Evaluation of the Flush Characteristics of Two Peripheral Vascular Access Catheters

Background: Peripheral vascular access is almost universal in current institutional healthcare.  The most common problem experienced with such catheters is clotting and occlusion, requiring that the device be changed.  A catheter with an internal valve to prevent backflow (Z5, Medikit Co., Ltd.) was recently developed to decrease this risk.  Since some catheter hubs with valves have been thought to have an increased risk of infection the same concern was raised for these Z5 catheters.  After a pilot study demonstrated that microorganisms introduced into Z5 catheters could grow to high numbers in the presence of blood, the current study was conducted.

Objective: Two different peripheral vascular access catheters, one with a valve (Z5) and one without (Insyte® Autoguard, IA, Becton Dickinson and Company) were evaluated, for the potential to become colonized with microorganisms.

Methods: Four dilutions of a suspension of Staphylococcus epidermidis (ATCC 12228) were created from a 0.5 McFarland standard matched solution (1 X 10⁸ CFU /mL).  A simulated vein filled with sterile defibrinated sheep blood was created using latex tubing attached to a three-way stopcock and a sterile syringe barrel.  Each catheter was then inserted into the tubing, the cannula was removed and the device was allowed to fill with blood.  Each catheter was then removed, connected to a needleless connector, and flushed with 10 mL of a designated bacterial suspension.  The catheters were then flushed with 10 mL of sterile saline, locked, and incubated in sterile Petri dishes at 35°C for 24 hours.  The following day each device was flushed five times with 1 mL of sterile saline.  The flush solution was collected and two serial ten-fold dilutions were made from each one.  One-tenth milliliter of the original flush suspension and 0.1 mL of each serial dilution were cultured on TSA with sheep blood to determine the number of bacteria in each sample.  Ten replicates were done for each condition.

Results: There was no difference between the bacteria recovered from the two groups of devices when flushed with 10 mL of a low concentration of bacteria (~147 CFU/mL).  For devices inoculated with 1600, 23,300, and 523,000 CFU/mL of S. epidermidis the Z5 catheter averaged >100,000 CFU/mL bacteria recovered from the ten replicates versus zero CFU for all IA catheters (p≤0.001).

Conclusions: This study demonstrated that the Z5 catheter was more likely to have bacteria persist and multiply in the lumen than the IA catheter.  We hypothesize that the design of the valve in the Z5 catheter may also allow blood to remain in the device which serves as a nutrient source and promotes bacterial growth to high numbers, potentially leading to an increased risk of infection.  Further studies would be required to determine the clinical significance of these findings.