Hyperbaric Oxygen Therapy
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Definition of Hyperbaric Oxygen Therapy
Hyperbaric oxygen (HBO) therapy involves the inhalation of 100% oxygen at an elevated (i.e., greater than sea-level) atmospheric pressure. In the treatment of wounds, this is typically between 2 to 2.5 atmospheric absolute (ATA). Originally developed for the treatment of decompression sickness, HBO therapy is used by some physicians in the management of a variety of wound types. The theory is that wounds have a reduced oxygen supply that impairs wound healing. By delivering oxygen to the body under hyperbaric conditions, tissue oxygen levels are raised, and this enhances wound healing. Many physicians use transcutaneous oxygen tension (TcPO2) with vascular assessment to help predict the healing potential in patients before they undergo HBO therapy. TcPO2 is a non-invasive quantitative assessment of the amount of oxygen in the tissue.
The delivery system for HBO uses either a monoplace (single person) chamber or multiplace (multiple persons) chamber. In monoplace chambers, the entire chamber is pressurized with 100% oxygen to the desired ATA. Multiplace chambers, which can accommodate between 2-12 patients, are pressurized (using compressed air) and the patients breathe 100% oxygen either via mask, head tent, or endotracheal tube. In either setting, the time the patient spends in the chamber under hyperbaric conditions is decided by the attending physician and generally ranges from one to two hours.
Potential risks for patients undergoing treatment with HBO therapy include pressure related traumas (e.g., barotraumatic otitis, pneumothorax) and adverse effects due to oxygen toxicity (e.g., myopia, seizures). Some patients may experience claustrophobia due to the confined space of the chambers. Most adverse events are selflimited and resolve after termination of therapy. Patients with barotraumatic otitis may require the placement of myringotomy tubes.
Therapeutic Mechanisms of Hyperbaric Oxygen Therapy
Hyperoxygenation HBO therapy provides immediate support to poorly-perfused tissue in areas of compromised blood flow. The increased pressure produced in a hyperbaric chamber results in a 10-15 fold increase in plasma oxygen concentration. This also produces a four-fold increase in the diffusing distance of oxygen from functioning capillaries. Although this form of hyperoxygenation is a temporary measure, it will serve to buy time and maintain tissue viability until corrective interventions can be implemented.
Neovascularization Therapeutic effects of HBO therapy also 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 ulcerations in soft tissue.
Mechanical Effect of Direct Pressure By utilizing the concept of Boyle’s Law, HBO therapy reduces the volume of intravascular or other free gases. This effect has established the basis for HBO therapy as the standard of care for decompression sickness and arterial gas embolism.
Vasoconstriction Hyperoxia-induced vascular constriction is another important mechanism.HBO therapy can decrease blood flow in normal tissue by 20% and reduce edema by 20%.
Antimicrobial Effect HBO therapy causes toxin inhibition and toxin inactivation in Clostridia perfringens infections (gas gangrene). Hyperoxygenation enhances phagocytes and white cell oxidative killing, and it has also been shown to enhance aminoglycocide activity. Recent research has demonstrated a prolonged post-antibiotic effect when HBO therapy is combined with tobramycin against pseudomonas aeroginosa.
Attenuation of Perfusion Injury This is the most recently discovered benefit of HBO therapy. Much of the damage associated with reperfusion is brought about by the inappropriate activation of leukocytes. HBO therapy can prevent such an inappropriate activation of leukocytes. This, in turn, preserves tissues that may otherwise be lost to ischemic reperfusion injury.
Undersea and Hyperbaric Medical Society (UHMS) Approved Indications for Hyperbaric Oxygen Therapy
HBOT has proven to be effective in the treatment of a wide variety of medical disorders. The Hyperbaric Oxygen Therapy Committee of the Undersea and Hyperbaric Medical Society (UHMS) continuously reviews the evidence for using hyperbaric oxygen for disease processes. Every two years, the UHMS makes recommendations as to which of the diseases are amenable to hyperbaric oxygen therapy and accepted by third party payers for reimbursement. The current list of the UHMS accepted indications are as follows:
- Air or Gas Embolism
- Carbon Monoxide Intoxication
- Clostridial Myonecrosis
- Crush Injuries
- Decompression Sickness
- Enhancement of Healing in Select Problem Wounds
- Exceptional Blood Loss (Anemia)
- Necrotizing Soft Tissue Infections
- Delayed Radiation Injury (Soft Tissue and Bony Necrosis)
- Osteomyelitis (Refractory)
- Skin Grafts and Flaps (Compromised)
- Thermal Burns
- Idiopathic Sudden Sensorineural Hearing Loss
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