Abstract:
A multiple lumen nasal cannula that can be used to delivery two separate supplies of gases to a patient. The multiple lumen nasal cannula includes a first lumen for delivering a first gas and a second lumen for delivering a second gas. The first lumen includes support structure that reduces the tendency of the cannula to kink and lock the delivery of gas to a patient. The cannula assembly includes a mixing chamber positioned near the patient such that the two supplies of gas are not mixed until a location approximate to delivery to the patient. The nasal cannula assembly includes a connecting device that allows the two separate supplies of gas to be correctly delivered to the two different lumens of the nasal cannula.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a medical device for providing medical gasses from at least one gas source to a patient. More specifically, the present invention relates to a multiple lumen cannula for delivering multiple medical gasses to a patient and mixing the gasses at a location proximal to the patient.  
       BACKGROUND OF THE INVENTION  
       [0002]     Patients that have respiratory difficulties often must be placed on a mechanical ventilator. These difficulties may be pathological in nature or may be due to the fact that a patient is too weak or sedated to independently proper respiration functions. Often, the patient may be spontaneously attempting to breathe but not able to complete a full respiratory cycle. In these cases mechanically assisted ventilation is provided. In mechanically assisted ventilation a combination and pressure and/or flow sensors detect a patient&#39;s breath attempt. This detection triggers the delivery of a mechanical breath. This breath is provided by the delivery of a pulse or plug of medical gases under a pressure that is sufficient to overcome the resistance of the patient&#39;s airway to fill the lungs. When this pulse of medical gas is discontinued the natural compliance of the patient&#39;s chest wall forces the delivered breath out of the patient in an expiratory phase.  
         [0003]     Mechanical ventilation can comprise the delivery of air, but often the breath that is delivered is formed of a mixture of various medical gasses. These gasses may include oxygen, helium, nitric oxide (NO), a drug aerosol, or, in the case of anesthesia delivery, an anesthetic agent. The proper combination of medical gasses would be decided upon by the clinician in response to the ailments of the patient.  
         [0004]     Efficient mechanical ventilation requires a quality ventilator-patient interface. This requires a quality seal around the patient airway thereby providing efficient delivery of the medical gasses. There are many varieties of ventilator-patient interfaces. These varieties include face masks which cover the patient&#39;s mouth and nose, an endotracheal tube, or a nasal cannula. While there are advantages to each of the patient interfaces a nasal cannula presents the advantage of providing a higher quality connection to the patient&#39;s respiratory system than a face mask while being less invasive than an endotracheal tube.  
         [0005]     In the delivery of some medical gasses to a patient it is desirable to keep the gasses separate until shortly before they are delivered to the patient. This may arise due to properties desired in each of the gasses, structural components of the mechanical ventilator, or because of adverse reactions between different medical gasses. One example of such adverse reactions is the reaction that takes place when oxygen is mixed with nitric oxide. Nitric oxide is a gas that, when inhaled, acts to dilate blood vessels in the lungs, improving oxygenation of the blood and reducing pulmonary hypertension. Therefore it is often desired to deliver a combination of nitric oxide to improve lung function with an increased concentration of oxygen to improve oxygen transfer. However, oxygen and nitric oxide react to form nitrogen dioxide (NO 2 ), a toxic substance. Therefore, to reduce the production of nitric oxide it is desirable to keep the supply of oxygen and nitric oxide separate until just before it is delivered to the patient.  
         [0006]     In many clinical or critical care situations a patient is connected to a wide variety of monitoring and/or support devices. These devices may include patient monitoring such as ECG, EMG, or EEG, fluid and/or nutritional support in the form of a catheter, patient waste removal, or respiratory support in the form of a mechanical ventilator. A challenge arises with this multitude of patient connections in keeping them tangle free and properly connected to the patient. This becomes difficult when the patient is moving, clinicians are moving about the patient, or the patient (and connected equipment) must be moved within the treatment facility. While data connections are more susceptible to disconnection from the patient gasses or fluid delivery connections are susceptible to kinks or entanglements in the lines resulting in restricted or interrupted delivery to the patient.  
         [0007]     Therefore it is desirable in the field of mechanical ventilation to provide a kink resistant nasal cannula that can separately deliver multiple medical gasses to a location proximal to a patient.  
       SUMMARY OF THE INVENTION  
       [0008]     In general, the present invention provides a kink resistant delivery means for medical gasses. A nasal cannula is provided with multiple lumens for the separate delivery of multiple medical gases. More specifically, a second lumen is disposed within a first lumen to provide for multiple medical gasses and additional structures within the cannula to provide kink resistance.  
