Oxygen applied at pressure greater than one atmosphere. Pressure is typically expressed as atmospheres, millimeters of mercury (mm Hg) or as pounds per square inch (psi). One atmosphere is ambient pressure at sea level, which is equivalent to 760 mm Hg., or 14.7 psi.
Systemic Hyperbaric Oxygen (HBO):
Hyperbaric oxygen administered in full body chambers. The patient breathes 100% oxygen intermittently while the pressure of the treatment chamber is increased to 2 -3 atmospheres, equivalent to 1500 – 2500 mm Hg or 30 – 45 psi.
Topical Hyperbaric Oxygen (THBO):
Oxygen applied directly to the base of an open wound at pressure slightly above atmospheric e.g. 1.03 atmospheres (22 mm Hg or 0.4 psi.).
Disposable, Topical Hyperbaric Oxygen devices:
Disposable THBO devices are designed to be used one time and discarded. (Earlier multiple use extremity chamber devices were heavy, awkward to handle and difficult to clean and disinfect, increasing the risk of cross contamination between patients, and making home care use impractical.)
PURPOSE OF TOPICAL HYPERBARIC OXYGEN THERAPY
Oxygen is required for all new cell growth. Tissue at the base of chronic or non healing wounds tends to be ischemic. Application of topical hyperbaric oxygen induces the growth of new blood vessels at the wound base. The new blood vessels allow an increased flow of oxygenated blood to the wound which begins the healing process.
As healing progresses, new granulation tissue that is exposed to hyperbaric oxygen is better vascularized. This in turn leads to higher tensile strength collagen being formed during wound healing, which reduces scarring and the risk of recidivism.
Another important benefit of hyperbaric oxygen is that it is bactericidal for anaerobic bacteria e.g. Staphylococcus aureus and E.coli.
The difference between systemic HBO and topical hyperbaric oxygen (THBO) in therapeutic approach is that systemic HBO increases blood oxygen levels. However, blood oxygen levels are normally adequate for wound healing. The problem is that oxygen delivery to the wound site can be limited by poor wound tissue vascularization.
Topical hyperbaric oxygen on the other hand delivers oxygen directly to the wound. Transcutaneous oxygen levels are increased, despite the lack of well vascularized wound tissue. In addition, because this therapy is topical and relatively low pressure, there is no systemic absorption of oxygen, and therefore no risk of pulmonary or central nervous system toxicity that can result from breathing high pressure (30 – 45 psi) oxygen in full body chambers.