Hyperbaric Oxygen Therapy

Physiology of Tissue Injury

The application of hyperbaric oxygen in the treatment of many conditions in animals is best understood by having an understanding of tissue injury and the healing mechanisms of the body.  

The body has a complicated set of reactions to injury that result in a cascade of biochemical mediators described clinically as inflammation. Most of these processes revolve around the blood vessels. The classic components of inflammation include the following:

  • Redness
  • Swelling
  • Heat
  • Pain
  • Loss of function

The role of blood vessels in injury is the reason for the above mentioned factors. All tissues have a certain density of capillary vessels. With injury, these vessels expand and become leaky, losing some of the plasma components into the surrounding tissue. This effect results in tissue swelling post injury. In certain circumstances, the swelling is so severe that the increased distance for oxygen diffusion is too far for normal perfusion to occur. In other situations, clotting of the blood vessels may occur resulting in complete loss of blood flow (ischemia). The result of either complication is tissue necrosis. The distance oxygen can diffuse is partly related to the concentration gradient. Increasing this gradient with hyperbaric oxygen therapy can increase the distance that oxygen can diffuse into these injured tissues.

Another mechanism of the effect of hyperoxygenation on tissue injury is vasoconstriction. This acts to reduce the hydrostatic pressure that forces fluid out of the capillaries into the tissues and therefore results in a reduction of tissue swelling.

Beyond inflammation the next issue is of the reparative response of the body’s tissues. A wound defect is filled with blood components that progress to a clot that covers the defect. As time passes, the connective tissue cells (fibroblasts) become activated and begin to produce new connective tissue (collagen) to fill the defect.

Concurrently, new blood vessel ingrowth begins to provide nutrients and oxygen in order for this process to proceed. In addition, the epithelium begins to spread out and divide to cover the defect. Appropriate nutrients and oxygen are required for this concert of healing to work.
In certain injuries, this process of healing is delayed as a result of the extent of the tissue injury, which impairs the delivery of oxygen and nutrients to the area. Veterinary HBOT decreases tissue swelling and therefore allows improved oxygen and nutrient delivery to the area. Hyperbaric oxygen therapy also assists in the production of epithelium covering the wound and stimulates fibroblast production of collagen.

Known and identified by many names including Veterinary HBOT (Hyperbaric Oxygen Therapy), Veterinary Hyperbarics or even Veterinary Oxygen Therapy in some areas, the results have been nothing short of remarkable.

Acute Conditions that may respond to HBOT.
Acute conditions including injuries sustained due to trauma to the legs or body, nervous system damage and surgical trauma (incisions), benefit from HBOT.

The general principal behind veterinary hyperbaric oxygen treatment, is that hyper-oxygenation reduces tissue swelling and enhances oxygen delivery to injured tissues by increasing the amount of dissolved oxygen in the plasma. Increasing oxygen aids in salvaging damaged tissue that would otherwise be lost from necrosis.

Chronic Conditions that may respond to Hyperbaric Oxygen Treatment.
Chronic conditions including poor healing wounds or wounds that involve a large surface area; bone infections; internal abscesses or other infections that result in tissue destruction, loss of blood supply, and necrosis, also benefit from HBOT. Acute injuries or inflammatory processes may progress to the chronic state if left untreated or are undiscovered until an advanced state. Using HBOT for these circumstances enhances normal body processes, such as stimulation of new blood vessel growth (angiogenesis), enhancing leukocyte ability to kill bacteria, stimulation of production of connective tissue cells (fibroblasts) and connective tissue (collagen).

Veterinary Hyperbaric Oxygen Therapy is an Adjunct to Other Therapies
Important factors in healing any wound or infection are, of course, an accurate diagnosis, along with selection of appropriate medical therapy. HBOT enhances the effectiveness of antibiotics and other treatments as well as their ability to reach the desired target destination. Many indications have been identified in horses where the application of HBOT may prove beneficial.

