Vascular access devices (VADs), such as peripheral intravenous catheters, PICC lines, or central lines, deliver medications and fluids directly into the bloodstream. Maintaining the functionality of these devices requires specific, routine care protocols to ensure they remain open and safe for patient use. The procedure known as flushing involves the manual injection of a solution through the device to clear the internal pathway. This precise action is a standard practice in healthcare settings, directly impacting the device’s longevity and patient safety.
The Essential Need for Line Flushing
Regular flushing is a mandatory procedure designed to preserve VAD functionality. The primary purpose is to keep the catheter patent, ensuring the internal lumen remains open and free of obstruction for fluid flow. Without routine clearing, the device is susceptible to internal blockage by blood components or residual medication.
Flushing also prevents the mixing of different, potentially incompatible substances within the catheter. Many intravenous medications can react chemically to form solid particles, known as precipitation. These precipitates can lodge inside the catheter, causing immediate blockage or damage. Flushing acts as a cleansing rinse between administrations to clear the line and prevent drug interactions within the VAD.
Distinct Functions of Saline and Heparin
Saline (0.9% sodium chloride solution) and heparin serve fundamentally different purposes in VAD maintenance. Saline is an isotonic fluid used purely for mechanical rinsing. It physically pushes out material left inside the catheter.
This rinsing action clears away medication residue, blood components, or fibrin deposits from the catheter walls before, between, and after infusions. Saline is the universal standard for flushing because it is a neutral solution compatible with virtually all medications and fluids.
Heparin is an active anticoagulant drug used to prevent blood clots when the VAD is not in active use. It functions as a “lock” solution, where a small volume is instilled and left to bathe the interior surface of the catheter and its tip. This maintains patency by stopping the body’s natural clotting process.
The decision to use a heparin lock depends on the VAD type and the patient’s clinical status. Many modern devices, especially peripheral lines, are maintained solely with saline, eliminating the risks associated with administering an anticoagulant. Heparin concentrations used for locking are typically very low, but the solution must be fully withdrawn before the next infusion to avoid accidental systemic delivery.
Determining the Correct Flushing Sequence
When administering medication or locking a VAD, the order of solutions is critical. The universal rule is that saline must always flush the line first, both before and after medication administration or before instilling a final locking solution. The initial saline flush ensures the catheter is open and functioning correctly before a drug is introduced.
This initial flush removes any existing lock solution, such as residual heparin, or blood that may have refluxed into the catheter tip. Failing to clear the line first means administered medication could mix with the lock solution or clotted blood, causing chemical incompatibility or immediate blockage.
The standard protocol for VADs requiring a heparin lock is summarized by the acronym SASH: Saline, Administer Medication, Saline, Heparin. The second saline flush, following the medication, rinses the drug entirely out of the catheter lumen. This prevents the medication from interacting with the final heparin lock solution, which could otherwise cause precipitation and occlusion.
For frequently accessed or peripheral VADs, the final heparin step is often omitted, simplifying the protocol to SAS: Saline, Administer Medication, Saline. Saline-only maintenance reduces the patient’s exposure to an anticoagulant drug. In all cases, the saline flush is the preceding step, ensuring a clean pathway for the final solution.
Clinical Consequences of Improper Flushing
Ignoring the correct flushing sequence or technique compromises patient safety and device function. The most common consequence is catheter occlusion, where the line becomes completely blocked by a thrombus or precipitated medication. This failure often necessitates the use of powerful thrombolytic agents to clear the line or, in severe cases, requires the VAD to be surgically removed and replaced.
Improperly clearing the line with saline between incompatible solutions can result in the formation of crystals or precipitates. If the second saline flush is skipped, the administered drug will react with the final heparin lock, causing a physical obstruction that permanently damages the line.
Procedural errors, including poor technique or incorrect flushing volume, elevate the risk of infection. Failure to clear blood or debris from the line’s internal surface creates a favorable environment for bacteria to colonize and form a biofilm. This colonization significantly increases the likelihood of a catheter-related bloodstream infection.