Every vascular access device begins to fail the moment it is inserted.

That statement may sound dramatic, but it reflects the reality of what happens inside every catheter. Within minutes of insertion, blood proteins begin to adsorb to the catheter surface. Fibrin starts to accumulate. Medications can leave microscopic residue within the lumen. Blood reflux may occur with every disconnection. Left unchecked, these seemingly insignificant events become the foundation for thrombotic occlusion, biofilm formation, and ultimately catheter failure.

Fortunately, one of the most effective interventions for preventing these complications requires no new technology, no expensive equipment, and only a few additional seconds of nursing time.

It is called proper flushing technique.

While clinicians spend considerable time learning insertion techniques, the long-term success of any vascular access device depends just as much on how it is maintained. Every flush is an opportunity to preserve catheter function, protect the vessel, and improve patient outcomes.

What Happens Inside a Catheter Between Uses?

Although a catheter may appear clean after medication administration, microscopic changes continue to occur within the lumen.

These include:

• Blood reflux into the catheter

• Protein adsorption to the catheter surface

• Fibrin deposition

• Medication residue

• Drug precipitate

• Lipid accumulation from parenteral nutrition

• Early biofilm development

These processes begin long before resistance is felt during a flush. Once established, they can contribute to catheter occlusion, infection, treatment delays, and premature catheter replacement.

Routine flushing interrupts these processes by removing residual blood and medications before they become clinically significant.

The Physics of a Flush

A flush is much more than pushing saline through a catheter.

The goal is to create sufficient flow to clear the entire internal surface of the catheter system—not simply move fluid from one end to the other.

A slow, continuous flush creates laminar flow, in which fluid moves in parallel layers with minimal mixing. While this confirms patency, it is less effective at removing debris adhered to the catheter walls.

The push-pause (pulsatile) techniquecreates brief bursts of turbulent flow that are more effective at dislodging blood, protein deposits, medication residue, and early fibrin accumulation.

Think of rinsing a dirty bottle. Running water slowly through the bottle removes some debris, but shaking the water inside cleans the walls much more effectively. The same principle applies inside a vascular access device.

What Do the 2024 INS Standards Recommend?

The 2024 Infusion Therapy Standards of Practice provide several evidence-based recommendations for flushing vascular access devices.

Flush Before and After Every Use

Flush the catheter:

• Before administering medications or fluids to assess patency

• Between incompatible medications

• After medication administration

• After blood sampling when appropriate

• Before locking the device

Use Preservative-Free 0.9% Sodium Chloride

For most vascular access devices, the recommended flushing solution is preservative-free 0.9% sodium chlorideunless the manufacturer’s Instructions for Use (IFU) specify otherwise.

Use an Adequate Flush Volume

The INS Standards recommend using a minimum flush volume equal to twice the internal volume of the catheter system, including the catheter, extension tubing, and needleless connector.

Larger flush volumes may be needed following blood products, parenteral nutrition, contrast media, lipid emulsions, or other viscous infusions to adequately clear the lumen.

Common Clinical Flush Volumes

The INS Standards emphasize flushing with at least twice the internal volume of the catheter system. The volumes below reflect common clinical practice and should always be considered alongside the manufacturer’s Instructions for Use (IFU) and your organization’s policies.

Clinical Pearl: Don’t memorize flush volumes—understand the principle. The objective is to completely clear the catheter system while following manufacturer recommendations and institutional policy.

Use the Push-Pause Technique

Rather than administering saline in one continuous push, use multiple short bursts:

Push → Pause → Push → Pause → Push

This pulsatile technique creates turbulence within the catheter lumen and more effectively removes blood and medication residue than a slow, continuous flush.

Maintain Positive Pressure

Blood reflux is a common contributor to catheter occlusion.

Maintaining positive pressure during syringe disconnection helps reduce blood reflux into the catheter lumen. Depending on the device, this may involve maintaining pressure on the syringe plunger while disconnecting or using anti-reflux needleless connectors.

The goal is simple:

Leave saline—not blood—at the catheter tip.

Choose the Appropriate Syringe

For most central vascular access devices, a 10-mL syringe or larger is recommended unless the manufacturer specifies otherwise.

Smaller syringes generate higher injection pressures, increasing the risk of catheter damage.

Remember:

It is pressure—not syringe volume—that matters.

Every Flush Is Also an Assessment

Flushing is not simply a maintenance task—it is a clinical assessment.

While flushing, evaluate for:

• Resistance

• Ease of injection

• Pain

• Swelling

• Leakage

• Blood return, when appropriate

• Patient discomfort

Never force a flush.

Unexpected resistance is valuable clinical information that should prompt further assessment rather than increased injection pressure.

Common Flush Technique Errors

Even experienced clinicians develop habits that increase the risk of catheter dysfunction.

Common mistakes include:

• Using insufficient flush volume

• Flushing too rapidly without using a push-pause technique

• Forgetting to flush between incompatible medications

• Failing to maintain positive pressure

• Using excessive force when resistance is encountered

• Assuming that an easy flush confirms full catheter function

• Neglecting to assess the patient while flushing

Each of these seemingly minor errors can shorten catheter life and increase the likelihood of occlusion.

BevelUp Clinical Pearls

• A catheter that flushes easily is not necessarily functioning normally.

• Push-pause flushing is designed to create turbulence—not speed.

• Larger flush volumes are often needed after blood products, lipid emulsions, parenteral nutrition, and contrast media.

• Never force saline through a resistant catheter.

• Successful vascular access depends just as much on maintenance as it does on insertion.

BevelUp Takeaway

Great vascular access doesn’t end with successful insertion.

It depends on meticulous maintenance.

Every flush is an opportunity to assess catheter function, prevent complications, preserve the vessel, and extend the life of the device. A few extra seconds spent using the proper technique today may prevent an unnecessary catheter replacement tomorrow.

The best vascular access clinicians understand that the catheter isn’t finished when it’s inserted—it’s just getting started.

References

Gorski LA, Hadaway L, Hagle ME, et al. Infusion Therapy Standards of Practice. J Infus Nurs. 2024;47(1 Suppl):S1-S285.

Infusion Nurses Society. Policies and Procedures for Infusion Therapy. 7th ed. Norwood, MA: Infusion Nurses Society; 2024.

Alexandrou E, Ray-Barruel G, Carr PJ, et al. Use of short peripheral intravenous catheters: Characteristics, management, and outcomes worldwide. J Hosp Med.2018;13(5):E1-E7.

Marsh N, Webster J, Ullman AJ, et al. Peripheral intravenous catheter failure: A secondary analysis of risks from a randomized controlled trial. BMJ Open.2020;10:e034385.

Guiffant G, Durussel JJ, Flaud P, et al. Flushing of intravascular access devices: Efficacy of pulsed versus continuous flushing. J Vasc Access. 2012;13(1):75-78.