Central venous catheters

Current Guidelines

The Infusion Nursing Standards of Practice establishes the national standard for all infusion therapy.1 This standard on flushing emphasizes the goals of maintaining patency and preventing contact between heparin and incompatible solutions. The standard incorporates the concepts of catheter flushing and locking. Flushing assesses catheter patency and functionality and removes the previously infused medication. Locking the catheter creates a closed column of fluid inside the catheter lumen intended to prevent blood from moving into the lumen.

Normal Saline

Flushing is accomplished with 0.9% sodium chloride or normal saline. The saline-filled syringe is attached to the catheter hub to determine if blood can be successfully aspirated indicating that nothing is obstructing the catheter’s tip. When blood aspiration is not possible with a short peripheral catheter, several factors may be involved. The catheter tip may have punctured the posterior wall of the vein and lie within the subcutaneous tissue. Additionally, the vein wall or a venous valve may be pulled over the catheter lumen, preventing blood backflow. This is possible in patients with anatomical changes caused by diseases or aging. The skin, vein walls, and subcutaneous tissue of geriatric patients become thinner, allowing the vein wall to easily occlude the catheter lumen. Dehydration or fluid volume deficit reduces the volume of blood flow and may allow the vein wall to occlude the catheter. Failure to aspirate blood from a central venous catheter is related to the catheter’s tip location, the tip’s position relative to the vein wall, the site of insertion, fibrin or thrombus development inside the catheter lumen and/or in the vein around the catheter tip, or catheter damage. All of these situations have the potential to produce serious problems for the patient.

Flushing is used to clear the catheter lumen of any medication that was previously instilled or infused. Medication incompatibility can produce drug precipitate that occludes the catheter lumen. Flushing with normal saline between each medication can prevent contact between incompatible drugs and prevent the formation of this occluding precipitate. This concern about drug incompatibility extends to heparin lock solution.

Normal saline is available in multi- and single-dose containers. Multidose vials of bacteriostatic normal saline contain benzyl alcohol as the preservative. One animal study recommends no more than 30 mL in 24 hours for adults8 and is contraindicated in infants.9 The purpose of the preservative is to allow multiple entries into the vial and is not intended to have an impact on catheter-related infection. This preservative produces a bacteriostatic effect by simply inhibiting the growth of organisms. It does not have the ability to actually kill organisms. There have been multiple outbreaks of infection associated with multiple dose vials of saline and heparin used for catheter flushing.10 For this reason, single-dose containers of preservative-free normal saline are recommended, including single-dose vials and prefilled syringes.11

The volume of normal saline used to flush catheters depends on the type of catheter and the kind of therapy being infused. The Infusion Nurses Society (INS) recently released a set of recommendations on quantities of flush solution.3 A short peripheral catheter is commonly flushed with a minimum of 2 mL, although a larger volume may be required to assess patency when a vesicant medication must be given. A central venous catheter is longer than a peripheral catheter, requiring a minimum of 5 mL for flushing. Blood sampling from the catheter or blood transfusion through the catheter requires a minimum of 10 mL, although 20 mL is often used.

Normal saline is commonly used to lock short peripheral catheters. Two meta-analyses published in 1991 confirmed that there was no difference in peripheral catheter patency when they were flushed with saline only.12,13 Practice quickly changed to eliminate the use of heparin solution in these catheters.

The use of normal saline as the locking solution for a central venous catheter depends on the specific brand of catheter or needleless connector being used. Catheters designed with an integral valve were introduced in the mid-1980s and now include valves on the internal (Groshong®, Bard Access Systems, Salt Lake City, UT; LifeValve, AngioDynamics, Queensbury, NY) and the external (PASV®, Navilyst Medical, Natick, MA; SoloPICC®, Bard Access Systems, Salt Lake City) ends of the catheter. These brands have instructions that allow for saline-only flushing. Because the opening pressure for the valve is greater than normal intrathoracic venous pressure, these valves remain closed until pressure is applied for infusion or aspiration.

