Why is citrate used to lock central venous catheter (CVC) lines?

Citrate Lock Solution for Central Venous Catheters

Low-concentration citrate (<5%) should be used as a central venous catheter (CVC) locking solution to help prevent catheter-related bloodstream infections (CRBSI) and CVC dysfunction. 1

Mechanism and Benefits of Citrate Lock Solution

Citrate serves two critical functions when used as a catheter lock solution:

1. Anticoagulant properties:

   • Citrate chelates calcium, which is essential for the coagulation cascade
   • Prevents thrombus formation within the catheter lumen
   • Maintains catheter patency between uses

2. Antimicrobial properties:

   • Creates an environment that inhibits bacterial growth
   • Prevents biofilm formation
   • Reduces risk of catheter-related bloodstream infections

Evidence Supporting Citrate Lock Use

The KDOQI guidelines specifically suggest using low-concentration citrate (<5%) CVC locking solution to help prevent CRBSI and CVC dysfunction. 2 This recommendation is based on evidence showing that citrate locks can significantly reduce infection rates compared to traditional heparin locks.

A systematic review and meta-analysis of 13 randomized controlled trials (1,770 patients) found that:

• Antimicrobial-containing citrate locks reduced the incidence of CRBSI (Risk Ratio 0.39)
• Low (1.04%-4%) to moderate (4.6%-7%) concentration citrate locks were associated with decreased CRBSI incidence
• Citrate locks significantly reduced bleeding episodes compared to heparin 3

Optimal Citrate Concentration

The evidence supports using low-concentration citrate:

• KDOQI guidelines recommend concentrations <5% 2
• Higher concentrations (30%-46.7%) have not shown additional benefits in preventing CRBSI 3
• Lower concentrations minimize potential side effects while maintaining efficacy

Combination with Other Agents

Citrate can be effectively combined with other agents:

• KDOQI recommends alteplase or urokinase plus citrate 4% per limb for restoring blood flow in occluded CVCs 2, 1
• Antimicrobial-containing citrate locks (citrate + gentamicin, citrate + taurolidine, or citrate + methylene blue + methylparaben + propylparaben) have shown superior prevention of CRBSI compared to heparin locks 3
• A randomized controlled trial in pediatric patients with hematological malignancies found that taurolidine-citrate lock solution (1.35% taurolidine and 4% citrate) significantly reduced bloodstream infections compared to heparin (0.3 vs 1.3 infections per 1000 catheter-days) 4

Safety Considerations

Citrate lock solutions are generally safe:

• Low-concentration citrate (<5%) has minimal systemic effects
• Higher concentrations may cause arrhythmias and other complications
• No significant difference in catheter thrombosis or dysfunction compared to heparin 3

Clinical Application Algorithm

1. For routine CVC maintenance:

   • Use low-concentration citrate (<5%) as the preferred lock solution
   • Apply after each catheter use or per institutional protocol

2. For patients with history of CRBSI:

   • Consider antimicrobial-containing citrate lock solutions
   • Options include citrate + taurolidine or other antimicrobial combinations

3. For occluded catheters:

   • Use alteplase or urokinase plus citrate 4% as recommended by KDOQI 2, 1

4. For patients at high risk of bleeding:

   • Citrate is particularly advantageous as it provides local anticoagulation without systemic effects

Practical Considerations

• Citrate lock solution should be instilled in a volume sufficient to fill the catheter lumen
• The solution should dwell in the catheter between uses
• Before next use, the lock solution should be aspirated rather than flushed to avoid systemic effects

In conclusion, citrate lock solutions provide dual benefits of preventing both catheter-related infections and thrombotic complications, making them an optimal choice for maintaining central venous catheter patency and reducing complications that impact patient morbidity and mortality.