Oxygen: kill or cure? Prehospital hyperoxia in the COPD patient

NLRX1 knockdown attenuates pro-apoptotic signaling and cell death in pulmonary hyperoxic acute injury

Hyperoxia is frequently used for treating acute respiratory failure, but it can cause acute lung injury. Nucleotide-binding domain and leucine-rich-repeat-containing family member X1 (NLRX1) is localized in mitochondria and involved in production of reactive oxygen species, inflammation, and apoptosis, which are the features of hyperoxic acute lung injury (HALI). The contribution of NLRX1 to HALI has not previously been addressed. Thus, to investigate the role of NLRX1 in hyperoxia, we generated a murine model of HALI in wild-type (WT) and NLRX1^-/- mice by exposure to > 95% oxygen for 72 h. As a result, NLRX1 expression was elevated in mice exposed to hyperoxia. In acute lung injury, levels of inflammatory cells, protein leakage, cell cytotoxicity, and pro-inflammatory cytokines were diminished in NLRX1^-/- mice compared to WT mice. In a survival test, NLRX1^-/- mice showed reduced mortality under hyperoxic conditions, and apoptotic cell death and caspase expression and activity were also lower in NLRX1^-/- mice. Furthermore, levels of the MAPK signaling proteins ERK 1/2, JNK, and p38 were decreased in NLRX1-deficient mice than in WT mice exposed to hyperoxia. The study shows that a genetic deficit in NLRX1 can suppress hyperoxia-induced apoptosis, suggesting that NLRX1 acts as a pivotal regulator of HALI.

Oxygen-induced hypercapnia: physiological mechanisms and clinical implications

Oxygen is probably the most commonly prescribed drug in the emergency setting and is a life-saving modality as well. However, like any other drug, oxygen therapy may also lead to various adverse effects. Patients with chronic obstructive pulmonary disease (COPD) may develop hypercapnia during supplemental oxygen therapy, particularly if uncontrolled. The risk of hypercapnia is not restricted to COPD only; it has also been reported in patients with morbid obesity, asthma, cystic fibrosis, chest wall skeletal deformities, bronchiectasis, chest wall deformities, or neuromuscular disorders. However, the risk of hypercapnia should not be a deterrent to oxygen therapy in hypoxemic patients with chronic lung diseases, as hypoxemia may lead to life-threatening cardiovascular complications. Various mechanisms leading to the development of oxygen-induced hypercapnia are the abolition of ‘hypoxic drive’, loss of hypoxic vasoconstriction and absorption atelectasis leading to an increase in dead-space ventilation and Haldane effect. The international guideline recommends a target oxygen saturation of 88% to 92% in patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD) and other chronic lung diseases at risk of hypercapnia.  Oxygen should be administered only when oxygen saturation is below 88%. We searched PubMed, EMBASE, and the CINAHL from inception to June 2022. We used the following search terms: “Hypercapnia”, “Oxygen therapy in COPD”, “Oxygen-associated hypercapnia”, “oxygen therapy”, and “Hypoxic drive”. All types of study are selected. This review will focus on the physiological mechanisms of oxygen-induced hypercapnia and its clinical implications.

The effect of 50% oxygen on PtCO2 in patients with stable COPD, bronchiectasis, and neuromuscular disease or kyphoscoliosis: randomised cross-over trials

BACKGROUND

High-concentration oxygen therapy causes increased arterial partial pressure of carbon dioxide (PaCO2) in patients with COPD, asthma, pneumonia, obesity and acute lung injury. The objective of these studies was to investigate whether this physiological response to oxygen therapy occurs in stable patients with neuromuscular disease or kyphoscoliosis, and bronchiectasis.

METHODS

Three randomised cross-over trials recruited stable patients with neuromuscular disease or kyphoscoliosis (n = 20), bronchiectasis (n = 24), and COPD (n = 24). Participants were randomised to receive 50% oxygen and 21% oxygen (air), each for 30 min, in randomly assigned order. The primary outcome was transcutaneous partial pressure of carbon dioxide (PtCO2) at 30 min. The primary analysis was a mixed linear model.

