Abstract:
The invention relates to a catheter ( 10 ) for neural blockades in anaesthesia. Said catheter consists of a flexible plastic tube in which a wire ( 16 ) is arranged for electrostimulation. The distal end of said wire ( 16 ) is conductively applied to a contact tip protruding out of the catheter ( 10 ). Said contact tip consists of a stopper ( 12 ) and a cap ( 14 ) which are positioned in the catheter ( 10 ), the cap being arranged in front of the distal end of said catheter ( 10 ) and covering the edge of the front surface thereof.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to the field of catheters, and in particular to a catheter for nerve blocks in anesthesia. 
   In anesthesia, for lengthy operations, postoperative pain therapy, and treatment of chronic pain states, the nerves supplying a specific region of the body are often blocked by an anesthetic. A catheter is used to introduce the anesthetic, and the distal end of the catheter is positioned as close as possible to the nerve to achieve an optimum effect with a minimal quantity of anesthetic. The catheter, which can remain in position for a long time if necessary, includes a long, thin, flexible plastic tube. 
   To insert the catheter into the sheath or canal of the nerve, a cannula is used to insert the catheter. U.S. Pat. No. 5,007,902 teaches replacement of such a cannula by a puncture cannula, in which case the puncture cannula is pulled away in order to insert the catheter. German patent DE 3643235 C1 teaches a puncture cannula whose internal canal emerges at the side behind the distal tip of the cannula, with the catheter being inserted and positioned by means of this puncture cannula. Once the catheter is in position, the cannula used for its insertion is removed. 
   U.S. Pat. No. 5,007,902 also teaches the use of electrical nerve stimulation for precise positioning of the catheter. In this case, a guide wire is inserted in the catheter, and its distal end protrudes slightly from the distal end of the catheter. The proximal end of the guide wire is electrically contactable for connection of a stimulator. Using electrical simulation, the position of the distal end of the catheter can be determined exactly while the catheter is being inserted into the sheath or canal of the nerve. Since the guide wire completely fills the internal cross section of the catheter, the wire has to be removed from the catheter as soon as the catheter is in place in order to apply the anesthetic through the catheter. If the catheter remains in place for a long period of time and further medication has to be introduced, it is often necessary to check the position of the catheter and possibly correct it. It is necessary for this purpose to insert a guide wire once again to determine the position of the distal end of the catheter by electrical stimulation. 
   It is also known that a thin wire can be disposed in the catheter for electrical stimulation, the cross section of which is smaller than the free internal cross section of the catheter. In this way, the wire does not impede introduction of a liquid through the catheter so that the wire can remain in the catheter. The position of the wire, fixedly disposed in the catheter, can be checked by electrical stimulation and corrected for the entire time that it is in place. However, if the thin end of the wire protrudes from the distal end of the catheter, there is a risk that the tip of the wire may cause damage and injury to the nerves while the catheter is being pushed forward. If the wire does not protrude from the distal end of the catheter, although this risk is reduced the electrical contact for electrical stimulation is no longer reliably assured. 
   Therefore, there is a need for a catheter for a nerve block that can be positioned by electrical stimulation, ensuring a reliable contact for electrical stimulation and a minimal risk of injury, and making it possible for the catheter position to be checked at any time by electrical stimulation. 
   SUMMARY OF THE INVENTION 
   A contact tip is placed in the distal end of the catheter, comprising a metal part inserted coaxially with a plug into the distal end of the catheter, protruding with a cap at the distal end of the catheter, and overlapping the edge surface thereof. For an electrically conductive connection between this contact tip and the proximal end, a thin wire is disposed in the catheter which is connected in an electrically conducting fashion with the plug of the contact tip. The contact tip with its cap forms the distal end of the catheter. The cap provides a reliable electrical contact over a large surface area for nerve stimulation. The blunt, rounded cap overlapping the distal end of the catheter also avoids the risk of injuring the nerve as the catheter slides forward. The plug inserted into the distal end of the catheter keeps the contact tip centered in the distal end of the catheter. The thin wire passing through the catheter in order to connect the distal contact tip with the proximal connector of the stimulator does not prevent a liquid such as an anesthetic from being introduced. Electrical stimulation is possible as the catheter is being inserted for exact positioning and can be repeated at any time while the catheter is in place to check, and if necessary correct, its position. 
   The contact tip can completely close off the distal end of the catheter. In this case, the liquid introduced through the catheter exits distally through outlet openings provided in the catheter wall at its distal end area immediately behind the contact tip. In another embodiment, the contact tip can have an axial hole through which the liquid can pass. In this case, outlet openings in the catheter wall are not necessary, but can be provided in order to enlarge the outlet cross section. The outlet openings in the catheter wall are preferably formed so that, with their center axis, that is the outlet direction, they form an acute angle of less than 90° with the center axis of the catheter, with this acute angle opening in the distal direction. The acute angle can be approximately 45° in one preferred embodiment. The shape of the outlet openings at an angle in the forward direction causes the liquid introduced through the catheter to exit in the distal direction so that the liquid, for example an anesthetic, is precisely applied. 
