A heplock is a small device attached to an IV catheter that keeps a vein accessible for medications or fluids without requiring a continuous drip. The name comes from “heparin lock,” because hospitals traditionally flushed the device with a blood-thinning solution called heparin to prevent clotting. Today, most facilities use plain saline instead, so you’ll also hear the terms “saline lock” or simply “IV lock.” The concept is the same: a capped-off IV line that sits ready in your vein until it’s needed.
How a Heplock Works
A heplock starts as a standard IV catheter, the same small flexible tube placed into a vein on your hand or arm. Instead of connecting it to a bag of fluid hanging on a pole, the nurse attaches a short extension tube with a cap or valve on the end. This cap seals the line so nothing flows in or out between uses. When it’s time for medication, a nurse can plug into the cap, deliver the drug, flush the line with saline, and seal it again.
The key advantage is freedom. With no fluid bag or tubing tethering you to an IV pole, you can move around, use the bathroom, and sleep more comfortably. In prehospital settings, paramedics have found that saline locks are easier to maintain than traditional fluid bags and make patient transport significantly smoother, with 92% of paramedics in one study reporting that locks improved transportation.
Why You Might Have One
Heplocks are used whenever a care team wants IV access available but doesn’t need fluids running constantly. Common scenarios include:
- Intermittent medications: antibiotics, pain medication, or chemotherapy given at scheduled intervals throughout the day
- Emergency readiness: keeping a vein open in case you need rapid drug delivery or fluids, such as during labor and delivery or post-surgery monitoring
- Outpatient infusions: receiving treatment at a clinic or at home where you’re disconnected between doses
Patients who need continuous fluid replacement, constant drug infusions, or are in critical situations like cardiac arrest typically get a full running IV instead.
Heparin vs. Saline: Why the Name Stuck
For decades, nurses flushed IV locks with diluted heparin, a blood thinner that prevented clots from forming inside the catheter. The practice was so widespread that “heplock” became the generic term for any capped IV line. But heparin carries real risks. Even small amounts can trigger a dangerous immune reaction called heparin-induced thrombocytopenia, where the body’s platelet count drops sharply and paradoxically causes blood clots. This reaction can happen with any form or amount of heparin, including the tiny doses used in flushes.
Heparin flushes also carry risks of overdose, allergic reactions, and drug interactions. Research showed that plain saline works just as well for peripheral (arm or hand) IV lines, so most hospitals have switched. For central venous catheters, which are larger lines placed in the chest or neck, some institutions still use heparin at concentrations of 10 to 100 units per milliliter because these lines are longer and more prone to clotting.
What Maintenance Looks Like
A heplock needs regular flushing to stay open and functional. For peripheral lines, nurses typically flush with about 5 mL of normal saline every 8 to 12 hours. Before and after each medication dose, the line gets flushed again to clear out any residual drug. After thicker substances like blood products or nutrition formulas, a larger 20 mL flush is used.
Between flushes, a small amount of solution (about 1 mL for a standard peripheral line) is left inside the catheter as a “lock” to keep blood from backing up and clotting in the tube. The extension tubing is then clamped shut. If you’re at home with a heplock, you’ll likely be asked to check the insertion site every four hours during waking hours and report any changes.
How Long It Can Stay In
CDC guidelines state that peripheral IV catheters in adults don’t need to be replaced more frequently than every 72 to 96 hours (three to four days) to reduce the risk of infection and vein irritation. In children, replacement is based on clinical need rather than a set schedule. Your care team will assess the site regularly and replace the catheter sooner if problems develop, or potentially leave it longer if everything looks healthy and the hospital’s policy allows it.
Complications to Watch For
Most heplocks work without issues, but complications can occur. In a large study of critically ill patients, about 21% of peripheral IV catheters eventually failed for one reason or another, with the two most common problems being fluid leaking into surrounding tissue (7.7%) and vein inflammation (7.5%). These numbers reflect an intensive care population, so rates in typical hospital or outpatient settings tend to be lower.
The signs worth paying attention to at the insertion site include:
- Redness, warmth, or swelling tracking along the vein, which suggests inflammation (phlebitis)
- Pain or tightness around the site, especially if the skin feels cool or puffy, which may mean fluid is leaking into tissue rather than entering the vein
- Burning or stinging during an infusion, which could indicate the catheter has shifted out of the vein
- Any drainage from around the catheter, particularly if it looks cloudy or has an odor, which points to infection
- Bleeding around the insertion site that doesn’t stop with light pressure
Local infections at IV sites typically appear two to three days after insertion. Numbness or tingling during or after placement can indicate nerve irritation, which is uncommon but worth reporting promptly.
Special Considerations for Infants
Heplocks in newborns require extra caution. The recommended heparin concentration for neonates is much lower than for adults, typically 0.5 units per milliliter compared to 10 or more units per milliliter in adult lines. Even commercially available pre-mixed heparin solutions (2 units/mL) may be too concentrated for very small babies. For infants weighing under about 3.3 pounds, routine heparin flush is generally not recommended due to the heightened risk of bleeding and other complications. The salt content of the flush solution also matters in newborns, since excess sodium can interfere with their developing kidneys and increase the risk of serious conditions affecting the brain and lungs.