Perioperative Supplemental Oxygen Does Not Worsen Long-Term Mortality of Colorectal Surgery Patients

Perioperative oxygen administration for adults undergoing major noncardiac surgery: a narrative review

Perioperative oxygen administration, a topic under continuous research and debate in anesthesiology, strives to optimize tissue oxygenation while minimizing the risks associated with hyperoxia and hypoxia. This review provides a thorough overview of the current evidence on the application of perioperative oxygen in adult patients undergoing major noncardiac surgery. The review begins by describing the physiological reasoning for supplemental oxygen during the perioperative period and its potential benefits while also focusing on potential hyperoxia risks. This review critically appraises the existing literature on perioperative oxygen administration, encompassing recent clinical trials and meta-analyses, to elucidate its effect on postoperative results. Future research should concentrate on illuminating the optimal oxygen administration strategies to improve patient outcomes and fine-tune perioperative care protocols for adults undergoing major noncardiac surgery. By compiling and analyzing available evidence, this review aims to provide clinicians and researchers with comprehensive knowledge on the role of perioperative oxygen administration in major noncardiac surgery, ultimately guiding clinical practice and future research endeavors.

Hemodynamic effects of intraoperative 30% versus 80% oxygen concentrations: an exploratory analysis

Background

Supplemental oxygen leads to an increase in peripheral vascular resistance which finally increases systemic blood pressure in healthy subjects and patients with coronary artery disease, heart failure, undergoing heart surgery, and with sepsis. However, it is unknown whether this effect can also be observed in anesthetized patients having surgery. Thus, we evaluated in this exploratory analysis of a randomized controlled trial the effect of 80% versus 30% oxygen on intraoperative blood pressure and heart rate.

Methods

We present data from a previous study including 258 patients, who were randomized to a perioperative inspiratory FiO₂ of 0.8 (128 patients) versus 0.3 (130 patients) for major abdominal surgery. Continuous arterial blood pressure values were recorded every three seconds and were exported from the electronic anesthesia record system. We calculated time-weighted average (TWA) and Average Real Variability (ARV) of mean arterial blood pressure and of heart rate.

Results

There was no significant difference in TWA of mean arterial pressure between the 80% (80 mmHg [76, 85]) and 30% (81 mmHg [77, 86]) oxygen group (effect estimate -0.16 mmHg, CI -1.83 to 1.51; p = 0.85). There was also no significant difference in TWA of heart rate between the 80 and 30% oxygen group (median TWA of heart rate in the 80% oxygen group: 65 beats.min^-1 [58, 72], and in the 30% oxygen group: 64 beats.min^-1 [58; 70]; effect estimate: 0.12 beats.min^-1, CI -2.55 to 2.8, p = 0.94). Also for ARV values, no significant differences between groups could be detected.

Conclusion

In contrast to previous results, we did not observe a significant increase in blood pressure or a significant decrease in heart rate in patients, who received 80% oxygen as compared to patients, who received 30% oxygen during surgery and for the first two postoperative hours. Thus, hemodynamic effects of supplemental oxygen might play a negligible role in anesthetized patients.

Clinical Trail Registration

https://clinicaltrials.gov/ct2/show/NCT03366857?term=vienna&cond=oxygen&draw=2&rank=1.

[Perioperative hyperoxia-More harmful than beneficial?]

BACKGROUND

The ideal perioperative oxygen concentration is controversial and study results are inconsistent.

OBJECTIVE

Current knowledge on the beneficial and adverse effects of perioperative hyperoxia.

MATERIAL AND METHODS

Narrative review RESULTS: Perioperative hyperoxia is unlikely to increase the incidence of atelectasis, pulmonary or cardiovascular complications or mortality. Few and small potential beneficial effects, such as reduction of surgical wound infections or postoperative nausea and vomiting have been demonstrated. According to the current state of evidence, it is recommended to avoid perioperative hyperoxia and to aim for normoxia instead.

