Oxynet Logo What is HBO Therapy ?


Section 1 What is hyperbaric oxygen?
Section 2 What is it used for?
Section 3 What is it not used for?
Section 4 How is it given?
Section 5 The different types of hyperbaric oxygen facility
Section 6 What does it feel like?
Section 7 What are the side effects?
Section 8 How can it be arranged?
Section 9 Quality of service
Section 10 Clinical audit
Section 11 Research
Section 12 European Committee on Hyperbaric Medicine
Section 13 Consensus Conference reports
Section 14 COST Action B14


Hyperbaric oxygen (HBO) is oxygen at high pressure. 
Air contains nearly 21% oxygen, and more than 78% nitrogen. In hyperbaric oxygen therapy (HBO), the oxygen percentage breathed by the patient is nearly or actually 100%, ie almost five times more than in air. The pressure of the oxygen breathed by the patient in HBO is usually more than 1.5 times (and can be as much as 3 times) greater than atmospheric pressure. So, HBOT can deliver to the patient nearly fifteen times as much oxygen as there is in air at normal pressure.

The extra oxygen is breathed in through the lungs, and dissolved in the blood plasma: it is then delivered to any part of the body with a good blood supply. The effects of this extra oxygen are different in different parts of the body: in some medical conditions it can save life, and in others it can promote healing and tissue repair.

It is also possible to have too much oxygen in the blood stream, which can lead to unwanted effects. So, HBO is like any other medicine or drug, with indications and contra-indications, correct doses, and potential side-effects.  Even though it is given in an unusual way, HBOT should not be seen as a miracle cure, or a sensational new discovery. It is a rational treatment in some medical conditions; but its benefits should not be over-estimated. Much has been made in the past of the benefits of hyperbaric oxygen in medical conditions where there is no evidence that it works. In fact, though, there is enough evidence that it works in some medical conditions to encourage the development of more treatment centres than there already are. 

To encourage the rational and safe provision of HBO, the European Committee on Hyperbaric Medicine, and the various national Hyperbaric Associations in Europe, are working together. International European Cooperation in this field of science and technology is also being supported by the European Commission, through its 'COST' Action B14. This is the background to this website.



HBO is used in a number of medical emergencies, where the patient might also need intensive care:

  1. Air or gas embolism. This is where gas bubbles travel in the blood stream, and may block blood flow in organs like the brain and spinal cord, or the heart. The bubbles may get into the blood from the lungs when under pressure (like when diving), or else at the time of a surgical operation or trauma. HBO acts in several ways when this happens.

In this condition, HBO must be given as quickly as possible to limit the damage to the tissues; and emergency transport to a safe and appropriate HBO facility must be organised.

  1. Decompression illness ('The Bends'). This is where bubbles of nitrogen form in tissues where it has been dissolved under pressure (like breathing compressed air when diving); but then when the pressure is removed (decompression) the nitrogen is no longer dissolved, and cannot get out of the tissue fast enough to be breathed out. Bubbles can form in all tissues of the body, but especially where a lot of nitrogen can be dissolved under pressure (in or through fat), and where the blood drainage through veins is slow and inefficient (like the brain and the spinal cord).

HBO acts in several ways when this happens:

In this condition, HBOT should be given as soon as is safely possible. Like in air embolism, emergency transport may be necessary to take the patient to an appropriate HBO facility.

  1. Carbon monoxide poisoning. Carbon monoxide (CO) can be breathed in from anything that is burning, such as a fire, a central heating system, or car exhaust. It does not matter what is burning (coal, oil, petroleum, wood, furniture) as long as it has carbon in it: and almost everything does. CO can also get into the body by breathing the fumes from paint-stripper. CO damages any tissue which normally uses oxygen, by blocking the delivery of oxygen to the cells as well as blocking its use inside the cells.

    HBO is only indicated in severe cases of poisoning. Oxygen at normal atmospheric pressure should be given by face-mask as soon as possible to any patient with this condition; and HBOT is reserved for patients who have been unconscious, or who have neurological symptoms or signs, or who are pregnant, or who have any other evidence of a severe exposure.

