Patent Publication Number: US-2021186394-A1

Title: Catheter extension set and related methods

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 62/951,736, filed Dec. 20, 2019, and entitled CATHETER EXTENSION SET AND RELATED METHODS, which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     A catheter is commonly used to infuse fluids into vasculature of a patient. For example, the catheter may be used for infusing normal saline solution, various medicaments, or total parenteral nutrition. The catheter may also be used for withdrawing blood from the patient. 
     The catheter may include an over-the-needle peripheral intravenous (“IV”) catheter. In this case, the catheter may be mounted over an introducer needle having a sharp distal tip. The catheter and the introducer needle may be 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 skin of the patient. The catheter and introducer needle are generally inserted at a shallow angle through the skin into vasculature of the patient. 
     In order to verify proper placement of the introducer needle and/or the catheter in the blood vessel, a clinician generally confirms that there is “flashback” of blood in a flashback chamber of the catheter assembly. Once placement of the needle has been confirmed, the clinician may temporarily occlude flow in the vasculature and remove the needle, leaving the catheter in place for future blood withdrawal or fluid infusion. 
     For blood withdrawal or collecting a blood sample from a patient, a blood collection container may be used. The blood collection container may include a syringe or a test tube with a rubber stopper at one end. In some instances, the blood collection container has had all or a portion of air removed from the test tube so pressure within the blood collection container is lower than ambient pressure. Such a blood collection container is often referred to as an internal vacuum or a vacuum tube. A commonly used blood collection container is a VACUTAINER® blood collection tube, available from Becton Dickinson &amp; Company. 
     The blood collection container may be coupled to the catheter. When the blood collection container is coupled to the catheter, a pressure in the vein is higher than a pressure in the blood collection container, which pushes blood into the blood collection container, thus filling the blood collection container with blood. A vacuum within the blood collection container decreases as the blood collection container fills, until the pressure in the blood collection container equalizes with the pressure in the vein, and the flow of blood stops. 
     Unfortunately, as blood is drawn into the blood collection container, red blood cells are in a high shear stress state and susceptible to hemolysis due to a high initial pressure differential between the vein and the blood collection container. Hemolysis may result in rejection and discard of a blood sample. The high initial pressure differential can also result in catheter tip collapse, vein collapse, or other complications that prevent or restrict blood from filling the blood collection container. As the blood collection container fills, a pressure differential between the vein and the blood collection container decreases, and filling of the blood collection tube with blood slows significantly. 
     The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one example technology area where some implementations described herein may be practiced. 
     SUMMARY 
     The present disclosure generally relates to an extension set for a vascular access device, as well as related devices, systems, and methods. In some embodiments, a vascular access system may include the extension set coupled to the vascular access device. In some embodiments, the vascular access device may include a catheter, a needle, or another device suitable for blood collection. 
     In some embodiments, during blood collection, the extension set may facilitate adjustment of flow resistance within the vascular access system based on a pressure state within the vascular access system. In further detail, in some embodiments, as a pressure differential between a vein of a patient and a blood collection container coupled to the vascular access system changes during blood collection, the extension set may be responsive and may facilitate adjustment of flow resistance within the vascular access system. In some embodiments, the extension set may decrease a risk of hemolysis. In some embodiments, the extension set may simultaneously decrease the risk of hemolysis and decrease blood collection time during a process of blood withdrawal. In some embodiments, the extension set may also reduce a risk of collapse of the vein and/or the vascular access device. 
     In some embodiments, in response to the pressure differential being high, such as when the blood collection container is first coupled to the vascular access system, the extension set may facilitate increased flow resistance within the vascular access system to distribute the pressure differential and reduce shear stress experienced by red blood cells. In some embodiments, as the blood collection container fills with blood, a vacuum within a fluid pathway of the vascular access system may decrease, and the pressure differential may decrease. Thus, in some embodiments, in order to shorten the blood collection time, the extension set may facilitate decreased flow resistance within the vascular access system while still maintaining the shear stress of the blood cells below a threshold level. 
     In some embodiments, the extension set may be configured to couple to a catheter assembly and may be referred to as a catheter extension set. In some embodiments, the extension set may include a distal end, which may include a luer adapter configured to couple to a catheter adapter or another suitable vascular access device. In some embodiments, the extension set may include a proximal end, which may include a blood collection device. In some embodiments, the blood collection device may include or correspond to a blood collection container. In some embodiments, the blood collection container may include a syringe, an evacuated blood collection tube, a small sample collection device, or any other container configured to collect blood from a patient via a pressure differential. In some embodiments, the blood collection device may include a needle assembly, which may include a needle configured to receive the blood collection container. In these and other embodiments, the blood collection container may include the evacuated blood collection tube. 
     In some embodiments, the extension set may include an extension tube, which may extend between the distal end of the extension set and the proximal end of the extension set. In some embodiments, the extension set may include a clamp, which may be disposed on the extension tube. In some embodiments, the clamp may be configured to move between a clamped position and an unclamped position. In some embodiments, the clamp may prevent or reduce fluid flow through the extension tube in response to the clamp being in the clamped position. 
     In some embodiments, the luer adapter may be a first luer adapter. In some embodiments, the blood collection device may include a second luer adapter. In some embodiments, the extension set may include a third luer adapter, which may be coupled to the second luer adapter. In some embodiments, the extension tube may include a distal end and a proximal end. In some embodiments, the distal end of the extension tube may be integrated with the first luer adapter. In some embodiments, the proximal end of the extension tube may be integrated with the third luer adapter. In other embodiments, the proximal end of the extension tube may be integrated with the blood collection device. 
     In some embodiments, the extension tube may include an absorbent material or an indicator tube. In some embodiments, an inner surface of the extension tube may include an absorbent material or an indicator tube. In some embodiments, the absorbent material and/or the indicator tube may include one or more markers. In some embodiments, blood within the extension tube may be configured to flow proximate the absorbent material or through the indicator tube. In some embodiments, in response to blood reaching or saturating a particular marker, a clinician may change the flow resistance within the vascular access system via the extension set. In some embodiments, to decrease the flow resistance within the vascular access system, the clinician may remove the extension set from the vascular access system, move the clamp to the unclamped position, or perform another action to decrease the flow resistance as may be further described in the present disclosure. 
     In some embodiments, the extension set may include one or more extension tubes. In some embodiments, the extension tube may be a first extension tube. In some embodiments, the extension set may include a second extension tube. In some embodiments, a flow resistance of the first extension tube may be greater than a flow resistance of the second extension tube. For example, the first extension tube may be longer than the second extension tube. Additionally or alternatively, in some embodiments, an inner diameter of the first extension tube may be less than an inner diameter of the second extension tube. In some embodiments, the flow resistance of the first extension tube may be equal to the flow resistance of the second extension tube. In some embodiments, the second extension tube may include any combination of length and inner diameter such that the flow resistance of the second extension tube is the same or less than the flow resistance of the first extension tube. 
     In some embodiments, the first extension tube and the second extension tube may extend between the distal end of the extension set and the proximal end of the extension set. In some embodiments, the clamp may be disposed on the second extension tube. In some embodiments, the second extension tube may extend through the clamp. In some embodiments, the second extension tube may include the absorbent material or the indicator tube. In some embodiments, blood within the second extension tube may be configured to flow proximate the absorbent material or through the indicator tube. 
