Clot formation risk in the clearing fluid after arterial catheter blood sampling: coagulation factors consumption over time - a prospective pilot study.

After blood sampling from an arterial catheter, the reinjection of the clearing fluid (a mixture of saline solution and blood) is proposed to limit blood loss. However, reinjecting clots may cause embolic complications. The primary objective was to assess fibrinogen consumption in the clearing fluid as an indicator of clot formation over time. Additionally, we searched for macroscopic clots, evaluated changes in prothrombin time, factors II and V. In this prospective observational pilot study, we enrolled adult patients in an intensive care unit with a radial artery catheter who required measurements of hemostasis parameters. We used a locally developed closed blood sampling system. Hemostasis parameters were measured in patients' pure blood (reference) and in the clearing fluid, at 2, 3, and 5 min after the complete filling of the reservoir. Thirty patients were included and 120 samples were analyzed. Fibrinogen levels decreased over time: median [interquartile range (IQR)] of 4.3 [IQR:3.1;5.9] as reference level, 3.6 [IQR:2.7;4.7] at 2 min (p < 0.001), 3.4 [IQR:2.1;4.3] at 3 min (p < 0.001) and 3.0 [IQR:1.7;4.1] g/L at 5 min (p < 0.001). No clot was macroscopically detected in any samples. An antiplatelet agent was administered in 11 (37%) patients. Unfractionated heparin anti-Xa activity was higher than 0.10 UI/ml in 17 (57%). Although no macroscopic clots were observed in the clearing fluid, its coagulation factors decreased over the 5 min following reservoir filling, indicating potential initiation of clot formation. Our findings stress the need for further studies assessing the safety of reinjecting clearing fluid as part of patient blood management.