Is Peri-operative Hyperoxemia a Risk Factor for Postoperative Complications?

Patients undergoing vascular surgery are at a significantly high risk of perioperative cardiovascular, cerebral and renal events compared to those undergoing non-vascular surgery. This could be because of co-morbidities that are common in this patient group. Additionally, smoking, which is common in this population, may be a contributing factor. Oxygen therapy has been used for decades in order to reduce the risk of myocardial infarction and stroke in patients undergoing vascular surgery and pre-existing co-morbidities in the belief that increased inspired oxygen increases oxygen delivery to tissues, thereby reducing the risk for hypoxia and cell death. However, several studies published recently have questioned the routine use of high inspired oxygen concentration (hyperoxia) to improve oxygen delivery, specifically in the neonatal period but possibly even following myocardial infarction. This could be explained by the fact that increasing inspired concentrations of oxygen cause vasoconstriction in cerebral and coronary arteries, thereby reducing blood flow. Additionally, increased oxygen causes excessive production of reactive oxygen species (ROS), and repercussion injury from oxidative stress. The latter can lead to apoptosis (cell death) in myocardial or cerebral neurons. Despite the high risks of administering oxygen when not needed, it is routinely used in hospitals all over the world without a doctors prescription. This study aims to assess peri-operative complications up to 1 year following vascular surgery in patients randomised to receive high inspired oxygen concentration (endpoint: SpO2 98 - 100%) or minimal inspired O2 concentration (endpoint: SpO2 \> 90%).