Patent Publication Number: US-2011073115-A1

Title: Tracheal cuff for providing seal with reduced pressure on the tracheal walls

Description:
BACKGROUND 
     The present disclosure relates generally to medical devices and, more particularly, to airway devices, such as tracheal tubes. 
     This section is intended to introduce the reader to aspects of the art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art. 
     In the course of treating a patient, a tube or other medical device may be used to control the flow of air, food, fluids, or other substances into the patient. For example, tracheal tubes may be used to control the flow of air or other gases through a patient&#39;s trachea. Such tracheal tubes may include endotracheal (ET) tubes, tracheotomy tubes, or transtracheal tubes. In many instances, it is desirable to provide a seal between the outside of the tube or device and the interior of the passage in which the tube or device is inserted. In this way, substances can only flow through the passage via the tube or other medical device, allowing a medical practitioner to maintain control over the type and amount of substances flowing into and out of the patient. 
     As many patients are intubated for several days, healthcare workers may need to balance achieving a high-quality tracheal seal with possible patient discomfort. For example, if improperly overinflated, the pressure and/or frictional force of certain types of inflated cuffs against the tracheal walls may result in some tracheal tissue damage. While a cuff may be inflated at lower pressure to avoid such damage, this may lower the quality of the cuff&#39;s seal against the trachea. Low cuff inflation pressures may also be associated with allowing folds to form in the walls of the cuff that may serve as leak paths for air as well as microbe-laden secretions. 
     Additionally, the quality of a cuff&#39;s seal against the tracheal passageway may suffer over the duration of a patient&#39;s intubation time. For example, a seal may be compromised when a patient coughs, which may dislodge the cuff from a sealed position. Further, when the endotracheal tube is jostled during patient transport or medical procedures, the force of the movement may shift the position of the inflatable cuff within the trachea, allowing gaps to form between the cuff and the tracheal walls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the disclosure may become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a partial cutaway view of an exemplary tracheal tube and cuff assembly inserted into a patient&#39;s trachea according to certain embodiments; 
         FIG. 2  is a perspective view of a tracheal tube with a cuff assembly in an expanded configuration; 
         FIG. 3  is a perspective view of a tracheal tube with a cuff assembly in a retracted configuration according to certain presently contemplated embodiments; 
         FIG. 4  is a perspective view of a tracheal tube with a cuff assembly with a half-barrel configuration; 
         FIG. 5  is a perspective view of a tracheal tube with a cuff assembly with an inflatable portion; 
         FIG. 6  is a perspective view of a tracheal tube with a cuff assembly with an interrupted barrel configuration; 
         FIG. 7  is a perspective view of a tracheal tube with a cuff assembly with an hourglass configuration; and 
         FIG. 8  is a perspective view of a tracheal tube with a cuff assembly and a traditional balloon cuff. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     A tracheal tube may be used to seal a patient&#39;s airway and provide positive pressure to the lungs when properly inserted into a patient&#39;s trachea. A high quality seal of a cuff against the tracheal walls may assist in isolating the lower airway and anchoring the tube in place. However, a conforming seal is often difficult to obtain over long-term intubation. Although physicians may attempt to determine the quality of a cuff seal by monitoring inflation pressure, the intracuff pressure may not provide an accurate picture of whether a cuff is overinflated (i.e., whether the cuff may have the potential to cause tracheal tissue damage). Because the intracuff pressure of tracheal cuffs may be influenced by the surrounding airway pressure, the pressure in the cuff may vary over the course of a breath cycle, increasing during inspiration and decreasing during exhalation. Such variability in the cuff pressure may lead to temporary and cyclical overinflation and underinflation in the cuff. Because the pressure is variable, monitoring the pressure at different points in the breath cycle may lead to different pressure measurements. Accordingly, determining whether a cuff is appropriately inflated may be complex. 
