Controlled flashback for vascular access devices

An extravascular system for accessing the vasculature of a patient may include a catheter assembly and an internal construct within the catheter assembly. At least one fluid flow space may exist between the internal construct and the catheter assembly.

BACKGROUND OF THE INVENTION

This invention relates generally to vascular access devices and methods, including catheter assemblies and devices used with catheter assemblies. Generally, vascular access devices are used for communicating fluid with the vascular system of patients. For example, catheters are used for infusing fluid, such as normal saline solution, various medicaments, and total parenteral nutrition, into a patient, withdrawing blood from a patient, or monitoring various parameters of the patient's vascular system.

A common type of intravenous (IV) catheter is an over-the-needle peripheral IV catheter. As its name implies, an over-the-needle catheter is mounted over an introducer needle having a sharp distal tip. At least the inner surface of the distal portion of the catheter tightly engages the outer surface of the needle to prevent peelback of the catheter and thus facilitate insertion of the catheter into the blood vessel. The catheter and the introducer needle are assembled so that the distal tip of the introducer needle extends beyond the distal tip of the catheter with the bevel of the needle facing up away from the patient's skin. The catheter and introducer needle are generally inserted at a shallow angle through the patient's skin into a blood vessel.

In order to verify proper placement of the needle and/or catheter in the blood vessel, the clinician generally confirms that there is “flashback”, or flow, of blood into a flashback chamber of the catheter assembly. Once proper placement of the catheter into the blood vessel is confirmed, the clinician may apply pressure to the blood vessel by pressing down on the patient's skin over the blood vessel distal of the introducer needle and the catheter. This finger pressure occludes the vessel, minimizing further blood flow through the introducer needle and the catheter.

The clinician may then withdraw the introducer needle from the catheter. The introducer needle may be withdrawn into a needle shield device that covers the needle tip and prevents accidental needle sticks. In general, a needle shield includes a housing, a sleeve, or other similar device that is designed such that when the needle is withdrawn from the patient, the needle tip will be trapped/captured within the needle shield. The purpose of these needle shield devices is to house the tip of the needle in a secure location, thereby avoiding the possibility of needle sticks.

The needle and needle shield device, if used with the needle, are then separated from the catheter, which is left in place to provide intravenous access to the patient. Other vascular access devices may then access the catheter in order to continue patient treatment. During the entire period of catheter use, systems and methods are needed to continuously verify and maintain the proper vascular access device position within the vasculature of a patient.

BRIEF SUMMARY OF THE INVENTION

The present invention has been developed in response to problems and needs in the art that have not yet been fully resolved by currently available vascular access systems and methods. Thus, these systems and methods are developed to provide more efficient vascular access systems and methods capable of controlling the rate, location, duration, visualization, and/or other parameters of blood flow through a vascular access device and/or providing continuous verification of proper vascular access device position within the vasculature of a patient.

An extravascular system for accessing the vasculature of a patient may include a catheter assembly and an internal construct within the catheter assembly. The catheter assembly may include a catheter housing and a catheter tubing secured to the catheter housing. The catheter housing may include an internal surface. The internal construct may be at least partially housed within the catheter assembly. The internal construct may include an external surface.

At least one flow groove may exist between the internal surface of the catheter housing and the external surface of the internal construct. At least one ridge may exist adjacent the at least one flow groove and between the internal surface of the catheter housing and the external surface of the internal construct. The at least one ridge may vary in height, and the at least one flow groove may vary in depth. The at least one flow groove may extend along the entire length of the internal construct. The at least one flow groove may include at least six flow grooves, and the at least one ridge may include at least six ridges.

The system may also include a retention construct and a corresponding retention structure in communication with the catheter assembly and the internal construct. The retention construct and the corresponding retention structure are capable of at least temporarily retaining the internal construct in a position relative to the catheter assembly. The corresponding retention structure may include a retention space that permits fluid to flow past the retention construct when the retention construct is engaged with the corresponding retention structure.

The internal construct may be a septum, and the septum may have a septal disk. The system may also include a tapered wedge. The catheter tubing may be secured to the catheter housing with the tapered wedge.

Various separate vascular access devices may be employed with the catheter assembly. The internal construct may be positioned within the catheter housing to accommodate for various lengths of separate vascular access devices that may be employed with the catheter assembly. The catheter assembly may be formed of at least a semi-transparent material.

A method of optimizing the fluid flow parameters of an extravascular system used to infuse fluids and/or to withdraw blood for testing, donation, or other use may include providing a catheter assembly having a catheter tubing and a catheter housing and providing an internal construct within the catheter housing. The internal construct may be disposed within the catheter housing such that blood is allowed to flow between the internal construct and the catheter housing. The method may further include determining a first fluid flow rate through the catheter housing and determining a second fluid flow rate through the catheter tubing. Determining the first fluid flow rate may include determining the rate at which blood flows between the internal construct and the catheter housing. Determining the second fluid flow rate may include estimating a rate at which blood would flow through the catheter housing in the absence of the internal construct. The method may additionally include ensuring that the first fluid flow rate is greater than the second fluid flow rate. Ensuring that the first fluid flow rate is greater than the second fluid flow rate may include varying the first fluid flow rate.

Determining the first fluid flow rate may include calculating the flow (Q) using the following equation.

Q=π·deq4·(P⁢⁢3-P⁢⁢2)128·μ·L·K⁢⁢3⁢_⁢2
Determining the second fluid flow rate may include estimating a flow (Qc) that would exist in the absence of the internal construct using the following equation.

An extravascular system for accessing the vasculature of a patient may include means for accessing the vascular system of a patient, means for controlling fluid flow, and/or means for channeling fluid. The means for accessing the vascular system of a patient allows fluid flow therethrough. The means for controlling fluid flow is at least partially housed within the means for accessing the vascular system of a patient. And the means for channeling fluid may direct or channel fluid between the means for controlling fluid flow and the means for accessing the vascular system of a patient.

The system may also include means for at least temporarily retaining the means for controlling fluid flow in a position relative to the means for accessing the vascular system of a patient. The means for channeling fluid is capable of channeling fluid past the means for at least temporarily retaining. The system may also include means for accommodating various lengths of separate vascular access devices that may be employed with the means for accessing the vascular system of a patient.

A method of optimizing the fluid flow parameters of an extravascular system used to access an extravascular system of a patient is also provided. The method may include providing a catheter assembly having a catheter tubing and a catheter housing and providing an internal construct within the catheter housing such that blood is allowed to flow between the internal construct and the catheter housing. The method may further include determining a first fluid flow rate through the catheter housing, such as by determining the rate at which blood flows between the internal construct and the catheter housing. Additionally, the method may include determining a second fluid flow rate through the catheter tubing, such as by estimating a rate at which blood would flow through the catheter housing in the absence of the internal construct. Moreover, the method may include disposing the internal construct within the catheter housing in a first configuration such that blood is metered to flow between the internal construct and the catheter housing at a first fluid flow rate less than the second fluid flow rate. The method may additionally include associating the internal construct and the catheter housing to provide at least one indwelling configuration and each of the indwelling configurations may provide a customized first fluid flow rate, which may be greater or less than the second fluid flow rate.