     In some embodiments, the first extension tube may be disposed within the second extension tube. In some embodiments, in response to the clamp being in the clamped position, blood may flow through the first extension tube, and blood flow between an outer surface of the first extension tube and an inner surface of the second extension tube may decrease or stop. In some embodiments, to decrease or stop the flow resistance within the vascular access system after the blood collection container is partially filled and the pressure differential has decreased, the clinician may move the clamp to the unclamped position to increase a flow rate given the pressure differential has decreased. 
     In some embodiments, the second extension tube may include a distal end and a proximal end. In some embodiments, the distal end of the first extension tube and the distal end of the second extension tube may be integrated with the first luer adapter. In some embodiments, the proximal end of the first extension tube and the proximal end of the second extension tube may be integrated with the third luer adapter. 
     In some embodiments, in response to the second luer adapter being tightened with respect to the third luer adapter, a first fluid pathway through the first extension tube may be open, and a second fluid pathway through the second extension tube may be closed. In some embodiments, in response to the second luer adapter being loosened with respect to the third luer adapter, the first fluid pathway through the first extension tube may be open, and the second fluid pathway through the second extension tube may be open. In some embodiments, to decrease the flow resistance within the vascular access system after the blood collection container is partially filled and the pressure differential has decreased, the clinician may loosen the second luer adapter with respect to the third luer adapter or move the second luer adapter from a tightened position to a loosened position. As a result, in these and other embodiments, a flow rate may increase. 
     In some embodiments, the extension set may include a pressure-sensitive valve within the extension set. In some embodiments, the pressure-sensitive valve may be disposed in the second extension tube. In some embodiments, the pressure-sensitive valve may be disposed in a portion of the fluid pathway of the extension set distal to the first extension tube and the second extension tube. In some embodiments, the fluid pathway of the extension set may extend through the proximal end of the extension set and the distal end of the extension set. In some embodiments, the fluid pathway of the extension set may include the first fluid pathway of the first extension tube and/or the second fluid pathway of the second extension tube. In some embodiments, the pressure-sensitive valve may be disposed at a junction of the first fluid pathway and the second fluid pathway. 
     In some embodiments, in response to a first predetermined pressure differential within the extension set, the pressure-sensitive valve may be open with respect to the first extension tube and closed with respect to the second extension tube. In some embodiments, in response to a second predetermined pressure differential within the extension set, the pressure-sensitive valve may be closed with respect to the first extension tube and open with respect to the second extension tube. In some embodiments, the first predetermined pressure differential may be greater than the second predetermined pressure differential. In some embodiments, the first predetermined pressure differential and the second predetermined pressure differential may correspond to the pressure differential between the vein of the patient and the blood collection container coupled to the vascular access system. 
     In some embodiments, a method of blood collection or collecting a blood sample may include inserting a catheter of a catheter system into vasculature of the patient. In some embodiments, the catheter system may include a catheter assembly, which may include a catheter adapter and the catheter. In some embodiments, the catheter may be secured within the catheter adapter and may extend distally from the catheter adapter. 
     In some embodiments, the method of blood collection may include coupling the extension set to the catheter adapter. In some embodiments, the method of blood collection may include blocking blood flow through the second extension tube. In some embodiments, after inserting the catheter of the catheter system into the vasculature of the patient, coupling the catheter extension set to the catheter adapter, and blocking blood flow through the second extension tube, the method of blood collection may include coupling a blood collection container to the blood collection device or the third luer adapter. In some embodiments, in response to coupling the blood collection container to the blood collection device or the third luer adapter, the blood collection container may begin to fill with blood. In some embodiments, in response to the blood collection container filling partially with blood, the method of blood collection may include opening the second extension tube such that increased blood flows through the second extension tube. 
     In some embodiments, the second extension tube may extend through the clamp. In these embodiments, blocking blood flow through the second extension tube may include moving the clamp to the clamped position, and opening the second extension tube may include moving the clamp to the unclamped position. In some embodiments, blocking blood flow through the second extension tube may include tightening the second luer with respect to the third luer adapter. In some embodiments, opening the second extension tube may include loosening the second luer with respect to the third luer adapter. 
     In some embodiments, the extension set may include a roller clamp. In some embodiments, the roller clamp may include a roller moveable within a track. In some embodiments, the first extension tube and the second extension tube may extend through the roller clamp generally perpendicular to the track. In some embodiments, when blood flow through the second extension tube is blocked, the roller may be disposed in a first position proximate the second extension tube. In some embodiments, opening the second extension tube may include moving the roller along the track away from the second extension tube and toward the first extension tube. 
     In some embodiments, the distal end of the extension set may include a three-way stopcock, which may include a first port, a second port, and a third port. In some embodiments, the first extension tube may be coupled with the first port, the second extension tube may be coupled to the second port, and the third port may include the first luer adapter configured to couple to the catheter adapter. In some embodiments, blocking blood flow through the second extension tube may include rotating the three-way stopcock to a first position. In some embodiments, opening the second extension tube may include rotating the three-way stopcock to a second position. 
     It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the invention, as claimed. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings. It should also be understood that the embodiments may be combined, or that other embodiments may be utilized and that structural changes, unless so claimed, may be made without departing from the scope of the various embodiments of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Example embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1A  is an upper perspective view of an example extension set, according to some embodiments; 
         FIG. 1B  is a cross-sectional view of the extension set of  FIG. 1A , according to some embodiments; 
         FIG. 1C  is an upper perspective view of the extension set of  FIG. 1A  coupled to an example catheter assembly, according to some embodiments; 
         FIG. 2A  is an upper perspective view of another example extension set, according to some embodiments; 
         FIG. 2B  is a cross-sectional view of the extension set of  FIG. 2B , according to some embodiments; 
         FIG. 2C  is an upper perspective view of the extension set of  FIG. 2A  coupled to the catheter assembly of  FIG. 1C , according to some embodiments; 
         FIG. 3A  is an upper perspective view of another example extension set, according to some embodiments; 
         FIG. 3B  is a cross-sectional view of the extension set of  FIG. 3A  coupled to another example catheter assembly, according to some embodiments; 
         FIG. 3C  is an upper perspective view of the extension set of  FIG. 3A  coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 4A  is an upper perspective view of another example extension set, according to some embodiments; 
         FIG. 4B  is an upper perspective view of the extension set of  FIG. 4A  coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 4C  is a cross-sectional view of the extension set of  FIG. 4A  coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 5A  is a schematic diagram of the extension set of  FIG. 3A , illustrating an example clamp in a clamped position prior to entry of blood into the extension set, according to some embodiments; 
         FIG. 5B  is a schematic diagram of the extension set of  FIG. 3A , illustrating blood flowing through an example first extension tube under a high initial pressure differential, according to some embodiments; 
         FIG. 5C  is a schematic diagram of the extension set of  FIG. 3A , illustrating the clamp removed or unclamped in response to a lower pressure differential, according to some embodiments; 
         FIG. 6A  is a cross-sectional view of an example second luer adapter and an example third luer adapter prior to being coupled together, according to some embodiments; 
         FIG. 6B  is a cross-sectional view of the second luer adapter and the third luer adapter of  FIG. 6A , illustrating the second luer adapter tightened with respect to the third luer adapter, according to some embodiments; 
         FIG. 6C  is a cross-sectional view of the second luer adapter and the third luer adapter of  FIG. 6A , illustrating the second luer adapter loosened with respect to the third luer adapter, according to some embodiments; 
         FIG. 7A  is an upper perspective view of an example roller clamp that may be used with the extension set of  FIG. 3A  or the extension set of  FIG. 4A , according to some embodiments; 
         FIG. 7B  is a cross-sectional view of the roller clamp of  FIG. 7A , illustrating an example roller in an example first position, according to some embodiments; 