RESULTS

Sixty six of the 68 participants had baseline PtCO2 values < 45 mmHg. The intervention baseline adjusted PtCO2 difference (95% CI) between oxygen and room air after 30 min was 0.2 mmHg (- 0.4 to 0.9), P = 0.40; 0.5 mmHg (- 0.2 to 1.2), P = 0.18; and 1.3 mmHg (0.7 to 1.8), P < 0.001, in the neuromuscular/kyphoscoliosis, bronchiectasis and COPD participants respectively.

CONCLUSIONS

The small increase in PtCO2 in the stable COPD patients with high-concentration oxygen therapy contrasts with the marked increases in PaCO2 seen in the setting of acute exacerbations of COPD. This suggests that the model of studying the effects of high-concentration oxygen therapy in patients with stable respiratory disease is not generalisable to the use of oxygen therapy in the acute clinical setting. Appropriate studies of high-concentration compared to titrated oxygen in acute clinical settings are needed to determine if there is a risk of oxygen-induced hypercapnia in patients with neuromuscular disease, kyphoscoliosis or bronchiectasis.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12615000970549 Registered 16/9/15, ACTRN12615000971538 Registered 16/9/15 and ACTRN12615001056583 Registered 7/10/15.

Oxygen Requirements for Acutely and Critically Ill Patients

Oxygen administration is often assumed to be required for all patients who are acutely or critically ill. However, in many situations, this assumption is not based on evidence. Injured body tissues and cells throughout the body respond both beneficially and adversely to delivery of supplemental oxygen. Available evidence indicates that oxygen administration is not warranted for patients who are not hypoxemic, and hyperoxia may contribute to increased tissue damage and mortality. Nurses must be aware of implications related to oxygen administration for all types of acutely and critically ill patients. These implications include having knowledge of oxygenation processes and pathophysiology; assessing global, tissue, and organ oxygenation status; avoiding either hypoxia or hyperoxia; and creating partnerships with respiratory therapists. Nurses can contribute to patients' oxygen status well-being by being proficient in determining each patient's specific oxygen needs and appropriate oxygen administration.

An audit of change in clinical practice: from oxygen-driven to air-driven nebulisers for prehospital patients with acute exacerbations of chronic obstructive pulmonary disease (AECOPD)

BACKGROUND

In developed countries, ambulances normally carry oxygen cylinders, but not compressed air. Treatment of acute exacerbations of chronic obstructive pulmonary disease (AECOPD) with oxygen-driven nebulisers can result in hypercapnia and acidosis. Attempts to avoid this have involved interrupted administration of oxygen. However, small battery-powered air nebulisers are now available. This study aims to compare the prehospital oxygen saturations and treatment of patients suffering from AECOPD before and after the introduction of air nebulisers.

METHODS

The oxygen saturations and treatment of 200 AECOPD patients before and 200 AECOPD patients after the introduction of air nebulisers were compared. Compliance with a target saturation of 88-92% was calculated.

RESULTS

The median final oxygen saturation was lower for the post-intervention category (94%) than the pre-intervention category (96%). There was an increase in air nebuliser use from 0 to 56% (P < 0.001) and a decrease in oxygen use from 100 to 71.5% (P < 0.001). There was a numerical increase in the proportion of patients arriving at hospital with oxygen saturations of 88-92% following introduction of the air nebulisers (24 vs 16.5%) and a decrease in patients arriving with high saturations (67.5 vs 76.5%). The likelihood of achieving the target oxygen saturations following introduction of air nebulisers increased (odds ratio 1.598; 95% confidence interval 0.974, 2.621).

CONCLUSION

The introduction of prehospital air nebulisers resulted in a reduction in oxygen therapy in patients with AECOPD and a lower median prehospital oxygen saturation. This study supports the use of air nebulisers in the prehospital setting.