Intraoperative Fractions of Inspiratory Oxygen Are Associated With Recurrence-Free Survival After Elective Cancer Surgery

Background: Choice of the fraction of inspiratory oxygen (FiO₂) is controversial. The objective of this analysis was to evaluate whether intraoperative FiO₂ was associated with recurrence-free survival after elective cancer surgery.

Methods and Analysis: In this single-center, retrospective study, we analyzed 1,084 patients undergoing elective resection of pancreatic (n = 652), colorectal (n = 405), or hepatic cancer (n = 27) at Heidelberg University Hospital between 2009 and 2016. Intraoperative mean FiO₂ values were calculated. For unstratified analyses, the study cohort was equally divided into a low- and a high-FiO₂ group. For cancer-stratified analyses, this division was done within cancer-strata. The primary outcome measure was recurrence-free survival until the last known follow-up. Groups were compared using Kaplan–Meier analysis. A stratified log rank test was used to control for different FiO₂ levels and survival times between the cancer strata. Cox-regression analyses were used to control for covariates. Sepsis, reoperations, surgical-site infections, and cardiovascular events during hospital stay and overall survival were secondary outcomes.

Results: Median FiO₂ was 40.9% (Q1–Q3, 38.3–42.9) in the low vs. 50.4% (Q1–Q3, 47.4–54.7) in the high-FiO₂ group. Median follow-up was 3.28 (Q1–Q3, 1.68–4.97) years. Recurrence-free survival was considerable higher in the high-FiO₂ group (p < 0.001). This effect was also confirmed when stratified for the different tumor entities (p = 0.007). In colorectal cancer surgery, increased FiO₂ was independently associated with increased recurrence-free survival. The hazard for the primary outcome decreased by 3.5% with every 1% increase in FiO₂. The effect was not seen in pancreatic cancer surgery and we did not find differences in any of the secondary endpoints.

Conclusions: Until definite evidence from large-scale trials is available and in the absence of relevant clinical conditions warranting specific FiO₂ values, perioperative care givers should aim for an intraoperative FiO₂ of 50% in abdominal cancer surgery as this might benefit oncological outcomes.

Effects of high versus low inspiratory oxygen fraction on postoperative clinical outcomes in patients undergoing surgery under general anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To determine whether high perioperative inspired oxygen fraction (FiO₂) compared with low FiO₂ has more deleterious postoperative clinical outcomes in patients undergoing non-thoracic surgery under general anesthesia.

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

High perioperative FiO₂ (≥0.8) vs. low FiO₂ (≤0.5).

MEASUREMENTS

The primary outcome was mortality within 30 days. Secondary outcomes were pulmonary outcomes (atelectasis, pneumonia, respiratory failure, postoperative pulmonary complications [PPCs], and postoperative oxygen parameters), intensive care unit (ICU) admissions, and length of hospital stay. A subgroup analysis was performed to explore the treatment effect by body mass index (BMI).

MAIN RESULTS

Twenty-six trials with a total 4991 patients were studied. The mortality in the high FiO₂ group did not differ from that in the low FiO₂ group (risk ratio [RR] 0.91, 95% confidence interval [CI] 0.42-1.97, P = 0.810). Nor were there any significant differences between the groups in such outcomes as pneumonia (RR 1.19, 95% CI 0.74-1.92, P = 0.470), respiratory failure (RR 1.29, 95% CI 0.82-2.04, P = 0.270), PPCs (RR 1.05, 95% CI 0.69-1.59, P = 0.830), ICU admission (RR 0.94, 95% CI 0.55-1.60, P = 0.810), and length of hospital stay (mean difference [MD] 0.27 d, 95% CI -0.28-0.81, P = 0.340). The high FiO₂ was associated with postoperative atelectasis more often (risk ratio 1.27, 95% CI 1.00-1.62, P = 0.050), and lower postoperative arterial partial oxygen pressure (MD -5.03 mmHg, 95% CI -7.90- -2.16, P < 0.001)_. In subgroup analysis of BMI >30 kg/m², these parameters were similarly affected between the groups.