         FIG. 7C  is a cross-sectional view of the roller clamp of  FIG. 7B , illustrating the roller in an example second position, according to some embodiments; 
         FIG. 8  is a cross-sectional view of another example extension set coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 9A  is an upper perspective view of another example extension set coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 9B  is an enlarged upper perspective view of a portion of the extension set of  FIG. 9A , according to some embodiments; 
         FIG. 9C  is a cross-sectional view of the extension set of  FIG. 9A , according to some embodiments; 
         FIG. 9D  is a transverse cross-sectional view of the extension set of  FIG. 9A , illustrating another example first extension tube disposed within an example second extension tube and the second extension tube clamped, according to some embodiments; 
         FIG. 9E  is a transverse cross-sectional view of the extension set of  FIG. 9A , illustrating the first extension tube disposed within the second extension tube, according to some embodiments; 
         FIG. 10A  is a cross-sectional view of a portion of another example first extension tube, illustrating an example absorbent material prior to entry of blood into the first extension tube, according to some embodiments; 
         FIG. 10B  is a cross-sectional view of the portion of the first extension tube of  FIG. 10A , illustrating the absorbent material in response to blood flowing through the first extension tube under a high initial pressure differential, according to some embodiments; 
         FIG. 11A  is a cross-sectional view of a portion of another example first extension tube, illustrating an example indicator tube prior to entry of blood into the first extension tube, according to some embodiments; 
         FIG. 11B  is a cross-sectional view of the portion of the first extension tube of  FIG. 11A , illustrating the indicator tube in response to blood flowing through the first extension tube under the high initial pressure differential, according to some embodiments; 
         FIG. 12A  is a cross-sectional view of an example junction between another example first extension tube and an example second extension tube, illustrating the junction prior to entry of blood into the junction, according to some embodiments; 
         FIG. 12B  is a cross-sectional view of the junction of  FIG. 12A , illustrating the junction in response to blood flowing through the junction under the high initial pressure differential, according to some embodiments; 
         FIG. 12C  is a cross-sectional view of the junction of  FIG. 12A , illustrating the junction in response to blood flowing through the junction under a lower pressure differential compared to the high initial pressure differential, according to some embodiments; 
         FIG. 13  is a partial cutaway view of another example extension set coupled to the catheter assembly of  FIG. 3B , according to some embodiments; 
         FIG. 14A  is an upper perspective view of an example catheter system, according to some embodiments; and 
         FIG. 14B  is an upper perspective view of another example catheter system, according to some embodiments. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring now to  FIGS. 1A-1C , in some embodiments, an extension set  10  may include a distal end  12 , which may include a luer adapter  14  configured to couple to a catheter adapter or another suitable vascular access device. In some embodiments, the extension set  10  may include a proximal end  16 , which may include a blood collection device  18 . In some embodiments, the blood collection device  18  may include or correspond to a blood collection container. In some embodiments, the blood collection container may include a syringe, an evacuated blood collection tube, a small sample collection device, or any other container configured to collect blood from a patient via a pressure differential. 
     In some embodiments, the blood collection device  18  may include a needle assembly  19 , which may include a needle  20  configured to receive a blood collection container. In these and other embodiments, the blood collection container may include the evacuated blood collection tube. In some embodiments, the blood collection container has all or a portion of air removed so pressure within the blood collection container is lower than ambient pressure. 
     In some embodiments, the needle assembly  19  may include one or more threads, which may be configured to couple to a holder  22 , which may be generally cylindrical and may be configured to hold the blood collection container. In some embodiments, the holder  22  may be integrally formed with the needle assembly  19  or coupled to the needle assembly  19  via bonding or another suitable method. In some embodiments, the holder  22  may surround the needle  20 . In some embodiments, the needle assembly  19  and the holder  22  may include or correspond to a luer lock access device, such as, for example, the VACUTAINER® LUER-LOK™ ACCESS DEVICE available from Becton Dickinson &amp; Company. In some embodiments, the holder  22  may include or correspond to the blood collection tube holder 127 described in U.S. Patent Application No. 62/928,69, filed Oct. 30, 2019, entitled “BLOOD COLLECTION SYSTEM WITH USER-ADJUSTED PRESSURE MANAGEMENT AND RELATED METHODS,” which is incorporated by reference in its entirety. 
     In some embodiments, the luer adapter  14  may be a first luer adapter  14 . In some embodiments, the extension set  10  may include a second luer adapter  24 . In some embodiments, the blood collection device  18  may include the second luer adapter  24 . In some embodiments, the needle  20  may be integrated with the second luer adapter  24 . In some embodiments, a proximal end of the needle  20  may be enveloped within an elastomeric sheath  26 . In some embodiments, the elastomeric sheath  26  may include an open distal end  28  and a closed proximal end  30 . In some embodiments, in response to the blood collection container pushing the elastomeric sheath  26  distally, the needle  20  may pierce the elastomeric sheath  26 , and the needle  20  may insert into a cavity of the blood collection container. 
     In some embodiments, the extension set  10  may include an extension tube  32 , which may extend between the distal end  12  of the extension set  10  and the proximal end  16  of the extension set  10 . In some embodiments, the extension tube  32  may be rigid or semi-rigid, which may reduce a likelihood of kinking. 
     In some embodiments, the extension set  10  may include a third luer adapter  34 , which may be coupled to the second luer adapter  24 . In some embodiments, the extension tube  32  may include a distal end  36  and a proximal end  38 . In some embodiments, the distal end  36  may be coupled to or integrated with the first luer adapter  14 . In some embodiments, the proximal end of the extension tube  32  may be coupled to or integrated with the third luer adapter  34 . In other embodiments, the proximal end of the extension tube  32  may be coupled to or integrated with the blood collection device  18 . 
     In some embodiments, the extension set  10  may act as a flow resistor in a fluid pathway of a catheter system, illustrated, for example, in  FIG. 1C , or another vascular access system. In some embodiments, the catheter system may include a catheter assembly  37 , which may include a catheter adapter  39  and a catheter  40 . In some embodiments, the catheter  40  may be secured within the catheter adapter  39  and may extend distally from the catheter adapter  39 . In some embodiments, the catheter adapter  39  may include a distal end  42 , a proximal end  44 , and a lumen extending through the distal end  42  and the proximal end  44 . In some embodiments, an introducer needle  45  may extend from a needle shield through the catheter  40 . 
     In some embodiments, the extension set  10  may be coupled to the catheter assembly  37  in any number of suitable ways. In some embodiments, the catheter assembly  37  may be integrated. In further detail, in some embodiments, another extension tube  46  may extend from a side port  48  the catheter adapter  39 . In some embodiments, a proximal end of the other extension tube  46  may include a fourth luer adapter  50 , which may be coupled to the first luer adapter  14 . In some embodiments, the catheter assembly  37  may be straight and/or the first luer adapter  14  may be coupled to the proximal end  44  of the catheter adapter  39 . In some embodiments, one or more of the first luer adapter  14 , the second luer adapter  24 , the third luer adapter  34 , and the fourth luer adapter  50  may include a slip or thread or clip male luer adapter, a slip or thread female luer adapter, a needleless connector, a blunt cannula, or another suitable access device. 
     In some embodiments, the catheter assembly  37  may include or correspond to any suitable catheter assembly, such as, for example, the BD NEXIVA™ Closed IV Catheter system, the BD CATHENA™ Catheter system, the BD VENFLON™ Pro Safely Shielded IV Catheter system, the BD NEOFLON™ IV Cannula system, the BD INSYTE™ AUTOGUARD™ BC Shielded IV Catheter system, or another suitable catheter assembly. In some embodiments, the catheter  40  may include a peripheral intravenous catheter (PIVC), a peripherally inserted central catheter (PICC), or a midline catheter. 
     In some embodiments, the fluid pathway of the catheter system may include one or more of the following: the catheter  40 , the catheter adapter  39 , the other extension tube  46 , the fourth luer adapter  50 , the first luer adapter  14 , the extension tube  32 , the third luer adapter  34 , the second luer adapter  24 , and the blood collection device  18 . In some embodiments, the extension set  10  may lower a flow rate of blood within the fluid pathway of the catheter system, which may in turn lower a shear rate for hemolysis management. In some embodiments, the catheter assembly  37  may be substituted with another type of vascular access device, such as, for example, a venipuncture device, an infusion disposable, a blood collection access device, or a blood collection container. 
     Blood cell experiences shear stress as it flows in a fluid pathway. The maximum shear stress is along the wall of the fluid pathway, or wall shear stress. Wall shear stress on blood cells is considered a major source of mechanical damage to blood cells. For a cylindrical fluid path, the wall shear stress is typically expressed as: 
     
