The effect of conservative oxygen therapy on systemic biomarkers of oxidative stress in critically ill patients

Hyperoxia in critically ill patients with sepsis and septic shock: a systematic review

BACKGROUND

In septic patients, hyperoxia may help with its bactericidal effects, but it may cause systemic impairments. The role of hyperoxia and the appropriate oxygen target in these patients is unknown. The aim of this systematic review was to summarize the available literature.

METHODS

We conducted a systematic search screening PubMed and Cochrane Library. Studies on adult patients with sepsis or septic shock and admitted to ICU addressing the topic of hyperoxia were included and described.

RESULTS

We included 12 studies, for a total of 15.782 included patients. Five studies were randomized controlled trials (RCTs) or analyses from RCTs, three were prospective observational studies, and four were retrospective observational studies. The definition of hyperoxia was heterogeneous across the included studies. Mortality was the most frequent outcome: six studies showed an increased rate or risk of mortality with hyperoxia, three found no differences, and one a protective effect of hyperoxia. At the critical appraisal assessment stage, no major methodological flaws were detected, except for a single-center, pilot study, with a lack of adjustment for confounders and imbalance between the groups.

CONCLUSION

The optimum range of oxygen level able to minimize risks and provide benefits in patients with sepsis or septic shock seems still unknown. Clinical equipoise between hyperoxia and normoxia is uncertain as conflicting evidence exists. Further studies should aim at identifying the best range of oxygenation and its optimal duration, investigating how effects of different levels of oxygen may vary according to identified pathogens, source of infection, and prescribed antibiotics in critically ill patients with sepsis and septic shock.

Randomization to a Liberal Versus Conservative Oxygenation Target: Redox Responses in Critically Ill Children

RATIONALE

Optimal systemic oxygenation targets in pediatric critical illness are unknown. A U-shaped relationship exists between blood oxygen levels and PICU mortality. Redox stress or iatrogenic injury from intensive treatments are potential mechanisms of harm from hyperoxia.

OBJECTIVES

To measure biomarkers of oxidative status in children admitted to PICU and randomized to conservative (oxygen-hemoglobin saturation [Sp o2 ] 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation targets.

DESIGN

Mechanistic substudy nested within the Oxygen in PICU (Oxy-PICU) pilot randomized feasibility clinical trial ( ClinicalTrials.gov : NCT03040570).

SETTING

Three U.K. mixed medical and surgical PICUs in university hospitals.

PATIENTS

Seventy-five eligible patients randomized to the Oxy-PICU randomized feasibility clinical trial.

INTERVENTIONS

Randomization to a conservative (Sp o2 88-92%) versus liberal (Sp o2 > 94%) peripheral oxygenation target.

MEASUREMENTS AND MAIN RESULTS

Blood and urine samples were collected at two timepoints: less than 24 hours and up to 72 hours from randomization in trial participants (March 2017 to July 2017). Plasma was analyzed for markers of ischemic/oxidative response, namely thiobarbituric acid-reactive substances (TBARS; lipid peroxidation marker) and ischemia-modified albumin (protein oxidation marker). Total urinary nitrate/nitrite was measured as a marker of reactive oxygen and nitrogen species (RONS). Blood hypoxia-inducible factor (HIF)-1a messenger RNA (mRNA) expression (hypoxia response gene) was measured by reverse transcription- polymerase chain reaction. Total urinary nitrate/nitrite levels were greater in the liberal compared with conservative oxygenation group at 72 hours (median difference 32.6 μmol/mmol of creatinine [95% CI 13.7-93.6]; p < 0.002, Mann-Whitney test). HIF-1a mRNA expression was increased in the conservative group compared with liberal in less than 24-hour samples (6.0-fold [95% CI 1.3-24.0]; p = 0.032). There were no significant differences in TBARS or ischemia-modified albumin.

CONCLUSIONS

On comparing liberal with conservative oxygenation targets, we show, first, significant redox response (increase in urinary markers of RONS), but no changes in markers of lipid or protein oxidation. We also show what appears to be an early hypoxic response (increase in HIF-1a gene expression) in subjects exposed to conservative rather than liberal oxygenation targets.

Conservative oxygen supplementation during Helmet CPAP therapy in patients with COVID-19 and respiratory failure: A pilot study

Background

Respiratory failure is a severe complication in COVID-19 pneumonia that, in addition to oxygen therapy, may require CPAP support. It has been postulated that COVID-19 lung injury may share some features with those observed in HALI. Thus, a correct target PaO2during oxygen supplementation may be crucial to protect the lung from further tissue damage. Aims of the study were: 1) to evaluate the effects of conservative oxygen supplementation during Helmet CPAP therapy on mortality and ICU admission in patients with COVID-19 and respiratory failure; 2) to evaluate the effect of conservative oxygen supplementation on new-onset organ failure and secondary pulmonary infections.

