Hyperoxemia as a risk factor for ventilator-associated pneumonia

A meta-analysis of the effects of transnasal high-flow oxygen therapy in gastrointestinal endoscopy

Purpose

This study aimed to systematically evaluate the clinical effects of using transnasal high-flow nasal cannula (HFNC) and conventional oxygen therapy (COT) in patients undergoing gastrointestinal endoscopy.

Methods

A comprehensive literature search was conducted from 2004 to April 2024 to collect relevant studies on the application of HFNC in patients undergoing gastrointestinal endoscopy. Multiple Chinese and English databases, including China National Knowledge Infrastructure (CNKI), Wanfang Data, Web of Science, PubMed, and Cochrane Library, were searched systematically for randomized controlled trials (RCTs). Two researchers independently screened the literature, extracted data, and assessed the risk of bias in the included studies. RevMan 5.4 software was utilized for conducting the network meta-analysis.

Results

A total of 12 RCTs involving 3,726 patients were included. Meta-analysis results showed that HFNC reduced the incidence of hypoxemia and improved the minimum oxygen saturation (SpO2) compared with COT [odds ratio (OR) = 0.39, 95% confidence interval (CI): 0.29-0.53], [mean difference (MD) = 4.07, 95% CI: 3.14-5.01], and the difference was statistically significant. However, the baseline SpO2 levels and incidence of hypercapnia were not statistically significantly different between the HFNC and COT groups [MD = -0.21, 95% CI: -0.49-0.07]; [OR = 1.43, 95% CI: 0.95-2.15]. In terms of procedure time, the difference between HFNC and COT was not statistically significant, and subgroup analyses were performed for the different types of studies, with standard deviation in the gastroscopy group (MD = 0.09, 95% CI: -0.07-0.24) and the endoscopic retrograde cholangiopancreatography group (MD = 0.36, 95% CI: -0.50-1.23). The results demonstrated a significant reduction in the adoption of airway interventions in the HFNC group compared to the COT group (OR = 0.16, 95% CI: 0.05-0.53), with a statistically significant difference; this result was consistent with those of the included studies.

Conclusion

The application of HFNC improves the incidence of hypoxemia, enhances oxygenation, and reduces airway interventions during gastrointestinal endoscopy. However, HFNC does not significantly affect baseline SpO2, hypercapnia, or procedure time. The limitations of this study must be acknowledged, and further high-quality studies should be conducted to validate these findings.

Pulmonary Events in ICU patients with hyperoxia: is it possible to relate arterial partial pressure of oxygen to coded diseases? A retrospective analysis

OBJECTIVE

Oxygen has been used liberally in ICUs for a long time to prevent hypoxia in ICU- patients. Current evidence suggests that paO2 >300 mmHg should be avoided, it remains uncertain whether an "optimal level" exists. We investigated how "mild" hyperoxia influences diseases and in-hospital mortality.

DESIGN

This is a retrospective study.

SETTING

112 mechanically ventilated ICU-patients were enrolled.

PATIENTS OR PARTICIPANTS

112 ventilated patients were included and categorized into two groups based on the median paO2 values measured in initial 24 h of mechanical ventilation: normoxia group (paO2 ≤ 100 mmHg, n = 43) and hyperoxia group patients (paO2 > 100 mmHg, n = 69).

INTERVENTIONS

No interventions were performed.

MAIN VARIABLES OF INTEREST

The primary outcome was the incidence of pulmonary events, the secondary outcomes included the incidence of other new organ dysfunctions and in-hospital mortality.

RESULTS

The baseline characteristics, such as age, body mass index, lactate levels, and severity of disease scores, were similar in both groups. There were no statistically significant differences in the incidence of pulmonary events, infections, and new organ dysfunctions between the groups. 27 out of 69 patients (39.1%) in the "mild" hyperoxia group and 12 out of 43 patients (27.9%) in the normoxia group died during their ICU or hospital stay (p = 0.54). The mean APACHE Score was 29.4 (SD 7.9) in the normoxia group and 30.0 (SD 6.7) in the hyperoxia group (p = 0.62).

CONCLUSIONS

We found no differences in pulmonary events, other coded diseases, and in-hospital mortality between both groups. It remains still unclear what the "best oxygen regime" is for intensive care patients.

Alveolar Hyperoxia and Exacerbation of Lung Injury in Critically Ill SARS-CoV-2 Pneumonia

Acute hypoxic respiratory failure (AHRF) is a prominent feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critical illness. The severity of gas exchange impairment correlates with worse prognosis, and AHRF requiring mechanical ventilation is associated with substantial mortality. Persistent impaired gas exchange leading to hypoxemia often warrants the prolonged administration of a high fraction of inspired oxygen (FiO2). In SARS-CoV-2 AHRF, systemic vasculopathy with lung microthrombosis and microangiopathy further exacerbates poor gas exchange due to alveolar inflammation and oedema. Capillary congestion with microthrombosis is a common autopsy finding in the lungs of patients who die with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome. The need for a high FiO2 to normalise arterial hypoxemia and tissue hypoxia can result in alveolar hyperoxia. This in turn can lead to local alveolar oxidative stress with associated inflammation, alveolar epithelial cell apoptosis, surfactant dysfunction, pulmonary vascular abnormalities, resorption atelectasis, and impairment of innate immunity predisposing to secondary bacterial infections. While oxygen is a life-saving treatment, alveolar hyperoxia may exacerbate pre-existing lung injury. In this review, we provide a summary of oxygen toxicity mechanisms, evaluating the consequences of alveolar hyperoxia in COVID-19 and propose established and potential exploratory treatment pathways to minimise alveolar hyperoxia.

Oxygenation target in acute respiratory distress syndrome

Determining oxygenation targets in acute respiratory distress syndrome (ARDS) remains a challenge. Although oxygenation targets have been used since ARDS was first described, they have not been investigated in detail. However, recent retrospective and prospective trials have evaluated the optimal oxygenation threshold in patients admitted to the general intensive care unit. In view of the lack of prospective data, clinicians continue to rely on data from the few available trials to identify the optimal oxygenation strategy. Assessment of the cost-benefit ratio of the fraction of inspired oxygen (FiO₂) to the partial pressure of oxygen in the arterial blood (PaO₂) is an additional challenge. A high FiO₂ has been found to be responsible for respiratory failure and deaths in numerous animal models. Low and high PaO₂ values have also been demonstrated to be potential risk factors in experimental and clinical situations. The findings from this literature review suggest that PaO₂ values ranging between 80 mmHg and 90 mmHg are acceptable in patients with ARDS. The costs of rescue maneuvers needed to reach these targets have been discussed. Several recent papers have highlighted the risk of disagreement between arterial oxygen saturation (SaO₂) and peripheral oxygen saturation (SpO₂) values. In order to avoid discrepancies and hidden hypoxemia, SpO₂ readings need to be compared with those of SaO₂. Higher SpO₂ values may be needed to achieve the recommended PaO₂ and SaO₂ values.

Changes of blood gas analysis in moderate-to-severe acute respiratory distress syndrome patients during long-term prone position ventilation: a retrospective cohort study

Background

Prone position ventilation (PPV) has been recommended for patients with acute respiratory distress syndrome (ARDS) to improve oxygenation. However, whether prolonged prone ventilation will aggravate hyperoxia and whether abdominal compression will aggravate permissive hypercapnia acidosis are topics of concern. We carried out a retrospective analysis to investigate the issues above.

Methods

Clinical data were collected from 97 moderate-to-severe ARDS patients who received PPV as part of their treatment in the intensive care unit (ICU) of the First Affiliated Hospital of Guangzhou Medical University from November 2015 to May 2021. We collected arterial blood gas of patients according to the 3 periods: supine position ventilation (SPV), PPV early stage (within 4 hours), and PPV middle and late stage (6 hours or later). We established a linear mixed-effects models with "body position changes, times of PPV, gender, age, baseline SOFA, and baseline APACHE II" as fixed effects, and individual and the number of prone positions as random intercept and random slope to investigate the effect of body position changes on blood gas analysis.

