The goal of this observational study is to learn how flow-based platelet function measured with the Total Thrombus-formation Analysis System (T-TAS) relates to early postoperative bleeding in adults undergoing cardiac surgery with cardiopulmonary bypass. The study will also evaluate how T-TAS changes during the perioperative period and how it compares with standard coagulation and platelet function tests.

The main questions it aims to answer are:

Is lower post-cardiopulmonary bypass T-TAS Platelet-chip (PL-chip) thrombus formation associated with increased postoperative chest tube drainage during the first 12 hours after surgery? How do T-TAS parameters change before surgery, immediately after cardiopulmonary bypass, and 24 hours after surgery? Are abnormal T-TAS results associated with blood transfusion requirements, major bleeding, re-exploration for bleeding, and length of stay in the intensive care unit and hospital? Does T-TAS provide complementary information compared with standard coagulation tests, von Willebrand factor (vWF) measurements, platelet aggregometry, and viscoelastic testing?

Participants will:

Undergo blood sampling at three predefined perioperative time points:

before anesthesia induction, immediately after cardiopulmonary bypass and heparin reversal with protamine, and 24 hours after surgery Have T-TAS testing, standard laboratory coagulation tests, vWF testing, platelet aggregometry, and viscoelastic testing performed on collected samples Have clinical, surgical, transfusion, and postoperative bleeding data collected during their hospital stay

The study is observational and does not require changes to routine clinical care or perioperative management.

Cardiac surgery requiring cardiopulmonary bypass (CPB) is frequently associated with perioperative hemostatic disturbances and clinically significant postoperative bleeding. The mechanisms involved are multifactorial and include platelet activation and dysfunction, hemodilution, inflammatory activation, acquired von Willebrand factor (vWF) abnormalities, fibrinolytic activation, exposure of blood to non-endothelial surfaces, hypothermia, and the effects of systemic anticoagulation and heparin reversal. These alterations contribute to increased transfusion requirements, re-exploration for bleeding, prolonged intensive care unit (ICU) stay, and increased perioperative morbidity.

Conventional coagulation tests incompletely characterize perioperative primary hemostatic dysfunction during cardiac surgery. Standard plasma-based coagulation assays provide limited information regarding platelet thrombus formation under physiologic flow conditions, while platelet aggregometry and viscoelastic testing assess only selected components of the hemostatic process. In addition, several perioperative alterations observed after CPB, particularly abnormalities involving platelet-vWF interactions under shear stress conditions, may not be adequately reflected by conventional laboratory methods.

The Total Thrombus-formation Analysis System (T-TAS) is a microfluidic flow chamber platform that evaluates thrombus formation in whole blood under controlled flow conditions. The Platelet-chip (PL-chip) primarily assesses platelet thrombus formation on collagen-coated microchannels under arterial shear flow conditions, integrating platelet adhesion, activation, aggregation, and vWF-dependent interactions. The AR-chip additionally incorporates activation of the coagulation cascade and fibrin formation. T-TAS therefore provides a functional assessment of thrombus formation under conditions that more closely resemble physiologic blood flow than conventional static coagulation assays or standard aggregometry techniques.

Although T-TAS has been investigated in several thrombotic and bleeding disorders, its perioperative behavior and potential clinical relevance in adult cardiac surgery with CPB remain insufficiently characterized. In particular, the association between post-CPB T-TAS parameters and early postoperative bleeding has not been clearly established, and the relationship between T-TAS and conventional coagulation, viscoelastic, platelet function, and vWF-related laboratory assessments remains incompletely understood in this clinical setting.

This study is a prospective, observational, single-center cohort study conducted at Hospital de la Santa Creu i Sant Pau (Barcelona, Spain). The study is designed to characterize perioperative alterations in flow-based platelet thrombus formation and to evaluate the relationship between T-TAS parameters and early postoperative bleeding after adult cardiac surgery requiring CPB.

The study will enroll adult patients undergoing elective or urgent cardiac surgical procedures requiring cardiopulmonary bypass. The study is strictly observational and does not mandate modifications in perioperative management, transfusion practice, coagulation management, surgical strategy, or postoperative care. All clinical decisions remain at the discretion of the treating surgical, anesthesiology, intensive care, perfusion, hematology, and transfusion teams.

