Abstract:
There is provided herein, a bite block ( 100 ) comprising an insertion channel ( 134 ) and an airway channel ( 132 ) wherein the airway channel is adapted to receive exhaled breath and wherein the first insert channel is adapted to pass a medical instrument. There is provided herein, a bite block comprising an oral insert channel, wherein a portion of said channel opens into a cavity ( 142 ) adapted to slidably receive an oral prong ( 270 ) the oral insert channel is adapted to receive exhaled breath.

Description:
FIELD 
       [0001]    The invention relates to medical appliances. 
       BACKGROUND 
       [0002]    Numerous medical procedures require the insertion of an instrument, such as an endoscope, down a person&#39;s mouth and into the body. Such is the case when performing, for example, an Esophagogastroduodenoscopy (EGD), a procedure comprising the insertion of a flexible endoscope through the mouth until reaching the duodenum (first and shortest part of the small intestine). The endoscope when inserted is used to provide a visual inspection of the organs, and optionally to perform medical procedures such as, for example, biopsies, incisions, and retrieval of foreign objects. 
         [0003]    Endoscopic procedures are usually performed while a patient is under topical or moderate sedation, although in some circumstances it may be performed while the patient is under general anesthesia. During moderate sedation or general anesthesia the patient is generally sedated intravenously to minimize gagging and to facilitate the procedure. A bite block is used to prevent the patient from biting on the endoscope, to facilitate the introduction of the endoscope into the mouth, and to maneuver the endoscope relatively freely while inserted in the mouth. 
         [0004]    A frequent occurrence when administering intravenous sedation is reduced breathing in the patient, which may lead to hypoxia, or a reduction of oxygen in the blood. It is then substantially common practice to administer oxygen or another breathable gas to the patient, usually through a nasal cannula, while the patient is sedated. Additionally, the patient&#39;s exhaled breath is typically monitored, by means of a capnograph, in order to corroborate that the patient&#39;s carbon dioxide levels in the blood and the tissues are within safe limits. 
         [0005]    A number of bite blocks have been adapted with features to supply oxygen, or optionally some other type of breathable gas, to a sedated patient. Some have been further adapted with features which allow the patient to be connected to a capnograph for measuring the carbon dioxide contents in the patient&#39;s exhaled breath. The following patents and/or publications describe different types of bite blocks adapted with some of these features, all of which are incorporated herein by reference. 
         [0006]    U.S. Pat. No. 5,273,032 “Oxygenating Oral Medical Appliance”, describes an “endoscopic mouth guard having a smoothly contoured, waisted tube merging into a peripheral flange at the front end of said tube, a manifold integral with the front face of said flange defining a closed ended, transverse distribution duct, and two open ended, upwardly directed branch ducts ending, in use, closely below the nostrils of a patient fitted with the guard, two further, open ended branch ducts extending rearwardly from said distributor duct into the bore of said tube, and a laterally and rearwardly directed tapered spigot on said manifold, defining an extension of said distributor duct, adapted to enter the bore of a gas supply tube. The finished guard is a single article of plastics material having a smooth hard surface.” 
         [0007]    U.S. Pat. No. 5,513,634 “Combination Integral Bite Block Airway and Nasal Cannula”, describes a “combination plastic relatively rigid bite block and soft nasal cannula intended for one-time use for supplying oxygen to a patient&#39;s nostrils during an endoscopic procedure. The cannula is fixed into the bite block by an integral clip portion of the cannula extending downwardly from a manifold portion and adhered to the bite block. Flexible nasal prongs extend upwardly from the manifold into the patient&#39;s nostrils to supply supplementary gas separately from air breathed through the patient&#39;s mouth.” 
         [0008]    US Patent Application Publication No. US 2007/0006878 A1 “Capnographic-oxygenating Oro-fiberscopic Bite block”, describes an oro-fiberscopic bite block. “The bite block is utilized during oral fiberscopic procedures. The bite block includes a main structure having an orifice sized to accommodate entry of a fiberscope, such as an endoscope, through the orifice. The bite block includes an extension extending inward from the main structure when positioned within the mouth of a patient. On each side of the orifice is a loop for handling and positioning the bite block within the patient&#39;s mouth. The bite block includes an exhalation tube running from the extension to a monitoring device which allows monitoring of the patient&#39;s expelled gases. In addition, an inhalation tube may be used to provide supplemental oxygen to the patient. The bite block is positioned in the mouth of the patient with the mouth of the patient surrounding the extension. The tubes include openings which are located on the extension and lie in the interior of the mouth to provide monitoring of uncontaminated gasses expelled by the patient.” 