Methods

This was a single-center, historically controlled study of patients with severe respiratory failure due to COVID-19 pneumonia, receiving either conservative or non-conservative oxygen supplementation during Helmet CPAP. A cohort receiving conservative oxygen supplementation was studied prospectively in which oxygen supplementation was administered with a target PaO2<100 mmHg. Results of this cohort were compared with those of a cohort who had received liberal oxygen supplementation.

Results

Seventy-one patients were included in the conservative cohort and 75 in the non-conservative cohort. Mortality rate was lower in the conservative cohort (22.5%versus62.7%, p<0.001). Rates of ICU admission and new-onset rate organ failure were lower in conservative cohort (14.1%versus37.3%, p=0.001, and 9.9%versus45.3% p<0.001, respectively).

Conclusions

In patients with COVID-19 and severe respiratory failure, conservative oxygen supplementation during Helmet CPAP was associated to improved survival, lower ICU admission rate and less new-onset organ failure.

Critically ill septic patients have elevated oxidative stress biomarkers: lack of attenuation by parenteral vitamin C

Patients with septic shock are under an intense inflammatory burden, which is closely associated with increased oxidative stress and depletion of antioxidants such as vitamin C. We hypothesized that patients with septic shock would present with elevated oxidative stress (assessed as F₂-isoprostanes) and that administration of parenteral vitamin C to these patients would attenuate F₂-isoprostane concentrations. We recruited 40 critically ill patients with septic shock into a randomized placebo-controlled trial and assessed the effect of short-term (4-day) parenteral vitamin C administration (100 mg/kg/d) on 8-isoprostane F_2α concentrations, which were measured using enzyme-linked immunosorbent assays. Sources of sepsis and intensive care unit severity scores were recorded. Smokers (n = 20) and nonsmoking controls (n = 50) were assessed for comparison. The median baseline 8-isoprostane F_2α concentration in the septic patients was 3.95 (interquartile range [Q1, Q3] 2.1, 6.63) ng/mg creatinine; this was higher than smokers 1.61 [1.25, 2.82] P = .007 ng/mg creatinine; P = .005) and nonsmoking controls 1.12 [0.76, 1.57] ng/mg creatinine; P < .0001). The 8-isoprostane F_2α concentrations in the placebo group did not vary significantly over the duration of the study. Although parenteral vitamin C administration significantly increased the vitamin C status of the patients within 24 hours, this did not affect their 8-isoprostane F_2α concentrations. In conclusion, patients with septic shock have elevated 8-isoprostane F_2α excretion, which short-term parenteral vitamin C administration is unable to attenuate. If vitamin C is to work by antioxidant mechanisms, then early administration, before the development of shock, may be required. This trial was registered at anzctr.org.au (ACTRN12617001184369).

Vitamins C and D and COVID-19 Susceptibility, Severity and Progression: An Evidence Based Systematic Review

Background and Objectives: Starting in early December 2019, the novel Coronavirus Disease (COVID-19) from infection with COVID-19 has caused a global pandemic. Many aspects of its pathogenesis and related clinical consequences are still unclear. Early diagnosis and dynamic monitoring of prognostic factors are essential to improve the ability to manage COVID-19 infection. This study aimed to provide an account of the role played by vitamins C and D on the onset, progression and severity of COVID-19. Clinical features and infection-related risk factors are also briefly discussed. Material and Methods: In March 2022, the main online databases were accessed. All the articles that investigate the possible role of vitamins C and D on COVID-19 susceptibility, severity and progression were considered. Results: The current evidence on vitamin C and D supplementation in patients with COVID-19 infection is inconsistent and controversial. In some studies, vitamins were used as coadjuvant of a formal experimental therapy, while in others as main treatment. Ethnicity and hospital setting (inpatient/outpatient) were also variable. Moreover, there was no consensus between studies in administration protocol: high heterogeneity in dosage, administration, and duration of the treatment were evident. Finally, some studies administered vitamins pre- and/or during COVID infection, in patients with different risk factors and infection severity. Conclusions: While waiting to develop a targeted, safe and effective therapy, it is important to investigate individual predisposition and proper disease management. Concluding, available data on the use of nutraceuticals in COVID-19 are inconsistent. However, there is a lack of evidence-based guidelines which recommend vitamin C and D supplementation in patients with COVID-19, and results from high quality randomised controlled trials (RCTs) are inconsistent. Current investigations so far are mostly observational, and include a relatively small sample size which can lead to biased results. Large-scale multicentre studies are therefore needed.

