Oxygen therapy in critical illness: precise control of arterial oxygenation and permissive hypoxemia

Protocol for a systematic review and individual participant data meta-analysis of optimizing oxygen therapy in critically ill patients

Background

Oxygen therapy is a cornerstone treatment of critically ill patients in the intensive care unit (ICU). Whether lower oxygenation therapy brings superior survival outcomes to higher oxygenation therapy is unknown.

Methods

We will search electronic databases: PubMed, Embase, Web of Science, the Cochrane Central Register of Controlled Trials (CENTRAL), International Clinical Trials Registry Platform (ICTRP), and ClinicalTrials.gov from inception to 1 January 2024. Two authors will independently screen for all eligible clinical studies. Emails will be sent for individual participant data. The statistical analyses will be conducted using STATA 15.0 software.

Results

We will evaluate the efficacy of lower oxygenation therapy compared with higher oxygenation therapy based on individual participant data.

Conclusion

This study will offer clinical evidence for oxygen therapy in ICU patients.

Effect of postoperative oxygen therapy regimen modification on oxygenation in patients with acute type A aortic dissection

Objective

In this study, we investigated the effect of various oxygen therapy regimens on oxygenation in patients with acute type A aortic dissection (AAD).

Methods

A quasi-randomized controlled trial was conducted, in which patients with AAD hospitalized for surgery from June to September 2021 were assigned to the control group (patients received conventional oxygen therapy after postoperative mechanical ventilation, weaning, and extubation) and those who were admitted from October to December 2021 were assigned to the observation group [patients underwent optimally adjusted therapy based on the treatment of the control group, which mainly included prioritized elevation of positive end-expiratory pressure (PEEP) and restricted use of the fraction of inspired oxygen (FiO2)].The postoperative oxygenation index, blood gas analysis, and duration of mechanical ventilation were compared between the two groups.

Results

There were significant differences in oxygenation observed at 2 h postoperatively between the groups. 12, 24, and 72 h postoperatively, the oxygenation index varied significantly between the two groups. There were statistically significant differences in the time effects of the oxygenation index and PaO2 between the two groups, as well as significant differences in the length of stay in the intensive care unit.

Conclusion

For the postoperative care of patients with AAD, it is suggested that the minimum FiO2 required for oxygenation of patients be maintained. In addition, it is possible to enhance PEEP as a priority when PaO2 is low.

Hyperoxia and brain: the link between necessity and injury from a molecular perspective

Oxygen (O2) supplementation is commonly used to treat hypoxia in patients with respiratory failure. However, indiscriminate use can lead to hyperoxia, a condition detrimental to living tissues, particularly the brain. The brain is sensitive to reactive oxygen species (ROS) and inflammation caused by high concentrations of O2, which can result in brain damage and mitochondrial dysfunction, common features of neurodegenerative disorders. Hyperoxia leads to increased production of ROS, causing oxidative stress, an imbalance between oxidants and antioxidants, which can damage tissues. The brain is particularly vulnerable to oxidative stress due to its lipid composition, high O2 consumption rate, and low levels of antioxidant enzymes. Moreover, hyperoxia can cause vasoconstriction and decreased O2 supply to the brain, posing a challenge to redox balance and neurodegenerative processes. Studies have shown that the severity of hyperoxia-induced brain damage varies with inspired O2 concentration and duration of exposure. Therefore, careful evaluation of the balance between benefits and risks of O2 supplementation, especially in clinical settings, is crucial.

Short-term hyperoxia induced mitochondrial respiratory chain complexes dysfunction and oxidative stress in lung of rats

BACKGROUND

Oxygen therapy is an alternative for many patients with hypoxemia. However, this practice can be dangerous as oxygen is closely associated with the development of oxidative stress.

METHODS

Male Wistar rats were exposed to hyperoxia with a 40% fraction of inspired oxygen (FIO2) and hyperoxia (FIO2 = 60%) for 120 min. Blood and lung tissue samples were collected for gas, oxidative stress, and inflammatory analyses.

RESULTS

Hyperoxia (FIO2 = 60%) increased PaCO2 and PaO2, decreased blood pH and caused thrombocytopenia and lymphocytosis. In lung tissue, neutrophil infiltration, nitric oxide concentration, carbonyl protein formation and the activity of complexes I and II of the mitochondrial respiratory chain increased. FIO2 = 60% decreased SOD activity and caused several histologic changes.

CONCLUSION

In conclusion, we have experimentally demonstrated that short-term exposure to high FIO2 can cause oxidative stress in the lung.

Effects of Oxygenation Targets on Mortality in Critically Ill Patients in Intensive Care Units: A Systematic Review and Meta-Analysis

BACKGROUND

The effects of oxygenation targets (partial pressure of arterial oxygen [Pao2], arterial oxygen saturation [Sao2]/peripheral oxygen saturation [Spo2], or inspiratory oxygen concentration [Fio2] on clinical outcomes in critically ill patients remains controversial. We reviewed the existing literature to assess the effects of lower and higher oxygenation targets on the mortality rates of critically ill intensive care unit (ICU) patients.

METHODS

MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials, and Web of Science databases were searched from their dates of inception to December 31, 2022, for randomized controlled trials (RCTs) comparing lower and higher oxygenation targets for critically ill patients ≥18 years of age undergoing mechanical ventilation, nasal cannula, oxygen mask, or high-flow oxygen therapy in the ICU. Data extraction was conducted independently, and RoB 2.0 software was used to evaluate the quality of each RCT. A random-effects model was used for the meta-analysis to calculate the relative risk (RR). We used the I2 statistic as a measure of statistical heterogeneity. Certainty of evidence was assessed according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) guidelines.

RESULTS

We included 12 studies with a total of 7416 patients participating in RCTs. Oxygenation targets were extremely heterogeneous between studies. The meta-analysis found no differences in mortality between lower and higher oxygenation targets for critically ill ICU patients (relative risk [RR], 1.00; 95% confidence interval [CI], 0.93-1.09; moderate certainty). The incidence of serious adverse events (RR, 0.93; 95% CI, 0.85-1.00; high certainty), mechanical ventilation-free days through day 28 (mean difference [MD], -0.05; 95%CI, -1.23 to 1.13; low certainty), the number of patients requiring renal replacement therapy (RRT) (RR, 0.96; 95% CI, 0.84-1.10; low certainty), and ICU length of stay (MD, 1.05; 95% CI, -0.04 to 2.13; very low certainty) also did not differ among patients with lower or higher oxygenation targets.

CONCLUSIONS

Critically ill ICU patients ≥18 years of age managed with lower and higher oxygenation targets did not differ in terms of mortality, RRT need, mechanical ventilation-free days through day 28, or ICU length of stay. However, due to considerable heterogeneity between specific targets in individual studies, no conclusion can be drawn regarding the effect of oxygenation targets on ICU outcomes.

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.

The effect of conservative oxygen therapy on mortality in adult critically ill patients: A systematic review and meta-analysis of randomised controlled trials

Background

Oxygen is the commonest intervention provided to critically ill patients requiring mechanical ventilation. Despite this, it is unclear how much oxygen should be administered to patients in order to promote the best clinical outcomes and it has been suggested that a strategy of conservative oxygen therapy (COT) may be advantageous. We therefore sought to answer the question of whether COT versus usual or liberal oxygen therapy was beneficial to adult patients receiving mechanical ventilation on an intensive care unit (ICU) by performing a systematic review and meta-analysis.

Methods

Studies were included if they were randomised controlled trials comparing COT to liberal or usual oxygen therapy strategies in acutely ill adults (aged ⩾18 years) admitted to an ICU, and reported an outcome of interest. Studies were excluded if they were limited to a specific single disease diagnosis. The review was registered on PROSPERO (CRD42022308436). Risk of bias was assessed using a modified Cochrane Risk of Bias assessment tool. Effect estimates were pooled using a random effects model with the between study variance estimated using restricted maximum likelihood and standard errors calculated using the method of Hartung-Knapp/Sidik-Jonkman. Between study heterogeneity was quantified using the I2 statistic. The certainty in the body of evidence was assessed using GRADE criteria.