         [0009]    PCT International Application Publication No. WO 2007/063532 “Endoscopic Bite Block”, describes a “bite block assembly adapted for capnography and oxygen delivery to a subject, the bite block assembly including a first capnography passageway adapted for passage therethrough of exhaled breath from the subject to a capnograph and a second oxygen delivery passageway, separate from the first passageway, adapted for passage therethrough of oxygen from an oxygen source to the mouth of the subject.” 
         [0010]    There is still a need in the art for improved bite blocks, systems including them and methods that would allow efficient breath sampling during medical procedures such as endoscopy. 
       SUMMARY 
       [0011]    An aspect of some embodiments of the invention relates to a device, such as a bite block device, a system, such as a bite block and an oral nasal breath sampling cannula, and method for sampling breath, for example for the purpose of capnographic measurements, while performing a medical procedure such as insertion of an endoscope. In addition, the device may also include oxygen delivery element(s). 
         [0012]    Since experience has shown that patients have a tendency to breath through their mouth during a procedure such as endoscopy, according to some embodiments, the device, system and method provide oxygen delivery and oxygen flow regulation means that facilitate the direction of the oxygen flow to the mouth and/or to the nose as needed and/or when needed. For example, when the bite block is in place the system is adapted to provide more oxygen to the mouth or even, only to the mouth. However, when the bite block is not in a patient&#39;s mouth the system is adapted to provide more oxygen to the nose or even, only to the nose. In addition, in many of the existing bite blocks adapted to deliver oxygen and allow capnographic measurements, problems have been encountered associated with the oxygen being delivered at a relatively higher pressure than that at which the exhaled breath is expelled by the patient. The higher pressure, at which the oxygen is delivered orally and/or nasally, occasionally forces the exhaled breath away from an entrance to exhaled breath collection means or allows oxygen into the sampling tubes. For example, when a patient is lightly breathing through the nose or not breathing through the nose at all, during endoscopy or due to any other reason, the collection of the exhaled breath may be diluted with the supplied oxygen, which affects the accuracy of the capnographic measurements. Another example may be during medical procedures known as MAC, monitoring anesthesia care, where U.E. procedures are performed using high levels of oxygen, typically in excess of 5 l/min. According to some embodiments, the device, system and method are adapted to improve breath sampling and to reduce dilution of the sampled breath with oxygen. Furthermore, the device, system and method are adapted to provide high oxygen delivery, optionally at rates up to  101 /hr. 
         [0013]    According to an aspect of some embodiments of the invention, orally delivered oxygen or optionally, any other breathable gas, delivered at a relatively high pressure, is substantially prevented from interfering with the free flow of orally exhaled breath, by separately channeling the oxygen through an oxygen channel and the exhaled breath through an airway channel, and by maintaining a substantial distance between the openings to these channels. The pressure of the oxygen at an opening of the airway channel is less than the pressure of the opposing exhaled breath and therefore, oxygen is substantially prevented from entering the airway channel and diluting the exhaled breath. Additionally, the oxygen channel may include a relatively large aperture at one end through which the oxygen flows from the oxygen channel into the back of the patient&#39;s mouth. The use of a relatively large aperture causes a pressure decrease in the flow of oxygen when exiting from the oxygen channel. Optionally, more than one oxygen channels may be used. Additionally or alternatively, the oxygen channel or channels may include several apertures. The distance between the two channel openings may be determined by the pressure at which the oxygen exits the oxygen channel in the bite block. For example, the airway channel may be designed to extend inwardly to the direction of the mouth of the patient relative to the oxygen channel. Optionally, the oxygen channel may be designed such that the oxygen flow is not directly in the direction into the back of the mouth of the patient, for example, slanted downwards. In this manner, an efficient collection of exhaled breath for capnographic measurements may be maintained while substantially high oxygen delivery is performed. In some embodiments of the invention, the oxygen channel may comprise one or more apertures in the insertion channel through which oxygen, or optionally a portion of the delivered oxygen, may flow out of the oxygen channel into the patient&#39;s mouth. 
