The administration of intravenous fluids and medication often involves the practice of “IV flushing.” Flushing an intravenous (IV) line means injecting a small volume of fluid into the catheter tubing to clear it out. The standard fluid used is Normal Saline, a sterile 0.9% solution of sodium chloride in water. This procedure is performed for reasons related to safety, catheter function, and medication effectiveness.
Maintaining Catheter Patency
The primary purpose of flushing the IV line is to ensure the catheter remains open and fully functional, a condition known as patency. Intravenous catheters, which are thin, flexible tubes inserted directly into a vein, are prone to becoming blocked when not in continuous use. This blockage often occurs because blood can flow back into the tip of the catheter, especially when the flow of medication or fluid stops.
This stagnant blood inside the catheter can quickly coagulate and form a clot. Once a catheter is occluded by a blood clot, it can no longer be used for administering fluids or medications. Flushing the line with saline pushes any residual blood or cells out of the catheter tip and into the larger bloodstream, where it is harmlessly diluted. This action is usually performed before and after a medication is given, and sometimes on a scheduled basis, to prevent obstructions.
Preventing Drug Incompatibility and Residue
Flushing the IV line also plays a role in maintaining the integrity of the medications a patient receives. It is common for a single IV access point to be used for multiple drugs and solutions throughout the day. If one medication is still lingering inside the IV tubing when a second medication is introduced, the two substances can interact chemically.
This mixing can lead to an incompatibility reaction, causing the drugs to precipitate, or form solid particles or crystals inside the line. Precipitates can cause a blockage and mean the patient is not receiving the full, intended dose of the medication. The saline flush acts as a neutral buffer, clearing all traces of the first drug from the catheter and tubing before the second drug reaches the access point. By isolating each drug administration, the saline ensures the full therapeutic effect of every dose is delivered.
The Safety of Normal Saline
The use of 0.9% sodium chloride solution, or Normal Saline, is based on the principle of isotonicity. This concentration of salt in water is formulated to match the natural salt concentration of the human body’s blood plasma. Solutions with this concentration are isotonic, meaning they have the same osmotic pressure as the body’s cells.
Injecting a fluid that is not isotonic, such as hypotonic sterile water, would cause a dangerous osmotic shift. A hypotonic solution would cause red blood cells to rapidly absorb water and swell, a process known as hemolysis. Because 0.9% saline is isotonic, it can be safely introduced directly into the vein without causing damaging fluid shifts across cell membranes, making it the most reliable agent for routine IV flushing.