Routine use of oxygen in the treatment of myocardial infarction: systematic review

Implementation of a titrated oxygen protocol in the out-of-hospital setting

Oxygen is one of the most frequently-used therapeutic agents in medicine and the most commonly administered drug by prehospital personnel. There is increasing evidence of harm with too much supplemental oxygen in certain conditions, including stroke, chronic obstructive pulmonary disease (COPD), neonatal resuscitations, and in postresuscitation care. Recent guidelines published by the British Thoracic Society (BTS) advocate titrated oxygen therapy, but these guidelines have not been widely adapted in the out-of-hospital setting where high-flow oxygen is the standard. This report is a description of the implementation of a titrated oxygen protocol in a large urban-suburban Emergency Medical Services (EMS) system and a discussion of the practical application of this out-of-hospital protocol.

Oxygen Therapy in Critical Illness: Friend or Foe? A Review of Oxygen Therapy in Selected Acute Illnesses

In recent years there has been a gradual shift away from using uncontrolled high concentrations of inspired oxygen in some acute illnesses. Oxygen is perhaps the most frequently used drug in medicine, and understanding the balance of benefits and harms is essential knowledge for all anaesthetists and intensivists. While current teaching and practice emphasise avoiding hypoxaemia over concerns about hyperoxaemia, it may transpire that oxygen excess is more harmful than previously thought. As with many interventions in intensive care medicine, striving to achieve physiological normality may sometimes do more harm than good, and tolerance of abnormal values may on occasion be in patients' best interests. Incorporating Single Best Answers (see page 197: answers on page 237).

Prehospital oxygen administration for chest pain patients decreases significantly following implementation of the 2010 AHA guidelines

OBJECTIVES

The purpose of this study was to examine trends in oxygen administration following the 2010 American Heart Association guidelines recommendation to withhold oxygen therapy for patients with uncomplicated presentations of ACS whose SpO2 is 94% or higher.

METHODS

Following IRB review and approval, we performed a retrospective analysis of data obtained from Fisdap(TM), a national, clinical skills tracking system for paramedic students between June 2010 and December 2012. Inclusion criteria included: 1) student consent for research, 2) cardiac chest pain recorded as the chief complaint, and 3) SpO2 data available for review. O2 administration, route, and dose were abstracted, and the percent of patient encounters with oxygen administration was calculated for each year. Unadjusted logistic regression was used to determine if O2 administration rates changed significantly over the study period. Unadjusted logistic regression was also used to determine if there was a difference in the odds of receiving oxygen based on a patient's SpO2 value.

RESULTS

10,552 patient encounters by 2,447 paramedic students from 195 paramedic programs representing 49 states were included for analysis. Prior to release of the new guidelines (2010), 71.9% (95% CI 69.8-74.0%) of patients with SpO2 ≥ 94% received supplemental O2. Rates of O2 administration were significantly lower in 2011 (64%; 95% CI 62.7-65.3%) and in 2012 (53.1%; 95% CI 51.5-54.7). The odds of a hemodynamically stable chest pain patient with SpO2 ≥ 94% receiving supplemental oxygen in 2011 were 1.4 times lower compared to patients in 2010 (95% CI 1.3-1.6). Similarly, the odds of patients in 2012 receiving supplemental oxygen were 2.3 times lower compared to patients in 2010 (95% CI 2.0-2.6). The odds of receiving supplemental oxygen decreased by 4% for each 1% increase in SpO2 beyond the 94% threshold (OR = 0.96; 95% CI 0.94-0.98).

CONCLUSIONS

The prehospital administration of supplemental O2 decreased significantly following release of the 2010 updated guidelines; however, our data revealed that 50% of patients not meeting criteria for administration still received supplemental O2.

Peripheral muscle microcirculatory alterations in patients with pulmonary arterial hypertension: a pilot study

BACKGROUND

Pulmonary microcirculation abnormalities are the main determinants of pulmonary arterial hypertension (PAH) pathophysiology. We hypothesized that PAH patients have peripheral tissue microcirculation alterations that might benefit from hyperoxic breathing. We evaluated peripheral muscle microcirculation with near-infrared spectroscopy, before and after hyperoxic breathing.

METHODS

Eight PAH subjects, 8 healthy subjects (controls) matched for age, sex, and body mass index, and 16 subjects with chronic heart failure and matched for functional capacity with the PAH subjects underwent near-infrared spectroscopy. Tissue O(2) saturation, defined as the hemoglobin saturation (%) in the microvasculature compartments, was measured on the thenar muscle. Then the 3-min brachial artery occlusion technique was applied before, during, and after 15 min of breathing 100% O(2). We calculated the oxygen consumption rate (%/min), the reactive hyperemia time, and the time needed for tissue O(2) saturation to reach its baseline value after the release of the occlusion.