         [0014]    In accordance with some embodiments of the invention, there is provided a bite block including an insertion channel through which a medical instrument, for example, an endoscope, may be inserted into the mouth of the patient. The bite block may further include an airway channel, which extends further into the mouth of the patient relative to the oxygen channel and to the insertion channel. In some embodiments of the invention, an opening may extend partially or entirely, along the length between the airway channel and the insertion channel. The bite block may also include an oxygen channel through which oxygen is delivered to the patient. The exhaled breath may freely flow through the airway channel towards a sampling port connected to the capnograph. The oxygen channel may be formed along a side of the insertion channel for patient comfort. Alternatively, the oxygen channel may be positioned in the bite block in any manner which permits high oxygen delivery, the distance between the airway channel and the oxygen channel preferably not less than the distance between the airway channel and the insertion channel. 
         [0015]    In some embodiments of the invention, the bite block comprises an extendable oral nasal cannula, which is substantially maintained inside the patient&#39;s nostrils generally independent of the patient&#39;s head position and of movement of the bite block. The airway channel opens into a cavity in a forward section of the bite block, external to the patient&#39;s mouth. An oral prong in the oral nasal cannula is adapted to slide in a generally lateral direction along a z-axis back and forth along the cavity, and to rotate and tilt relative to a y-axis substantially perpendicular to the direction of sliding, in order to compensate for movement of the bite block relative to the patient&#39;s mouth. Additionally, the oral prong is adapted to slidingly extend in and out of an oral prong extension in a generally vertical direction along the y-axis substantially extending the length of the oral prong. A large degree of freedom of movement in the oral prong, and thereby in the oral nasal cannula, substantially reduces the possibility that the nasal prong may slip out of the bite block due to movement of the bite block relative to the patient&#39;s mouth. As a result, substantially continuous flow of exhaled breath is maintained to the capnograph. In some embodiments of the invention, the bite block comprises an airway channel which includes an opening to which the oral prong is affixed. Exhaled breath may then flow through the opening in the airway channel into the oral prong. In some embodiments of the invention, the bite block may include an oral prong as an integral part of the bite block. The oral prong may be connected to one or more nasal prongs. The integral oral prong may open into a roof of the airway channel. 
         [0016]    In addition, according to some embodiments, the device and system may be adjustable to fit different patients. 
         [0017]    In accordance with an embodiment of the invention, there is provided a bite block comprising an insertion channel and an airway channel, wherein the airway channel is adapted to pass substantially free flow of breath, and wherein the insertion channel is adapted to pass substantially free flow of breath and to pass a medical instrument. Optionally, a portion of the airway channel opens into a cavity adapted to receive an oral prong, wherein the oral prong is adapted to sample breath from a patient. Optionally, the cavity is further adapted to allow relative motion between the bite block and the prong without substantially reducing the breath sampling. 
         [0018]    In accordance with some embodiments of the invention, the airway channel is adapted to receive an oral prong, wherein the oral prong is adapted to sample breath from a patient. 
         [0019]    In accordance with some embodiments of the invention, the airway channel is adapted to pass substantially free flow of breath through a duct. Optionally, the duct is further adapted to enable a viewer to view the position of an oral prong functionally connected to the bite block. 
         [0020]    In accordance with some embodiments of the invention, the bite block further comprises an oxygen channel located in proximity to the insertion channel, wherein the oxygen channel is adapted to direct oxygen towards the inside of the mouth of a patient. Optionally, the airway channel is adapted to protrude further into the back of the mouth relative to the insertion channel and/or the oxygen channel. Additionally or alternatively, the bite block is adapted to reduce the flow of oxygen from the oxygen channel into the airway channel, such that the oxygen pressure is adapted to be lower than the opposing pressure created by the exhaled breath, so that the exhaled breath can push back out of the mouth the oxygen, and at least partially prevent oxygen from reaching the airway channel opening and consequently diluting the sampled breath. 
         [0021]    In accordance with an embodiment of the invention, there is provided a bite block comprising an airway channel, wherein the airway channel is adapted to pass substantially free flow of breath and wherein a portion of the airway channel opens into a cavity adapted to receive an oral prong for sample breath from a patient. The cavity is further adapted to allow relative motion between the bite block and the prong without substantially reducing the breath sampling. Optionally, the bite block further comprises an insertion channel adapted to pass substantially free flow of breath, and to pass a medical instrument. 