Results

Among the 97 patients received PPV included, 51 were ICU survivors. Arterial partial pressure of oxygen (PaO₂) and PaO₂/fraction of inspired oxygen (FiO₂) ratio were significantly higher at the early, middle and late stages of PPV than those in SPV [PFR (mmHg): 158 (118.00, 203.00) vs. 161 (129.00, 202.75) vs. 123 (91.75, 163.00), P<0.05]. Despite the synchronized reduction of FiO₂, the incidence of hyperoxia in the prone position was still significantly higher than that in the supine position [hyperoxia (%):33.33 vs. 33.56 vs. 12.42, P<0.05]; there was no significant change in arterial carbon dioxide partial pressure (PaCO₂) at each stage of PPV, but there was a significant increase in PH at PPV middle and late stages than those at early stage [PH: 7.39 (7.34, 7.42) vs. 7.37 (7.31, 7.41), P<0.05].

Conclusions

Although PPV improves the patients' oxygenation, the associated incidence of hyperoxia exceeds 33%. Down-regulate FiO₂ more sharply after PPV is necessary, if oxygenation conditions permit. PPV may alleviate the acidosis associated with permissive hypercapnia in ARDS patients treated with lung protective ventilation strategy (LPVS).

Development and Validation of a Nomogram for Predicting Postoperative Pulmonary Infection in Patients Undergoing Lung Surgery

OBJECTIVES

To develop and validate a nomogram for predicting postoperative pulmonary infection (PPI) in patients undergoing lung surgery.

DESIGN

Single-center retrospective cohort analysis.

SETTING

A university-affiliated cancer hospital PARTICIPANTS: A total of 1,501 adult patients who underwent lung surgery from January 2018 to December 2020.

INTERVENTIONS

Observation for PPI within 7 days after lung surgery.

MEASUREMENTS AND MAIN RESULTS

A complete set of demographics, preoperative variables, and postoperative follow-up data was recorded. The primary outcome was PPI; a total of 125 (8.3%) out of 1,501 patients developed PPI. The variables with p < 0.1 in univariate logistic regression were included in the multivariate regression, and multivariate logistic regression analysis showed that surgical procedure, surgical duration, the inspired fraction of oxygen in one-lung ventilation, and postoperative pain were independent risk factors for PPI. A nomogram based on these factors was constructed in the development cohort (area under the curve: 0.794, 95% CI 0.744-0.845) and validated in the validation cohort (area under the curve: 0.849, 95% CI 0.786-0.912). The calibration slope was 1 in the development and validation cohorts. Decision curve analysis indicated that when the threshold probability was within a range of 0.02-to-0.58 and 0.02-to-0.42 for the development and validation cohorts, respectively, the nomogram model could provide a clinical net benefit.

CONCLUSIONS

The authors developed and validated a nomogram for predicting PPI in patients undergoing lung surgery. The prediction model can predict the development of PPI and identify high-risk groups.

[Oxygen reserve index: a new parameter for oxygen therapy]

Oxygen reserve index (ORI) is a novel dimensionless index used for noninvasive, real-time, and continuous monitoring of oxygenation, and ORI value ranges from 0 to 1, which reflects the range of 100-200 mmHg for arterial partial pressure of oxygen. ORI combined with pulse oximetry may help to accurately adjust the concentration of inspired oxygen and prevent hyperoxemia and hypoxemia. ORI is suitable for various clinical situations, and the medical staff should master this novel parameter and use it properly to assess the oxygenation of patients. In addition, several limitations of ORI should be noticed during clinical application.

Comparing restrictive versus liberal oxygen strategies for trauma patients - the TRAUMOX2 trial: protocol for a randomised clinical trial

INTRODUCTION

Supplemental oxygen is commonly used in trauma patients, although it may lead to hyperoxaemia that has been associated with pulmonary complications and increased mortality. The primary objective of this trial, TRAUMOX2, is to compare a restrictive versus liberal oxygen strategy the first 8 hours following trauma.

METHODS AND ANALYSIS

TRAUMOX2 is an investigator-initiated, international, parallel-grouped, superiority, outcome assessor-blinded and analyst-blinded, randomised, controlled, clinical trial.Adult patients with suspected major trauma are randomised to eight hours of a restrictive or liberal oxygen strategy. The restrictive group receives the lowest dosage of oxygen (>21%) that ensures an SpO₂ of 94%. The liberal group receives 12-15 L O₂/min or FiO₂=0.6-1.0.The primary outcome is a composite of 30-day mortality and/or development of major respiratory complications (pneumonia and/or acute respiratory distress syndrome).With 710 participants in each arm, we will be able to detect a 33% risk reduction with a restrictive oxygen strategy if the incidence of our primary outcome is 15% in the liberal group.

ETHICS AND DISSEMINATION

TRAUMOX2 is carried out in accordance with the Helsinki II Declaration. It has been approved by the Danish Committee on Health Research Ethics for the Capital Region (H-21018062) and The Danish Medicines Agency, as well as the Dutch Medical Research Ethics Committee Erasmus MS (NL79921.078.21 and MEC-2021-0932). A website (www.traumox2.org) is available for updates and study results will be published in an international peer-reviewed scientific journal.

TRIAL REGISTRATION NUMBERS

EudraCT 2021-000556-19; NCT05146700.

The effect of varying inhaled oxygen concentrations of high-flow nasal cannula oxygen therapy during gastroscopy with propofol sedation in elderly patients: a randomized controlled study

BACKGROUND

Despite evidence that high-flow nasal cannula oxygen therapy (HFNC) promotes oxygenation, its application in sedated gastroscopy in elderly patients has received little attention. This study investigated the effect of different inhaled oxygen concentrations (FiO₂) of HFNC during sedated gastroscopy in elderly patients.

METHODS

In a prospective randomized single-blinded study, 369 outpatients undergoing regular gastroscopy with propofol sedation delivered by an anesthesiologist were randomly divided into three groups (n = 123): nasal cannula oxygen group (Group C), 100% FiO₂ of HFNC group (Group H100), and 50% FiO₂ of HFNC (Group H50). The primary endpoint in this study was the incidence of hypoxia events with pulse oxygen saturation (SpO₂) ≤ 92%. The secondary endpoints included the incidence of other varying degrees of hypoxia and adverse events associated with ventilation and hypoxia.

RESULTS

The incidence of hypoxia, paradoxical response, choking, jaw lift, and mask ventilation was lower in both Group H100 and Group H50 than in Group C (P < 0.05). Compared with Group H100, Group H50 showed no significant differences in the incidence of hypoxia, jaw lift and mask ventilation, paradoxical response, or choking (P > 0.05). No patients were mechanically ventilated with endotracheal intubation or found to have complications from HFNC.

CONCLUSION

HFNC prevented hypoxia during gastroscopy with propofol in elderly patients, and there was no significant difference in the incidence of hypoxia when FiO₂ was 50% or 100%.

TRIAL REGISTRATION

This single-blind, prospective, randomized controlled trial was approved by the Ethics Committee of Nanjing First Hospital (KY20201102-04) and registered in the China Clinical Trial Center (20/10/2021, ChiCTR2100052144) before patients enrollment. All patients signed an informed consent form.

Supplemental Oxygen Alters the Airway Microbiome in Cystic Fibrosis

Features of the airway microbiome in persons with cystic fibrosis (pwCF) are correlated with disease progression. Microbes have traditionally been classified for their ability to tolerate oxygen. It is unknown whether supplemental oxygen, a common medical intervention, affects the airway microbiome of pwCF. We hypothesized that hyperoxia significantly impacts the pulmonary microbiome in cystic fibrosis. In this study, we cultured spontaneously expectorated sputum from pwCF in artificial sputum medium under 21%, 50%, and 100% oxygen conditions using a previously validated model system that recapitulates microbial community composition in uncultured sputum. Culture aliquots taken at 24, 48, and 72 h, along with uncultured sputum, underwent shotgun metagenomic sequencing with absolute abundance values obtained with the use of spike-in bacteria. Raw sequencing files were processed using the bioBakery pipeline to determine changes in taxonomy, predicted function, antimicrobial resistance genes, and mobile genetic elements. Hyperoxia reduced absolute microbial load, species richness, and diversity. Hyperoxia reduced absolute abundance of specific microbes, including facultative anaerobes such as Rothia and some Streptococcus species, with minimal impact on canonical CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. The effect size of hyperoxia on predicted functional pathways was stronger than that on taxonomy. Large changes in microbial cooccurrence networks were noted. Hyperoxia exposure perturbs airway microbial communities in a manner well tolerated by key pathogens. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting. IMPORTANCE The airway microbiome in persons with cystic fibrosis (pwCF) is correlated with lung function and disease severity. Supplemental oxygen use is common in more advanced CF, yet its role in perturbing airway microbial communities is unknown. By culturing sputum samples from pwCF under normal and elevated oxygen conditions, we found that increased oxygen led to reduced total numbers and diversity of microbes, with relative sparing of common CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting.

