Medical Guide lines to note for equine safety:

The risks associated are minimal if it is properly applied. As with any drug therapy, there are occasions where unanticipated reactions occur, but these are rare. Thousands of animals have been successfully treated with this therapy. Oxygen toxicity and barotrauma are two effects of administering oxygen under pressure that are continuously monitored for during therapy. The incidence of these effects is minimized by proper dosing, frequency, and duration of pressure and oxygen and proper compression and decompression procedures.

Haim Bitterman, MD, of Technion Israel Institute of Technology, noted that the most common patient complaint is middle ear discomfort resulting from the elevated pressure.

Other problems, such as changes in vision, lung damage and edema (fluid swelling), and seizures, were less common and usually went away when treatment stopped.

The most serious potential side effect is oxygen toxicity. While long more than five hours exposures to hyperbaric oxygen treatment are usually required to induce oxygen poisoning, University of Pennsylvania researchers noted a wide range of tolerance levels in humans.

The other major organ system oxygen poisoning can affect is the central nervous system. Signs ranging from dizziness and nausea to seizures might arise without warning but are usually seen if exposed to pressures of 2 atmospheres for 4+ hours or 3 atmospheres for 3+ hours (Lambertsen CJ, Clark JM, Gelfand R, et al, 1987). 

For this reason, HBOT is not recommend HBOT for horses with any condition (e.g., a fever) that would lower the animal's threshold for developing seizures. This also is one of the reasons operators, as a standard procedure check each horse's temperature immediately prior to placing him in the chamber.

While mandated safety guidelines have not been established for HBOT in horses, most technicians treat horses in accordance with recommendations for humans. In particular, that after treating several hundred horses, it is believed that HBOT in the range of 2 to 3 atmospheres of pressure can be used as safely in horses as it is in humans. 

In the treatment for horses, the standard treatment time is 60 minutes at 2 atmospheric pressures at which horses do not exhibit any side effects.

According to the Veterinary Hyperbaric Medicine Society (VHMS) position statement, the use of HBOT has the potential to accelerate the normal healing process and thus the potential to enhance the health and welfare of the horse.