Results

Nine eligible studies with 5727 participants fulfilled all eligibility criteria. Trials varied in their definitions of COT and liberal or usual oxygen therapy. The pooled estimate of risk ratio for 90 day mortality for COT versus comparator was 0.99 (95% confidence interval 0.88-1.12, 95% prediction interval 0.82-1.21). There was low heterogeneity among studies (I2 = 22.4%). The finding that mortality was similar for patients managed with COT or usual/liberal oxygen therapy was graded as moderate certainty.

Conclusions

In critically ill adults admitted to an ICU, COT is neither beneficial nor harmful when compared to usual or liberal oxygen therapy. Trials to date have been inconsistent in defining both COT and liberal or usual oxygen therapy, which may have had an impact on the results of this meta-analysis. Future research should focus on unifying definitions and outcome measures.

Investigation and Analysis of the Current Status of Rationality and Standardization of Oxygen Therapy in Hospitalized Adult Patients

Objective

To investigate the rationality and standardization of oxygen therapy for hospitalized adult patients, so as to provide a basis for improving the quality of oxygen therapy care.

Methods

Self-designed "Inpatient Oxygen Therapy Status Questionnaire", using a cross-sectional survey, surveyed 185 oxygen inhalation patients in a tertiary general hospital from August 3-15, 2020, based on the formulation and promulgation of the Chinese Nursing Association The "Nursing care for adult patient with oxygen therapy" standard evaluates the rationality of clinical oxygen therapy implementation and the standardization of nursing measures.

Results

The reasonable rate of oxygen therapy for hospitalized adult patients was 19.46%, and the standardized rate of nursing measures was 54.52%. The reasonable and standardized rates of medical wards were higher than those of surgical and specialized wards, and were statistically significant (P<0.05). The incidence of complications of oxygen therapy was positively correlated with the rationality of oxygen therapy and the standardized data of nursing measures.

Conclusion

The clinical oxygen therapy nursing practice and the standard of "Nursing care for adult patient with oxygen therapy" are quite inadequate. There are differences in the quality of oxygen therapy in different wards. Nursing managers should strengthen training and management, standardize nursing behaviors, and improve the quality of oxygen therapy and ensure oxygen therapy for patients' safety.

Targeting CXCR1 alleviates hyperoxia-induced lung injury through promoting glutamine metabolism

Although increasing evidence suggests potential iatrogenic injury from supplemental oxygen therapy, significant exposure to hyperoxia in critically ill patients is inevitable. This study shows that hyperoxia causes lung injury in a time- and dose-dependent manner. In addition, prolonged inspiration of oxygen at concentrations higher than 80% is found to cause redox imbalance and impair alveolar microvascular structure. Knockout of C-X-C motif chemokine receptor 1 (Cxcr1) inhibits the release of reactive oxygen species (ROS) from neutrophils and synergistically enhances the ability of endothelial cells to eliminate ROS. We also combine transcriptome, proteome, and metabolome analysis and find that CXCR1 knockdown promotes glutamine metabolism and leads to reduced glutathione by upregulating the expression of malic enzyme 1. This preclinical evidence suggests that a conservative oxygen strategy should be recommended and indicates that targeting CXCR1 has the potential to restore redox homeostasis by reducing oxygen toxicity when inspiratory hyperoxia treatment is necessary.

Influence of Age on Hyperoxia-Induced Cardiac Pathophysiology in Type 1 Diabetes Mellitus (T1DM) Mouse Model

Mechanical ventilation often results in hyperoxia, a condition characterized by excess SpO2 levels (>96%). Hyperoxia results in changes in the physiological parameters, severe cardiac remodeling, arrhythmia development, and alteration of cardiac ion channels, all of which can point toward a gradual increase in the risk of developing cardiovascular disease (CVD). This study extends the analysis of our prior work in young Akita mice, which demonstrated that exposure to hyperoxia worsens cardiac outcomes in a type 1 diabetic murine model as compared to wild-type (WT) mice. Age is an independent risk factor, and when present with a major comorbidity, such as type 1 diabetes (T1D), it can further exacerbate cardiac outcomes. Thus, this research subjected aged T1D Akita mice to clinical hyperoxia and analyzed the cardiac outcomes. Overall, aged Akita mice (60 to 68 weeks) had preexisting cardiac challenges compared to young Akita mice. Aged mice were overweight, had an increased cardiac cross-sectional area, and showed prolonged QTc and JT intervals, which are proposed as major risk factors for CVD like intraventricular arrhythmias. Additionally, exposure to hyperoxia resulted in severe cardiac remodeling and a decrease in Kv 4.2 and KChIP2 cardiac potassium channels in these rodents. Based on sex-specific differences, aged male Akita mice had a higher risk of poor cardiac outcomes than aged females. Aged male Akita mice had prolonged RR, QTc, and JT intervals even at baseline normoxic exposure. Moreover, they were not protected against hyperoxic stress through adaptive cardiac hypertrophy, which, at least to some extent, is due to reduced cardiac androgen receptors. This study in aged Akita mice aims to draw attention to the clinically important yet understudied subject of the effect of hyperoxia on cardiac parameters in the presence of preexisting comorbidities. The findings would help revise the provision of care for older T1D patients admitted to ICUs.

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.

Conservative versus conventional oxygen therapy in type I acute respiratory failure patients in respiratory intensive care unit, Zagazig University

The present study aimed to assess the effect of a conservative (permissive hypoxemia) versus conventional (normoxia) protocol for oxygen supplementation on the outcome of type I respiratory failure patients admitted to respiratory intensive care unit (ICU). This randomized controlled clinical trial was carried out at the Respiratory ICU, Chest Department of Zagazig University Hospital, for 18 months, starting in July 2018. On admission, 56 enrolled patients with acute respiratory failure were randomized in a 1:1 ratio into the conventional group [oxygen therapy was supplied to maintain oxygen saturation (SpO2) between 94% and 97%] and the conservative group (oxygen therapy was administered to maintain SpO2 values between 88% and 92%). Different outcomes were assessed, including ICU mortality, the need for mechanical ventilation (MV) (invasive or non-invasive), and ICU length of stay. In the current study, the partial pressure of oxygen was significantly higher among the conventional group at all times after the baseline reading, and bicarbonate was significantly higher among the conventional group at the first two readings. There was no significant difference in serum lactate level in follow-up readings. The mean duration of MV and ICU length of stay was 6.17±2.05 and 9.25±2.22 days in the conventional group versus 6.46±2.0 and 9.53±2.16 days in the conservative group, respectively, without significant differences between both groups. About 21.4% of conventional group patients died, while 35.7% of conservative group patients died without a significant difference between both groups. We concluded that conservative oxygen therapy may be applied safely to patients with type I acute respiratory failure.

Postoperative awake prone position in geriatric patients with hip fractures: a protocol for a randomized controlled trial on the efficacy of postoperative prone position in reducing pulmonary complications and improving oxygenation

INTRODUCTION

Postoperative pulmonary complications (PPCs) are prevalent in geriatric patients with hip fractures. Low oxygen level is one of the most important risk factors for PPCs. Prone position has been proven efficacy in improving oxygenation and delaying the progress of pulmonary diseases, especially in patients with acute respiratory distress syndrome induced by multiple etiologies. The application of awake prone position (APP) has also attracted widespread attention in recent years. A randomized controlled trial (RCT) will be carried out to measure the effect of postoperative APP in a population of geriatric patients undergoing hip fracture surgery.

METHODS

This is an RCT. Patients older than 65 years old admitted through the emergency department and diagnosed with an intertrochanteric or femoral neck fracture will be eligible for enrollment and assigned randomly to the control group with routine postoperative management of orthopedics or APP group with an additional prone position for the first three consecutive postoperative days (PODs). Patients receiving conservative treatment will not be eligible for enrollment. We will record the difference in the patient's room-air-breathing arterial partial pressure of oxygen (PaO₂) values between the 4^th POD (POD 4) and emergency visits, the morbidity of PPCs and other postoperative complications, and length of stay. The incidence of PPCs, readmission rates, and mortality rates will be followed up for 90 PODs.