Epidermal Growth Factor Receptor Inhibition Is Protective in Hyperoxia-Induced Lung Injury

Aims

Studies have linked severe hyperoxia, or prolonged exposure to very high oxygen levels, with worse clinical outcomes. This study investigated the role of epidermal growth factor receptor (EGFR) in hyperoxia-induced lung injury at very high oxygen levels (>95%).

Results

Effects of severe hyperoxia (100% oxygen) were studied in mice with genetically inhibited EGFR and wild-type littermates. Despite the established role of EGFR in lung repair, EGFR inhibition led to improved survival and reduced acute lung injury, which prompted an investigation into this protective mechanism. Endothelial EGFR genetic knockout did not confer protection. EGFR inhibition led to decreased levels of cleaved caspase-3 and poly (ADP-ribosyl) polymerase (PARP) and decreased terminal dUTP nick end labeling- (TUNEL-) positive staining in alveolar epithelial cells and reduced ERK activation, which suggested reduced apoptosis in vivo. EGFR inhibition decreased hyperoxia (95%)-induced apoptosis and ERK in murine alveolar epithelial cells in vitro, and CRISPR-mediated EGFR deletion reduced hyperoxia-induced apoptosis and ERK in human alveolar epithelial cells in vitro. Innovation. This work defines a protective role of EGFR inhibition to decrease apoptosis in lung injury induced by 100% oxygen. This further characterizes the complex role of EGFR in acute lung injury and outlines a novel hyperoxia-induced cell death pathway that warrants further study.

Conclusion

In conditions of severe hyperoxia (>95% for >24 h), EGFR inhibition led to improved survival, decreased lung injury, and reduced cell death. These findings further elucidate the complex role of EGFR in acute lung injury.

Too much tolerance for hyperoxemia in mechanically ventilated patients with SARS-CoV-2 pneumonia? Report from an Italian intensive care unit

Background

In COVID-19 patients requiring mechanical ventilation, the administration of high oxygen (O2) doses for prolonged time periods may be necessary. Although life-saving in most cases, O2 may exert deleterious effects if administered in excessive concentrations. We aimed to describe the prevalence of hyperoxemia and excessive O2 administration in mechanically ventilated patients with SARS-CoV-2 pneumonia and determine whether hyperoxemia is associated with mortality in the Intensive Care Unit (ICU) or the onset of ventilator-associated pneumonia (VAP).

Materials and methods

Retrospective single-center study on adult patients with SARS-CoV-2 pneumonia requiring invasive mechanical ventilation for ≥48 h. Patients undergoing extracorporeal respiratory support were excluded. We calculated the excess O2 administered based on the ideal arterial O2 tension (PaO2) target of 55-80 mmHg. We defined hyperoxemia as PaO2 > 100 mmHg and hyperoxia + hyperoxemia as an inspired O2 fraction (FiO2) > 60% + PaO2 > 100 mmHg. Risk factors for ICU-mortality and VAP were assessed through multivariate analyses.

Results

One hundred thirty-four patients were included. For each day of mechanical ventilation, each patient received a median excess O2 of 1,121 [829-1,449] L. Hyperoxemia was found in 38 [27-55]% of arterial blood gases, hyperoxia + hyperoxemia in 11 [5-18]% of cases. The FiO2 was not reduced in 69 [62-76]% of cases of hyperoxemia. Adjustments were made more frequently with higher PaO2 or initial FiO2 levels. ICU-mortality was 32%. VAP was diagnosed in 48.5% of patients. Hyperoxemia (OR 1.300 95% CI [1.097-1.542]), time of exposure to hyperoxemia (OR 2.758 [1.406-5.411]), hyperoxia + hyperoxemia (OR 1.144 [1.008-1.298]), and daily excess O2 (OR 1.003 [1.001-1.005]) were associated with higher risk for ICU-mortality, independently of age, Sequential Organ failure Assessment score at ICU-admission and mean PaO2/FiO2. Hyperoxemia (OR 1.033 [1.006-1.061]), time of exposure to hyperoxemia (OR 1.108 [1.018-1.206]), hyperoxia + hyperoxemia (OR 1.038 [1.003-1.075]), and daily excess O2 (OR 1.001 [1.000-1.001]) were identified as risk factors for VAP, independently of body mass index, blood transfusions, days of neuromuscular blocking agents (before VAP), prolonged prone positioning and mean PaO2/FiO2 before VAP.

Conclusion

Excess O2 administration and hyperoxemia were common in mechanically ventilated patients with SARS-CoV-2 pneumonia. The exposure to hyperoxemia may be associated with ICU-mortality and greater risk for VAP.

Intraoperative High Fraction of Inspiratory Oxygen is Independently Associated with Worse Outcome After Living-Donor Liver Transplantation: A Retrospective Study

Background

Ischemia and reperfusion injury is an important factor that determines graft function after liver transplantation, and oxygen plays a crucial role in this process. However, the relationship between the intraoperative high fraction of inspiratory oxygen (FiO₂) and living-donor-liver-transplantation (LDLT) outcome remains unclear.

Patients and Methods

A total of 199 primary adult-to-adult LDLT cases in Kyoto University Hospital between January 2010 and December 2017 were enrolled in this study. The intraoperative FiO₂ was averaged using the total amount of intraoperative oxygen and air and defined as the calculated FiO₂ (cFiO₂). The cutoff value of cFiO₂ was set at 0.5.

Results

Between the cFiO₂ <0.5 (n = 156) and ≥0.5 group (n = 43), preoperative recipients’ background, donor factors, and intraoperative parameters were almost comparable. Postoperatively, the cFiO₂ ≥0.5 group showed a higher early allograft dysfunction (EAD) rate (P = 0.049) and worse overall graft survival (P = 0.036) than the cFiO₂ <0.5 group. Although the cFiO₂ ≥0.5 was not an independent risk factor for EAD in multivariable analysis (OR 2.038, 95%CI 0.992–4.186, P = 0.053), it was an independent risk factor for overall graft survival after LDLT (HR 1.897, 95%CI 1.007–3.432, P = 0.048).

Conclusion

The results of this study suggest that intraoperative high FiO₂ may be associated with worse graft survival after LDLT. Avoiding higher intraoperative FiO₂ may be beneficial for LDLT recipients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00268-022-06544-7.

Supplemental oxygen for traumatic brain injury: A systematic review

BACKGROUND

Oxygen supplementation is recommended after traumatic brain injury (TBI) but excessive oxygen may be harmful. The aim of this study was to investigate the effect of supplemental oxygen or high/low inspiratory oxygen fraction (FiO₂ ) for TBI patients on in-hospital mortality.

METHODS

We searched Medline (Pubmed), EMBASE and the Cochrane Library for interventional and observational studies fulfilling the following criteria: TBI patients >17 years (population); initial use of supplemental oxygen/high (≥0.6) FiO₂ (intervention) vs no supplemental oxygen/low (<0.6) FiO₂ (control) for spontaneously breathing or mechanically ventilated TBI patients, respectively with in-hospital mortality as primary outcome. Secondary outcomes were 30-day and 1-year mortality, length of stay in hospital or intensive care unit, days on mechanical ventilation, complications, and neurological impairment.

