The proposed study involves using two different high-resolution microscopic imaging techniques to examine the health and platelet invasion of clot in patients who were given 1:1 protamine / heparin and compare this to clot from patients who had heparin reversed using the PRODOSE algorithm. Patients will be treated according to the routine clinical practice of their individual care team.

Sample collection at RPH

Patients will have a total of 14ml of blood taken during the procedure.

The first 7ml will be taken after induction of anaesthesia along with routine blood gas and coagulation sampling through the routinely indwelling arterial catheter. The initial sample must be taken before any heparin has been administered. This will be used to fill 2 x 3.5ml citrated (green top) blood tubes. These will be clearly labelled as "pre-heparin" with a Tissue Bank ID number.

The second 7ml will be taken 5 minutes after heparin has been reversed with protamine after cessation of cardiopulmonary bypass. It will again be taken at the same time as routine sampling for blood gas and coagulation studies. Analog to the first sample, it will again be divided and used to fill 2 x 3.5ml citrated (green top) blood tubes. These will be clearly labelled as "post-protamine" with the same ID number and whether "1:1" or a "PRODOSE algorithm determined" protamine: heparin ratio was used.

In keeping with clinical routine, ROTEM coagulation testing and full blood counts will be requested as seen necessary by the clinical team.

The samples will be sent to Royal Papworth Hospital (RPH) Tissue Bank for initial processing. Samples need to be processed within 4 hours of blood draw.

After initial processing, samples will be sent for confocal imaging to the MRC Laboratory of Molecular Biology (LMB) and for SEM imaging to the University of Oxford respectively.

Clinical data to be collected (to be completed by anaesthetic team).

1. Demographic information: Age / Gender / Weight / Height / Medication history;
2. Type of surgery;
3. Cardiac drug history and antiplatelets / anticoagulants and timing;
4. Coagulation tests (ACT / ROTEM) at the following points: a) Pre-heparin, b) Post-heparin, pre-CPB, c) Throughout CPB, c) Post-protamine;
5. Full blood count at the following points: a) Pre-surgery and date of sample, b) Post-protamine; 6) CPB and x-clamp times, nadir temperature

Inclusion Criteria:

• undergoing elective, uncomplicated single procedure cardiac surgery with anticipated CPB duration < 120 min
• with all anticoagulant drugs stopped at least 5 days before surgery, apart from aspirin
• with normal full blood count and clotting screen pre-OP.

Exclusion Criteria:

• emergency surgery
• inability to stop anticoagulants except aspirin for 5 days pre-OP
• complex surgery with anticipated CPB duration > 120min
• operations planned to be done at temperature on CPB < 34 degrees
• operations requiring deep hypothermic circulatory arrest, solid organ transplantation
• know blood dyscrasia
• intra-operative blood or blood product transfusion or post-operative coagulopathy

Patients undergoing elective, uncomplicated single procedure cardiac surgery with anticipated CPB duration < 120 min

Small observational study so IPD not relevant