       
         
           
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     in which  P is the pressure drop along a path with a length of L and an interior radius of r. k is shrinkage index. 
     To fill a certain volume of collection tube, V, with a flow rate of Q, the time needed can be simply assessed by: 
     
       
         
           
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     in which μ is the dynamic viscosity of the fluid. Hemolysis is typically associated with both the wall shear stress and the time a blood cell is exposed to wall shear stress. From literature, it has been widely considered that hemolysis index can be approached as a function of: 
       HI (%)= A*t   α *τ β 
 
     in which A, α, and β are coefficients. 
     In principle, the hemolysis index is related to pressure gradient and cross-sectional characteristic dimension: 
     
       
         
           
             
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     In some embodiments, a length of the extension tube  32  may be selected based on one or more of the following: a gauge and/or length of a particular catheter, a particular catheter assembly configuration, or a clinical setup. In some embodiments, the extension tube  32  may include a length L from the first luer adapter  14  to the second luer adapter  24 . In some embodiments, the extension tube  32  may include an inner diameter D. 
     Fluid flow in an extension tube with a tubular fluid pathway therethrough can be analyzed using Poiseuille&#39;s equation: 
     
       
         
           
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     where ΔP is a change in pressure gradient across the length of the extension tube, D and L are the inner diameter and length, respectively, of the tubular fluid pathway through the extension tube, μ is the viscosity of a fluid, and 
     
       
         
           
             
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     is the fluid resistance. The extension tube may include or correspond to the extension tube  32 . Since μ is the viscosity of the fluid and not part of the extension tube geometry, a geometric factor G f  is defined such that R f  (the fluid resistance) is 
     
       
         
           
             
               
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     In some embodiments, the extension tube  32  may have multiple sections with lengths (L 1 , L 2 , L 3 ) and inner diameters of (D 1 , D 2 , D 3 ), the geometric factor is then: 
     
       
         
           
             
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     In some embodiments, the extension tube  32  may have an inner diameter that changes over the length of the extension tube, the geometric factor is then: 
     
       
         
           
             
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     In some embodiments, the extension tube  32  may have a cross section that is not circular. In this case, the geometric factor can be determined by measuring the flow rate (Q) at given pressure (ΔP) with known viscosity (μ) fluid: 
     
       
         
           
             
