Background: The use of 100% oxygen during intubation and extubation is common practice in anaesthetic rooms and theatres across the UK. There is uncertainty what the optimum FiO2 should be intraoperatively. An FiO2 of 100 is thought to cause atelectasis and cellular toxicity. Administration of 80% oxygen is associated with an increase mortality in cancer patients compared with 30%1. Other evidence shows high FiO2 decreases surgical site infection and does not increase the postoperative atelectasis2 .The Royal Marsden (RMH) is a specialist cancer hospital treating a variety of pathology, all ages and ASA grade I-IV patients.We investigated if our use of FiO2 has changed from 2010 to 2015.
Materials and methods: RMH uses an automatic system where all clinical data is recorded from the start to the end of anaesthesia. The data captured automatically and therefore is not user dependent or subject to recall bias.
Results: There were 18529 patients over 6 years. The number of patients was lower in 2010 and 2015. The mean FiO2 decreased gradually from 61.33 in 2010 to 57.3 in 2014 and then sharply decreased to 36.03 in 2015. The case mix and the ASA of the patients have not changed over this time (data not shown). 

Year	No. of patients	Mean FiO2
2010	1451	61.33
2011	3555	61.10
2012	4072	60.20
2013	4177	58.30
2014	3540	57.30
2015	1734	36.03
[Mean FiO2]


Conclusions: The data shows a change in practice with a gradual reduction in FiO2 and a drop during 2015. There was a change in behaviour of our anaesthetists away from high FiO2, reflecting a desire to reduce the perceived side effects of high FiO2.Interestingly the literature to supports both high and relatively lower FiO2. This conflicting evidence is unhelpful to clinicians and a review of the evidence to create guidance is needed.
References: 
1. Meyhoff CS et al. Increased long-term mortality after a high perioperative inspiratory oxygen fraction during abdominal surgery: follow-up of a randomized clinical trial. Anesth Analg. (2012) Oct;115(4):849-54 
2.Hovaguimian, F et al, MR Effect of intraoperative high inspired oxygen fraction on surgical site infection, postoperative nausea and vomiting, and pulmonary function: Systematic review and meta-analysis of randomized controlled trials. Anesthesiology. (2013).Aug 119 303-16

Intraoperative FiO2: Is practice following the evidence?