DISCUSSION

We describe the protocol for a single-center RCT that will evaluate the efficacy of postoperative APP treatment in reducing pulmonary complications and improving oxygenation in geriatric patients with hip fractures.

ETHICS AND DISSEMINATION

This protocol was approved by the independent ethics committee (IEC) for Clinical Research of Zhongda Hospital, Affiliated to Southeast University, and is registered on the Chinese Clinical Trial Registry. The findings of the trial will be disseminated through peer-reviewed journals.

ETHICS APPROVAL NUMBER

2021ZDSYLL203-P01 TRIAL REGISTRATION: ChiCTR ChiCTR2100049311 . Registered on 29 July 2021.

TRIAL STATUS

Recruiting. Recruitment is expected to be completed in December 2024.

Predicting Persistent Acute Respiratory Failure in Acute Pancreatitis: The Accuracy of Two Lung Injury Indices

BACKGROUND/AIMS

Early and accurate identification of patients with acute pancreatitis (AP) at high risk of persistent acute respiratory failure (PARF) is crucial. We sought to determine the accuracy of simplified Lung Injury Prediction Score (sLIPS) and simplified Early Acute Lung Injury (sEALI) for predicting PARF in ward AP patients.

METHODS

Consecutive AP patients in a training cohort from West China Hospital of Sichuan University (n = 912) and a validation cohort from The First Affiliated Hospital of Nanchang University (n = 1033) were analyzed. PARF was defined as oxygen in arterial blood/fraction of inspired oxygen < 300 mmHg that lasts for > 48 h. The sLIPS was composed by shock (predisposing condition), alcohol abuse, obesity, high respiratory rate, low oxygen saturation, high oxygen requirement, hypoalbuminemia, and acidosis (risk modifiers). The sEALI was calculated from oxygen 2 to 6 L/min, oxygen > 6 L/min, and high respiratory rate. Both indices were calculated on admission.

RESULTS

PARF developed in 16% (145/912) and 22% (228/1033) (22%) of the training and validation cohorts, respectively. In these patients, sLIPS and sEALI were significantly increased. sLIPS ≥ 2 predicted PARF in the training (AUROC 0.87, 95% CI 0.84-0.89) and validation (AUROC 0.81, 95% CI 0.78-0.83) cohorts. sLIPS was significantly more accurate than sEALI and current clinical scoring systems in both cohorts (all P < 0.05).

CONCLUSIONS

Using routinely available clinical data, the sLIPS can accurately predict PARF in ward AP patients and outperforms the sEALI and current existing clinical scoring systems.

Oxygen saturation targets for adults with acute hypoxemia in low and lower-middle income countries: a scoping review with analysis of contextual factors

Knowing the target oxygen saturation (SpO₂) range that results in the best outcomes for acutely hypoxemic adults is important for clinical care, training, and research in low-income and lower-middle income countries (collectively LMICs). The evidence we have for SpO₂ targets emanates from high-income countries (HICs), and therefore may miss important contextual factors for LMIC settings. Furthermore, the evidence from HICs is mixed, amplifying the importance of specific circumstances. For this literature review and analysis, we considered SpO₂ targets used in previous trials, international and national society guidelines, and direct trial evidence comparing outcomes using different SpO₂ ranges (all from HICs). We also considered contextual factors, including emerging data on pulse oximetry performance in different skin pigmentation ranges, the risk of depleting oxygen resources in LMIC settings, the lack of access to arterial blood gases that necessitates consideration of the subpopulation of hypoxemic patients who are also hypercapnic, and the impact of altitude on median SpO₂ values. This process of integrating prior study protocols, society guidelines, available evidence, and contextual factors is potentially useful for the development of other clinical guidelines for LMIC settings. We suggest that a goal SpO₂ range of 90-94% is reasonable, using high-performing pulse oximeters. Answering context-specific research questions, such as an optimal SpO₂ target range in LMIC contexts, is critical for advancing equity in clinical outcomes globally.

Recent trends in the nanozeolites-based oxygen concentrators and their application in respiratory disorders

Medical-grade oxygen is the basic need for all medical complications, especially in respiratory-based discomforts. There was a drastic increase in the demand for medical-grade oxygen during the current pandemic. The non-availability of medical-grade oxygen led to several complications, including death. The oxygen concentrator was only the last hope for the patient during COVID-19 pandemic around the globe. The demands also are everlasting during other microbial respiratory infections. The yield of oxygen using conventional molecular zeolites in the traditional oxygen concentrator process is less than the yield noticed when its nano-form is used. Nanotechnology has enlightened hope for the efficient production of oxygen by such oxygen concentrators. Here in the current review work, the authors have highlighted the basic structural features of oxygen concentrators along with the current working principle. Besides, it has been tried to bridge the gap between conventional oxygen concentrators and advanced ones by using nanotechnology. Nanoparticles being usually within 100 nm in size have a high surface area to volume ratio, which makes them suitable adsorbents for oxygen. Here authors have suggested the use of nano zeolite in place of molecular zeolites in the oxygen concentrator for efficient delivery of oxygen by the oxygen concentrators.

Hyperoxia by short-term promotes oxidative damage and mitochondrial dysfunction in rat brain

Oxygen (O₂) therapy is used as a therapeutic protocol to prevent or treat hypoxia. However, a high inspired fraction of O₂ (FIO₂) promotes hyperoxia, a harmful condition for the central nervous system (CNS). The present study evaluated parameters of oxidative stress and mitochondrial dysfunction in the brain of rats exposed to different FIO₂. Male Wistar rats were exposed to hyperoxia (FIO₂ 40 % and 60 %) compared to the control group (FIO₂ 21 %) for 2 h. Oxidative stress, neutrophilic infiltration, and mitochondrial respiratory chain enzymes were determined in the hippocampus, striatum, cerebellum, cortex, and prefrontal cortex after O₂ exposure. The animals exposed to hyperoxia showed increased lipid peroxidation, formation of carbonyl proteins, N/N concentration, and neutrophilic infiltration in some brain regions, like hippocampus, striatum, and cerebellum being the most affected. Furthermore, CAT activity and activity of mitochondrial enzyme complexes were also altered after exposure to hyperoxia. Rats exposed to hyperoxia showed increase in oxidative stress parameters and mitochondrial dysfunction in brain structures.

Supplemental oxygen strategies in infants with bronchopulmonary dysplasia after the neonatal intensive care unit period: study protocol for a randomised controlled trial (SOS BPD study)

INTRODUCTION

Supplemental oxygen is the most important treatment for preterm born infants with established bronchopulmonary dysplasia (BPD). However, it is unknown what oxygen saturation levels are optimal to improve outcomes in infants with established BPD from 36 weeks postmenstrual age (PMA) onwards. The aim of this study is to compare the use of a higher oxygen saturation limit (≥95%) to a lower oxygen saturation limit (≥90%) after 36 weeks PMA in infants diagnosed with moderate or severe BPD.

METHODS AND ANALYSIS

This non-blinded, multicentre, randomised controlled trial will recruit 198 preterm born infants with moderate or severe BPD between 36 and 38 weeks PMA. Infants will be randomised to either a lower oxygen saturation limit of 95% or to a lower limit of 90%; supplemental oxygen and/or respiratory support will be weaned based on the assigned lower oxygen saturation limit. Adherence to the oxygen saturation limit will be assessed by extracting oxygen saturation profiles from pulse oximeters regularly, until respiratory support is stopped. The primary outcome is the weight SD score at 6 months of corrected age. Secondary outcomes include anthropometrics collected at 6 and 12 months of corrected age, rehospitalisations, respiratory complaints, infant stress, parental quality of life and cost-effectiveness.

ETHICS AND DISSEMINATION

Ethical approval for the trial was obtained from the Medical Ethics Review Committee of the Erasmus University Medical Centre, Rotterdam, the Netherlands (MEC-2018-1515). Local approval for conducting the trial in the participating hospitals has been or will be obtained from the local institutional review boards. Informed consent will be obtained from the parents or legal guardians of all study participants.