Circulating protein carbonyls are specifically elevated in critically ill patients with pneumonia relative to other sources of sepsis

BACKGROUND

Septic shock is a life-threatening dysregulated response to severe infection and is associated with elevated oxidative stress. We aimed to assess protein carbonyls in critically ill patients with different sources of sepsis and determine the effect of vitamin C intervention on protein carbonyl concentrations.

METHODS

Critically ill patients with septic shock (n = 40) were recruited, and sources of sepsis and ICU severity scores were recorded. The patients were randomised to receive either intravenous vitamin C (100 mg/kg body weight/day) or placebo infusions. Blood samples were collected at baseline and daily for up to three days for measurement of cell counts, vitamin C concentrations, protein carbonyls, C-reactive protein, and myeloperoxidase concentrations.

RESULTS

Protein carbonyl concentrations increased 2.2-fold in the cohort over the duration of the study (from 169 to 369 pmol/mg protein; p = 0.03). There were significant correlations between protein carbonyl concentrations and ICU severity scores (APACHE III r = 0.47 and SOFA r = 0.37; p < 0.05) at baseline. At study admission, the patients with pneumonia had nearly 3-fold higher protein carbonyl concentrations relative to the patients with other sources of sepsis (435 vs 157 pmol/mg protein, p < 0.0001). The septic patients had deficient vitamin C status at baseline (9.8 ± 1.4 μmol/L). This increased to 456 ± 90 μmol/L following three days of intravenous vitamin C intervention. Vitamin C intervention did not attenuate the increase in protein carbonyl concentrations.

CONCLUSIONS

Circulating protein carbonyls are specifically elevated in critically ill patients with pneumonia relative to other sources of sepsis. The reasons for this are currently unclear and may indicate a mechanism unique to pulmonary sources of sepsis. Intravenous vitamin C administration did not attenuate the increase in protein carbonyls over time.

Plasma Ascorbic Acid Levels in Critically Ill Pediatric Patients

Ascorbic acid, or vitamin C, is a physiological antioxidant that has been found to be deficient in critically ill adults with sepsis and acute respiratory distress system. In adults, ascorbic acid supplementation has been shown to reduce the need for vasopressors and mechanical ventilation. This study aimed to describe the prevalence of ascorbic acid deficiency in critically ill pediatric patients. This prospective, single-centered study analyzed 34 patients aged 1 month to 18 years old with septic shock and/or acute respiratory failure requiring mechanical ventilation in a quaternary, urban, pediatric intensive care unit. Plasma ascorbic acid levels were measured by high-performance liquid chromatography within 24 hours of meeting eligibility criteria. The median level was 23.34 µM (IQR [11.45, 39.14]). Twenty-three patients had repeat samples that were collected 3 to 5 days later. The median for repeat samples was higher at 42.41 µM (IQR [13.08, 62.43]). Patients who were enterally fed had significantly higher levels than those who were not (62.4 ± 7.7 µM vs. 32.4 ± 7.1 µM; p = 0.03). Ascorbic acid levels vary widely among critically ill children with septic shock and/or respiratory failure requiring mechanical ventilation, but one-half of our patients had deficient levels that are typically seen in scurvy. Further studies are warranted to investigate the significance of low levels as well as the impact of normalizing levels through nutritional support.

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.

Perioperative supplemental oxygen and oxidative stress in patients undergoing moderate- to high-risk major abdominal surgery - A subanalysis of randomized clinical trial

STUDY OBJECTIVE

Oxidative stress plays a pivotal role in the development and aggravation of cardiovascular diseases. The influence of intraoperative inspired oxygen concentrations on oxidative stress is still not entirely known. Therefore, we evaluated in this sub-study if supplemental oxygen affects the oxidation-reduction potential in patients at-risk for cardiovascular complications undergoing moderate- to high-risk major abdominal surgery.

DESIGN

Sub-study of a prospective parallel-arm double-blinded single-center superiority randomized trial.

SETTING

Operating room and postoperative recovery area.

INTERVENTION

Administration of 0.8 FiO₂ versus 0.3 FiO₂ throughout surgery and for the first two postoperative hours.

