Flow Controlled Ventilation in Cardiac Surgery

The aim of the study is to investigate flow-controlled ventilation (FCV) during cardiac surgery requiring cardiopulmonary bypass. Previous preclinical trials have already shown improved oxygenation and CO2 removal within a significantly reduced respiratory minute volume as an expression of more efficient gas exchange with FCV compared to volume controlled ventilation (VCV). Preliminary data of our own animal study comparing individualized FCV by compliance guided pressure settings with state-of-the-art low tidal volume pressure controlled ventilation (PCV) confirmed previous findings with a significantly improved oxygenation by 20% while reducing respiratory minute volume. We therefore assume that FCV may be a more lung protective ventilation method.

Open heart surgery requires bridging of the heart and lung function with a cardiopulmonary bypass (CPB) performed by a heart-lung machine. During this time the lung is most frequently not ventilated at all and lies collapsed in the chest for several hours. After weaning from CPB, the lungs must be recruited and ensure sufficient gas exchange of the blood. Not surprisingly, the incidence of postoperative pulmonary complications (PPC) at 20-30% is comparatively high after cardiac surgery and is the leading cause of perioperative mortality. Based on previous trials we expect improved oxygenation and thus arterial partial pressure of oxygen (pO2) is the main primary outcome parameter of this study. Furthermore, we expect improved recruitment of lung tissue due to controlled expiratory flow in FCV without the need of recruitment maneuvers, which may cause deleterious effects on lung tissue. Thus, lung tissue aeration assessed by Hounsfield units analyses of a postoperative computed tomography will be a secondary outcome parameter.

Inclusion criteria

• Male and female subjects >18 years
• Body weight >40 kg
• Elective cardiac surgery with CPB and without ventilation during CPB
• American Society of Anaesthesiologists (ASA) risc classification I-IV
• Written informed consent

Exclusion criteria

• Emergency surgery
• Female subjects known to be pregnant
• Known participation in another interventional clinical trial
• High risk cardiac surgery such as double valve surgery, re-cardiac surgery, intraoperative cardiac arrest or pre-existing high grade cardiomyopathy (ejection fraction <30%)
• Closing operation field without chest closure due to hemodynamic instability
• Acute endocarditis under antibiotic treatment
• Minimal invasive valve surgery via thoracotomy (MIC)