Perioperative bleeding remains a major challenge in cardiac surgery, particularly in procedures involving cardiopulmonary bypass (CPB). Excessive postoperative bleeding increases intensive care unit stays, morbidity, and mortality, making accurate and rapid coagulation assessment crucial for guiding transfusion therapy. Traditional laboratory tests such as prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen levels, and platelet counts are commonly used, but they have important limitations. These tests require plasma separation and often take 30–90 minutes to return results, delaying critical clinical decisions. Additionally, they measure isolated components of coagulation and may not reflect the dynamic process of clot formation occurring in whole blood.
This prospective observational study conducted at the Lithuanian University of Health Sciences Hospital aimed to evaluate whether viscoelastic testing using rotational thromboelastometry (ROTEM) could better predict perioperative bleeding compared with platelet aggregometry and standard laboratory tests. The study included 79 adult patients undergoing elective cardiac surgery with CPB between October 2023 and November 2024. Blood samples were collected before surgery and after heparin reversal with protamine to measure ROTEM parameters, platelet aggregation, and conventional laboratory markers.
To accurately quantify blood loss, researchers used the Hb/kg Index, which calculates hemoglobin mass loss normalized to body weight. This metric provides a more physiologic measurement of bleeding compared with traditional chest tube drainage methods, which can be confounded by irrigation fluid, dilution, or patient size differences. The Hb/kg Index therefore allowed a more precise assessment of the relationship between coagulation parameters and actual blood loss.
The study population had a median age of 67 years, and the procedures included coronary artery bypass grafting, valve surgery, and combined operations. Cardiopulmonary bypass time averaged around 88 minutes. Following surgery, significant reductions in platelet count and fibrinogen concentration were observed. Platelet counts decreased by approximately 26%, and fibrinogen levels dropped by a similar proportion. Postoperative thrombocytopenia occurred in about 35% of patients, while hypofibrinogenemia—defined as fibrinogen levels below 2.5 g/L—was present in about 30% of the cohort.
Despite these reductions in platelet counts and evidence of impaired platelet aggregation, neither platelet count nor platelet aggregation testing correlated with the measured blood loss. Standard coagulation markers such as INR and aPTT also showed no meaningful association with the Hb/kg Index. This finding highlights the limited predictive value of conventional coagulation testing when assessing bleeding risk in the immediate postoperative period following cardiac surgery.
In contrast, viscoelastic parameters measuring clot firmness demonstrated significant correlations with blood loss. Specifically, FIBTEM A10, a ROTEM parameter that reflects the fibrinogen contribution to clot formation, showed a strong inverse relationship with the Hb/kg Index. Lower FIBTEM A10 values were associated with greater blood loss, indicating that reduced clot strength—driven primarily by fibrinogen deficiency—plays a key role in postoperative bleeding after CPB.
Receiver operating characteristic (ROC) analysis further confirmed the diagnostic value of FIBTEM A10 in detecting hypofibrinogenemia. The analysis identified a cutoff value of 12 mm as an optimal threshold for identifying patients with fibrinogen levels below 2.5 g/L. This threshold demonstrated excellent diagnostic performance, with a sensitivity of 96% and a negative predictive value of 97.4%. In clinical terms, a FIBTEM A10 value above 12 mm effectively rules out clinically significant fibrinogen deficiency.
The study also evaluated viscoelastic indicators related to platelet contribution to clot strength, such as PLTEM (calculated as EXTEM minus FIBTEM). While PLTEM parameters correlated with platelet counts, they did not predict blood loss. Platelet aggregometry similarly failed to demonstrate a meaningful relationship with bleeding outcomes. These findings suggest that platelet quantity or aggregation capacity alone may not be the primary determinant of early postoperative bleeding after cardiac surgery.
Instead, the results support the concept that fibrinogen is the “first factor to fall” during CPB-associated coagulopathy. Hemodilution, inflammatory activation, and consumptive coagulation processes during extracorporeal circulation can rapidly reduce fibrinogen levels. When fibrinogen is insufficient, the fibrin mesh that stabilizes the clot becomes weak, diminishing the overall strength of the clot even when platelet counts remain adequate.
These findings align with modern patient blood management guidelines, which increasingly recommend viscoelastic-guided transfusion algorithms in cardiac surgery. By rapidly identifying fibrinogen deficiency through ROTEM parameters such as FIBTEM A10, clinicians can administer targeted therapy—such as fibrinogen concentrate or cryoprecipitate—rather than relying on empirical transfusion strategies. This approach may improve bleeding control while reducing unnecessary blood product use.
The authors acknowledge several limitations, including the single-center design and relatively small sample size. However, the study provides important prospective evidence supporting the role of viscoelastic testing in perioperative bleeding management.
In conclusion, the study demonstrates that reduced clot firmness driven by fibrinogen deficiency is the primary determinant of bleeding following cardiopulmonary bypass. Viscoelastic testing—particularly FIBTEM A10—offers a rapid and reliable method for identifying hypofibrinogenemia and guiding transfusion strategies in cardiac surgery patients.
