hyperoxia hyperoxia hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (o2) or higher than normal partial pressure of oxygen. hyperoxiaspecialtyemergency medicinesymptoms irritation congestion and edema of the lungs complications oxygen toxicity seizures death risk factors hyperbaric oxygen therapy underwater diving in medicine, it refers to excessive oxygen in the lungs or other body tissues, and results from raised alveolar oxygen partial pressure - that is, alveolar oxygen partial pressure greater than that due to breathing air at normal (sea level) atmospheric pressure. this can be caused by breathing air, at pressure above normal, or by breathing other gas mixtures with a high oxygen fraction, high ambient pressure or both. the body is tolerant of some deviation from normal inspired oxygen partial pressure, but a sufficiently elevated level of hyperoxia can lead to oxygen toxicity over time, with the mechanism related to the partial pressure, and the severity related to the dose. hyperoxia is the opposite of hypoxia; hyperoxia refers to a state in which oxygen supply to the tissues is excessive, and hypoxia refers to a state in which oxygen supply is insufficient. supplementary oxygen administration is widely used in emergency and intensive care medicine and can be life-saving in critical conditions, but too much can be harmful and affects a variety of pathophysiological processes. reactive oxygen species are known problematic by-products of hyperoxia which have an important role in cell signaling pathways. there are a wide range of effects, but when the homeostatic balance is disturbed, reactive oxygen species tend to cause a cycle of tissue injury, with inflammation, cell damage, and cell death. in the environment, hyperoxia refers to an abnormally high oxygen concentration in a body of water or other habitat. signs and symptoms associated with hyperoxia is an increased level of reactive oxygen species (ros), which are chemically reactive molecules containing oxygen. these oxygen containing molecules can damage lipids, proteins, and nucleic acids, and react with surrounding biological tissues. the human body has naturally occurring antioxidants to combat reactive molecules, but the protective antioxidant defenses can become depleted by abundant reactive oxygen species, resulting in oxidation of the tissues and organs. the symptoms produced from breathing high concentrations of oxygen for extended periods have been studied in a variety of animals, such as frogs, turtles, pigeons, mice, rats, guinea pigs, cats, dogs and monkeys. the majority of these studies reported the occurrence of irritation, congestion and edema of the lungs, and even death following prolonged exposures. oxygen toxicity main article: oxygen toxicity the supplementation of oxygen can lead to oxygen toxicity, also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning. there are two main types of oxygen toxicity: central nervous system (cns) toxicity, and pulmonary and ocular toxicity. temporary exposure to high partial pressures of oxygen at greater than atmospheric pressure can lead to central nervous system toxicity (cns). an early but serious sign of cns oxygen toxicity is a grand-mal seizure, also known as a generalized tonic-clonic seizure. this type of seizure consists of a loss of consciousness and violent muscle contractions. signs and symptoms of oxygen toxicity are usually prevalent, but there are no standard warning signs that a seizure is about to ensue. the convulsion caused by oxygen toxicity does not lead to hypoxia, a side effect common to most seizures, because the body has an excess amount of oxygen when the convulsion begins. the seizures can lead to drowning, however, if the convulsion is suffered by a diver still in the water. prolonged exposure to higher oxygen levels at atmospheric pressure can lead to pulmonary and ocular toxicity. symptoms of oxygen toxicity may include disorientation, respiratory problems, myopia, or accelerated development of cataracts. prolonged exposure to higher than normal partial pressures of oxygen can result in oxidative damage to cell membranes. signs of pulmonary (lung) oxygen toxicity begin with slight irritation in the trachea. a mild cough usually ensues, followed by greater irritation and a worse cough until breathing becomes quite painful and the cough becomes uncontrollable. if supplementation of oxygen is continued, the individual will notice tightness in the chest, difficulty breathing, shortness of breath, and if exposure is continued, fatality due to lack of oxygen. cause oxygen supplied at greater than atmospheric pressure has been known to damage plants, animals, and aerobic bacteria such as escherichia coli. the damaging effects vary depending on the specimen used, its age, physiological state, and diet. evidence indicates that hyperoxia may be harmful, but robust data from interventional studies is limited. the supplementation of oxygen has been a common procedure of pre-hospital treatment for many years. guidelines include cautions about chronic obstructive pulmonary disease (copd). these guidelines stress the use of 28% oxygen masks and caution the dangers of hyperoxia. long-term use of supplemental oxygen improves survival in patients with copd, but can lead to lung injury. an additional cause of hyperoxia is related to underwater diving with breathing apparatus. divers breath a mixture of gasses which must include oxygen, and the partial pressure of oxygen in any given gas mixture will increase with depth. atmospheric air becomes hyperoxic during the dive, and a hyperoxic gas mixture known as nitrox is used to reduce the risk of decompression sickness by substituting oxygen for part of the nitrogen content. breathing nitrox can lead to oxygen toxicity due to the high partial pressure of oxygen if used too deep or for too long. protocols for the safe use of raised oxygen partial pressure in diving are well established and used routinely by recreational scuba divers, military combat divers and professional saturation divers alike. the highest risk of hyperoxia is in hyperbaric oxygen therapy, where it is a high probability side effect of the treatment for more serious conditions, and is considered an acceptable risk as it can be managed effectively without apparent long term effects. oxygen rebreathers are also used for normobaric routine work and emergency response in non-breatheable atmospheres, or in circumstances where the suitability of the ambient gas for breathing is unknown or may change without warning, such as firefighting, underground rescue, and work in confined spaces. supplemental oxygen is also used for high altitude exposures in aviation and mountaineering. in all these cases, the maximum concentration is naturally limited by the ambient pressure, but the lower limit is usually more difficult to control, and the immediate consequences of hypoxia are generally more serious that the immediate consequences of hyperoxia, so there is a tendency to provide a larger margin for error for hypoxia, and the user is exposed to hyperoxic conditions for much of the time. mechanism