Hyperbaric Oxygen Therapy: Healing Under Pressure

Oxygen is one of the most crucial components of the energy production process that fuels body tissues. It sustains life and enables injured tissues to heal. In recent years, a very effective procedure for helping heal many ailments has developed from the idea that for optimum healing, more oxygen than is normally contained in and surrounding our bodies can be beneficial. As usual, when human medicine makes a breakthrough, it isn't long until someone figures out how to help horses with that same type of therapy. Enter hyperbaric oxygen therapy (HBOT) for horses.

How It Works

Hyperbaric oxygen therapy involves subjecting the patient to high levels of oxygen under pressure in a special chamber. At normal atmospheric pressure, there is a limit to the amount of oxygen carried by red blood cells and only a tiny amount of oxygen is dissolved in the plasma. HBOT is discussed in terms of atmospheres absolute (ATA). Atmospheric pressure at sea level is equal to 1 ATA. Higher pressure than this on the body 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 ATA of pressure. Thus when you are 33 feet under water, you are experiencing 2 ATA (one from normal atmospheric pressure and one from the addition of 33 feet of sea water). This gives an idea of the pressure you would feel in an oxygen chamber. Treatments in a chamber are given at 1.5 to three times the pressure of one atmosphere.

Increasing the amount of air breathed cannot significantly improve oxygen delivery to the body by way of hemoglobin, even if you breathe pure oxygen. But with increased pressure, the oxygen level in blood plasma increases, with higher delivery to all body tissues. Under these conditions, oxygen is physically dissolved in the plasma, even in the veins (which ordinarily carry only blood that is depleted of oxygen). The dissolved oxygen is more readily utilized by the body than the oxygen carried by red blood cells.

In humans, pressure chambers are used to speed healing of soft tissue injuries, aid recovery of stroke victims, and in treating many problems--including carbon monoxide poisoning, coma, burns, circulatory problems, Lyme disease, lung abscesses, difficult wounds, bone infections, hard-to-treat infections (especially those caused by anaerobic bacteria), traumatic brain injuries, spider bites resulting in necrotic (dead) tissue, and diabetes (preventing non-healing infections and amputations). Many studies show HBOT's efficacy in treating wounds and ischemic tissue (that is deprived of blood), reducing edema, and stimulating the immune system.

The patient is put in a chamber and the air pressure is slowly increased. When it reaches the prescribed pressure, pure oxygen is put in to replace the air. Normal partial pressure of oxygen in the arterial system is about 100 mm of mercury (mmHg). The oxygen level in the air inhaled at a pressure of three atmospheres (in a pressure chamber) would be near 2,280 mmHg. The actual amount in the arterial blood would be somewhat less than that, but this is a much higher amount than is normally dissolved in the blood, says Fairfield Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, of Hagyard-Davidson-McGee Veterinary Associates in Lexington, Ky. The oxygen is forced into the blood and body fluids, making its way to any damaged areas of the body that can't be reached by normal blood circulation or areas where vessels have been hindered by injury or infection.

HBOT for Horses

A few years ago, the first pressure chamber for horses was created by Equinox Technologies Limited in Vancouver, British Columbia, and the first available unit was purchased by Doug Herthel, DVM, for his Alamo Pintado Equine Medical Center in Los Olivos, Calif. It was a mobile unit built like a large trailer that held two horses at a time.

Equinox had taken their first experimental chamber to two racetracks in Canada, where it was tested on racing injuries in Thoroughbreds and Standardbreds. Herthel had been trying to develop a similar chamber for about six years. "We actually started building one in 1994, but the mechanics of it became too difficult. We were working with a Navy contractor, making one from concrete, but testing showed it wouldn't hold up to pressure. After Equinox came up with theirs, we were ecstatic," says Herthel.

He now treats horses from all over the country with a newer version of the chamber. It is in use every day, treating two to four horses daily.

Since then, more units have been put into clinics, distributed by a company called Equine Oxygen Therapy. There are HBOT chambers at WinStar Farm and Hagyard-Davidson-McGee Equine Hospital in Lexington, Ky.; KESMARC (an equine rehabilitation center) in Versailles, Ky.; Fossil Creek Veterinary Clinic in Loveland, Colo. (under the direction of Kara Keesling, DVM); and the University of Tennessee in Knoxville.