RESULTS

Compared to the controls, the PAH subjects had a significantly lower resting tissue O(2) saturation (65.8 ± 14.9% vs 82.1 ± 4.0%, P = .005), a trend toward a lower oxygen consumption rate (35.3 ± 9.1%/min vs 43.4 ± 19.7%/min, P = .60), and a significantly higher reactive hyperemia time (3.0 ± 0.6 min vs 2.0 ± 0.3 min, P < .001). The PAH subjects also had lower tissue O(2) saturation (P = .08), lower peripheral arterial oxygen saturation (P = .01), and higher reactive hyperemia time (P = .02) than the chronic heart failure subjects. After hyperoxic breathing, the PAH subjects had increased tissue O(2) saturation (65.8 ± 14.9% to 71.4 ± 14.5%, P = .01), decreased oxygen consumption rate (35.3 ± 9.1%/min to 25.1 ± 6.6%/min, P = .01), and further increased reactive hyperemia time (3.0 ± 0.6 min to 4.2 ± 0.7 min, P = .007).

CONCLUSIONS

The PAH subjects had substantial impairments of peripheral muscle microcirculation, decreased tissue O(2) saturation (possibly due to hypoxemia), slower reactive hyperemia time, (possibly due to endothelium dysfunction), and peripheral systemic vasoconstriction. Acute hyperoxic breathing improved resting tissue O(2) saturation (an expression of higher oxygen delivery) and decreased the oxygen consumption rate and reactive hyperemia time during reperfusion, possibly due to increased oxidative stress and evoked vasoconstriction.

The medical use of oxygen: a time for critical reappraisal

Oxygen treatment has been a cornerstone of acute medical care for numerous pathological states. Initially, this was supported by the assumed need to avoid hypoxaemia and tissue hypoxia. Most acute treatment algorithms, therefore, recommended the liberal use of a high fraction of inspired oxygen, often without first confirming the presence of a hypoxic insult. However, recent physiological research has underlined the vasoconstrictor effects of hyperoxia on normal vasculature and, consequently, the risk of significant blood flow reduction to the at-risk tissue. Positive effects may be claimed simply by relief of an assumed local tissue hypoxia, such as in acute cardiovascular disease, brain ischaemia due to, for example, stroke or shock or carbon monoxide intoxication. However, in most situations, a generalized hypoxia is not the problem and a risk of negative hyperoxaemia-induced local vasoconstriction effects may instead be the reality. In preclinical studies, many important positive anti-inflammatory effects of both normobaric and hyperbaric oxygen have been repeatedly shown, often as surrogate end-points such as increases in gluthatione levels, reduced lipid peroxidation and neutrophil activation thus modifying ischaemia-reperfusion injury and also causing anti-apoptotic effects. However, in parallel, toxic effects of oxygen are also well known, including induced mucosal inflammation, pneumonitis and retrolental fibroplasia. Examining the available 'strong' clinical evidence, such as usually claimed for randomized controlled trials, few positive studies stand up to scrutiny and a number of trials have shown no effect or even been terminated early due to worse outcomes in the oxygen treatment arm. Recently, this has led to less aggressive approaches, even to not providing any supplemental oxygen, in several acute care settings, such as resuscitation of asphyxiated newborns, during acute myocardial infarction or after stroke or cardiac arrest. The safety of more advanced attempts to deliver increased oxygen levels to hypoxic or ischaemic tissues, such as with hyperbaric oxygen therapy, is therefore also being questioned. Here, we provide an overview of the present knowledge of the physiological effects of oxygen in relation to its therapeutic potential for different medical conditions, as well as considering the potential for harm. We conclude that the medical use of oxygen needs to be further examined in search of solid evidence of benefit in many of the current clinical settings in which it is routinely used.

p53's choice of myocardial death or survival: Oxygen protects infarct myocardium by recruiting p53 on NOS3 promoter through regulation of p53-Lys(118) acetylation

Myocardial infarction, an irreversible cardiac tissue damage, involves progressive loss of cardiomyocytes due to p53-mediated apoptosis. Oxygenation is known to promote cardiac survival through activation of NOS3 gene. We hypothesized a dual role for p53, which, depending on oxygenation, can elicit apoptotic death signals or NOS3-mediated survival signals in the infarct heart. p53 exhibited a differential DNA-binding, namely, BAX-p53RE in the infarct heart or NOS3-p53RE in the oxygenated heart, which was regulated by oxygen-induced, post-translational modification of p53. In the infarct heart, p53 was heavily acetylated at Lys¹¹⁸ residue, which was exclusively reversed in the oxygenated heart, apparently regulated by oxygen-dependent expression of TIP60. The inhibition of Lys¹¹⁸ acetylation promoted the generation of NOS3-promoting prosurvival form of p53. Thus, oxygenation switches p53-DNA interaction by regulating p53 core-domain acetylation, promoting a prosurvival transcription activity of p53. Understanding this novel oxygen-p53 survival pathway will open new avenues in cardioprotection molecular therapy.

Ventilator management in the cardiac intensive care unit

Patients admitted to the Cardiac Intensive Care Unit (CICU) are of increasing complexity and often require ventilatory support. A deep understanding of respiratory physiology and the interactions between the cardiovascular and respiratory systems is essential. Ventilatory support should be tailored to the specific patient condition, ensuring effective minute ventilation, reducing work of breathing and minimizing adverse hemodynamic effects. The weaning process can stress the cardiovascular system and cardiac failure is a common cause of failure to wean. Identification of patients likely to fail and prompt pre-emptive intervention is crucial for successful weaning and avoiding complications related to prolonged mechanical ventilation.