Acute oxygen therapy: a review of prescribing and delivery practices

Oxygen is a commonly used drug in the clinical setting and like other drugs its use must be considered carefully. This is particularly true for those patients who are at risk of type II respiratory failure in whom the risk of hypercapnia is well established. In recent times, several international bodies have advocated for the prescription of oxygen therapy in an attempt to reduce this risk in vulnerable patient groups. Despite this guidance, published data have demonstrated that there has been poor uptake of these recommendations. Multiple interventions have been tested to improve concordance, and while some of these interventions show promise, the sustainability of these interventions are less convincing. In this review, we summarize data that have been published on the prevalence of oxygen prescription and the accurate and appropriate administration of this drug therapy. We also identify strategies that have shown promise in facilitating changes to oxygen prescription and delivery practice. There is a clear need to investigate the barriers, facilitators, and attitudes of clinicians in relation to the prescription of oxygen therapy in acute care. Interventions based on these findings then need to be designed and tested to facilitate the application of evidence-based guidelines to support sustained changes in practice, and ultimately improve patient care.

How do health-care professionals perceive oxygen therapy? A critical interpretive synthesis of the literature

Oxygen is one of the commonest health-care interventions worldwide. This might suggest that health-care professionals (HCPs) would be knowledgeable and familiar with its uses and limitations. Yet it is apparent, through clinical audit, that oxygen is probably misunderstood by many HCPs. The aim of this critical interpretive synthesis (CIS) is to explore qualitative and quantitative literature in relation to HCPs beliefs and perceptions of oxygen therapy. A systematic search in Medline, Cinahl, Embase, British Nursing Index and PsychInfo using search terms, such as, oxygen therapy, chronic respiratory disease, HCPs and perceptions yielded 1514 studies of which 12 contained data relevant to the review question. Two reviewers independently screened the articles for eligibility against inclusion and exclusion criteria, and data were selected and synthesized with an integrative and interpretive approach using CIS. This allowed diverse empirical evidence to be synthesized to develop existing and new interpretations of data.Three synthetic constructs were interpreted from the available literature, namely, oxygen for symptom relief, levels of knowledge and understanding and oxygen as a therapy for HCPs. The literature alludes to deep-seated beliefs that exist. In order to enhance practice, these beliefs and cultures need to be challenged. Further research is needed to explore HCPs’ perceptions of oxygen therapy in order to inform the seemingly resistant adoption of evidence based practice in relation to oxygen.

Oxygen therapy: time to move on?

This analysis examines the roots of clinical practice regarding oxygen therapy and finds that some aspects have changed very little over the past 200 years. Oxygen is commonly prescribed and administered as a therapy across all healthcare settings, particularly for the treatment and management of respiratory conditions, both acute and chronic. Yet despite its widespread use and recent advances in understanding and guidance, poor practice and controversies regarding its use persist. This historical analysis highlights origins in practice that may suggest where the roots of these fallacies lie, highlighting potential ambiguities and myths that have permeated clinical and social contexts. It can be considered that based on clinical presumptions and speculation the prolific and injudicious use of oxygen was encouraged and the legacy for today's practice seeded. The conjectures proposed here may enable modern day erroneous beliefs to be confronted and clinical practice to move on.

Recognition of simulated cyanosis by color-vision-normal and color-vision-deficient subjects

There are anecdotal reports that the recognition of cyanosis is difficult for some color-deficient observers. The chromaticity changes of blood with oxygenation in vitro lie close to the dichromatic confusion lines. The chromaticity changes of lips and nail beds measured in vivo are also generally aligned in the same way. Experiments involving visual assessment of cyanosis in vivo are fraught with technical and ethical difficulties A single lower face image of a healthy individual was digitally altered to produce levels of simulated cyanosis. The color change is essentially one of saturation. Some images with other color changes were also included to ensure that there was no propensity to identify those as cyanosed. The images were assessed for reality by a panel of four instructors from the NSW Ambulance Service training section. The images were displayed singly and the observer was required to identify if the person was cyanosed or not. Color normal subjects comprised 32 experienced ambulance officers and 27 new recruits. Twenty-seven color deficient subjects (non-NSW Ambulance Service) were examined. The recruits were less accurate and slower at identifying the cyanosed images and the color vision deficient were less accurate and slower still. The identification of cyanosis is a skill that improves with training and is adversely affected in color deficient observers.

