Optimization of cardiopulmonary bypass prime fluid to preserve microcirculatory perfusion during on-pump coronary artery bypass graft surgery: PRIME study protocol for a double-blind randomized trial

Background Acute microcirculatory perfusion disturbances and organ edema are important factors leading to organ dysfunction during cardiac surgery with cardiopulmonary bypass (CPB). Priming of the CPB system with crystalloid or colloid fluids, which inevitably leads to hemodilution, could contribute to this effect. However, there is yet no optimal evidence-based strategy for this type of priming. Hence, we will investigate different priming strategies to reduce hemodilution and preserve microcirculatory perfusion.Methods The PRIME study is a single-center double-blind randomized trial. Patients undergoing elective coronary artery bypass graft surgery with CPB will be randomized into three groups of prime fluid strategy: (1) gelofusine with crystalloid, (2) albumin with crystalloid, or (3) crystalloid and retrograde autologous priming. We aim to include 30 patients, 10 patients in each arm. The primary outcome is the change in microcirculatory perfusion. Secondary outcomes include colloid oncotic pressure; albumin; hematocrit; electrolytes; fluid balance and requirements; transfusion rates; and endothelial-, glycocalyx-, inflammatory- and renal injury markers. Sublingual microcirculatory perfusion will be measured using non-invasive sidestream dark field video microscopy. Microcirculatory and blood measurements will be performed at five consecutive time points during surgery up to 24 h after admission to the intensive care unit.Discussion PRIME is the first study to assess the effect of different prime fluid strategies on microcirculatory perfusion in cardiac surgery with CPB. If the results suggest that a specific crystalloid or colloid prime fluid strategy better preserves microcirculatory perfusion during on-pump cardiac surgery, the current study may help to find the optimal pump priming in cardiac surgery.Trial registration ClinicalTrials.gov NCT05647057. Registered on 04/25/2023. ClinicalTrials.gov PRS: Record Summary NCT05647057, all items can be found in the protocol.