Feasibility study on full closed-loop control ventilation (IntelliVent-ASV™) in ICU patients with acute respiratory failure: a prospective observational comparative study

INTRODUCTION

IntelliVent-ASV™ is a full closed-loop ventilation mode that automatically adjusts ventilation and oxygenation parameters in both passive and active patients. This feasibility study compared oxygenation and ventilation settings automatically selected by IntelliVent-ASV™ among three predefined lung conditions (normal lung, acute respiratory distress syndrome (ARDS) and chronic obstructive pulmonary disease (COPD)) in active and passive patients. The feasibility of IntelliVent-ASV™ use was assessed based on the number of safety events, the need to switch to conventional mode for any medical reason, and sensor failure.

METHOD

This prospective observational comparative study included 100 consecutive patients who were invasively ventilated for less than 24 hours at the time of inclusion with an expected duration of ventilation of more than 12 hours. Patients were ventilated using IntelliVent-ASV™ from inclusion to extubation. Settings, automatically selected by the ventilator, delivered ventilation, respiratory mechanics, and gas exchanges were recorded once a day.

RESULTS

Regarding feasibility, all patients were ventilated using IntelliVent-ASV™ (392 days in total). No safety issues occurred and there was never a need to switch to an alternative ventilation mode. The fully automated ventilation was used for 95% of the total ventilation time. IntelliVent-ASV™ selected different settings according to lung condition in passive and active patients. In passive patients, tidal volume (VT), predicted body weight (PBW) was significantly different between normal lung (n = 45), ARDS (n = 16) and COPD patients (n = 19) (8.1 (7.3 to 8.9) mL/kg; 7.5 (6.9 to 7.9) mL/kg; 9.9 (8.3 to 11.1) mL/kg, respectively; P 0.05). In passive ARDS patients, FiO2 and positive end-expiratory pressure (PEEP) were statistically higher than passive normal lung (35 (33 to 47)% versus 30 (30 to 31)% and 11 (8 to 13) cmH2O versus 5 (5 to 6) cmH2O, respectively; P< 0.05).

CONCLUSIONS

IntelliVent-ASV™ was safely used in unselected ventilated ICU patients with different lung conditions. Automatically selected oxygenation and ventilation settings were different according to the lung condition, especially in passive patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01489085.

Oxygen therapy for acute myocardial infarction

BACKGROUND

Oxygen (O₂) is widely used in people with acute myocardial infarction (AMI) although it has been suggested it may do more harm than good. Previous systematic reviews have concluded that there was insufficient evidence to know whether oxygen reduced, increased or had no effect on heart ischaemia or infarct size, as did our original Cochrane review on this topic in 2010. The wide dissemination of the lack of evidence to support this widely-used intervention since 2010 may stimulate the needed trials of oxygen therapy, and it is therefore important that this review is updated regularly.

OBJECTIVES

To review the evidence from randomised controlled trials to establish whether routine use of inhaled oxygen in acute myocardial infarction (AMI) improves patient-centred outcomes, in particular pain and death.

SEARCH METHODS

The following bibliographic databases were searched last in July 2012: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE (OVID), EMBASE (OVID), CINAHL (EBSCO) and Web of Science (ISI). LILACS (Latin American and Caribbean Health Sciences Literature) and PASCAL were last searched in May 2013. We also contacted experts to identify any studies. We applied no language restrictions.

SELECTION CRITERIA

Randomised controlled trials of people with suspected or proven AMI (ST-segment elevation myocardial infarction (STEMI) or non-STEMI), less than 24 hours after onset, in which the intervention was inhaled oxygen (at normal pressure) compared to air and regardless of cotherapies provided these were the same in both arms of the trial.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed the titles and abstracts of identified studies to see if they met the inclusion criteria, and independently undertook the data extraction. The quality of studies and the risk of bias were assessed according to guidance in the Cochrane Handbook. The primary outcomes were death, pain and complications. The measure of effect used was the risk ratio (RR) with a 95% confidence interval (CI).

MAIN RESULTS

The updated search identified one new trial. In total, four trials involving 430 participants were included and 17 deaths occurred. The pooled RR of death was 2.05 (95% CI 0.75 to 5.58) in an intention-to-treat analysis and 2.11 (95% CI 0.78 to 5.68) in participants with confirmed AMI. While suggestive of harm, the small number of deaths recorded means that this could be a chance occurrence. Pain was measured by analgesic use. The pooled RR for the use of analgesics was 0.97 (95% CI 0.78 to 1.20).

AUTHORS' CONCLUSIONS

There is no conclusive evidence from randomised controlled trials to support the routine use of inhaled oxygen in people with AMI. A definitive randomised controlled trial is urgently required, given the mismatch between trial evidence suggestive of possible harm from routine oxygen use and recommendations for its use in clinical practice guidelines.

Oxygen therapy in patients with chest pain of acute onset: single centre audit experience

Introduction:

Although oxygen therapy has been commonly used in the treatment of acute coronary syndromes, evidence shows that oxygen administration is not always beneficial to patients with acute chest pain and in certain circumstances may, in fact, be harmful. Hence, several national and international organizations have issued guidelines restricting its use to hypoxic patients only.

