Patent Publication Number: US-2019175772-A1

Title: System and method for in situ sterilization

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is claims the benefit of provisional U.S. patent application Ser. No. 62/596,495, filed. Dec. 8, 2017. The disclosure of the prior application is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The several embodiments of this disclosure relate to antimicrobial devices and methods for their sterilization. More particularly, the several embodiments teach systems and methods for sterilizing certain surfaces, and/or adjacent regions of certain surfaces, of a catheter or wound dressing in situ using coronal discharge plasma generation. 
     BACKGROUND OF THE INVENTION 
     Catheters may be useful for several medical applications, including moving, draining, or collecting bod fluids. However, use of catheters may result in complications, such as infections. Catheter-associated infections may result from bacteria being introduced into the body, for example by bacterial adhesion along the exterior (body-facing) surface of the catheter or bacteria migrating along the interior (lumen-facing) surface of the catheter. 
     Conventional medical sterilization may involve high-pressure steam, ethylene oxide gas, or peroxide gas. These methods may involve high temperatures relative to normal body temperature, use of dangerous or harmful gases ethylene oxide), a vacuum environment, or a prolonged degassing process that may take several days. Therefore, conventional sterilization methods may not be well suited for use in the body (in situ). 
     Because of these limitations, conventional methods of catheter sterilization may involve removing the catheter from the body, sterilizing the catheter by some means, and reinserting the catheter into the body. Alternatively, the catheter may be removed from the body and replaced with a new sterile catheter. Frequent removal and insertion of catheters into and out of the body of a patient greatly increases the risk of infection to that patient. Moreover, in some medical applications, such as pulmonary artery catheterization (PAC) wherein a catheter is situated within the pulmonary or arterial system, it may be impractical to remove the catheter for sterilization or replacement. 
     A less conventional medical sterilization method is to utilize coronal discharge plasma generation. This method, sometimes called plasma jet, may be carried out at ambient temperatures and in the atmospheric environment. Although the plasma jet technique has been applied to sterilization of exposed surfaces (surfaces of a medical device outside a patient&#39;s body), the technique has significant limitations when applied to catheters in situ, most notably a risk of harming the patient. 
     To create a plasma jet, plasma may be generated via electric ty in a narrow tube and then discharged through the open end of the tube using a flow of air through the tube. However, utilizing a catheter as the tube to generate a sterilizing plasma jet may be problematic due to the build-up of air and plasma within the body. Further, the air and plasma discharging from the in situ end of the catheter into the body may apply significant forces or force gradients within the body that may physically damage organs or tissues. Additional the air and plasma discharge itself may damage organs or tissues by plasma-induced cellular death or particulate contamination due to improperly filtered air. 
     Catheter-related infections can be a major cause of prolonged hospitalization. Further, significant antibiotic use associated with treating catheter-related infections can be a major cause of the ongoing and increased antibiotic resistance of certain infectious agents. This necessitates the development of a technology that permits a catheter to be sterilized while within a patient&#39;s body. 
     This disclosure teaches systems and methods for sterilizing a catheter or part a catheter that is inside the body, part of a catheter that is outside the body and adjacent to a part of the catheter that inside the body, or parts of a catheter assembly or un such as a sheath in a Swan-Ganz catheter, using coronal discharge plasma generation. Coronal discharge plasma act to sterilize the surface of the catheter and possibly also adjacent body surfaces or body cavities. 
     BRIEF SUMMARY OF THE INVENTION 
     The several embodiments of this disclosure relate to a catheter or catheter assembly that can be sterilized in situ via plasma generated by coronal discharge. A coronal discharge is an electrical discharge caused by the ionization of a gas or liquid adjacent o an electrically charged object. The object, called an electrode, may be any conductor (or semiconductor or insulator) capable of accepting charged particles. The terms conductor and electrode may be used interchangeably in this disclosure. Further, the charged particles may be electrons, but they may also be molecular or atomic particles or ions having positive or negative charge. 
