An intravenous (IV) line provides a direct pathway into the bloodstream for delivering fluids, medications, and nutrients. Maintaining the functionality of this line is a routine part of medical care that involves IV flushing. Flushing is the administration of a small amount of sterile solution, typically 0.9% Normal Saline, into the IV catheter. The primary objective is to preserve the patency of the line, keeping the catheter open and fully functional. This action helps prevent complications that could interrupt treatment.
The Purpose and Mechanics of IV Flushing
Flushing an IV line prevents the buildup of materials that could lead to an occlusion. Within the small diameter of the catheter, blood components like fibrin and medication residues can accumulate, creating a sticky film that narrows the internal passage. The saline flush acts as an internal cleaning cycle, pushing these substances out of the catheter’s tip and into the patient’s circulation where they disperse safely. Flushing is also used between the administration of two incompatible medications to clear the line of the first drug, preventing a chemical reaction.
The how of flushing relies on a specific method called the “push-pause” technique. This technique involves injecting the saline in short, intermittent bursts rather than a single continuous stream. This action creates turbulence inside the catheter lumen. This turbulent flow is significantly more effective at dislodging adherent debris and residue than a smooth, laminar flow.
Another technique is the positive pressure method, which is used to prevent blood from flowing backward into the catheter tip when the syringe is disconnected. As the final portion of the saline is injected, the clamp on the IV line is closed while the plunger is still being pushed. This sequence ensures a small amount of positive pressure remains within the catheter, which helps to counteract the negative pressure that occurs when the syringe is removed, preventing blood reflux into the line.
Standard Volumes for Peripheral IV Lines
The Peripheral Intravenous (PIV) line, typically placed in the arm or hand, requires a relatively small saline volume. The standard volume used to flush an adult PIV is between 3 milliliters (mL) and 5 mL of 0.9% Normal Saline. This volume is sufficient to clear the short length of the catheter and any attached extension tubing.
The minimum volume used for a flush should be at least twice the internal volume of the catheter and any add-on devices. While 3 mL may be enough to clear a short catheter, 5 mL is often recommended as a general standard to ensure the entire system is thoroughly rinsed. PIVs are flushed before and after medication administration to prepare the line and clear residual drug. If the line is not in continuous use, it is converted to a “saline lock” and flushed routinely, often every 8 or 12 hours, to maintain patency.
Flushing Requirements for Central Venous Access Devices
Central Venous Access Devices (CVADs) include PICCs, tunneled catheters, and implanted ports, and they require a distinct and more stringent flushing protocol. Because CVADs are much longer, with the tip residing in a large central vein near the heart, they require a significantly larger volume of saline to ensure complete clearance. The standard flushing volume for an adult CVAD is 10 mL of 0.9% Normal Saline.
This larger 10 mL volume is necessary to account for the substantial priming volume of the longer catheter and its port reservoir. After drawing blood samples or administering viscous fluids, the volume may be increased to 20 mL to 30 mL to ensure all residue is removed from the line’s inner walls. CVADs are flushed after every use or on a regular maintenance schedule, such as daily or weekly, depending on the device type.
Before any fluid is injected into a CVAD, confirming blood return is a necessary safety step to ensure the catheter tip is correctly positioned and the line is functioning. Always use a 10 mL or larger syringe for CVAD flushes, even when injecting a smaller volume, because smaller syringes generate higher pressure that could potentially damage the catheter wall. Some CVADs, particularly implanted ports, may require a final “locking” solution, such as heparin or citrate, following the saline flush to maintain patency during periods of non-use.