The effect of haemodilution on antithrombin concentration during cardiac surgery.

The effect of haemodilution on antithrombin concentration was investigated in 73 patients undergoing elective cardiac surgery with and without cardiopulmonary bypass. In patients who required cardiopulmonary bypass (n = 45), the antithrombin concentration fell to 52% of baseline during surgery (24.2 mg.dl(-1) to 12.6 mg.dl(-1)), and the haemoglobin level fell to 55% (136 g.l(-1) to 75 g.l(-1)). In patients who did not require cardiopulmonary bypass (n = 28), the antithrombin concentration fell to 82% of baseline (23.7 mg.dl(-1) to 19.5 mg.dl(-1)), and the haemoglobin concentration fell to 78% (141 g.l(-1) to 109 g.l(-1)). The overall correlation coefficient (r) for changes in antithrombin and haemoglobin concentrations was 0.76. The results indicate that most of the decrease in concentration of antithrombin during cardiac surgery is a consequence of cardiopulmonary bypass and is due to haemodilution. This data demonstrates that the percentage decrease in haemoglobin concentration can be used to estimate the percentage decrease in antithrombin concentration that occurs during cardiac surgery, if blood products that might effect the results are not administered between measurements.