MEASUREMENTS

The primary outcome was the static oxidation-reduction potential (sORP) and the oxidation-reduction potential capacity (cORP) between both groups. The secondary outcome was the trend of sORP and cORP in the overall study population. We assessed sORP and cORP before induction of anesthesia, 2 h after induction of anesthesia, within 2 h after surgery and on the first and third postoperative day.

MAIN RESULTS

258 patients were analyzed. 128 patients were randomly assigned to the 80% oxygen group and 130 patients were randomly assigned to the 30% oxygen group. Postoperative sORP values did not differ significantly between the 80% and 30% oxygen group (effect estimate: -1.162 mV,95% CI: -2.584 to 0.260; p = 0.109). On average, we observed a change in sORP of 5.288 mV (95% CI:4.633 to 5.913, p < 0.001) per day. cORP values did not differ significantly between the 80% and 30% oxygen group (effect estimate: -0.015μC, (95%CI: -0.062 to 0.032; p = 0.524). On average, we observed a change in cORP values of -0.170μC (95%CI: -0.194 to -0.147, p < 0.001) per day.

CONCLUSION

In contrast to previous reports, we could not find any evidence of an association between intraoperative supplemental oxygen and perioperative oxidative stress assessed by sORP and cORP.

TRIAL REGISTRATION

clinicaltrials.gov: NCT03366857https://clinicaltrials.gov/ct2/show/NCT03366857?term=vienna&cond=oxygen&draw=2&rank=1.

Neutrophils Isolated from Septic Patients Exhibit Elevated Uptake of Vitamin C and Normal Intracellular Concentrations despite a Low Vitamin C Milieu

Vitamin C (ascorbate) plays an important role in neutrophil function and is accumulated by the cells either directly via vitamin C transporters (SVCT) or indirectly following oxidation to dehydroascorbic acid. Septic patients are known to have significantly depleted plasma ascorbate status, but little is known about the ascorbate content of their circulating cells. Therefore, we assessed the ascorbate concentrations of plasma, leukocytes and erythrocytes from septic patients and compared these to healthy controls. Non-fasting blood samples were collected from healthy volunteers (n = 20) and critically ill patients with sepsis (n = 18). The ascorbate content of the plasma and isolated neutrophils and erythrocytes was measured using HPLC and plasma myeloperoxidase concentrations were determined using ELISA. Ex vivo uptake of ascorbate and dehydroascorbic acid by neutrophils from septic patients was also assessed. Neutrophils isolated from septic patients had comparable intracellular ascorbate content to healthy volunteers (0.33 vs. 0.35 nmol/10⁶ cells, p > 0.05), despite significantly lower plasma concentrations than the healthy controls (14 vs. 88 µmol/L, p < 0.001). In contrast, erythrocytes from septic patients had significantly lower intracellular ascorbate content than healthy controls (30 vs. 69 µmol/L, p = 0.002), although this was 2.2-fold higher than the matched plasma concentrations in the patients (p = 0.008). Higher concentrations of myeloperoxidase, a source of reactive oxygen species, were observed in the septic patients relative to healthy controls (194 vs. 14 mg/mL, p < 0.0001). In contrast to neutrophils from healthy volunteers, the neutrophils from septic patients demonstrated elevated uptake of extracellular ascorbate. Overall, neutrophils from septic patients exhibited comparable intracellular ascorbate content to those from healthy controls, despite the patients presenting with hypovitaminosis C. The mechanisms involved are currently uncertain, but could include increased generation of dehydroascorbic acid in septic patients, enhanced basal activation of their neutrophils or upregulation of their vitamin C transporters.

Oxygen therapy for critically Ill and post-operative patients

Nearly all patients receiving treatment in a peri-operative or intensive care setting receive supplemental oxygen therapy. It is biologically plausible that the dose of oxygen used might affect important patient outcomes. Most peri-operative research has focussed on oxygen regimens that target higher than normal blood oxygen levels. Whereas, intensive care research has mostly focussed on conservative oxygen regimens which assiduously avoid exposure to higher than normal blood oxygen levels. While such conservative oxygen therapy is preferred for spontaneously breathing patients with chronic obstructive pulmonary disease, the optimal oxygen regimen in other patient groups is not clear. Some data suggest that conservative oxygen therapy might be preferred for patients with hypoxic ischaemic encephalopathy. However, unless oxygen supplies are constrained, routinely aggressively down-titrating oxygen in either the peri-operative or intensive care setting is not necessary based on available data. Targeting higher than normal levels of oxygen might reduce surgical site infections in the perioperative setting and/or improve outcomes for intensive care patients with sepsis but further research is required and available data are not sufficiently strong to warrant routine implementation of such oxygen strategies.