    HBO acts in several different ways in this condition:

The main aim of HBOT in CO poisoning is to prevent long-term effects of the CO, such as memory problems and difficulties with balance and coordination. It may also help the patient to recover more quickly than with normal atmospheric oxygen therapy. There is evidence that it may also save life in some cases.

  1. Clostridial myonecrosis ('gas gangrene'). This is an infection by a bacterium called clostridium perfringens, which grows and spreads most rapidly in a low-oxygen containing environment. There are usually other bacteria with it. Tissues poorly supplied with blood, for instance where blood vessels are blocked or damaged, are most prone to this infection. The bacteria kill normal cells in the area of infection, and tend to spread rapidly. In the process, they release gas into the tissues, which can be felt by hand and seen on X-rays. They also release poisonous chemicals (including 'alpha-toxin') into the rest of the body; this can damage organs like the heart and kidneys, and cause death.

    HBO at three atmospheres pressure stops the bacteria from spreading locally, and reduces the amount of alpha-toxin being produced. This gives more time for antibiotics to work, and for the infected tissues to be removed by surgery.

    The mortality from this infection can be reduced by the early use of HBO; and if the patient survives, HBO can reduce the amount of tissue which has to be removed. 

  1. Other aggressive infections. There are a number of other infections of skin and muscle which can spread rapidly and damage the organs of the body. Examples are Fournier's Gangrene and Necrotizing Fasciitis. In these infections, the bacteria are usually mixed; but they can mainly survive well in oxygen. So, these infections can develop in previously normal skin and muscle.

    HBO improves the body's own defence systems, because the white cells (which attack bacteria) need extra oxygen to work properly. This gives more time for antibiotics to work, and for the infected tissues to be removed by surgery. The mortality from this infection can be reduced by the early use of HBO; and if the patient survives, HBO can reduce the amount of tissue which has to be removed.

  2. Crush injury. When a hand or foot, or a whole limb, are crushed, the damaged tissues may swell rapidly. This may compress the blood vessels running through the damaged area. So, the tissues beyond the crushed area may have a poor oxygen supply, which may lead to infections and other complications. In the damaged area itself, the swelling stops oxygen from reaching tissues which need to be repaired; and so, it becomes difficult to lay down new connective ('scar') tissue. After this, other complications may develop, which can affect the other organs of the body. It is common for amputation to become necessary.

    HBO works in different ways, but can never substitute for surgical removal of tissues damaged beyond repair. The extra oxygen reduces swelling, by slowing the leak of fluid out of the damaged blood vessels. It also reaches tissues in the damaged area, allowing them to recover. The extent of tissue removal, and the need for amputation, are therefore reduced. In order to work, however, HBO must be used as early as possible.

  1. Burns. When soft tissues (such as skin and muscle) are damaged by burning, the blood flow in the damaged area is sharply reduced. This causes an area of swelling which radiates away from the area of damage, in all directions. The swelling may extend deep into muscles, and over the surrounding skin, and cause more damage than the initial injury. 

    HBO can help to reduce this swelling. The extra oxygen slows down the leak of fluid out of the damaged blood vessels. It also reaches tissues in the damaged area, allowing them to recover. The extent of tissue removal, and the need for amputation, are therefore reduced. In order to work, however, HBO must be used as early as possible.

  2. Sudden deafness. There is evidence that the prompt use of HBO in patients who have lost their hearing suddenly, may reduce the duration and extent of hearing loss. This is the subject of current research.

  3. Severe haemorrhagic anaemia. In those patients who suffer serious blood loss, and who are unable for any reason to receive blood transfusion, the prompt use of HBO may help with short-term survival. Such patients commonly require intensive care at the same time. There is evidence that HBO may accelerate the production of a hormone called erythropoietin, which promotes the production of new red blood cells and haemoglobin, to replace what has been lost.

  4. Near-hanging. There is some evidence that the extent of brain damage after near-hanging can be reduced by the prompt use of HBO. 

There are a number of other conditions where HBO is used, where there is more time for planning, and where courses of treatment tend to be longer than for emergency referrals.