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     The G f  value may be selected to reduce the max shear stress for each catheter gauge to be the same or less than the max shear stress of a 21G VACUTAINER® UTLRATOUCH™ push button blood collection set (available from Becton Dickinson &amp; Company), which was previously considered the gold standard for blood draws. In some embodiments, G f  may be equal to or more than 3.83E+06 (l/in 3 ) when a 18G catheter is used, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, G f  may be equal to or more than 3.27E+06 (l/in 3 ) when a 20G catheter is used, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, G f  may be equal to or more than 3.33E+06 (l/in 3 ) when a 22G catheter is used, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, G f  may be equal to or more than 1.50E+07 (l/in 3 ) when a 24G catheter is used, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, G f  may include another value. In some embodiments, G f  value may be selected to reduce the max shear stress for each catheter gauge to be the same or less than the max shear stress of a 25G VACUTAINER® ULTRATOUCH™ push button blood collection set (available from Becton Dickinson &amp; Company). 
     In some embodiments, when a 18G catheter is used, G f  may be equal to 3.83E+06 (l/in 3 ) plus or minus 10 percent, plus or minus 25 percent, plus or minus 50 percent, or plus or minus 75 percent, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, when a 20G catheter is used, G f  may be equal to 3.27E+06 (l/in 3 ) plus or minus 10 percent, plus or minus 25 percent, plus or minus 50 percent, or plus or minus 75 percent, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, when a 22G catheter is used, G f  may be equal to 3.33E+06 (l/in 3 ) plus or minus 10 percent, plus or minus 25 percent, plus or minus 50 percent, or plus or minus 75 percent, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, when a 24G catheter is used, G f  may be equal to 1.50E+07 (l/in 3 ) plus or minus 10 percent, plus or minus 25 percent, plus or minus 50 percent, or plus or minus 75 percent, which may reduce the wall sheer stress to reduce hemolysis. In some embodiments, G f  may include another value, which may be selected based on a gauge of the catheter. In some embodiments, G f  values may be selected to be the same for 22G through 18G catheters. 
     In some embodiments, the fluid pathway of the catheter system, which may include one or more of the needle assembly  19 , the extension tube  32 , and the catheter assembly  37  (which may include the other extension tube  46 ), may include an entirety of a blood collection pathway through which blood flows during blood collection. The system geometric factor G fs  for the fluid pathway of the catheter system can be determined in similar fashion as described earlier. In some embodiments, the system geometric factor G fs  may be equal to or more than 7.34E+06 (l/in 3 ). In some embodiments, G fs  may include another value. In some embodiments, the system geometric factor G fs  may be 7.34E+06 (l/in 3 ) plus or minus 10 percent, plus or minus 25 percent, plus or minus 50 percent, or plus or minus 75 percent. In some embodiments, G fs  may include another value, which may be selected based on a gauge of the catheter. 
     Referring now to  FIGS. 2A-2C , an extension set  52  is illustrated, according to some embodiments. In some embodiments, the extension set  52  may be similar or identical to the extension set  10  of  FIGS. 1A-1C  in terms of one or more included features and/or operation. In some embodiments, the proximal end of the extension tube  32  may be integrated with the blood collection device  18 . In some embodiments, the extension set  52  may include a clamp  54 , which may be disposed on the extension tube  32 . In some embodiments, the clamp  54  may be configured to move between a clamped position and an unclamped position or between a more clamped position and a less clamped position. In some embodiments, the clamp  54  may prevent or reduce fluid flow through the extension tube  32  in response to the clamp  54  being in the clamped position. 
     In some embodiments, the clinician may adjust flow resistance within the catheter system by manually changing fluid characteristics of the catheter system via the clamp  54 . In some embodiments, in response to the clamp  54  being in the clamped position, flow resistance within the catheter system may be increased and blood flow through the extension tube  32  may be reduced. In these embodiments, a risk of hemolysis may be reduced. In some embodiments, to decrease the flow resistance within the catheter system after the blood collection container nears filling, the clinician may move the clamp to the unclamped position, which may allow faster blood collection when a risk of hemolysis is reduced. 
     In some embodiments, the clamp  54  may include a slide clamp, which may include a slot that becomes progressively narrower. In these and other embodiments, the extension tube  32  may be flexible and compliant. In some embodiments, the clinician may adjust an inner diameter of the extension tube  32  by adjusting a depth of the extension tube  32  within the slot of the slide clamp. The clinician may in turn adjust a flow resistance within the extension set  52 . In some embodiments, the clamp  54  may include a roller clamp, a slide clamp, a pinch clamp, or another suitable type of clamp. 
     Referring now to  FIGS. 3A-3C , an extension set  56  is illustrated, according to some embodiments. In some embodiments, the extension set  56  may be similar or identical to the extension set  10  of  FIGS. 1A-1C  and/or the extension set  52  in terms of one or more included features and/or operation. In some embodiments, the extension set  56  may include one or more extension tubes. In some embodiments, the extension tube  32  may include or correspond to a first extension tube  58  of the extension set  56 . In some embodiments, the extension set  56  may include a second extension tube  60 . 
     It is understood that in some embodiments, any suitable first lumen may be substituted for the first extension tube  58  and/or any suitable second lumen may be substituted for the second extension tube  60 . Thus, in some embodiments, a particular extension set may not include the first extension tube  58  and/or the second extension tube  60  and may instead include the first lumen and/or the second lumen. In some embodiments, the first lumen and the second lumen may be disposed in a single multi-lumen extension tube or any other suitable structure. In some embodiments, a distal end of the single multi-lumen extension tube may be coupled to or integrated with the first luer adapter  14 . In some embodiments, a proximal end of the single multi-lumen extension tube may be coupled to or integrated with the third luer adapter  34 . In some embodiments, a proximal end of the single multi-lumen extension tube may be coupled to or integrated with the blood collection device  18 . 