Bill Casner, chairman and co-owner of WinStar Farm; Hub Johnson, owner of KESMARC; and Bain are partners in Equine Oxygen Therapy. Bain serves as vice president and medical adviser for the group.

This partnership has designed several models for horses. "The function of our chambers has not changed, but we keep improving them for ease of use, operator safety, and comfort and safety of the horse," says Johnson. "The most recent model--which was just installed at Hagyard-Davidson-McGee--is the biggest one in existence at present. It is more than nine feet in diameter, opens at the back and front, and is stationary. The one we are designing now is a round stall, 10 feet in diameter and 9 1/2 feet tall. It's recessed into a concrete pad, so the horse doesn't have to walk up a ramp. He goes through a 42-inch door, you turn him loose, and he can walk around without being restrained in any way. A horse with laminitis can even lie down to be more comfortable."

The first model was less than eight feet in diameter, and there wasn't much head room for a horse. It was designed to be taken around the country. Horses accustomed to a trailer were comfortable in it, and foals were small enough to turn around in it, but young, inexperienced horses often became frantic. The larger chambers available now seem to work better.

A horse being treated is put into the chamber for 30-90 minutes once a day, for however many treatments are needed for that particular condition.

"It's usually a 90-minute treatment, once the chamber is up to pressure," says Herthel. "Some conditions require only one or two treatments; others need 10 to 20 treatments. In severe cases of laminitis, we may treat a horse twice a day."

Not only does the treatment increase oxygen levels, but the pressure helps reduce swelling anywhere in the body. Herthel uses it for severe limb edema, lymphangitis, etc. "Any instance where there is swelling--in the brain, the foot, or intestines--the oxygen therapy is helpful," he says. "The pressure per square inch in the chamber is incredible. It's like being 60 feet under water."

Herthel says that care must be taken using HBOT. Short daily treatments are better than prolonged sessions, since exposure to high-pressure oxygen for long periods could lead to oxygen toxicity.

"You also take precautions to have the humidity in the chamber just right, and ground the horse," says Herthel. "If there's any static electricity in there, you could have a major fire." For good airway health, air breathed in should not be too dry. In order to ground the horse, depending on the chamber, either a rubber strap can be attached to the horse's body or the horse can stand on a rubber mat.

Commonly Treated Conditions

HBOT is one of the most powerful tools available as an adjunctive form of therapy, and in some cases it works well as the primary therapy in horses, says Casner. Colic and laminitis are the number one and two killers, respectively, of horses, and oxygen therapy (in conjunction with other therapies) can be very useful in treating both.

Colic--HBOT helps restore blood flow to tissues after colic surgery. Herthel says it also reduces obstructive swelling in the intestinal tissue and improves oxygenation of the resection (after abdominal surgery to correct colon torsion, small intestine strangulation, etc.). Herthel has found that many colic cases respond much better to surgery when treated with HBOT before and after surgery.

Johnson says HBOT is used in human medicine to relieve or prevent gaseous buildup after abdominal surgeries. "This also works well in horses, and we are hoping there will be a study on gas colics," he says.

Laminitis and navicular syndrome--HBOT can arrest laminitis in the early stages, Casner says. "If you can treat the horse before the structures in the foot collapse (before there's crushing of the blood vessels), it is very effective," explains Casner. "In older stallions, the two things that most commonly kill them are colic and laminitis."

Effects of oxygen therapy on problems like navicular syndrome and laminitis are now being studied. Researchers at the University of Tennessee are starting controlled studies on laminitis to get the data needed to document the effects of HBOT.

"They will be working with different stages of laminitis, with a control group to make comparisons, to see how well this really works," says Johnson.

"At Hagyard-Davidson-McGee Equine Hospital, they've treated acute onset cases of laminitis that resolved very quickly and successfully," says Johnson. "There's a better success rate if you can start treatment right away, rather than waiting a week--after the damage is done. We are hoping that after the controlled studies are published, the veterinary community will embrace this, and people will start HBOT earlier in the course of the disease."

