Ionized Calcium and Bleeding in Cardiac Surgery

This retrospective study investigates the association between perioperative plasma ionized calcium concentration and perioperative bleeding in open-heart surgery. Excluding patients who meet exclusion criteria, the study will include all applicable adult patients who underwent cardiac surgery at Helsinki University Hospital between January 2021 and March 2026. As clinical routine, during both cardiac surgery and the subsequent intensive care period, multiple blood gas analyses were performed, including measurements of plasma ionized calcium concentration. Time-weighted averages of all measurements will be calculated across different phases of surgery (pre-CPB, on -CPB, post-CPB) and the first 24 hours of ICU stay (0-6 h, 6-12 h, 12-24 h). Perioperative bleeding will be assessed using the Universal Definition of Perioperative Bleeding (UDPB) classification validated for cardiac surgery. In addition to chest drain output, this classification accounts for blood products administered to treat bleeding (red blood cells, platelets, and fresh frozen plasma), pharmacological coagulation factor concentrates (fibrinogen/cryoprecipitate, PCC, aFVIIa) and surgical interventions (open sternum, resternotomy). The association between plasma ionized calcium and UDPB class will be assessed with regression models. The primary analysis will be the association between time-weighted mean plasma ionized calcium level during the post-CPB phase as a continuous variable and dichotomous UDPB (UDPB 3-4 vs. UDPB 0-2) in patients who did not receive blood products during the post-CPB phase. One secondary and two sensitivity analyses will be performed