Treatment consists of placing the patient in a specially designed clear plastic pressure chamber. Once the chamber’s hatch is closed, the patient breathes 100% oxygen at twice normal atmospheric pressure. Because of the risk of fire, the patient is dressed in a plain cotton gown, and takes nothing into the chamber except a bottle of drinking water. A grounding strap is worn on the wrist to prevent the building of static electricity and a spark. Hearing aids, dentures, and medication patches are all removed before the treatment, which normally lasts two hours. A course of therapy typically requires 30 “dives” over a period of six weeks, though acute conditions (thermal burns, compromised grafts, or carbon monoxide poisoning) may need just a few.
Under normal atmospheric conditions, oxygen is simply a requirement of metabolism. At higher pressures and concentrations, its physiologic effects increase. For example, in a patient with bends, gas embolism, or gas gangrene, high-pressure oxygen compresses the gas bubbles trapped in capillaries and tissues, restoring normal blood flow. At three times atmospheric pressure, sufficient oxygen is dissolved in plasma that the body’s resting metabolic needs can be met without hemoglobin. Failing grafts and skin flaps, severe anemia, and vascular insufficiency all respond to this mechanism of action.
Vasoconstriction caused by HBOT reduces capillary hydrostatic pressure and edema in crush injury and compartment syndrome. High oxygen concentration allows this metabolite to diffuse farther outside capillaries spread apart by edema fluid, thus reaching hypoxic cells. High oxygen gradients stimulate new growth of blood vessels to help heal diabetic foot ulcers and radiation damaged tissue. Even brief exposure to hyperbaric oxygen causes fibroblasts to increase collagen production to create the framework for reconstruction.
HBOT doubles the killing power of hypoxic white blood cells. This process inhibits anaerobic bacteria, suppresses exotoxins and destroys some clostridia and cytolytic toxins. Transport of certain antibiotics across bacterial cell walls is also enhanced, causing these drugs to work more efficiently. In addition, intracranial abscesses, invasive mycoses, and chronic foot ulcers can respond to the anti-infective mechanisms of HBOT.