Is heparin really necessary in the lock and, if so, how much?

The literature on the issue of whether heparin is necessary in an intermittent peripheral venous access device (lock) is critically reviewed. Issues explored include loss of patency, development of phlebitis, duration of lock placement, type of cannula material, sample size, risk of toxicity with heparin flush solutions, risk of clot embolism, and physical or chemical incompatibilities. Available studies indicate that heparin is not necessary to maintain fluoroethylenepropylene (FEP-Teflon) peripheral venous access devices unless the lock is used to obtain blood specimens. Considering the benefit-to-risk ratio for the use of heparin, it is advisable to maintain FEP-Teflon locks with normal saline alone. When locks are used to obtain blood specimens, as in a pharmacokinetic study, then a dilute heparin flush solution should be used. Whether heparin is necessary for the maintenance of locks composed of other materials is uncertain. Newer, less thrombogenic materials such as ethylene tetrafluoroethylene may also obviate the need for heparin, but comparative trials in a larger number of patients are needed for confirmation. When heparin is used, an effort should be made to avoid systemic toxicities by using the lowest known effective concentration (10 units/mL) pending further studies.