Aim:

To audit and change the inappropriate practice of administering oxygen therapy indiscriminately to patients with acute chest pain.

Setting:

Emergency department, coronary care unit and heart assessment centre in a large teaching hospital.

Methods:

The authors identified 100 patients who presented with acute chest pain and collected data on oxygen prescription, administration and documentation from clinical notes and observation charts.

Results:

Only 71% of patients in a hospital setting were correctly assessed for requiring oxygen therapy. After introducing local guidelines and a series of lectures, this rose to 94%. A third audit showed sustained change, with 96% of patients being appropriately assessed for needing oxygen therapy.

Discussion:

The introduction of local guidelines and a series of lectures improved handling of oxygen in patients presenting with acute chest pain.

Relationship between heart rate variability, blood pressure and arterial wall properties during air and oxygen breathing in healthy subjects

Previous studies reported that normobaric hyperoxia influences heart rate, arterial pressure, cardiac output and systemic vascular resistance, but the mechanisms underlying these changes are still not fully understood. Several factors are considered including degeneration of endothelium-derived nitric oxide by reactive oxygen species, the impact of oxygen-free radicals on tissues and alterations of autonomic nervous system function. Recently, new devices for the detailed non-invasive assessment of large and small arteries have been developed. Therefore, the aim of our study was to assess heart rate variability (HRV) as a potential indicator of autonomic balance and its relation to blood pressure and vascular properties during medical air (MAB) and 100% oxygen breathing (OXB) in healthy volunteers. In 12 healthy subjects we assessed heart rate and blood pressure variability, baroreflex sensitivity, respiratory frequency, common carotid artery diameter and its wall distensibility, as well as changes in the digital artery pulse waveform, stroke index and systemic vascular resistance during MAB and OXB. Mean and systolic blood pressure have increased significantly while digital pulse amplitude and carotid artery diameter were significantly lower during hyperoxia. Heart rate variability measures did not differ during MAB and OXB. However, the correlations between spectral HRV components and those hemodynamic parameters which have changed due to hyperoxia varied substantially during MAB (correlated significantly) and OXB (no significant correlations were noted). Our findings suggest that autonomic nervous system might not be the main mediator of the cardiovascular changes during 100% oxygen breathing in healthy subjects. It seems that the direct vascular responses are initial consequences of hyperoxia and other cardiovascular parameter alterations are secondary to them.

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

OBJECTIVE

The management of hypoxemia in critically ill patients is challenging. Whilst the harms of tissue hypoxia are well recognized, the possibility of harm from excess oxygen administration, or other interventions targeted at mitigating hypoxemia, may be inadequately appreciated. The benefits of attempting to fully reverse arterial hypoxemia may be outweighed by the harms associated with high concentrations of supplemental oxygen and invasive mechanical ventilation strategies. We propose two novel related strategies for the management of hypoxemia in critically ill patients. First, we describe precise control of arterial oxygenation involving the specific targeting of arterial partial pressure of oxygen or arterial hemoglobin oxygen saturation to individualized target values, with the avoidance of significant variation from these levels. The aim of precise control of arterial oxygenation is to avoid the harms associated with inadvertent hyperoxia or hypoxia through careful and precise control of arterial oxygen levels. Secondly, we describe permissive hypoxemia: the acceptance of levels of arterial oxygenation lower than is conventionally tolerated in patients. The aim of permissive hypoxemia is to minimize the possible harms caused by restoration of normoxemia while avoiding tissue hypoxia. This review sets out to discuss the strengths and limitations of precise control of arterial oxygenation and permissive hypoxemia as candidate management strategies in hypoxemic critically ill patients.

DESIGN

We searched PubMed for references to "permissive hypoxemia/hypoxaemia" and "precise control of arterial oxygenation" as well as reference to "profound hypoxemia/hypoxaemia/hypoxia," "severe hypoxemia/hypoxaemia/hypoxia." We searched personal reference libraries in the areas of critical illness and high altitude physiology and medicine. We also identified large clinical studies in patients with critical illness characterized by hypoxemia such as acute respiratory distress syndrome.

SUBJECTS

Studies were selected that explored the physiology of hypoxemia in healthy volunteers or critically ill patients.

SETTING

The data were subjectively assessed and combined to generate the narrative.

RESULTS

Inadequate tissue oxygenation and excessive oxygen administration can be detrimental to outcome but safety thresholds lack definition in critically ill patients. Precise control of arterial oxygenation provides a rational approach to the management of arterial oxygenation that reflects recent clinical developments in other settings. Permissive hypoxemia is a concept that is untested clinically and requires robust investigation prior to consideration of implementation. Both strategies will require accurate monitoring of oxygen administration and arterial oxygenation. Effective, reliable measurement of tissue oxygenation along with the use of selected biomarkers to identify suitable candidates and monitor harm will aid the development of permissive hypoxemia as viable clinical strategy.

CONCLUSIONS

Implementation of precise control of arterial oxygenation may avoid the harms associated with excessive and inadequate oxygenation. However, at present there is no direct evidence to support the immediate implementation of permissive hypoxemia and a comprehensive evaluation of its value in critically ill patients should be a high research priority.