     In some embodiments, a flow resistance of the first extension tube  58  may be greater than a flow resistance of the second extension tube  60 . For example, the first extension tube  58  may be longer than the second extension tube  60 , as illustrated, for example, in  FIGS. 3A-3C . Additionally or alternatively, in some embodiments, an inner diameter of the first extension tube  58  may be less than an inner diameter of the second extension tube  60 , as illustrated, for example, in  FIGS. 4A-4C . In some embodiments, the flow resistance of the first extension tube  58  may be equal to the flow resistance of the second extension tube  60 . In some embodiments, the second extension tube  60  may include any combination of length and inner diameter such that the flow resistance of the second extension tube  60  is the same or less than the flow resistance of the first extension tube  58 . 
     In some embodiments, the first extension tube  58  and the second extension tube  60  may extend between a distal end  12  of the extension set  56  and a proximal end  16  of the extension set  56 . In some embodiments, the proximal end  16  of the extension set may include the blood collection device  18  or the third luer connector  34 . In some embodiments, a clamp  54  may be disposed on the second extension tube  60 . In some embodiments, the second extension tube  60  may extend through the clamp  54 . 
     In some embodiments, the second extension tube  60  may include a distal end  62  and a proximal end  64 . In some embodiments, a distal end  66  of the first extension tube  58  and the distal end  62  of the second extension tube  60  may be integrated with the first luer adapter  14 , as illustrated, for example, in  FIG. 3B . In some embodiments, a proximal end  68  of the first extension tube  58  and the proximal end  64  of the second extension tube  60  may be integrated with the third luer adapter  34  or there may be one or more components between the proximal ends  64 ,  68  and the third luer adapter  34 , such as, for example, a short tubing. In some embodiments, the proximal end  68  of the first extension tube  58  and the proximal end  64  of the second extension tube  60  may be integrated with the blood collection device  18 . 
     In some embodiments, in response to the clamp  54  being in the clamped position, flow resistance may be increased as blood may flow through the first extension tube  58 . In some embodiments, in response to the clamp  54  being in the clamped position, blood flow through the second extension tube  60  may be reduced or nothing. In some embodiments, to decrease the flow resistance after the blood collection container is partially filled and the pressure differential has decreased, the clinician may move the clamp  54  to the unclamped position, which may allow faster blood collection. An example blood collection container  69  is illustrated in  FIGS. 3B-3C . 
     Referring now to  FIGS. 4A-4C , an extension set  70  is illustrated, according to some embodiments. In some embodiments, the extension set  70  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , and the extension set  56  of  FIGS. 3A-3C . In some embodiments, an inner diameter of the first extension tube  58  may be less than an inner diameter of the second extension tube  60 . In some embodiments, the first extension tube  58  and the second extension tube  60  may be a same length. 
     Referring now to  FIGS. 5A-5C , a schematic diagram of an extension set having multiple extension tubes is illustrated, according to some embodiments. The extension set may correspond to the extension set  56  or the extension set  70 , for example. In some embodiments, as illustrated in  FIG. 5A , the clamp  54  may be in the clamped position prior to entry of blood into the extension set. In some embodiments, as illustrated in  FIG. 5B , blood may flow through the first extension tube  58  in response to the second extension tube  60  being clamped. In some embodiments, as illustrated in  FIG. 5C , in response to the clamp being removed, unclamped, or less clamped, increased blood may flow through the second extension tube  60 , which may increase a total amount of blood flowing through the extension set. 
     Referring now to  FIGS. 6A-6C , a portion of an extension set  72  is illustrated, according to some embodiments. In some embodiments, the extension set  72  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , and the extension set  70  of  FIGS. 4A-4C . 
     In some embodiments, in response to the second luer adapter  24  being tightened with respect to the third luer adapter  34 , a first fluid pathway  74  through the first extension tube  58  may be open, and a second fluid pathway  76  through the second extension tube  60  may be closed. In some embodiments, in response to the second luer adapter  24  being loosened with respect to the third luer adapter  34 , the first fluid pathway  74  through the first extension tube  58  may be open, and the second fluid pathway  76  through the second extension tube  60  may be open. In some embodiments, to decrease the flow resistance within the extension set  72  after the blood collection container is partially filled and the pressure differential has decreased, the clinician may loosen the second luer adapter  24  with respect to the third luer adapter  34  or move the second luer adapter  24  from a tightened position to a loosened position. In some embodiments, the second luer adapter  24  and the third luer adapter  34  may include corresponding threads, and the second luer adapter  24  may be unthreaded with respect to the third luer adapter  34  to move the second luer adapter  24  from the tightened position to the loosened position. 
     In some embodiments, the extension set  72  may include a third extension tube  78 , which may be integrated with the third luer adapter  34 . In some embodiments, the third luer adapter  34  may include one or more openings  80 , each in fluid communication with a particular extension tube. In some embodiments, the opening  80  in fluid communication with the first extension tube  58  may remain open in response to the second luer adapter  24  being in the loosened position and the tightened position with respect to the third luer adapter  34 . 
     In some embodiments, the openings  80  in fluid communication with the second extension tube  60  and/or the third extension tube  78  may be blocked by the second luer adapter  24  when the second luer adapter  24  is in the tightened position with respect to the third luer adapter  34 , as illustrated, for example, in  FIG. 6B . In some embodiments, the openings  80  in fluid communication with the second extension tube  60  and/or the third extension tube  78  may be unblocked in response to the second luer adapter  24  being in the loosened position with respect to the third luer adapter  34 , as illustrated, for example, in  FIG. 6C . In these embodiments, the second luer adapter  24  may be spaced apart from the openings  80  in fluid communication with the second extension tube  60  and/or the third extension tube  78 . 
     Referring now to  FIGS. 7A-7C , a portion of an extension set  82  is illustrated, according to some embodiments. In some embodiments, the extension set  82  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , and the extension set  72  of  FIGS. 6A-6C . 
