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The effects of environmental hypoxia on substrate utilisation during exercise: a meta-analysis.
Griffiths, A, Shannon, OM, Matu, J, King, R, Deighton, K, O'Hara, JP
Journal of the International Society of Sports Nutrition. 2019;(1):10
Abstract
BACKGROUND A better understanding of hypoxia-induced changes in substrate utilisation can facilitate the development of nutritional strategies for mountaineers, military personnel and athletes during exposure to altitude. However, reported metabolic responses are currently divergent. As such, this systematic review and meta-analysis aims to determine the changes in substrate utilisation during exercise in hypoxia compared with normoxia and identify study characteristics responsible for the heterogeneity in findings. METHODS A total of six databases (PubMed, the Cochrane Library, MEDLINE, SPORTDiscus, PsychINFO, and CINAHL via EBSCOhost) were searched for published original studies, conference proceedings, abstracts, dissertations and theses. Studies were included if they evaluated respiratory exchange ratio (RER) and/or carbohydrate or fat oxidation during steady state exercise matched for relative intensities in normoxia and hypoxia (normobaric or hypobaric). A random-effects meta-analysis was performed on outcome variables. Meta-regression analysis was performed to investigate potential sources of heterogeneity. RESULTS In total, 18 studies were included in the meta-analysis. There was no significant change in RER during exercise matched for relative exercise intensities in hypoxia, compared with normoxia (mean difference: 0.01, 95% CI: -0.02 to 0.05; n = 31, p = 0.45). Meta-regression analysis suggests that consumption of a pre-exercise meal (p < 0.01) and a higher exercise intensity (p = 0.04) when exposed to hypoxia may increase carbohydrate oxidation compared with normoxia. CONCLUSIONS Exposure to hypoxia did not induce a consistent change in the relative contribution of carbohydrate or fat to the total energy yield during exercise matched for relative intensities, compared with normoxia. The direction of these responses appears to be mediated by the consumption of a pre-exercise meal and exercise intensity.
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Associations between ventilator settings during extracorporeal membrane oxygenation for refractory hypoxemia and outcome in patients with acute respiratory distress syndrome: a pooled individual patient data analysis : Mechanical ventilation during ECMO.
Serpa Neto, A, Schmidt, M, Azevedo, LC, Bein, T, Brochard, L, Beutel, G, Combes, A, Costa, EL, Hodgson, C, Lindskov, C, et al
Intensive care medicine. 2016;(11):1672-1684
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Abstract
PURPOSE Extracorporeal membrane oxygenation (ECMO) is a rescue therapy for patients with acute respiratory distress syndrome (ARDS). The aim of this study was to evaluate associations between ventilatory settings during ECMO for refractory hypoxemia and outcome in ARDS patients. METHODS In this individual patient data meta-analysis of observational studies in adult ARDS patients receiving ECMO for refractory hypoxemia, a time-dependent frailty model was used to determine which ventilator settings in the first 3 days of ECMO had an independent association with in-hospital mortality. RESULTS Nine studies including 545 patients were included. Initiation of ECMO was accompanied by significant decreases in tidal volume size, positive end-expiratory pressure (PEEP), plateau pressure, and driving pressure (plateau pressure - PEEP) levels, and respiratory rate and minute ventilation, and resulted in higher PaO2/FiO2, higher arterial pH and lower PaCO2 levels. Higher age, male gender and lower body mass index were independently associated with mortality. Driving pressure was the only ventilatory parameter during ECMO that showed an independent association with in-hospital mortality [adjusted HR, 1.06 (95 % CI, 1.03-1.10)]. CONCLUSION In this series of ARDS patients receiving ECMO for refractory hypoxemia, driving pressure during ECMO was the only ventilator setting that showed an independent association with in-hospital mortality.
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Oxygen Saturation Targets for Extremely Preterm Infants after the NeOProM Trials.
Stenson, BJ
Neonatology. 2016;(4):352-8
Abstract
Five randomized controlled trials comparing lower (85-89%) versus higher (91-95%) pulse oximeter saturation (SpO2) targets for extremely preterm infants have now been reported from the United States of America, Canada, the United Kingdom, Australia and New Zealand. These trials included more than 4,800 infants, and they provide robust evidence to permit comparison of these target ranges and consider the next steps for clinicians and researchers. The lower SpO2 range was associated with a significant increase in the risk of death. There was no significant difference between the two target ranges in the rate of disability at 18-24 months, including blindness. A significant difference between groups in the risk of the composite primary outcome of death or disability in favour of the higher SpO2 range was mainly attributable to the difference between groups in the risk of death. The lower target range did not reduce bronchopulmonary dysplasia or severe visual impairment, but it did increase the risk of necrotizing enterocolitis requiring surgery or causing death. The trials provide no reason to prefer SpO2 targets below 90% and indicate the importance of more trials to see if a further survival advantage can be identified. The safety of targets above 95% has not been evaluated. The five trials were designed to be similar to facilitate an individual patient data meta-analysis, and this Neonatal Oxygen Prospective Meta-Analysis (NeOProM) may provide further insights.