Infections--HBOT increases blood flow to the infection site, which increases the amount of antibiotic delivery. The extra oxygen also increases the effectiveness of the antibiotic, magnifying the way it works against bacteria. Herthel says that high-dose oxygen "tends to potentiate the effect of some antibiotics, such as sulfamethoxazole (SMZ). You are also getting 15 times the amount of oxygen to a tissue that was lacking oxygen due to infection or poor circulation." Oxygen also stimulates faster cell turnover, and thus faster healing.

Casner says, "Oxygen acts to kill bacteria. Most bacteria causing serious infection are anaerobic--working best in an environment without oxygen. At pressure, with oxygen at a higher level, it is also detrimental to aerobic bacteria."

Extra oxygen also helps white blood cells function better to kill the organisms.

Bain adds, "Certain antibiotics such as gentocin and amikacin don't work well in low-oxygen environments. Oxygen therapy enhances their function and gives a whole combination of benefits. HBOT is an adjunctive therapy; we are still using antibiotics and anti-inflammatory drugs and other treatments. It's a component process in which everything is working together."

Abscesses--Internal abscesses (such as in the lungs or the abdomen) are sometimes not diagnosed early. Johnson says, "By the time they are diagnosed, there is a thick-walled capsule of connective tissue around them that keeps antibiotics from reaching the site. This results in prolonged antibiotic treatment (often with no resolution of the abscess) at high cost to the owner, and potentially fatal consequences for the horse. HBOT helps the antibiotic get to the site and enhances its ability to fight the infection."

Bone injuries--Casner says studies have been done in which fractures were created in rabbits, with HBOT used to treat one group and a control group without treatment. The rabbits were euthanized to determine the amount of healing. In the rabbits treated with HBOT, the bones healed not only faster, but stronger.

Septicemia and joint ill in foals--At Hagyard-Davidson-McGee, Bain and Nathan Slovis, DVM, Dipl. ACVIM, evaluated HBOT for treating foals with septic joints. In 2002, all the foals which came into the clinic with septic joints went through a standard protocol using systemic antibiotics, lavage to flush the joints with antibiotics, etc. After 30 to 90 days' treatment, they took the foals which were hopeless (which would ordinarily be euthanized) and moved them into a test group. They continued to use their standard treatments, but combined them with HBOT. They had a 60% recovery rate in foals which were going to be put down!

Infection eats the bone away, but with oxygen treatment the joints healed and the integrity of the bone was regenerated. Bain says, "The changes we see on X rays in these foals indicates dead bone. Even though we have the foals on antibiotics, there is poor blood supply to dead bone; the antibiotics don't get there and are not very active if they do. Even if the foal survives, the body has to clean up all that dead tissue. HBOT stimulates and enhances the clean-up process and healing process to speed resorption of dead bone. It can also help salvage some tissues that would otherwise go on to die."

Soft tissue injuries--Many injuries result in inflammation and swelling. Studies have shown that soft tissue injuries treated with HBOT recover in half the time. New blood vessels form more quickly, improving blood supply to injured areas, and there is swift reduction in edema (swelling). Since oxygen is normally carried by red blood cells, any tissues with a compromised blood supply suffer from poor healing. But with HBOT, oxygen is forced into all body fluids and delivered to areas with restricted circulation.

Injured tendons and ligaments respond well to treatment; HBOT can be useful in dealing with bowed tendons, surgical repair of tendon or ligament injuries, etc. Surgical traumas (incisions) also heal faster with HBOT, as do large surface wounds and pressure sores. It decreases tissue swelling and helps salvage damaged tissues in traumatic injury. In chronic wounds, it assists growth of new skin and stimulates collagen production.

Bain says, "In a severe wound with lots of tissue damage, there is usually a certain amount of sloughing away. Using HBOT early in treatment may salvage some of the tissues that have lost their blood supply; we can sometimes save bits around the margin and reduce the amount of tissue lost."

Reproductive problems--Herthel wrote an article three years ago describing how he'd treated some older stallions for laminitis and noticed an increase in fertility. After reading that, Casner decided to treat WinStar's stallion Kris S. in the chamber, and there was a very dramatic change. The stallion's covers in the breeding shed had declined, but after HBOT treatments his libido increased (along with his sperm count), and the morphology (cell structure) of his semen was much improved.