Catheters with the valve located in the bloodstream may be affected by the fibrin and thrombosis that attach to all catheters. This can impact the function of the valve and is often referred to as persistent withdrawal occlusion (PWO). Clinical outcomes were compared between a group of 28 Groshong tunneled catheters flushed with 5 mL of normal saline and a group of 23 Groshong tunneled catheters flushed with 2.5 mL of heparin 100 units per mL. This nonrandomized study found that PWO occurred less frequently in the heparin group. All saline-flushed catheters displayed intraluminal adherent clots, whereas none in the heparin group had intraluminal clots on explantation. The authors recommended the use of heparin in this valved catheter to decrease clot formation and improve catheter functionality14 (Table 2).

A randomized study compared a nonvalved peripherally inserted central catheter (PICC) with the PASV PICC in 362 patients. The nonvalved catheters were locked with 10 units per mL of heparin and the valved catheters were locked with normal saline. All catheters were flushed after each use or every 8 hours with the valved catheter flushed with saline, producing a lower rate of occlusion15 (Table 2).

Several brands of needleless connectors also include instructions for saline-only flushing when these devices are attached to the catheter hub. These instructions are based on the design of the connector that overcomes blood reflux from disconnection of the administration set or syringe, commonly known as a positive displacement mechanical valve. Not all brands of these connectors include instructions for saline locking, making it imperative that each nurse understand the specific type of connector being used and the associated instructions.

Heparin

Dilute heparin is recommended as the solution to lock most central venous catheters in the absence of a valved catheter or needleless connector with saline-only instructions. The concentration and volume of heparin locking solution varies greatly; however, the INS Flushing Protocol recommendations provide some guidance. Based on expert consensus and a review of primarily descriptive literature, this protocol recommends the use of 10 units per mL of heparin for locking most central venous catheters. The only indication for heparin at a dose of 100 units per mL is for implanted ports.3 Many port manufacturers have historically recommended use of 100 units per mL of heparin for monthly flushing, and there is a dearth of published studies using lower concentrations. Because of concern about frequent use of higher-concentration heparin to maintain patency of central venous catheters, the lower, 10-unit heparin concentration has evolved over the years as standard practice.

The volume of heparin required to properly lock the catheter depends on the priming volume of the catheter plus any add-on devices. The Infusion Nursing Standards of Practice call for the minimum volume to be equal to twice the internal volume of the catheter system. The INS Flushing Protocol recommends a minimum of 5 mL for central venous catheters to ensure meeting this standard. This overflow should allow for properly filling the entire system, but the excess may have negative aspects.

Published studies assessing the use of catheter flushing and locking solutions have numerous variations, such as patient populations, volume and concentration of solutions used, method of data collection, type of healthcare setting, and study end points16-18 (Table 2). For these reasons, it is very difficult to pool data for a meaningful analysis. One study assessed flushing and locking procedures with PICCs; however, the majority of the catheters had tip locations in the midclavicular location, which is known for a higher rate of vein thrombosis.16 Vein thrombosis presents with signs very similar to lumen occlusion, making it difficult to distinguish between the two conditions.

A multicenter German study assessed for the presence of vein thrombosis when various doses of subcutaneous LMWH were given. The study also reported that patients receiving a flushing protocol using fewer than 250 units per mL of heparin were associated with greater rates of thrombosis than patients receiving a flushing protocol using more than 500 units per mL of heparin.19 Other studies have assessed the patency of venous and arterial catheters with the continuous infusion of saline versus saline with 1 unit per mL of heparin but provide no useful information about the question of locking catheters.20,21

Changes in technology drive the increasing questions about the elimination of heparin lock solution and total reliance on normal saline for locking catheters. Catheters with an integral valve are routinely flushed and locked with normal saline; however, the valve does not contraindicate the use of heparin locking solution.

