The purpose of this study is to investigate the impact of supraphysiologic oxygen (hyperoxia) on myocardial function in anaesthetized patients undergoing non-cardiac vascular surgery.

Up to 110 patients with either proven coronary artery disease (CAD) or two or more risk factors for CAD undergoing elective or non-emergent non-cardiac vascular surgery will be recruited. Three blood samples for levels of myocardial biomarkers will be obtained at different perioperative time points (before anaesthesia induction, 2 hours after skin closure and 24 hours after the end of the surgery). The three myocardial biomarkers investigated are high-sensitive Troponin T (hsTnT), N-terminal (NT)-pro hormone BNP (NT-proBNP) and heart-type fatty acid binding protein (H-FABP). In the timeframe shortly after the induction of anaesthesia and prior to the start of surgery, myocardial strain as a marker of cardiac function will be measured by transesophageal echocardiography (TEE). Echocardiography measurements will be acquired at two different oxygen states for each patient.The fraction of inspired oxygen (FiO2) will be adjusted to reach a normoxaemic state (FiO2=0.3) and a hyperoxic state (FiO2=0.8). Patients will be randomized to which oxygen level is investigated first. Thereafter, the patients are again randomly assigned to either the normoxaemic or the hyperoxic state for the remainder of the perioperative treatment until 2 hours after skin closure. Surgery will be performed as planned by the treating team. Differences in the perioperative levels of myocardial biomarkers at the different time points and their dynamics will be assessed. Echocardiography images will be analyzed in a blinded manner for cardiac function and systolic and diastolic strain parameters. The results will help anaesthesiologists to better weigh risks and benefits when selecting an inspired oxygen fraction in such patients, and will help to evaluate hyperoxia as a risk factor for myocardial injury.

Inclusion Criteria:

• Written informed consent
• Patients eligible for the study should be scheduled for elective or non-emergent non-cardiac vascular surgery under general anaesthesia with endotracheal intubation, and have either
• proven CAD and will undergo high- or intermediate surgical risk procedure according to European (European Society of Cardiology, ESC / European Society of Anaesthesiology and Intensive Care, ESAIC) guidelines on non-cardiac surgery.

or

• two or more risk factors for CAD and will undergo high- or intermediate surgical risk procedures according to European ESC/ESAIC guidelines on non-cardiac surgery.

Exclusion Criteria:

• Acute coronary event 30 days before surgery
• Acute congestive heart failure
• Hemodynamic instability before induction of aneasthesia (vasopressor or inotrope infusion since hospitalization for index surgery)
• Atrial fibrillation or other severe arrhythmia
• Severe pulmonary disease (dependent on oxygen therapy or the Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 4 or severe carbon monoxide diffusion impairment or severe pulmonary hypertension)
• Preoperative oxygen saturation (SpO2) below 90% on room air
• Increased risk of oxygen toxicity (e.g., chemotherapy for malignancy within 3 months, bleomycin treatment, airway laser surgery)
• Scheduled surgery in the thoracic cavity
• ICU admission for respirator weaning and delayed extubation
• Pre-existing surgical site infection (SSI)
• Current active signs of systemic inflammatory response syndrome (SIRS) or sepsis according The Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3)
• Pregnancy
• Emergency surgery (to be performed within less than 12 hours of scheduling)
• Ambulatory surgery
• Baseline hs-TnT level elevated above 65ng/L

TEE images will be coded and analysed in batches at a later date by a blinded reader