These and other features and advantages of the present invention may be incorporated into certain embodiments of the invention and will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. The present invention does not require that all the advantageous features and all the advantages described herein be incorporated into every embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The presently preferred embodiments of the present invention will be best understood by reference to the drawings, wherein like reference numbers indicate identical or functionally similar elements. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description, as represented in the figures, is not intended to limit the scope of the invention as claimed, but is merely representative of presently preferred embodiments of the invention.

Referring toFIG. 1, a cross section view of an extravascular system10shows a vascular access device such as a catheter assembly12having an internal construct such as a septum14at least partially housed within the catheter assembly12. The cross section view of the extravascular system10ofFIG. 1is a view taken along lines A-A ofFIG. 2.FIG. 2is a proximal end view of the extravascular system10revealing the internal construct or septum14housed within the catheter assembly12.

Referring collectively toFIGS. 1 and 2, the catheter assembly12includes an insertion portion such as a catheter tubing16secured to the distal internal end of a catheter housing18. The catheter tubing16includes a lumen20through which a needle may be inserted in order to access the vasculature of a patient. At its distal tip22, the catheter tubing16forms a taper that narrows towards the point of the distal tip of a needle that may be inserted within the catheter tubing16. The tapered tip22is formed in order to enable the tip22of the catheter tubing16to easily penetrate the tissue of a patient through which the needle and catheter tubing16are inserted. Ultimately, the tapered tip22of the catheter tubing will be advanced into the vasculature of a patient and the needle will be withdrawn from the catheter tubing16.

The proximal end of the catheter tubing16expands to form an increased diameter and cross section24as the catheter tubing16enters an internal lumen of the distal end of the catheter housing18. The portion of the catheter tubing16with the expanded diameter24is tapered such that the catheter tubing16will not easily separate from the corresponding tapered internal lumen of the distal portion of the catheter housing18. To provide additional security capable of maintaining the position of the catheter tubing16within the catheter housing18, a wedge26may be placed within the internal lumen of the distal end of the catheter housing18and against the interior surface of the expanded portion24of the catheter tubing16. The wedge26functions at least in part to force the expanded portion24of the catheter tubing16against the internal surface of the distal portion of the catheter housing18. By forcing the material of the expanded portion24against the internal surface of the distal portion of the catheter housing18, the wedge26ensures that the catheter tubing16remains securely connected to the catheter housing18.

In addition, the wedge26also provides a tapered lumen28within the wedge26at the distal portion of the wedge26. The wedge26also includes a tapered lumen30at its proximal end. The tapered lumen28of the wedge26further serves to secure the catheter tubing16to the catheter housing18. In addition, the tapered lumen28serves to guide the distal tip of a needle through the narrowing lumen of the extravascular system10towards the distal portion of the extravascular system10. Tapered lumen30of wedge26provides a similar function as the tapered lumen28, in that the tapered lumen30provides a further guided narrowing of the lumen of the extravascular system10through which the tip of a needle may travel in order to reach its temporary destination at the distal end of the extravascular system10. Tapered lumen30provides guidance and protection capable of ensuring that the tip of the needle does not stick against any internal surfaces of the housing18as the tip of the needle is advanced through the lumen of the extravascular system10. The internal surface of the wedge26may be a low friction surface or any other type of surface capable of successfully guiding the sharp point of the tip of a needle through a lumen of, for example, a progressively narrowing diameter without permitting the point of the tip of the needle to stick into any surface of the wedge26.

Preferably, the wedge26, catheter tubing16, housing18, and septum14of the extravascular system10will be formed of a transparent material. The transparent, or semi-transparent properties of the materials of the extravascular system10will enable a clinician or other user of the extravascular system10to visualize the flow of blood and/or other liquids in addition to the operation of internal components such as the internal construct or septum14and/or the tip or other portions of a needle as such internal components move within the interior of the catheter assembly12. A clinician or operator of the extravascular system10who is able to visualize the internal environment and operations of the catheter assembly12will be able to operate the extravascular system10more effectively.

At the proximal tapered end30of the wedge26, the internal lumen32of the catheter housing18broadens to form a chamber large enough to house a movable internal construct such as the septum14along a length of the lumen32which is greater than the total length of the septum14. The chamber may be formed as a barrel34that includes an internal diameter that corresponds with an external diameter of the septum14, such that the external surface of the septum14communicates with the internal surface of the barrel34. The barrel34may include a relatively smooth internal surface36at the proximal end of the catheter housing18. As the barrel34continues from the relatively smooth surface36in a distal direction, the internal surface36of the barrel34may taper or narrow at a section38towards a more distal section of the barrel34. The more distal section of the barrel34within the housing18will form one or more flow and/or flash grooves40within the internal surface of the barrel34, housing18, and/or the external surface of the septum14. The flow grooves40form channels through which fluid may travel between an internal surface of the catheter housing18and an external surface of the septum14.

The barrel34may include a length that is greater than the length of the septum14. Preferably, the barrel34, and flash grooves40within the barrel34, will include a length great enough to accommodate a variety of depths that may be penetrated by a variety of tips of vascular access devices that will be inserted into the lumen32of the catheter housing18in order to come into communication with the proximal end42of the septum14. For example, a tip of a Luer access device may be inserted as a separate vascular access device into the proximal end of the catheter assembly12and may come into direct contact with the proximal end of the septum14. The Luer tip may then force the septum14in a distal direction to a maximum depth. At the maximum depth, the Luer tip is unable to further advance the septum14in a distal direction within the lumen32. The length of the barrel34and/or grooves40may be great enough to accommodate the maximum insertion depth of the septum14under the influence of any Luer tip. Conversely, Luer tips capable of only minimal depth insertion may be applied to advance the septum14only a minimal amount within the lumen32of the catheter housing18. The length of the barrel34and/or flash grooves40may similarly accommodate this minimal insertion depth.

The septum14may be advanced from the proximal end of the internal lumen32of the catheter assembly12towards the distal end of the lumen32under the influence of a separate vascular access device which may be used in conjunction with or as a part of the extravascular system10. The septum14may be advanced by exerting force upon the proximal end42of the septum14. As the septum14advances through the internal lumen32from the proximal end of the lumen32towards the distal end of the lumen32, the external surface of the septum14will come into contact with the internal surface of the lumen32as the lumen32internal surface tapers along section38towards the distal portion having the flow grooves40.

The septum14, and/or internal surface of the lumen32, barrel34, and/or housing18, may include a retention construct or ring44. For example, the retention ring44may be formed at the distal end of the septum14or along the length of the septum. The retention ring44is a formation of material along the external surface of the septum14capable of coming into greater or more intense contact with surfaces of the lumen32, barrel34, and/or housing18. For example, as the septum14is advanced through the barrel34along the tapered section38and against the grooves40, the retention ring44will be compressed by the ridges of the flow grooves40, causing the septum14to reside in a relatively secure and relatively unmovable position within the barrel34.

