Hyperbaric oxygen therapy (HBO2) has many uses. The Undersea and Hyperbaric Medical Society is the international body that sets standards for the use of hyperbaric medicine. There are currently 14 approved indications for hyperbaric medicine and many more unapproved conditions where hyperbaric oxygen therapy may be useful. Hyperbaric oxygen therapy consists of placing a patient into a pressurized chamber of up to 3 atmospheres (ATM) of pressure. The surrounding ambient pressure at sea level is 1 ATM. Each additional ATM of pressure is equal to 33 feet of depth of sea water or 14.7 pounds per square inch (psi). The elevated pressure combined with exposure to 100% oxygen has many physiologic effects on the body. Many of these physiologic changes have been shown to improve wound healing in chronic wounds. This has been proven in many controlled studies. One of the most pronounced effects is the increase of oxygen concentration in the plasma. The normal oxygen concentration of plasma at sea level is 3 mL/L. At a pressure of 3 ATM breathing 100% oxygen, the plasma oxygen concentration approaches 60 mL/L. Studies have shown that this is enough to keep swine alive after all of their red blood cells have been removed and is sufficient to supply the resting oxygen requirement for most tissues. This also results in the delivery of higher oxygen concentrations to ischemic tissue. Another effect of hyperbaric oxygen therapy is decreasing surrounding edema and increasing neovascularity in ischemic tissue. Hyperbaric oxygen therapy can potentiate certain antibiotics such as aminoglycosides and quinolones. It can also be bacteriostatic and bacteriocidal at higher concentrations. Hyperbaric oxygen therapy neutralizes alpha exotoxins produced by bacteria such as Clostridium. It promotes neutrophil mediated bacterial killing ability in hypoxic tissue. Hyperbaric oxygen therapy prevents the release of proteases and free radicals in certain injuries, thereby decreasing vasoconstriction, edema, and cellular damage. 
Refractory diabetic wounds are often chronically or acutely infected and have compromised vascularity. Arterial compromise is usually of the small distal arteries, but larger arteries can also be involved. There can be venous congestion causing venous stasis ulcers in conjunction with arterial compromise and other changes associated with diabetes such as neuropathy and edema.
The conditions approved by the Undersea and Hyperbaric Medical Society for hyperbaric oxygen therapy include:
There are numerous off label indications such as autism, stroke, and attention deficit hyperactivity disorder (ADHD) that have not been proven to respond to hyperbaric oxygen therapy. A specific indication for hyperbaric oxygen therapy in wound healing is in cases of Wagner grade 3 diabetic wounds refractory to at least 30 days of conventional therapy. The Wagner scale categorizes the severity of diabetic foot wounds. This scale is as follows:
Most contraindications to hyperbaric oxygen therapy are related to issues of barotrauma. This is when there is physical injury to an area where there is a closed air filled space such as the lung or middle ear. Injury results from expansion of trapped gases with the changing pressure from the hyperbaric dive resulting in rupture of the compartment (perforation of a tympanic membrane or pneumothorax). The only true absolute contraindication is an untreated pneumothorax. Diving a patient in this situation will lead to fast progression of a tension pneumothorax and certain death. More relative contraindications are the presence of pulmonary blebs and emphysema with carbon dioxide retention. Administration of certain drugs is a relative contraindication. Disulfiram blocks superoxide dismutase which protects against oxygen toxicity (a known risk of hyperbaric oxygen therapy). Cisplatinum and sulfamylon impair wound healing. Bleomycin can cause interstitial pneumonitis. Sinusitis, seizures, pregnancy, implanted devices such as pacemakers and epidural pumps are also relative contraindications. Claustrophobia, especially in cases of the monoplace chamber, can be an issue. 
Hyperbaric oxygen therapy is administered in an approved and inspected the pressurized chamber. The chambers are either monoplace chambers which hold only one patient at a time or multiplace chambers which can accommodate several patients and an overseeing physician. The multiplace chambers can accommodate a wider variety of patients such as those on ventilators or those who need special accessory equipment that would not fit into a monoplace chamber. This activity regulates everything from the exhaust carbon dioxide to the purity of the oxygen and air. Frequent inspections are mandated, and the staff has to be specially trained to over see hyperbaric dives. There is also a safety director appointed to each facility ensuring compliance with specifications. The most catastrophic event associated with a hyperbaric dive is a failure of the chamber or fire. Hopefully, the frequent inspections and keen vigilance of the staff will avoid failure of the chamber. Fire prevention is also at the forefront of concern with dives. Three things are needed for a fire; a combustible material, a spark or fire source, and oxygen. Patients are limited to what they can bring into the chamber. No oils, electronics, or other non-approved items are allowed. They must wear only specially approved gowns, and no street clothes are permitted. Patients are also grounded to prevent static sparks. Any non-approved electronic equipment can only be used away from the open chamber.
The physicians and all personnel including the cleaning staff must have special training in hyperbaric medicine and the chambers. Each over seeing physician must complete at least a 40-hour training course in hyperbaric medicine. Physicians can also get certified in undersea and hyperbaric medicine through a year-long fellowship. Hyperbaric techs must also take a 40-hour hyperbaric course. There is an appointed safety officer who has extra safety and maintenance training. Cleaning personnel must be aware of precautions needed to clean the acrylic monoplace chambers and the other special details in caring for and maintaining multiplace chambers.
Before recommending hyperbaric oxygen therapy for a wound, the patient must have undergone at least thirty days of failed standard therapy consisting of mechanical and chemical debridements, application of acceptable wound products such as alginates and collagens, and treating underlying issues such as infection, malnutrition and pressure relief. Patients then must have insurance approval for reimbursement. They then undergo orientation and a detailed history and physical exam to rule out the presence of any existing contraindications. They must demonstrate the ability to clear their ears by Valsalva and show no signs of claustrophobia for the monoplace chambers. They are also carefully instructed on what is allowed and prohibited in the chambers as well as all possible risks of diving. Wound patients usually require a transcutaneous oximetry (TCOM) test to confirm that they will probably respond to hyperbaric oxygen therapy. Blood glucose and pressure are checked before each dive as these number will change during an actual dive. Ear drums and breath sounds are also checked pre-dive and post-dive to rule out barotrauma. 
Hyperbaric dives follow specific proven dive protocols depending on the condition being treated. Dives last around two hours daily with two 10-minute oxygen breaks to prevent oxygen seizures. They usually go to a pressure of 2.4 ATM at 100% oxygen. A typical dive routine lasts for 33 sessions but can be extended if need be.
The most common complication of hyperbaric oxygen therapy is barotrauma. Barotrauma is caused by expansion of gases in a confined space. The most common barotrauma is rupture or irritation of the tympanic membrane. Other more serious injuries include pneumothorax, rupture of small vessels, and damage of the inner, middle and external ear canals. More serious hazards include oxygen seizures, convulsions, and pulmonary edema and hemorrhage. Catastrophic complications are chamber fires and explosions. 
Hyperbaric oxygen therapy has an added dimension to the armamentarium of treating complicated chronic wounds. It may not help all patients, but it has been proven to lend benefit to many patients with specific wound-healing issues.
Good knowledge of indications for hyperbaric medicine is mandatory for anyone treating chronic wounds. Not all wounds are approved for hyperbaric therapy but proper referral and initiation of hyperbaric treatment is a must. Correct assessment by the primary caregiver wound specialist and hyperbaric physician must be a mainstay for maximum effect and best results for wound healing.