Identifying target audiences: who are the guidelines for? : article 1 in Integrating and coordinating efforts in COPD guideline development. An official ATS/ERS workshop report

BACKGROUND

Professional societies, like many other organizations around the world, have recognized the need to use rigorous processes to ensure that health care recommendations are informed by the best available research evidence. Different clinical practice guidelines addressing the management of the same disease may vary widely in the evidence used and the format of the recommendations, with the result that not all are appropriate for all audiences. This is the first of a series of 14 articles that clinicians, methodologists, and researchers from around the world prepared to advise those developing guidelines in respiratory and other diseases about the potential impact of identifying the target audiences for their clinical practice guidelines.

METHODS

In this review we address the following questions. (1) Which audiences are interested in a chronic obstructive pulmonary disease (COPD) guideline? (2) How many audiences can be addressed in a single COPD guideline? (3) What is the purpose of the guidelines? (4) Who should be included on the guideline panel? We collected information by searching PubMed and reviewing information from groups that are currently making and using respiratory disease guidelines, as well as from workshop discussions. Our conclusions are based on available evidence, consideration of what guideline developers are doing, and the opinions of those who attended the workshop.

RESULTS AND CONCLUSIONS

Clinicians desire COPD and other guidelines that are concise, use evidence from practices similar to theirs, and whose authors have expertise in providing care in similar settings and with similar patients. In the case of COPD, barriers to generalists' use of guidelines include lack of awareness of the guidelines, failure to embrace the diagnostic methods as capable of providing definitive confirmation of COPD, and, most importantly, failure of previous guidelines to address the treatment of COPD in the context of the broad range of multiple morbidities that affect most people with COPD. COPD specialists may require guidelines with more details regarding complex COPD management. The purpose of the guidelines may determine the appropriate audience. Guidelines developed to improve care by enhancing education may have a very different audience than guidelines designed to improve care by limiting the scope of practice, punishing noncompliance, or saving money. The purpose will drive dissemination and implementation strategies, but should not influence the methods used to develop a guideline. Clinicians desire guidelines, but data suggest that the current development systems, content, format, and dissemination strategies may need to be altered to fit these audiences. After the purpose and audience are determined, the guideline committee must decide how to fairly address these audiences, which will usually require seeking their input.

Supplemental oxygen therapy: Important considerations in oral and maxillofacial surgery

The administration of supplemental oxygen is an essential element of appropriate management for a wide range of clinical conditions; crossing different medical and surgical specialities. The present review summarizes the role of supportive oxygen therapy in various clinical conditions encountered in our day-to-day practice in the speciality of oral and maxillofacial surgery; including major trauma, shock, sepsis; perioperative and postoperative considerations and in patients with various other medical comorbidities. Regular and judicious use of oxygen as a drug is thus recommended in our day-to-day practice in oral and maxillofacial surgery to reduce the morbidity and improve the prognosis of patients.

Randomized controlled trial of high concentration oxygen in suspected community-acquired pneumonia

OBJECTIVE

To determine whether high concentration oxygen increases the PaCO(2) in the treatment of community-acquired pneumonia.

DESIGN

Randomized controlled clinical trial in which patients received high concentration oxygen (8 L/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturations between 93 and 95%) for 60 minutes. Transcutaneous CO(2) (PtCO(2)) was measured at 0, 20, 40 and 60 minutes.

SETTING

The Emergency Departments at Wellington, Hutt and Kenepuru Hospitals.

PARTICIPANTS

150 patients with suspected community-acquired pneumonia presenting to the Emergency Department. Patients with chronic obstructive pulmonary disease (COPD) or disorders associated with hypercapnic respiratory failure were excluded.

MAIN OUTCOME VARIABLES

The primary outcome variable was the proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes. Secondary outcome variables included the proportion of patients with a rise in PtCO(2) ≥8 mmHg at 60 minutes.