Hypoxia induces myocardial regeneration in zebrafish

BACKGROUND

Hypoxia plays an important role in many biological/pathological processes. In particular, hypoxia is associated with cardiac ischemia. which, although initially inducing a protective response, will ultimately lead to the death of cardiomyocytes and loss of tissue, severely affecting cardiac functionality. Although myocardial damage/loss remains an insurmountable problem for adult mammals, the same is not true for adult zebrafish, which are able to completely regenerate their heart after extensive injury. Myocardial regeneration in zebrafish involves the dedifferentiation and proliferation of cardiomyocytes to replace the damaged/missing tissue; at present, however, little is known about what factors regulate this process.

METHODS AND RESULTS

We surmised that ventricular amputation would lead to hypoxia induction in the myocardium of zebrafish and that this may play a role in regulating the regeneration of the missing cardiac tissue. Using a combination of O(2) perturbation, conditional transgenics, in vitro cell culture, and microarray analysis, we found that hypoxia induces cardiomyocytes to dedifferentiate and proliferate during heart regeneration in zebrafish and have identified a number of genes that could play a role in this process.

CONCLUSION

These results indicate that hypoxia plays a positive role during heart regeneration, which should be taken into account in future strategies aimed at inducing heart regeneration in humans.

Rational use of oxygen in medical disease and anesthesia

PURPOSE OF REVIEW

Supplemental oxygen is often administered during anesthesia and in critical illness to treat hypoxia, but high oxygen concentrations are also given for a number of other reasons such as prevention of surgical site infection (SSI). The decision to use supplemental oxygen is, however, controversial, because of large heterogeneity in the reported results and emerging reports of side-effects. The aim of this article is to review the recent findings regarding benefits and harms of oxygen therapy in anesthesia and acute medical conditions.

RECENT FINDINGS

Large randomized trials have not found significant reductions in SSI with 80% oxygen during and after abdominal surgery and cesarean section. There is no documented benefit of hyperbaric oxygen treatment for acute ischemic stroke, and there is emerging data to suggest increased mortality with normobaric supplemental oxygen for myocardial infarction without heart failure. Survival and neurologic outcome seem to be adversely affected by hyperoxia in patients with return of spontaneous circulation after cardiac arrest.

SUMMARY

The benefits of supplemental oxygen are not yet confirmed, and new findings suggest that potential side-effects should be considered if the inspired oxygen concentration is increased above what is needed to maintain normal arterial oxygen saturation.

Perioperative oxygen toxicity

This article challenges the use of hyperoxia in the perioperative period. It describes the biochemical and physiologic basis for both the direct and indirect adverse effects of oxygen. The reasons for using hyperoxia in the perioperative period are critically evaluated, and the evidence and guidelines for oxygen use in common acute medical conditions are reviewed.

Hyperoxia during early reperfusion does not increase ischemia/reperfusion injury

OBJECTIVE

Oxygen is routinely administered to patients undergoing acute myocardial infarction as well as during revascularization procedures and cardiac surgery. Because reactive oxygen species are mediators of ischemia/reperfusion injury, increased oxygen availability might theoretically aggravate myocardial injury during reperfusion. We hypothesized that ventilation with a hyperoxic gas at start of reperfusion might increase ischemia/reperfusion injury.

METHODS

Rats were anesthetized with isoflurane and ventilated with 40% oxygen. The animals were subjected to 40 min of regional myocardial ischemia and 120 min of reperfusion. In the test group, rats (n=11) were ventilated with a normobaric hyperoxic gas (95% O2) during the last 10 min of ischemia and the first 10 min of reperfusion. Control rats (n=14) were ventilated with 40% O2 throughout the experiments. Due to irreversible reperfusion arrhythmias, one animal in the hyperoxia group and six animals in the control group were excluded. Hearts (n=8 in the control group and n=10 in the test group) were harvested for measurement of infarct size.

RESULTS

The incidence of lethal arrhythmias was 1/11 in the test group and 6/14 in the control group (p=0.06). Reperfusion with normobaric hyperoxia did not influence infarct size (20±8% of area at risk) compared with the normoxia group (24±8% and of area at risk), respectively (mean±SD, p>0.2).

CONCLUSION

Normobaric hyperoxia during early reperfusion did not increase ischemia/reperfusion injury.

Hyperoxia reversibly alters oxygen consumption and metabolism

Aim. Ventilation with pure oxygen (hyperoxic ventilation: HV) is thought to decrease whole body oxygen consumption (VO₂). However, the validity and impact of this phenomenon remain ambiguous; until now, under hyperoxic conditions, VO₂ has only been determined by the reverse Fick principle, a method with inherent methodological problems. The goal of this study was to determine changes of VO₂, carbon dioxide production (VCO₂), and the respiratory quotient (RQ) during normoxic and hyperoxic ventilation, using a metabolic monitor. Methods. After providing signed informed consent and institutional acceptance, 14 healthy volunteers were asked to sequentially breathe room air, pure oxygen, and room air again. VO₂, VCO₂, RQ, and energy expenditure (EE) were determined by indirect calorimetry using a modified metabolic monitor during HV. Results. HV reduced VO₂ from 3.4 (3.0/4.0) mL/kg/min to 2.8 (2.5/3.6) mL/kg/min (P < 0.05), whereas VCO₂ remained constant (3.0 [2.6/3.6] mL/kg/min versus 3.0 [2.6/3.5] mL/kg/min, n.s.). After onset of HV, RQ increased from 0.9 (0.8/0.9) to 1.1 (1.0/1.1). Most changes during HV were immediately reversed during subsequent normoxic ventilation. Conclusion. HV not only reduces VO₂, but also increases the respiratory quotient. This might be interpreted as an indicator of the substantial metabolic changes induced by HV. However, the impact of this phenomenon requires further study.