         [0022]    In accordance with some embodiments of the invention, the airway channel is adapted to pass substantially free flow of breath through a duct. Optionally, the duct is further adapted to enable a viewer to view the position of an oral prong functionally connected to the bite block. 
         [0023]    In accordance with some embodiments of the invention, the bite block further comprises an oxygen channel located in proximity to the channel, wherein the oxygen channel is adapted to direct oxygen towards the inside of the mouth of a patient. Optionally, the airway channel is adapted to protrude further into the back of the mouth relative to the insertion channel and/or said oxygen channel. Additionally or alternatively, the bite block is adapted to reduce the flow of oxygen from the oxygen channel into the airway channel, such that the oxygen pressure is adapted to be lower than the opposing pressure created by the exhaled breath, so that the exhaled breath can push back out of the mouth the oxygen, and at least partially prevent oxygen from reaching the airway channel opening and consequently diluting the sampled breath. 
         [0024]    In accordance with an embodiment of the invention, there is provided a system for sampling breath, the system comprising: a bite block comprising an insertion channel and an airway channel, wherein the airway channel is adapted to pass substantially free flow of breath, and wherein said an insertion channel is adapted to pass substantially free flow of breath and to pass a medical instrument; and a valve adapted to regulate oxygen delivery to the oxygen channel. 
         [0025]    In accordance with some embodiments of the invention, the airway channel opens into a cavity adapted to receive an oral prong, wherein the oral prong is adapted to sample breath from a patient. Optionally, the cavity is further adapted to allow relative motion between the bite block and the prong without substantially reducing the breath sampling. 
         [0026]    In accordance with some embodiments of the invention, the airway channel is adapted to receive an oral prong, wherein the oral prong is adapted to sample breath from a patient. Optionally, the airway channel is adapted to pass substantially free flow of breath through a duct. Additionally, the duct is further adapted to enable a viewer to view the position of an oral prong functionally connected to said bite block. 
         [0027]    In accordance with some embodiments of the invention, the system further comprises an oxygen channel located in proximity to the insertion channel, wherein the oxygen channel is adapted to direct oxygen towards the inside of the mouth of a patient. Optionally, airway channel extends further into the mouth relative to the insertion channel and/or the oxygen channel. 
         [0028]    In accordance with some embodiments of the invention, there is provided a system for sampling breath, the system comprising: a bite block comprising an airway channel, wherein the airway channel is adapted to pass substantially free flow of breath and wherein a portion of the airway channel opens into a cavity adapted to receive an oral prong for sampling breath from a patient, the cavity is further adapted to allow relative motion between said bite block and said prong without substantially reducing the breath sampling; and a valve adapted to regulate oxygen delivery to said oxygen channel. Optionally, the system further comprising an insertion channel adapted pass substantially free flow of breath and to pass a medical instrument. 
         [0029]    In accordance with an embodiment of the invention, there is provided a system for sampling breath, the system comprising: a bite block comprising an insertion channel and an airway channel, wherein the airway channel is adapted to pass substantially free flow of breath and wherein the insertion channel is adapted to pass substantially free flow of breath and to pass a medical instrument; and an oral nasal cannula adapted to sample breath. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0030]    Examples illustrative of embodiments of the invention are described below with reference to figures attached hereto. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0031]      FIG. 1  schematically shows an isometric front view of an exemplary bite block adapted for capnography and oxygen delivery to a patient, in accordance with an embodiment of the invention; 
           [0032]      FIG. 2  schematically shows an isometric back view of the exemplary bite block in  FIG. 1  in accordance with an embodiment of the invention; 
           [0033]      FIG. 3  schematically shows an isometric front view of an exemplary bite block comprising an oral nasal cannula and an oxygen tube; 
           [0034]      FIG. 4  schematically shows an back view of the exemplary bite block in  FIG. 3  in accordance with an embodiment of the invention; and 
           [0035]      FIG. 5  schematically shows a cross-sectional view A-A of the exemplary bite block of  FIG. 3 , in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    Reference is made to  FIGS. 1 and 2  which schematically show an isometric front view and back view, respectively, of an exemplary bite block  100  adapted for passing a medical instrument, perform capnography and if required, deliver oxygen to a patient, in accordance with an embodiment of the invention. Bite block  100  comprises an external section  101  and an oral insert, which may be refereed to as a mouthpiece  111 . Mouthpiece  111  is adapted to be placed inside a patient&#39;s mouth, while external section  101  is configured to be fitted over the mouth and to substantially restrict movement of the mouthpiece inside the patient&#39;s mouth. External section  101  comprises a main body portion  102 , which includes an opening  104  to an insertion channel  134 . Insertion channel  134  is adapted to receive a medical instrument, for example an endoscope, which is inserted through opening  104  and extends through insertion channel  134  into a patient&#39;s mouth. Main body portion  102  comprises a first lateral section  103  which laterally extends from one side of main body portion  102  towards a first attachment  112 . On the other side of main body portion  102 , a second lateral section  105  laterally extends towards a second attachment  113 . First attachment  112  and second attachment  113  comprise openings  114  and  115 , respectively, the attachments adapted to receive a strap, or some other means of fixing the bite block to a patient&#39;s mouth, generally by attaching the strap, or other means, around the back of the head of the patient. Optionally, more than one strap or other means of attachment may be used to fix the bite block to the patient&#39;s mouth. 