     In one embodiment, one or more pairs of conductors may be embedded into the catheter wall one conductor being an anode and the other conductor being a cathode. In another embodiment, one or more pairs of conductors may be embedded in a sheath surrounding a catheter external and adjacent to the point of entry of the catheter into the body. In another embodiment, one or more pairs of conductors may be embedded in a bandage, gauze, or dressing external and adjacent to the point of entry of the catheter into the body, or proximal to an incision, port, wound or opening into the body. 
     A voltage potential may be applied across the anode-cathode pair. When the distance between the conductors is sufficiently small, and/or the voltage between the conductors is sufficiently high, a large electric field may be created between the conductors that may ionize the air between and adjacent to the conductors. This ionization is a coronal discharge, which may sterilize the air, catheter surfaces, and body surfaces adjacent to the plasma. The applied voltage may be AC or DC depending on, for example, the desired cycle time or intensity of coronal discharges. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings presented are for illustrative purposes only of selected embodiments and do not depict all possible embodiments or implementations thereof. The drawings are not intended to limit the scope of the present disclosure. 
         FIG. 1  is perspective view of a first embodiment. 
         FIG. 2  a cross-sectional view of the first embodiment taken along line A-A of  FIG. 1  (transverse to a longitudinal axis of the catheter). 
         FIG. 3  is a cross-sectional view of a second embodiment taken transverse to a longitudinal axis of the catheter. 
         FIG. 4  is a cross-sectional view of a third embodiment taken transverse to a longitudinal axis of the catheter. 
         FIG. 5  is a cross-sectional view of a fourth embodiment taken transverse to a longitudinal axis of the catheter. 
         FIG. 6  is a side view of a fifth embodiment (parallel to a longitudinal axis of the catheter). 
         FIG. 7  is cross-sectional view of the fifth embodiment taken along line B-B of  FIG. 5  (transverse to a longitudinal axis of the catheter). 
         FIG. 8  is cross-sectional view of the fifth embodiment taken along line C-C of  FIG. 6  (transverse to a longitudinal axis of the catheter). 
         FIGS. 9 a -9 c    are perspective views of a sixth embodiment. 
         FIG. 10  is a cross-sectional view of a seventh embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following embodiments are exemplary and the concepts associated therewith may be embodied in various and alternative forms. Some features may be exaggerated or minimized to show details of particular components. Therefore, specific functional or structural details disclosed herein are not to be interpreted as limiting in any way but merely as representative of these particular disclosed embodiments with the understanding that these may vary with respect to other exemplary embodiments. 
     The following numerals are used to identify the corresponding elements in the figures for the several embodiments.
       10  catheter     20  catheter assembly     30  bandage     100  cathode     102  anode     104  catheter lumen     106  catheter wall     108  patient tissue     110  catheter exterior surface     112  catheter interior surface     114  patient body cavity     116  insulating material     118   a,b  anode-cathode pair     120  conductive mesh     122  secondary catheter     200  balloon     300  atmospheric space     302  apex     400  contamination sheath     410   a,b  collar     420  introducer sheath     500  bandage interior     510  bandage surface   

       FIG. 1  shows a catheter  10  having a catheter wall  106  defined by an exterior surface  110  and an interior surface  112 . The catheter  10  and/or catheter lumen  104  may have any cross-sectional shape whether circular, oval, smooth, lagged, or otherwise (see  FIG. 5  for an example of a non-circular catheter  10 ). A lumen  104  is contained within the space created by a circumference of the interior surface  112 . Fluid may flow through the catheter lumen  104  or any other space external to or along the catheter exterior surface  110 . This fluid may be bodily fluid that naturally flows through the patient body cavity  114  or any other type of fluid injected into the patient body cavity  114  such as saline. 