RESULTS

The proportion of patients with a rise in PtCO(2) ≥4 mmHg at 60 minutes was greater in the high concentration oxygen group, 36/72 (50.0%) vs 11/75 (14.7%), relative risk (RR) 3.4 (95% CI 1.9 to 6.2), P < 0.001. The high concentration group had a greater proportion of patients with a rise in PtCO(2) ≥8 mmHg, 11/72 (15.3%) vs 2/75 (2.7%), RR 5.7 (95% CI 1.3 to 25.0), P = 0.007. Amongst the 74 patients with radiological confirmation of pneumonia, the high concentration group had a greater proportion with a rise in PtCO(2) ≥4 mmHg, 20/35 (57.1%) vs 5/39 (12.8%), RR 4.5 (95% CI 1.9 to 10.6) P < 0.001.

CONCLUSIONS

We conclude that high concentration oxygen therapy increases the PtCO(2) in patients presenting with suspected community-acquired pneumonia. This suggests that the potential increase in PaCO(2) with high concentration oxygen therapy is not limited to COPD, but may also occur in other respiratory disorders with abnormal gas exchange.

Low-fractional oxygen concentration continuous positive airway pressure is effective in the prehospital setting

OBJECTIVE

The objective of this study was to determine the effects of low-fractional concentration of inspired oxygen (FiO(2)) continuous positive airway pressure (CPAP) in prehospital noninvasive ventilation (NIV). With increasing concerns about the detrimental effects of hyperoxia, we sought to determine whether CPAP using a low FiO(2) (28%-30%) was effective in the prehospital setting.

METHODS

The study was a six-month prospective, nonblinded observational study conducted in a large, busy urban emergency medical services (EMS) system (Las Vegas, NV).

RESULTS

A total of 340 patients participated in the study. Most patients presented with symptoms consistent with a diagnosis of congestive heart failure/acute pulmonary edema (47.4%), followed by chronic obstructive pulmonary disease (COPD) (40.9%), asthma (22.7%), and pneumonia (15.9%). Improvements were seen in respiratory rate (p = 0.00) and oxygen saturation (p = 0.00). The overall CPAP discontinuation rate was 16.5%. The most common reason for CPAP discontinuation was anxiety/claustrophobia. The total number of patients requiring prehospital intubation was 5.6%. Subjective paramedic assessment of patient status at hospital delivery found that 71.5% of patients' conditions were improved, 15.1% remained unchanged, and 13.4% were worse.

CONCLUSIONS

CPAP using a low FiO(2) (28%-30%) was highly effective in the treatment of commonly encountered prehospital respiratory emergencies.

Using titrated oxygen instead of high flow oxygen during an acute exacerbation of chronic obstructive pulmonary disease (COPD) saves lives

QUESTION

In patients with a suspected acute exacerbation of COPD, does titrated oxygen in the pre-hospital setting change mortality, length of hospital stay and blood gas measurements?

DESIGN

Cluster randomised controlled trial in which paramedics were allocated to deliver titrated or high flow oxygen. Randomisation sequence was concealed prior to allocation.

SETTING

Ambulance service and emergency department in Hobart, Australia.

PARTICIPANTS

People who were: transported by ambulance to the emergency department, aged ≥35 years, breathless, and were thought to have COPD based on their acute symptoms, a patient-stated history of COPD, or a smoking history of > 10 pack-years. Randomisation of 64 paramedics allocated 32 to the titrated oxygen group and 30 to the high flow oxygen group. Over the study duration, 179 and 226 patients were allocated to the titrated and high flow oxygen groups, respectively.

INTERVENTIONS

Patients in both groups received basic support, nebulised bronchodilators, intravenous dexamethasone and, if necessary, intravenous or intramuscular salbutamol. In addition, the intervention group received titrated oxygen via nasal prongs, with the aim of maintaining arterial oxygen saturation, measured via a pulse oximeter (SpO(2)) between 88% and 92%. Nebulised therapy was delivered by compressed air. The control group received high flow oxygen (8 to 10 L/min) via a non-rebreather face mask. Nebulised therapy was delivered by compressed oxygen at 6 to 8 L/min.