     Provided herein are anchoring cuffs for tracheal tubes that do not rely, or rely less on cuff inflation to achieve anchoring and/or sealing of the airway, particularly after initial placement. Such cuff assemblies may be used instead of or in addition to traditional inflatable balloon cuffs. In some exemplary embodiments, a cuff may be mechanically expanded rather than inflated with a gas or a liquid. For example, a mechanically expanded cuff may form a cone or umbrella-shaped structure when expanded within the trachea. The umbrella structure may form a seal with the tracheal walls with less surface area of contact on the tissue, which may in turn reduce the possibility of tracheal damage associated with improper inflation or positioning of the cuff. Further, because an umbrella cuff structure may rely on mechanical contact rather than inflation pressure to form a seal, the seal may be achieved at substantially lower pressures relative to a traditional cuff. In certain disclosed embodiments, such as those that incorporate a traditional balloon cuff, intracuff pressure of the inflated balloon may be used initially to place and seal the cuff, and may also be relied upon at times thereafter to ensure proper operation, but reliance on intracuff pressure alone is reduced or eliminated by the alternative structures disclosed below. Because the disclosed structures are associated with generally lower sealing pressures, they may improve overall safety for the patient. 
     The disclosed tracheal tubes, systems, and methods may be used in conjunction with any appropriate medical device, including without limitation a feeding tube, an endotracheal tube, a tracheotomy tube, a circuit, an airway accessory, a connector, an adapter, a filter, a humidifier, a nebulizer, nasal cannula, or a supraglottic mask/tube. The tracheal cuffs of the present techniques may be incorporated into systems that facilitate mechanical ventilation of a patient, such as a ventilator. Such systems may typically include connective tubing, a gas source, a monitor, and/or a controller. The controller may be a digital controller, a computer, an electromechanical programmable controller, or any other control system. Further, the devices and techniques provided herein may be used to intubate a trauma victim, an intubated patient, a patient with a tracheotomy, an anesthetized patient, a cardiac arrest victim, a patient suffering from airway obstruction, or a patient suffering from respiratory failure. 
       FIG. 1  shows an exemplary tracheal tube system  10  that has been inserted into the trachea of a patient. The system  10  includes a tracheal tube  12 , shown here as an endotracheal tube, with a cuff assembly  14  that, as shown, may be mechanically expanded to form a seal against the tracheal walls  20 . By relying on mechanical expansion rather than the pressure of a fluid held by an inflated balloon, the pressure exerted on the tracheal walls  20  may be reduced. Typically, balloon cuffs associated with tracheal tubes are inflated within a patient&#39;s trachea such that the intracuff pressure is approximately 20-30 cm H 2 O. In certain embodiments, cuff assemblies  14  as provided herein may perform adequate tracheal sealing at low pressures. An exemplary cuff assembly  14  may be expanded so that the cuff assembly  14  lightly touches the tracheal walls  28  to initiate and maintain the seal. It is envisioned that a cuff assembly  14  may effectively seal a patient&#39;s trachea at exerted pressures of less than 20 cm H 2 O, less than 10 cm H 2 O or less than 5 cm H 2 O. 
       FIG. 2  is a perspective view of the tracheal tube  12  with the cuff assembly  14  in an expanded position, which may correspond to a position for forming a seal with the tracheal walls  20 . As shown, the cuff assembly  14  may form an umbrella-shaped structure with one end  24  that is adhered to or otherwise attached to the tracheal tube  12 . The other end  26  may be opened, such that the cuff assembly serves to seal the space distal to the cuff assembly  14  from the space proximal to the cuff assembly  14 , but does so without being inflated or having a balloon structure. It is envisioned that the cuff assembly  14  may be attached to the tracheal tube  12  in either a convex shape relative to the proximal end  28 , as shown in  FIG. 2 , or a concave shape relative to the proximal end  28 . The cuff assembly  14  expands radially outward from the axis of the tube  12 . 
     The tracheal tube  12  may include a mechanism for expanding and retracting the cuff assembly  14 . In one embodiment, the cuff assembly  14  may include a channel  30  or opening in the material  40  of the cuff assembly  14  that may accommodate a string, wire, fiber, flexible rod, or similar structure  32 . For example, the channel  30  may be formed by a hem (e.g. folding over and attaching an end) of the cuff assembly material  40 . Alternatively, the channel may be a separate structure appropriately attached to a surface (e.g., interior or exterior) of the cuff assembly  14 . The string  32  may at least partially encircle a circumference of the open end  26  of the cuff assembly  14 , such that when the string  32  is pulled, the cuff assembly  14  retracts in a manner similar to a drawstring pouch, but when the string  32  is relaxed, the cuff assembly  14  assumes the expanded position. This expansion as a result of the relaxation of the string  32  may be a result of natural shape memory or rigidity of the material  40  and/or supporting ribs  38 . Accordingly, relaxing the string  32  may allow these structures to return to a relaxed position while tightening the string  32  may apply a constricting force on the structures that prevents them from expanding. The string  32  may be threaded through a lumen  34  formed in the walls of the tube  12  that extends outward from the tube  12  so that a pull  36  or tab on the end of string  32  is accessible to an operator when the tube  12  is fully inserted into a patient. 