Needleless connectors introduce more confusion. These devices now include split septum systems and mechanical valve systems. The split septum group is divided into those that require a blunt cannula and those that will accept the male luer end of a syringe or administration set. Mechanical valves have numerous internal designs, including compressible sleeves and collapsing bellows or springs. Some, but not all, needleless connectors have instructions for saline-only flushing and locking. Published research has provided very little information regarding the issue of the most effective locking solution.

Few published studies are available that compare different locking solutions for central venous catheters.
Two studies in a pediatric population used sequential cohorts to compare different types of needleless connectors and a variety of locking solutions.22,23 One small, randomized prospective study used a positive displacement mechanical valve on all patients with peripherally inserted central catheters and compared flushing with heparin and flushing with saline only. The authors rejected the saline-only locking procedure, citing the cost of the declotting procedure on 6% of their PICCs annually24 (Table 2).

A recent randomized prospective study compared a twice-weekly flush of heparin (concentration and volume not reported) using a “standard CVC cap” with a weekly flush of normal saline using a positive displacement mechanical valve25 (Table 2).

Patient age is another factor in the concern about catheter flushing. A 2009 policy recommendation from the American Society of Health-System Pharmacists concluded, “The data are conflicting and insufficient to support the recommendation of a preferred solution for line maintenance in neonatal patients at this time.” They went on to emphasize the need for decreasing practice variations through standardized concentrations of heparin and the recommended the use of “manufacturer-prepackaged products” as the best method to provide safe care for neonates.26 This recommendation suggests that prefilled syringes for catheter flushing could eliminate the risk associated with preparing syringes on the nursing unit.

The value of using normal saline exclusively for maintaining catheter patency has not been well established. The use of add-on needleless connectors with instructions for saline-only flushing and locking procedures adds greater confusion; however, there is a trend toward greater complications with saline-only flushing. There are limited studies on valved catheters, and they have conflicting results based on where the valve is located.

