The Cryopreserved vs. Liquid Platelets Trial

Inclusion Criteria: 1. Cardiac surgery patients identified preoperatively as having a high risk of platelet transfusion by either: * the ACSePT (Australian Cardiac Surgery Platelet Transfusion (score)) risk prediction tool score ≥1 OR * the judgement of the clinicians caring for the patient 2. Written informed consent obtained prior to surgery Exclusion Criteria: 1. Aged less than 18 years 2. Females of child-bearing age (18- 55 years) who are RhD (Rhesus type D)-negative or whose RhD (Rhesus type D) status is unknown 3. Receipt of platelet transfusion during this hospital admission 4. Deep Vein Thrombosis or Pulmonary Emboli first diagnosed within the preceding 6 months 5. More than one lifetime episode of Deep Vein Thrombosis or Pulmonary Emboli 6. Known inherited or acquired bleeding disorder (e.g. haemophilia, von Willebrand Disease, idiopathic thrombocytopenic purpura, aplastic anaemia, haematological malignancy, chronic liver disease), or any undiagnosed bleeding condition, if (and only if) such a disorder or condition is associated with a significant laboratory abnormality at the time of preoperative screening. i.e. * preoperative platelet count \<50 000 or * INR (International Normalised Ratio) \>2 or * aPTT (Activated Partial Thromboplastin Time) \> 2 x upper limit of normal. 7. Treatment with warfarin, IV heparin or low-molecular weight heparin at "full" therapeutic anticoagulant doses, or other anticoagulant or anti-platelet medications such as factor Xa inhibitors (rivaroxaban, apixaban); factor II inhibitors (dabigatran); adenosine diphosphate receptor inhibitors (clopidogrel, prasugrel, ticagrelor, ticlopidine); glycoprotein IIB/IIIA inhibitors (abciximab, eptifibatide, tirofiban); phosphodiesterase inhibitors (cilostazol); or adenosine reuptake inhibitors (dipyridamole) UNLESS this medication has been discontinued in advance of surgery and its effect allowed to dissipate. 8. Known allergy to dimethylsulphoxide (DMSO) 9. Planned presence of an arterial line and central venous catheter for less than 12 hours postoperatively. 10. Known objection to receipt of human blood components 11. The treating physician believes it is not in the best interest of the patient to be randomised in this trial 12. Previous enrolment during this admission in a clinical trial of a medication or technique thought to influence bleeding, with the exception of any trial of aspirin (i.e. trials involving aspirin are permitted), OR previous enrolment in a clinical trial with a protocol that affects the transfusion of blood products. 13. Previous enrolment in this study