     The cuff assembly material  40  may be formed from any material that is may exert sufficient pressure to form a seal against the tracheal walls  20  when in the expanded state, but may also exert low pressures on the tracheal wall  20  (e.g., less than 20-30 cm H 2 O) when expanded to form the seal. For example, the cuff assembly material  40  may be a flexible polymer such as polyethylene. In one embodiment, the cuff assembly material  40  may be formed from a shape-shifting polymer or a shape memory material that is configured to change shape upon exposure to a certain temperature, chemical stimulus, or a magnetic field, such as those described in U.S. Pat. Nos. 6,388,043 and 6,720,402, the specifications of which are incorporated by reference in its entirety for all purposes. In one embodiment, the cuff assembly material  40  may be formed from shape-memory alloys, such as NiTi, CuZnAl, and CuAINi alloys. 
     In another embodiment, the cuff assembly material  40  may be soft and conformable, such as Dow Pellethane® 2363-80A or polyvinyl chloride (PVC). The stiffness of the cuff assembly  14  to form the seal may be provided by support ribs  38  that are formed into, embedded, overmolded by, or otherwise disposed on the cuff assembly material  40  or connecting/between separate panels of cuff assembly material  40 . The support ribs  38  may be formed by any suitably stiff material as provided. In embodiments in which the cuff assembly material  40  and/or the support ribs  38  are formed from a material having shape memory, it is envisioned that the shape memory of the cuff assembly  14  may be in the expanded state, such that the default state of the cuff assembly  14  is expanded and force may be exerted to restrain the cuff assembly  14  in the retracted state (such as for intubation and extubation of the patient). 
     The cuff assembly  14  may also include a mucoadhesive layer that may include a variety of mucoadhesive compositions and/or agents to further seal the cuff assembly  14  to the mucosal tissue of the tracheal walls  20 . Suitable mucoadhesives include, but are not limited to hydroxypropyl cellulose, hydroxypropyl methylcellulose, hydroxyethylcellulose, ethylcellulose, carboxymethylcellulose, dextran, cyclodextrins, polysaccharide gums (e.g. guar gum, xanthan gum), polyvinyl pyrrolidone, pectins, starches, collagen, gelatin, alginic acid, hyaluronic acid, fibronectin, casein, acrylic acid polymers, polymers of acrylic acid esters, poly(acrylamide), vinyl polymers, vinyl copolymers, polymers of vinyl alcohols, alkoxy polymers, polyethylene oxide polymers, poly(propylene oxide), poly(propylene glycol), poly(ethylene glycol), poly(methacrylic acid), polyethers, and any combination of the above. Such combinations may include homopolymers and copolymers of the polymers provided as well as mixtures and semi-interpenetrating and interpenetrating networks that include the polymers. In specific embodiments, the mucoadhesive may be a biocompatible polymer, for example polyacrylic acid, that is cross-linked with an acceptable agent to create an insoluble gel. The use of an insoluble gel may provide the advantage of adherence to the mucosal tissue for relatively long periods of time. For patients that experience longer intubation times, mucoadhesives such as cross-linked polyacrylic acid polymers, such as polycarbophils (e.g., Noveon and Carbomer), may be appropriate for use for three to five days or longer. Polycarbophil-based polymers are weak acids and contain many negatively-charged carboxyl-groups. The multiple negative charges on these polymers promote hydrogen-bonding between the polymers and the negatively-charged mucin glycoproteins that mediate attachment of mucus to the epithelial lining. The mucoadhesive may also include chitosan, a deacetylated derivative of chitin, which is a natural biopolymer. A mucoadhesive polymer may also include acrylic acid polymers (e.g. Carbopol® 940, also known as Carbomer® 940, Carbopol 934P and Carbopol® 980, products of BF Goodrich), methyl vinyl/maleic acid copolymers (e.g. Gantrez® S-97, a product of International Specialty Products), polyvinyl pyrrolidone also known as povidone (e.g. Plasdone® K-90, a product of International Specialty Products). These polymers impart relatively high viscosity at relatively low concentrations. They may therefore be incorporated onto the cuff assembly  14  in amounts ranging from about 0.01% to about 10% by weight relative to the total composition. These viscosity-modifying agents further act to improve the film adhesion of the composition to mucous membranes. 