     In some embodiments, the extension set  82  may include a roller clamp  84 . In some embodiments, the roller clamp  84  may include a roller  86  moveable within a track  88 . In some embodiments, the first extension tube  58  and the second extension tube  60  may extend through the roller clamp  84  generally perpendicular to the track  88 . In some embodiments, when blood flow through the second extension tube  60  is blocked, the roller  86  may be disposed in a first position proximate the second extension tube  60 , as illustrated, for example, in  FIG. 7B , and may pinch the second extension tube  60 . In some embodiments, opening the second extension tube  60  may include moving the roller  86  along the track  88  away from the second extension tube  60  and toward the first extension tube  58 . In some embodiments, when blood flow through the first extension tube  58  is blocked, the roller  86  may be disposed in a second position proximate the first extension tube  58 , as illustrated, for example, in  FIG. 7C , and may pinch the first extension tube  58 . 
     Referring now to  FIG. 8 , an extension set  90  is illustrated, according to some embodiments. In some embodiments, the extension set  90  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , and the extension set  82  of  FIGS. 7A-7C . 
     In some embodiments, the distal end  12  of the extension set  90  may include a three-way stopcock  92 , which may include a first port  94 , a second port  96 , and a third port  98 . In some embodiments, the first extension tube  58  may be coupled with the first port  94 , the second extension tube  60  may be coupled to the second port  96 , and the third port  98  may include the first luer adapter  14  configured to couple to the catheter adapter  39 . In some embodiments, blocking blood flow through the second extension tube  60  may include rotating the three-way stopcock  92  to a first position. In some embodiments, opening the second extension tube  60  may include rotating the three-way stopcock  92  to a second position. 
     Referring now to  FIGS. 9A-9E , an extension set  100  is illustrated, according to some embodiments. In some embodiments, the extension set  100  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . 
     In some embodiments, the first extension tube  58  may be disposed within the second extension tube  60 . In some embodiments, in response to the clamp  54  being in the clamped position, blood may flow through the first extension tube  58 , and blood flow between an outer surface of the first extension tube  58  and an inner surface of the second extension tube  60  may decrease, as illustrated, for example, in  FIG. 9D . In some embodiments, to increase the flow resistance within the catheter system after the blood collection container  69  is partially filled and the pressure differential has decreased, the clinician may move the clamp  54  to the unclamped position such that blood flows between the outer surface of the first extension tube  58  and the inner surface of the second extension tube  60 , as illustrated, for example, in  FIG. 9E . In some embodiments, the first extension tube  58  may be longer than the second extension tube  60  and/or an inner diameter of the first extension tube  58  may be less than an inner diameter of the second extension tube  60 . 
     In some embodiments, the first extension tube  58  may be configured to collapse at a different pressure differential than the second extension tube  60 . In some embodiments, the second extension tube  60  may include a lower durometer than the first extension tube  58 . In some embodiments, the second extension tube  60  may be configured to collapse at a lower pressure differential than the first extension tube  58 . In some embodiments, at the lower pressure differential, the second extension tube  60  may contact the first extension tube  58  to reduce or stop blood flow between the outer surface of the first extension tube  58  and the inner surface of the second extension tube  60 . In some embodiments, in response to the blood collection container  18  partially filling with blood, the blood flow between the outer surface of the first extension tube  58  and the inner surface of the second extension tube  60  may increase. 
     Referring now to  FIGS. 10A-10B , in some embodiments, an inner surface of the first extension tube  58  may include an absorbent material  104 . In some embodiments, blood within the first extension tube  58  may be configured to flow proximate the absorbent material  104 . In some embodiments, in response to blood reaching or saturating a particular portion of the absorbent material  104 , as illustrated, for example in  FIG. 10B , or an entirety of the absorbent material  104 , the clinician may change the flow resistance via a particular extension set. In some embodiments, the particular extension set may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . 
     In some embodiments, the first fluid pathway  74  through the first extension tube  58  may be narrowed proximate the absorbent material  104 , such as through an island  106 , which may be disposed within the first fluid pathway  74 . In some embodiments, blood may flow around the island  106  in a distal to proximal direction, as illustrated, for example, in  FIG. 10B . 
     Referring now to  FIGS. 11A-11B , in some embodiments, the first extension tube  58  may include an indicator pathway or tube  108 , which may include a first end and a second end connected to a primary portion of the first fluid pathway  74  of the first extension tube  58 . In some embodiments, blood within the first extension tube  58  may be configured to flow through the indicator tube  108 , which may include a smaller diameter than the primary portion of the first fluid pathway  74 . 
     In some embodiments, the indicator tube  108  may include one or more markers  110 , which may include grooves configured to collect blood or lines. In some embodiments, the markers  110  may provide a visual indicator to the clinician. In some embodiments, in response to blood reaching a particular marker  110 , as illustrated, for example in  FIG. 11B , or all of the markers  110 , the clinician may change the flow resistance via a particular extension set. In some embodiments, the particular extension set may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . 
     Referring now to  FIGS. 12A-12C , in some embodiments, the first extension tube  58  and the second extension tube  60  may join at a junction  112 . In some embodiments, the junction  112  may be disposed within the first luer adapter  14 , proximal to the first luer adapter  14 , or at another location within a particular extension set. In some embodiments, the particular extension set may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . 
     In some embodiments, the particular extension set may include a pressure-sensitive valve  114 . In some embodiments, the pressure-sensitive valve  114  may be disposed at a junction of the first fluid pathway  74  and the second fluid pathway  76 . In some embodiments, the pres sure-sensitive valve  114  may be disposed in the second extension tube  60 . In some embodiments, the pressure-sensitive valve  114  may be disposed in a portion of the fluid pathway of the particular extension set distal to the first extension tube  58  and the second extension tube  60 . In some embodiments, the fluid pathway of the particular extension set may extend through the proximal end  16  and the distal end  12 . In some embodiments, the fluid pathway of the particular extension set may include the first fluid pathway  74  and/or the second fluid pathway  76 . 