These Include:

  • Wounds (traumatic, surgical, etc)
  • Traumatic injuries with soft tissue swelling
  • Skin, muscle, tendons or ligamentous injury
  • Severe muscle swelling
  • Post-injection reactions (Clostridial myositis)
  • Spider bites
  • Bone infection
  • Bone and soft tissue healing after orthopedic procedures
  • Head and spinal injury
  • Hypoxic-ischemic encephalopathy (birth asphyxia or dummy foal syndrome)
  • Chronic infections
  • Lung and abdominal abscesses
  • Intestinal diseases
  • Gastric ulcer healing
  • Colitis
  • Prevention of ischemia reperfusion injury post colon torsion
  • Any intestinal ischemic injury
  • Laminitis or founder

Wound Applications for Veterinary Hyperbaric Oxygen Therapy.
HBOT is effective for many types of wounds including massive degloving injuries to the lower leg, large surface wounds from trauma, injection reactions, spider bites and pressure sores from prolonged recumbency as with debilitated animals or neonatal foals. Hyperbaric oxygen treatments help decrease tissue swelling and therefore salvage damaged tissues when used in the case of traumatic injuries. In the case of chronic wounds, HBOT assists the epithelium covering the wound and stimulates fibroblast production of collagen.

Veterinary Hyperbaric Oxygen for Bone Infections
Situations where bone infections can occur in horses include the following:

  • Complication of bacterial septicemia in foals
  • Complication following joint injections
  • Complication following orthopedic surgery in foals or adults

The pathophysiology of bone infection involves the following:

  • Bacteremia (blood borne bacteria) or local invasion
  • Bacterial localization in sinusoidal capillaries
  • Suppurative inflammatory response within the medullary space
  • Destruction of capillary structure
  • Increased intraosseous pressure
  • Decreased tissue partial pressure of oxygen (pO2)
  • Necrosis of tissue
  • Destruction of supportive structure and growth centers

Along with the above, the following alterations occur to impair the bone’s ability to respond:

  • Impaired blood flow
  • Tissue hypoxia
  • Tissue necrosis and destruction
  • Ineffective leukocyte function
  • Impaired antibiotic delivery
  • Impaired antibiotic function (as many antibiotics require specific amounts of oxygen to be effective)
  • Poor bone “wound” healing

Uses of HBOT in bone infections include the following:

  • Increased diffusion of oxygen from the blood vessels
  • Enhancement of neovascularization (angiogenesis)
  • Stimulation of collagen production to build new bone
  • Improvement of blood flow by reduction of edema via vasoconstriction
  • Enhancement of leukocyte ability to kill bacteria
  • Enhancement of delivery and activity of antibiotics

Applications of Veterinary Hyperbaric Oxygen for Chronic Infectious Processes
Internal abscesses may occur in the lungs (Rhodococcus equi) or in the abdomen (Rhodococcus equi, Streptococcus equi) and are rarely diagnosed early in the course of the disease. When these abscesses are diagnosed, there is a thick-walled fibrous connective tissue capsule surrounding them that impairs antibiotics from reaching the affected area.

This results in prolonged antibiotic treatment often with no resolution of the illness at a high cost to the owner and potentially fatal consequences for the animal. HBOT enhances the effectiveness of antibiotics and other treatments as well as their ability to reach the desired target destination.

HBOT for Neurologic Injuries
Head and spinal trauma often result in severe loss of body function. The Neurologic deficits are thought to result from swelling of tissue within a confined space, the loss of blood and oxygen supply and the sequential biochemical effects of these on the nervous tissue.

Hypoxic-ischemic encephalopathy, a common syndrome in foals (often termed the “dummy foal syndrome”), is considered to be related to the loss of blood flow and/or oxygen at some point during the birthing process. Any of the above mentioned problems benefit from the application of HBOT in an effort to reduce the swelling of tissue and salvage the injured nervous tissue.

Other Applications for Hyperbaric Oxygen Treatment
HBOT can be used for training injuries in equine athletes. The beneficial effects would include reduction of tissue swelling, reduction of pain associated with swelling and inflammation, and enhancement of the connective tissue repair process.