Background: Evidence-based guidelines from the World Health Organization (WHO) have recommended a high (80%) fraction of inspired oxygen (FiO 2 ) to reduce surgical site infection in adult surgical patients undergoing general anaesthesia with tracheal intubation. However, there is ongoing debate over the safety of high FiO 2 . We performed a systematic review to define the relative risk of clinically relevant adverse events (AE) associated with high FiO 2 . Methods: We reviewed potentially relevant articles from the WHO review supporting the recommendation, including an updated (July 2018) search of EMBASE and PubMed for randomised and non-randomised controlled studies reporting AE in surgical patients receiving 80% FiO 2 compared with 30e35% FiO 2 . We assessed study quality and performed meta-analyses of risk ratios (RR) comparing 80% FiO 2 against 30e35% for major complications, mortality, and intensive care admission. Results: We included 17 moderateegood quality trials and two non-randomised studies with serious-critical risk of bias. No evidence of harm with high FiO 2 was found for major AE in the meta-analysis of randomised trials: atelectasis RR 0.91 [95% confidence interval (CI) 0.59e1.42); cardiovascular events RR 0.90 (95% CI 0.32e2.54); intensive care admission RR 0.93 (95% CI 0.7e1.12); and death during the trial RR 0.49 (95% CI 0.17e1.37). One non-randomised study reported that high FiO 2 was associated with major respiratory AE [RR 1.99 (95% CI 1.72e2.31)]. Conclusions: No definite signal of harm with 80% FiO 2 in adult surgical patients undergoing general anaesthesia was demonstrated and there is little evidence on safety-related issues to discourage its use in this population.

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Objectives: We aimed to assess the evidence for the use of 8-isoprostane in exhaled breath condensate (EBC) as a biomarker in adult asthma. Design: A systematic review and meta-analysis of EBC 8-isoprostane. Methods: We searched a number of online databases (including PubMed, Embase and Scopus) in January 2016. We included studies of adult non-smokers with EBC collection and asthma diagnosis conducted according to recognised guidelines. We aimed to pool data using random effects meta-analysis and assess heterogeneity using I 2 . Results: We included twenty studies, the findings from which were inconsistent. Seven studies (n = 329) reported 8-isoprostane levels in asthma to be significantly higher than that of control groups, whilst six studies (n = 403) did not.Only four studies were appropriate for inclusion in a random effects meta-analysis of mean difference. This found a statistically significant between-groups difference of 22pg/ml.Confidence in the result is limited by the small number of studies and by substantial statistical heterogeneity (I 2 = 94). Conclusion: The clinical value of EBC 8-isoprostane as a quantitative assessment of oxidative stress in asthma remains unclear due to variability in results and methodological heterogeneity. It is essential to develop a robust and standardised methodology if the use of EBC 8-isoprostane in asthma is to be properly evaluated.