RESULTS

We screened 4846 citations. Two interventional studies comparing high vs low FiO₂ for mechanically ventilated TBI patients were included. No difference in in-hospital mortality was found. The first study found a statistically significant shorter length of stay in the intensive care unit for the high FiO₂ -group (6.5 [4.6-11.4] vs. 11.4 [5.8-17.2] days, p = 0.02). The second study found a lower disability at 6 months in the high FiO₂ -group with low disability in 25 (73.5%) vs. 15 (44.1%), moderate disability in 9 (26.5%) vs. 16 (47.1%), and severe disability in 0 (0.0%) vs. 3 (8.8%), p = 0.02.

CONCLUSION

Evidence on the effect of initial use of high/low FiO₂ for TBI patients on in-hospital mortality was extremely limited. Evidence on the use of supplemental oxygen for spontaneously breathing TBI patients is lacking.

The Effect of Conservative Oxygen Therapy in Reducing Mortality in Critical Care Patients: A Meta-Analysis and Trial Sequential Analysis

Background: Conservative oxygen therapy can prevent both hypoxemia and hyperoxemia, but the effect on the prognosis of patients admitted to the intensive care unit (ICU) remains controversial.

Methods: All controlled studies comparing conservative oxygen therapy and conventional oxygen therapy in adult patients admitted to the ICU were searched. The primary outcome was mortality, and the secondary outcomes were length of ICU stay (ICU LOS), length of hospital stay (hospital LOS), length of mechanical ventilation (MV) hours, new organ failure during ICU stay, and new infections during ICU stay.

Results: Nine trials with a total of 5,759 patients were pooled in our final studies. Compared with conventional oxygen therapy, conservative oxygen therapy did not reduce overall mortality (Z = 0.31, p = 0.75) or ICU LOS (Z = 0.17, p = 0.86), with firm evidence from trial sequential analysis, or hospital LOS (Z = 1.98, p = 0.05) or new infections during the ICU stay (Z = 1.45, p = 0.15). However, conservative oxygen therapy was associated with a shorter MV time (Z = 5.05, p < 0.00001), reduction of new organ failure during the ICU stay (Z = 2.15, p = 0.03) and lower risk of renal replacement therapy (RRT) (Z = 2.18, p = 0.03).

Conclusion: Conservative oxygen therapy did not reduce mortality but did decrease MV time, new organ failure and risk of RRT in critically ill patients.

Systematic Review Registration: identifier [CRD42020171055].

Dangers of hyperoxia

Oxygen (O2) toxicity remains a concern, particularly to the lung. This is mainly related to excessive production of reactive oxygen species (ROS). Supplemental O2, i.e. inspiratory O2 concentrations (FIO2) > 0.21 may cause hyperoxaemia (i.e. arterial (a) PO2 > 100 mmHg) and, subsequently, hyperoxia (increased tissue O2 concentration), thereby enhancing ROS formation. Here, we review the pathophysiology of O2 toxicity and the potential harms of supplemental O2 in various ICU conditions. The current evidence base suggests that PaO2 > 300 mmHg (40 kPa) should be avoided, but it remains uncertain whether there is an "optimal level" which may vary for given clinical conditions. Since even moderately supra-physiological PaO2 may be associated with deleterious side effects, it seems advisable at present to titrate O2 to maintain PaO2 within the normal range, avoiding both hypoxaemia and excess hyperoxaemia.

miR-181c-5p mediates apoptosis of vascular endothelial cells induced by hyperoxemia via ceRNA crosstalk

Oxygen therapy has been widely used in clinical practice, especially in anesthesia and emergency medicine. However, the risks of hyperoxemia caused by excessive O₂ supply have not been sufficiently appreciated. Because nasal inhalation is mostly used for oxygen therapy, the pulmonary capillaries are often the first to be damaged by hyperoxia, causing many serious consequences. Nevertheless, the molecular mechanism by which hyperoxia injures pulmonary capillary endothelial cells (LMECs) has not been fully elucidated. Therefore, we systematically investigated these issues using next-generation sequencing and functional research techniques by focusing on non-coding RNAs. Our results showed that hyperoxia significantly induced apoptosis and profoundly affected the transcriptome profiles of LMECs. Hyperoxia significantly up-regulated miR-181c-5p expression, while down-regulated the expressions of NCAPG and lncRNA-DLEU2 in LMECs. Moreover, LncRNA-DLEU2 could bind complementarily to miR-181c-5p and acted as a miRNA sponge to block the inhibitory effect of miR-181c-5p on its target gene NCAPG. The down-regulation of lncRNA-DLEU2 induced by hyperoxia abrogated its inhibition of miR-181c-5p function, which together with the hyperoxia-induced upregulation of miR-181c-5p, all these significantly decreased the expression of NCAPG, resulting in apoptosis of LMECs. Our results demonstrated a ceRNA network consisting of lncRNA-DLEU2, miR-181c-5p and NCAPG, which played an important role in hyperoxia-induced apoptosis of vascular endothelial injury. Our findings will contribute to the full understanding of the harmful effects of hyperoxia and to find ways for effectively mitigating its deleterious effects.

Conservative oxygen therapy for critically ill patients: a meta-analysis of randomized controlled trials

Objective

Conservative oxygen strategy is recommended in acute illness while its benefit in ICU patients remains controversial. Therefore, we sought to conduct a systematic review and meta-analysis to examine such oxygen strategies’ effect and safety in ICU patients.

Methods

We searched PubMed, Embase, and the Cochrane database from inception to Feb 15, 2021. Randomized controlled trials (RCTs) that compared a conservative oxygen strategy to a conventional strategy in critically ill patients were included. Results were expressed as mean difference (MD) and risk ratio (RR) with a 95% confidence interval (CI). The primary outcome was the longest follow-up mortality. Heterogeneity, sensitivity analysis, and publication bias were also investigated to test the robustness of the primary outcome.

Results

We included seven trials with a total of 5265 patients. In general, the conventional group had significantly higher SpO₂ or PaO₂ than that in the conservative group. No statistically significant differences were found in the longest follow-up mortality (RR, 1.03; 95% CI, 0.97–1.10; I²=18%; P=0.34) between the two oxygen strategies when pooling studies enrolling subjects with various degrees of hypoxemia. Further sensitivity analysis showed that ICU patients with mild-to-moderate hypoxemia (PaO₂/FiO₂ >100 mmHg) had significantly lower mortality (RR, 1.24; 95% CI, 1.05–1.46; I²=0%; P=0.01) when receiving conservative oxygen therapy. These findings were also confirmed in other study periods. Additional, secondary outcomes of the duration of mechanical ventilation, the length of stay in the ICU and hospital, change in sequential organ failure assessment score, and adverse events were comparable between the two strategies.

Conclusions

Our findings indicate that conservative oxygen therapy strategy did not improve the prognosis of the overall ICU patients. The subgroup of ICU patients with mild to moderate hypoxemia might obtain prognosis benefit from such a strategy without affecting other critical clinical results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40560-021-00563-7.

Hyperbaric hyperoxemia as a risk factor for ventilator-acquired pneumonia?

OBJECTIVES

Ventilator-acquired pneumonia (VAP) is the leading cause of serious associated infections in Intensive Care Units (ICU) and is associated with significant morbidity. The use of hyperbaric oxygen therapy (HBOT) in patients on mechanical ventilation may increase exposure to certain risk factors such as hyperoxemia and the need for multiple transfers. The aim of our study was to assess the relationship between HBOT and VAP.

METHOD

This retrospective observational study was performed from March 2017 to March 2018 in a 10-bed ICU using HBOT. All patients receiving mechanical ventilation (MV) for more than 48 hours were eligible. VAP was defined using clinical and radiological criteria. Data collection was carried out via digital medical records. Risk factors for VAP were determined by univariate and multivariate analysis.

