These WHO guidelines which were updated in 2018, are valid for any country and suitable to local adaptations, and take account of the strength of available scientific evidence, the cost and resource implications, and patient values and preferences. The 2018 edition of the guidelines includes the revision of the recommendation regarding the use of 80% fraction of inspired oxygen (high FiO2) in surgical patients under general anaesthesia with tracheal intubation and the update of the section on implementation. Between 2017 and 2018, WHO re-assessed the evidence on the use of high FiO2 by updating the systematic review related to the effectiveness of this intervention to reduce SSI and commissioning an independent systematic review on adverse events potentially associated with it. Based on the updated evidence, the GDG decided to revise the strength of the recommendation from strong to conditional.