         [0009]     An additional aspect of the present invention comprises the monitoring of each of the medical gasses within the nasal cannula. This monitoring detects the pressure within the lumen of the medical gas being delivered to the patient. This pressure may be monitored as a differential pressure between the multiple lumens of the nasal cannula. As a further aspect of the present invention, the differential pressure measurement may be used to determine the state of the medical gas delivery to the patient via the nasal cannula. This state may include the detection of normal operation, a kink in the nasal cannula, or disconnection of the ventilator-patient interface.  
         [0010]     In another aspect of the present invention, the patient triggering means or means for detecting a patient breath attempt may be disposed within the nasal cannula to provide more accurate detection of patient breath attempts and triggering of the delivery of pulses of medical gas to the patient.  
         [0011]     In a still further aspect of the present invention, the multiple lumen cannula of the present invention comprises a mixing chamber disposed at one end of the cannula proximal to the patient interface. The mixing chamber provides for the mixing of medical gasses at a location proximal to the patient for delivery to the patient.  
         [0012]     In a final aspect of the nasal cannula of the present invention, the nasal cannula comprises a connection assembly that facilitates the connection of the sources of medical gas to the multiple lumen cannula of the present invention. This connection assembly provides the low resistance delivery of the medical gasses from their source to the multiple lumens of the cannula. The connection means for each lumen of the multiple lumen cannula is morphologically different thus insuring the proper connection of the multiple lumens of the cannula. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic diagram of the ventilator system of the present invention;  
         [0014]      FIG. 2  is a perspective view of the cannula assembly of the present invention;  
         [0015]      FIG. 3  is a section view taking along line  3 - 3  of  FIG. 2  illustrating the connection assembly;  
         [0016]      FIG. 4   a  is an end view of the coaxial dual lumen cannula of a first embodiment of the invention;  
         [0017]      FIG. 4   b  is a perspective view of the coaxial dual lumen cannula;  
         [0018]      FIG. 5   a  is a perspective view of a dual lumen cannula of a second embodiment of the invention;  
         [0019]      FIG. 5   b  is an end view of the dual lumen cannula shown in  FIG. 5   a;    
         [0020]      FIGS. 6   a  and  6   b  illustrate a connection assembly for the second embodiment of the dual lumen cannula;  
         [0021]      FIG. 7  is a section view of the gas mixing chamber attached to the cannula of the present invention; and  
         [0022]      FIGS. 8   a - 8   d  are graphs representative of the pressure change sequence that may be detected within the cannula of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0023]     Referring to  FIG. 1 , a ventilator system  10  for delivering one or more medical gasses to a patient  12  is shown. The ventilator system  10  delivers a quantity of medical gas from supply tanks  14  and  16  to a patient  12  via a mechanical ventilator  18 . The medical gases in supply tanks  14  and  16  may comprise, but are not limited to, air, oxygen, nitrogen dioxide (NO 2 ) helium, and a drug aerosol. Within the mechanical ventilator  18  is a CPU  20  that controls the electrical and mechanical components of the mechanical ventilator  18 , including a first valve  22  and a second valve  24  disposed within conduits  26  and  28  respectively to control the flow of medical gas from supply tanks  14  and  16 . In an embodiment of the present invention, first valve  22  and second valve  24  may be solenoid valves but it is understood that any valve with the suitable time response to control medical gas flow may be used. First t-connector  30  and second t-connector  32  are disposed along conduits  26  and  28  respectively and provide a connection via conduits  34  and  26  respectively to differential pressure transducer  38 . Differential pressure transducer  38  relays the differential pressure information to CPU  20  via electrical connection  40 . CPU  20  may use this differential pressure data to control elements of the mechanical ventilator  18  including the ventilator engine  42  via electrical connection  44 , first valve  22  via electrical connection  46 , and second valve  24  via electrical connection  48 .  