TRIAL REGISTRATION NUMBER

NL7149/NTR7347.

Evaluation of a New Smartphone Powered Low-cost Pulse Oximeter Device

Background

Measurement of blood oxygen saturation is a vital part of monitoring coronavirus 2019 (COVID-19) patients. Pulse oximetry is commonly used to measure blood oxygen saturation and pulse rate for appropriate clinical intervention. But the majority of direct-to-consumer grade pulse oximeters did not pass through in-vivo testing, which results in their accuracy being questionable. Besides this, the ongoing COVID-19 pandemic exposed the limitations of the device in resource limited areas since independent monitoring is needed for COVID-19 patients. The purpose of this study was to perform an in-vivo evaluation of a newly developed smartphone powered low-cost pulse oximeter.

Methods

The new prototype of a smartphone powered pulse oximeter was evaluated against the standard pulse oximeter by taking measurements from fifteen healthy volunteers. The accuracy of measurement was evaluated by calculating the percentage error and standard deviation. A repeatability and reproducibility test were carried out using the ANOVA method.

Results

The average accuracy for measuring spot oxygen saturation (SPO2) and pulse rate (PR) was 99.18% with a standard deviation of 0.57 and 98.78% with a standard deviation of 0.61, respectively, when compared with the standard pulse oximeter device. The repeatability and reproducibility of SPO2 measurements were 0.28 and 0.86, respectively, which is in the acceptable range.

Conclusion

The new prototype of smartphone powered pulse oximeter demonstrated better performance compared to the existing low-cost fingertip pulse oximeters. The device could be used for independent monitoring of COVID-19 patients at health institutions and also for home care.

Development of Low-Cost and Portable Pulse Oximeter Device with Improved Accuracy and Accessibility

Purpose

Methods

Results

Conclusion

Effects of Acute Hypobaric Hypoxia Exposure on Cardiovascular Function in Unacclimatized Healthy Subjects: A "Rapid Ascent" Hypobaric Chamber Study

Background: This study aimed to observe the effects of a fast acute ascent to simulated high altitudes on cardiovascular function both in the main arteries and in peripheral circulation. Methods: We examined 17 healthy volunteers, between 18 and 50 years old, at sea level, at 3842 m of hypobaric hypoxia and after return to sea level. Cardiac output (CO) was measured with Doppler transthoracic echocardiography. Oxygen delivery was estimated as the product of CO and peripheral oxygen saturation (SpO2). The brachial artery’s flow-mediated dilation (FMD) was measured with the ultrasound method. Post-occlusion reactive hyperemia (PORH) was assessed by digital plethysmography. Results: During altitude stay, peripheral oxygen saturation decreased (84.9 ± 4.2% of pre-ascent values; p < 0.001). None of the volunteers presented any hypoxia-related symptoms. Nevertheless, an increase in cardiac output (143.2 ± 36.2% of pre-ascent values, p < 0.001) and oxygen delivery index (120.6 ± 28.4% of pre-ascent values; p > 0.05) was observed. FMD decreased (97.3 ± 4.5% of pre-ascent values; p < 0.05) and PORH did not change throughout the whole experiment. Τhe observed changes disappeared after return to sea level, and normoxia re-ensued. Conclusions: Acute exposure to hypobaric hypoxia resulted in decreased oxygen saturation and increased compensatory heart rate, cardiac output and oxygen delivery. Pre-occlusion vascular diameters increase probably due to the reduction in systemic vascular resistance preventing flow-mediated dilation from increasing. Mean Arterial Pressure possibly decrease for the same reason without altering post-occlusive reactive hyperemia throughout the whole experiment, which shows that compensation mechanisms that increase oxygen delivery are effective.

Oxygen Targets During Mechanical Ventilation in the ICU: A Systematic Review and Meta-Analysis

Patients admitted to intensive care often require treatment with invasive mechanical ventilation and high concentrations of oxygen. Mechanical ventilation can cause acute lung injury that may be exacerbated by oxygen therapy. Uncertainty remains about which oxygen therapy targets result in the best clinical outcomes for these patients. This review aims to determine whether higher or lower oxygenation targets are beneficial for mechanically ventilated adult patients.

ICONIC study—conservative versus conventional oxygenation targets in intensive care patients: study protocol for a randomized clinical trial

Background

Oxygen therapy is a widely used intervention in acutely ill patients in the intensive care unit (ICU). It is established that not only hypoxia, but also prolonged hyperoxia is associated with poor patient-centered outcomes. Nevertheless, a fundamental knowledge gap remains regarding optimal oxygenation for critically ill patients. In this randomized clinical trial, we aim to compare ventilation that uses conservative oxygenation targets with ventilation that uses conventional oxygen targets with respect to mortality in ICU patients.

Methods

The “ConservatIve versus CONventional oxygenation targets in Intensive Care patients” trial (ICONIC) is an investigator-initiated, international, multicenter, randomized clinical two-arm trial in ventilated adult ICU patients. The ICONIC trial will run in multiple ICUs in The Netherlands and Italy to enroll 1512 ventilated patients. ICU patients with an expected mechanical ventilation time of more than 24 h are randomized to a ventilation strategy that uses conservative (PaO₂ 55–80 mmHg (7.3–10.7 kPa)) or conventional (PaO₂ 110–150 mmHg (14.7–20 kPa)) oxygenation targets. The primary endpoint is 28-day mortality. Secondary endpoints are ventilator-free days at day 28, ICU mortality, in-hospital mortality, 90-day mortality, ICU- and hospital length of stay, ischemic events, quality of life, and patient opinion of research and consent in the emergency setting.

Discussion

The ICONIC trial is expected to provide evidence on the effects of conservative versus conventional oxygenation targets in the ICU population. This study may guide targeted oxygen therapy in the future.

Trial registration

Trialregister.nl NTR7376. Registered on 20 July, 2018.

[Chronic respiratory failure correction in cicatricial laryngeal and tracheal stenosis using helium-oxygen mixture]

The article provides a review of the literature on the development of chronic respiratory failure in patients with chronic cicatricial stenosis of the larynx and cervical trachea. The authors provide data on the etiology, pathogenetic features of the course of cicatricial stenosis of the larynx and trachea, the reasons for the development of chronic respiratory failure, the effect of hypoxemia on general metabolic processes in the body and on regeneration processes, as well as on methods of their correction and improvement of the postoperative period. The methods of respiratory impact on chronic respiratory failure in these patients are considered, based on the experience of a number of researchers and technical advances in recent years.

Urine Output Is Associated With In-hospital Mortality in Intensive Care Patients With Septic Shock: A Propensity Score Matching Analysis

Background: The relationship between urine output (UO) and in-hospital mortality in intensive care patients with septic shock is currently inconclusive. Methods: The baseline data, UO, and in-hospital prognosis of intensive care patients with septic shock were retrieved from the Medical Information Mart for Intensive Care IV (MIMIC-IV) database. By drawing receiver operating characteristic (ROC) curves and comparing the areas under the ROC curves (AUC) to determine the predictive value of UO for in-hospital mortality, and by drawing the Kaplan-Meier curves to compare the difference in in-hospital mortality between different groups of UO. Results: Before and after the propensity score matching (PSM) analysis, UO was always a risk factor for in-hospital mortality in patients with septic shock. The AUC of UO was comparable to the Sequential Organ Failure Assessment (SOFA) scoring system, while the AUC of combining UO and SOFA was greater than that of SOFA. The median survival time of the high-UO group (UO > 0.39 ml/kg/h, before PSM; UO > 0.38 ml/kg/h, after PSM) was longer than that of the low-UO group. Compared with the high-UO group, the hazard ratios (HR) of the low-UO group were 2.6857 (before PSM) and 1.7879 (after PSM). Conclusions: UO is an independent risk factor for septic shock. Low levels of UO significantly increase the in-hospital mortality of intensive care patients with septic shock. The predictive value of UO is comparable to the SOFA scoring system, and the combined predictive value of the two surpasses SOFA alone.

