Discussion of Therapeutic Rationale

HyperBaric Oxygen therapy can be defined as intermittent breathing of 100% oxygen while the patient is exposed to an ambient pressure greater than one atmosphere absolute.  Hyperbaric oxygen therapy has experimental and clinical studies defining the physiological effects of the hyperbaric environment and its current clinical indications.  The primary mechanisms producing a therapeutic benefit from hyperbaric oxygen therapy are reduction in volume of gas-filled spaces leading to "bubble" size reduction and absorption and the hyperoxygenation of perfused tissue beds.  The significant increases in arterial PO2 which can be obtained in the hyperbaric environment can significantly increase dissolved oxygen content (6.8 ml O2/100 ml blood at 3 ATA breathing 100% oxygen) and increase the diffusion distance for oxygen at the capillary level.

Intermittent increases in arterial PO2 to levels produces during hyperbaric oxygen therapy have a variety of secondary effects which may be beneficial in certain clinical conditions.  Vasoconstriction is caused by the arterial hyperoxia which occurs during treatment but sufficient perfusion is maintained to produce supra-normal tissue PO2's.  This may result in a reduction of tissue edema formation in conditions such as crush injury, compartment syndrome, and reperfusion after ischemic injury.

Oxygen has direct antibacterial effects which are more marked in anaerobic rather than aerobic infections as well as specific effect to block the alpha exotoxin produced by Clostridium specied.  Phagocytic function may also be enhanced, particularly in hypoxic conditions such as are present in many infected wounds.  Hyperbaric oxygen therapy has also been shown in animal modems to improve host outcome in fulminant sepis although mechanisms have not been identified.

One of the most significant clinical benefits is the improvement in healing of certain hypoxic wounds.  Intermittent exposure to hyperbaric oxygen improves collagen synthesis by fibroblasts and stimulates angiogenesis.  Although all of the underlying mechanisms have not been fully elucidated, the clinical benefits of intermittent therapy in properly selected patients are significant.

Hyperbaric oxygen therapy can be administered in either an oxygen filled monoplace (single patient) or air filled multiplace (multiple patient) chamber in which patients breath 100% oxygen using a mask or hood.

The multiplace chamber allows complex medical care to be provided in the hyperbaric environment when required and enables more patients to be treated at one time improving efficiency.

In subsequent issues of Pressure Points specific indications and mechanisms of action will be reviewed in more detail.

Pressure Points is a publication of the Department of Hyperbaric Medicine, Southeast Texas Center for Wound Care and Hyperbaric Medicine.