Hyperbaric Medicine In Depth

Hyperbaric oxygen (HBO) therapy is the intermittent administration of 100% oxygen at pressure greater than sea level.  The technique can be implemented in a walk-in (multiplace) chamber, compressed to depth with air, in which the patient breathes 100% oxygen through a mask, head tent, or endotracheal tube.  Alternatively, the patient can be treated in a monoplace (one person) chamber pressurized with 100% oxygen.  In either case, the arterial partial pressure of oxygen will approach 1500 mmHg at a pressure equivalent of 33 feet of seawater.

During the 1930’s, oxygen at pressure was proposed as a treatment for decompression sickness (the bends).  In the early 1960’s, Dutch investigators showed the efficacy of HBO in the treatment of gas gangrene and anemic states.  Later that decade, it became the standard therapy for U.S. Navy diving casualties.  Subsequent studies have shown the importance of oxygen in the treatment of problem wounds, enhancement of white blood cell (WBC) killing, preservation of compromised tissue, and the promotion of angiogenesis.  Some centers are using this modality in the treatment of acute thermal injury.  The clinical indications for the use of HBO as an adjunct to traditional medical and surgical regimens continue to be expanded and refined.

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The mechanism of action of HBO relates to its ability to deliver substantial increases of oxygen to hypoxic peripheral tissue.  Oxygen inhaled at pressure dissolves in plasma.  At 3 atm, an arterial oxygenation of nearly 2200 mm Hg may be achieved, a quantity sufficient to maintain life in the absence of the red blood cell and hemoglobin.  Exposure to oxygen at pressure causes vasoconstriction and subsequent reduction in blood flow, which then results in the beneficial effect of a reduction of edema and less extravasation or bleeding in areas of capillary damage.  Despite the reduction in blood flow, the tenfold increase in oxygen content of plasma more than compensates to oxygenation the peripheral tissues.

Tissue oxygen levels play a major role in the physiology of wound healing, white cell function, and blood flow.  Abnormally low tissue oxygen levels (5-15 mmHg) are often present in nonhealing tissue. The low levels result in diminished white blood cell (WBC) killing and decreased collagen synthesis by fibroblasts.  Raising tissue oxygen levels to 30 to 40 mmHg provides the substrate necessary for fibroblasts to lay down a collagen matrix for support of capillary growth into avascular or hypo-vascular areas.  HBO can increase tissue oxygen tensions to levels high enough to allow for efficient WBC killing of bacteria, fibroblast production of collagen, and stimulation of angiogenesis, possibly through increased production of vascular endothelial growth factor.  Although treatments are usually 90 to 120 minutes once or twice daily, tissue oxygen levels remain above baseline values for some time.

In addition to the traditional indications for hyperbaric oxygen therapy, there are new applications that are being explored in the scientific community. As we learn more about how hyperbaric oxygen affects stem cells, neuroplasticity and the production of nitric oxide (a molecule critical to vascular health), we will be able to look at expanded therapeutic uses of HBOT. These investigational applications of hyperbaric oxygen therapy can be discussed with your hyperbaric physician to determine if there is any potential benefit to treatment.

Hyperbaric oxygen therapy is safe. The risks and benefits can be discussed between you and your doctor.