Many new therapies and medical treatments that are developed for use in humans are rapidly adapted for use in horses. A number of veterinarians across the United States have adopted one of these, hyperbaric oxygen therapy (or HBOT), for treating everything from chronic wounds in horses to infertility. Scientists originally developed this modality to treat scuba divers with decompression sickness ("the bends") and have studied HBOT use for many human conditions for more than 20 years. Its use in animals, however, is often controversial. In this article we’ll discuss the theories behind HBOT and evidence both for and against its use in equine medicine.

What it is and How it Works
During hyperbaric oxygen therapy treatments the equine patient is placed in a large metal chamber that is then pressurized up to two or sometimes three times the normal atmospheric pressure. The air is replaced with high concentrations of pure oxygen, and the patient remains in this environment for an hour or more before the chamber operator depressurizes the unit. Depending on the reason for treatment, physicians or veterinarians usually prescribe multiple treatment sessions, with human patients undergoing anywhere from 10 to 14 treatments for minor conditions to more than 50 HBOT treatments for severe conditions such as bone infections.¹ Horses suffering from serious conditions might undergo anywhere from two to 30 treatments, depending on the condition. Horses being treated as part of a health maintenance program generally need fewer sessions overall. For instance, some veterinarians believe racehorses will have a shorter recovery time after a racing effort if HBOT is integrated into their training and racing programs.

Steve Adair, MS, DVM, Dipl. ACVS, ACVSMR, associate professor of equine surgery at the University of Tennessee’s College of Veterinary Medicine, says a normal equine treatment session begins with a 15- to 20-minute period during which the pressure is raised from 1 atmosphere to 2.5 atmospheres. (Atmospheric pressure at sea level is equal to 1 atmosphere, and exposure to higher pressure would be similar to what a person would experience under water; each 33 feet–10 meters–of sea water provides an equivalent increase of 1 atmosphere.) Next, the chamber operator maintains the unit at the elevated pressure for 60 minutes. At the end of one hour, the chamber operator slowly (over another 15 or 20 minutes) brings the unit back to normal atmospheric pressure.

So how does HBOT work? Veterinarians and physicians who prescribe the therapy explain that the elevated pressure and oxygen concentration in the chamber combine to force more oxygen into the patient’s bloodstream with each breath. This increases the amount of oxygen dissolved in the blood and is thought to make oxygen more available to injured tissues. They say this can promote healing, especially in large wounds where blood supply has been compromised. One study has shown that it causes the inflammatory cells to form free radicals (which these inflammatory cells need in order to function properly and, thus, kill harmful microorganisms) and increases the efficacy of certain antibiotics; for these reasons, HBOT is often used to treat long-standing infections