RESULTS

Forty-two (23%) of the 182 patients enrolled developed at least one episode of VAP. One hundred and twenty-four (68%) patients received HBOT. The incidence rate of VAP was 34 per 1000 ventilator days. The occurrence of VAP was significantly associated with immunosuppression (p<0.029), MV duration (5 [3-7] vs 8 [5-11.5] days, p<0.0001), length of stay (8 [5-13] vs 19.5 [13-32] days, p<0.0001), reintubation (p<0.0001), intra-hospital transport (p = 0.001), use of paralytic agents (p = 0.013), tracheotomy (p = 0.003) and prone position (p = 0.003). The use of HBOT was not associated with the occurrence of VAP. Multivariate analysis identified reintubation (OR: 8.3 [2.6-26.6]; p<0.0001), intra-hospital transport (OR: 3.5 [1.3-9.2]; p = 0.011) and the use of paralytic agents (OR: 3.3 [1.3-8.4]; p = 0.014) as independent risk factors for VAP.

CONCLUSION

Known risk factors for VAP are to be found within our ICU population. HBOT, however, is not an extra risk factor for VAP within this group. Further experimental and clinical investigations are needed to understand the impact of HBOT on the occurrence of VAP and on physiological microbiome.

Target arterial PO2 according to the underlying pathology: a mini-review of the available data in mechanically ventilated patients

There is an ongoing discussion whether hyperoxia, i.e. ventilation with high inspiratory O2 concentrations (FIO2), and the consecutive hyperoxaemia, i.e. supraphysiological arterial O2 tensions (PaO2), have a place during the acute management of circulatory shock. This concept is based on experimental evidence that hyperoxaemia may contribute to the compensation of the imbalance between O2 supply and requirements. However, despite still being common practice, its use is limited due to possible oxygen toxicity resulting from the increased formation of reactive oxygen species (ROS) limits, especially under conditions of ischaemia/reperfusion. Several studies have reported that there is a U-shaped relation between PaO2 and mortality/morbidity in ICU patients. Interestingly, these mostly retrospective studies found that the lowest mortality coincided with PaO2 ~ 150 mmHg during the first 24 h of ICU stay, i.e. supraphysiological PaO2 levels. Most of the recent large-scale retrospective analyses studied general ICU populations, but there are major differences according to the underlying pathology studied as well as whether medical or surgical patients are concerned. Therefore, as far as possible from the data reported, we focus on the need of mechanical ventilation as well as the distinction between the absence or presence of circulatory shock. There seems to be no ideal target PaO2 except for avoiding prolonged exposure (> 24 h) to either hypoxaemia (PaO2 < 55-60 mmHg) or supraphysiological (PaO2 > 100 mmHg). Moreover, the need for mechanical ventilation, absence or presence of circulatory shock and/or the aetiology of tissue dysoxia, i.e. whether it is mainly due to impaired macro- and/or microcirculatory O2 transport and/or disturbed cellular O2 utilization, may determine whether any degree of hyperoxaemia causes deleterious side effects.

Hyperoxia After Return of Spontaneous Circulation in Cardiac Arrest Patients

Current guidelines emphasize the use of 100% oxygen during cardiopulmonary resuscitation after cardiac arrest. When patients are ventilated for variable periods after return of spontaneous circulation (ROSC), hyperoxia causes increased morbidity and mortality by overproduction of reactive oxygen species. Various patient, volunteer, and animal studies have shown the harmful effects of hyperoxia. This mini-review article aims to expand the potential clinical spectrum of hyperoxia on individual organ systems leading to organ dysfunction. A framework to achieve and maintain normoxia after ROSC is proposed. Despite the harmful considerations of hyperoxia in critically ill patients, additional safety studies including dose-effect, level and onset of the reactive oxygen species effect, and safe hyperoxia applicability period after ROSC, need to be performed in various animal and human models to further elucidate the role of oxygen therapy after cardiac arrest.

The Positive Allosteric Modulation of alpha7-Nicotinic Cholinergic Receptors by GAT107 Increases Bacterial Lung Clearance in Hyperoxic Mice by Decreasing Oxidative Stress in Macrophages

Supplemental oxygen therapy with supraphysiological concentrations of oxygen (hyperoxia; >21% O2) is a life-saving intervention for patients experiencing respiratory distress. However, prolonged exposure to hyperoxia can compromise bacterial clearance processes, due to oxidative stress-mediated impairment of macrophages, contributing to the increased susceptibility to pulmonary infections. This study reports that the activation of the α7 nicotinic acetylcholine receptor (α7nAChR) with the delete allosteric agonistic-positive allosteric modulator, GAT107, decreases the bacterial burden in mouse lungs by improving hyperoxia-induced lung redox imbalance. The incubation of RAW 264.7 cells with GAT107 (3.3 µM) rescues hyperoxia-compromised phagocytic functions in cultured macrophages, RAW 264.7 cells, and primary bone marrow-derived macrophages. Similarly, GAT107 (3.3 µM) also attenuated oxidative stress in hyperoxia-exposed macrophages, which prevents oxidation and hyper-polymerization of phagosome filamentous actin (F-actin) from oxidation. Furthermore, GAT107 (3.3 µM) increases the (1) activity of superoxide dismutase 1; (2) activation of Nrf2 and (3) the expression of heme oxygenase-1 (HO-1) in macrophages exposed to hyperoxia. Overall, these data suggest that the novel α7nAChR compound, GAT107, could be used to improve host defense functions in patients, such as those with COVID-19, who are exposed to prolonged periods of hyperoxia.

Intensivists' response to hyperoxemia in mechanical ventilation patients: The status quo and related factors

BACKGROUND

Due to the still sparse literature in China, the investigation of hyperoxemia management is required. Thus, we aim to conduct a retrospective study to provide more information about hyperoxemia management in intensive care unit (ICU) patients.

METHODS

We retrospectively screened the medical records of adult patients (age ≥18 years) who required mechanical ventilation (MV) ≥24 hours from January 1, 2018, to December 31, 2018. All arterial blood gas (ABG) tested during MV was retrieved, and MV settings were recorded. The median arterial partial pressure of oxygen (PaO₂) >120 mmHg (1 mmHg=0.133 kPa) was defined as mild to moderate hyperoxemia, and PaO₂ >300 mmHg as extreme hyperoxemia. Intensivists' response to hyperoxemia was assessed based on the reduction of fraction of inspired oxygen (FiO₂) within one hour after hyperoxemia was recorded. Multivariable logistic regression analysis was performed to determine the independent factors associated with the intensivists' response to hyperoxemia.

RESULTS

A total of 592 patients were finally analyzed. The median Acute Physiology and Chronic Health Evaluation II (APACHE II) score was 21 (15-26). The PaO₂, arterial oxygen saturation (SaO₂), FiO₂, and positive end expiratory pressure (PEEP) were 96.4 (74.0-126.0) mmHg, 97.8% (95.2%-99.1%), 0.4 (0.4-0.5), and 5 (3-6) cmH₂O, respectively. Totally 174 (29.39%) patients had PaO₂ >120 mmHg, and 19 (3.21%) patients had extreme hyperoxemia at PaO₂ >300 mmHg. In cases of mild to moderate hyperoxemia with FiO₂ ≤0.4, only 13 (2.20%) patients had a decrease in FiO₂ within one hour. The multivariable logistic regression analysis showed that a positive response was independently associated with FiO₂ (odds ratio [OR] 1.09, 95% confidence interval [CI] 1.06-1.12, P<0.001), PaO₂ (OR 1.01, 95% CI 1.00-1.01, P=0.002), and working shifts (OR 5.09, 95% CI 1.87-13.80, P=0.001).

CONCLUSIONS

Hyperoxemia occurs frequently and is neglected in most cases, particularly when mild to moderate hyperoxemia, hyperoxemia with lower FiO₂, hyperoxemia during night and middle-night shifts, or FiO₂ less likely to be decreased. Patients may be at a risk of oxygen toxicity because of the liberal oxygen strategy. Therefore, further research is needed to improve oxygen management for patients with MV in the ICUs.