         [0037]    Mouthpiece  111  comprises insertion channel  134 , an airway channel  132  and an oxygen channel  136 . Insertion channel  134  extends from opening  104  along a major portion of the length of the mouthpiece to an end opening  131 . Insertion channel  134  is formed by a surface  145  which is usually supported by the tongue when the mouthpiece is inserted in the patient&#39;s mouth, and a surface  143  which provides a biting surface for the patient&#39;s lower teeth. Surfaces  145  and  143  are contoured with rounded edges to substantially reduce any possible harm to the patient&#39;s mouth and/or tongue, and/or patient discomfort, typically associated with sharp edges. 
         [0038]    Protruding from first lateral section  103  is an oxygen tube adapter  108 , adapted to receive an oxygen tube for orally administering oxygen to the patient. Alternatively, oxygen tube adapter  108  may protrude from second lateral section  105 . Optionally, the oxygen tube adapter may protrude from first lateral section  103  and second lateral section  105 , or from other parts of bite block  100 . Oxygen channel  136  extends from oxygen tube adapter  108  laterally along a length of insertion channel  134 . Oxygen channel  136  is adapted to conduct oxygen flowing into oxygen tube adapter  108  through an opening  110 , and through aperture  137  at the other end of oxygen channel  136 , into the mouth of the patient. Optionally, oxygen channel  136  may extend the whole length of insertion channel  134 . Oxygen channel  136  is formed by a substantially curved surface  138  to reduce any possible harm to the patient&#39;s mouth and/or tongue, and/or patient discomfort, typically associated with sharp edges. In accordance with an embodiment of the invention, aperture  137  is of a relative large diameter, generally in the range of 0.5-20 mm, for example, 2 mm, 3 mm, 5 mm, 8 mm, 12 mm, 15 mm, 18 mm, adapted to create a pressure decrease in the oxygen flow when flowing out of oxygen channel  136  into the mouth of the patient. Optionally, oxygen channel  136  may include more than one aperture. Additionally or alternatively, oxygen channel  136  may comprise one or more apertures, such as aperture  137  in insertion channel  134  through which oxygen, or optionally a portion of the delivered oxygen, may flow out of the oxygen channel into the patient&#39;s mouth. 
         [0039]    In accordance with an embodiment of the invention, airway channel  132  is adapted to receive exhaled breath from the patient and to allow exhaled breath and inhaled air to flow freely back and forth along the channel. The exhaled breath free flows along airway channel  132  in the direction of a cavity  142 , included in the forward section of the airway channel. Airway channel  132  extends from cavity  142  in a direction inwardly, or deeper, into the mouth of the patient a distance d compared to insertion channel  134 . The distance d is measured in a direction along an x-axis from an opening  135  comprised in airway channel  132  to opening  131  and generally ranges from 5 mm-20 mm, for example 5 mm, 8 mm, 12 mm, 16 mm, 20 mm. In accordance with an embodiment of the invention, the pressure of the oxygen at opening  135  of airway channel  132  is less than the pressure of the opposing exhaled breath and therefore, oxygen is substantially prevented from entering airway channel  132  and diluting the exhaled breath. 