CONCLUSIONS

The use of high FiO₂ compared to low FiO₂ did not affect the short-term mortality, although it may increase the incidence of atelectasis in adult, non-thoracic patients undergoing surgical procedures. Nor were there any significant differences in other secondary outcomes.

Exploring Hyperoxia Effects in Cancer-From Perioperative Clinical Data to Potential Molecular Mechanisms

Increased inspiratory oxygen concentration is constantly used during the perioperative period of cancer patients to prevent the potential development of hypoxemia and to provide an adequate oxygen transport to the organs, tissues and cells. Although the primary tumours are surgically removed, the effects of perioperative hyperoxia exposure on distal micro-metastases and on circulating cancer cells can potentially play a role in cancer progression or recurrence. In clinical trials, hyperoxia seems to increase the rate of postoperative complications and, by delaying postoperative recovery, it can alter the return to intended oncological treatment. The effects of supplemental oxygen on the long-term mortality of surgical cancer patients offer, at this point, conflicting results. In experimental studies, hyperoxia effects on cancer biology were explored following multiple pathways. In cancer cell cultures and animal models, hyperoxia increases the production of reactive oxygen species (ROS) and increases the oxidative stress. These can be followed by the induction of the expression of Brain-derived neurotrophic factor (BDNF) and other molecules involved in angiogenesis and by the promotion of various degrees of epithelial mesenchymal transition (EMT).

Variable oxygen administration in surgical and medical wards evaluated by 30-day mortality-An observational study

BACKGROUND

Several studies in surgery and initial management of critical illness have indicated harmful effects of short-term exposure to hyperoxia. Exposure to and consequences of excessive oxygen administration in hospital wards are sparsely investigated. The aim of this study was to investigate the association between excessive oxygen administration in patients admitted to surgical or medical wards and 30-day mortality.

METHODS

We included patients in the Capital Region of Denmark who were admitted to hospital in 2014 for either myocardial infarction, acute exacerbation of chronic obstructive pulmonary disease (COPD), hip fracture or open abdominal surgery. We defined groups of inadequate, adequate or excessive oxygen administration based on peripheral oxygen saturation and oxygen administration values in the first 48 hours after admission. The primary outcome was mortality within 30 days, and data were analysed with multivariable logistic regression for age, gender and comorbidities.

RESULTS

We retrieved data from 11 196 patients, of which 81% had adequate, 18% had excessive and 1.8% inadequate oxygen administration. Mortality at 30 days was 4.2%, 7.6% and 27%, respectively, OR 1.46 (95%CI 1.16-1.84), P = .001 for patients with excessive compared to adequate oxygen administration. The association was significant in subgroups of patients admitted for acute exacerbation of COPD (OR 1.67, 95%CI 1.19-2.34) and myocardial infarction (OR 3.50, 95%CI 1.55-7.89).

CONCLUSION

Patients who received excessive oxygen administration in surgical and medical wards during the first 48 hours of admission had a higher mortality risk within 30 days compared to patients with adequate oxygen administration. However, inadequate oxygen therapy still renders highest mortality and should be avoided.

Supplemental Intraoperative Oxygen and Long-term Mortality: Subanalysis of a Multiple Crossover Cluster Trial

BACKGROUND

Whether supplemental oxygen worsens long-term mortality remains unclear, with contradictory trial results. The authors therefore tested the hypothesis that supplemental oxygen (80% vs. 30%) increases the hazard for long-term mortality.

METHODS

The authors conducted a post hoc analysis of a large multiple crossover cluster trial in which more than 5,000 colorectal surgeries on 4,088 adults were allocated to receive either 30% or 80% inspired oxygen during general anesthesia. The authors assessed the effect of 80% versus 30% target-inspired oxygen on long-term mortality and calculated Kaplan-Meier survival estimates. Analysis was restricted to patients with a home address in Ohio because the authors could obtain reliable vital status information from the Ohio Department of Health (Columbus, Ohio) for them.

