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Hyperbaric oxygen (HBO) is a mode of therapy in which the patient breathes 100 percent oxygen at pressures greater than normal atmospheric (sea level) pressure. Hyperbaric oxygen therapy involves the systemic delivery of oxygen at values two or three times greater than atmospheric pressure by dissolving oxygen in the plasma, in addition to 100% saturation of the hemoglobin molecule.
Several beneficial mechanisms are associated with intermittent exposure to hyperbaric does of oxygen. Either alone, or in combination with other medical and surgical procedures, these mechanisms serve to enhance the healing or detoxification process of treatable conditions.
Hyperoxygenation provides immediate support to poorly perfused tissue in areas of compromised blood flow. The elevated pressure within the hyperbaric chamber results in an increase in plasma oxygen concentration, producing a four-fold increase in perfusing delivery of oxygen from functioning capillaries. While this form of hyperoxygeneration is only a temporary measure, it will help maintain tissue viability until corrective measures can be implemented or a new blood supply is established.
Neovascularization represents an indirect and delayed response to hyperbaric oxygen exposure. Therapeutic effects include enhanced fibroblast division, neoformation of collagen and capillary angiogenesis in areas of sluggish neovascularization such as late radiation damaged tissue, refractory osteomyelitis and chronic ulcers.
Hyperoxia-enhanced antimicrobial activity has been shown to enhance tissue penetration at a number of levels. Hyperbaric oxygen causes toxin inhibition and toxin inactivation in Clostridial perfringens infections (gas gangrene). Hyperoxia enhances phagocytosis and white cell oxidative killing, and has been shown to enhance aminoglycocide activity. Recent research has demonstrated a prolonged post-antibiotic effect, when hyperbaric oxygen is combined with tobramycin against Pseudomonas aeruginosa.
Direct pressure utilizes the concept of Boyle's Law to reduce the volume of intravascular or other free gas. For more than a century this mechanism has formed the basis of hyperbaric oxygen therapy as the standard of care for decompression sickness and cerebral arterial gas embolism (CAGE). Commonly associated with divers, CAGE may also be a iatrogenic event in modern medical practice. It results in significant morbidity and mortality and remains grossly underdiagnosed.
Hyperoxia-induced vasoconstriction is another important mechanism. It occurs with HBO and is helpful in managing intermediate compartment syndrome and other acute ischemias in injured extremities, and reducing interstitial edema in grafted tissue. Studies in burn wound applications have indicated a significant decrease in fluid resuscitation requirements when HBO therapy is added to standard burn wound management protocols.
Attenuation of reperfusion injury is the most recent mechanism to be discovered. Much of the damage associated with reperfusion is brought about by the inappropriate activation of leukocytes. Following an ischemic interval the total injury pattern is the result of two components: a direct irreversible injury component from hypoxia, and an indirect injury which is largely mediated by the inappropriate activation of leukocytes. The net effect is the preservation of marginal tissues that would otherwise be lost to ischemia-reperfusion injury by suppressing the leukocyte response and down regulating ischemia promoting regulators.
The Undersea and Hyperbaric Medical Society suggest the following indications are appropriate when referring Hyperbaric Oxygen Therapy treatment:
Safe time-dose limits have been established for hyperbaric oxygen exposure, and these limitations form the basis for today's treatment protocols.
Emergency cases may only require one or two treatments, where as 30 to 40 treatments may be necessary to treat angiogenesis. Treatment times vary according to the clinical response of each patient. With the exception of decompression sickness and cerebral arterial gas embolism, treatments last approximately two hours. These treatments may be administered once, twice or three times daily. The average wound healing session is 90 minutes, compared to a dive injury that usually exceeds two and a half hours.
Hyperbaric Oxygen Therapy is offered as a referral and consultation service only. To refer a patient for evaluation during normal business hours, Monday through Friday, 8:30 a.m. to 5:00 p.m., call the Norman Knight Hyperbaric Medicine Center at (617) 573-4411.
A 24-hour consultation and treatment response is available for emergencies: carbon monoxide poisoning; gas gangrene; cerebral arterial gas embolism. Please call (617) 573-4411.
Hyperbaric Medicine Practice
2nd Edition
Eric P. Kindwall, M.D. and Harny T. Whelan, M.D.
Best Publishing, 1999
UHMS Report - Guidelines
For Clinical Multiple Hyperbaric Facilities
10531 Metropolitan Avenue
Kensington, MD 20895
Daniel G. Deschler, M.D., Director
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