         [0040]    Airway channel  132  is formed by a substantially curved surface  140  which may slope upwards in the direction of the roof of the mouth when the mouthpiece is inserted in the patient&#39;s mouth, and substantially curved surface  141  which provides a biting surface for the patient&#39;s upper teeth. Upward sloping of surface  140  allows for a larger opening  135  in airway channel  132  much like a funnel, opening  135  adapted to capture relatively large amounts of exhaled breath. The funnel design of airway channel  132 , provided by sloping surface  140 , provides for substantial free flow of breath in the airway channel. Surfaces  140  and  141  are contoured with rounded edges to substantially reduce any possible harm to the patient&#39;s mouth and/or to reduce patient discomfort, typically associated with sharp edges. In some embodiments of the invention, an opening may extend, partially or entirely, along the length between airway channel  132  and insertion channel  134 . 
         [0041]    In accordance with an embodiment of the invention the dimensions of cavity  142  are such that they allow an oral nasal cannula (not shown) to move, relative to bite block  100 , linearly inside the cavity along the x-axis and/or y-axis and and/or z-axis, and/or angularly about the x and/or y and/or z axis, Relative motion of the oral nasal cannula substantially compensates for movement of bite block  100  relative to a patient&#39;s mouth, allowing oral nasal cannula to remain inserted in cavity  142  generally at all times. Cavity  142  is formed from a substantially vertical inner surface  144  of a section of main portion  102 , a section of first lateral section  103 , and a section of second lateral section  105 . A border  146  perpendicularly extends from surface  141  at the border of the airway channel  132  with cavity  142 , and generally serves to demarcate the border between the mouthpiece and the external section. A cavity floor  148  comprises a surface adapted to support the oral nasal cannula when fitted into the cavity. Cavity  142  further comprises a duct  106  in inner surface  144  adapted to allow exhaled breath and inhaled air to flow freely in and out of airway channel  132 . Duct  106  may also be used by a viewer to view the position of the oral nasal cannula inside the cavity. 
         [0042]    Reference is made to  FIG. 3  which schematically shows an isometric front view of an exemplary bite block comprising an oral nasal cannula and an oxygen tube, to  FIG. 4  which schematically shows a back view of the exemplary bite block in  FIG. 3 , and to  FIG. 5  which schematically shows a cross-sectional view A-A of the exemplary bite block of  FIG. 3  and  FIG. 4 , in accordance with an embodiment of the invention. 
         [0043]    Bite block  200  is the same or substantially similar to bite block  100  shown in  FIGS. 1 and 2 , additionally comprising an oral nasal cannula  260  positioned inside cavity  242  and an oxygen tube  290 , including a valve  291 , attached to the bite block at an oxygen tube adapter  208 . Bite block  200  comprises an external section  201 , a mouthpiece  211 , a main body portion  202 , an opening  204 , an insertion channel  234 , a first lateral section  203 , a first attachment  212 , a second lateral section  205 , a second attachment  213 , openings  214  and  215 , an airway channel  232 , an oxygen channel  236 , an end opening  231 , a surface  245 , a surface  243 , oxygen channel  236 , a curved surface  238 , a cavity  242 , an opening  235 , a curved surface  240 , a curved surface  241 , a vertical inner surface  244 , a border  246 , a cavity floor  248 , and a duct  206 , all the same or substantially similar to that shown in  FIGS. 1  and/or  2  at  101 ,  111 ,  102 ,  104 ,  134 ,  103 ,  112 ,  105 ,  113 ,  114 ,  115 ,  132 ,  136 ,  131 ,  145 ,  143 ,  136 ,  138 ,  142 ,  135 ,  140 ,  141 ,  144 ,  146 ,  148 , and  106 . It may be appreciated from  FIG. 5  that curved surface  240  is a sloping surface extending from opening  231  to intersect curved surface  241 , such that a height h 1  of airway channel  232  is a maximum at opening  231  and decreases to a height h 2  at the intersection with surface  241 . The relatively large opening in airway channel  232  allows for better collection of orally exhaled breath from the patient. Height h 1  of airway channel  232  is generally limited by the structure of the mouth and is typically in a range of 5-25 mm, for example, 10 mm, 14 mm, 16 mm, or 20 mm. Height h 2  of airway channel  232  is generally limited by the size of the bite, and is typically in a range of 1-10 mm, for example, 2 mm, 3.5 mm, or 5 mm. Optionally, heights h 1  and h 2  may be the same. 