Low Tidal Volume Ventilation in Patients without Acute Respiratory Distress Syndrome: A Paradigm Shift in Mechanical Ventilation

Protective ventilation with low tidal volume has been shown to reduce morbidity and mortality in patients suffering from acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Low tidal volume ventilation is associated with particular clinical challenges and is therefore often underutilized as a therapeutic option in clinical practice. Despite some potential difficulties, data have been published examining the application of protective ventilation in patients without lung injury. We will briefly review the physiologic rationale for low tidal volume ventilation and explore the current evidence for protective ventilation in patients without lung injury. In addition, we will explore some of the potential reasons for its underuse and provide strategies to overcome some of the associated clinical challenges.

A randomized controlled trial of oxygen therapy in acute myocardial infarction Air Verses Oxygen In myocarDial infarction study (AVOID Study)

BACKGROUND

The role of routine supplemental oxygen for patients with uncomplicated acute myocardial infarction (AMI) has recently been questioned. There is conflicting data on the possible effects of hyperoxia on ischemic myocardium. The few clinical trials examining the role of oxygen in AMI were performed prior to the modern approach of emergent reperfusion and advanced medical management.

METHODS

Air Verses Oxygen In myocarDial infarction study (AVOID Study) is a prospective, multi-centre, randomized, controlled trial conducted by Ambulance Victoria and participating metropolitan Melbourne hospitals with primary percutaneous coronary intervention capabilities. The purpose of the study is to determine whether withholding routine supplemental oxygen therapy in patients with acute ST-elevation myocardial infarction but without hypoxia prior to reperfusion decreases myocardial infarct size. AVOID will enroll 490 patients, >18 years of age with acute ST-elevation myocardial infarction of less than 12 hours duration.

CONCLUSIONS

There is an urgent need for clinical trials examining the role of oxygen in AMI. AVOID will seek to clarify this important issue. Results from this study may have widespread implications on the treatment of AMI and the use of oxygen in both the pre-hospital and hospital settings.

High-concentration versus titrated oxygen therapy in ST-elevation myocardial infarction: a pilot randomized controlled trial

BACKGROUND

The optimal approach to oxygen therapy in ST-elevation myocardial infarction (STEMI) is uncertain.

METHODS

A randomized controlled trial was undertaken in which 136 patients presenting with their first STEMI uncomplicated by cardiogenic shock or marked hypoxia were randomized to receive high-concentration (6 L/min via medium concentration mask) or titrated oxygen (to achieve oxygen saturation 93%-96%) for 6 hours after presentation. The main outcome variables were 30-day mortality and infarct size assessed by troponin T level at 72 hours. Secondary outcomes included a meta-analysis of mortality data from this study and previous randomized controlled trials, and infarct size was assessed by magnetic resonance imaging at 4 to 6 weeks.

RESULTS

There were 1 of 68 and 2 of 68 deaths in the high-concentration and titrated oxygen groups, respectively; a meta-analysis including these data with those from the 2 previous studies showed an odds ratio for mortality of high-concentration oxygen compared with room air or titrated oxygen of 2.2 (95% CI 0.8-6.0). There was no significant difference between high-concentration versus titrated oxygen in troponin T (ratio of mean levels 0.74, 95% CI 0.50-1.1, P = .14), infarct mass (mean difference -0.8 g, 95% CI -7.6 to 6.1, P = .82), or percent infarct mass (mean difference -0.6%, 95% CI -5.6 to 4.5, P = .83).

CONCLUSION

This study found no evidence of benefit or harm from high-concentration compared with titrated oxygen in initially uncomplicated STEMI. However, our estimates have wide CIs, and as a result, large randomized controlled trials are required to resolve the clinical uncertainty.

Oxygen therapy for acute myocardial infarction-then and now. A century of uncertainty

For about 100 years, inhaled oxygen has been administered to all patients suspected of having an acute myocardial infarction. The basis for this practice was the belief that oxygen supplementation raised often-deficient arterial oxygen content to improve myocardial oxygenation, thereby reducing infarct size. This assumption is conditional and not evidence-based. While such physiological changes may pertain in some patients who are hypoxemic, considerable data suggest that oxygen therapy may be detrimental in others. Acute oxygen therapy may raise blood pressure and lower cardiac index, heart rate, cardiac oxygen consumption, and blood flow in the cerebral and renal beds. Oxygen also may lower capillary density and redistribute blood in the microcirculation. Several reports now confirm that these changes occur in humans. In patients with both acute coronary syndromes and stable coronary disease, oxygen administration may constrict the coronary vessels, lower myocardial oxygen delivery, and may actually worsen ischemia. There are no large, contemporary, randomized studies that examine clinical outcomes after this intervention. Hence, this long-accepted but potentially harmful tradition urgently needs reevaluation. Clinical guidelines appear to be changing, favoring use of oxygen only in hypoxemic patients, and then cautiously titrating to individual oxygen tensions.

