Catheters for the introduction or removal of fluids may be located in various venous locations and cavities throughout the body. Several types of catheters have been developed for fluid transduction applications including multiple lumen catheters, such as a dual lumen catheter in which one lumen introduces fluids and one lumen removes fluids, and multiple catheter assemblies, which comprise multiple, individual, typically single lumen catheters which are inserted through one or more incisions into an area to be catheterized. Examples of multiple catheter assemblies include the Tesio catheter and the SchonCath® catheter.
 To insert any catheter into a blood vessel, it is generally necessary to identify the vessel by aspiration with a long hollow needle in accordance with the Seldinger technique. When blood enters a syringe attached to the needle, the syringe is disconnected and a thin guide wire is passed through the needle into the interior of the vessel. The needle is then removed, leaving the guide wire within the vessel. The guide wire projects beyond the surface of the skin.
 Once the guide wire is placed within the vessel, a physician may choose to pass a catheter into the vessel directly over the guide wire, and remove the guide wire, leaving the catheter in position within the vessel. Alternatively, a dilator device can be passed over the guide wire to enlarge the hole. A catheter is then passed over the guide wire, and the guide wire and dilator are removed. Although employing a dilator is particularly useful when the catheter to be inserted is significantly larger in diameter than the guide wire, removing a dilator in the manner prescribed by most catheterization methods is associated with increased bleeding and the formation of blood clots at the insertion site.
 Double catheter assemblies used for rapid withdrawal and/or infusion of blood and blood components or products and used repeatedly over weeks to months, are usually of a size equal to or larger than 12 French. They may be designed as two assemblies joined together through most of their length or as in the SchonCath® and Tesio double catheter systems designed as two independent catheters with lumens and inserted together either attached at some point or independent in which each lumen has a diameter of usually greater than 6 French. Such retained assemblies are preferably made of soft material to minimize trauma to the vessels during prolonged contact, and are therefore often difficult to insert without bending, kinking or crimping during insertion. When using these retained assemblies, a physician may find it is necessary to use an introducer sheath to facilitate insertion.
 An introducer sheath is simply a large, stiff thin-walled tube which serves as a temporary conduit for the permanent catheter which is being placed. The introducer sheath is positioned by placing a dilator device inside of the introducer sheath and passing both the dilator and the introducer sheath together into the vessel. A guide wire, left in the vessel after insertion of the dilator-sheath assembly as described above, and the dilator(s) is (are) then removed, leaving the thin-walled introducer sheath in place. The dilator must be removed in order for the catheter to pass into and through the sheath. When the dilator is removed the sheath is left open with nothing to prevent blood from issuing out nor air from entering in. Thus significant blood loss can occur if there is any delay caused by difficulty in passing the catheter assembly into the sheath. An additional complication is that, with the dilator out, if the patient inspires deeply and creates negative pressure, air is sucked into the central vessels through the open sheath and results in air embolisn Air embolism is a potentially very serious complication and may be fatal.
 In the case of a Tesio catheter assembly, an individual catheter, without a hub or an anchoring device, may be passed through the sheath and into the vessel. The sheath is then removed over the catheter. When a connecting means such as a retaining sleeve, or any type of anchoring device such as a Dacron® or other fabric anchoring cuff is permanently attached to the catheter, the sheath must be either larger than the cuff or comprise a tear-away portion which splits into two parts as the sheath is retracted. Even when no cuff is present and a tunneling procedure is commonly not performed, as with a Tesio assembly used for acute catheterization (U.S. pat. No. 5,776,111), the assembly is so large and flexible that a sheath is often necessary to facilitation insertion. Once inserted, each of the proximal ends of the catheters in the assembly is stabilized, either by means of an anchoring device, subcutaneous tunneling as in chronic catheterization, or by affixing to the patient's skin as in acute catheterization.
 Typical anchoring devices for such catheters and other venous and body cavity catheters and shunts involve use of a tissue ingrowth cuff, generally made of a fabric such as Dacron® or the like, fitted on a proximal portion of the catheter for stabilization of the catheter in a single position if the catheter is to be left in that position for a significant length of time. Surrounding tissue cells grow into the fabric stabilizing the catheter in that particular location. In using catheters having a fabric cuff, or other retaining devices or fittings, one stabilizing technique includes creating a subcutaneous tunnel, or similar opening, several centimeters caudal to the insertion site of the catheter for stabilization of the catheter using the cuff or other device. Subcutaneous tunnels and stabilizing devices are typically used, for example, for multi-lumen catheters and for catheter assemblies such as the Tesio and the SchonCath®.
