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The Undersea and Hyperbaric Medicine Society1 has developed a list of conditions for which hyperbaric oxygen (HBO) therapy is an effective treatment modality (Table 18.1-1).2 For this chapter, we consider the diagnoses that lend themselves most clearly to emergency medicine practice—co poisoning, gas gangrene, necrotizing fasciitis, acute traumatic peripheral ischemia, decompression sickness (DCS), air-gas embolism, and exceptional blood loss anemia.

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Table 18.1-1 Indications for Hyperbaric Oxygen Therapy 
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Hyperbaric Physiology

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HBO therapy is the application of pressures >1 atmosphere absolute (ATA), (or 1.3 to avoid any confusion with topical HBO/topical o2) to an environment of 100% oxygen. This causes the Po2 to increase in proportion to the increase in ambient pressure. True HBO therapy only refers to the systemic delivery of oxygen via the lungs and is not related to “topical oxygen therapy,” in which only a specific body part is subjected to locally delivered oxygen under pressure.

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HBO therapy is delivered in a hyperbaric chamber. Chambers that are capable of treating multiple individuals simultaneously are called multiplace chambers, whereas single patient units are called monoplace chambers. Monoplace chambers are the most common types used in the hospital setting (Figure 18.1-1). Multiplace chambers allow an assistant to enter the chamber with a patient.

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Figure 18.1-1.
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Monoplace chamber.

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Under normobaric conditions, everyone is exposed to one atmosphere of pressure as measured at sea level. A person at sea level has downward pressure exerted on his body equal to the weight of the atmosphere above him. Atmospheric pressure is measured using various equivalent units: 1 atmosphere of pressure is equal to 14.7 lb per square in., 760 mm Hg, or 760 Torr. When all pressures to which a person is exposed are summed up, the result is called atmospheres absolute. This accounts for the atmospheric pressure at sea level plus any additional pressure applied.

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In dive medicine, a branch of hyperbaric medicine that deals with scuba diving and other compressed air conditions, it is customary to refer to pressure in terms of feet of seawater. One atmosphere is equal the pressure exerted by 33 ft (10 m) of seawater. At the depth of 33 ft of seawater, a diver is exposed to 2 ATA—one from the atmosphere above the water, and one from the pressure ...

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