Arterial Versus Venous Sampling for Activated Coagulation Time Measurements During Cardiac Surgery: A Comparative Study

Objective: Activated coagulation times (ACTs) are widely used for monitoring anticoagulation during cardiac surgery. Significant variability of this test is well known. Variability in test results was studied, which may arise from the sample drawing site.

Design: Prospective study.

Setting: University hospital. Participants: Sixty-five patients scheduled for surgery requiring cardiopulmonary bypass were enrolled in the study.

Intervention: ACTs were assessed using the Hemochron 801 ACT machine. Samples were collected (1) baseline I from the arterial catheter before anesthetic induction, (2) baseline II from the arterial and venous collection sites after pulmonary artery catheterization, (3) after heparin administration, (4) 10 minutes after blood collection number 3, and (5) after protamine administration.

Measurements and main results: At the baseline II, the ACT measures using venous blood were significantly higher than that obtained using an arterial sample (p = 0.001). There was no significant difference in ACT measures obtained using either arterial or venous blood samples at the other time points. After heparin administration, the ACT variability in individual patients was quite striking, with ranges of up to 600 seconds in repeated measures.

Conclusion: During the period of systemic anticoagulation, there is great individual variability between ACT measures obtained from venous and arterial samples. Further studies are required to analyze the cause of differences at the baseline and the source of variable coagulation times after heparin.