         [0044]    Oxygen tube  290  is connected to bite block  200  by means of a rotational nipple  274  which is inserted into oxygen tube adapter  208 . Optionally, rotational nipple  274  is a fixed nipple not adapted for rotational motion. Oxygen, or some other type of breathable gas, is delivered to the bite block through oxygen tube  290 . The gas flows through the nipple into oxygen tube adapter  208  and through oxygen channel  236  into a patient&#39;s mouth. 
         [0045]    Valve  291  is adapted to regulate oxygen flow in the direction of oxygen tube adapter  208  and oxygen channel  236 , and in the direction of oral nasal cannula  260 . Oxygen flow to oral nasal cannula  260  may be maintained, when bite block  200  is removed, through a nasal oxygen tube (not shown) extending from valve  291  to opening  268  in oral nasal cannula  260 . 
         [0046]    Oral nasal cannula  260  comprises a main body  262  from which extend two nasal prongs  264  adapted to be inserted into the patient&#39;s nostrils for exhaled breath collection. The exhaled breath from the patient&#39;s nostrils flows through the nasal prongs into a breath conduit  276 . Breath conduit  276  leads through main body  262  to an exit opening  269  to which a breath sampling tube may be connected for delivering the exhaled breath to a capnograph. 
         [0047]    Main body  262  further comprises oxygen delivery holes such as, for example hole  266 , through which oxygen, or some other breathable gas, flows out of the main body into the patient&#39;s nostrils. The oxygen is delivered to the oral nasal cannula through a nasal oxygen tube which connects to opening  268  at one end of the main body. Opening  268  leads to a conduit  263  in main body  262  through which the oxygen flows to the oxygen delivery holes. Alternatively, opening  268  leads to a conduit  263 , through which oxygen may flow into prongs (not shown). 
         [0048]    An oral prong  270  comprising a hollow tube with a cut-away tip  274  is attached to the bottom side of main body  262 . In accordance with an embodiment of the invention oral prong  270  comprises a hollow oral prong extension  272  into which the oral prong may be slidingly inserted into and retracted from, substantially extending the length of the oral prong when fully retracted. Optionally, oral prong  270  and oral prong extension  272  are fixed with respect to one another. Oral prong extension  272 , comprises a hollow tube with a cut-away tip  273 , and is adapted to be inserted into cavity  242 . 
         [0049]    Oral prong  270  is usually positioned in cavity  242  in a vertical position along a y-axis, supported by an extended abutment of oral prong extension  272  with inner surface  244 , and by an abutment of cut-away tip  273  with cavity surface  248 . Oral prong  270  is generally oriented such that an opening in cut-away tip  273  faces in the direction of airway channel  232 . In accordance with an embodiment of the invention, oral prong  270  is adapted to sample the breath of a patient in airway channel  232 . Orally exhaled breath flowing through airway channel  232  may flow with ease into oral prong extension  272  through cut-away tip  273 , and into oral prong  270  through cut-away tip  274 . The orally exhaled breath flowing into oral prong  270  flows through the prong into conduit  276  in main body  262  where it may combine with exhaled breath from the patient&#39;s nostrils. The exhaled breath then flows out exit opening  269 . 
         [0050]    In accordance with an embodiment of the invention oral prong  270  is adapted to slide in a generally lateral direction, relative to bite block  200 , along a z-axis back and forth along the cavity floor  248 , and to rotate and tilt relative to the y-axis substantially perpendicular to the direction of sliding. A large degree of freedom in movement in oral prong  270 , and thereby in oral nasal cannula  260 , substantially compensates for movement of bite block  200  relative to a patient&#39;s mouth, allowing oral nasal cannula  260  to remain inserted in cavity  242  generally at all times. In some embodiments of the invention, bite block  200  comprises an airway channel  232  which includes an opening to which oral prong  270  is affixed. Exhaled breath may then flow through the opening in airway channel  232  into oral prong  270 . 
         [0051]    In the description and claims of embodiments of the present invention, each of the words, “comprise” “include” and “have”, and forms thereof, are not necessarily limited to members in a list with which the words may be associated. 
         [0052]    The invention has been described using various detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments may comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the invention that are described and embodiments of the invention comprising different combinations of features noted in the described embodiments will occur to persons with skill in the art. The scope of the invention is limited only by the claims.