     Carbopol® 980, in certain embodiments, may be 2-3% by weight of the total composition. 
       FIG. 3  is a perspective view of the cuff assembly  14  in the retracted position. Retraction may occur by a mechanical process, such as a tightening of a string  32  (or similar structure). For example, if the string  32  is threaded through the channel  30 , drawing two ends of the string  32  tight may provide enough restraining force to collapse the material  40  or support ribs  38  in the manner of a drawstring pouch. In an alternative embodiment, the cuff assembly  14  may include a collapsible ring or other structure attached to the material  40  or each of the support ribs  38 , for example on the surface opposing the tissue-contacting surface of the cuff assembly  14 . The collapsible ring may be coupled to the string  32  such that when the string  32  is tightened, the ring collapses and the force of the ring collapse overcomes the natural rigidity of the material  40  or support ribs  38  and causes the cuff assembly  14  to retract. In another embodiment, a series of strings  32  may be coupled to each support rib  38 . The plurality of strings  32  may be attached to pull  36 . When pull  36  is actuated to tighten the strings  32 , each individual string may pull on its respective support rib  38 . 
     As noted, the material  40  or support ribs  38  may be formed from a material with shape memory. The shape memory may be temperature-sensitive. Accordingly, retraction may take place by exposing the cuff assembly  14  to an appropriate temperature change (e.g., a blast of cold air). Alternatively, a change to a retracted configuration of the shape memory material may be triggered by exposure to a magnetic field or a chemical stimulus. While the retraction may take place through mechanical or other active techniques, it is envisioned that the expandable ribs  38  or material  40  may be formed so that a physician may physically break the seal of the expanded cuff assembly  14  with sufficient force. For example, for a cuff assembly  14  that is convex with respect to the proximal end  28  of the tube  12 , just the force of pulling the tube out may cause the cuff assembly  14  to retract sufficiently to allow the seal to break. For a cuff assembly  14  in the opposite orientation, the cuff assembly material  40  may be selected so that the force of a physician actively pulling the tube  12  out of the trachea may break the ribs  38 , which may then result in retraction of the cuff assembly  14 . In such an embodiment the ribs  38  may be embedded or overmolded within the material  40  so that even upon breaking, no pieces of the ribs  38  would break off of the cuff assembly  14 . 
     The slope and general shape of the concave or convex cuff assembly  14  may influence the amount of mechanical pressure exerted on the tracheal walls. For example, in addition to more umbrella-shaped structures, the cuff assembly  14  may form a generally half-barrel configuration, shown in  FIG. 4 , in which the support ribs  38  curve outward but at the point of contact with the tracheal walls  20 , are generally straight and elongated. Such a configuration may exert greater total pressure on the tracheal walls relative to an umbrella configuration, but may also serve to dissipate the pressure along a larger surface area, which would lead to lower exerted pressure at any individual point on the tracheal walls  20 . In addition, because the seal may be formed with more total surface area of the cuff assembly  14 , shown as sealing region  42 , certain configurations may provide sealing advantages. Further, cuff assemblies  14  as provided may be configured to have fully expanded diameters that are greater than the average diameter of a patient&#39;s trachea (e.g., about 1.5× greater). In such embodiments, the cuff assembly  14  may not be able to fully expand within the trachea, which may provide the ongoing pressure to form the seal as the cuff assembly pushes on the tracheal walls  20 . In addition, for cuff assemblies  14  that are in the convex orientation with respect to the proximal end  28  of the tube  12  (e.g., with the open end  26  facing a distal end  27  of the tube  12 ), the pressure of the cuff assembly  14  may change with the airway pressure changes. For example, the pressure increase in the lower airway during inspiration may cause the cuff assembly  14  to exert greater pressure on the walls of the trachea by pushing on the structure from the underside of the cuff assembly  14 . In contrast, for a cuff assembly  14  in the opposite orientation (e.g., with an open end  26  facing a proximal end  28  of the tube  12 ), increased pressure during inspiration may be met with resistance from the overall stiffness of the cuff assembly  14 . In such an orientation, the pressure on the tracheal walls  20  may remain substantially the same or may slightly decrease with increased pressure in the lower airway space. 