The septum14may include a slit46through which the point, tip, and cannula of a needle may penetrate and extend. The septum14may include other additional features which will be described in detail herein, including flow spaces48and ridges50at the proximal end42of the septum14. The flow spaces48enable fluid to flow from the tip of a separate vascular access device into an interior chamber52of the septum14when the ridges50are in direct contact with at least one surface of the mating vascular access device.

Referring toFIG. 3, a close-up cross section view of a distal portion of the septum14is shown housed within the catheter housing18. The close-up view reveals the retention ring44retained by a corresponding retention structure or lack of structure, such as a retention space54, that has been formed in order to temporarily retain the retention ring44within the retention space54until the septum14is moved by a separate vascular access device. Thus, the retention space54functions in cooperation with the retention ring44to ensure that the septum14remains located within its proper position after initial manufacturing assembly and prior to engagement with a separate vascular access device during operation of the extravascular system10.

The flow grooves40are also shown within the close-up view ofFIG. 3extending from the distal end of the barrel34through the retention space54and beyond the retention ring44in a proximal direction. The flash grooves40thus permit the travel of fluid past the septum14in order to provide an operator of the extravascular system10with a visual confirmation of proper location of the tip22of the catheter tubing and/or the tip of a needle within the vasculature of a patient during operation of the extravascular system10. The flash grooves40function to provide flashback confirmation of blood around the exterior surface of the septum14both while the retention ring44is lodged within the retention space54and after the retention ring44has advanced out of the retention space54and along the flash groove40portion of the barrel34. Thus, the flash grooves40function to provide initial, secondary, and tertiary flashback during operation of the extravascular system10regardless of the location and/or depth of penetration of the septum14within the lumen32.

Referring toFIG. 4, a side view of the catheter housing18of the catheter assembly12is shown and will be described in greater detail. In addition to the features already described, the external surface of the catheter housing18may include one or more threads56or other means of attachment capable of securing the proximal portion of the catheter housing18to the distal portion or other portion of a mating vascular access device which may be used to access the internal lumen32of the catheter housing18. The vascular access device will have corresponding male or female threads capable of engaging with the threads56.

The transparent, semi-transparent, and/or translucent material of the catheter housing18reveals the interior structure of the catheter housing18, as will be described in greater detail herein. The external diameter of the catheter housing18forms a narrowing taper from the proximal end of the catheter housing18as it advances towards the distal end of the catheter housing18. The gradual, narrowing taper of the catheter housing18may exist as a result of the corresponding gradual and narrowing taper of the lumen32and other lumens within the catheter housing18as those lumens advance towards the distal end of the catheter housing18. Since a uniform amount of material and/or structural stability may, in certain applications, be necessary or desirable to ensure proper operation of the catheter housing18and catheter assembly12along the length of the catheter housing18, the catheter housing18may be narrowed as the internal lumens32are narrowed. In addition, narrowing the external diameter of the catheter housing18towards the distal tip of the catheter housing18will decrease the amount of material present at the insertion site within the tissue of a patient. Since an operator of the extravascular system10will need and/or prefer an unobstructed view and operation space at the site of needle and/or catheter tip22insertion, a decreased amount of material at the distal end of the catheter housing18is preferred.

Referring toFIG. 5, a proximal end view of the catheter housing18ofFIG. 4is shown. The proximal end view reveals the threads56located on the exterior surface of the catheter housing18, the lumen32extending through the axial center of the catheter housing18, the internal surface of the barrel34, and six flash grooves40formed between flash groove ridges58within the distal portion of the barrel34. The six flash grooves40are uniformly spaced around the axial center of the catheter housing18in order to ensure uniform structural support, stability, and guidance with which the exterior surface of the septum14may communicate. By providing a uniform array of flash grooves40and corresponding flash groove ridges58, a septum14or other internal construct may progress in a predictable, continuous manner towards the distal end of the lumen32of the catheter housing18. Further, the uniform array of the flash grooves40and their corresponding flash groove ridges58may increase the ease of manufacturing the catheter housing18. A number of manufacturing techniques known in the art may be used to manufacture the catheter housing18. In the event that the flash grooves40are formed using a cutting process, two opposing flash grooves40may be cut at the same time since the two opposing flash grooves40are linearly aligned with each other.

Referring toFIG. 6, a distal end view of the catheter housing18ofFIG. 4is shown. The distal end view of the catheter housing18reveals the threads56on the external surface of the catheter housing18, the tapering proximal end60of the catheter housing18, a relatively blunt distal end62of the catheter housing18having a rounded edge64, and the internal tapering lumen32through the axial center of the catheter housing18.

Referring toFIG. 7, a cross section view of the catheter housing18ofFIGS. 4 through 6is shown taken along lines A-A ofFIG. 6. The cross section view of the catheter housing18reveals the relatively blunt distal end62having a rounded edge64, an external tapered section60of the distal end of the catheter housing18, a generally tapered external portion corresponding to the barrel34, and the external threads56along the external portion of the catheter housing18. Along the internal surfaces of the catheter housing18, the cross section view reveals a generally tapered and smooth proximal internal surface36narrowing its diameter as the internal surface36travels from the proximal end of the housing18towards the tapered section38. The internal surface36further narrows its diameter as it travels along the grooves40, in a distal direction, towards the retention space54. The interior surface36may be formed, for example, as a six percent female Luer conical fitting according to ISO standard 594-1. The interior surface36may be formed in order to accommodate any of a variety of male Luer tips.

A retention space54is formed within each ridge58. Each ridge58separates one flash groove40from another flash groove40. The ridges58increase in height just distal from the retention spaces54and between the retention spaces54and the distally-located remainder of the narrowing lumen32. The retention spaces54are not as deep as the grooves40. That is, the grooves40cut deeper into the material of the catheter housing18than the retention spaces54. Thus, when the retention ring44is housed within the retention spaces54, there is still adequate space within each groove40between the outer surface of the retention ring44and the inner surface of the catheter housing18through which fluid may pass.

The limited amount of space between the retention ring44and the surface of the catheter housing18permits a controlled amount of flashback to occur during operation of the extravascular system10while the septum14is positioned within the retention spaces54. After the septum14is advanced distally, such that the retention ring44is moved from the retention spaces54to the tops of the ridges58, the space between the outer surface of the retention ring44and the inner surface of the catheter housing18will increase as the volume of the flash grooves40also increases.

As the volume of the flash grooves40increases, a greater amount of fluid will be permitted to flow between the septum14and the interior surface of the catheter housing18. This increased amount of fluid flow may be controlled and/or used by an operator and/or clinician of the extravascular system10in order to monitor and/or adjust the positioning of a needle and/or catheter12tip within the vasculature of a patient. As shown inFIG. 7, the flashback volume within the flashback grooves40will increase after the septum14is engaged by the tip of a separate vascular access device. However, the flashback volume within any flashback chamber and/or space such as the flashback grooves40may increase, decrease, and/or remain constant depending upon the particular use and/or configuration of the components of the extravascular system10. For example, the opposite of that shown inFIG. 7may be provided such that once the septum14is engaged by the tip of a separate access device, the retention ring44may move from a position of greater flashback volume to a position of lesser flashback volume as the corresponding flash grooves40decrease in volume.