 In a typical tunneling procedure, the skin is anesthetized in a linear fashion for a distance of about 6-8 centimeters caudal to the insertion site. If tunneling is used for venous insertion, a second incision is made and a tunneling device such as a trocar is passed into the incision and out through the skin at the point of catheter insertion creating a subcutaneous tunnel. The catheter is attached to the tunneling device and pulled back through the skin tunnel.
 For a self-retaining, double catheter assembly, such as a SchonCath®, in which the individual catheters are either permanently or adjustably linked in one location along their length by a retaining sleeve, subcutaneous anchoring is accomplished by positioning the retaining sleeve below the incision site and outside the area to be catheterized. The sleeve renders the assembly self-retaining such that the double tunneling procedure necessary to insert, for example, a Tesio catheter, is optional.
 Both an adjustable catheter according to U.S. pat. No. 5,718,692 and a Tesio catheter permit independent insertion and removal of the individual catheters such that dialysis need not be unnecessarily prolonged. Further, because the individual catheters in these assemblies can be adjusted within the vessel and in relation to one another, a physician is able to optimize catheter placement for a given location on a given patient. The ability to adjust individual catheters within a multiple catheter assembly represents a significant advantage over multiple lumen catheters, since positioning of catheters is particularly important to proper catheter functioning. For example, if the tip of a central venous catheter is not properly located within a vessel, the catheter may cause the condition of cardiac arrhythmia or otherwise inhibit blood flow. If the catheter tip is not properly located within a body cavity there may not be sufficient access to the tip to allow bodily fluid to properly flow through the catheter. Further, the catheter tip may damage a vessel wall and surrounding tissue if not properly placed within the vessel.
 In addition to providing more desirable flow characteristics with less vessel damage than multiple lumen catheters, multiple catheter assemblies are generally formed of flexible catheter materials, and thus, provide more comfortable and efficient catheterization procedures than are possible with multiple lumen catheters. While beneficial for chronic catheterizations, multiple catheter assemblies are also useful for acute catheterizations, since these assemblies can be straightforwardly modified for convenient use during acute procedures (e.g. the Tesio assembly for acute procedures, U.S. pat. No. 5,776,111), and can be inserted through a single incision as described in U.S. pat. No. 5,624,413.
 In view of the significant advantages offered by multiple catheter assemblies, there is significant interest in developing safer, more direct methods of inserting multiple catheter assemblies. Current single-incision insertion methods for double catheter assemblies require the use of dilator devices which, when removed during most catheterization procedures, can cause increased bleeding and clot formation at the insertion site and create an increased chance of forming an air embolism in the vessel. Thus, there is a need in the art for a simple method of inserting a double catheter assembly, such as a Schon catheter assembly, which requires only one procedure and which decreases the patient health risks associated with standard catheterization methods. The present invention fills this need.
 The present invention includes a method for inserting a multiple catheter assembly into an area of a body to be catheterized, the assembly comprising a first and a second catheter, the method comprising the steps of (a) accessing an area to be catheterized and creating an access site, (b) inserting an introducer sheath into the area to be catheterized, (c) inserting a first guide wire and a second guide wire into the introducer sheath, (d) at least partially inserting a first dilator and a second dilator into the area to be catheterized, (e) removing the first dilator and the second dilator and blocking the flow of one or more of blood and air into and out of the area to be catheterized, (f) passing the distal portion of the first catheter over the first guide wire and passing the distal portion of the second catheter over the second guide wire, and (g) inserting each of the first and second catheters in juxtaposed relation into the area to be catheterized and blocking the flow of one or more of blood and air into and out of the area to be catheterized. In this embodiment, the area to be catheterized is a blood vessel, such as an internal jugular vein of a human. In this preferred embodiment, the vein is proximal to the right atrium of the heart of the human, and that the distal portion of the first catheter is closer to the heart than the distal portion of the second catheter.
 In one embodiment of the invention, the multiple catheter assembly further comprises a retaining sleeve, and the method firther comprises making an incision at the access site and creating a recessed area directly under the incision, which recessed area is sized to contain the retaining sleeve.
 In another embodiment, the method further comprises attaching removable connectors, each including, for example, an extension tube having a clamp for controlling fluid flow through the connector, and each having fluid passageways therethrough to the proximal portions of the first and second catheters.
 In yet other embodiments, each of the first dilator and the second dilator has a diameter of 11 French when measured in the transverse direction, and each of the two wires is from about 100 centimeters in length to about 120 centimeters in length.
