Physician’s Guide to Hyperbaric Oxygen Therapy
Why hyperbaric oxygen (HBO) therapy?
HBO therapy is a type of therapy in which the patient breathes 100 percent oxygen at pressures greater than normal atmospheric pressure. In contrast to attempts to force oxygen into tissues by topical application at levels only slightly higher than atmospheric pressure, HBO therapy involves the systemic delivery of oxygen at values two to three times greater than atmospheric pressure.
What are the therapeutic benefits of hyperbaric oxygen (HBO) therapy?
Several beneficial mechanisms are associated with intermittent exposure to hyperbaric doses of oxygen either alone or more commonly in combination with other medical and surgical procedures, HBO therapy serves to enhance the healing process.
- Hyperoxygenation provides immediate support to poorly perfused tissue in areas of compromised blood flow. The elevated pressure within the hyperbaric chamber results in a 10 to 15 fold increase in plasma oxygen concentration. This translates to arterial oxygen values of between 1,500 and 2,000 mmHg, producing a four-fold increase in the diffusing distance of oxygen from functioning capillaries. While this form of hyperoxygenation is only a temporary measure, it will serve to buy time and maintain tissue viability until corrective measures can be implemented or a new blood supply is established.
- Neovascularization represents an indirect and delayed response to HBO 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 demonstrated at a number of levels. HBO 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 aminoglycoside activity. Recent research has demonstrated a prolonged post-antibiotic effect when HBO 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 HBO therapy as the standard of care for cerebral arterial gas embolism (CAGE). Commonly associated with divers, CAGE is also an iatrogenic event that may occur in modern medical practice. It results in significant morbidity and mortality and remains grossly underdiagnosed.
- Hyperoxia-induced vasoconstriction is another important therapy. It occurs without component hypoxia 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. HBO reduces the indirect component of injury by preventing the inappropriate activation of leukocytes. The net effect is the preservation of marginal tissues that would otherwise be lost to ischemia-reperfusion injury.
Appropriate indications for hyperbaric referral
- Acute carbon monoxide poisoning
- Cerebral arterial gas embolism and iatrogenically induced
- Chronic osteomyelitis - refractory to antibiotics and debridement
- Clostridial myonecrosis - gas gangrene
- Compromised skin flaps and grafts
- Crush injury; compartment syndrome - other acute ischemias
- Enhancement of healing - problem wounds, diabetic foot lesions
- Exceptional blood loss anemia - patient refusal of blood, cross matching difficulties
- Necrotizing soft tissue infections - subcutaneous tissue, muscle, fascia
- Late radiation tissue injury - bone or soft tissue complications
- Osteoradionecrosis - mandible
- Thermal burns - acute management; wound healing support
Oxygen, when breathed under increased atmospheric pressure, is a potent drug. In addition to the beneficial effects that have been discussed, hyperbaric oxygen (HBO) can produce noticeable toxic effects if administered indiscriminately. Safe time-dose limits have been established for HBO exposure, and these limitations form the basis for today's treatment protocols.
Emergency cases, such as carbon monoxide poisoning or cerebral arterial gas embolism may only require one or two treatments. In those cases for which angiogenesis is the primary goal, as many as 30 to 40 treatments may be necessary. The precise number of treatments will often depend upon the clinical response of each patient.
Treatments last approximately two hours. These treatments may be given once, twice or occasionally three times daily, and can be provided in both inpatient or outpatient settings.
Patient referral and consultation procedures
Hyperbaric oxygen (HBO) therapy is offered as a referral and consultation service. Consultation is available on a 24-hour basis and is provided by a team of physicians trained in hyperbaric medicine under the American Medical Association/Undersea and Hyperbaric Medical Society approved courses.
Where HBO therapy is considered appropriate, a treatment protocol and schedule will be established, and the hyperbaric consultant's recommendations communicated to the referring physician. The referring/primary care physician will remain responsible for the patient's general medical management and will be updated from a hyperbaric perspective as appropriate.