Perioperative blood sampling will be performed at predefined study time points selected to characterize dynamic perioperative changes in primary hemostasis:

• Preoperative baseline before anesthesia induction and after vascular access placement.
• Immediate post-CPB sampling after separation from bypass and heparin reversal with protamine.
• Postoperative sampling at approximately 24 hours after surgery.

T-TAS measurements will include PL-chip analysis as the principal study exposure variable. Atheroma-chip (AR-chip) analysis may additionally be performed in predefined exploratory contexts, particularly in situations of marked thrombocytopenia or severe perioperative hemostatic impairment. T-TAS quality assurance procedures include standardized sample handling, recording of reagent and cartridge lot numbers, predefined processing workflows, and duplicate testing in a subset of samples for internal quality control purposes.

Additional perioperative laboratory assessments may include standard coagulation tests, fibrinogen concentration, platelet count, hemoglobin and hematocrit, D-dimer levels, vWF antigen and activity measurements, platelet aggregometry, and viscoelastic testing according to protocol feasibility and sample availability. Multimeric vWF analysis may be performed in a prospectively defined subset of participants.

Clinical and procedural variables prospectively recorded include demographic characteristics, type of surgical procedure, redo surgery status, duration of CPB and aortic cross-clamping, nadir temperature, rewarming profile, heparin and protamine dosing, antifibrinolytic therapy, CPB prime characteristics, cell-saver utilization, transfusion exposure, and perioperative bleeding-related outcomes.

Postoperative bleeding assessment includes prospective recording of chest tube drainage during the early postoperative period. Additional clinically relevant outcomes include transfusion exposure, major bleeding events, surgical re-exploration for bleeding, ICU length of stay, hospital length of stay, and in-hospital mortality. Major bleeding definitions are based on prespecified Bleeding Academic Research Consortium Coronary Artery Bypass Grafting-related bleeding criteria (BARC-CABG criteria).

The principal analytical objective is to evaluate the association between post-CPB PL-chip thrombus formation and early postoperative bleeding severity. Planned analyses include regression-based modeling of postoperative drainage volume as a continuous variable with adjustment for clinically relevant perioperative covariates. Secondary analyses include longitudinal characterization of perioperative T-TAS trajectories, exploratory evaluation of associations between T-TAS and clinically relevant bleeding-related outcomes, and assessment of correlations between T-TAS parameters and conventional laboratory, viscoelastic, platelet aggregometry, and vWF-related measurements.

The study additionally aims to explore whether T-TAS may provide complementary functional information beyond currently available coagulation and platelet function tests in the setting of adult cardiac surgery with CPB. Analyses evaluating the incremental value of T-TAS relative to conventional clinical and laboratory variables are planned as exploratory objectives.

All study data will be collected prospectively using predefined case report forms and entered into a secure Research Electronic Data Capture (REDCap) database with coded participant identifiers. A predefined data dictionary and standardized operational definitions will be used to ensure consistency of data collection across the study. Quality control procedures include prospective review of data completeness, verification of major clinical outcomes, documentation of missing or unavailable laboratory measurements, and internal consistency review before database lock.

Missing data patterns will be evaluated prospectively. If clinically relevant missingness is identified in key analytical variables, multiple imputation strategies may be considered according to a predefined statistical analysis framework. Due to the exploratory and mechanistic nature of several secondary objectives, analyses beyond the principal endpoint evaluation will primarily be considered hypothesis-generating.

The study is expected to improve understanding of perioperative primary hemostatic dysfunction under CPB conditions and to provide foundational data for future biomarker-guided bleeding risk stratification and targeted hemostatic management strategies in cardiac surgery.

Inclusion Criteria:

1. Adults aged 18 years or older
2. Undergoing elective or urgent cardiac surgery requiring cardiopulmonary bypass
3. Ability to provide written informed consent

Exclusion Criteria:

1. Cardiac surgery performed without cardiopulmonary bypass
2. Emergency cardiac surgery
3. Preoperative anticoagulation not reversed at the time of surgery
4. Refusal or withdrawal of informed consent
5. Known pregnancy

Adult patients undergoing elective or urgent cardiac surgery requiring cardiopulmonary bypass at a tertiary academic cardiac surgery center. Participants are recruited prospectively during routine perioperative clinical care and undergo perioperative assessment of flow-based platelet function using the Total Thrombus-formation Analysis System (T-TAS).