to  10  we see that the cannula  100  is secured at its base to the back of the neonates head using strap  150 . The strap connects at the base of the neonates skull on the back of the neck. It connects to the cannula  100  by way of a sliding strap  152 . This strap is secured by way of clips to the hard plastic body  138  allowing the securing strap  150  substantial relative movement with respect to the cannula  100  as the neonate twists its head while providing adequate restraining force directly on the cannula  100  without any twisting of the cannula  100 . In one embodiment this is accomplished by a plastic e.g. acetal sliding strap which engages into sliding clips on the outer face of the cannula. The teflon strap is adjustably attached to the neck strap  150  to allow the tension to be adjusted to a comfortable level.  
         [0071]    What has been described is an improved nasal cannula for use with a CPAP respirator. The improvement reduces the likelihood 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 deadspace high flow through the manifold so rebreathing of expired CO 2  is minimised.