PLTS-1 is a multicentre, randomized, controlled, pilot trial, using a conventional, parallel group, two-armed design at 2 cardiac surgery centres in Canada. The study is designed to assess the feasibility of a future, definitive RCT to determine the non-inferiority of cold-stored platelets compared to conventional platelets with respect to hemostatic effectiveness (total number of allogeneic blood products transfused within 24 hours after CPB), as well as safety.

Inclusion Criteria:

Adult (≥18 years old) patients undergoing elective cardiac surgery with CPB will be eligible for inclusion if they are planned to undergo at least moderately complex surgery or have a preoperative platelet count ≤150,000 x106/L (this is a group at high risk of requiring platelet transfusions post-CPB).

Moderately complex index surgery is defined as:

1. repair/replacement of more than one valve;
2. aorta (root/ascending/arch) replacement;
3. any combination of coronary artery bypass grafting, valve repair/replacement, or aorta (root/ascending/arch) replacement; or
4. re-do procedures consisting of a repair or revision of a prior cardiac intervention.

Exclusion Criteria:

Patients will be excluded if cold-stored platelets are not going to be available at the time of surgery or if the patient:

1. has a congenital or acquired hemostatic disorder (including platelet refractoriness due to anti-platelet and anti-human leukocyte antigen [HLA] antibodies) and/or requires specially matched platelets (including patients with anaphylaxis to blood due to Immunoglobulin A [IgA] deficiency),
2. has known contraindications to heparin, thereby excluding cases where non-reversible anticoagulants (i.e. argatroban) are used,
3. is on warfarin or direct oral anticoagulants (dabigatran, rivaroxaban, apixaban or edoxaban) within 3 days prior to surgery,
4. is on antiplatelet drugs within 5 days prior to surgery (excluding acetylsalicylic acid [ASA]),
5. refuses allogeneic blood products,
6. has a known pregnancy,
7. has already enrolled in this study,
8. is enrolled in another interventional clinical trial where routine care and management are altered,
9. has hemodynamic instability defined as critical care admission, vasopressor, or inotrope dependence prior to index surgery, or
10. has pre-operative requirement for, or expected post-operative dependence upon mechanical circulatory support (i.e., intra-aortic balloon pump, ventricular assist device).

This will be a blinded randomized trial, with clinical personnel, patients, family members, and outcome assessors blinded to group allocation. Given that the platelets will be different temperatures (but identical in appearance), an unblinded blood bank technologist, who will not have access to the collected study data, will blind the platelets by placing them in an insulated tamper-proof container accompanied by a pair of disposable insulated gloves. The clinician(s) directly handling the product at the time of transfusion will wear the insulated gloves to prevent unblinding (simulations have shown this to be an effective strategy). The platelets will also have blinded study labels and come prepared in identical collection bags.