   These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is an axial section through the distal end of the catheter in a first embodiment; 
       FIG. 2  is a corresponding view of a second embodiment; 
       FIG. 3  is a corresponding view of a third embodiment; 
       FIG. 4  is a corresponding view of a fourth embodiment; 
       FIG. 5  is a corresponding view of a fifth embodiment; and 
       FIG. 6  is a lateral view of the distal end of the catheter without the contact tip, in partial axial section. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a cross section view of a catheter  10 . The catheter  10  is a flexible tube, made for example of plastic or polyamide. The length of the catheter  10  depends on its application. For peripheral plexus anesthesia, the length of the catheter  10  is approximately 400 mm, while for peridural and spinal anesthesia a length of for example 900 mm may be used. The diameter of the catheter  10  also depends on the application. For example, a 19 G catheter has an external diameter of 1 mm and an internal diameter of 0.5 mm. A 20 G catheter has an external diameter of 0.8 mm and an internal diameter of 0.4 mm. It is possible to use a still thinner catheter with correspondingly smaller diameters. 
   The catheter  10  includes a contact tip that is placed in the distal end of the catheter  10 , and is formed as a metal part. The contact tip includes a plug  12  and a cap  14 , in one piece. The plug  12  has the shape of a circular cylinder whose external diameter corresponds to the internal diameter of the catheter  10 . This makes it possible to insert the plug  12  of the contact tip into the distal end of the catheter  10  so that the plug  12  is held with a snug fit in the catheter  10 . The external diameter of the cap  14  corresponds to the external diameter of the catheter  10 . When the contact tip is inserted into the distal end of the catheter  10 , the plug  12  is pushed into the lumen of the catheter  10  until the cap  14  abuts the distal end surface of the catheter  10 . Since the diameter of the plug  12  corresponds to the internal diameter of the catheter  10 , the plug  12  holds the contact tip in the center at the distal end of the catheter  10  with the cap  14  overlapping and covering the edge surface of the catheter  10 . At the outer periphery, the cap  14  fits flush to the catheter  10  so that the cap  14  fits seamlessly into the outer periphery of the catheter  10 . 
   For an electrically conductive connection of the contact tip with a stimulator (not shown) connected at the proximal end of the catheter, a thin wire  16  is disposed in the catheter  10 . The diameter of the wire  16  is considerably smaller than the internal diameter of the catheter  10 , so that a considerable portion of the lumen of the catheter  10  remains free for a liquid to pass through. The diameter of the wire  16  is for example 0.2 mm. The proximal end of the wire  16  is contactable with the stimulator in a manner not shown. The distal end of the wire  16  is connected in an electrically conducting fashion with the plug  12  of the contact tip, for example soldered, glued, embossed, or laser-welded. A number of embodiments of the contact tip are described below. 
   In the embodiment of  FIG. 1 , the plug  12  and the cap  14  are closed. The cap  14  is in the shape of a hemisphere whose curved portion is on the distal side. The wire  16  is soldered coaxially into a blind hole provided coaxially in the inside end surface of the plug  12 . 
   In the embodiment of  FIG. 2 , the cap  14  is also in the shape of a hemisphere. A through-hole  18  passes through the contact tip (i.e., through the plug  12  and the cap  14 ), and runs eccentrically and axially parallel thereto. The blind hole that receives the wire  16  is located axially parallel and externally diametral to the through-hole  18 . 
   In the embodiment of  FIG. 3 , the cap  14  is also hemispherical. The through-hole  18  passes coaxially through the plug  12  and the cap  14 . The wire  16  is soldered into a groove formed axially in the outer periphery of the plug  12 . 
   In the embodiment of  FIG. 4 , the cap  14  is in the shape of a flat plate that extends from a smooth distal end surface starting at the outer circumference with a radius of curvature and makes a transition to the cylindrical circumferential surface of the catheter  10 . As in the embodiment of  FIG. 3 , the through-hole  18  is coaxial and the wire  16  is set in an axial circumferential groove. 
   In the embodiment of  FIG. 5 , the cap  14  is in the shape of a hemisphere. The through-hole  18  is coaxial, and has a larger diameter toward the inside end of the plug  12 . A hollow bushing  20  is inserted into this enlarged section of through-hole  18 , and includes an inside wall to which the wire is electrically connected. 
   If the contact tip has an axial through-hole  18 , a liquid such as an anesthetic can be added through the catheter  10  and exit through this through-hole  18 . If the contact tip is closed, as for example in the embodiment of  FIG. 1 , one or more outlet openings  22  are provided in the distal end area of the catheter  10  behind the contact tip, through which openings the liquid can exit. Such outlet openings  22  can also be provided in cases where the contact tip has an axial through-hole  18  to enlarge the cross section for the added liquid to exit. 
   The outlet openings  22  may have any shape, cross section, and arrangement. A design such as that shown in  FIG. 6  is preferable. In this design, the outlet openings  22  are provided in the wall of the catheter  10  such that the center axis of the outlet opening  22  makes an acute angle with the center axis of the catheter  10  (e.g., an angle of 45°), with this acute angle opening in the distal direction. In this way, the liquid added is directed distally through the outlet openings  22 . Three outlet openings  22  are provided, making angles of 120° with each other in the circumferential direction. This ensures that the liquid added is dispensed evenly over the entire periphery of the distal end of the catheter  10 . In order for the outlet openings  22  not to weaken the wall of the catheter  10 , the outlet openings  22  are preferably offset axially from each other. 
   Although the present invention has been shown and described with respect to several preferred embodiments thereof, various changes, omissions and additions to the form and detail thereof, may be made therein, without departing from the spirit and scope of the invention.