When to Use Heparin Lock vs Saline Lock for IV Access
For regularly accessed central venous catheters and peripheral IVs, use normal saline flush alone—heparin provides no additional benefit and should not be routinely used. 1
Algorithm for Lock Solution Selection
Use Saline Lock (Normal Saline 0.9%) When:
Central venous catheters accessed daily or frequently (multiple times per day): Routine heparin cannot be recommended over saline due to lack of proven benefit 1
Peripheral IV locks: Multiple meta-analyses confirm saline is equally effective as heparin for maintaining patency, preventing phlebitis, and increasing duration 2, 3
Catheters closed for short periods (<8 hours): Normal saline flushing alone is sufficient 4
Implanted ports (Port-a-Caths) with modern protocols: Normal saline is non-inferior to heparin for preventing occlusion, reflux dysfunction, and flow dysfunction 4
Close-ended valve catheters (e.g., Groshong): Use saline only per manufacturer instructions 4
Use Heparin Lock (5-10 U/mL) When:
Intermittently accessed central venous catheters: Flushing with 5-10 U/mL heparinized saline 1-2 times weekly helps maintain patency 1, 4
Implanted ports closed >8 hours: Heparinized solutions (typically 100 U/mL) should be used as a lock after proper saline flushing 4
Open-ended catheter lumens remaining closed >8 hours: Heparin lock is recommended 4
Manufacturer specifically recommends heparin: Follow device-specific instructions 4
Critical Evidence Supporting Saline Over Heparin
The European Society for Clinical Nutrition and Metabolism (ESPEN) explicitly recommends against routine heparin lock with Grade B recommendation and 95.5% agreement, stating saline should be the standard. 4
The evidence base is robust:
A 2013 randomized trial of 802 cancer patients showed NS locks had an incidence rate of 3.70% for functional complications versus 3.92% for heparin (relative risk 0.94,95% CI 0.67-1.32), establishing non-inferiority 5
A 1991 meta-analysis of 15 studies (n=3,490) found average effect size of 0.0573 for patency with 95% credibility interval ranging from -0.2267 to 0.3413, confirming saline equals heparin effectiveness 2
A 2024 umbrella review of systematic reviews found no evidence that heparin was more effective than normal saline in reducing occlusion, catheter-related infections, or thrombosis 3
Important Safety Considerations and Pitfalls
Heparin Risks to Avoid:
Heparin promotes intraluminal biofilm formation, potentially increasing catheter-related bloodstream infection risk 4, 6
Never use heparin immediately before or after lipid-containing parenteral nutrition: Heparin facilitates lipid precipitation; always interpose a saline flush between lipid infusion and heparin 4, 6
Potential systemic effects: Risks include thrombocytopenia and bone disease, which outweigh thrombosis risk in most cases 6
Special Populations:
Newborns with PICCs: Heparin has shown effectiveness in preventing occlusion, but potential risks have not been defined, so routine use cannot be recommended 1
Children receiving home parenteral nutrition: Insufficient evidence to advocate prophylactic anticoagulants for reducing catheter-related thrombosis, occlusion, and infection 1
Practical Flushing Protocol
When using saline locks:
- Flush with volume at least twice the catheter volume 6
- Use ≥10 mL syringes to prevent excessive pressure that could damage the catheter 6, 7
- Employ turbulent push-pause technique to create turbulence that clears the catheter lumen 6, 7
- Maintain strict aseptic technique during all catheter access 1, 4
When heparin is indicated:
- Use 5-10 U/mL concentration for intermittent flushing 1, 4
- Most authors suggest 50-500 U/mL range when higher concentrations are needed 4
- Flush with saline first, then lock with heparin 4
Cost Considerations
Switching from heparin to saline locks could save an estimated $109-218 million annually in U.S. healthcare dollars while maintaining equivalent quality of care and eliminating problems associated with anticoagulant effects and drug incompatibilities. 2