RESULTS

A total of 3,471 qualifying colorectal surgeries performed in 2,801 patients were analyzed, including 1,753 (51%) surgeries in 1,577 patients given 80% oxygen and 1,718 surgeries in 1,551 patients given 30% oxygen. The observed incidence of death after a median of 3 yr was 13% (234 of 1,753) in the 80% oxygen group and 14% (245 of 1,718) in the 30% oxygen group. The estimated hazard ratio for mortality was 0.94 (95% CI, 0.78 to 1.13; P = 0.493).

CONCLUSIONS

In this post hoc analysis of a large, controlled trial, supplemental oxygen did not increase postoperative mortality.

EDITOR’S PERSPECTIVE

O2 No Longer the Go2: A Systematic Review and Meta-Analysis Comparing the Effects of Giving Perioperative Oxygen Therapy of 30% FiO2 to 80% FiO2 on Surgical Site Infection and Mortality

OBJECTIVE

To determine the effects of perioperative high (80%) versus low (30%) fraction of inspired oxygen (FiO₂) on surgical site infection (SSI) and mortality in adult surgical patients.

BACKGROUND

The routine use of high fraction perioperative oxygen in patients is "standard of care" and recommended by the World Health Organisation; however, whether there is truly any benefit to this therapy has been challenged by some authors. Questions have also been raised about the possibility of harm from oxygen therapy.

METHOD

Randomised control trials comparing high-to-low FiO₂ were located by searching MEDLINE, Embase, CENTRAL and Web of Science. The primary outcomes were SSI up to 15 days and up to any time point postoperatively and mortality up to 30 days. The data were analysed using random effects meta-analysis.

RESULTS

Twelve studies involving 10,212 participants were included. At 15 days postoperatively, and at the longest point of post-operative follow-up, there was no statistically significant reduction in the risk of SSI when comparing patients who received a perioperative FiO₂ of 30% to those with an FiO₂ of 80% (RR 1.41, 95% CI 1.00-2.01, p 0.05 and RR 1.23, 95% CI 1.00-1.51, p 0.05). There was no statistically significant difference in mortality between the 30% FiO₂ and the 80% FiO₂ groups (RR 1.12, 95% CI 0.56-2.22, p 0.76).

CONCLUSION

This meta-analysis showed no statistically significant difference in post-operative SSI or mortality when comparing patients receiving an FiO₂ of 80% to those receiving an FiO₂ of 30%.

Investigating Disturbances of Oxygen Homeostasis: From Cellular Mechanisms to the Clinical Practice

Soon after its discovery in the 18th century, oxygen was applied as a therapeutic agent to treat severely ill patients. Lack of oxygen, commonly termed as hypoxia, is frequently encountered in different disease states and is detrimental to human life. However, at the end of the 19th century, Paul Bert and James Lorrain Smith identified what is known as oxygen toxicity. The molecular basis of this phenomenon is oxygen's readiness to accept electrons and to form different variants of aggressive radicals that interfere with normal cell functions. The human body has evolved to maintain oxygen homeostasis by different molecular systems that are either activated in the case of oxygen under-supply, or to scavenge and to transform oxygen radicals when excess amounts are encountered. Research has provided insights into cellular mechanisms of oxygen homeostasis and is still called upon in order to better understand related diseases. Oxygen therapy is one of the prime clinical interventions, as it is life saving, readily available, easy to apply and economically affordable. However, the current state of research also implicates a reconsidering of the liberal application of oxygen causing hyperoxia. Increasing evidence from preclinical and clinical studies suggest detrimental outcomes as a consequence of liberal oxygen therapy. In this review, we summarize concepts of cellular mechanisms regarding different forms of disturbed cellular oxygen homeostasis that may help to better define safe clinical application of oxygen therapy.