In some implementations of the systems and methods of the present disclosure, the extravascular system10may include a catheter assembly and an internal construct associated so as to provide at least two configurations. For example, the extravascular system may provide one or more insertion configurations and one or more indwelling configurations. In some implementations, one of the insertion configurations may correspond to the configuration having the retention ring44disposed in the retention space54. Similarly, one or more of the indwelling configurations may be provided by the configurations wherein the internal construct14is moved distally and the retention ring44is supported on the flash ridges58. As discussed above, depending on the intended usage of the extravascular system10, the relative flow rates permitted in the various configurations may be selected to provide the desired functionality. For example, the flow rate may be greater or lesser in an insertion configuration and/or in an indwelling configuration. Additional discussion of flow rates in different configurations and methods of configuring the catheter assembly and the internal construct to provide the desired flow rates are discussed in greater detail below.

Referring toFIG. 8, a side view of the septum14is shown. The septum14includes a tapered conical nose66at its distal end adjacent the retention ring44. The retention ring44provides the greatest diameter68of the septum14. The septum14forms a generally cylindrical shape and includes at least one flow space48and contact surface50at the proximal end of the septum14.

Referring toFIG. 9, a proximal end view of the septum14ofFIG. 8is shown. The proximal end view illustrates the internal view of the slit70through which the point, tip, and/or cannula of a needle may extend. The slit70may be formed after molding the septum14and is seen inFIG. 9through the internal chamber52of the septum14. The proximal end view of the septum14also reveals the retention ring44forming the outer most surface along the circumference of the septum14. The proximal end view also reveals three contact surfaces50separated by three corresponding flow spaces48.

Referring toFIG. 10, a distal end view of the septum14ofFIG. 8is shown. The distal end view reveals the distal surface of the slit70cut across the axial center of the septum14. The distal end view also reveals the tapered nose66tapering towards the increased diameter of the retention ring44. The retention ring44forms the outer most circumferential surface of the septum14.

Referring toFIG. 11, the septum14ofFIGS. 8 through 10is shown in cross section view taken along lines A-A ofFIG. 10. The cross section view of the septum14reveals the slit70cut, molded, or otherwise formed through a septal disk72. The septal disk72forms a barrier capable of sealing fluid from without the internal chamber52of the septum14from the space within the internal chamber52. The disk72and slit70function to permit the passage of a needle through the slit70while limiting the passage of any fluid between the external surface of the needle and the internal surface of slit70of the disk72.

In one embodiment, the materials, dimensions, and/or orientations of the slit70and/or disk72may be modified in order to permit a certain amount of fluid flow between the external surface of a needle and the internal surface of the slit70when a needle is extending through the slit70. For example, a simple straight cut slit such as that shown inFIG. 9may in certain septal disks72having certain material properties permit a triangular shaped space on either end of the slit70to exist when a needle is extending through the slit70. Fluid such as blood and/or other infusate fluid may be transferred through the triangular shaped spaces between the needle and the ends of the slit70.

Such spaces may be preferable depending upon the desired use of the extravascular system10in order to provide blood flashback and/or other fluid communication helpful to the operation of the system10. However, such spaces may not be desired, for example where an operator of the system10desires to view the passage of all fluid within the extravascular system10and there are fluid routes alternate to the spaces. In examples where the septum14is formed of a material that is either not transparent or is difficult to see through, an operator wishing to visualize all fluid flow within the extravascular system10will prefer a system fluid travels only through visible fluid routes. For example, a system where the slit70seals entirely around the outer surface of the cannula of a needle such that no fluid may pass through the slit70and into the internal chamber52may advantageously require all fluid to pass around the exterior surface of the septum14, past the retention ring44, and between the exterior surface of the septum14and the interior surface of the transparent catheter housing18.

The cross section ofFIG. 11also partially illustrates two of the three flow spaces48separated from each other by a single contact surface50. As previously described, the contact surfaces50form a platform against which the tip of a male Luer or other structure of another vascular access device may be contacted. When the tip of a male Luer contacts the contact surfaces50, the tip may exert force against the contact surfaces50in order to advance the septum14in a distal direction within the lumen32of the catheter assembly12. If the proximal portion of the septum14included a continuous contact surface50for a tip of a male Luer to contact, any fluid transferred from within the lumen of the male Luer tip would be forced directly into, rather than around, the internal chamber52of the septum14.

Because the septal disk72is formed to be concave towards the proximal direction of the internal chamber52, after the needle has been withdrawn from the slit70, the slit70will become closed and sealed to fluid transfer. With the slit70closed within the convex septal disk72, no fluid will be permitted to escape the internal chamber52of the septum14. Thus, the purpose of an extravascular system10that enables fluid to be infused into the vascular system of a patient would be thwarted in such a system having a continuous contact surface50on the proximal portion of the septum14. Thus, to alleviate the fluid barrier that would otherwise exist, the flow spaces48have been cut, molded, or otherwise formed within the proximal portion of the septum14.

The fluid flow spaces48permit fluid to flow from within the lumen of a tip of a male Luer or other vascular access device into the internal chamber52, then from the internal chamber52through the fluid flow spaces48, and ultimately from the fluid flow spaces48distally around the external surface of the septum14within grooves formed on either the exterior surface of the septum14and/or the internal surface of the catheter housing18, such as the grooves40. Any number of flow spaces48and/or contact surfaces50may be formed in order to achieve the objective of providing a contact surface against which an additional vascular access device may contact and providing a means of flowing fluid through the extravascular system10into the vasculature of a patient. The flow spaces48may also vary in location. For example, the flow spaces48may be formed as holes through the center, midway between the proximal and distal ends of the septum14, such that fluid may flow into the chamber52, through the flow spaces48, and on towards the vasculature of a patient.

Referring toFIG. 12, a perspective view of the side and proximal end of the septum14is shown. The proximal view reveals the three contact surfaces50and the three corresponding flow channels48, the tapered end66, and the retention ring44. In addition, the outer surface of the septum14includes at least one flow channel or flow groove74through which fluid may travel. The at least one flow groove74is formed to originate at each of the contact surfaces50in the proximal end of the septum14and terminate at the retention ring44. In certain embodiments, the flow grooves74may extend through the retention ring44. The flow grooves74may be formed for purposes similar to the flow grooves40, that is, at least to provide fluid travel between the exterior surface of the septum14and the interior surface of the catheter housing18.

Referring toFIG. 13, a perspective view of the septum14illustrates the side and distal portions of the septum14. The perspective view illustrates the slit70within the disk72, the disk72surrounded by the tapered surface66, the tapered surface66adjacent the retention ring44, the at least one flow groove74terminating at the retention ring44and originating at a contact surface50, and the flow spaces48separated by the contact surfaces50. The septal disk72of the septum14described with reference toFIGS. 8 through 13is formed at the distal end of the septum14. However, the septal disk72may be formed along any portion of the length of the internal space52of the septum14. Further, various other configurations, features, structures, and/or orientations of the features of the septum14may be modified depending on the preferred use of an extravascular system10, as will be described and shown in another example of a septum in the following drawings.

