What causes thrombosis during central venous cannulation?

Causes of Thrombosis During Central Venous Cannulation

Thrombosis during central venous cannulation is primarily caused by catheter-related factors (position, size, type), insertion technique, and patient-specific risk factors, with improper catheter tip position being the most significant modifiable risk factor.

Catheter-Related Factors

Position of the Catheter

• Catheter tip position: Higher thrombosis rates occur when the catheter tip is positioned above the junction of the superior vena cava and right atrium 1
• Insertion site: Left-sided insertion significantly increases thrombotic complications compared to right-sided placement 1, 2
• Venous access site: Femoral vein placement has higher thrombosis risk compared to jugular or subclavian sites 1

Catheter Characteristics

• Catheter size: Larger diameter catheters increase thrombosis risk, with rates of 1% for 4F, 6.6% for 5F, and 9.8% for 6F catheters 3
• Number of lumens: Triple-lumen catheters have higher thrombosis risk than double-lumen designs 1
• Catheter type: External catheters have higher thrombosis risk than implanted ports 1

Insertion Technique Factors

• Duration of placement procedure: Procedures exceeding 25 minutes increase thrombosis risk 1
• Multiple insertion attempts: More than one CVC placement attempt increases thrombotic risk 1
• Previous catheter insertion at the same site increases risk 1

Mechanical and Material-Related Causes

• Catheter kinking: Creates flow disturbances that promote thrombosis 1
• Pinch-off syndrome: Compression of the catheter between the first rib and clavicle, more common with subclavian access 1
• Catheter tip occlusion against vessel wall: Disrupts normal blood flow 1
• Tight sutures: Can restrict catheter function and promote thrombosis 1

Medication and Infusate-Related Factors

• Inappropriate medication concentration: Precipitates can form in the catheter lumen 1
• High pH or low pH solutions: Can cause precipitation and thrombosis 1
• Calcium phosphate precipitates: Form when incompatible solutions mix 1
• Lipid emulsions: Can promote thrombosis when administered improperly 1
• High-osmolarity and high-protein nutrition formulas: Increase thrombosis risk 1

Types of Catheter-Related Thrombosis

1. Intraluminal clot: Forms inside the catheter lumen 1
2. Fibrin sheath: Forms along the length of the catheter 1
3. Mural thrombosis: Forms on the vessel wall 1
4. Venous thrombosis: Occludes the vein containing the catheter 1

Clinical Implications and Prevention

Prevention Strategies

• Optimal catheter tip placement: Position at the junction of superior vena cava and right atrium 2
• Use smallest gauge catheter possible for clinical needs 2, 3
• Prefer right-sided insertion over left-sided 2
• Use ultrasound guidance during insertion 1
• Regular flushing with 0.9% normal saline 1

High-Risk Considerations

• Patients with cancer have significantly higher thrombosis risk 1, 2
• Previous history of venous thromboembolism increases risk 2
• Consider alternative access in patients with chronic kidney disease (eGFR <45 mL/min) to preserve veins for potential future hemodialysis 2, 4

Pitfalls and Caveats

• Doppler ultrasound guidance during insertion does not significantly reduce thrombosis risk 1
• Catheter-related thrombosis is often asymptomatic (only 0.5-28% of cases have symptoms) 1
• Clinical diagnosis is only possible in 40-47% of cases, making vigilant monitoring essential 1
• Avoid positioning catheter tips in the right atrium, as this may increase risk of atrial thrombus formation 5
• Thrombosis can occur even with proper technique and positioning, requiring regular assessment of catheter function 1