Casner says HBOT has also worked well for mares they hadn't been able to get in foal. "We treated four out of five mares one year that had been bred on multiple covers," he says. "We finally put them in the chamber, and they got in foal the next time they cycled. We don't entirely understand why it worked, but suspect there may have been a bacteria involved that we were able to eliminate with the oxygen treatment. We probably also enhanced the integrity of the uterine lining."

Johnson has also treated mares which were unable to conceive. "One mare went to the breeding shed 16 times in two years without becoming pregnant. After three treatments in the chamber, she was bred, and had a live, healthy foal this spring," he says.

Bleeders--Casner uses HBOT on horses which have bled (suffered from exercise-induced pulmonary hemorrhage, or EIPH). "Many of them have chronic infections in the back of their lungs," he says. "We bring them to the farm, put them in the chamber, and give them five or six treatments in combination with antibiotics. We've had very good results in clearing up the infection and healing the lung tissue."

Dummy foals and other neurological problems--"We use it on dummy foals because it reduces edema," says Casner. "The oxygen in a pressure chamber has the ability to penetrate the cerebrospinal fluid." Head and spinal trauma often create neurological damage, thought to result from swelling of these tissues within a confined space, loss of blood and oxygen supply, and the sequential effects of these factors on nervous tissue. HBOT reduces the swelling and increases the blood supply.

"We've also used HBOT experimentally on EPM," says Casner. "There are many things it holds promise for; it will be another strong tool in the veterinarian's arsenal."

Spreading the Word

"HBOT is an amazing tool, and the veterinary community is starting to embrace it, but there are some who are so traditional in their forms of treatment that they continue to be very narrow in their vision--though there are volumes of clinical research in the human field to support this therapy," says Casner.

"Dr. Bain says hyperbarics is the most significant veterinary tool since the ultrasound machine," Casner adds. "He recently worked with a racehorse with a lung abscess that was treated with conventional methods for 30 days and continuing to worsen. The trainer then requested that hyperbarics be combined with traditional treatment. Dr. Bain was then able to heal the horse in a very short time."

But veterinarians who have chambers are cautious about using this routinely even though they want to. "I use the term 'cautious' only in the spirit of selecting appropriate patients for HBOT treatments and not just treating any willy-nilly problem," says Bain. "The theoretical applications are considered for each patient's clinical problem before considering HBOT as a treatment modality."

"Oxygen therapy is nothing short of miraculous in treating many problems--especially infections--but the question a lot of people have is that if it's so good, why aren't more veterinarians doing it? Many vets have never heard of it; this treatment was not taught in vet school, and until recently there were no equine chambers," explains Casner. "Most veterinarians have no experience with it. But this will eventually change."

Herthel says HBOT is such a powerful tool, "that the way we use it, oxygen is a drug." He feels that eventually more veterinarians and equine clinics will use this, and that there should be a chamber in every major horse center.

"It can save a horse in many situations where there is no hope otherwise," says Herthel. "We have horses doing fine today that had acute laminitis and would not have made it without the oxygen therapy. We've treated many horses with bone infections that would have died. Some of the colics with intestinal obstruction, and some horrific infected wounds, can turn around quickly with oxygen treatment."

This useful tool can make the difference between life or death for many horses, he says. However, HBOT can get expensive with one treatment session running $400-$500. The type of injury or illness being treated will determine how many sessions are needed.

Bain says that since HBOT is such a new therapeutic modality to the horse, there isn't much research out there yet. "We've had a few small clinical case studies that Dr. Herthel has done or that we've done here at our hospital," says Bain. "But there have been no basic research projects yet at academic institutions involving the horse specifically. Many medical schools have hyperbaric facilities, however. Duke University is a leader in this field, along with the University of Kansas Medical Center and George Washington University. They have what they call a 'magic list' of things that Medicare will pay for (including wounds, diabetic wounds, chronic bone infections, burn injuries, etc.), and this is basically how HBOT is applied to human medicine.

"Usually medicine looks at what animal research has done and applies it to humans," says Bain. "We are looking at what they are doing with people and applying it to horses--and hoping this will find its place in veterinary medicine."


WinStar Farm

WinStar was the first Thoroughbred farm in Kentucky to have a pressure chamber on the farm. "I brought the first unit here in 2001, and everyone who saw that huge chamber thought I was nuts," says Bill Casner, chairman and co-owner. "But I strongly believed in this, due to the volumes of clinical research about it in the human medical field going back 45 years."