         [0024]     After first t-connector  30  and second t-connector  32 , the medical gasses travel via conduit  50  and  52  respectively to cannula assembly  54 . The cannula assembly  54  generally includes a connection assembly  56 , a cannula  58 , a mixing chamber  60  and patient interface  62 . The conduits  50  and  52  connect to connection assembly  56  of the cannula assembly  54 . Connection assembly  56  supplies the medical gas from the conduits  50  and  52  to the first and second lumens of cannula  58 , the details of which will be discussed below. Cannula  58  may be approximately two meters in length to provide adequate gas connection between the patient  12  and the mechanical ventilator  18  with a suitable range of motion and connection. The gas mixing chamber  60  is disposed at the end of cannula  58  proximal to the patient  12 . Within gas mixing chamber  60 , the first and second lumens of the cannula  58  provide the gaseous connection to facilitate the mixing of the two previously separate medical gasses. Gas mixing chamber  60  allows for the medical gasses to be delivered to patient  12  via patient interface means  62  as a homogenous mixture. Patient interface means  62  in the present embodiment comprises a nasal cannula, but it is understood that alternative patient interface means may be used, including a face mask or an endotracheal tube.  
         [0025]     Referring to  FIG. 2 , cannula assembly  54  comprises connection assembly  56 , cannula  58 , and gas mixing assembly  60 . Medical gas is supplied to connection assembly  56  via conduits  50  and  52 . Conduits  50  and  52  are respectively attached to first supply port  64  and second supply port  66  of the connection assembly  56 . Connection assembly  56  is connected to cannula  58  via a cannula supply port  68 .  
         [0026]      FIG. 3  illustrates a section view of the connection assembly taken along line  3 - 3  of  FIG. 2 . As illustrated in  FIG. 3 , the connection assembly  56  includes a first supply port  64  that receives the oxygen conduit  50  and the second supply port  66  that receives the gas conduit  52 . The first supply port  64  directs the supply of oxygen into the lumen chamber  80  through the passageway  88 . The lumen chamber  80  is in fluid communication with the annular supply port  68 , which receives the cannula  58 .  
         [0027]     The second supply port  66  receives the therapeutic gas and directs the gas to an internal passageway  83  that receives an extended portion of the cannula  58  in a manner to be described in great detail below.  
         [0028]     In the preferred embodiment of the invention, the connection assembly  56  is formed from PVC, which is appropriate for transmitting medical gases. However, other appropriate materials could be utilized while operating with the scope of the present invention.  
         [0029]     The multiple lumen design  90  of a first embodiment of the present invention can be seen in  FIG. 4  with a first outer lumen  70  and disposed within it a second lumen  72 .  FIG. 4   b  depicts the first lumen  70  stripped away from second lumen  72  to facilitate proper insertion of the dual-lumen cannula  90  into cannula supply port  68 . Referring back to  FIG. 3 , upon insertion of cannula into cannula supply port  68 , the extended portion  74  of second lumen  72  extends through lumen chamber  80  to conduit  78  leading from second supply port  66 . The extended portion  75  is sealed within the passageway  83 , such as with a solvent bond, to provide a gaseous connection from supply tank to second lumen  72 .  
         [0030]     As extended portion  74  extends into the passageway  83 , the leading edge  81  of the first lumen  70  is disposed within cannula supply port  68  until the leading edge  81  abuts the annular ring  82 . The first lumen  70  is sealingly connected to the cannula supply port  68  by means of an adhesive, such as a solvent bond. Annular ring  82  provides an additional seal between connection assembly  56  and cannula  58  while allowing for a gaseous connection between first lumen  70  and lumen chamber  80 . As can be understood in  FIG. 3 , the medical gas, such as oxygen, from the supply tank is supplied to the lumen chamber  80  by the first supply port  64  and the passageway  88 . The medical gas flows through the lumen chamber  80  and into the first, outer lumen  70  through the opening defined by the annular ring  82 . The second, therapeutic drug is supplied to the connection assembly  56  through the second supply port  66  and passes through the conduit  78 . The second gas enters the extended portion  74  of the second, inner lumen  72  such that the two separate supplies of gases can be delivered to the respective inner and outer lumens  70 , 72 .  
         [0031]     Referring back to  FIG. 2 , the dual lumen cannula  58  provides the gaseous connection between connection assembly  56  and gas mixing chamber  60 . As depicted in the cross-section view of  FIG. 4 , the cannula  90  may comprise a coaxial design. In the coaxial multiple lumen cannula  90 , kink resistance and structural support is provided by a plurality of ridges  92  that extend from the outer wall  93  of the first lumen  70  to the outer wall  95  of the second lumen  72 . These ridges  92  are preferably made of the same PVC material as the rest of the cannula  58 .  
         [0032]     As can be understood in  FIGS. 4   a  and  4   b , the outer lumen  70  includes a series of flow passageways  97  positioned between the series of ridges  92 . The flow passageways  97  provide an area for the gas to flow between the first lumen  70  and the second lumen  72 . The second lumen  72  includes a center passageway  99  that allows gases to flow through the second lumen  72 . In the first embodiment shown in  FIGS. 4   a  and  4   b , the flow passageways  97  and center passageway  99  are coaxial.  
