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Hyperbaric oxygen (HBO) therapy involves breathing oxygen with the body exposed to an ambient pressure greater than that of sea level. HBO therapy results in the systemic delivery of oxygen that produces supraphysiologic oxygen tension in perfused tissues. The effects of HBO therapy are due to the combined effects of both increased ambient pressure and increased oxygen tension.1

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HBO therapy is delivered in a hyperbaric chamber. Monoplace chambers accommodate a single occupant and are typically clear, acrylic, plastic, cylindrical units with a door at one end (Figure 1). An attendant monitors the patient from the outside and communicates via intercom. Specially designed cardiopulmonary monitoring devices, intravenous infusion pumps, and ventilators enable critically ill patients to be treated in most monoplace chambers. Multiplace chambers can simultaneously treat multiple patients and will accommodate medical personnel inside the chamber (chamber tender or assistant) to perform hands-on patient assessment and care (Figure 2). Monoplace chambers generally use 100% oxygen for pressurization, whereas multiplace units are pressurized with air and patients breathe oxygen using tight-fitting facemasks, a hood, or endotracheal tube while inside. Most HBO chamber facilities have equipment and treatment protocols analogous to an intensive care unit.

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Ambient pressure is an important concept in HBO therapy. At sea level, the pressure exerted by the air column (the atmosphere) above is quantified as 1 atmospheres absolute of pressure (1 ATA), 14.7 lb per square inch, 760 mm Hg, or 760 torr. Once a patient is placed inside a chamber, the ambient pressure is increased by the gradual inflow of compressed gas, either oxygen or air. Most HBO therapy takes place with an ambient pressure between 2.0 and 3.0 ATA.

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In hyperbaric and diving medicine, the increased ambient pressure was originally described as of feet of sea water (fsw) or meters of sea water (msw) for both HBO treatment and during scuba diving. One atmosphere is equal to the pressure exerted by 33 fsw (10 msw), so starting at sea level, the ambient pressure is 1 ATA, and at a depth of 33 fsw, the ambient pressure would be 2 ATA. Describing an HBO treatment at either 2 ATA or 33 fsw communicates equivalent pressure.

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A typical HBO treatment lasts 90 to 120 minutes. The initial pressurization phase is done over 10 to 15 minutes to allow for equalization of pressures within the sinuses and middle ear as ambient pressure increases. Pressure is then maintained at the desired levels for 40 to 90 minutes, followed by depressurization over 5 to 10 minutes. In a monoplace chamber, the patient is surrounded by and breathes 100% oxygen during the entire treatment. If desired, air breaks are ...

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