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Course Description Introduction Overview of Catheter Flushing Current Guidelines Clinical Issues with Heparin Side Effects of Heparin Lock Solution Costs Potential Alternative Locking Solutions Clinical Decisions References Bio Disclaimer Print Article	Show All Current Guidelines The Infusion Nursing Standards of Practice establishes the national standard for all infusion therapy.1 This standard on flushing emphasizes the goals of maintaining patency and preventing contact between heparin and incompatible solutions. The standard incorporates the concepts of catheter flushing and locking. Flushing assesses catheter patency and functionality and removes the previously infused medication. Locking the catheter creates a closed column of fluid inside the catheter lumen intended to prevent blood from moving into the lumen. Normal Saline Flushing is accomplished with 0.9% sodium chloride or normal saline. The saline-filled syringe is attached to the catheter hub to determine if blood can be successfully aspirated indicating that nothing is obstructing the catheter’s tip. When blood aspiration is not possible with a short peripheral catheter, several factors may be involved. The catheter tip may have punctured the posterior wall of the vein and lie within the subcutaneous tissue. Additionally, the vein wall or a venous valve may be pulled over the catheter lumen, preventing blood backflow. This is possible in patients with anatomical changes caused by diseases or aging. The skin, vein walls, and subcutaneous tissue of geriatric patients become thinner, allowing the vein wall to easily occlude the catheter lumen. Dehydration or fluid volume deficit reduces the volume of blood flow and may allow the vein wall to occlude the catheter. Failure to aspirate blood from a central venous catheter is related to the catheter’s tip location, the tip’s position relative to the vein wall, the site of insertion, fibrin or thrombus development inside the catheter lumen and/or in the vein around the catheter tip, or catheter damage. All of these situations have the potential to produce serious problems for the patient. Flushing is used to clear the catheter lumen of any medication that was previously instilled or infused. Medication incompatibility can produce drug precipitate that occludes the catheter lumen. Flushing with normal saline between each medication can prevent contact between incompatible drugs and prevent the formation of this occluding precipitate. This concern about drug incompatibility extends to heparin lock solution. Normal saline is available in multi- and single-dose containers. Multidose vials of bacteriostatic normal saline contain benzyl alcohol as the preservative. One animal study recommends no more than 30 mL in 24 hours for adults8 and is contraindicated in infants.9 The purpose of the preservative is to allow multiple entries into the vial and is not intended to have an impact on catheter-related infection. This preservative produces a bacteriostatic effect by simply inhibiting the growth of organisms. It does not have the ability to actually kill organisms. There have been multiple outbreaks of infection associated with multiple dose vials of saline and heparin used for catheter flushing.10 For this reason, single-dose containers of preservative-free normal saline are recommended, including single-dose vials and prefilled syringes.11 The volume of normal saline used to flush catheters depends on the type of catheter and the kind of therapy being infused. The Infusion Nurses Society (INS) recently released a set of recommendations on quantities of flush solution.3 A short peripheral catheter is commonly flushed with a minimum of 2 mL, although a larger volume may be required to assess patency when a vesicant medication must be given. A central venous catheter is longer than a peripheral catheter, requiring a minimum of 5 mL for flushing. Blood sampling from the catheter or blood transfusion through the catheter requires a minimum of 10 mL, although 20 mL is often used. Normal saline is commonly used to lock short peripheral catheters. Two meta-analyses published in 1991 confirmed that there was no difference in peripheral catheter patency when they were flushed with saline only.12,13 Practice quickly changed to eliminate the use of heparin solution in these catheters. The use of normal saline as the locking solution for a central venous catheter depends on the specific brand of catheter or needleless connector being used. Catheters designed with an integral valve were introduced in the mid-1980s and now include valves on the internal (Groshong®, Bard Access Systems, Salt Lake City, UT; LifeValve, AngioDynamics, Queensbury, NY) and the external (PASV®, Navilyst Medical, Natick, MA; SoloPICC®, Bard Access Systems, Salt Lake City) ends of the catheter. These brands have instructions that allow for saline-only flushing. Because the opening pressure for the valve is greater than normal intrathoracic venous pressure, these valves remain closed until pressure is applied for infusion or aspiration. Catheters with the valve located in the bloodstream may be affected by the fibrin and thrombosis that attach to all catheters. This can impact the function of the valve and is often referred to as persistent withdrawal occlusion (PWO). Clinical outcomes were compared between a group of 28 Groshong tunneled catheters flushed with 5 mL of normal saline and a group of 23 Groshong tunneled catheters flushed with 2.5 mL of heparin 100 units per mL. This nonrandomized study found that PWO occurred less frequently in the heparin group. All saline-flushed catheters displayed intraluminal adherent clots, whereas none in the heparin group had intraluminal clots on explantation. The authors recommended the use of heparin in this valved catheter to decrease clot formation and improve catheter functionality14 (Table 2). A randomized study compared a nonvalved peripherally inserted central catheter (PICC) with the PASV PICC in 362 patients. The nonvalved catheters were locked with 10 units per mL of heparin and the valved catheters were locked with normal saline. All catheters were flushed after each use or every 8 hours with the valved catheter flushed with saline, producing a lower rate of occlusion15 (Table 