         [0033]     In the dual-lumen cannula  90  depicted in  FIG. 4 , the cross-sectional area of the center passageway  99  of the second lumen  72  and the combined area of the series of flow passageways  97  contained within the outer lumen  70  are selected based upon the flow rate of the gases being delivered through each of the first and second lumens  70 , 72 . The flow area within each of the first and second lumens is proportional to the lumen resistance, which in turn is proportional to the gas flow through the lumen. In order to equalize the pressure differential between the first and second lumens, the flow area included in each of the lumens is selected to produce a very small pressure differential during typical gas flow rates. For example, if the gas flow rate through the center passageway  99  is significantly less than the flow rate through the series of flow passageways  97 , the flow area of the center passageway  99  should be small to create approximately the same back pressure as the outer lumen  70 . The selection of the flow areas allows a differential pressure sensor to be used to monitor the pressures within the first and second lumens  70 , 72 .  
         [0034]     Referring now to  FIG. 5 , the cannula  94  may alternatively comprise a double lumen cannula design in which the lumens are not coaxial. The double lumen cannula  94  comprises a first lumen  101  with an outer wall  103  and a second lumen  105  with an outer wall  107 . However, as opposed to the coaxial multiple lumen cannula discussed previously, in the double lumen cannula  94 , the first lumen  101  and the second lumen  105  share a portion of their outer walls  103  and  107 , respectively, so that the first lumen  101  and second lumen  105  are in a parallel relationship along the length of the cannula  94 . The double lumen cannula  94  of the second embodiment provides the same structural and kink resistance properties as the coaxial multiple lumen cannula  90 . The kink resistance and structural support of the double lumen  94  is supplied by a thicker outer wall of the second lumen  105 , as well as by the plurality of ridges  109  that extend from the outer wall of the first lumen  101  towards the central axis  98 , as shown in  FIG. 5   b.    
         [0035]     As discussed above, the flow areas contained within the first lumen  101  and the second lumen  105  are selected to create an equal back pressure for the preferred gas flow rates through both of the first and second lumens  101 , 105 . The matching pressures within the first and second lumens  103 , 105  allow a differential pressure sensor to be utilized to monitor the flow through the double lumen cannula  94 .  
         [0036]     The double lumen cannula  94  shown in  FIG. 5  utilizes an alternative connection assembly  100 , depicted in  FIG. 6 , rather than the connection assembly  56  for use with coaxial multiple lumen cannula  90 . Connection assembly  100  is depicted in  FIG. 6  with  FIG. 6   a  depicting the ventilator side  102  and  FIG. 6   b  depicting the patient side  104  of connection assembly  100 . Ventilator side  102  comprises a first supply port  106  for gaseous connection with conduit  50  and a second supply port  108  for gaseous connection with conduit  52 . Patient side  104  of connection assembly  100  comprises a cannula supply port  110 . However, because the double lumen cannula  94  has an asymmetrical cross section, the potential exists for misconnection of the double lumen cannula  94  to the cannula supply port  110 . Therefore, as depicted in  FIG. 5   b , the outer wall  107  of second lumen  105  comprises a morphologically different region  112  at the ventilator connection end of the double lumen cannula  94 . The morphologically different region  112  is complementary to morphologically different receptor  116  formed in the connection assembly  100 . The complementary nature of morphologically distinctive receptor  116  thus insures that the ventilator end of double lumen cannula  94  may only be connected to connection assembly  100  in a single, proper orientation.  
         [0037]     Referring now to  FIGS. 2 and 7 , the cannula  58 , which in  FIG. 7  is depicted as coaxial multiple lumen cannula  90 , is inserted into ventilator end  118  of gas mixing assembly  60 . The cannula  90  is inserted until its outer end  119  abuts annular ring  122 , which separates the ventilator end  118  from the patient end  120  of the gas mixing assembly  60 . Patient end  120  of gas mixing assembly  60  includes a mixing chamber  124  for the mixing of the medical gasses separately supplied by first lumen  70  and the second lumen  72 . The mixing assembly  60  allows the gasses to remain separate until a location proximate to the patient wherein a homogenous mixture of the medical gasses may be formed just prior to delivery to the patient via a patient connection means  62 . In  FIG. 7 , the connecting means  62  is shown as a nasal cannula; however it is understood that alternative suitable patient connection means may also be used.  
