Why is a heparin (anticoagulant) lock preferred over a saline lock for maintaining patency in intermittent intravenous (IV) lines?

Heparin Lock vs Saline Lock for Intermittent IV Lines

For intermittent IV lines that are accessed infrequently (closed >8 hours), heparin lock (5-10 U/mL) is preferred over saline lock because it maintains patency better, while for frequently accessed lines (closed <8 hours), saline alone is sufficient. 1

Key Decision Algorithm

For Intermittently Accessed Central Lines

• Use heparin lock (5-10 U/mL) when:
  • The catheter will remain closed for more than 8 hours 1
  • Implanted ports are being used 1
  • Open-ended catheter lumens will remain closed for more than 8 hours 1
  • Flushing frequency: 1-2 times weekly 2, 1

For Frequently Accessed Lines

• Use saline lock alone when:
  • The catheter is accessed frequently or closed for short periods (<8 hours) 1
  • The line is being used on a daily basis 2

Evidence Supporting This Distinction

The 2018 ESPGHAN/ESPEN/ESPR/CSPEN guidelines make a critical distinction that explains the confusion around this topic: routine heparin use for daily-accessed CVCs cannot be recommended over saline (conditional recommendation against), BUT for intermittently accessed CVCs, heparinized saline 1-2 times weekly helps maintain patency (conditional recommendation for). 2

Multiple meta-analyses have shown that intermittent flushing with heparin is no more beneficial than saline for most frequently-used central venous access devices. 1 However, this evidence applies primarily to lines in regular use, not those sitting idle for extended periods.

Why the Distinction Matters

The frequency of access is the determining factor:

• When lines are used frequently, the mechanical action of regular flushing with saline prevents clot formation 1
• When lines sit idle for >8 hours, blood stasis increases thrombosis risk, making heparin's anticoagulant properties beneficial 1

Peripheral IV Locks: A Different Story

For peripheral IV locks (not central lines), the evidence is clearer: saline is equally effective as heparin for maintaining patency. Studies in neonates and children showed no difference in duration of patency between 10 U/mL heparin and normal saline for peripheral locks. 3, 4 A 1998 meta-analysis confirmed that intermittent heparin flushes at 10 U/mL in peripheral venous catheters had no benefit over normal saline. 5

Common Pitfalls to Avoid

• Don't use heparin immediately before or after lipid-containing parenteral nutrition - heparin may facilitate lipid precipitation; always interpose a saline flush 1
• Don't use heparin in close-ended valve catheters - these should be flushed with saline only per manufacturer instructions 1
• Don't confuse frequency of access with type of catheter - the access pattern matters more than the catheter type for this decision 1

Heparin Concentration When Indicated

When heparin is appropriate, use 5-10 U/mL for intermittent flushing 2, 1, though concentrations between 50-500 U/mL are also supported in the literature 1. The lower concentrations (5-10 U/mL) are preferred to minimize systemic anticoagulant effects while maintaining local patency. 6