[Rational use of oxygen in anesthesiology and intensive care medicine]

Oxygen (O(2)) is the most frequently used pharmaceutical in anesthesiology and intensive care medicine: Every patient receives O(2) during surgery or during a stay in the intensive care unit. Hypoxia and hypoxemia of various origins are the most typical indications which are mentioned in the prescribing information of O(2): the goal of the administration of O(2) is either an increase of arterial O(2) partial pressure in order to treat hypoxia, or an increase of arterial O(2) content in order to treat hypoxemia. Most of the indications for O(2) administration were developed in former times and have seldom been questioned from that time on as the short-term side-effects of O(2) are usually considered to be of minor importance. As a consequence only a small number of controlled randomized studies exist, which can demonstrate the efficacy of O(2) in terms of evidence-based medicine. However, there is an emerging body of evidence that specific side-effects of O(2) result in a deterioration of the microcirculation. The administration of O(2) induces arteriolar constriction which will initiate a decline of regional O(2) delivery and subsequently a decline of tissue oxygenation. The aim of the manuscript presented is to discuss the significance of O(2) as a pharmaceutical in the clinical setting.

Non-invasive cardiac output and oxygen delivery measurement in an infant with critical anemia

OBJECTIVE

To assess the combination of a non-invasive blood oxygen content (CaO(2)) monitor and a non-invasive cardiac output (CO) monitor to continuously measure oxygen delivery (DO(2); DO(2) = CaO(2) × CO).

METHODS

DO(2) was assessed during blood transfusions in an infant with acute hemolytic anemia following admission (~48 h). CaO(2) was measured by Pulse Co-Oximetry, which also provides estimates of hemoglobin (Hgb) concentration and percent oxygen saturation. CO was measured by Electrical Velocimetry, which also provides an estimate of stroke volume (SV). Lactate levels, an indirect measure of adequate DO(2), were assessed during the initial 8 h following admission.

RESULTS

Incremental blood transfusions during the first 36 h increased Hgb from 2.7 to 9.5 g/dL during which time heart rate (HR) normalized from 156 to 115 beats/min. Lactate levels decreased from 20 to 0.8 mmol/L in the first 7 h. Non-invasive Hgb and CaO(2) measurements were well correlated with invasive Hgb and CaO(2) measures (r (2) = 0.88; P = 0.019; r (2) = 0.86; P = 0.0074, respectively). CO decreased from 2.47 ± 0.06 to 1.28 ± 0.02 L/min and SV decreased from 15.9 ± 0.4 to 11.1 ± 0.2 mL/beat. Mean arterial blood pressure was stable throughout the admission with systemic vascular resistance increasing from 407.6 ± 15.2 to 887.7 ± 30.1 dynes-s/cm(5). DO(2) was estimated to increase from 120.2 ± 18.9 to 182.4 ± 5.6 mL O(2)/min.

CONCLUSIONS

Non-invasive continuous CO and CaO(2) monitors are shown in this single case to provide continuous DO(2) measurement. The ability to assess DO(2) may improve hemodynamic monitoring during goal directed therapies.

The SOS pilot study: a RCT of routine oxygen supplementation early after acute stroke--effect on recovery of neurological function at one week

Mild hypoxia is common after stroke and associated with poor long-term outcome. Oxygen supplementation could prevent hypoxia and improve recovery. A previous study of routine oxygen supplementation showed no significant benefit at 7 and 12 months. This pilot study reports the effects of routine oxygen supplementation for 72 hours on oxygen saturation and neurological outcomes at 1 week after a stroke.

METHODS

Patients with a clinical diagnosis of acute stroke were recruited within 24 h of hospital admission between October 2004 and April 2008. Participants were randomized to oxygen via nasal cannulae (72 h) or control (room air, oxygen given only if clinically indicated). Clinical outcomes were assessed by research team members at 1 week. Baseline data for oxygen (n = 148) and control (n = 141) did not differ between groups.

RESULTS

The median (interquartile range) National Institutes of Health Stroke Scale (NIHSS) score for the groups at baseline was 6 (7) and 5 (7) respectively. The median Nocturnal Oxygen Saturation during treatment was 1.4% (0.3) higher in the oxygen than in the control group (p<0.001) during the intervention. At 1 week, the median NIHSS score had reduced by 2 (3) in the oxygen and by 1 (2) in the control group. 31% of participants in the oxygen group and 14% in the control group had an improvement of ≥4 NIHSS points at 1 week doubling the odds of improvement in the oxygen group (OR: 2.9).

CONCLUSION

Our data show that routine oxygen supplementation started within 24 hours of hospital admission with acute stroke led to a small, but statistically significant, improvement in neurological recovery at 1 week. However, the difference in NIHSS improvement may be due to baseline imbalance in stroke severity between the two groups and needs to be confirmed in a larger study and linked to longer-term clinical outcome.