The Emerging Role of Vitamin C in the Prevention and Treatment of COVID-19

Investigation into the role of vitamin C in the prevention and treatment of pneumonia and sepsis has been underway for many decades. This research has laid a strong foundation for translation of these findings into patients with severe coronavirus disease (COVID-19). Research has indicated that patients with pneumonia and sepsis have low vitamin C status and elevated oxidative stress. Administration of vitamin C to patients with pneumonia can decrease the severity and duration of the disease. Critically ill patients with sepsis require intravenous administration of gram amounts of the vitamin to normalize plasma levels, an intervention that some studies suggest reduces mortality. The vitamin has pleiotropic physiological functions, many of which are relevant to COVID-19. These include its antioxidant, anti-inflammatory, antithrombotic and immuno-modulatory functions. Preliminary observational studies indicate low vitamin C status in critically ill patients with COVID-19. There are currently a number of randomized controlled trials (RCTs) registered globally that are assessing intravenous vitamin C monotherapy in patients with COVID-19. Since hypovitaminosis C and deficiency are common in low-middle-income settings, and many of the risk factors for vitamin C deficiency overlap with COVID-19 risk factors, it is possible that trials carried out in populations with chronic hypovitaminosis C may show greater efficacy. This is particularly relevant for the global research effort since COVID-19 is disproportionately affecting low-middle-income countries and low-income groups globally. One small trial from China has finished early and the findings are currently under peer review. There was significantly decreased mortality in the more severely ill patients who received vitamin C intervention. The upcoming findings from the larger RCTs currently underway will provide more definitive evidence. Optimization of the intervention protocols in future trials, e.g., earlier and sustained administration, is warranted to potentially improve its efficacy. Due to the excellent safety profile, low cost, and potential for rapid upscaling of production, administration of vitamin C to patients with hypovitaminosis C and severe respiratory infections, e.g., COVID-19, appears warranted.

Patients Undergoing Myeloablative Chemotherapy and Hematopoietic Stem Cell Transplantation Exhibit Depleted Vitamin C Status in Association with Febrile Neutropenia

Patients undergoing myeloablative chemotherapy and hematopoietic stem cell transplantation (HSCT) experience profound neutropenia and vulnerability to infection. Previous research has indicated that patients with infections have depleted vitamin C status. In this study, we recruited 38 patients with hematopoietic cancer who were undergoing conditioning chemotherapy and HSCT. Blood samples were collected prior to transplantation, at one week, two weeks and four weeks following transplantation. Vitamin C status and biomarkers of inflammation (C-reactive protein) and oxidative stress (protein carbonyls and thiobarbituric acid reactive substances) were assessed in association with febrile neutropenia. The vitamin C status of the study participants decreased from 44 ± 7 µmol/L to 29 ± 5 µmol/L by week one (p = 0.001) and 19 ± 6 µmol/L by week two (p < 0.001), by which time all of the participants had undergone a febrile episode. By week four, vitamin C status had increased to 37 ± 10 µmol/L (p = 0.1). Pre-transplantation, the cohort comprised 19% with hypovitaminosis C (i.e., <23 µmol/L) and 8% with deficiency (i.e., <11 µmol/L). At week one, those with hypovitaminosis C had increased to 38%, and at week two, 72% had hypovitaminosis C, and 34% had outright deficiency. C-reactive protein concentrations increased from 3.5 ± 1.8 mg/L to 20 ± 11 mg/L at week one (p = 0.002), and 119 ± 25 mg/L at week two (p < 0.001), corresponding to the development of febrile neutropenia in the patients. By week four, these values had dropped to 17 ± 8 mg/L (p < 0.001). There was a significant inverse correlation between C-reactive protein concentrations and vitamin C status (r = -0.424, p < 0.001). Lipid oxidation (thiobarbituric acid reactive substances (TBARS)) increased significantly from 2.0 ± 0.3 µmol/L at baseline to 3.3 ± 0.6 µmol/L by week one (p < 0.001), and remained elevated at week two (p = 0.003), returning to baseline concentrations by week four (p = 0.3). Overall, the lowest mean vitamin C values (recorded at week two) corresponded with the highest mean C-reactive protein values and lowest mean neutrophil counts. Thus, depleted vitamin C status in the HSCT patients coincides with febrile neutropenia and elevated inflammation and oxidative stress.