Background: This study aims to investigate the reliability of activated clotting time (ACT) by using different discard volumes from the heparinized arterial line.

Methods: Between January 2007 and October 2007, 106 of 116 patients (70 males, 36 female; mean age 55.2±15.3 years; range 18 to 81 years) who met inclusion criteria and underwent cardiac surgery were included. Ninety-one patients underwent coronary artery bypass graft (CABG) surgery, including eight with mitral valve replacement and seven with aortic valve replacement. After control ACT was taken from the arterial line, the line was flushed with saline solution containing heparin at a concentration of 2 IU/ml. Blood samples were taken from the arterial line adding different discard volumes to the dead space. Group names were given according to discard volumes. Dead space plus 2 ml discard volumes (group 2), dead space plus 4 ml (group 4), dead space plus 6 ml (group 6), dead space plus 10 ml (group 10), dead space plus 15 ml (group 15), dead space plus 20 ml (group 20) were defined.

Results: The differences between each of the mean heparinized arterial sample and mean control ACT were; in group 2, 40.1 limits of agreement: +87.8 to –7.6, in group 4, 23.5 limits of agreement: +59.6 to –12.6, in group 6, 16.2 limits of agreement: +49.8 to –17.3, in group 10, 12.5 limits of agreement: +40.1 to –15.2, in group 15, 7.4 limits of agreement: +38.4 to –23.6, in group 20, 5.6 limits of agreement: +29.2 to –18. The differences of 10 ml, 15 ml and 20 ml were not significantly different (p=0.17).

Conclusion: In our study, the mean ACT values of heparinized arterial line samples were higher than control ACT. However, due to the normal values of ACT between 80-120, we accept that minimum dead space plus 6 ml discard volume should be withdrawn.

Keywords : Activated clotting time; arterial blood sampling; discard volume; heparin