Referring toFIG. 14, a cross section view of an alternate embodiment of a catheter housing18and a septum14is shown. The catheter housing18may house a wedge26having a distal taper28and a proximal taper30. The catheter housing18may also form threads56on its proximal external portion capable of engaging with corresponding threads on an additional vascular access device. The additional vascular access device may be inserted into the proximal end of the catheter housing18in order to come into contact with one or more contact surfaces50and advance the septum14distally within an internal lumen32of the catheter housing18. As the septum14advances distally through the lumen32, the volume within flash grooves40may increase between the exterior surface of a retention ring44of the septum14and an interior surface of the catheter housing18, as will be described in greater detail with reference toFIG. 15.

Referring toFIG. 15, a close-up cross section view of a portion of the septum14and catheter housing18is shown. The close-up cross section view illustrates that the depth of a groove40increases as the groove40advances distally along the internal lumen32of the catheter housing18. The grooves40of varying depth along the lumen32provide an environment that may be manipulated by an operator of the extravascular system10to which the catheter housing18may form part, in order to control the rate of flashback within the grooves40.

For example, an operator of the extravascular system10desiring a minimal flashback rate may advance the septum14in a distal direction within the lumen32to a minimal distance, such that the outer surface of the septum14such as the retention ring44is in contact with the ridges58between the grooves40at a point where the grooves40have a minimum depth. At a minimum depth, the grooves40will only permit a minimum amount of fluid communication and/or blood flashback to travel through the grooves40, between the outer surface of the septum14and the inner surface of the catheter housing18. Conversely, an operator who desires a maximum rate of fluid flow and/or blood flashback will advance the septum14through the lumen32to a point at which the exterior surface of the septum14corresponds with a maximum depth in the flow grooves40.

Returning toFIG. 14, the septum14is shown within the lumen32having been advanced to a maximum flow groove40depth, such that fluid will flow and/or blood will flashback within the grooves40and between the exterior surface of the retention ring44and the interior surface of the catheter housing18at a maximum flow rate. The maximum depth of the grooves40exists both in the location shown that corresponds with the retention ring44and at any point distal therefrom. The space between the current location of the septum14and the maximum insertion location of the septum14within the lumen32ofFIG. 14illustrates a distance76which compensates for and accommodates the differences in various Luer lengths that may be employed in conjunction with the catheter assembly12described with reference toFIG. 14. The distance compensation76has been discussed previously with reference to the embodiment illustrated inFIGS. 1 through 7.

Referring toFIG. 16, a proximal end view of the catheter housing18and septum14is shown. The proximal end view reveals the threads56on the external surface of the catheter housing18. The septum14is shown housed within the lumen32of the catheter housing18. The septum14reveals four contact surfaces50separating four corresponding flow spaces48. The lumen32also includes eight flow grooves40forming a volume between the exterior surface of the septum14and the interior surface of the lumen32of the catheter housing18.

Referring toFIG. 17, a proximal view of the catheter housing18without the septum14is shown. The proximal view reveals the lumen32extending through the axial center of the housing18. Eight flow channels40are uniformly spaced around the axial center of the housing18by neighboring flow channel ridges58.

Referring toFIG. 18, a side view of the septum14described with reference toFIGS. 14 through 16is shown. The side view of the septum14reveals a tapered distal end78having four flow channels80formed therein, a retention ring44forming the largest diameter of the septum14, a body82including four wide flow channels84, and a proximal end86including four flow channels48and four contact surfaces50. The distal end78of the septum14may include a flow ring88formed around its circumference in order to promote the distribution of fluids from one flow channel80to another flow channel80. Thus, the septum14described with reference toFIG. 18includes multiple flow channels, rings, and/or grooves80,88,84, and/or48capable of facilitating the communication of fluid into and around the exterior surface of the septum14. Fluid is able to travel through these grooves in between surfaces of the septum14and/or surfaces of the catheter housing18.

Referring now toFIG. 19, a proximal end view of the septum14ofFIG. 18is shown. The proximal end view illustrates the proximal surface of a slit70formed through a septal disk72. The proximal view also illustrates four contact surfaces50separating four flow spaces48and four flow channels84from each other.

Referring toFIG. 20, a distal end view of the septum14described with reference toFIGS. 18 and 19is shown. In the distal end view, the distal surface of the slit70formed within the disk72is shown. Also shown are four distal contact surfaces78separating four distal flow spaces80. The four distal flow spaces80are formed both within the distal end78and at least a portion of the retention ring44.

Referring toFIG. 21, a proximal perspective view of the septum14shows the proximal end and side of the septum14with its various features.

Referring toFIG. 22, a distal perspective view of the septum14shows the distal end and side of the septum14with its various features.

Referring collectively toFIGS. 23 through 25, a method of using an extravascular system10including a catheter housing18and septum14is described. In use, an operator or clinician will access the vasculature of a patient with the tip of a needle housed within the insertion portion of a catheter tubing16. Upon insertion of the tip of the needle into the vasculature, blood will flow into the inner lumen of the cannula of the needle, out a small exit point within or near the distal end of the needle, between the catheter tubing16and the exterior surface of the cannula, and in a proximal direction along the extravascular system10, giving the operator visual confirmation of proper placement of the needle tip within the vasculature of the patient. The blood will continue to flow along the inner lumen of the extravascular system10from the catheter tubing16into the wedge26and ultimately into the flash grooves40. The flash grooves40may operate to meter the volumetric flow rate of the blood out of the proximal portion of the catheter housing18and permit continued tertiary flashback confirmation to an operator of the extravascular system10.

As discussed briefly above, the extravascular systems of the present disclosure may be adapted to provide two or more configurations, including an insertion configuration. It is important for the clinician to observe the flashback of blood during the insertion process to ensure that the extravascular system is properly positioned in the vasculature. However, too much flashback can result in blood spilling or leaking out of the proximal end of the catheter assembly. Particularly problematic in conventional systems is the time period between withdrawal of the needle and attachment of another vascular access device, such as an IV line. Accordingly, as suggested above, the relationship between the retention construct44and the corresponding retention structure, such as flow grooves40and ridges58, may provide a space through which fluid, including blood, may flow. More particularly, the relationship between the retention construct and the corresponding retention structure may provide a flow space adapted to meter the fluid flow to a desired rate.