Biological effects of the oxygen molecule in critically ill patients

The medical use of oxygen has been widely and frequently proposed for patients, especially those under critical care; however, its benefit and drawbacks remain controversial for certain conditions. The induction of oxygen therapy is commonly considered for either treating or preventing hypoxia. Therefore, the concept of different types of hypoxia should be understood, particularly in terms of their mechanism, as the effect of oxygen therapy principally varies by the physiological characteristics of hypoxia. Oxygen molecules must be constantly delivered to all cells throughout the human body and utilized effectively in the process of mitochondrial oxidative phosphorylation, which is necessary for generating energy through the formation of adenosine triphosphate. If the oxygen availability at the cellular level is inadequate for sustaining the metabolism, the condition of hypoxia which is characterized as heterogeneity in tissue oxygen tension may develop, which is called dysoxia, a more physiological concept that is related to hypoxia. In such hypoxic patients, repetitive measurements of the lactate level in blood are generally recommended in order to select the adequate therapeutic strategy targeting a reduction in lactate production. Excessive oxygen, however, may actually induce a hyperoxic condition which thus can lead to harmful oxidative stress by increasing the production of reactive oxygen species, possibly resulting in cellular dysfunction or death. In contrast, the human body has several oxygen-sensing mechanisms for preventing both hypoxia and hyperoxia that are employed to ensure a proper balance between the oxygen supply and demand and prevent organs and cells from suffering hyperoxia-induced oxidative stress. Thus, while the concept of hyperoxia is known to have possible adverse effects on the lung, the heart, the brain, or other organs in various pathological conditions of critically ill patients, and no obvious evidence has yet been proposed to totally support liberal oxygen supplementation in any subset of critically ill patients, relatively conservative oxygen therapy with cautious monitoring appears to be safe and may improve the outcome by preventing harmful oxidative stress resulting from excessive oxygen administration. Given the biological effects of oxygen molecules, although the optimal target levels remain controversial, unnecessary oxygen administration should be avoided, and exposure to hyperoxemia should be minimized in critically ill patients.

Pulmonary infections complicating ARDS

Pulmonary infection is one of the main complications occurring in patients suffering from acute respiratory distress syndrome (ARDS). Besides traditional risk factors, dysregulation of lung immune defenses and microbiota may play an important role in ARDS patients. Prone positioning does not seem to be associated with a higher risk of pulmonary infection. Although bacteria associated with ventilator-associated pneumonia (VAP) in ARDS patients are similar to those in patients without ARDS, atypical pathogens (Aspergillus, herpes simplex virus and cytomegalovirus) may also be responsible for infection in ARDS patients. Diagnosing pulmonary infection in ARDS patients is challenging, and requires a combination of clinical, biological and microbiological criteria. The role of modern tools (e.g., molecular methods, metagenomic sequencing, etc.) remains to be evaluated in this setting. One of the challenges of antimicrobial treatment is antibiotics diffusion into the lungs. Although targeted delivery of antibiotics using nebulization may be interesting, their place in ARDS patients remains to be explored. The use of extracorporeal membrane oxygenation in the most severe patients is associated with a high rate of infection and raises several challenges, diagnostic issues and pharmacokinetics/pharmacodynamics changes being at the top. Prevention of pulmonary infection is a key issue in ARDS patients, but there is no specific measure for these high-risk patients. Reinforcing preventive measures using bundles seems to be the best option.

Lung and gut microbiota are altered by hyperoxia and contribute to oxygen-induced lung injury in mice

Inhaled oxygen, although commonly administered to patients with respiratory disease, causes severe lung injury in animals and is associated with poor clinical outcomes in humans. The relationship between hyperoxia, lung and gut microbiota, and lung injury is unknown. Here, we show that hyperoxia conferred a selective relative growth advantage on oxygen-tolerant respiratory microbial species (e.g., Staphylococcus aureus) as demonstrated by an observational study of critically ill patients receiving mechanical ventilation and experiments using neonatal and adult mouse models. During exposure of mice to hyperoxia, both lung and gut bacterial communities were altered, and these communities contributed to oxygen-induced lung injury. Disruption of lung and gut microbiota preceded lung injury, and variation in microbial communities correlated with variation in lung inflammation. Germ-free mice were protected from oxygen-induced lung injury, and systemic antibiotic treatment selectively modulated the severity of oxygen-induced lung injury in conventionally housed animals. These results suggest that inhaled oxygen may alter lung and gut microbial communities and that these communities could contribute to lung injury.

Systematic review of oxygenation and clinical outcomes to inform oxygen targets in critically ill trauma patients

BACKGROUND

Oxygen therapy is frequently administered to critically ill trauma patients to avoid hypoxia, but optimal oxygenation strategies are not clear.

METHODS

We conducted a systematic review of oxygen targets and clinical outcomes in trauma and critically ill patients. We searched Ovid MEDLINE, Cochrane Library, Embase, and Web of Science Core Collection from 1946 through 2017. Our initial search yielded 14,774 articles with 209 remaining after abstract review. We reviewed full text articles of human subjects with conditions of interest, an oxygen exposure or measurement, and clinical outcomes, narrowing the review to 43 articles. We assessed article quality using Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) criteria.

RESULTS

Of the 43 final studies meeting inclusions criteria, 17 focused on trauma and 26 studies focused on medical and/or surgical critical illness without trauma specifically. Four trauma studies supported lower oxygenation/normoxia, two supported higher oxygenation, and 11 supported neither normoxia nor higher oxygenation (five neutral and six supported avoidance of hypoxia). Fifteen critical illness studies supported lower oxygenation/normoxia, one supported higher oxygenation, and 10 supported neither normoxia nor higher oxygenation (nine neutral and one supported avoidance of hypoxia). We identified seven randomized controlled trials (four high quality, three moderate quality). Of the high-quality randomized controlled trials (none trauma-related), one supported lower oxygenation/normoxia and three were neutral. Of the moderate-quality randomized controlled trials (one trauma-related), one supported higher oxygenation, one was neutral, and one supported avoidance of hypoxia.

CONCLUSION

We identified few trauma-specific studies beyond traumatic brain injury; none were high quality. Extrapolating primarily from nontrauma critical illness, reduced oxygen administration targeting normoxia in critically ill trauma patients may result in better or equivalent clinical outcomes. Additional trauma-specific trials are needed to determine the optimal oxygen strategy in critically injured patients.

LEVEL OF EVIDENCE

Systematic review, level IV.

The Impact of Hyperoxia on Outcome of Patients Treated with Noninvasive Respiratory Support

Objective

Oxygen therapy is one of the most common treatment modalities for hypoxemic patients, but target goals for normoxemia are not clearly defined. Therefore, iatrogenic hyperoxia is a very common situation. The results from the recent clinical researches about hyperoxia indicate that hyperoxia can be related to worse outcomes than expected in some critically ill patients. According to our literature knowledge, there are not any reports researching the effect of hyperoxia on clinical course of patients who are not treated with invasive mechanical ventilation. In this study, we aimed to determine the effect of hyperoxia on mortality, and length of stay and also possible side effects of hyperoxia on the patients who are treated with oxygen by noninvasive devices.

Materials and Methods

One hundred and eighty-seven patients who met inclusion criteria, treated in Dokuz Eylul University Medical Intensive Care Unit between January 1, 2016, and October 31, 2018, were examined retrospectively. These patients' demographic data, oxygen saturation (SpO₂) values for the first 24 hours, APACHE II (Acute Physiology and Chronic Health Evaluation II) scores, whether they needed intubation, if they did how many days they got ventilated, length of stay in intensive care unit and hospital, maximum PaO₂ values of the first day, oxygen treatment method of the first 24 hours, and the rates of mortality were recorded.

Results

Hyperoxemia was determined in 62 of 187 patients who were not treated with invasive mechanic ventilation in the first 24 hours of admission. Upon further investigation of the relation between comorbid situations and hyperoxia, hyperoxia frequency in patients with COPD was detected to be statistically low (16% vs. 35%, p < 0.008). Hospital mortality was significantly high (51.6% vs. 35.2%, p < 0.04) in patients with hyperoxia. When the types of oxygen support therapies were investigated, hyperoxia frequency was found higher in patients treated with supplemental oxygen (nasal cannula, oronasal mask, high flow oxygen therapy) than patients treated with NIMV (44.2% vs. 25.5%, p < 0.008). After exclusion of 56 patients who were intubated and treated with invasive mechanical ventilation after the first 24 hours, hyperoxemia was determined in 46 of 131 patients. Mortality in patients with hyperoxemia who were not treated with invasive mechanical ventilation during hospital stay was statistically higher when compared to normoxemic patients (41.3% vs 15.3%, p < 0.001).

