As hyperbaric-oxygen therapy (HBOT) – the use of oxygen under pressure – gains wider acceptance in human medicine, its application
in equine and small-animal veterinary medicine has been growing, too.
Hyperbaric oxygen chambers and therapy now are used in about a dozen equine veterinary facilities and in several small-animal
clinics around the country.
Step right in: Shelena Hoberg, a veterinary technician and certified hyperbaric technician at Equine Oxygen Therapy in Versailles,
Ky., leads a horse into the chamber.
They are used in human medicine to help treat some diseases (with Medicare approval) and conditions such as acute carbon-monoxide
poisoning, decompression illness, gas embolism, gas gangrene, progressive necrotizing infections and preservation of skin
grafts. The list has become extensive.
For horses, HBOT is used to assist healing and to speed recovery of poor-healing wounds, certain aerobic and anaerobic infections,
bone (osteomyelitis) and necrotizing soft-tissue infections. It is also reportedly showing some benefit in patients with hypoxic-ischemic
encephalopathy, tendinous and ligamentous injuries, respiratory conditions, as well as intestinal ischemic injury like colon
torsion and small-intestinal strangulation.
In a hyperbaric oxygen chamber, horses breathe air at 2 to 3 atmospheres absolute, or about two to three times the normal
environmental pressure at sea level.
Normal oxygen delivery to the tissues is dependent upon the proportion of O2 in the air, lung function, red-cell hemoglobin (Hb) and blood pressure.
Under normal circumstances, Hb is 97 percent saturated with oxygen, with a very small amount dissolved in the blood plasma.Via
the mitochondrial oxygen-transport system, the partial pressure of oxygen is reduced in a cascade of succeeding decreases,
ultimately delivering oxygen to tissues at a significant decrease in partial pressure as blood flow exits the lungs and progresses
to the cells.
At normal atmospheric pressure (1ATA), the pO2, or partial pressure of oxygen, the amount dissolved in the plasma, will increase only slightly. Increasing the pressure
of the horse's environment in the HBOT chamber allows for delivery of an enhanced amount of oxygen to the tissues, by significantly
increasing the pO2. Most hyperbaric therapy involves an increase in pressure to 3ATA, with a dramatic increase in oxygen delivery to the tissues,
about 2280mmHg of oxygen, instead of the normal 160mmHg.
Setting the dials: Victor Torres, farm manager at Equine Oxygen Therapy in Versailles, Ky., powers up the chamber for a patient.
Hyperparic oxygen therapy for equine use began about six years ago. It is considered adjunctive therapy, not a sole treatment
HBOT and wound healing
The failure of wound healing often is due to persistent infection, malperfusion and hypoxia, cellular failure, unrelieved
pressure or recurrent trauma.
Hyperbaric oxygen therapy produces a directly proportional increase in the plasma volume fraction of transported oxygen and
delivery to the injured tissues. With increased cellular and muscle pO2, the tissues become saturated with oxygen, assisting the healing process.
Hyperoxygenation allows for reversal of localized tissue hypoxia, which may be secondary to ischemia or other factors of the
compromised, non-healing wound site. For the hypoxic wound, HBOT corrects the pathophysiology related to oxygen deficiency
and impaired wound healing.
According to the Hyperbaric Oxygen Committee report in 2003, "a key factor in HBOT's enhancement of the hypoxic wound
environment is its ability to establish adequate oxygen availability within the vascularized connective tissue compartment
that surrounds the wound."
Neutrophils, fibroblasts, macrophages and osteoclasts all depend on an oxygen-sufficient environment to adequately promote
healing. Proper wound healing is promoted with "improved leukocyte function of bacterial killing, antibiotic potentiation
and enhanced collagen synthesis," which occurs during periods of increased tissue pO2.