Additionally, the retention construct and the corresponding retention structure may be adapted to provide a variable flow space dependent at least in part on the position of the internal construct within the catheter housing. For example, it may be desirable to provide one or more insertion configurations and one or more indwelling configurations. When the extravascular assembly10is being inserted into a patient's vasculature, it may be preferred to provide an insertion configuration adapted to meter the fluid flow rate through the flow space between the retention construct and the corresponding retention structures, such as to limit the flow of blood during flashback to avoid exposure. In some implementations, the retention construct and the corresponding retention structure may be adapted to allow a fluid flow rate within a predetermined, target insertion flow rate range. For example, while a particular target rate may be desired, variations between patients', such as varying blood pressures or other factors, may result in an extravascular system adapted to provide a flow space allowing a flow rate within a given range of the target rate. One exemplary target flow rate may correspond to a progression of the fluid at a rate of about one inch per minute. In some implementations, a suitable flow rate range may correspond to a progression of fluid at a rate of at least about one inch per minute. While faster and slower rates are acceptable, during insertion such faster or slower rates may complicate the procedures of the clinicians.

During the use of the extravascular system, volumetric flow rate of the fluids is important to control the volume of fluid passing through the system. Additionally, however, during insertion of the extravascular systems when the flashback is being controlled, it is important to control the progress of the fluid through the catheter assembly so as to reduce the likelihood of the fluid reaching the proximal end of the catheter assembly. As can be appreciated, the progress of the fluid through the catheter assembly in the flow space created by the relationship between the retention construct and the corresponding retention structure will be determined by the volumetric flow rate and the geometries of the flow spaces. As used herein, flow rate may refer to volumetric flow rates and/or flow rates measured by the progress of a fluid through a system.

At any point during blood flashback in the extravascular system10, the catheter tip22of the catheter tubing16may be threaded into the vasculature of the patient and the needle may be removed from the extravascular system10. As the needle is withdrawn, the slit70within the septal disk72removes blood from the needle on the distal side of the septal disk72. When the needle is completely removed from the slit70, the slit70seals the axial flow path. When the axial flow path through the axial center of the extravascular system10is completely sealed, blood is forced to travel around the exterior surface of the septum14through the flow grooves40, providing continued flashback confirmation. It should be noted that during and after the withdrawal of the needle from the extravascular system, the internal construct14may remain in its insertion configuration to meter the flow of fluids past the internal construct. Accordingly, in implementations where the metered flow rate limits the progression rate of the fluid through the catheter housing, such limits may remain after the needle is withdrawn.

In most utilizations of an extravascular system10, the catheter housing18will then be coupled to a vascular access device after the needle is withdrawn. As illustrated inFIG. 24, the catheter housing18is accessed with the male tip90of a separate vascular access device92. As the tip90exerts force upon the contact surfaces50of the septum14, the septum14is collapsed within the flow grooves40and forced in a distal direction to a second or indwelling configuration. In some implementations, multiple indwelling configurations may be available by forcing the septum14in the distal direction to a greater or lesser degree. As illustrated, moving the septum14in a distal direction will open the volume of the flow grooves40to a greater volume and provide the separate vascular access device92with less restricted vascular access through which the device92may infuse fluids. The fluids travel from the lumen94of the device92into a chamber52of the septum14, from the chamber52through flow spaces48, from the flow spaces48around the exterior surface of the septum14and through the flow grooves40distally towards the vasculature of a patient. After infusion, the device92may then be removed from the catheter housing18as shown inFIG. 25.

Thus, the embodiments described with reference toFIGS. 1 through 25provide an extravascular system10having a compact, single component such as the septum14capable of collapsing upon Luer activation and operating as a valve that may be integrated into a number of catheter assemblies12. Such catheter assemblies12may include any conventional vascular access device such as a peripheral, PICC, midline, and/or arterial catheter assembly. The septum14is located within the interior lumen32of the respective catheter assembly12. A septum may act in part as a blood barrier sealing around the exterior surface of the cannula of a needle to prevent blood from passing through the central axis of the extravascular system10. A septum engages the internal diameter of the catheter housing and also provides a range of motion within the lumen32of the catheter housing18capable of accommodating a variety of Luer penetration depths.

The septum14collapses into a flow groove40space of the barrel34when accessed by a Luer, providing a potential variation in fluid communication among the various fluid chambers of the extravascular system10. The internal surface of the catheter housing and/or the external surface of the septum may include flow grooves to provide a primary path of blood and/or infusate fluid transfer before, during, and after the septum is activated or otherwise advanced distally within the lumen32. The flash grooves on any surface within the extravascular system10may be formed as axial or other grooves that are capable of allowing blood to bypass the outer retention ring44of the septum14, thus giving an operator of the extravascular system10a tertiary blood flashback confirmation at a controlled rate. The controlled rate may be carefully calculated and examples of such calculations will be described herein.

The embodiments described with reference toFIGS. 1 through 25provide multiple advantages over conventional extravascular systems. For example, the extravascular system prevents uncontrolled amounts of blood from spilling out of the proximal end of the catheter housing18while not entirely eliminating blood flashback therein. Such blood flashback may continue to flow within visible chambers of the extravascular system10at a controlled rate, permitting an operator of the extravascular system10enough time to operate the extravascular system10, exchange its preferred or necessary components or other vascular access devices. For example, as discussed above, a target flow rate may allow the blood to progress through the catheter housing at a rate of about one inch per minute. The controlled blood flow rate will prohibit blood from flowing through the extravascular system10at a rapid and uncontrolled rate capable of causing leaking or spilling during system10operation.

In addition, the internal septum14of the system10does not require a change in current clinical therapy of present extravascular systems. Rather, an operator of the system10may use the system10as the operator would any other extravascular system. However, the advantages of the present system will be available to such a system.

Further, the septum14and any equivalent or variation thereof may be employed within existing catheter platforms. And, as mentioned previously, the length of the barrel34accommodates various Luer access device penetration depths to provide an extravascular system10of relatively universal application. Since not all separate vascular access devices and/or male tips of Luer access devices are available in every country and/or clinical setting, a universal female Luer tip adapter on the proximal end of the catheter assembly12provides a significant advantage for the present invention.

Further, the controlled flashback features of the embodiments described with reference toFIGS. 1 through 25present advantages over previous valves that are completely sealed and impede any flow of blood through an extravascular system. By providing controlled flow in the relatively unsealed system10, an operator of the system10is provided with critical information necessary to properly locate, place, and maintain a needle and/or catheter tip within the vasculature of a patient during all steps of the operation of the extravascular system10. Such continuous information is not available during all operative steps in other previous valves and/or extravascular systems. The septum14is a single component that also eliminates the need in previous systems to provide multiple components capable of piercing through the septum14and/or the slit70of the septum14in order to provide fluid access to a separate vascular access device after the septum14is activated. Because a septum14includes multiple fluid passageways such as the fluid spaces48, fluid may flow into and around the septum14without any further obstruction after the septum14has been activated upon and towards flow grooves40having adequate volume to receive the infused fluid from the separate vascular access device. Thus, where previous systems would have sent the fluid flow through the central axis of the system10, the present system10provides a primary flow path that is around the exterior surface of the septum14.

In addition to the flow spaces48and/or holes formed within the walls of the body82of the septum14, or as an alternate flow path thereto, other flash features such as holes through the internal septal disk72or other features that provide fluid communication between various fluid chambers of the system10at various steps of operation of the system10may be employed in order to provide fluid communication for blood flashback, blood withdrawal, and for fluid infusion into the vasculature of a patient.

