Hyperbaric Oxygen - Not Just For Divers
By Fred Bove, M.D., Ph.D
There are many uses for an hyperbaric chamber other than treatment of diving accidents. Of particular interest is the growing field of hyperbaric oxygen therapy. Oxygen is necessary for the function of cell tissues and organs in the body. Many forms of illness and injury cause inadequate oxygen delivery, with resulting dysfunction or damage.
Tissue injury often damages blood vessels. Lack of blood usually means lack of oxygen as well, but if oxygen partial pressure can be increased, oxygen will diffuse through the tissue and preserve function. This can be done by breathing pure oxygen at one atmosphere, which will raise oxygen partial pressure from 159 to 760 millimeters of mercury (21 to 100 percent of one ATA). To reach levels of oxygen partial pressure higher than 760 millimeters of mercury, ambient pressure must be increased and this is done in an hyperbaric chamber.
The accompanying table shows partial pressure of oxygen for different depths when using air and pure oxygen. Most medical treatments limit oxygen exposure to 45 feet to minimize risk for oxygen toxicity. Treatments for diving accidents (DCS, AGE) provide oxygen at 60 feet but avoid toxicity by providing frequent air breaks. A common treatment protocol is pure oxygen at 33 feet for 60 to 90 minutes. This can be repeated daily for two or more weeks. This exposure has minimal risk for oxygen toxicity and appears successful in treating a variety of medical disorders.
Hyperbaric oxygen has also been used to treat carbon monoxide poisoning, gas gangrene and other acute infections, severe burns, some forms of crush injuries, chronic bone infections and tissue injury that occurs after radiation treatment for cancer.
Oxygen Toxicity: Although we think of oxygen as essential for life, too much will cause damage to cells and organs. For divers, the most dangerous form results in toxicity of the brain. This is especially risky when using a pure oxygen diving system. These closed circuit diving systems are used by the military because they are completely bubble free. Their depth limit for prolonged use is 25 feet (about 1.75 ATA pressure and about 1.4 ATA oxygen partial pressure when the system equilibrates at 82 percent oxygen). Dive time at deeper depths is shortened considerably to avoid oxygen seizures.
Working divers limit oxygen partial pressure to 1.3 to 1.4 ATA, while clinical exposures in an hyperbaric chamber can be continuous for 60 to 90 minutes at 33 feet or 20 minutes with a five minute air break at 60 feet. The higher chamber exposures are possible because there is no work or exercise involved and the temperature is held constant around 75F. Oxygen toxicity limits based on 1.3 ATA maximum oxygen partial pressure in diving will occur at 181 feet using air, 101 feet using 32 percent oxygen or 74 feet using 40 percent oxygen.
Types of Hyperbaric Chambers: Two basic types of chambers are in use today; the single person chamber (monoplace), and a large multiperson chamber (multiplace). Monoplace chambers are usually compressed with 100 percent oxygen and are used primarily for treatment of medical disorders. Tables for treating decompression sickness and arterial air embolism using 100 percent oxygen without air breaks are available for monoplace chambers. Some monoplace chambers are compressed with air and the subject breathes oxygen through a mask. All multiplace chambers are compressed with either air or a mixture of helium and oxygen. Individual breathing masks supply 100 percent oxygen or some other gas mixture. Air breaks, when needed, are accomplished by removing the mask.
Chamber Safety: The most serious safety concern in using hyperbaric chambers is fire. Because of the increased oxygen partial pressure in the compressed chamber air, often enriched further by oxygen leaking from breathing masks, fires will spread rapidly at high intensity. Chamber fires are usually catastrophic and often result in loss of lives. In well managed chamber operations, fire suppression systems are used; oxygen percentage in the chamber air is monitored continuously and prevented from increasing. Patients are required to remove all material from pockets, electronic devices are prohibited and most facilities will not allow street shoes into the chamber. Even a thin film of oil carried into the chamber can create a source for a spontaneous flash fire. If you need treatment in an hyperbaric chamber, you will be told about the safety measures you should follow. When breathing pure oxygen at 60 feet be sure to ask about the early symptoms of oxygen toxicity.
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