Conclusion

We report that hyperoxemia increases the hospital mortality in patients treated with noninvasive respiratory support. At the same time, we determined that hyperoxemia frequency was lower in COPD patients and the ones treated with NIMV. Conservative oxygen therapy strategy can be suggested to decrease the hyperoxia prevalence and mortality rates.

PROtective Ventilation with a low versus high Inspiratory Oxygen fraction (PROVIO) and its effects on postoperative pulmonary complications: protocol for a randomized controlled trial

BACKGROUND

Postoperative pulmonary complications (PPCs) are the most common perioperative complications following surgical site infection (SSI). They prolong the hospital stay and increase health care costs. A lung-protective ventilation strategy is considered better practice in abdominal surgery to prevent PPCs. However, the role of the inspiratory oxygen fraction (FiO₂) in the strategy remains disputed. Previous trials have focused on reducing SSI by increasing the inhaled oxygen concentration but higher FiO₂ (80%) was found to be associated with a greater incidence of atelectasis and mortality in recent research. The trial aims at evaluating the effect of different FiO₂ added to the lung-protective ventilation strategy on the incidence of PPCs during general anesthesia for abdominal surgery.

METHODS AND DESIGN

PROtective Ventilation with a low versus high Inspiratory Oxygen fraction trial (PROVIO) is a single-center, prospective, randomized controlled trial planning to recruit 252 patients undergoing abdominal surgery lasting for at least 2 h. The patients will be randomly assigned to (1) a low-FiO₂ (30% FiO₂) group and (2) a high-FiO₂ (80% FiO₂) group in the lung-protective ventilation strategy. The primary outcome of the study is the occurrence of PPCs within the postoperative 7 days. Secondary outcomes include the severity grade of PPCs, the occurrence of postoperative extrapulmonary complications and all-cause mortality within the postoperative 7 and 30 days.

DISCUSSION

The PROVIO trial assesses the effect of low versus high FiO₂ added to a lung-protective ventilation strategy on PPCs for abdominal surgery patients and the results should provide practical approaches to intraoperative oxygen management.

TRIAL REGISTRATION

www.ChiCTR.org.cn , identifier: ChiCTR18 00014901 . Registered on 13 February 2018.

Restrictive vs liberal oxygen for trauma patients-the TRAUMOX1 pilot randomised clinical trial

INTRODUCTION

Hyperoxaemia is commonly observed in trauma patients but has been associated with pulmonary complications and mortality in some patient populations. The objectives of this study were to evaluate whether maintenance of normoxia is feasible using a restrictive oxygen strategy in the initial phase after trauma and to evaluate the incidence of 30-day mortality and/or major pulmonary complications.

METHODS

Forty-one adult trauma patients admitted to our trauma centre were randomised to 24 hours of restrictive oxygen therapy (no supplemental oxygen if the arterial oxyhaemoglobin saturation (SpO₂ ) was at least 94%, n = 21) or liberal oxygen therapy (intubated patients: FiO₂ 1.0 in the trauma bay, 0.8-1.0 elsewhere; spontaneously breathing patients: 15 L/min via a non-rebreather mask, n = 20). Two blinded anaesthesiologists evaluated major in-hospital pulmonary complications within 30 days.

RESULTS

Protocol compliance was high, as the median arterial oxygen tension was significantly lower in the restrictive group (10.8 kPa [9.7-12.0] vs 30.4 kPa [23.7-39.0], P < 0.0001). There were seven episodes of SpO₂ below 90% in the restrictive group and one episode in the liberal group. Thirty-day mortality and/or major in-hospital pulmonary complications occurred in 4/20 (20%) in the restrictive group and in 6/18 (33%) in the liberal group: two patients in each group died within 30 days and the incidence of major in-hospital pulmonary complications was 2/20 (10%) in the restrictive group and 4/18 (22%) in the liberal group.

CONCLUSION

Maintenance of normoxia using a restrictive oxygen strategy following trauma is feasible. This pilot study serves as the basis for a larger clinical trial.

The effect of hyperoxia on mortality in critically ill patients: a systematic review and meta analysis

Background

Studies investigating the role of hyperoxia in critically ill patients have reported conflicting results. We did this analysis to reveal the effect of hyperoxia in the patients admitted to the intensive care unit (ICU).

Methods

Electronic databases were searched for all the studies exploring the role of hyperoxia in adult patients admitted to ICU. The primary outcome was mortality. Random-effect model was used for quantitative synthesis of the adjusted odds ratio (aOR).

Results

We identified 24 trials in our final analysis. Statistical heterogeneity was found between hyperoxia and normoxia groups in patients with mechanical ventilation (I² = 92%, P < 0.01), cardiac arrest(I² = 63%, P = 0.01), traumatic brain injury (I² = 85%, P < 0.01) and post cardiac surgery (I² = 80%, P = 0.03). Compared with normoxia, hyperoxia was associated with higher mortality in overall patients (OR 1.22, 95% CI 1.12~1.33), as well as in the subgroups of cardiac arrest (OR 1.30, 95% CI 1.08~1.57) and extracorporeal life support (ELS) (OR 1.44, 95% CI 1.03~2.02).

Conclusions

Hyperoxia would lead to higher mortality in critically ill patients especially in the patients with cardiac arrest and ELS.

Electronic supplementary material

The online version of this article (10.1186/s12890-019-0810-1) contains supplementary material, which is available to authorized users.

Impact of hyperoxemia on mortality in critically ill patients with ventilator-associated pneumonia

Background

The objective of this study was to assess the impact of hyperoxemia on mortality in critically ill patients with ventilator-associated pneumonia (VAP).

Methods

This observational study was performed in a 50-bed mixed intensive care unit (ICU) during a 1-year period. Quantitative microbiological confirmation was required for VAP diagnosis. Hyperoxemia was defined as peripheral capillary oxygen saturation (SpO₂) ≥98%. SpO₂ was hourly collected in all study patients during the whole period of mechanical ventilation. The primary objective was to assess the influence of hyperoxemia on ICU mortality.

Results

Ninety-three patients with VAP were all included in this study. ICU-mortality rate was 32% (30 of 93 patients). The mean percentage of time spent with hyperoxemia in survivors and nonsurvivors at ICU admission, before, after or at the time of VAP diagnosis was not significantly different. Multivariate analysis identified age, and sequential organ dysfunction assessment at the day of VAP occurrence as independent risk factors for ICU mortality [odds ratio (OR) =1.04 (95% CI, 1.01-1.08) per year, P=0.019; 1.19 (95% CI, 1.06-1.34) per point, P=0.003; respectively]. The time spent with hyperoxemia before VAP occurrence was not significantly associated with mechanical ventilation free days, or ICU length of stay.

Conclusions

Hyperoxemia at ICU admission, or during ICU stay, had no significant impact on ICU mortality in critically ill patients with VAP.

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.

A pilot study of hyperoxemia on neurological injury, inflammation and oxidative stress

BACKGROUND

Normobaric hyperoxia is used to alleviate secondary brain ischaemia in patients with traumatic brain injury (TBI), but clinical evidence is limited and hyperoxia may cause adverse events.

METHODS

An open label, randomised controlled pilot study comparing blood concentrations of reactive oxygen species (ROS), interleukin 6 (IL-6) and neuron-specific enolase (NSE) between two different fractions of inspired oxygen in severe TBI patients on mechanical ventilation.

