When to Use Heparin for Line Flushing
Heparin flushes should be reserved for specific catheter types that will remain closed for more than 8 hours—specifically implanted ports and open-ended catheter lumens—while most central venous catheters in frequent use should be flushed with saline alone. 1
Primary Recommendation Based on Guidelines
The ESPEN guidelines provide clear, evidence-based direction on this question:
- Most central venous access devices can be safely flushed and locked with saline solution alone when not in use (Grade B evidence) 1
- Heparinized solutions should only be used as a lock (after proper saline flushing) when:
- Recommended by the manufacturer
- For implanted ports or open-ended catheter lumens
- When scheduled to remain closed for more than 8 hours (Grade C evidence) 1
The Evidence Behind This Recommendation
Three separate meta-analyses of randomized controlled trials concluded that intermittent flushing with heparin is no more beneficial than normal saline alone for maintaining catheter patency. 1 This is a critical finding that challenges traditional practice patterns.
Key Nuances:
- Proper saline flushing technique is more important than heparin itself 1
- The concentration of heparin (when used) matters less than the flushing protocol
- For catheters in frequent use (accessed daily), there is no need for heparinization when closed for short periods (<8 hours) 1
Specific Clinical Scenarios
When Heparin IS Indicated:
Infrequently accessed catheters:
- Implantable ports
- Open-ended catheter lumens not used daily
- Hemodialysis or apheresis devices 1
Suggested concentrations: 50-500 units/mL (Grade C) 1
Suggested frequency for unused lumens:
- Small caliber catheters (≤5 Fr): weekly flushing
- Large caliber catheters (≥6 Fr): every 3-4 weeks 1
When Heparin is NOT Indicated:
- Hospital-based parenteral nutrition (typically continuous infusion or short intervals) 1
- Close-ended valve catheters (should use saline only per manufacturer instructions) 1
- Catheters in frequent use (Grade A evidence for saline) 1
Pediatric Considerations:
The 2018 ESPGHAN/ESPEN pediatric guidelines recommend:
- Routine heparin flush for daily-use CVCs cannot be recommended over saline (conditional recommendation against) 2
- For intermittently accessed CVCs: 5-10 U/mL heparinized saline 1-2 times weekly can be used (conditional recommendation for) 2
Critical Safety Considerations
Lipid Precipitation Risk:
Heparin should NEVER be used immediately before or after lipid-containing parenteral nutrition (Grade B) 1
- Always interpose a saline flush between heparin and lipid solutions
- Heparin facilitates precipitation of lipids, which can cause catheter occlusion
Arterial Lines:
The AAGBI guidelines specifically recommend saline-heparin as the only safe solution for arterial line flushes to prevent medication errors (particularly insulin administration errors) 3
Practical Algorithm for Decision-Making
Step 1: Identify catheter type
- Implanted port or open-ended lumen → Consider heparin
- Close-ended valve catheter → Saline only
- Standard CVC → Proceed to Step 2
Step 2: Assess frequency of access
- Daily use or continuous infusion → Saline only
- Closed >8 hours between uses → Consider heparin lock
Step 3: Check for contraindications
- Lipid-containing PN planned → Saline only (with saline buffer if heparin needed later)
- Manufacturer recommendations → Follow specific guidance
Step 4: If heparin indicated
- Flush with saline first
- Lock with heparin 50-500 U/mL
- Document clearly to prevent confusion with therapeutic heparin
Common Pitfalls to Avoid
- Using heparin "just because we always have" - The evidence doesn't support routine heparinization of frequently accessed lines
- Forgetting the saline flush before heparin - This is more important than the heparin itself
- Mixing heparin with lipid solutions - Always use saline as a buffer
- Confusing catheter lock flush vials with therapeutic heparin vials - This medication error can be fatal 4
The evidence strongly supports a saline-first approach for most intravenous lines, with heparin reserved for specific situations where catheters remain unused for extended periods.