The embodiments described with reference toFIGS. 1 through 25and any other embodiments within the scope of the present invention enable the passage of air, blood, and/or other fluid to pass at a controlled rate with varying blood densities, viscosities, venous pressures, and/or atmospheric pressures. As described above, the flow rate around the internal construct14may vary depending on the intended usage of the extravascular system and the current operational configuration of the extravascular system. For example, when the extravascular assembly has been inserted and fluids are being infused or blood is being withdrawn, the flow rate around the valve of the septum14preferably may be greater than the flow rate within the catheter tubing16between the internal surface of the catheter tubing16and the external surface of the needle cannula, especially with regards to the flow of blood through the system10. In the context of withdrawing blood for donation or analysis, the sheer and exposure time may be minimized in order to prevent hemolysis by ensuring that the catheter tubing16is the flow rate limiter within the system10. Thus, the geometry of the various flow spaces within the extravascular system may be defined to allow for the catheter tubing16to be the flow rate limiter rather than other portions of the system10. However, various other portions of the system10may become the flow rate limiter in order to achieve various alternate objectives of a system10, such as to control the flashback rate. Various calculations may be performed in order to determine appropriate size of various flow channels within the extravascular system10in order to achieve the principles discussed herein. Exemplary equations and calculations are presented below together with exemplary values for the variables of the equations. While the calculations presented below are illustrative of the methods of using the equations, they may not be representative of the variable values or results of extravascular assemblies. For example, the flow rates, sizes, and other values may vary from those presented herein.

The following equations may be used to size the flow and/or flash grooves40and/or any other channel through which fluid may flow in an extravascular system10in order to minimize hemolysis, maximize flow rate through the system10, and/or allow controlled flashback of blood prior to access by a separate vascular access device92. The following calculations assume fluid properties that are similar to blood, including viscosity and density, such as H2O with glycerin. The following calculations also assume that the atmospheric pressure at the tip of the catheter tubing16is at zero pounds per square inch (psi) both before and just prior to insertion into the vascular system of a patient.

The flow rate through the extravascular system10may be limited by the configuration of any one or more flow spaces. As discussed above, in some implementations or during certain phases of use, it may be preferred for the flow rate to be limited at least in part by the internal construct14and in other circumstances it may be preferred for the flow rate to be limited primarily by the catheter tubing16. One critical flow space includes the flow rate through the flow grooves40adjacent or near the septum14. The flow rate through the area of the flow grooves40may be calculated using the following equation:

Q=π·deq4·(P⁢⁢3-P⁢⁢2)128·μ·L·K⁢⁢3⁢_⁢2
where Q equals the flow rate through the flow grooves40.

In the above equation, deq is the equivalent diameter of the area of all flow grooves40combined. The equivalent diameter of the area of the flow grooves40may be calculated using the following calculation:

deq=4·Aπ
where A equals the flow groove area, which is calculated by measuring the dimensions of the flow grooves40when the septum14is in a given position. It should be noted that the flow groove area A may vary when the septum is in different positions, such as an insertion configuration compared to an indwelling configuration, and the flow rate through the grooves Q will vary accordingly. The variable P3 is an arbitrary pressure which may exist within the extravascular system10. The variable P2 is the atmospheric pressure. The variable μ equals

0.0002⁢lbin·s
and represents parameters of simulated blood flow through the flow grooves40. The variable L represents the length along the flow grooves40through which fluid must flow in order to pass the entire length of the septum14. The variable K3—2 represents the loss factor moving from the proximal end of the wedge26to the proximal end of the septum14. The loss factor may be calculated along any length within the extravascular system10. In common extravascular systems10, the loss factor includes multiple 90 degree bends and fluid transitions from a reservoir into a channel and from a channel into a reservoir. Other factors may be included within the loss factor calculation.

In an illustrative example, the variable A may equal 0.0054 inches squared and the pressure values may provide P3 equal to 0.922 psi and P2 equal to 0 psi. As indicated, the variable μ represents a parameter determined from simulated blood flow through the grooves, and may be equal to

0.0002⁢⁢lbin·s.
The length L may be any suitable measurement, and for purposes of this illustration may be equal to 0.2043 inches. Continuing with the illustrative calculation, the loss factor calculation is 7.5 for each of six separate flow grooves40, yielding a total loss factor (K3—2) of 45. Applying the values of the variables in the equation above to calculate flow rate (Q) yields a result of Q equals

241.2245⁢mLmin.
the flow rate of 241.2245 is the volumetric flow rate of fluid, which may be blood or another comparable fluid such as intravenous fluids, as it exits the flow grooves40between the exterior surface of the septum14and the interior surface of the catheter housing18and at the proximal end of the septum14.

In addition to determining the flow rate (Q) through the flow grooves40in the presence of a septum14, one may desire to determine the flow rate through the catheter tubing16within the system10in the absence of a septum14. Such a calculation will reveal the maximum flow rate through the system10in the absence of a septum14and may be used to reduce the risk of contaminating or spoiling fluids passing through the catheter, such as blood withdrawn for analysis or donation and/or infused fluids. Where the flow rate in the absence of a septum14is the same as or similar to the flow rate through a common catheter assembly, equations for determining this flow rate have been researched and published previously, such as by M. Keith Sharp, “Scaling of Hemolysis in Needles and Catheters”, Annuals of Biomedical Engineering, Vol. 26, pp. 787-797, 1998. One suitable method of calculating this flow rate, identified as variable Qcmay use the following equation:

The variable d1 is the inner diameter at the most distal tip of the catheter tubing16, which for purposes of calculation may be assumed to creep or approach the outer diameter of a cannula of a needle that would function with the catheter tubing16. The inner diameter of the catheter tubing16at the most distal tip of the catheter tubing16will vary depending on the gauge of needle that is used in combination with the particular tubing16. Multiple needle gauges from 14 through 24 and their associated catheter tubing16diameters are illustrated in the following table.

The variables P3 and P1 include different pressures both within the system10(P3) and at the most distal tip of the catheter16(P1). These pressures may include various values, such as 0.922 psi for variable P3 and 0 psi for variable P1. The variable μ may include the same value as described earlier, that is,

0.0002⁢lbin·s.
The variable L1—2 represents the length of the catheter tubing16from its most distal tip to its most proximal end. For example, the length from tip22to the proximal end of the proximal taper30as shown inFIG. 1, may vary from one system10to another depending upon the specific gauge of the needle employed with the catheter tubing16. The following table sets forth examples of various values of the length of the catheter tubing with corresponding needle gauges.

The variable K1—2 represents the loss factor across the length of the catheter tubing16. The loss factor K1—2 may be calculated using the following calculation.