 In multiple embodiments, the incision made at the access site is from about 1 centimeter in length to about 1.5 centimeters in length, and the method further comprises closing the incision made at the access site. Optionally, the method comprises subcutaneously securing a proximal portion of the first catheter and a proximal portion of the second catheter by forming at least one subcutaneous tunnel and threading the proximal portion of at least one of the first and second catheters therethrough.
 In a preferred embodiment, the sum of the diameters of the first and second dilators is at least 3 French greater than the sum of the diameters of the first and second catheters, and step (d) of the method described above farther comprises maneuvering each of the first and second dilators vigorously and circumferentially within the area to be catheterized.
 In various embodiments of the invention, the proximal portions of the first and second catheters each include at least one subcutaneous securement device. In other embodiments, the first catheter is longer than the second catheter, as measured longitudinally.
 In another aspect, the invention includes a kit for performing an insertion of a multiple catheter assembly into a human, the kit comprising one or more components selected from the group consisting of a multiple catheter assembly comprising a first catheter and a second catheter, an introducer sheath, a dilator, a guide wire, and an instructional material, wherein the instructional material provides one or more of an outline, an illustration, and a description of a method for inserting a multiple catheter assembly into an area of a human to be catheterized, the method comprising the steps of:
 (a) accessing an area to be catheterized and forming an access site,
 (b) inserting an introducer sheath into the area to be catheterized,
 (c) inserting a first guide wire and a second guide wire into the introducer sheath,
 (d) at least partially inserting a first dilator and a second dilator into the area to be catheterized,
 (e) removing the first dilator and the second dilator and blocking the flow of one or more of blood and air into and out of the area to be catheterized,
 (f) passing the distal portion of the first catheter over the first guide wire and passing the distal portion of the second catheter over the second guide wire, and
 (g) inserting each of the first and second catheters in juxtaposed relation into the area to be catheterized and blocking the flow of one or more of blood and air into and out of the area to be catheterized.
 Optionally, a kit of the invention can further comprise one or more of a replacement catheter, a syringe, a tunneling device, a connector, and a clamp.
 In another embodiment, the instructional material of a kit included in the invention provides one or more of an outline, an illustration, and a description of a method for inserting a multiple catheter assembly into an area of a human to be catheterized, the method further comprising the steps of making an incision at the access site and creating a recessed area directly under the incision, which recessed area is sized to contain the retaining sleeve; and at least partially inserting a first dilator and a second dilator into the area to be catheterized and maneuvering each of the first and second dilators vigorously and circumferentially within the area to be catheterized,
 The foregoing summary, as well as the following detailed description of preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings plural embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentality's shown. In the drawings, elements are not necessarily drawn to exact scale, and like numerals are used to indicate like elements throughout. In the drawings:
 Certain terminology is used in the following description for convenience only and is not limiting. The words “right,” “left,” “lower” and “upper” designate directions in the drawings to which reference is made. The words “proximal” and “distal” refer to directions away from and closer to, respectively, for example, the insertion ends of the first and second catheters in a double catheter assembly according to the present invention. The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import. The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an introducer sheath” can refer to one introducer sheath or to more than one introducer sheath, unless specifically stated otherwise.
 Referring now to the drawings in detail, there is shown in
 As shown in
 As shown in
 It will be understood from this disclosure, that additional catheters (not shown), including multiple lumen catheters, which may have distal portions inserted into the area to be catheterized in a manner as shown in
 The catheter assemblies
 The first catheter
 Suitable, preferred, biocompatible elastomers for use in forming the catheters
 As shown in
 While the circular cross section is preferred in order to achieve efficient fluid flow in each lumen
 In addition, while two lumens
 As illustrated in
 The catheters
 The catheters
 A retaining sleeve
 Regardless of the configuration of the edges
 In hemodialysis applications, wherein the retaining sleeve
 The catheter assembly
 In a preferred embodiment of catheterization shown in
 The retaining sleeve
 The retaining sleeve
 In the alternative catheter assembly
 The first catheter
 The second proximal end
 In alternative embodiments, such as those in which the method is used for an acute catheterization, the catheter assembly is secured by affixing the assembly externally to the body of the patient. For example, a Tesio catheter assembly (U.S. Pat. No. 5,776,111), which may be inserted by the present method and which is designed specifically for acute catheterizations, is not secured by subcutaneous tunneling as shown in
 In the method of the present invention, a vein
 In accordance with the Seldinger technique, a narrow needle would normally be inserted through the access site
 Following placement of the introducer sheath
 Following insertion of the guide wires into the vein
 Once the recessed area
 The selection of a dilator for a given catheterization procedure is also important. The dilators for a catheter procedure are selected such that the sum of the diameters of the first and second dilators, each measured at its widest transverse section, is at least 3 French units greater than the sum of the diameters of the first and second catheter lumens
 In prior insertion techniques, the next step would be the removal of the guide wires and the insertion of a sheath over a dilator, both inserted over a wire. The diameter of the sheath would be at least equal to the sum of the 1 st and 2nd catheter lumens
 In the present invention, the insertion of the dilator-sheath assembly is eliminated. After removal of the dilators the sheath assembly is not inserted and the flow of air, blood, or both to the area to be catheterized
 In accordance with the method of the present invention, the distal portion of each catheter in the double catheter assembly
 Once the multiple catheter assembly
 In alternative embodiments, a catheter assembly
 As applied to catheter assembly
 In the disclosed embodiment, all incisions are closed before the catheterization procedure begins. If necessary, catheterization may be performed with an open incision, although the preferred technique is to close all incisions before performing catheterization.