RESULTS

We enrolled 27 patients in the Fi O₂ 0.40 group and 38 in the Fi O₂ 0.70 group; 19 and 23 patients, respectively, completed biochemical analyses. In baseline, there were no differences between Fi O₂ 0.40 and Fi O₂ 0.70 groups, respectively, in ROS (64.8 nM [22.6-102.1] vs. 64.9 nM [26.8-96.3], P = 0.80), IL-6 (group 92.4 pg/ml [52.9-171.6] vs. 94.3 pg/ml [54.8-133.1], P = 0.52) or NSE (21.04 ug/l [14.0-30.7] vs. 17.8 ug/l [14.1-23.9], P = 0.35). ROS levels did not differ at Day 1 (24.2 nM [20.6-33.5] vs. 29.2 nM [22.7-69.2], P = 0.10) or at Day 2 (25.4 nM [21.7-37.4] vs. 47.3 nM [34.4-126.1], P = 0.95). IL-6 concentrations did not differ at Day 1 (112.7 pg/ml [65.9-168.9) vs. 83.9 pg/ml [51.8-144.3], P = 0.41) or at Day 3 (55.0 pg/ml [34.2-115.6] vs. 49.3 pg/ml [34.4-126.1], P = 0.95). NSE levels did not differ at Day 1 (15.9 ug/l [9.0-24.3] vs. 15.3 ug/l [12.2-26.3], P = 0.62). There were no differences between groups in the incidence of pulmonary complications.

CONCLUSION

Higher fraction of inspired oxygen did not increase blood concentrations of markers of oxidative stress, inflammation or neurological injury or the incidence of pulmonary complications in severe TBI patients on mechanical ventilation.

Prognosis value of partial arterial oxygen pressure in patients with septic shock subjected to pre-hospital invasive ventilation

OBJECTIVE

Mechanical ventilation can help improve the prognosis of septic shock. While adequate delivery of oxygen to the tissue is crucial, hyperoxemia may be deleterious. Invasive out-of-hospital ventilation is often promptly performed in life-threatening emergencies. We propose to determine whether the arterial oxygen pressure (PaO₂) at the intensive care unit (ICU) admission is associated with mortality in patients with septic shock subjected to pre-hospital mechanical ventilation.

METHODS

We performed a monocentric retrospective observational study on 77 patients. PaO₂ was measured at ICU admission. The primary outcome was mortality at day 28 (D28).

RESULTS

Forty-nine (64%) patients were included. The mean PaO₂ at ICU admission was 153 ± 77 and 202 ± 82 mm Hg for alive and deceased patients respectively. Mortality concerned 18% of patients for PaO₂ < 100, 25% for 100 < PaO₂ < 150 and 57% for a PaO₂ > 150 mm Hg. PaO₂ was significantly associated with mortality at D28 (p = 0.04). Using propensity score analysis including SOFA score, pre-hospital duration, lactate, and prehospital fluid volume expansion, association with mortality at D28 only remained for PaO₂ > 150 mm Hg (p = 0.02, OR [CI95] = 1.59 [1.20-2.10]).

CONCLUSIONS

In this study, we report a significant association between hyperoxemia at ICU admission and mortality in patients with septic shock subjected to pre-hospital invasive mechanical ventilation. The early adjustment of the PaO₂ should be considered for these patients to avoid the toxic effects of hyperoxemia. However, blood gas analysis is hard to get in a prehospital setting. Consequently, alternative and feasible measures are needed, such as pulse oximetry, to improve the management of pre-hospital invasive ventilation.

Intubation trachéale et choc septique : état des lieux

La place de l’intubation dans le choc septique reste mal définie sans recommandation dictée par les sociétés savantes. Cette problématique met en balance les effets potentiellement bénéfiques de la ventilation mécanique (amélioration de l’oxygénation, repos musculaire diaphragmatique…) et délétères (risque du geste d’intubation, atrophie diaphragmatique, lésions pulmonaires induites par la ventilation, vasoplégie liée à la sédation…). L’intubation ne se discute pas lors des cas extrêmes de coma profond ou d’insuffisance respiratoire aiguë sévère. Néanmoins, la place de l’intubation dans les situations intermédiaires est actuellement peu étudiée et non codifiée. Cette mise au point a pour but d’apporter au lecteur une synthèse des résultats issus des dernières grandes études sur le choc septique. L’analyse suggère une association probable, non exclusive, entre gravité et taux d’intubation, qui reste à préciser. Bien que ces études n’aient pas étudié cette question, les données générales décrivent les caractéristiques « patient » et les données ventilatoires. Enfin, les résultats d’une étude spécifique sur le sujet et le projet de recherche en cours INTUBATIC (inclusions terminées) sont présentés, ce qui apportera peut-être une réponse à cette question dans les mois à venir.

Perioperative respiratory complications: current evidence and strategy discussed in 2017 JA symposium

Respiratory management during general anesthesia aims to safely secure the airway and maintain adequate ventilation to deliver oxygen to the vital organs, maintaining homeostasis even during surgery. Despite its clinical importance, anesthesiologists often encounter difficulties in properly managing respiration during the perioperative period, leading to severe respiratory complications. In this year's JA symposium, 5 editorial board members of Journal of Anesthesia (JA) who are experts in the field of respiratory management in anesthesia discussed the following topics: quitting smoking before surgery: exposure to passive smoke is damaging to children, ventilator-associated pneumonia, high inspiratory oxygen concentration and lung injury, aspiration pneumonia, and postoperative respiratory management strategy in patients with obstructive sleep apnea. We hope that this special article regarding this year's JA symposium may be useful for JA readers to manage clinical anesthesia on a daily basis.

Relationship between hyperoxemia and ventilator associated pneumonia

Previous studies suggest a relationship between hyperoxemia and ventilator-associated pneumonia (VAP). Hyperoxemia is responsible for denitrogenation phenomena, and inhibition of surfactant production, promoting atelectasis in mechanically ventilated patients. Further, hyperoxemia impairs the efficacy of alveolar macrophages to migrate, phagocyte and kill bacteria. Oxygen can also cause pulmonary-specific toxic effect called hyperoxic acute lung injury leading to longer duration of mechanical ventilation. All these hyperoxic effects are well-known risk factors for VAP. A recent retrospective large single center study identified hyperoxemia as an independent risk factor for VAP. However, two recent randomized controlled trials evaluated the impact of conservative oxygen strategy versus a liberal strategy, but did not confirm the role of hyperoxemia in lower respiratory tract infection occurrence. In this review, we discuss animal and human studies suggesting a relationship between these two common conditions in mechanically ventilated patients and potential interventions that should be evaluated. Further large prospective studies in carefully selected groups of patients are required to confirm the potential role of hyperoxemia in VAP pathogenesis and to evaluate the impact of a conservative oxygen strategy vs. a conventional strategy on the incidence of VAP.

A journey between high altitude hypoxia and critical patient hypoxia: What can it teach us about compression and the management of critical disease?

High altitude sickness (hypobaric hypoxia) is a form of cellular hypoxia similar to that suffered by critically ill patients. The study of mountaineers exposed to extreme hypoxia offers the advantage of involving a relatively homogeneous and healthy population compared to those typically found in Intensive Care Units (ICUs), which are heterogeneous and generally less healthy. Knowledge of altitude physiology and pathology allows us to understanding how hypoxia affects critical patients. Comparable changes in mitochondrial biogenesis between both groups may reflect similar adaptive responses and suggest therapeutic interventions based on the protection or stimulation of such mitochondrial biogenesis. Predominance of the homozygous insertion (II) allele of the angiotensin-converting enzyme gene is present in both individuals who perform successful ascensions without oxygen above 8000 m and in critical patients who overcome certain disease conditions.

Does hyperoxia enhance susceptibility to secondary pulmonary infection in the ICU?

Hyperoxia is common practice in the acute management of circulatory shock, and observational studies report that it is present in more than 50 % of mechanically ventilated patients during the first 24 h after intensive care unit (ICU) admission. On the other hand, "oxygen toxicity" due to the increased formation of reactive oxygen species limits its use due to serious deleterious side effects. However, formation of reactive oxygen species to boost bacterial killing is one of the body's anti-microbial auto-defense mechanisms and, hence, O2 has been referred to as an antibiotic. Consequently, hyperoxia during the peri-operative period has been advocated for surgical patients in order to reduce surgical site infection. However, there is ample evidence that long-term exposure to hyperoxia impaired bacterial phagocytosis and thereby aggravated both bacterial burden and dissemination. Moreover, a recent retrospective study identified the number of days with hyperoxia, defined as a PaO2 > 120 mmHg only, as an independent risk factor of ventilator-associated pneumonia in patients needing mechanical ventilation for more than 48 h. Since so far the optimal oxygenation target is unknown for ICU patients, "conservative" O2 therapy represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.