     In some embodiments, in response to a first predetermined pressure differential within the particular extension set, the pressure-sensitive valve  114  may be open with respect to the first extension tube  58  and closed with respect to the second extension tube  60 . In some embodiments, in response to a second predetermined pressure differential within the particular extension set, the pressure-sensitive valve  114  may remain open with respect to the first extension tube  58  and open with respect to the second extension tube  60 . In some embodiments, the first predetermined pressure differential may be greater than the second predetermined pressure differential. In some embodiments, the first predetermined pressure differential and the second predetermined pressure differential may correspond to the pressure differential between the vein of the patient and the blood collection container coupled to the particular extension set. In some embodiments, the pressure-sensitive valve  114  may include any suitable type of pressure-sensitive valve. In some embodiments, an inner surface of the particular extension set may include one or more grooves proximate the pressure-sensitive valve. In some embodiments, the grooves may allow blood to bypass the pressure-sensitive valve  114  and flow into the first extension tube  58  but not the second extension tube  60 . 
     In some embodiments, a method of blood collection or collecting a blood sample may include inserting a catheter of a catheter system into vasculature of the patient. In some embodiments, the catheter system may include a catheter assembly, which may include a catheter adapter and the catheter. In some embodiments, the catheter may be secured within the catheter adapter and may extend distally from the catheter adapter. 
     Referring now to  FIG. 13 , in some embodiments, a pressure-sensitive valve  116  may be disposed within the second extension tube  60 , which may be shorter than the first extension tube  58  and/or include a larger inner diameter than the first extension tube  58 . In some embodiments, the pressure-sensitive valve  116  may include a duckbill valve, as illustrated, for example, in  FIG. 13 , or another suitable type of pressure-sensitive valve. For example, the pressure-sensitive valve  116  may include a spring-loaded plunger or ball. In some embodiments, the second extension tube  60  may be more compliant than the first extension tube  58  and thus may close at a lower pressure differential than the first extension tube  58 . 
     In some embodiments, in response to a first predetermined pressure differential within a particular extension set, the pressure-sensitive valve  116  may be closed and not allow blood to flow through the second extension tube  60 . In some embodiments, in response to a second predetermined pressure differential within the particular extension set, the pressure-sensitive valve  116  may open. In some embodiments, the first predetermined pressure differential may be greater than the second predetermined pressure differential. In some embodiments, the particular extension set may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . 
     Referring now to  FIG. 14A , a catheter system  118  is illustrated, according to some embodiments. In some embodiments, the catheter system  118  may include an extension set  120 , which may be integrated with the catheter assembly  37 . In further detail, in some embodiments, the distal end  12  of the extension set  120  may be integrated with an adapter  122  of the catheter assembly  37 , as illustrated, for example, in  FIG. 14A , or integrated with the catheter adapter  39  itself. In these and other embodiments, the extension set  120  may not be removable from the catheter system  118 . In some embodiments, the distal end of the first extension tube  58  or the distal end of the extension tube  32  may be integrated with the adapter  122  or the catheter adapter  39 . In some embodiments, the adapter  122  may include a Y-adapter, a T-adapter, or another suitable adapter. 
     In some embodiments, the first extension tube  58  and/or the second extension tube  60  (see, for example,  FIGS. 4-9 ) may be integrated into the side port  48 . In some embodiments, the other extension tube  46  may be similar or identical to the first extension tube  58  in terms of one or more included features and/or operation. In some embodiments, the extension set  120  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . In some embodiments, the extension set  120  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension sets of  FIGS. 9-13 . 
     Referring now to  FIG. 14B , a catheter system  124  is illustrated, according to some embodiments. In some embodiments, the catheter system  124  may include an extension set  126 , which may be coupled to or integrated with an instrument delivery device  127 , which may deliver a probe, a catheter, or a guidewire through a particular catheter assembly (as illustrated, for example, in  FIG. 14A ). In some embodiments, the first extension tube  58  and/or the second extension tube  60  (see, for example,  FIGS. 4-9 ) may be integrated into the instrument delivery device  127 . 
     In some embodiments, the extension set  126  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension set  10  of  FIGS. 1A-1C , the extension set  52  of  FIGS. 2A-2C , the extension set  56  of  FIGS. 3A-3C , the extension set  70  of  FIGS. 4A-4C , the extension set  72  of  FIGS. 6A-6C , the extension set  82  of  FIGS. 7A-7C , and the extension set  90  of  FIG. 8 . In some embodiments, the extension set  126  may be similar or identical to one or more of the following in terms of one or more included features and/or operation: the extension sets of  FIGS. 9-13 . 
     In some embodiments, the instrument delivery device  127  may include any suitable instrument delivery device. In some embodiments, the instrument delivery device  127  may be further described in U.S. patent application Ser. No. 16/037,246, filed Jul. 17, 2018, entitled “EXTENSION HOUSING A PROBE OR INTRAVENOUS CATHETER,” U.S. patent application Ser. No. 16/388,650, filed Apr. 18, 2019, entitled “INSTRUMENT DELIVERY DEVICE HAVING A ROTARY ELEMENT,” U.S. patent application Ser. No. 16/037,319, filed Jul. 17, 2018, entitled “MULTI-DIAMETER CATHETER AND RELATED DEVICES AND METHODS,” U.S. patent application Ser. No. 16/502,541, filed Jul. 3, 2019, entitled “DELIVERY DEVICE FOR A VASCULAR ACCESS INSTRUMENT,” U.S. patent application Ser. No. 16/691,217, filed Nov. 21, 2019, entitled “SYRINGE-BASED DELIVERY DEVICE FOR A VASCULAR ACCESS INSTRUMENT,” U.S. Patent Application No. 62/794,437, filed Jan. 18, 2019, entitled “CATHETER DELIVERY DEVICE AND RELATED SYSTEMS AND METHODS,” and U.S. Patent Application No. 62/830,286, filed Apr. 5, 2019, entitled “VASCULAR ACCESS INSTRUMENT HAVING A FLUID PERMEABLE STRUCTURE AND RELATED DEVICES AND METHODS,” which are incorporated by reference in their entirety. 
     All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art and are to be construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.