Effects of oxygen on post-surgical infections during an individualised perioperative open-lung ventilatory strategy: a randomised controlled trial

BACKGROUND

We aimed to examine whether using a high fraction of inspired oxygen (FIO₂) in the context of an individualised intra- and postoperative open-lung ventilation approach could decrease surgical site infection (SSI) in patients scheduled for abdominal surgery.

METHODS

We performed a multicentre, randomised controlled clinical trial in a network of 21 university hospitals from June 6, 2017 to July 19, 2018. Patients undergoing abdominal surgery were randomly assigned to receive a high (0.80) or conventional (0.3) FIO₂ during the intraoperative period and during the first 3 postoperative hours. All patients were mechanically ventilated with an open-lung strategy, which included recruitment manoeuvres and individualised positive end-expiratory pressure for the best respiratory-system compliance, and individualised continuous postoperative airway pressure for adequate peripheral oxyhaemoglobin saturation. The primary outcome was the prevalence of SSI within the first 7 postoperative days. The secondary outcomes were composites of systemic complications, length of intensive care and hospital stay, and 6-month mortality.

RESULTS

We enrolled 740 subjects: 371 in the high FIO₂ group and 369 in the low FIO₂ group. Data from 717 subjects were available for final analysis. The rate of SSI during the first postoperative week did not differ between high (8.9%) and low (9.4%) FIO₂ groups (relative risk [RR]: 0.94; 95% confidence interval [CI]: 0.59-1.50; P=0.90]). Secondary outcomes, such as atelectasis (7.7% vs 9.8%; RR: 0.77; 95% CI: 0.48-1.25; P=0.38) and myocardial ischaemia (0.6% [n=2] vs 0% [n=0]; P=0.47) did not differ between groups.

CONCLUSIONS

An oxygenation strategy using high FIO₂ compared with conventional FIO₂ did not reduce postoperative SSIs in abdominal surgery. No differences in secondary outcomes or adverse events were found.

CLINICAL TRIAL REGISTRATION

NCT02776046.

Survival Analysis and Interpretation of Time-to-Event Data: The Tortoise and the Hare

Survival analysis, or more generally, time-to-event analysis, refers to a set of methods for analyzing the length of time until the occurrence of a well-defined end point of interest. A unique feature of survival data is that typically not all patients experience the event (eg, death) by the end of the observation period, so the actual survival times for some patients are unknown. This phenomenon, referred to as censoring, must be accounted for in the analysis to allow for valid inferences. Moreover, survival times are usually skewed, limiting the usefulness of analysis methods that assume a normal data distribution. As part of the ongoing series in Anesthesia & Analgesia, this tutorial reviews statistical methods for the appropriate analysis of time-to-event data, including nonparametric and semiparametric methods—specifically the Kaplan-Meier estimator, log-rank test, and Cox proportional hazards model. These methods are by far the most commonly used techniques for such data in medical literature. Illustrative examples from studies published in Anesthesia & Analgesia demonstrate how these techniques are used in practice. Full parametric models and models to deal with special circumstances, such as recurrent events models, competing risks models, and frailty models, are briefly discussed.

Association between perioperative hyperoxia and cerebrovascular complications after laparotomy-A post-hoc follow-up study

BACKGROUND

Perioperative hyperoxia has been linked to increased long-term mortality. Vasoconstrictive and cellular side effects to hyperoxia have been suggested to increase the risk of coronary and cerebral ischemia. The aim of this post-hoc analysis of a large randomized trial was to compare the effects of 80% vs 30% perioperative oxygen on the long-term risk of stroke or transient cerebral ischemia (TCI) in patients undergoing abdominal surgery.

METHODS

A total of 1386 patients were randomized to 80% or 30% perioperative oxygen during acute or elective open abdominal surgery. Median follow-up was 3.9 years. Primary outcome was a composite of the long-term occurrence of stroke or TCI. Secondary outcomes included long-term mortality without stroke or TCI, and incidences of neurological admission, psychiatric admission, and dementia. Outcomes were analyzed in Cox regression models.