     A cathode  100  and/or an anode  102  may be embedded on or within the catheter wall  106 . Alternatively, one conductor may be embedded on or within the catheter wall  106 , for example the cathode  100 , and the other conductor may be formed by the patient&#39;s body, for example the anode  102  (not illustrated). The catheter wall  106  may be electrically insulating, or alternatively or in addition, the cathode  100  and/or the anode  102  may be encased within a layer of insulating material  116 . The insulating material  116  may provide additional electrical insulation around the cathode  100  and/or the anode  102 . 
     While the catheter  10  is in use, the catheter  10  may be positioned within a patient body cavity  114  that may be defined by a cavity wall of patient tissue  108 . A voltage potential may be applied to the cathode  100  and/or anode  102 . Alternatively, an electric current may be driven into or out of the cathode  100  and/or anode  102 . The voltage or electric current may be AC or DC, having fixed or variable amplitude, frequency, or phase (if multiphase). The cathode-anode naming convention of the conductors is not meant to a particular conductor to a conventional polarity, for example the cathode  100  may be electrically charged positively or negatively and the anode  102  may be electrically charged negatively or positively, respectively. 
     The cathode  100  and the anode  102  may be disposed adjacent to each other as shown in  FIGS. 1-5 , or the cathode  100  and the anode  102  may be disposed on substantially opposite sides of the catheter lumen  104  (not illustrated). The cathode  100  and the anode  102  may spiral around the catheter lumen  104  as a pair as shown in  FIG. 1 ; they may spiral around the catheter lumen  104  independently (e.g., in opposite directions); they may run substantially parallel with the catheter lumen  104  as indicated in  FIGS. 4-5 ; or they may be oriented in an arbitrary manner. 
       FIG. 3  shows an optional conductive mesh that may be embedded within (or on) the catheter wall  106 . The conductive mesh  120  may be electrically coupled to either the cathode  100  or the anode  102 , or the conductive mesh  120  may serve as a ground plane. 
     An adjacent cathode  100  and anode  102  may form an anode-cathode pair  118   a  as shown in  FIGS. 1-5 . There may be multiple anode-cathode pairs  118 , for example an anode-cathode pair  118   a  and an anode-cathode pair  118   b  as shown in  FIGS. 4-5 . The number of anode-cathode pairs  118  may be based on a number of factors, for example the circumference or wall thickness of the catheter  10 , the intended use or ease-of-use of the catheter  10 , or the desired manufacturing cost. Configuring the cathode  100  and the anode  102  into pairs or wires may help prevent intermingling of these wires to provide simpler manufacturing or more efficient electrical properties of the catheter  10 . Each anode-cathode pair  118  may be driven by the same or a separate power supply that may or may not share a common ground or a common phase. 
     One advantage of configuring the cathode  100  and the anode  102  adjacent to each other is to reduce the distance between the cathode  100  and the anode  102 . This may increase the electric field (volts/meter) between the cathode  100  and the anode  102  for a given applied voltage between the cathode  100  and the anode  102 . A high electric field may be beneficial to generating a plasma-inducing coronal discharge. Consequently, for patient-safety reasons it may be desirable to induce a coronal discharge using a lower voltage applied to a closely separated cathode  100  and anode  102  rather than using a higher voltage applied to a distantly separated cathode  100  and anode  102 . Additionally, a lower voltage may increase the electrical efficiency of the system. 
     A voltage potential applied or induced between the cathode  100  and the anode  102  may create a sufficiently large electric field gradient to ionize the air or matter between and adjacent to the cathode  100  and the anode  102 . The voltage and/or current applied to or induced upon the cathode  100  and the anode  102  may be AC or DC to achieve a desired cycle time or intensity of coronal discharges. This ionization may lead to a coronal discharge, which may in turn create plasma capable of causing significant cellular death of bacteria or microorganisms (bacteriocidal), or which may sufficiently damage bacteria and microorganisms to inhibit or prevent their reproduction (bacteriostatic), while causing no or minimal harm or damage to adjacent patient tissue  108 . Consequently, the air, catheter exterior surface  110 , catheter interior surface  112 , patient body cavity  114 , and/or the patient tissue  108  may be effectively and safely sterilized. 
