Use of heparin in arterial lines

We read with interest the article by Heap et al. (Anaesthesia 1997; 52: 640–5) on the effect of heparin in arterial lines on coagulation studies performed on blood sampled from such lines. While this is encouraging in demonstrating little clinical effect, provided at least 4.5 ml of blood is withdrawn first, we question whether heparin is necessary at all. Stimulated by an article in the nursing literature [1] we omitted heparin from 10 consecutive arterial lines in the ITU and could find no observable difference. Following this, we have not put heparin in our arterial lines for the last 3 years and have found no reason to revert to adding heparin. Consequently the question of validity of coagulation studies does not arise.