OUTCOME MEASURES

The primary outcome was pre-and in-hospital mortality. Secondary outcomes were length of hospital stay and blood gas measurements.

RESULTS

The primary outcome was captured for all enrolled patients. According to the intention to treat (ITT) analysis, mortality in the intervention and control groups was 4% (n = 7) and 9% (n = 21), respectively. The relative risk was 0.42 (95% CI 0.20 to 0.89). Similar results were demonstrated when only those patients who had a physician-confirmed diagnosis of COPD were included in the analyses (mortality of 2%, n = 2, vs 9%, n = 11, and relative risk of 0.22, 95% CI 0.05 to 0.9]). The ITT analysis did not demonstrate between-group differences in the secondary outcomes.

CONCLUSION

In patients with a suspected acute exacerbation of COPD, using titrated oxygen to maintain SpO(2) between 88% and 92% reduced the risk of mortality by 58%. Physiotherapists working in acute care should strive to ensure that these patients are not treated with high-flow oxygen.

Effect of high flow oxygen on mortality in chronic obstructive pulmonary disease patients in prehospital setting: randomised controlled trial

OBJECTIVES

To compare standard high flow oxygen treatment with titrated oxygen treatment for patients with an acute exacerbation of chronic obstructive pulmonary disease in the prehospital setting.

DESIGN

Cluster randomised controlled parallel group trial.

SETTING

Ambulance service in Hobart, Tasmania, Australia.

PARTICIPANTS

405 patients with a presumed acute exacerbation of chronic obstructive pulmonary disease who were treated by paramedics, transported, and admitted to the Royal Hobart Hospital during the trial period; 214 had a diagnosis of chronic obstructive pulmonary disease confirmed by lung function tests in the previous five years.

INTERVENTIONS

High flow oxygen treatment compared with titrated oxygen treatment in the prehospital (ambulance/paramedic) setting.

MAIN OUTCOME MEASURE

Prehospital or in-hospital mortality.

RESULTS

In an intention to treat analysis, the risk of death was significantly lower in the titrated oxygen arm compared with the high flow oxygen arm for all patients (high flow oxygen n=226; titrated oxygen n=179) and for the subgroup of patients with confirmed chronic obstructive pulmonary disease (high flow n=117; titrated n=97). Overall mortality was 9% (21 deaths) in the high flow oxygen arm compared with 4% (7 deaths) in the titrated oxygen arm; mortality in the subgroup with confirmed chronic obstructive pulmonary disease was 9% (11 deaths) in the high flow arm compared with 2% (2 deaths) in the titrated oxygen arm. Titrated oxygen treatment reduced mortality compared with high flow oxygen by 58% for all patients (relative risk 0.42, 95% confidence interval 0.20 to 0.89; P=0.02) and by 78% for the patients with confirmed chronic obstructive pulmonary disease (0.22, 0.05 to 0.91; P=0.04). Patients with chronic obstructive pulmonary disease who received titrated oxygen according to the protocol were significantly less likely to have respiratory acidosis (mean difference in pH 0.12 (SE 0.05); P=0.01; n=28) or hypercapnia (mean difference in arterial carbon dioxide pressure -33.6 (16.3) mm Hg; P=0.02; n=29) than were patients who received high flow oxygen.

CONCLUSIONS

Titrated oxygen treatment significantly reduced mortality, hypercapnia, and respiratory acidosis compared with high flow oxygen in acute exacerbations of chronic obstructive pulmonary disease. These results provide strong evidence to recommend the routine use of titrated oxygen treatment in patients with breathlessness and a history or clinical likelihood of chronic obstructive pulmonary disease in the prehospital setting.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Register ACTRN12609000236291.