He says there are many pressure chambers around the world used in human medicine; some countries have many more than we do.

At WinStar, Casner uses the pressure chamber for many things, including horses with injuries or infections, bleeders, infertile mares or stallions, and foals with septic joints. "We had a filly sell this year that would have been dead (a 100% loss, since she was not insured) without the hyperbaric treatment. She was a very nice filly, and had no problems after her recovery--and she sold very well," says Casner.


Hub and Kirsten Johnson installed the second unit in the United States at their farm in Texas before relocating to Kentucky. This was shortly after Doug Herthel, DVM, got one in Los Olivos, Calif.

"I was doing research on the Internet and learned about hyperbaric chambers and called people all over the country trying to figure out how to get one built for horses," says Kirsten Johnson. "All the manufacturers of chambers for human use told me it would be too expensive. We'd given up, then six months later heard that Dr. Herthel had one. So we contacted Equinox and got our first one in 2000."

Since then they have used HBOT in treating a wide variety of problems, saving many horses. Recently they treated a Clydesdale which was mauled by another stallion in a tie stall. "He had a piece torn out of his shoulder and neck 25 inches long and 18 inches wide. Before the horse was brought to us he had been in a hospital for 12 days and the wound had become severely infected," says Johnson. The horse had quit eating and had given up. Then he was brought to KESMARC. After his second treatment in the chamber, he started eating again and the wound began healing rapidly.

"The horse's owner is a veterinarian, and learned about us on the Internet," says Johnson. "Using HBOT we were able to reduce the size of the wound by 120 square inches in 10 days. It's now only three inches long and three-quarters of an inch wide. All the skin and hair is growing back (in its original color, with little scarring), and the horse has returned to competition at a national level.

"In our rehabilitation business we've treated many kinds of injuries and tough infections," Johnson continues. "I could give 1,000 examples of what we call one-horse wonders. The main problem is that sometimes we don't get to work on the horses until a problem is long-standing and everything else has been tried; the owners have given up and the horse is brought here as a last resort. But we've had a good share of successes in spite of this. If horse owners could know about HBOT and use it earlier, imagine the amount of money and horses' lives that could be saved.

"We've been fortunate to have come into contact with doctors and specialists in the human field who have been very helpful and supportive of our conversion of hyperbarics into the veterinary field," concludes Johnson. "Our mission is to take this technology and make the safest chamber we can for horses."

Hagyard-Davidson-McGee Equine Hospital

This equine practice is in its third year using HBOT. "We initially used it for birth asphyxia in newborn foals, and are still learning about that," says Fairfield Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, of Hagyard-Davidson-McGee. "We've used it for a large number of bone infections--a frequent cause of loss in young foals."

The first chamber they used was small and wouldn't accommodate an adult horse; they put the foal on a tray that would slide in and out. The foals had to be anesthetized, heavily sedated, or in a coma to lie on the tray. Many would wake up and bump their heads before the treatment was over.

"We needed a bigger space," says Bain. "Now we are using a very large chamber with two doors. We can take an injured horse straight in and straight out, without having to worry about backing him out."--Heather Smith Thomas


Pressure chambers are not a new idea. As early as the 17th Century, one innovative physician was treating patients in crude, airtight enclosures with pressurized air forced in with a hand bellows. A few people continued doing this type of treatment, but their claims for curing anything and everything eventually gave it a bad reputation.

Pressure chambers in common use during the past 100 years were designed for saving deep sea divers who came to the surface too quickly, suffering from the "bends" (decompression sickness, a painful condition in which bubbles of nitrogen gas form in the blood or body tissues due to sudden lowering of pressure on the body). Divers could be put into a pressurized chamber and gradually have the air pressure brought to normal.

In recent years, medicine has taken a new look at hyperbaric oxygen therapy. Chambers have become popular for helping heal sports injuries and getting elite athletes back into competition faster. There are also chambers at a number of university hospitals and medical centers. Interest in this field is growing, and although it has only recently become available in veterinary medicine, its supporters are enthusiastic that it will eventually play a very important role.--Heather Smith Thomas

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.

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