2). Several brands of needleless connectors also include instructions for saline-only flushing when these devices are attached to the catheter hub. These instructions are based on the design of the connector that overcomes blood reflux from disconnection of the administration set or syringe, commonly known as a positive displacement mechanical valve. Not all brands of these connectors include instructions for saline locking, making it imperative that each nurse understand the specific type of connector being used and the associated instructions. Heparin Dilute heparin is recommended as the solution to lock most central venous catheters in the absence of a valved catheter or needleless connector with saline-only instructions. The concentration and volume of heparin locking solution varies greatly; however, the INS Flushing Protocol recommendations provide some guidance. Based on expert consensus and a review of primarily descriptive literature, this protocol recommends the use of 10 units per mL of heparin for locking most central venous catheters. The only indication for heparin at a dose of 100 units per mL is for implanted ports.3 Many port manufacturers have historically recommended use of 100 units per mL of heparin for monthly flushing, and there is a dearth of published studies using lower concentrations. Because of concern about frequent use of higher-concentration heparin to maintain patency of central venous catheters, the lower, 10-unit heparin concentration has evolved over the years as standard practice. The volume of heparin required to properly lock the catheter depends on the priming volume of the catheter plus any add-on devices. The Infusion Nursing Standards of Practice call for the minimum volume to be equal to twice the internal volume of the catheter system. The INS Flushing Protocol recommends a minimum of 5 mL for central venous catheters to ensure meeting this standard. This overflow should allow for properly filling the entire system, but the excess may have negative aspects. Published studies assessing the use of catheter flushing and locking solutions have numerous variations, such as patient populations, volume and concentration of solutions used, method of data collection, type of healthcare setting, and study end points16-18 (Table 2). For these reasons, it is very difficult to pool data for a meaningful analysis. One study assessed flushing and locking procedures with PICCs; however, the majority of the catheters had tip locations in the midclavicular location, which is known for a higher rate of vein thrombosis.16 Vein thrombosis presents with signs very similar to lumen occlusion, making it difficult to distinguish between the two conditions. A multicenter German study assessed for the presence of vein thrombosis when various doses of subcutaneous LMWH were given. The study also reported that patients receiving a flushing protocol using fewer than 250 units per mL of heparin were associated with greater rates of thrombosis than patients receiving a flushing protocol using more than 500 units per mL of heparin.19 Other studies have assessed the patency of venous and arterial catheters with the continuous infusion of saline versus saline with 1 unit per mL of heparin but provide no useful information about the question of locking catheters.20,21 Changes in technology drive the increasing questions about the elimination of heparin lock solution and total reliance on normal saline for locking catheters. Catheters with an integral valve are routinely flushed and locked with normal saline; however, the valve does not contraindicate the use of heparin locking solution. Needleless connectors introduce more confusion. These devices now include split septum systems and mechanical valve systems. The split septum group is divided into those that require a blunt cannula and those that will accept the male luer end of a syringe or administration set. Mechanical valves have numerous internal designs, including compressible sleeves and collapsing bellows or springs. Some, but not all, needleless connectors have instructions for saline-only flushing and locking. Published research has provided very little information regarding the issue of the most effective locking solution. Few published studies are available that compare different locking solutions for central venous catheters. Two studies in a pediatric population used sequential cohorts to compare different types of needleless connectors and a variety of locking solutions.22,23 One small, randomized prospective study used a positive displacement mechanical valve on all patients with peripherally inserted central catheters and compared flushing with heparin and flushing with saline only. The authors rejected the saline-only locking procedure, citing the cost of the declotting procedure on 6% of their PICCs annually24 (Table 2). A recent randomized prospective study compared a twice-weekly flush of heparin (concentration and volume not reported) using a “standard CVC cap” with a weekly flush of normal saline using a positive displacement mechanical valve25 (Table 2). Patient age is another factor in the concern about catheter flushing. A 2009 policy recommendation from the American Society of Health-System Pharmacists concluded, “The data are conflicting and insufficient to support the recommendation of a preferred solution for line maintenance in neonatal patients at this time.” They went on to emphasize the need for decreasing practice variations through standardized concentrations of heparin and the recommended the use of “manufacturer-prepackaged products” as the best method to provide safe care for neonates.26 This recommendation suggests that prefilled syringes for catheter flushing could eliminate the risk associated with preparing syringes on the nursing unit. The value of using normal saline exclusively for maintaining catheter patency has not been well established. The use of add-on needleless connectors with instructions for saline-only flushing and locking procedures adds greater confusion; however, there is a trend toward greater complications with saline-only flushing. There are limited studies on valved catheters, and they have conflicting results based on where the valve is located. up scroll Pause or Play down
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