Arterial and venous thrombelastograph® variables differ during cardiac surgery

The Thrombelastograph® (TEG®; Haemoscope Corp., Skokie, IL) coagulation analyzer is an effective point-of-care monitor for routine clinical practice and clinical research. Prior investigators have used either arterial or venous samples of blood for TEG® measurements. We conducted this prospective cohort study to determine potential differences in TEG® variables between arterial and venous blood samples. Arterial and venous samples were drawn from 40 cardiac surgical patients, yielding 134 pairs for comparison. Twenty-nine comparisons (control) were between arterial and arterial samples and were not significantly different. For the arterial and venous comparisons (n = 105), mean (±SD) arterial and venous values were the following: reaction time, 10 ± 2 mm vs 13 ± 4 mm, P = 0.004; maximum amplitude, 59 ± 9 mm vs 49 ± 12 mm, P < 0.001; α angle, 61 ± 10 degrees vs 51 ± 14 degrees, P < 0.001; K, 5 ± 2 mm vs 8 ± 4 mm, P = 0.007; and lysis, 2.5 ± 1.7 vs 2.5 ± 2.0 (not significant), arterial versus venous, respectively. Arterial blood samples demonstrated TEG® values reflecting stronger (larger maximum amplitude) and faster (shorter reaction time and K value, wider α angle) clot formation. The results suggest that users of TEG® coagulation analyzers should be consistent with the site of blood sampling given the potential differences obtained.