Effect of heparin in arterial line flushing solutions on platelet count: a randomised double-blind study

Arterial catheters are widely used in intensive care units for continuous blood pressure monitoring and blood sampling. Studies have examined the effect of heparin on patency of arterial catheters but not on platelet counts. Heparin is a naturally occurring anticoagulant that helps prevent clotting and is given to prevent and treat thrombosis. It has many other effects, including reducing platelet counts.

A prospective, randomised, double-blind study compared the effects of heparinised and normal saline (both administered via a continuous flush device to an arterial catheter) on patients' platelet counts. All patients admitted to a mixed medical-surgical ICU between April and December 2003 were eligible for entry. Exclusion criteria were age under 16 years, known sensitivity to heparin, pre-existing coagulopathy that precluded heparin, or requirement for therapeutic heparin. Lines were inserted into radial, brachial or femoral arteries. A 500 mL bag of saline for the flush was injected with numbered syringes, containing either normal saline (NS, 35 patients) or 500 IU heparin (HS, 30 patients), and pressurised. Platelet count was assessed daily.

Mean platelet counts were 234.6 x 10(9)/L (NS) versus 256.6 x 10(9)/L (HS). Comparison using the central limit theorem showed means were not different at the 95% confidence interval (- 77.6 to 37 x 10(9)/L).

Use of heparin in normal saline as a continuous flush for an arterial catheter does not reduce platelet counts in critically ill patients.