     Some catheters have a smooth outer surface in which there are few if any air gaps between the patient tissue  108  and the catheter exterior surface  110 . However, because plasma may be more efficiently generated by coronal discharge in dry or gaseous conditions compared to moist or fluidic conditions, it may be desired to create air pockets on the catheter exterior surface  110 . This may be achieved in several ways, for example by a textured, corrugated, dimpled, or ribbed segment of catheter exterior surface  110 . This uneven segment of the catheter exterior surface  110  may extend along some or all of the length of the catheter  10  and it may have variably dimensioned peaks, troughs, and gaps. The catheter exterior surface  110  may or may not contact patient tissue  108 . 
       FIG. 5  shows a catheter  10  having a longitudinally corrugated catheter exterior surface  110  such that an atmospheric space  300  exists between adjacent anode-cathode pairs  118 . ( FIG. 5  shows four anode-cathode pairs  118  but only two are labeled). 
       FIGS. 6-8  shows a catheter  10  having a ribbed (helical) catheter exterior surface  110  ( FIG. 6  is a side view,  FIG. 7  is a transverse cross-sectional view, and  FIG. 8  a close-up longitudinal cross-sectional view). An atmospheric space  300  exists between each pair of adjacent apexes  302  of the ribbing on the catheter exterior surface  110 . 
     Additionally, atmospheric space  300  may be created by modulating the chemical or physical properties of the catheter wall  106 . For example, microscopic atmospheric space  300  may be created when part or all of the catheter wall  106  comprises a permeable material. 
       FIGS. 9 a -9 c    show a catheter assembly  20  that may be used in a pulmonary artery catheterization (PAC) medical procedure, sometimes called Swan-Ganz catheterization. The catheter assembly  20  comprises a catheter  10  that may enter the patient body through an introducer sheath  420 . The introducer sheath  420  may be attached to a first tubular collar  410   a  that is adjacent to the patient tissue  108 . A second tubular collar  410   b  may be coupled to the first collar  410   a  by means of a tubular contamination sheath  400  that may be flexible or rigid. The catheter  10  is disposed axially, through the first collar  410   a , the second collar  410   b,  and the contamination sheath  400 . The contamination sheath  400  may be composed of a suitable plastic, rubber, or other elastomeric material.  FIGS. 9 a -9 c    depict the contamination sheath  400  as being transparent. 
     One or more secondary catheters  122 , instrumentation wires, sensor leads, fiber-optic cables, conduits, channels, or other sensors, tools, or implements may be disposed within the primary catheter lumen  104 . For example,  FIGS. 9 a -9 c    show a secondary catheters  122  that terminates into a balloon  200  that may be inflated within a patient body cavity  114  or adjacent to a patient organ. 
     The catheter  10  may be advanced into or withdrawn from the patient body by axial translation through the contamination sheath  400  and through one or both of the first collar  410   a  and the second collar  410   b.  A purpose of the contamination sheath  400  is to maintain sterility of the catheter  10  during and between successive advancements and withdrawals. The contamination sheath  400  may, but need not be, be flexible, compressible, extendable, elastic, pliant, or foldable (longitudinally pliant similar to an accordion). This helps prevent a segment of atmosphere-exposed catheter  10  from entering the contamination sheath  400  during advancement of the catheter  10  and/or helps prevent a segment of non-atmosphere-exposed catheter  10  from within the contamination sheath  400  to be exposed to the atmosphere during withdrawal of the catheter  10 . However, even with a longitudinally pliant contamination sheath  400 , is possible to translate a potentially non-sterile segment of the catheter  10  (atmosphere-exposed) into the contamination sheath  400  though the second collar  410   b,  as shown in  FIG. 9 b   , which may introduce bacteria and microorganisms to the interior cavity of the contamination sheath  400 . When this occurs, subsequently translating a segment of the catheter  10  out from the contamination sheath  400  though the first collar  410   a  and into a patient, as shown in  FIG. 9 c   , may introduce those bacteria and microorganisms into the patient body. 
