About Hyperbaric Medicine

What is Hyperbaric Oxygen Therapy?

What are the Beneficial Mechanisms?

Indications for Hyperbaric Referral

Treatment Protocols

Delivery Systems

What is Hyperbaric Oxygen Therapy?

Hyperbaric oxygen is a mode of therapy in which the patient breathes 100% oxygen at pressures greater than normal atmospheric (sea level) pressure. In contrast with attempts to force oxygen into tissues by topical applications at levels only slightly higher than atmospheric pressure, hyperbaric oxygen therapy involves the systemic delivery of oxygen at levels two to three times greater than atmospheric pressure.

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What are the Beneficial Mechanisms?

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, these mechanisms serve to enhance the healing process of treatable conditions.

1. HYPEROXYGENATION provides immediate support to poorly perfused tissue in areas of acutely compromised blood flow. The elevated pressure within the hyperbaric chamber results in a 10-15 fold increase in plasma oxygen concentration. This translates to arterial oxygen values of between 1,500 and 2000 mmHg, thereby 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 often serve to buy time and maintain tissue viability until corrective measures can be implemented or a new blood supply established.
   

2. NEOVASCULARIZATION represents an indirect and delayed response to serial hyperbaric oxygenation. 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 ulcerations in soft tissue.
   

3. Hyperoxia enhanced ANTIMICROBIAL ACTIVITY has been demonstrated 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 aminoglycocide activity. It prolongs the post-antibiotic effect, when hyperbaric oxygen is combined with tobramycin against Pseudomonas aeroginosa.
   

4. 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 for hyperbaric oxygen therapy as the standard of care for decompression sickness and cerebral arterial gas embolism. Commonly associated with divers, CAGE is a frequent iatrogenic event in modern medical practice. It results in significant morbidity and mortality, grossly under diagnosed and under treated.
   

5. Hyperoxia-induced VASOCONSTRICTION is another important mechanism. 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 hyperbaric oxygen therapy is added to standard burn wound management protocols.
   

6. ATTENUATION OF REPERFUSION INJURY is the most recently identified mechanism. 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. Hyperbaric oxygen reduces the indirect component of injury by preventing such activation through a down-regulation of leukocyte receptor sites. The net effect is the preservation of marginal tissues that may otherwise be lost to ischemia-reperfusion injury.

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Indications for Hyperbaric Referral *

• Acute Carbon Monoxide Poisoning
  - smoke inhalation; cyanide poisoning
• Cerebral Arterial Gas Embolism
  - decompression or iatrogenically induced
• Chronic Osteomyelitis
  - refractory to antibiotics and debridement
• Clostridial Myonecrosis
  - gas gangrene
• Crush Injury; Compartment Syndrome
  - other acute ischemias
• Compromised Skin Grafts and Skin Flaps
• Decompression Sickness
• Enhancement of Healing
  - problem wounds, diabetic foot ulcers
• Exceptional Blood Loss Anemia
  - patient refusal of blood; cross matching difficulties
• Intracranial Abscess
• Late Radiation Tissue Injury
  - bone or soft tissue complications
• Necrotizing Soft Tissue Infections
  - subcutaneous tissue, muscle, fascia
• Thermal Burns
  - acute management; wound healing support

* Undersea and Hyperbaric Medical Society, 2008

The UHMS added 'Intracranial Abscess' and 'Idiopathic Sudden Sensorineural Healing Loss' since their 2008 referenced publication.

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Treatment Protocols

Oxygen, when breathed under increased atmospheric pressure, is a potent drug. Besides the beneficial effects discussed above, hyperbaric oxygen can produce noticeable toxic effects if administered indiscriminately. Safe time-dose limits have been established for hyperbaric oxygen exposure, and these profiles form the basis for today's treatment protocols. It is only quite recently that disease-specific hyperoxic dosing has been introduced.

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 20 to 40 treatments may be necessary. The precise number of treatments often depend upon the clinical response of each patient. Transcutaneous oximetry can provide more exacting dose schedules for wound healing referrals, thereby improving clinical outcomes and cost effectiveness.

Periods of exposure usually last approximately two hours. Decompression sickness and cerebral arterial gas embolism may require five or more hours. Treatments may be given once, twice or occasionally three times daily, and can be provided in both inpatient or outpatient settings.

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Delivery Systems

Hyperbaric oxygen therapy is administered in a pressurized chamber. Two distinct types of chambers are available.

Multiplace Chambers - These units can accommodate between 2-18 or more patients, depending upon configuration and size. They commonly incorporate a minimum pressure capability of 6.0 atmospheres absolute. Patients are accompanied by hyperbaric staff members, who may enter and exit the chamber during therapy via an adjacent access lock or compartment. The multiplace chamber is compressed on air. Patients are provided with oxygen via and individualized delivery system. Dedicated air compressors and high pressure volume receivers provide the chamber air supply. A specialized fire suppression system is necessary.

Space Requirements - Depending upon the size of the complex, a multiplace facility will require between 4,000 and 10,000 square feet of space. Weight constraints dictate that the chamber be ideally located on the ground/basement level.

Advantages include constant patient attendance and evaluation (particularly useful in treating evolving neurological diseases such as decompression sickness and cerebral arterial gas embolism), and multiple patients treated per session.

Disadvantages include high capitalization and staffing costs, large space requirements and risk of decompression sickness in the attending staff.

Monoplace Chambers - These units, first introduced in the 1960's are designed for single occupancy. They are usually constructed of acrylic, have a pressure capability of 3.0 atmospheres absolute, and are compressed with 100% oxygen. Technical innovations have allowed critically-ill and ventilatory-dependent patients to undergo therapy in the monoplace chamber. The high flow oxygen requirement is ideally supplied via a hospital's existing liquid oxygen system.

Space Requirements - A single unit could operate effectively within approximately 400-500 square feet of space. A two-chamber program will operate most effectively in approximately 800-1,200 square feet of space.

Advantages include most cost efficient delivery of hyperbaric oxygen (capitalization and operating costs), and no risk of decompression sickness.

Disadvantages include relative patient isolation and increased fire hazard.

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