Role of SatO2, PaO2/FiO2 Ratio and PaO2 to Predict Adverse Outcome in COVID-19: A Retrospective, Cohort Study

COVID-19 respiratory failure is a life-threatening condition. Oxygenation targets were evaluated in a non-ICU setting. In this retrospective, observational study, we enrolled all patients admitted to the University Hospital of Genoa, Italy, between 1 February and 31 May 2020 with an RT-PCR positive for SARS-CoV-2. PaO2, PaO2/FiO2 and SatO2% were collected and analyzed at time 0 and in case of admission, patients who required or not C-PAP (groups A and B) were categorized. Each measurement was correlated to adverse outcome. A total of 483 patients were enrolled, and 369 were admitted to hospital. Of these, 153 required C-PAP and 266 had an adverse outcome. Patients with PaO2 <60 and >100 had a higher rate of adverse outcome at time 0, in groups A and B (OR 2.52, 3.45, 2.01, respectively). About the PaO2/FiO2 ratio, the OR for < 300 was 3.10 at time 0, 4.01 in group A and 4.79 in group B. Similar odds were found for < 200 in any groups and < 100 except for group B (OR 11.57). SatO2 < 94% showed OR 1.34, 3.52 and 19.12 at time 0, in groups A and B, respectively. PaO2 < 60 and >100, SatO2 < 94% and PaO2/FiO2 ratio < 300 showed at least two- to three-fold correlation to adverse outcome. This may provide simple but clear targets for clinicians facing COVID-19 respiratory failure in a non ICU-setting.

A feasibility randomised controlled trial of targeted oxygen therapy in mechanically ventilated critically ill patients

BACKGROUND

Despite oxygen being the commonest drug administered to critically ill patients we do not know which oxygen saturation (SpO2) target results in optimal survival outcomes in those receiving mechanical ventilation. We therefore conducted a feasibility randomised controlled trial in the United Kingdom (UK) to assess whether it would be possible to host a larger national multi-centre trial to evaluate oxygenation targets in mechanically ventilated patients.

METHODS

We set out to recruit 60 participants across two sites into a trial in which they were randomised to receive conservative oxygenation (SpO2 88-92%) or usual care (control - SpO2 ≥96%). The primary outcome was feasibility; factors related to safety and clinical outcomes were also assessed.

RESULTS

A total of 34 patients were recruited into the study until it was stopped due to time constraints. A number of key barriers to success were identified during the course of the study. The conservative oxygenation intervention was feasible and appeared to be safe in this small patient cohort and it achieved wide separation of the median time-weighted average (IQR) SpO2 at 91% (90-92%) in conservative oxygenation group versus 97% (96-97%) in control group.

CONCLUSION

Whilst conservative oxygenation was a feasible and safe intervention which achieved clear group separation in oxygenation levels, the model used in this trial will require alterations to improve future participant recruitment rates in the UK.

Impact of Permissive Hypoxia and Hyperoxia Avoidance on Clinical Outcomes in Septic Patients Receiving Mechanical Ventilation: A Retrospective Single-Center Study

BACKGROUND

Septic patients often require mechanical ventilation due to respiratory dysfunction, and effective ventilatory strategies can improve survival. The effects of the combination of permissive hypoxia and hyperoxia avoidance for managing mechanically ventilated patients are unknown. This study examines these effects on outcomes in mechanically ventilated septic patients.

METHODS

In a retrospective before-and-after study, we examined adult septic patients (aged ≥18 years) requiring mechanical ventilation at a university hospital. On April 1, 2017, our mechanical ventilation policy changed from a conventional oxygenation target (SpO2: ≥96%) to more conservative targets with permissive hypoxia (SpO2: 88-92% or PaO2: 60 mmHg) and hyperoxia avoidance (reduced oxygenation for PaO2 > 110 mmHg). Patients were divided into a prechange group (April 2015 to March 2017; n = 83) and a postchange group (April 2017 to March 2019; n = 130). Data were extracted from clinical records and insurance claims. Using a multiple logistic regression model, we examined the association of the postchange group (permissive hypoxia and hyperoxia avoidance) with intensive care unit (ICU) mortality after adjusting for variables such as Sequential Organ Failure Assessment (SOFA) score and PaO2/FiO2 ratios.

RESULTS

The postchange group did not have significantly lower adjusted ICU mortality (0.67, 0.33-1.43; P = 0.31) relative to the prechange group. However, there were significant intergroup differences in mechanical ventilation duration (prechange: 11.0 days, postchange: 7.0 days; P = 0.01) and ICU stay (prechange: 11.0 days, postchange: 9.0 days; P = 0.02).

CONCLUSIONS

Permissive hypoxia and hyperoxia avoidance had no significant association with reduced ICU mortality in mechanically ventilated septic patients. However, this approach was significantly associated with shorter mechanical ventilation duration and ICU stay, which can improve patient turnover and ventilator access.

Oxygen sensing, anaesthesia and critical care: a narrative review

In 2019, the scientists who discovered how cells sense and adapt to oxygen availability were awarded the Nobel Prize. This elegant sensing pathway is conserved throughout evolution, and it underpins the physiology and pathology that we, as clinicians in anaesthesia and critical care, encounter on a daily basis. The purpose of this review is to bring hypoxia-inducible factor, and the oxygen-sensing pathway as a whole, to the wider clinical community. We describe how this unifying mechanism was discovered, and how it orchestrates diverse changes such as erythropoiesis, ventilatory acclimatisation, pulmonary vascular remodelling and altered metabolism. We explore the lessons learnt from genetic disorders of oxygen sensing, and the wider implications in evolution of all animal species, including our own. Finally, we explain how this pathway is relevant to our clinical practice, and how it is being manipulated in new treatments for conditions such as cancer, anaemia and pulmonary hypertension.

Hyperoxaemia and hypoxaemia are associated with harm in patients with ARDS

BACKGROUND

Oxygen therapy is routinely administered to mechanically ventilated patients. However, there remains uncertainty about the optimal oxygen titration target in patients with the acute respiratory distress syndrome (ARDS).

METHODS

Prospectively identified adult patients meeting the Berlin definition of ARDS between 1st January 2014 and 13th December 2016 were analyzed. Oxygen exposure variables were collected at 6-hourly intervals. The primary exposure was the average time-weighted partial pressure of arterial oxygen (PaO2) calculated over a maximum of 7 days from meeting ARDS criteria. The primary outcome was ICU mortality. Univariable and multivariable logistic regression analyses were performed to assess the impact of exposure variables on clinical outcomes. Results are presented as odds ratio [95% confidence interval].

RESULTS

202 patients were included in the final analysis. Overall ICU mortality was 31%. The average time-weighted PaO2 during the first 7 days of ARDS was similar between non-survivors and survivors (11.3 kPa [10.2, 12.5] (84.8 mmHg [76.5, 93.8]) vs. 11.9 kPa [10.9, 12.6] (89.3 mmHg [81.8, 94.5]); p = 0.08). In univariable and multivariable analysis, average time-weighted PaO2 demonstrated a U-shaped relationship with ICU mortality. There was a similar relationship identified with hospital mortality.

CONCLUSIONS

In patients with ARDS, the predicted probability of both ICU and hospital mortality was lowest when the average time-weighted PaO2 was between 12.5 and 14 kPa (93.8-105.0 mmHg), suggesting this is a reasonable oxygenation target for clinicians to aim for.