         [0038]     In a further aspect of the invention, a patient trigger sensor  126  may be disposed within mixing chamber  124  so that in the absence of gas flow through either of the nasal cannula lumens, a patient trigger may be detected. This provides a location proximate to the patient for the detection of a patient breath attempt, is used to trigger the delivery of a breath of medical gas from the ventilator, which would then be supplemented with a pulse of medical gas from supply tanks  14  and/or  16 . The detection of this patient trigger would be sent along connection  128  to CPU  20  to facilitate the control over the ventilator system  10 . Alternatively, the patient trigger sensor  126  may be disposed within one or both of the nasal cannulas  130 . In the absence of gas flow through one of the nasal cannula channels, that particular lumen is used to measure the pressure in the mixing chamber or end of the cannula. The pressure at the base of the alternate gas tube is measuring the pressure at the point of the t-connector. In a further aspect of the present invention, the patient trigger sensor  126  may be replaced by an additional function by differential pressure transducer  38  wherein the differential pressure detected by differential pressure transducer  38  is used to detect the patient breathing attempt trigger when there is an absence of gas flow through either of the nasal cannula lumens  70  and  74  respectively.  
         [0039]     In another aspect of the present invention, the differential pressure transducer  38  may provide data for the monitoring of the connection and/or gas flow within the cannula  56  of the present invention. As depicted in  FIGS. 8   a - d,  deviations from a normal or expected gas flow or pressure profile would be indicative of inadequate flow, cannula disconnection, or cannula kinking.  FIG. 8   a  depicts the normal, expected differential pressure profile within the gas mixing chamber  60  of the cannula assembly  54 . The gasses are delivered through first and second lumens at their different patterns, therefore the differential pressure profile exhibits five regions a-d in a differential pressure detection cycle. Regions a and e are representative of when there is no gas flow being supplied from supply tanks  14  or  16 . Region b is representative of the period when a proper gas flow is being supplied by supply tank  14  to the patient. This gas supply continues throughout region c as well, but in region c proper gas supply from supply tank  16  is also provided thereby producing the shift in differential pressure within the gas mixing chamber  60 . In region d, the pulse of medical gas supplied from supply tank  14  has ceased and as such the only medical gas supply is that supplied from supply tank  16  as the differential pressure indicates. Finally in region e both pulses of medical gas from the supply tanks  14  and  16  have ceased and no differential pressure in the gas mixing chamber  60  is sensed by differential pressure transducer  38 .  
         [0040]      FIG. 8   b  depicts the differential pressure profile that would be indicative of an alarm condition and/or system failure because of inadequate gas flow through one or both of the lumens. When the pulse of medical gas in the first lumen begins to flow in region b, the signal from the differential pressure transducer is only half the amplitude of that same portion of the cycle in  FIG. 8   a . Because the resistance within the cannula is assumed to be linear, it can be expected that only half the requested flow has been achieved. This indication is visible throughout the entire pulse of the first medical gas by the reduced differential pressure signal detected in regions b and c.  
         [0041]      FIG. 8   c  depicts the differential pressure profile of the alarm condition of a disconnected nasal cannula. In  FIG. 8   c  the same sequence of gas pulsing through the nasal cannula is present that was seen in  FIGS. 8   a  and  b;  however, because of the near absence of back pressure when one or both of the nasal cannulas are disconnected, there is very little change in the signal during the gas pulsing. Therefore a differential pressure profile such as shown in  FIG. 8   c  is indicative of a disconnected nasal cannula.  
         [0042]     Finally in  FIG. 8   d  another differential pressure profile indicative of the alarm condition of a kinked nasal cannula is shown. Once again, the differential pressure profile has the same sequence of gas pulses that are seen in the normal operation differential pressure profile; however, in the event of a kinked nasal cannula, the result will be a spike in the signal from the differential pressure transducer. The spike in the signal in region b is indicative of a kink in the first lumen and the spike in the signal in region d is indicative of a kink in the second lumen. Therefore,  FIG. 8   d  depicts a complete kink of both the first and second lumens of the cannula of the present invention.  
         [0043]     The differential pressure profile detected by the differential pressure transducer  38  thus provides a means for detecting a patient breath attempt thus triggering the delivery of a ventilator breath and pulses of supplemental medical gasses. The differential pressure transducer  38  also provides the additional functionality of monitoring the gas flow in the lumens of the multiple lumen cannula of the present invention as well as monitoring the quality of the patient connection to the cannula of the present invention.