K⁢⁢1⁢_⁢2=f·L⁢⁢1⁢_⁢2d⁢⁢1
The variable f within the calculation above represents the friction factor across the length of the catheter tubing16. The friction factor, similar to variables d1 and L1—2, will vary depending on the needle gauge employed with the catheter tubing16. The following table illustrates various friction factors that correlate to various needle gauges taken from M. Keith Sharp, “Scaling of Hemolysis in Needles and Catheters”, Annuals of Biomedical Engineering, Vol. 26, pp. 787-797, 1998. The friction factor corresponding to each needle gauge is representative of the friction factor across the length of a corresponding catheter tubing.

Using the equation above to calculate the loss factor across the length of the catheter tubing16, various values that correspond to various needle gauges may be calculated for the variable K1—2, as shown in the following table.

By incorporating each of the values for the variables above into the equation to calculate volumetric flow rate leaving the catheter22without a septum14, that is, the flow rate Qc, will yield the results illustrated in the table below.

By comparing the results for the flow rate Q and the flow rate Qcin the examples above, it is apparent that the flow rate Q through the flow grooves40of

241.2245⁢mLmin
is greater than the flow rate Qcthrough the catheter tubing16for all gauge sizes with exception of a 14 gauge needle. Accordingly, the parameters and values used in the illustrative example for determining flow rate Q may correspond to an extravascular system configured in an indwelling position in which the fluid flow is relatively unrestricted or unmetered by the internal construct14. In some implementations, it may be preferred to ensure that the catheter tubing16and/or catheter tip22is the flow rate limiter rather than the septum14when in an indwelling position. Accordingly, the illustrative example above may be suitable for use with 16 gauge needles and smaller. For 14 gauge needles and larger, the area of the flow grooves40or any other flow channels may be increased sufficient to ensure that the catheter tip22and/or catheter tubing16is the flow rate limiter within the system10, when such a configuration is desired, such as to minimize hemolysis and/or to maximize flow rate. However, as mentioned above, in other implementations or during other phases of use, it may be preferred to control and meter the fluid flow rate through the catheter housing by way of the internal construct14applying flow restrictions.

Referring toFIG. 26, results similar to those calculated above are illustrated in a chart comparing flow within a catheter tubing16accommodating a 14 gauge needle, flow within a catheter tubing16accommodating an 18 gauge needle, and the flow within the grooves40surrounding a septum14. The results indicated in the chart ofFIG. 26again confirm that the flow rate through the flow grooves40surrounding the septum14is greater than the flow rate through a catheter tube16accommodating an 18 gauge needle but not greater than the flow rate through a catheter tubing16accommodating a 14 gauge needle. In addition to calculating and comparing various flow rates within the extravascular system10, calculations determining the blood shear stress and exposure time across the flow grooves40near the septum14may be helpful in order to determine the expected level of hemolysis within the system10. Determining the expected level of hemolysis within the flow grooves40may enable a manufacturer of the system10to determine the appropriate flow groove dimensions and area. The hemolysis of the flow grooves40may be calculated by a constant C·exp(S), where the variable S represents the exposure to sheer stress that may be calculated using the following equation.

S=t_fgto⁢(τ_fgτ⁢⁢o-1)2
The variable t_fg may be calculated using the following calculation, which measures the blood exposure time to sheer stress.

t_fg=32·μ·L2(P⁢⁢6-P⁢⁢5)·deq2
The variables μ, L, and deq have already been defined previously. The variable P5 equals 0 psi and the variable P6 equals 69000 Pa (the vapor pressure of blood, or the maximum vacuum which may be pulled on a syringe before causing cell damage within blood). Applying the values previously mentioned herein to the variables of the equation above yields a result of t_fg equals 1.64×10−5seconds for the blood exposure time to sheer stress. It should be noted that the value of t_fg will vary depending on the input variables, such as the flow area (deq) and the length (L); in general it has been observed that t_fg may have any value greater than 1×10−6. The variable toequals 0.0158 seconds. The variable τ_fg may be calculated to determine the sheer stress of blood in the flow channels40using the following equation.

τ_fg=(P⁢⁢6-P⁢⁢5)·deq4·L
The result of the above equation is τ_fg equals

70012.0303⁢dynecm2.
The variable τo is

Applying the values above to the variables of the equations above yields a result for the hemolysis within the flow grooves40equal to

5.7664⁢mgd⁢⁢1.
Because the hemolysis level of

5.7664⁢mgd⁢⁢1
is below

10⁢mgd⁢⁢1
(the threshold of visual hemolysis) and below

30⁢mgd⁢⁢1
(the threshold in which no interference occurs with chemical assays), the area of the flow grooves40in the example above is sufficient to maintain a desired level of hemolysis.

The illustrative calculations above are generally directed towards determining the flow rates and conditions when the septum14is positioned in an indwelling configuration, which generally provides greater flow rates and larger flow spaces. However, such calculations and similar calculations may also be helpful in determining the operating conditions and/or manufacturing specifications for configuring the extravascular system10in an insertion configuration adapted to meter fluid flow with the internal construct14. For example, it may be desirable to determine the amount of time an operator may permit blood to flow through the system10before blood begins to spill out of the proximal end of the system10. The calculation of the amount of time needed for blood to travel from the distal most tip of the catheter tubing16to the most proximal end of the catheter housing18may be included in calculation and consideration of multiple variables, such as the venous pressure, the atmospheric pressure, the length of the septum14, the area of the flash grooves40, the loss factor moving across the length of the system10, the volumetric flow rate of blood through the system10, and the total volume within the system10capable of housing blood. Similar to the discussion above, illustrative calculations utilizing exemplary values for the variables are provided below. While the exemplary values for the variables used below may be accurate for some implementations, other extravascular systems10within the scope of the present disclosure may provide different results. For example, the examples below produce a total time of 0.3982 seconds to fill the space in the inner chamber32between the proximal end of the septum14and the proximal end of the catheter housing18. However, other systems may take more time to fill the same. Exemplary extravascular systems10within the scope of the present disclosure may provide an insertion configuration adapted to provide a flow rate corresponding to a fluid progression rate of about one inch per minute, as discussed above.

The time to fill the space within the chamber32will be calculated by the total fill volume (fill_volume) divided by the flow rate (Q_vg) of fluid within the system10. The following examples of equations and variables may be employed within a calculation to determine the time to fill the space within the end of the chamber32.
P—v=0.5·psi (Average Venous Pressure)
P—rs=0·psi (Venting to Atmosphere)
L=0.2043·in (Valve Length)
A—vg=0.001·in2(Flash Groove Area)

The loss factors mentioned in any of the calculations above may include any environment within the system10capable of causing a variation in friction. For purposes of simplicity, the 90 degree bends, reservoir to channel entrance, and channel to reservoir entrance have been used. However, any variety of frictional loss factors capable of calculation may be used such as frictional loss factors at valves, 180 degree return bends, pipe entrances (reservoir to pipes), elbows, tees, pipe exits (pipe to reservoir), and/or any other frictional loss factor environment. Such frictional loss factor environments may include globes, angles, gates, spring checks, flanged and/or threaded return bends, square connections, rounded connections, re-entries, 90 degree angles, 45 degree angles, line flows, branch flows, and/or any other frictional loss factor environmental structure.