TRIAL REGISTRATION

Controlled-Trials.com ISRCTN12362720; European Clinical Trials Database 2004-001866-41.

Improving the safety of oxygen therapy in the treatment of acute myocardial infarctions

AIM

The article examines the evidence for giving oxygen routinely to patients with suspected myocardial infarction, and addresses the challenges in changing practice.

BACKGROUND

It has been thought that administering oxygen to patients suffering from acute myocardial infarctions may be beneficial, but there is a lack of supporting evidence. Furthermore there is evidence that the use of oxygen in some circumstances may not improve clinical outcome. Despite conflicting evidence, guidelines in the past have recommended supplementary oxygen as part of treatment. Therefore it was necessary to understand and identify best practice.

METHODS

Evidence was collated using electronic databases. Search terms included 'acute myocardial infarction' 'acute coronary syndrome' 'oxygen' and 'hypoxia', 'hyperoxaemia'.

CONCLUSION

A systematic review of studies did not confirm that the use of routine oxygen in the acute stages of a myocardial infarction reduces myocardial ischemia. In reality, some evidence suggests that oxygen may even increase myocardial ischemia. Therefore it is crucial that emergency care nurses/practitioners across the world use observation skills and monitoring such as pulse oximetry to recognise the clinical need for supplementary oxygen to be given to a patient.

Is hyperoxic ventilation important to treat acute coronary syndromes such as myocardial infarction?

After reviewing the literature, I was unable to find hard evidence that the use of supplemental oxygen (hyperbaric or normobaric) in an uncomplicated acute myocardial infarction (AMI) is beneficial, and there is some evidence that it may be harmful.

Concepts in hypoxia reborn

The human fetus develops in a profoundly hypoxic environment. Thus, the foundations of our physiology are built in the most hypoxic conditions that we are ever likely to experience: the womb. This magnitude of exposure to hypoxia in utero is rarely experienced in adult life, with few exceptions, including severe pathophysiology in critical illness and environmental hypobaric hypoxia at high altitude. Indeed, the lowest recorded levels of arterial oxygen in adult humans are similar to those of a fetus and were recorded just below the highest attainable elevation on the Earth's surface: the summit of Mount Everest. We propose that the hypoxic intrauterine environment exerts a profound effect on human tolerance to hypoxia. Cellular mechanisms that facilitate fetal well-being may be amenable to manipulation in adults to promote survival advantage in severe hypoxemic stress. Many of these mechanisms act to modify the process of oxygen consumption rather than oxygen delivery in order to maintain adequate tissue oxygenation. The successful activation of such processes may provide a new chapter in the clinical management of hypoxemia. Thus, strategies employed to endure the relative hypoxia in utero may provide insights for the management of severe hypoxemia in adult life and ventures to high altitude may yield clues to the means by which to investigate those strategies.

Oxygen therapy for acute myocardial infarction

BACKGROUND

Oxygen (O(2)) is widely recommended for patients with myocardial infarction yet a narrative review has suggested it may do more harm than good. Systematic reviews have concluded that there was insufficient evidence to know whether oxygen reduced, increased or had no effect on the heart ischaemia or infarct size.

OBJECTIVES

To review the evidence from randomised controlled trials to establish whether routine use of inhaled oxygen in acute myocardial infarction (AMI) improves patient-centred outcomes, in particular pain and death.

SEARCH STRATEGY

The following bibliographic databases were searched (to the end of February 2010): Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE, MEDLINE In-Process, EMBASE, CINAHL, LILACS and PASCAL, British Library ZETOC, Web of Science ISI Proceedings. Experts were also contacted to identify any studies. No language restrictions were applied.

SELECTION CRITERIA

Randomised controlled trials of people with suspected or proven AMI, less than 24 hours after onset, in which the intervention was inhaled oxygen (at normal pressure) compared to air and regardless of co-therapies provided these were the same in both arms of the trial.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed the titles and abstracts of identified studies to see if they met the inclusion criteria and independently undertook the data extraction. The quality of studies and the risk of bias were assessed according to guidance in the Cochrane Handbook. The primary outcomes were death, pain and complications. The measure of effect used was the relative risk (RR).

MAIN RESULTS

Three trials involving 387 patients were included and 14 deaths occurred. The pooled RR of death was 2.88 (95% CI 0.88 to 9.39) in an intention-to-treat analysis and 3.03 (95% CI 0.93 to 9.83) in patients with confirmed AMI. While suggestive of harm, the small number of deaths recorded meant that this could be a chance occurrence. Pain was measured by analgesic use. The pooled RR for the use of analgesics was 0.97 (95% CI 0.78 to 1.20).

AUTHORS' CONCLUSIONS

There is no conclusive evidence from randomised controlled trials to support the routine use of inhaled oxygen in patients with acute AMI. A definitive randomised controlled trial is urgently required given the mismatch between trial evidence suggestive of possible harm from routine oxygen use and recommendations for its use in clinical practice guidelines.

Oxygen therapy-use and abuse in acute myocardial infarction patients

In August 2008, an article was published in Heart entitled, "The Routine Use of Oxygen in the Treatment of Myocardial Infarction." This article stimulated me to opine on this topic, which has been an interest of mine for many years.