An intravenous (IV) line is a thin, flexible catheter inserted into a vein, typically in the arm or hand. This access point provides a direct route into the bloodstream for delivering fluids, medications, or drawing blood samples. When the IV is not actively infusing, it is maintained as a “saline lock” or “heparin lock.” This requires “flushing,” which is the routine procedure of pushing a small volume of sterile solution, usually 0.9% normal saline, through the catheter to keep it functional.
The Primary Role of IV Flushing
Flushing is a standard procedure intended to maintain the patency of the catheter and prevent complications. The primary function is to clear the internal space, or lumen, of the catheter of any residual substances. This is especially important when switching between different medications to prevent drug-drug interactions, as certain drugs are chemically incompatible and can precipitate if they mix within the narrow tubing.
A second, equally important role is to prevent the patient’s blood from backing up into the catheter tip. When the line is not actively infusing fluid, the slight negative pressure created in the vein can draw a small amount of blood back into the catheter. If this blood is left stagnant, it will quickly begin to clot. Regular flushing with a sterile solution keeps the internal surface of the catheter clean and prevents this backflow from initiating the clotting cascade.
Immediate Risk: Catheter Occlusion
The most immediate and common consequence of failing to flush an IV line is catheter occlusion, or blockage. The human body naturally reacts to the foreign material of the catheter by initiating the clotting process. When blood backs up into the line, the fibrin in the blood rapidly forms a clot inside the narrow lumen of the catheter.
Stagnant blood provides the material for a thrombus to form, which can either partially or completely block the line. A partial occlusion may still allow fluids to be pushed in, but it prevents the healthcare provider from being able to withdraw blood, which is a key sign of a malfunctioning line. A complete thrombotic occlusion means the line is lost, as no fluid can be pushed through without meeting significant resistance. Attempting to force a flush against this resistance can be dangerous, potentially causing the catheter to rupture or pushing the clot into the bloodstream.
Treating a fully clotted line often requires the administration of specialized declotting agents, such as thrombolytic drugs. Otherwise, it requires the painful process of removing the old line and inserting a new one to regain venous access.
Systemic Dangers: Infection and Embolism
Beyond losing the functionality of the IV, not flushing introduces systemic dangers to the patient, primarily through infection and embolism. A blocked or poorly maintained catheter creates a perfect environment for microorganisms to colonize. Residual blood, fluid, or drug precipitates left in the catheter lumen can act as a breeding ground for bacteria, leading to the formation of a sticky, protective layer called biofilm.
This bacterial colonization can rapidly lead to a Catheter-Related Bloodstream Infection (CRBSI), a serious and potentially fatal complication. Bacteria from the biofilm are shed directly into the patient’s bloodstream, causing sepsis, a life-threatening response that can lead to organ failure. Central IV lines, which terminate in a large vein near the heart, carry a particularly high risk for this type of systemic infection.
Furthermore, an unflushed line significantly increases the risk of an embolism. If a blood clot forms inside the catheter and is not dissolved, it can be accidentally dislodged, becoming a thromboembolism that travels through the circulatory system. Depending on the size of the clot, this can lead to a pulmonary embolism, which blocks blood flow to the lungs, or a stroke if the clot travels to the brain. Attempts to force a flush into a clotted line can also inadvertently push air into the vein, resulting in a potentially life-threatening air embolism.
Standard Flushing Protocols
Healthcare professionals follow strict, established protocols to ensure the safety and functionality of all IV lines. The general rule of practice is to flush the line “before and after” every use, meaning prior to administering medication and immediately afterward. For lines that are not in continuous use, they are flushed at regular, scheduled intervals, often every 8 to 12 hours, to maintain patency.
The standard solution used is sterile 0.9% sodium chloride, referred to as normal saline, a solution compatible with the body’s tissues. A specific technique, known as the “push-pause” or “pulsatile” method, is often employed, particularly for central lines. This involves injecting the flush solution in short, rapid bursts with brief pauses in between, which creates turbulence within the catheter lumen. This turbulent flow is significantly more effective at dislodging and clearing any deposits from the catheter walls than a slow, continuous injection. The procedure requires specific syringe sizes, typically 10-milliliter syringes, to avoid generating excessive pressure that could damage the catheter.