 The method of catheter insertion provided by present invention offers significant advantages over prior art methods of inserting double catheter assemblies, including the ability to insert two catheters with a single insertion procedure that is significantly safer, by reducing bleeding, undesirable clotting, and the potential for developing an air embolism during the procedure. Double catheter assemblies such as the Tesio catheter which are not attached and are usually placed separately require a second puncture of a central vessel such a the internal jugular or subclavian veins. This may result in twice the potential for inadvertent puncture of the internal jugular artery or subclavian artery and associated hemorrhagic complications or of a lung and resultant pneumotherax. The current method allows effective insertion of such an assembly by means of a single vessel puncture and thus theoretically halves the risk of such complications.
 In another aspect, the invention includes a kit which is useful in performing a method of the invention. A “kit” is any package, container, or other components which are promoted, distributed, or sold as a unit for performing a method of the invention, or as separate components with the intention that the components be used cooperatively by the recipient to perform a method of the invention. By way of example, a kit of the invention can comprise one or more components useful for inserting a self-retaining or non-self-retaining double catheter assembly into the internal jugular vein of a human patient for the purpose of hemodialysis according to a method described herein. Although an exemplary kit is now described, the contents of other useful kits will be apparent to the skilled artisan in light of the present disclosure.
 The present invention includes a kit comprising at least one of each of a multiple catheter assembly, an introducer sheath, and a dilator, at least two guide wires, and an instructional material which outlines, illustrates, or describes a method included in the present invention. The multiple catheter assembly can be, for example, a Tesio catheter assembly, a SchonCath assembly, or other multiple catheter assembly requiring a two wire insertion procedure, and may be included in a kit which also comprises an introducer sheath, two dilators, two guide wires and an instructional material. A kit can further comprise one or more replacement catheters, and can optionally include one or more of a disposable syringe, a tunneling device, a connector, and a clamp.
 Each of the components of a kit described herein can be promoted, distributed, or sold either as a unit or as separate components to be used cooperatively. By way of example, the instructional material can be affixed to a container which contains one or more of the catheter insertion components described herein, or the instructional material can be shipped together with one or more containers which individually contain one or more catheter insertion components. By way of alternative example, the instructional material may be shipped separately from the catheter insertion components with the intention that the instructional material and the catheter insertion components be used cooperatively by the recipient.
 The instructional material included in a kit of the invention can be a publication, a recording, a diagram, or any other medium of expression which can be used to communicate one or more of the steps of a catheter insertion method included in the present invention. The instructional material can also include any medium of expression which is used to communicate the parameters within which to perform the steps of a method of the invention, and troubleshooting indications and precautions as would be obvious to one skilled in the art after reading the present disclosure. The instructional material of a kit included in the invention may comprise a plurality of materials which can be provided with one or more components of the kit. By way of example, an instructional material can comprise a document which lists the steps of the present catheterization method, and which is provided with an introducer sheath of the kit, and a videographic material which illustrates the method as performed on the internal jugular vein of a human patient, and which is provided with a double catheter assembly of the kit.
 The disclosure of every patent, patent application, and publication cited herein is hereby incorporated herein by reference in its entirety.
 While the present invention has been disclosed with reference to specific embodiments, it is apparent that other embodiments and variations of this invention can be devised by others skilled in the art without departing from the true spirit and scope of the invention. The appended claims include all such embodiments and equivalent variations.