Introduction: Although the use of the heart-lung machine (HLM) is routine in cardiac operating theaters, there is still a lack of evidence-based guidelines concerning the optimal speed to reach full flow during initiation to reduce critical episodes of cerebral ischemia. Therefore, we have designed a study to compare two distinct initiation times for the commencement of cardiopulmonary bypass (CPB). 

Methods: We conducted a randomized, monocentric, double-blind, prospective study to assess the impact of two different CPB initiation speeds – rapid initiation at 30 s and slow initiation at 180 s – on cerebral tissue oxygenation (TOI via NIRS), arterial oxygen pressure, hematocrit (HCT) variation, and the incidence of postoperative delirium. The target flow rate was set at 2.4 L/min/m², with adjustments made according to the patient’s body surface area. 

Results: The absolute values of the tissue oxygenation index (TOI) and HCT showed no differences between the study during the first 180 s following commencement of CPB. Patients in the fast group exhibited significantly lower arterial oxygen pressure at the initiation of the (P < 0.05). Additionally, patients in the fast group experienced a higher incidence of delirium in the second and third days following surgery. While clinically relevant, the elevated incidence of delirium fell short of being statistically significant, with post-operative days 2 and 3 having P-values of 0.06 and 0.08, respectively. 

Conclusion: The results of this study indicate that, despite the absence of a significant difference in TOI between the study groups, patients in the slow group exhibited a not statistically significant trend for a lower incidence of delirium, as defined by CAMICU-7, in comparison to those in the fast group.