       FIG. 9 a    shows a cathode  100  and the anode  102  (comprising an anode-cathode pair  118   a ) embedded within the contamination sheath  400 . One or both of the cathode  100  and the anode  102  may be disposed on or within the contamination sheath  400 , or alternatively one both of the cathode  100  and the anode  102  may be disposed on or within the catheter  10  as illustrated in previous figures. Additionally, there may be multiple anode-cathode pairs  118  as previously discussed. The cathode  100  and the anode  102  may spiral about the catheter  10  as shown in  FIGS. 9 a   - 9   c.  Alternatively, they may ran parallel to the catheter  10  or they may be oriented in an arbitrary manner as indicated in the discussion of previous embodiments. 
       FIG. 9 b    shows the catheter  10  having been translated into the contamination sheath  400  through the second collar  410   b  (also the contamination sheath  400  has been compressed longitudinally and is therefore illustrated as having wrinkles). To kill any bacteria or microorganisms that may have been carried into the contamination sheath  400 , the cathode  100  and/or the anode  102  may be electrified to generate a sterilizing coronal discharge plasma as previously described. Therefore, a segment of the catheter  10  that may be subsequently translated out from contamination sheath  400  through the second collar  410   b  and into the patient body, as shown in  FIG. 9 c   , is sterile. 
     Due to the accordion-like behavior of the contamination sheath  400 , it may have many folds and wrinkles. This can make it difficult to fully sterilize the interior of the contamination sheath  400  using conventional methods such as by injecting a sterilizing fluid or gel. Such a fluid or gel may not reach all the folds and creases within the contamination sheath  400  (and it may also impede the translation of the catheter  10  by clogging the openings in the collars  410  or by drying out). In contrast, sterilization via coronal discharge plasma generated by conductors embedded within or adjacent to the contamination sheath  400  may more easily kill bacteria and microorganisms hiding in these folds and wrinkles. Moreover, these folds and wrinkles, combined with the generally dry environment within the contamination sheath  400 , create air pockets that may increase the efficiency of generating sterilizing coronal discharge plasma as previously discussed. 
       FIG. 10  shows a bandage  30  wherein the cathode  100  and the anode  102  are embedded within a material comprising the bandage interior  500 . The cathode  100  and/or the anode  102  may be encased in an insulating material  116  as shown, or they may be embedded in one or more dielectric layers within the bandage interior  500  (not illustrated). In the case wherein the cathode  100  and the anode  102  are defined by electrical wires, such wires may be routed, woven, layered, or disposed on or within the bandage interior  500  in any suitable manner that may enable coronal discharge upon sufficient electrification thereof. Alternatively, one conductor may be embedded on or within the bandage interior  500 , for example the cathode  100 , and the other conductor may be formed by the patient&#39;s body, for example the anode  102  (not illustrated). 
     The bandage surface  510  may be positioned adjacent to patient tissue  108  to dress a wound, for example. The bandage surface  510  may create atmospheric spaces  300  adjacent to the patient tissue  108  by means of a texture, corrugation, dimpling, or ribbing of the bandage surface  510  defining a plurality of apexes  302 . As previously described, a voltage and/or current may be applied to the cathode  100  and/or anode  102  of sufficient magnitude to induce a sterilizing coronal discharge. 
     The foregoing embodiments are exemplary and should not be interpreted as limiting the scope of the several embodiments. Various implementations and combinations of these embodiments have been recognized and anticipated. In some cases, features of embodiments can be combined in different ways and still achieve desirable results. Additionally, the several embodiments depicted in the accompanying figures do not necessarily require the particular depiction shown to achieve desirable results.