Prolonged oxygen exposure causes the mobilization and functional damage of stem or progenitor cells and exacerbates cardiac ischemia or reperfusion injury in healthy mice

Oxygen is often administered to patients and occasionally to healthy individuals as well; however, the cellular toxicity of oxygen, especially following prolonged exposure, is widely known. To evaluate the potential effect of oxygen exposure on circulating stem/progenitor cells and cardiac ischemia/reperfusion (I/R) injury, we exposed healthy adult mice to 100% oxygen for 20 or 60 min. We then examined the c-kit-positive stem/progenitor cells and colony-forming cells and measured the cytokine/chemokine levels in peripheral blood. We also induced cardiac I/R injury in mice at 3 h after 60 min of oxygen exposure and examined the recruitment of inflammatory cells and the fibrotic area in the heart. The proportion of c-kit-positive stem/progenitor cells significantly increased in peripheral blood at 3 and 24 h after oxygen exposure for either 20 or 60 min (p < .01 vs. control). However, the abundance of colony-forming cells in peripheral blood conversely decreased at 3 and 24 h after oxygen exposure for only 60 min (p < .05 vs. control). Oxygen exposure for either 20 or 60 min resulted in significantly decreased plasma vascular endothelial growth factor levels at 3 h, whereas oxygen exposure for only 60 min reduced plasma insulin-like growth factor 1 levels at 24 h (p < .05 vs. control). Protein array indicated the increase in the levels of some cytokines/chemokines, such as CXCL6 (GCP-2) at 24 h after 60 min of oxygen exposure. Moreover, oxygen exposure for 60 min enhanced the recruitment of Ly6g- and CD11c-positive inflammatory cells at 3 days (p < .05 vs. control) and increased the fibrotic area at 14 days in the heart after I/R injury (p < .05 vs. control). Prolonged oxygen exposure induced the mobilization and functional impairment of stem/progenitor cells and likely enhanced inflammatory responses to exacerbate cardiac I/R injury in healthy mice.

Future trends in measuring physiology in free-living animals

Thus far, ecophysiology research has predominantly been conducted within controlled laboratory-based environments, owing to a mismatch between the recording technologies available for physiological monitoring in wild animals and the suite of behaviours and environments they need to withstand, without unduly affecting subjects. While it is possible to record some physiological variables for free-living animals using animal-attached logging devices, including inertial-measurement, heart-rate and temperature loggers, the field is still in its infancy. In this opinion piece, we review the most important future research directions for advancing the field of 'physiologging' in wild animals, including the technological development that we anticipate will be required, and the fiscal and ethical challenges that must be overcome. Non-invasive, multi-sensor miniature devices are ubiquitous in the world of human health and fitness monitoring, creating invaluable opportunities for animal and human physiologging to drive synergistic advances. We argue that by capitalizing on the research efforts and advancements made in the development of human wearables, it will be possible to design the non-invasive loggers needed by ecophysiologists to collect accurate physiological data from free-ranging animals ethically and with an absolute minimum of impact. In turn, findings have the capacity to foster transformative advances in human health monitoring. Thus, we invite biomedical engineers and researchers to collaborate with the animal-tagging community to drive forward the advancements necessary to realize the full potential of both fields. This article is part of the theme issue 'Measuring physiology in free-living animals (Part II)'.

Hypoxemia During One-Lung Ventilation: Does It Really Matter?

PURPOSE OF REVIEW

Hypoxemia during one-lung ventilation, while decreasing in frequency, persists as an intraoperative challenge for anesthesiologists. Discerning when desaturation and resultant hypoxemia correlates to tissue hypoxia is challenging in the perioperative setting and requires a thorough understanding of the physiology of oxygen delivery and tissue utilization.

RECENT FINDINGS

Oxygen delivery is not directly correlated with peripheral oxygen saturation in patients undergoing one-lung ventilation, emphasizing the importance of hemoglobin concentration and cardiac output in avoiding tissue hypoxia. While healthy humans can tolerate acute hypoxemia without long-term consequences, there is a paucity of evidence from patients undergoing thoracic surgery. Increasingly recognized is the potential harm of hyperoxic states, particularly in the setting of complex patients with comorbid diseases.

SUMMARY

Anesthesiologists are left to determine an acceptable oxygen saturation nadir that is individualized to the patient and procedure based on an understanding of oxygen supply, demand, and the consequences of interventions.

Hypoxia-dependent signaling in perioperative and critical care medicine

A critical goal of patient management for anesthesiologists and intensivists is to maintain oxygen homeostasis in patients admitted to operation theaters and intensive care units. For this purpose, it is imperative to understand the strategies of the body against oxygen imbalance—especially oxygen deficiency (hypoxia). Adaptation to hypoxia and maintenance of oxygen homeostasis involve a wide range of responses that occur at different organizational levels in the body. These responses are greatly influenced by perioperative patient management including factors such as perioperative drugs. Herein, the influence of perioperative patient management on the body's response to oxygen imbalance was reviewed with a special emphasis on hypoxia-inducible factors (HIFs), transcription factors whose activity are regulated by the perturbation of oxygen metabolism. The 2019 Nobel Prize in Physiology or Medicine was awarded to three researchers who made outstanding achievements in this field. While previous studies have reported the effect of perioperatively used drugs on hypoxia-induced gene expression mediated by HIFs, this review focused on effects of subacute or chronic hypoxia changes in gene expression that are mediated by the transcriptional regulator HIFs. The clinical implications and perspectives of these findings also will be discussed. Understanding the basic biology of the transcription factor HIF can be informative for us since anesthesiologists manage patients during the perioperative period facing the imbalances the oxygen metabolism in organ and tissue. The clinical implications of hypoxia-dependent signaling in critical illness, including Coronavirus disease (COVID-19), in which disturbances in oxygen metabolism play a major role in its pathogenesis will also be discussed.

Effects of Normoxia, Hyperoxia, and Mild Hypoxia on Macro-Hemodynamics and the Skeletal Muscle Microcirculation in Anesthetised Rats

Objectives: Excessive oxygen (O₂) administration may have a negative impact on tissue perfusion by inducing vasoconstriction and oxidative stress. We aimed to evaluate the effects of different inhaled oxygen fractions (FiO₂) on macro-hemodynamics and microvascular perfusion in a rat model.

Methods: Isoflurane-anesthetised spontaneously breathing male Wistar rats were equipped with arterial (carotid artery) and venous (jugular vein) catheters and tracheotomy, and randomized into three groups: normoxia (FiO₂ 21%, n = 6), hyperoxia (FiO₂ 100%, n = 6) and mild hypoxia (FiO₂ 15%, n = 6). Euvolemia was maintained by infusing Lactate Ringer solution at 10 ml/kg/h. At hourly intervals for 4 h we collected measurements of: mean arterial pressure (MAP); stroke volume index (SVI), heart rate (HR), respiratory rate (by means of echocardiography); arterial and venous blood gases; microvascular density, and flow quality (by means of sidestream dark field videomicroscopy on the hindlimb skeletal muscle).

Results: MAP and systemic vascular resistance index increased with hyperoxia and decreased with mild hypoxia (p < 0.001 in both cases, two-way analysis of variance). Hyperoxia induced a reduction in SVI, while this was increased in mild hypoxia (p = 0.002). The HR increased under hyperoxia (p < 0.05 vs. normoxia at 3 h). Cardiax index, as well as systemic O₂ delivery, did not significantly vary in the three groups (p = 0.546 and p = 0.691, respectively). At 4 h, microvascular vessel surface (i.e., the percentage of tissue surface occupied by vessels) decreased by 29 ± 4% in the hyperoxia group and increased by 19 ± 7 % in mild hypoxia group (p < 0.001). Total vessel density and perfused vessel density showed similar tendencies (p = 0.003 and p = 0.005, respectively). Parameters of flow quality (microvascular flow index, percentage of perfused vessels, and flow heterogeneity index) remained stable and similar in the three groups.

Conclusions: Hyperoxia induces vasoconstriction and reduction in skeletal muscle microvascular density, while mild hypoxia has an opposite effect.

Randomised controlled trial of oxygen therapy and high-flow nasal therapy in African children with pneumonia

Purpose

The life-saving role of oxygen therapy in African children with severe pneumonia is not yet established.

Methods

The open-label fractional-factorial COAST trial randomised eligible Ugandan and Kenyan children aged > 28 days with severe pneumonia and severe hypoxaemia stratum (SpO₂ < 80%) to high-flow nasal therapy (HFNT) or low-flow oxygen (LFO: standard care) and hypoxaemia stratum (SpO₂ 80–91%) to HFNT or LFO (liberal strategies) or permissive hypoxaemia (ratio 1:1:2). Children with cyanotic heart disease, chronic lung disease or > 3 h receipt of oxygen were excluded. The primary endpoint was 48 h mortality; secondary endpoints included mortality or neurocognitive sequelae at 28 days.