RESULTS

Stroke or TCI occurred in 20 (3.0%) patients given 80% oxygen vs 22 (3.2%) patients given 30% oxygen with an adjusted hazard ratio (HR) of 0.96 [95% CI 0.52-1.76]. Composite secondary outcome of death, stroke, or TCI had a HR of 1.21 [95% CI 1.00-1.47] for 80% compared to 30% oxygen. HRs for secondary outcomes were HR 1.14 [95% CI 0.79-1.64] for neurological admission, 1.34 [95% CI 0.95-1.88] for psychiatric admission and 0.54 [95% CI 0.16-1.80] for dementia.

CONCLUSION

Stroke or TCI did not seem related to perioperative inspiratory oxygen fraction. Due to few events, this study cannot exclude that perioperative hyperoxia increases risk of mortality, stroke, or TCI after abdominal surgery.

Effectiveness of 80% vs 30-35% fraction of inspired oxygen in patients undergoing surgery: an updated systematic review and meta-analysis

BACKGROUND

In 2016, the World Health Organization (WHO) strongly recommended the use of a high fraction of inspired oxygen (FiO₂) in adult patients undergoing general anaesthesia to reduce the risk of surgical site infection (SSI). Since then, further trials have been published, trials included previously have come under scrutiny, and one article was retracted. We updated the systematic review on which the recommendation was based.

METHODS

We performed a systematic literature search from January 1990 to April 2018 for RCTs comparing the effect of high (80%) vs standard (30-35%) FiO₂ on the incidence of SSI. Studies retracted or under investigation were excluded. A random effects model was used for meta-analyses; the sources of heterogeneity were explored using meta-regression.

RESULTS

Of 21 RCTs included, six were newly identified since the publication of the WHO guideline review; 17 could be included in the final analyses. Overall, no evidence for a reduction of SSI after the use of high FiO₂ was found [relative risk (RR): 0.89; 95% confidence interval (CI): 0.73-1.07]. There was evidence that high FiO₂ was beneficial in intubated patients [RR: 0.80 (95% CI: 0.64-0.99)], but not in non-intubated patients [RR: 1.20 (95% CI: 0.91-1.58); test of interaction; P=0.048].

CONCLUSIONS

The WHO updated analyses did not show definite beneficial effect of the use of high perioperative FiO₂, overall, but there was evidence of effect of reducing the SSI risk in surgical patients under general anaesthesia with tracheal intubation. However, the evidence for this beneficial effect has become weaker and the strength of the recommendation needs to be reconsidered.

Safety of 80% vs 30-35% fraction of inspired oxygen in patients undergoing surgery: a systematic review and meta-analysis

BACKGROUND

Evidence-based guidelines from the World Health Organization (WHO) have recommended a high (80%) fraction of inspired oxygen (FiO₂) 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 FiO₂. We performed a systematic review to define the relative risk of clinically relevant adverse events (AE) associated with high FiO₂.

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% FiO₂ compared with 30-35% FiO₂. We assessed study quality and performed meta-analyses of risk ratios (RR) comparing 80% FiO₂ against 30-35% for major complications, mortality, and intensive care admission.

RESULTS

We included 17 moderate-good quality trials and two non-randomised studies with serious-critical risk of bias. No evidence of harm with high FiO₂ was found for major AE in the meta-analysis of randomised trials: atelectasis RR 0.91 [95% confidence interval (CI) 0.59-1.42); cardiovascular events RR 0.90 (95% CI 0.32-2.54); intensive care admission RR 0.93 (95% CI 0.7-1.12); and death during the trial RR 0.49 (95% CI 0.17-1.37). One non-randomised study reported that high FiO₂ was associated with major respiratory AE [RR 1.99 (95% CI 1.72-2.31)].

CONCLUSIONS

No definite signal of harm with 80% FiO₂ 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.

