Abstract

Saline, given continuously or intermittently, is often used to maintain the patency of indwelling intravenous needles or cannulae. Clotting is however prevented more effectively by giving heparin. The doses recommended for this purpose have varied from 3.3 to 1000 units given in volumes of 0.2 to 1.0 ml.^{1 2} In a careful study an effective dose of heparin was found to be 10 units in 1 ml 0.9% saline, 8-hourly or after each use of the cannula or needle.³ Common methods are to use 0.5 ml of a 1000 unit/ml heparin solution, or a smaller dose prepared by diluting heparin from a multi-dose vial. The amount of heparin so used is thus greater than that required to prevent clotting,³ and accidental systemic heparinisation may occur, especially in neonates.⁴ The use of multi-dose vials also risks bacterial contamination.