CATHETER LOCKING SOLUTIONS

Abstract

Avoidance of clotting in catheter lumens between treatments usually entails locking with an anticoagulant solution such as heparin. Catheter manufacturers specify internal volume of the catheters and it is commonly assumed that injection of this precise volume is safe and efficient. However, it has been shown that aPTT increases after instillation of the heparin lock volume specified by the manufacturer. We have investigated this phenomenon in-vitro, employing dye and saline dilution and found that injection of the catheter volume results in spillage of up to 15 % of the catheter volume into the patient's blood. Depending on fluid dynamics of the instillation process and catheter compliance, the concentration of the locking solution at the catheter tip is much reduced. Side holes contribute to the initial loss of the locking solution during injection is well as to the subsequent loss to flowing blood. Thus, the locking solution composition and instillation methods are relevant safety issues. These aspects are especially important for antimicrobial or antibiotic catheter locking solutions intended to prevent catheter related infection. Antibiotics and antibiotic/anticoagulant mixtures have the potential to promote bacterial resistance. Concentrated citric acid was sold previously as a lock solution but was withdrawn in the US market after a fatal overdose. In order to achieve uniform concentration of the locking solute throughout the catheter lumen, “overfilling” is necessary which is only sate if the systemic effect of the locking solution is negligible.