Normobaric hyperoxia therapy for traumatic brain injury and stroke: a review

Traumatic brain injury (TBI) and acute ischaemic stroke are major causes of mortality and morbidity and there is an urgent demand for new neuroprotective strategies following the translational failure of neuroprotective drug trials. Oxygen therapy--especially normobaric, may offer a simple and effective therapeutic strategy which we review in this paper. Firstly we review mechanisms underlying the therapeutic effects of hyperoxia (both normobaric and hyperbaric) including mitochondrial rescue, stabilisation of intracranial pressure, attenuation of cortical spreading depression and inducing favourable endothelial-leukocyte interactions, all effects of which are postulated to decrease secondary injury. Next we survey studies using hyperbaric oxygen therapy for TBI and stroke, which formed the basis for early studies on normobaric hyperoxia. Thirdly, we present clinical studies of the efficacy of normobaric hyperoxia on TBI and stroke, emphasising their safety, efficacy and practicality. Finally we consider safety concerns and side effects, particularly pulmonary pathology, respiratory failure and theoretical risks in paediatric patients. A neuroprotective role of normobaric hyperoxia is extremely promising and further studies are warranted.

Pre-hospital oxygen therapy in acute exacerbations of chronic obstructive pulmonary disease

BACKGROUND

High concentration oxygen is commonly administered during acute exacerbations of chronic obstructive pulmonary disease (AECOPD). The aim of this study was to determine the association between oxygen, severity markers and poor outcomes in AECOPD.

METHODS

In an audit of patients with AECOPD arriving by ambulance to the Emergency Department of Wellington Hospital, details of oxygen administration, clinical outcomes and severity markers were documented. The main outcome measure was a composite of death, assisted ventilation, or respiratory failure. Associations between oxygen therapy, severity markers and poor clinical outcomes were assessed by logistic regression.

RESULTS

Of 250 patients 77 (31%) died, required assisted ventilation or were in respiratory failure. Increased oxygen flow was associated with increasing risk of death, assisted ventilation or respiratory failure with an odds ratio (OR) of 1.2 (95% CI 1.0-1.4) per 1 L/min oxygen flow. Increasing PaO(2) was associated with a greater risk of a poor outcome with an OR of 1.1 (95% CI 1.0-1.3) per 10 mmHg higher PaO(2). Home oxygen (OR 2.8, 95% CI 1.5-5.1), previous respiratory failure (OR 2.6, 95% CI 1.5-4.6), previous ventilation (OR 3.2, 95% CI 1.7-5.9) and home nebulizer use (OR 2.4, 95% CI 1.4-4.3) were associated with an increased risk of a poor outcome.

CONCLUSION

In AECOPD high flow oxygen in the ambulance is associated with poor clinical outcomes. A number of easily identified markers of chronic disease severity indicate an increased risk of a poor clinical outcome.

The influence of oxygenotherapy on the hypercapnia in patients with chronic obstructive pulmonary disease

Background/Aim. Oxygen therapy is a necessary therapeutic method in treatment of severe chronic respiratory failure (CRF), especially in phases of acute worsening. Risks which are to be taken into consideration during this therapy are: unpredictable increase of carbon dioxide in blood, carbonarcosis, respiratory acidosis and coma. The aim of this study was to show the influence of oxygen therapy on changes of arterial blood carbon dioxide partial pressure. Methods. The study included 93 patients in 104 admittances to the hospital due to acute exacerbation of CFR. The majority of the patients (89.4%) had chronic obstructive pulmonary disease (COPD), while other causes of respiratory failure were less common. The effect of oxygenation was controlled through measurement of PaO2 and PaCO2 in arterial blood samples. To analyze the influence of oxygen therapy on levels of carbon dioxide, greatest values of change of PaO2 and PaCO2 values from these measurements, including corresponding PaO2 values from the same blood analysis were taken. Results. The obtained results show that oxygen therapy led to the increase of PaO2 but also to the increase of PaCO2. The average increase of PaO2 for the whole group of patients was 2.42 kPa, and the average increase of PaCO2 was 1.69 kPa. There was no correlation between the initial values of PaO2 and PaCO2 and changes of PaCO2 during the oxygen therapy. Also, no correlation between the produced increase in PaO2 and change in PaCO2 during this therapy was found. Conclusion. Controlled oxygen therapy in patients with severe respiratory failure greatly reduces the risk of unwanted increase of PaCO2, but does not exclude it completely. The initial values of PaO2 and PaCO2 are not reliable parameters which could predict the response to oxygen therapy.

