Optimized Cardiopulmonary Bypass Flow Strategy Based on Ideal Body Weight in Obese Patients Undergoing Cardiac Surgery

Cardiopulmonary bypass (CPB) pump flow is typically calculated according to body surface area (BSA) derived from actual body weight and temperature, following the 2024 European guidelines recommending an indexed flow of 2.4 L/min/m². However, in obese patients, using actual weight leads to a high BSA and thus elevated pump flow, increasing technical challenges such as the need for larger cannulas, higher circulating blood volume, and elevated pump speeds. These adjustments may increase risks of hemodilution, transfusion, and hemolysis. Given that lean body mass in obese patients is similar to that of non-obese patients of the same height-and that aerobic metabolism depends on lean mass-adjusting CPB flow based on ideal body weight rather than actual weight could reduce transfusions and associated complications. Several observational studies support the concept of using ideal body weight for CPB flow calculation in obese patients. Despite this, no randomized controlled trial has yet addressed the clinical impact of this approach. Given the increasing prevalence of obesity and the practical challenges it poses during cardiac surgery, a controlled clinical trial is warranted. The investigators hypothesize that adjusting the cardiopulmonary bypass (CPB) flow according to the ideal body weight rather than the actual body weight in obese patients could reduce the need for blood transfusions and limit the associated complications.

Inclusion Criteria: * Patients aged over 18 years * Patients with obesity (BMI \> 30 kg/m²) * Scheduled cardiac surgery under cardiopulmonary bypass (CPB): * Coronary artery bypass grafting (CABG) * Aortic valve replacement * Mitral valve repair or replacement * Surgery on the aortic root (aortic tube, Bentall procedure, Tirone David, or others) * Combined surgery * Affiliation to a social security scheme * Written informed consent Exclusion Criteria: * Minors * BMI \< 30 kg/m² * Off-pump cardiac surgery * Surgery on the aortic arch * Planned perioperative hypothermia \< 32ºC * Emergency surgery * Heart transplantation or mechanical circulatory support surgery * Infectious endocarditis * Participation in another clinical trial within the past 30 days * Pregnant, parturient, or breastfeeding women * Patients under guardianship, curatorship, or deprived of civil rights * Advanced chronic kidney disease (renal clearance \< 30 ml/min) * Coexisting disease with a high probability of death within 6 months * Preoperative anemia (hemoglobin \< 10 g/dL) * Body surface area (actual body weight) \> 2.5 m²