How often you flush a central line with heparin depends on the type of line and whether it’s actively being used. For lines in regular use, flushing typically happens at least once daily or after each use. For implanted ports that aren’t being accessed, the standard interval is every four weeks, though evidence supports safely extending that to every six to eight weeks.
Flush Frequency by Central Line Type
Not all central lines follow the same schedule. The type of device you have determines both how often you flush and whether heparin is even necessary.
PICC lines: When a PICC line is in active use, you flush it before and after each medication or infusion. If the line isn’t being used regularly, flushing once a day is common, though some providers recommend once a week depending on the catheter design. Your care team will give you a specific schedule based on your situation.
Tunneled catheters (like Hickman or Groshong lines): These are flushed after each use. When not in use, most protocols call for flushing at least once daily or every other day for each lumen. Groshong catheters have a valve that reduces blood backflow, so some institutions allow weekly flushing with saline alone instead of heparin.
Implanted ports: Ports that aren’t being accessed need a maintenance flush every four weeks. Most manufacturers recommend this interval, though systematic reviews suggest that flushing every eight weeks does not increase complications. The Oncology Nursing Society and CDC guidelines allow flexibility, recommending a flush every four to eight weeks when the port is not in use. During the COVID-19 pandemic, many clinics extended intervals to reduce patient visits without seeing higher blockage rates.
The SASH Method
When you’re using a central line for medications or infusions, flushing follows a specific sequence known as SASH: Saline, Administer (your medication), Saline, Heparin. The saline flushes before and after the medication clear the line and prevent drug interactions inside the tubing. The final heparin flush locks the line to keep blood from clotting inside it until the next use.
If you’re only flushing for maintenance (no medication being given), the sequence is simpler: saline flush followed by a heparin lock.
How Much Heparin to Use
The most commonly used concentration for central line flushing is 100 units per mL, with a volume of 3 to 5 mL per lumen. That delivers roughly 300 to 500 units of heparin per flush. Some protocols use lower concentrations (as low as 10 units per mL) and others go higher, but 100 units per mL in a 5 mL volume is the standard you’ll encounter most often.
For the saline portion of the flush, guidelines recommend at least 10 mL to adequately clear the catheter. After blood draws, blood transfusions, or thick infusions like parenteral nutrition, a 20 mL saline flush is better because these products are more likely to leave residue that can build up and block the line. Always use a syringe that’s 10 mL or larger, since smaller syringes generate higher pressure that can damage the catheter.
Does Heparin Actually Prevent Blockages?
This is less settled than you might expect. A Cochrane review pooling data from 10 studies and over 1,600 patients found that heparin locking may reduce central line blockages compared to saline alone, but the evidence was rated low-certainty. The reviewers concluded they could not confirm that heparin prevents blockages better than normal saline.
In practice, many hospitals have shifted to saline-only flushing for certain catheter types, particularly those with valved tips. Heparin remains standard for implanted ports during maintenance periods and for open-ended catheters, where the risk of blood backflow and clotting is higher. If your care team uses saline only, that’s a reasonable approach supported by current evidence.
Risks of Heparin Flushes
Even in the small doses used for flushing, heparin carries a real, if uncommon, risk: heparin-induced thrombocytopenia, or HIT. This is an immune reaction where your body forms antibodies against heparin, causing your platelet count to drop. Paradoxically, it can trigger dangerous blood clots rather than prevent them.
About 1 to 3 percent of patients receiving full therapeutic doses of heparin develop HIT. The risk from flush doses is lower, but documented cases exist. In one report, three patients developed HIT from daily flushes of just 200 units of heparin (2 mL of a 100 units per mL solution). Each had been flushing daily for several weeks before symptoms appeared.
Signs of HIT include unexplained bruising, a new blood clot, or a sudden drop in platelet count on bloodwork. If you’re flushing with heparin regularly and notice unusual bruising or swelling, bring it up with your care team. This is one reason some institutions prefer saline-only protocols when the evidence supports it.
Tips for Flushing at Home
If you’re managing a central line at home, consistency matters more than perfection. Flush at roughly the same time each day to build the habit. Before each flush, wash your hands thoroughly and clean the catheter hub with an alcohol swab for at least 15 seconds, letting it dry completely before connecting your syringe.
Use a slow, steady push-pause technique when flushing. Push about 1 mL, pause briefly, push another mL, and repeat. This creates small turbulent swirls inside the catheter that help clear residue from the walls more effectively than one continuous push. If you feel resistance when flushing, stop. Forcing fluid into a blocked line can damage the catheter or push a clot into your bloodstream. Contact your care team if the line won’t flush smoothly.
Keep a simple log of when you flush, noting any resistance or problems. This helps your care team troubleshoot issues early and gives you a reliable way to confirm you haven’t missed a scheduled flush.