The wound environment, microbial virulence and postoperative infection: Practical lessons for the surgeon

For the practicing surgeon, the development of a postoperative wound infection represents a major complication that can be both costly and disabling. As a result, surgeons apply multiple methods of prevention including skin decontamination, use of antibiotics, irrigation with or without antiseptics and meticulous use of technique. In elective surgery, however, most wound infections cannot be predicted. In this review we discuss emerging concepts in wound infection pathogenesis and include a discussion on how the wound environment may directly activate bacteria to express a more harmful or virulent phenotype. Based on these emerging concepts, we provide the practicing surgeon with molecular level evidence to explain why some methods of wound infection protection may be useful while others are not.

Oxygen supplementation for critically ill patients-A protocol for a systematic review

BACKGROUND

In critically ill patients, hypoxaemia is a common clinical manifestation of inadequate gas exchange in the lungs. Supplemental oxygen is therefore given to all critically ill patients. This can result in hyperoxaemia, and some observational studies have identified harms with hyperoxia. The objective of this systematic review is to critically assess the evidence of randomised clinical trials on the effects of higher versus lower inspiratory oxygen fractions or targets of arterial oxygenation in critically ill adult patients.

METHODS

We will search for randomised clinical trials in major international databases. Two authors will independently screen and select references for inclusion using Covidence, extract data and assess the methodological quality of the included randomised clinical trials using the Cochrane risk of bias tool. Any disagreement will be resolved by consensus. We will analyse the extracted data using Review Manager and Trial Sequential Analysis. To assess the quality of the evidence, we will create a 'Summary of Findings' table containing our primary and secondary outcomes using the GRADE assessment.

DISCUSSION

Supplemental oxygen administration is widely recommended in international guidelines despite lack of robust evidence of its effectiveness. To our knowledge, no systematic review of randomised clinical trials has investigated the effects of oxygen supplementation in critically ill patients. This systematic review will provide reliable evidence to better inform future trialists and decision-makers on clinical practice on supplemental oxygen administration in critically ill patients.

Effect of intraoperative hyperoxia on the incidence of surgical site infections: a meta-analysis

BACKGROUND

Whether supplemental intraoperative oxygen reduces surgical site infections remains unclear. Recent recommendations from the World Health Organization and Center for Disease Control to routinely use high inspired oxygen concentrations to reduce infection risk have been widely criticized. We therefore performed a meta-analysis to evaluate the influence of inspired oxygen on infection risk, including a recent large trial.

METHODS

A systematic literature search was performed. Primary analysis included all eligible trials. Sensitivity analyses distinguished studies of colorectal and non-colorectal surgeries, and excluded studies with high risk of bias. Another post-hoc sensitivity analysis excluded studies from one author that appear questionable.

RESULTS

The primary analysis included 26 trials (N=14,710). The RR [95%CI] for wound infection was 0.81 [0.70, 0.94] in the high vs. low inspired oxygen groups. The effect remained significant in colorectal patients (N=10,469), 0.79 [0.66, 0.96], but not in other patients (N=4,241), 0.86 [0.69, 1.09]. When restricting the analysis to studies with low risk of bias, either by strict inclusion criteria (N=5,047) or by researchers' judgment (N=12,547), no significant benefit remained: 0.84 [0.67, 1.06] and 0.89 [0.76, 1.05], respectively.

CONCLUSIONS

When considering all available data, intraoperative hyperoxia reduced wound infection incidence. However, no significant benefit remained when analysis was restricted to objective- or investigator-identified low-bias studies, although those analyses were not as well-powered. Meta-analysis of the most reliable studies does not suggest that supplemental oxygen substantively reduces wound infection risk, but more research is needed to fully answer this question.

WHO Needs High FIO2?

World Health Organization and the United States Center for Disease Control have recently recommended the use of 0.8 FIO₂ in all adult surgical patients undergoing general anaesthesia, to prevent surgical site infections. This recommendation has arisen several discussions: As a matter of fact, there are numerous studies with different results about the effect of FIO₂ on surgical site infection. Moreover, the clinical effects of FIO₂ are not limited to infection control. We asked some prominent authors about their comments regarding the recent recommendations.