Results

The trial was stopped early after enrolling 1852/4200 children, including 388 in the severe hypoxaemia stratum (median 7 months; median SpO₂ 75%) randomised to HFNT (n = 194) or LFO (n = 194) and 1454 in the hypoxaemia stratum (median 9 months; median SpO₂ 88%) randomised to HFNT (n = 363) vs LFO (n = 364) vs permissive hypoxaemia (n = 727). Per-protocol 15% of patients in the permissive hypoxaemia group received oxygen (when SpO₂ < 80%). In the severe hypoxaemia stratum, 48-h mortality was 9.3% for HFNT vs. 13.4% for LFO groups. In the hypoxaemia stratum, 48-h mortality was 1.1% for HFNT vs. 2.5% LFO and 1.4% for permissive hypoxaemia. In the hypoxaemia stratum, adjusted odds ratio for 48-h mortality in liberal vs permissive comparison was 1.16 (0.49–2.74; p = 0.73); HFNT vs LFO comparison was 0.60 (0.33–1.06; p = 0.08). Strata-specific 28 day mortality rates were, respectively: 18.6, 23.4 and 3.3, 4.1, 3.9%. Neurocognitive sequelae were rare.

Conclusions

Respiratory support with HFNT showing potential benefit should prompt further trials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00134-021-06385-3.

Oxygen Therapy Lowers Right Ventricular Afterload in Experimental Acute Pulmonary Embolism

OBJECTIVES

To investigate if oxygen could unload the right ventricle and improve right ventricle function in a porcine model mimicking intermediate-high risk acute pulmonary embolism.

DESIGN

Controlled, blinded, animal study.

SETTING

Tertiary university hospital, animal research laboratory.

SUBJECTS

Female, Danish pigs (n = 16, approximately 60 kg).

INTERVENTIONS

Acute autologous pulmonary embolism was induced until doubling of baseline mean pulmonary arterial pressure. Group 1 animals (n = 8) received increasing Fio2 (40%, 60%, and 100%) for time intervals of 15 minutes returning to atmospheric air between each level of Fio2. In group 2 (n = 8), the effects of Fio2 40% maintained over 75 minutes were studied. In both groups, pulmonary vasodilatation from inhaled nitric oxide (40 parts per million) was used as a positive control.

MEASUREMENTS AND MAIN RESULTS

Effects were evaluated by biventricular pressure-volume loop recordings, right heart catheterization, and arterial and mixed venous blood gasses. Pulmonary embolism increased mean pulmonary arterial pressure from 15 ± 4 to 33 ± 6 mm Hg (p = 0.0002) and caused right ventricle dysfunction (p < 0.05) with troponin release (p < 0.0001). In group 1, increasing Fio2 lowered mean pulmonary arterial pressure (p < 0.0001) and pulmonary vascular resistance (p = 0.0056) and decreased right ventricle volumes (p = 0.0018) and right ventricle mechanical work (p = 0.034). Oxygenation was improved and pulmonary shunt was lowered (p < 0.0001). Maximal hemodynamic effects were seen at Fio2 40% with no additional benefit from higher fractions of oxygen. In group 2, the effects of Fio2 40% were persistent over 75 minutes. Supplemental oxygen showed the same pulmonary vasodilator efficacy as inhaled nitric oxide (40 parts per million). No adverse effects were observed.

CONCLUSIONS

In a porcine model mimicking intermediate-high risk pulmonary embolism, oxygen therapy reduced right ventricle afterload and lowered right ventricle mechanical work. The effects were immediately present and persistent and were similar to inhaled nitric oxide. The intervention is easy and safe. The study motivates extended clinical evaluation of supplemental oxygen in acute pulmonary embolism.

Conservative oxygen supplementation versus usual oxygen supplementation among septic medical intensive care units patients: A before-after investigation

Patients admitted in the intensive care unit (ICU) are always managed with excessive high fraction of inspired oxygen and have hyperoxia for a significant period of time, which has potential harms. The guidelines for the management of patients in ICUs do not provide the target values for partial pressure of oxygen or arterial oxyhemoglobin saturations. The study was a before-after investigation comparing two time periods in which different oxygenation strategies were applied. Data of oxygen control, outcome measures, and mortality of a total of 273 patients (>18 years) admitted at least for 2 days in ICUs and received treatment for the sepsis were retrospectively collected and analyzed. Patients were received usual oxygen supplementation (targeted partial pressure of oxygen: 150 mmHg; a high fraction of inspired oxygen: 0.4; UOS cohort; n = 142) or conservative oxygen supplementation (targeted partial pressure of oxygen: 70-100 mmHg; a high fraction of inspired oxygen as low as possible; COS cohort; n = 131). Mechanical ventilation-free hours were significantly higher for patients of COS cohort than those of UOS cohort (77.99 ± 21.26 h/patient vs 70.01 ± 23.57 h/patient, p = 0.016). ICUs length of stays of patients of COS cohort was fewer than those of UOS cohort (7.05 ± 2.13 days/patient vs 7.69 ± 2.43 days/patients, p = 0.016). The probability of survival of patients was higher among patients of COS cohort than those of UOS cohort (p = 0.049). A higher number of patients from UOS cohort needed vasopressors than those from COS cohort (55 vs 35, p = 0.039). Conservative oxygen supplementation to maintain partial pressure of oxygen was improved outcome measures and decreases mortality as compared to that of usual oxygen supplementation.Level of Evidence: III.Technical Efficacy Stage: 4.

Effects of perioperative oxygen concentration on oxidative stress in adult surgical patients: a systematic review

BACKGROUND

The fraction of inspired oxygen (FiO2) administered during general anaesthesia varies widely despite international recommendations to administer FiO2 0.8 to all anaesthetised patients to reduce surgical site infections (SSIs). Anaesthetists remain concerned that high FiO2 administration intraoperatively may increase harm, possibly through increased oxidative damage and inflammation, resulting in more complications and worse outcomes. In previous systematic reviews associations between FiO2 and SSIs have been inconsistent, but none have examined how FiO2 affects perioperative oxidative stress. We aimed to address this uncertainty by reviewing the available literature.

METHODS

EMBASE, MEDLINE, and Cochrane databases were searched from inception to March 9, 2020 for RCTs comparing higher with lower perioperative FiO2 and quantifying oxidative stress in adults undergoing noncardiac surgery. Candidate studies were independently screened by two reviewers and references hand-searched. Methodological quality was assessed using the Cochrane Collaboration Risk of Bias tool.

RESULTS

From 19 438 initial results, seven trials (n=422) were included. Four studies reported markers of oxidative stress during Caesarean section (n=328) and three reported oxidative stress during elective colon surgery (n=94). Risk of bias was low (four studies) to moderate (three studies). Pooled results suggested high FiO2 was associated with greater malondialdehyde, protein-carbonyl concentrations and reduced xanthine oxidase concentrations, together with reduced antioxidant markers such as superoxide dismutase and total sulfhydryl levels although total antioxidant status was unchanged.

CONCLUSIONS

Higher FiO2 may be associated with elevated oxidative stress during surgery. However, limited studies have specifically reported biomarkers of oxidation. Given the current clinical controversy concerning perioperative oxygen therapy, further research is urgently needed in this area.

