title: The air-bubble method of locking central-vein catheters with acidified, concentrated sodium chloride as a bactericidal agent: in vitro studies.
abstract: BACKGROUND
  Soft, cuffed indwelling catheters are used for hemodialysis access and intravenous infusions. The majority of these catheters are removed as a result of infection caused by contamination of the catheter hub during the connection/disconnection procedures. To prevent clot formation in the lumen, these catheters are routinely "locked" with heparin or some other anticoagulant. None of the anticoagulants commonly used as locking solutions demonstrates any significant bactericidal properties. The primary goal of this study was the development of a catheter locking method that retains anticoagulant properties at the catheter tip and bactericidal properties at the catheter hub. The second goal was to find a solution that possesses excellent bactericidal properties but is not detrimental in the event of injection into the patient's blood stream. The bactericidal properties of acidified, concentrated saline (ACS) were compared to concentrated trisodium citrate and to commonly used bactericidal agents such as povidone iodine, sodium hypochlorite, and chlorhexidine.
  
  
  METHODS
  In preliminary studies, the rate of diffusion of solutes was measured in glass tubes. In another set of experiments, the mixing of two solutions (anticoagulant and bactericide) separated by an air bubble ("air-bubble method") was observed in stationary and moving systems. The final series of studies compared the bactericidal properties of ACS to other bactericidal solutions mentioned above.
  
  
  RESULTS
  The solutions diffused swiftly in the glass tubes, and by the third day, both solutions were mixed. The air-bubble method prevented mixing in both stationary and moving systems. The bactericidal properties of ACS were superior to all other tested solutions.
  
  
  CONCLUSIONS
  The proposed method of catheter locking with anticoagulant at the catheter tip and ACS at the catheter hub separated by an air bubble is a promising technique and clinical studies are warranted.
authors.affiliation: Department of Medicine, Division of Nephrology, University of Missouri, Columbia, Missouri, U.S.A. MooreH@health.missouri.edu
authors.forename: Harold L
authors.initials: HL
authors.lastname: Moore
authors.forename: Zbylut J
authors.initials: ZJ
authors.lastname: Twardowski