Oxygen is the chemical element on which life rests as we know it and to which we belong. It is necessary for the normal functioning of most living organisms on Earth. If it does not exist at all (anoxia) or the body does not get enough of it (hypoxia), all the biochemical processes that allow a smooth life cycle of body cells fail.
We know that oxygen is a medicine, but we also know that with oxygen, not everything is just so beautiful. Oxygen can also be a very dangerous poison. Oxygen toxicity, in addition to the most common manifestation on the central nervous system, affects the lungs and eyes.
For most divers, but also for emergency physicians, the concept of toxic effects of oxygen is related to its effect on the central nervous system. And causing oxygen epilepsy. Much less known is its effect on the lungs. It is, however, a topic well known to saturation and other professional divers. But today, many recreational divers use equipment previously reserved only for technical dives with higher percentages of oxygen. Now imagine a situation where a diver with gas mixtures and increased oxygen partial pressure gets hurt.
He then gets a dysbaric diving disease. Immediately in first aid on board, he receives the prescribed 100% oxygen on request. He is taken over by the emergency medical team and given oxygen in transport. After admission to the emergency department of the competent hospital, they continue with oxygen. So far everything says that when something happens to a diver we consider it a decompression sickness until another is proven. And we put him on recompression treatment with an abundance of hyperbaric oxygen. Upon completion, he goes to the hospital ward waiting for new recompression treatment. It happens that they reconnect it to oxygen here as well. It is a story that is not a figment of the imagination, it happens in reality. And it doesn’t end well. Therefore, it is necessary to keep in mind the consequences of too long action of oxygen on the lung tissue and prevent their development.
Oxygen epilepsy is a serious disorder that passes with the cessation of the action of pure oxygen, most often without sequelae. The toxic effects of oxygen on lung tissue (formerly known as the Lorrain-Smith effect) may, however, be irreversible. This phenomenon is not yet fully understood. But it is thought to be due to natural by-products of cellular respiration called reactive oxygen species – ROS. ROS can damage cell structures such as cell membranes and cause oxidative stress. They usually begin with a dry cough, followed by chest pain, tingling when breathing, and difficulty breathing. One possible oversight in medical facilities is that it is about oxygen being dry. Therefore it irritates and tries to alleviate this symptom with humidifiers. Cessation of inhalation of pure or high-percentage oxygen usually stops these symptoms very quickly. Whether it is diving or staying in a pressure chamber.
Exposure to hyperbaric oxygen
Exposure to hyperbaric oxygen is useful in many situations as a preventative and cure for many conditions and diseases. Properly applied, this medical procedure is one of the safest. Every diver has all the benefits, but also all the side effects of oxygen. The laws of physics are the same with increasing ambient pressure, whether in the sea or in a barochamber. Some clinical studies have shown that multiple exposures to barochamber treatment (hyperbaric oxygen therapy, HBOT) slightly reduce some pulmonary functions. Primarily the small airways. At the same time, peak flow (Peak ExpiratoryFlow, PEF) and forced vital capacity (FVC) are slightly improved in people without any lung disease. Standard HBOT treatments are safe for patients. This “standard” means up to 2.4 bar (14 meters depth) over 60 to 90 minutes.
Toxic effects of oxygen on the lungs and other non-neurological organ systems
To better understand the potentially fatal dangers of hypoxia and hyperoxia, it is necessary to recall the basic physical facts. At sea level, the air is made up of approximately 21% oxygen. Which in the lungs gives an alveolar oxygen pressure (PAO2) of about 100 mmHg. Plasma hemoglobin is almost completely saturated (97-100%). And there is minimal dissolved oxygen in the plasma. Therefore, assuming a hemoglobin concentration of 12 g / dL, the combined whole blood oxygen content is about 16.2 ml O2 / dL. Under hyperbaric conditions, by inhaling 100% oxygen at a pressure of three bar (20 meters depth) the PAO2 value rises to about 2280 mmHg. According to Henry’s law the combined oxygen content of whole blood increases by 42%, to 23.0 ml O2 / dL completely by increasing the oxygen dissolved in the plasma. It is also the basis of HBOT’s action.
Oxygen in the body is involved in the production of adenosine triphosphate (ATP). One of the main components of intracellular energy transfer and metabolic processes. To maintain metabolism, the average person uses about six ml of O2 / dL blood.
Slower development of oxygen toxicity may follow prolonged exposure to lower oxygen levels. Such development of changes requires many hours or days of exposure to pure oxygen under normobaric conditions. But significantly faster with exposure to pure oxygen or its increased concentration at elevated pressure. So in diving or in a barochamber when, in addition to oxygen epilepsy, symptoms of acute pulmonary oxygen poisoning can also appear. The main organ affected is the lungs with the development of potentially permanent changes in the lung tissue. – Pulmonary fibrosis, but many other parts of the body can also be affected. Therefore, the term “whole body toxicity” is used for the affected parts of the body other than the central nervous system (CNS).
This generally does not worry divers who dive in no-decompression mode. Even when inhaling oxygen-enriched mixtures. But they can occur during intense diving activities. Especially at greater depths or during long decompression oxygen treatments for decompression sickness in the hyperbaric chamber. Symptoms include chest pain or discomfort, cough, inability to take deep breaths without pain or coughing, fluid in the lungs, and decreased vital capacity. Other, non-pulmonary symptoms of whole-body oxygen toxicity include skin tingling and itching, headache, dizziness, nausea, vision changes, and a dramatic decrease in aerobic capacity during exposure to exertion.
How to reduce the risk of oxygen poisoning
The risk of oxygen poisoning can be reduced by intermittent oxygen inhalation. Making occasional “breaks” when breathing air or a mixture with a reduced oxygen concentration. Both therapeutic recompression and standard HBOT treatments are based on this. This is how to avoid oxygen convulsions. But also acute and late pulmonary and other bodily manifestations of oxygen poisoning.
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