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Oxygen toxicity

Atul Malhotra, MD
David R Schwartz, MD
Richard M Schwartzstein, MD
Section Editor
Scott Manaker, MD, PhD
Deputy Editor
Geraldine Finlay, MD


Although supplemental oxygen is valuable in many clinical situations, excessive or inappropriate supplemental oxygen can be deleterious [1]. According to human and animal studies, high concentrations of inspired oxygen can cause a spectrum of lung injury, ranging from mild tracheobronchitis to diffuse alveolar damage (DAD) [2-6]. The latter is histologically indistinguishable from that observed in the acute respiratory distress syndrome (ARDS). The mechanisms and clinical consequences of oxygen toxicity are reviewed here. Specific issues related to the administration of oxygen are discussed separately. (See "The evaluation, diagnosis, and treatment of the adult patient with acute hypercapnic respiratory failure" and "Long-term supplemental oxygen therapy".)


Hyperoxia is not precisely defined but significant elevations of the partial arterial pressure of oxygen (PaO2) are found only when the fraction of inspired oxygen (FiO2) is greater than 21 percent of atmospheric pressure. Adverse events may result from increased oxygen tension in the alveoli, blood, or at the cellular level. Hyperoxia appears to produce cellular injury through increased production of reactive oxygen intermediates (ROIs), such as the superoxide anion, the hydroxyl radical, and hydrogen peroxide [7,8]. When the production of these (ROIs) increases and/or the cell's antioxidant defenses are depleted, they can react with and impair the function of essential intracellular macromolecules, resulting in cell death [9].

Oxygen free radicals may also promote a deleterious inflammatory response, leading to secondary tissue damage and/or apoptosis [10-12]. Much of the evidence supporting direct cellular injury due to ROIs comes from studies in transgenic mice with altered superoxide dismutase activity. Mice with augmented antioxidant mechanisms are relatively tolerant to hyperoxia, while manganese superoxide dismutase knockout mice die shortly after birth with extensive mitochondrial injury within degenerating neurons and cardiac myocytes [13-15]. Data from animal models suggest possible roles for insulin growth factor 1 [16] and angiopoietin 2 [17] in the pathogenesis of hyperoxia-induced lung injury.

The respiratory tract is exposed to the highest concentrations of oxygen in the body, placing airway lining cells and alveoli at the greatest risk for hyperoxic cytotoxicity [18]. Hyperoxia may also increase susceptibility to mucous plugging, atelectasis, and secondary infection by impairing both mucociliary clearance and the bactericidal capacity of immune cells [19-24].


High fractions of inspired oxygen (FiO2) have been associated with several effects on lung tissue/gas exchange including diminished lung volumes and hypoxemia due to absorptive atelectasis, accentuation/production of hypercapnia, and damage to airways and pulmonary parenchyma. The term "oxygen toxicity" is usually reserved for the last of these consequences, ie, tracheobronchial and alveolar damage.

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Literature review current through: Nov 2017. | This topic last updated: Aug 03, 2017.
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