Oxygen, the lead actor in the pathophysiologic drama: enactment of the trinity of normoxia, hypoxia, and hyperoxia in disease and therapy

Aerobic life has evolved a dependence on molecular oxygen for its mere survival. Mitochondrial oxidative phosphorylation absolutely requires oxygen to generate the currency of energy in aerobes. The physiologic homeostasis of these organisms is strictly maintained by optimal cellular and tissue-oxygenation status through complex oxygen-sensing mechanisms, signaling cascades, and transport processes. In the event of fluctuating oxygen levels leading to either an increase (hyperoxia) or decrease (hypoxia) in cellular oxygen, the organism faces a crisis involving depletion of energy reserves, altered cell-signaling cascades, oxidative reactions/events, and cell death or tissue damage. Molecular oxygen is activated by both nonenzymatic and enzymatic mechanisms into highly reactive oxygen species (ROS). Aerobes have evolved effective antioxidant defenses to counteract the reactivity of ROS. Although the ROS are also required for many normal physiologic functions of the aerobes, overwhelming production of ROS coupled with their insufficient scavenging by endogenous antioxidants will lead to detrimental oxidative stress. Needless to say, molecular oxygen is at the center of oxygenation, oxidative phosphorylation, and oxidative stress. This review focuses on the biology and pathophysiology of oxygen, with an emphasis on transport, sensing, and activation of oxygen, oxidative phosphorylation, oxygenation, oxidative stress, and oxygen therapy.

A calibration method for quantitative BOLD fMRI based on hyperoxia

The estimation of changes in CMR(O2) using functional MRI involves an essential calibration step using a vasoactive agent to induce an isometabolic change in CBF. This calibration procedure is performed most commonly using hypercapnia as the isometabolic stimulus. However, hypercapnia possesses a number of detrimental side effects. Here, a new method is presented using hyperoxia to perform the same calibration step. This procedure requires independent measurement of Pa(O2), the BOLD signal, and CBF. We demonstrate that this method yields results that are comparable to those derived using other methods. Further, the hyperoxia technique is able to provide an estimate of the calibration constant that has lower overall intersubject and intersession variability compared to the hypercapnia approach.

Normobaric hyperoxia delays perfusion/diffusion mismatch evolution, reduces infarct volume, and differentially affects neuronal cell death pathways after suture middle cerebral artery occlusion in rats

Normobaric hyperoxia (NBO) has been shown to extend the reperfusion window after focal cerebral ischemia. Employing diffusion (DWI)- and perfusion (PWI)-weighted magnetic resonance imaging (MRI), the effect of NBO (100% started at 30 mins after middle cerebral artery occlusion (MCAO)) on the spatiotemporal evolution of ischemia during and after permanent (pMCAO) and transient suture middle cerebral artery occlusion (tMCAO) was investigated (experiment 3). In two additional experiments, time window (experiment 1) and cell death pathways (experiment 2) were investigated in the pMCAO model. In experiment 1, NBO treatment reduced infarct volume at 24 h after pMCAO by 10% when administered for 3 h (P>0.05) and by 44% when administered for 6 h (P<0.05). In experiment 2, NBO acutely (390 mins, P<0.05) reduced in situ end labeling (ISEL) positivity in the ipsilesional penumbra but increased contralesional necrotic as well as caspase-3-mediated apoptotic cell death. In experiment 3, CBF characteristics and CBF-derived lesion volumes did not differ between treated and untreated animals, whereas the apparent diffusion coefficient (ADC)-derived lesion volume essentially stopped progressing during NBO treatment, resulting in a persistent PWI/DWI mismatch that could be salvaged by delayed (3 h) reperfusion. In conclusion, NBO (1) acutely preserved the perfusion/diffusion mismatch without altering CBF, (2) significantly extended the time window for reperfusion, (3) induced lasting neuroprotection in permanent ischemia, and (4) although capable of reducing cell death in hypoperfused tissue it also induced cell death in otherwise unaffected areas. Our data suggest that NBO may represent a promising strategy for acute stroke treatment.