     While the previously disclosed embodiments exert mechanical pressure rather than inflation pressure (e.g., they do not include components that are inflatable or that trap air in a fully enclosed structure), in an alternative embodiment, the cuff assembly  14  may include inflatable components that, when inflated, form the umbrella-shaped cuff assembly  14 .  FIG. 5  is a perspective view of an alternative cuff assembly  14  that may be inflated to form a convex or concave structure. In contrast to inflatable balloon cuffs, the cuff assembly  14  as depicted maintains an open end  26 . The inflatable portion of the cuff assembly  14  merely provides stiffness to the cuff assembly material  40 . Having inflatable components may allow ease of expansion and retraction, as the cuff assembly  14  may be inflated (e.g., filled with any suitable fluid, such as air, liquid, or an inflatable foam) or deflated by lumen  46  terminating in opening  48  in fluid communication with the inflatable portion of cuff assembly  14 , which may be either located on a portion of the tube  12  between sheets of the cuff assembly material  40 , or may extend into the inflatable space of the cuff assembly  14 . The lumen  46  may extend outside of the tube  12  so that an end is accessible to an operator for inflating or deflating the cuff assembly. In an alternative embodiment, a cuff assembly  14  may include inflatable support ribs  38  to provide stiffness to form the seal. In such an embodiment, the ribs  38  may be inflated via one or more inflation lumens  46 . While the depicted assembly  14  may rely at least in part on inflation pressure to form a seal, the pressure against the tracheal walls may be reduced due to the shape of the structure and the reduced volume of trapped fluid inside the cuff assembly as compared to the total surface area. 
     In certain embodiments, a cuff assembly may include both concave and convex structures.  FIG. 6  depicts a cuff assembly  14  that includes a convex cuff assembly  14   a  and a concave cuff assembly  14   b  relative to the proximal end  28 . Such a dual-coned configuration may result in greater surface area of the cuff assembly  14  in contact with the tracheal walls  20 . Indeed, such an assembly, by forming an interrupted barrel shape that is similar to the shape of an inflated balloon cuff, may simulate the sealing surface area of a traditional balloon cuff, but with lower pressures associated with mechanical pressure rather than inflation pressure. The individual cuff assembly structures  14   a  and  14   b  may be expanded and retracted by any suitable method. As shown, each cuff assembly  14  may include a separate drawstring  32  threaded through one or more lumens  34  that may be drawn within channel  30  by tightening the string with pull  36 . The cuff assembly structure  14   b  forms a bowl that may trap secretions. Such an arrangement may obstruct the flow of secretions into the lungs, where they may cause clinical complications. The cuff assembly  14  may include a suction lumen that terminates in an opening within the bowl that may allow clinicians to suction any accumulated secretions. 
     Instead of the depicted interrupted barrel arrangement, in an alternative configuration, the cuff assembly  14  may form an hourglass configuration, as shown in  FIG. 7 . In such a configuration, an open end of cone  14   b  may face the trapped airway space (represented by arrows  54 ) of the distal end  27  of the tube  12 . In such an arrangement, the attached ends  24   a  and  24   b  may be attached at the same location on the tube  12 . The tube  12  may also include a suction lumen  50  that terminates in opening  52  for suctioning any accumulated secretions from the bowl formed by structure  14   a.    
     The cuff assemblies  14  may also provide certain benefits when used in conjunction with a traditional inflatable cuff. As shown in  FIG. 8 , a concave cuff assembly  14  relative to the proximal end  28  may be located proximally to a traditional balloon cuff  60  that is inflated via inflation lumen  62  that terminates in opening  64 . The cuff assembly  14  forms a bowl that may trap secretions before they encounter any leak paths present on balloon  60 . Suction lumen  50  that terminates in opening  52  within the bowl may allow clinicians to suction any accumulated secretions. 
     While the disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the embodiments provided herein are not intended to be limited to the particular forms disclosed. Rather, the various embodiments may cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the following appended claims.