Pulsative Flushing As A Strategy To Prevent Bacterial Colonization Of Vascular Access Devices
Introduction
Intravascular catheters are the most frequently used medical devices in hospitals. However, they are associated with a life-threatening catheter-related bloodstream infection (CR-BSI), which is one of the main hospital-acquired infections as the incidence ranges from 0.1 to 11.3 per 1,000 catheter days.1–3 CR-BSI is associated with morbidity, psychological suffering, mortality, and additional medical cost. The high rate of these infections is explained by the fact that bacterial colonization of indwelling catheters is frequently reported: 25% of indwelling intravenous catheters become colonized with bacteria.
To reduce CR-BSI, behavioral interventions for health care workers can be conducted, but the impact of such interventions varies greatly, ranging from nonsignificant decreases to significant reductions of CR-BSIs. Currently in France, it is recommended that implanted ports be flushed with 10 mL of sterile saline solution by pulsative flushing in order to prevent obstruction, which is a potential source of infection.
In a previous study, the effectiveness of pulsative flushing of catheters versus continuous flushing was demonstrated to remove a protein layer present on the endoluminal wall of the catheter.
The question that arises is whether this flushing policy could be an effective means to reduce the colonization of the endoluminal space. The purpose of the present study was to assess, in controlled flow conditions, the bacteriological effectiveness of pulsative flushing on catheters polluted by the same protein solution supplemented with a Staphylococcus aureus broth of known concentration. The aim was to demonstrate the advantage of using a pulsative flushing technique versus a continuous flushing technique in preventing the accumulation of bacteria on the catheter endoluminal wall, before the biofilm formation. The bacteriological efficacy of this method was measured by the amount of S. aureus collected after flushing the lumen of tested catheters.
Discussion
This study demonstrated experimentally that the amount of S. aureus recovered after pulsative flushing is greater than that recovered after continuous flushing. Although we did not have the opportunity to observe the intraluminal surface of catheters by electron microscopy, these results allow for the assumption that the elimination of S. aureus from this surface would be more effective after pulsative flushing compared with continuous flushing. No similar studies have been found in literature. Although peripheral catheters were used in this work, the results can be extrapolated to all catheters because the flushing efficacy depends on the technique used. It isa physical hydrodynamics characteristic that can be applied to all cannula.
We noticed that even if there is a clear difference between the two methods in the rate of contamination, the number of colonies varies greatly from one test to another within a single method, while the same S. aureus inoculum was used for all tests. The variability of these results could be explained by the fact that bacteria are living organisms whose metabolism and ability of adhesion may undergo some variations over time.
The genus Staphylococcus was chosen in this work because staphylococci are known to bind to intravascular catheters. S. aureus and Staphylococcus epidermidis are the most frequently species recovered in CR-BSI as they are major skin contaminant species. The species S. aureus was chosen in order to easily identify the inoculated bacteria from any external catheter contamination by commensal bacteria.
Staphylococcal infections associated with indwelling medical devices involve the formation of a biofilm. These infections are chronic or relapsing and often induce removal of the infected medical device. Catheter removal is mandatory in case of CR-BSI due to S. aureus, because of its significant morbidity.
Staphylococcal adherence to either a biotic or abiotic surface is the critical first event in the establishment of an infection. Bacterial cells adhere to the endoluminal matrix, which is made of serum proteins. FN and albumin were selected in this work because both are physiological blood proteins. Furthermore, FN easily and strongly adheres to biomaterials and to blood products and also promotes the adhesion of albumin and other proteins.
Adherence of S. aureus appears to be dependent on the presence of host-tissue ligands, including FN and collagen.18FN in plasma contains a strong binding site for S. aureusas well as marked affinity for inert plastics and, therefore, may provide a substrate for bacterial adherence to indwelling catheters. FN proteins reproduce the adherence of staphylococci in vitro in presence of blood. Russel et al showed that FN significantly increased in vitro the adherence of S. aureus to polyvinyl-chloride and polyurethane catheters. Vaudaux et al showed that in the presence of serum, the level of staphylococcal adherence to explanted cover slips was 20 times higher than that of adherence to unimplanted coverslips. Adherence to explanted coverslips was caused by FN deposits on the foreign body surface and was inhibited in a dose-related fashion by specific antibodies to FN. Compared with non-inserted catheters, which allowed only minimal adherence, previously inserted catheters promoted significant adherence of staphylococcal isolates from patients with intravenous device infection.
This high ability of staphylococcal adherence requires the use of an effective method such as pulsative flushing to detach the bacteria before the irreversible formation of a biofilm. The elimination of biofilms on intravascular catheters is indeed a challenge for practitioners. The difficulty of eradicating biofilms encourages eliminating quickly the bacterial colonization from the endoluminal surface of the catheter, before the first steps of biofilm formation (attachment of planktonic cells and formation of micro-colonies). In addition, if the flushing removes the germs possibly present before the stage of irreversible attachment during the formation of the biofilm, the risk of dispersing a large inoculum of bacteria into the bloodstream, which may be a risk factor for bacteremia, is then reduced.
In the literature, few studies on flushing hydro-dynamics have been provided and until the present study, there was no proof of the antimicrobial efficacy of the pulsative flushing technique for catheters. In a previous study, using the same method as the one applied in this work, Guiffant et al concluded that hydrodynamics is critical for removing proteins from the endoluminal wall of a catheter and that he adjunction of an intermittent component in the flow increases this effect.
According to Donlan, 28–30 bacterial cells behave as particles in a liquid, and the rate of settling and deposition on a submerged surface will depend largely on the characteristics of the velocity distribution of the liquid in the vicinity of the submerged surfaces. Under very low linear velocities, the cells can easily traverse the hydrodynamic boundary layer. As the velocity increases, the protein and microorganism deposits decrease. High linear velocities induce substantial shear forces, resulting in the detachment of these cells. The flushing of venous catheters is a complex process, where convection and diffusion are coupled with chemical interactions associated with protein adhesion and disadhesion. Moreover, the flushing efficacy could be enhanced by heating up the flushing solution to body temperature, as shown by Guiffant et al.
In terms of flushing, it is essential to consider bacterial adhesion and colonization. Royon et al explained that the mass balance of proteins attached to the catheter wall has to be considered: over time, the chemical interactions between proteins increase, inducing inefficient flushing.11By extension, this would be the same process with microorganisms, meaning that in clinical practice, flushing should be repeated frequently.
Among all the CR-BSI prevention strategies related to peripheral and central catheters, pulsative flushing is a simple, effective, and inexpensive technique, associated with good practice. Pulsative flushing appears to be efficient in reducing catheter bacterial colonization to prevent bacteremia. Further studies would be necessary to confirm in vivo the results of this in vitro study.
To read the original and complete study click the following link:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4230174/pdf/mder-7-379.pdf