The oxygen cascade in patients treated with hemodialysis and native high-altitude dwellers: lessons from extreme physiology to benefit patients with end-stage renal disease

Patients treated with hemodialysis (HD) repeatedly undergo intradialytic low arterial oxygen saturation and low central venous oxygen saturation, reflecting an imbalance between upper body systemic oxygen supply and demand, which are associated with increased mortality. Abnormalities along the entire oxygen cascade, with impaired diffusive and convective oxygen transport, contribute to the reduced tissue oxygen supply. HD treatment impairs pulmonary gas exchange and reduces ventilatory drive, whereas ultrafiltration can reduce tissue perfusion due to a decline in cardiac output. In addition to these factors, capillary rarefaction and reduced mitochondrial efficacy can further affect the balance between cellular oxygen supply and demand. Whereas it has been convincingly demonstrated that a reduced perfusion of heart and brain during HD contributes to organ damage, the significance of systemic hypoxia remains uncertain, although it may contribute to oxidative stress, systemic inflammation, and accelerated senescence. These abnormalities along the oxygen cascade of patients treated with HD appear to be diametrically opposite to the situation in Tibetan highlanders and Sherpa, whose physiology adapted to the inescapable hypobaric hypoxia of their living environment over many generations. Their adaptation includes pulmonary, vascular, and metabolic alterations with enhanced capillary density, nitric oxide production, and mitochondrial efficacy without oxidative stress. Improving the tissue oxygen supply in patients treated with HD depends primarily on preventing hemodynamic instability by increasing dialysis time/frequency or prescribing cool dialysis. Whether dietary or pharmacological interventions, such as the administration of L-arginine, fermented food, nitrate, nuclear factor erythroid 2-related factor 2 agonists, or prolyl hydroxylase 2 inhibitors, improve clinical outcome in patients treated with HD warrants future research.

Automatic oxygen administration and weaning in patients following mechanical ventilation

PURPOSE

To evaluate efficacy of FreeO2 device in oxygen weaning of patients after being liberated from mechanical ventilation (MV).

METHODS

Prospective crossover cohort study in patients admitted to ICU and after MV weaning. FreeO2 curves were recorded during constant flow and FreeO2 modes. Oxygenation parameters and O2 consumption were assessed.

RESULTS

Fifty one records were obtained in 51 patients (median age, 62 years, 54.9% had COPD, admission for acute respiratory failure in 96%). NIV was used initially in 68.6%. For a median records duration of 2.04 h, the time spent within target SpO2 range was significantly higher with FreeO2 mode compared to constant O2 flow mode [86.92% (77.11-92.39) vs 43.17% (5.08-75.37); p < 0.001]. Time with hyperoxia was lower with FreeO2 mode: 8.68% (2.96-15.59) vs 38.28% (2.02-86.34). Times with hypoxaemia, and with severe desaturation, were similar. At the end of FreeO2 mode, O2 flow was lower than 1 l/min in 28 patients (54.9%), with a median of 0.99 l/min.

CONCLUSIONS

For the purpose of oxygen weaning in patients recovering from MV, automatic O2 titration with FreeO2 was associated with a substantial reduction in O2 delivery and better oxygenation parameters in comparison with constant O2 flow.

Human adaptation to hypoxia in critical illness

The syndrome of critical illness is a complex physiological stressor that can be triggered by diverse pathologies. It is widely believed that organ dysfunction and death result from bioenergetic failure caused by inadequate cellular oxygen supply. Teleologically, life has evolved to survive in the face of stressors by undergoing a suite of adaptive changes. Adaptation not only comprises alterations in systemic physiology but also involves molecular reprogramming within cells. The concept of cellular adaptation in critically ill patients is a matter of contention in part because medical interventions mask underlying physiology, creating the artificial construct of "chronic critical illness," without which death would be imminent. Thus far, the intensive care armamentarium has not targeted cellular metabolism to preserve a temporary equilibrium but instead attempts to normalize global oxygen and substrate delivery. Here, we review adaptations to hypoxia that have been demonstrated in cellular models and in human conditions associated with hypoxia, including the hypobaric hypoxia of high altitude, the intrauterine low-oxygen environment, and adult myocardial hibernation. Common features include upregulation of glycolytic ATP production, enhancement of respiratory efficiency, downregulation of mitochondrial density, and suppression of energy-consuming processes. We argue that these innate cellular adaptations to hypoxia represent potential avenues for intervention that have thus far remained untapped by intensive care medicine.

Oxygen therapy practices in the acutely ill medical patients: A social media-based nationwide study of clinicians’ preferences and summary of current recommendations

Oxygen is the most commonly used drug in emergency medicine. The aim of this study was to identify healthcare professionals’ preferences regarding oxygen therapy in common medical emergencies. An online 9-part-questionnaire was distributed through Facebook to doctors and nurses working in Greek hospitals. The questionnaire included background information of the respondents and addressed individual preferences regarding best oxygenation parameter and oxygen targets in specific acute settings. We received 678 responses and we included 663 in our analysis. We found significant differences between doctors’ and nurses’ attitudes towards oxygenation targets in ARDS, sepsis, acute coronary syndrome, and post cardiac-arrest patients. Nurses preferred a more conservative oxygen strategy compared to doctors. Furthermore, nurses favor SaO2 as the best oxygenation parameter, while doctors prefer PaO2. In our survey, the type of hospital and department of the respondents did not affect the preferred oxygen strategy. Social media-based survey research is feasible and effective. In this single country study, doctors showed a tendency to liberally administer oxygen in acutely ill medical patients. On the other hand, Greek nurses preferred a more conservative approach.

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.

Hypoxia-inducible factors in metabolic reprogramming during sepsis

Sepsis is a highly heterogeneous syndrome that is caused by an imbalanced host response to infection. Despite huge investments, sepsis remains a contemporary threat with significant burden on health systems. Vascular dysfunction and elevated oxygen consumption by highly metabolically active immune cells result in tissue hypoxia during inflammation. The transcription factor hypoxia-inducible factor-1a (HIF1α), and its family members, plays an important role in cellular metabolism and adaptation to cellular stress caused by hypoxia. In this review, we discuss the role of HIF in sepsis. We show possible mechanisms by which the inflammatory response activated during sepsis affects the HIF pathway. The activated HIF pathway in turn changes the metabolism of both innate and adaptive immune cells. As HIF expression in leukocytes of septic patients can be directly linked with mortality, we discuss multiple ways of interfering with the HIF signaling pathway.

Effects of the duration of postresuscitation hyperoxic ventilation on neurological outcome and survival in an asphyxial cardiac arrest rat model

Cardiac arrest leads to sudden cessation of oxygen supply and cerebral hypoxia occurs when there is not sufficient oxygen supplied to the brain. Current Guidelines for adult cardiopulmonary resuscitation (CPR) and emergency cardiovascular care recommend the use of 100% oxygen during resuscitative efforts to maximize the probability of achieving the return of spontaneous circulation (ROSC). However, the optimal strategy for oxygen management after ROSC is still debatable. The aim of the present study was to evaluate the effects of the duration of post-resuscitation hyperoxic ventilation on neurological outcomes in asphyxial cardiac arrest rats treated with targeted temperature management (TTM). Asphyxia was induced by blocking the endotracheal tube in 80 adult male Sprague-Dawley rats. CPR begun after 7 min of untreated cardiac arrest. Animals were randomized to either the normoxic control under normothermia (NNC) group or to one of the 4 experimental groups (n = 16 each) immediately after ROSC: ventilated with 100% oxygen for 0 (O₂_0h), 1 (O₂_1h), 3 (O₂_3h), or 5 (O₂_5h) h and ventilated with room air thereafter under TTM. Physiological variables were recorded at baseline and during the 6 h postresuscitation monitoring period. Animals were closely observed for 96 h to assess neurologic recovery and survival. There were no significant differences in baseline measurements between groups, and all animals were successfully resuscitated. There were significant interactions between the duration of 100% oxygen administration and hemodynamics as well as, myocardial and cerebral injuries. Among all the durations of hyperoxic ventilation investigated, significantly lower neurological deficit scores and higher survival rates were observed in the O₂_3h group than in the NNC group. In conclusion, postresuscitation hyperoxic ventilation leads to improved PaO₂, PaCO₂, hemodynamic, myocardial and cerebral recovery in asphyxial cardiac arrest rats treated with TTM. However, the beneficial effects of high concentration-oxygen are duration dependent and ventilation with 100% oxygen during induced hypothermia contributes to improved neurological recovery and survival after 96 h.