  1. Ischemic skin flaps and grafts. Oxygen treatment is not usually applied where a skin graft is growing well; even if it is infected, HBO would not be a first-line treatment. However, if the graft is based on host tissue which is poorly supplied with blood, and there is evidence that the graft is not fully successful, then HBO can be used.

    HBO helps to reduce congestion in the blood vessels of the graft, such as when the veins in the graft are not working properly.
    HBO also helps with the circulation of blood through the graft, by making the red blood cells better able to move through the narrowest capillaries, and making the blood platelets less likely to clump together and block the flow.
    In the longer term, HBO helps to develop new blood vessels through the graft, which maintains the benefit of the earlier treatments. By this means, the proportion of a graft which may survive can be increased: this saves much time and discomfort, and of course expense, in the long run.

    If part or all of the graft has actually died, then HBO will not work: in this case, HBO may help to maintain the viable part of the graft after the dead part has been removed at surgery.

  1. Refractory osteomyelitis. Chronic inflammation of bone can follow on from trivial injuries, or from infection developing alongside orthopaedic implants (like rods and plates to support broken bones). Infection plays an important part in this process, but is not the primary problem. This disease develops usually, where there is some reason why the bone is not able to heal itself properly, such as poor blood supply, or another medical problem like diabetes, or steroid medication. The resulting pain and immobility are disabling, and can prevent the patient from getting on with their normal work or living. Surgery in the affected bone is difficult, because it may only spread the infection, or make another wound in the bone which it cannot heal properly.

    HBO helps to resist infection, by providing extra oxygen to supply the white cells which normally destroy bacteria. The extra oxygen also promotes the activity of fibre-producing cells, which normally lay down the framework of new tissue. Later, it may also help in the growth of new blood vessels into the affected area, which helps to maintain the benefit of the earlier treatments.

    However, necessary surgery (like the removal of infected implants and dead bone) cannot be avoided just because HBO is being used. The timing of surgery and the use of the right antibiotics should be planned at the same time as the HBO.

  2. Radiation bone and soft tissue damage. This makes up the majority of non-emergency work in European HBO facilities. Intensive radiation, used to treat cancer, often in the area of the head and neck, may also damage normal bones and organs which lie in the line of the X-rays. This commonly involves the jaw; but it may also affect the pelvis, where the cancer has been in the internal organs. The X-rays damage the small blood vessels which run through the bone or soft tissue, so that a long-term process of shortage of oxygen and inflammation is set up. Over months or years after such treatment, the symptoms of tissue degeneration build up, with pain and limited movement, and sometimes with sticky fluid being leaked into the mouth or through the skin. This problem progresses relentlessly, unless it is stopped by aggressive treatment. Surgery in the affected tissues may make the situation worse, by making a new wound which the bone or tissue cannot heal properly. This problem is not primarily an infection; however, infection can rapidly develop in the affected tissue, which may make the situation suddenly much worse. 

    HBO works not only by helping the white cells in the affected tissue to resist infection. It also supplies the normal cells responsible for healing with enough oxygen to begin to work properly. In the long run, the gradient of oxygen level between the normal tissue and the affected tissue encourages new blood vessels to grow, and this helps to maintain the benefit of the earlier treatments.

  3. Problem wounds. Wounds of any sort which are failing to heal, may benefit from HBO. The field where there is most evidence for this benefit is in the treatment of foot wounds in diabetes, where the problem may get worse for a variety of reasons, including poor blood supply and infection. In this situation, HBO must be used alongside other kinds of treatment, like appropriate antibiotics and surgery, and above all good foot care, to get the best results.

This list of applications of HBO is agreed by the European Committee for Hyperbaric Medicine, and by the European Underwater and Baromedical Society, as reasonable and justified by the evidence in the literature.



HBO is
not used for diseases where there is no evidence that it works. There have been many claims through the years that HBOT would help as a 'miracle cure' in problems like ageing skin, or might even prolong normal healthy life. Where there is doubt about the clinical effectiveness of HBO, it is provided only as part of formal research and development programmes.



The oxygen is breathed in by the patient. This means that the patient must first be inside a space (usually a chamber) where the pressure can be increased and decreased by fine control. Secondly, the patient must be supplied with pure oxygen through a system of pipes which can also withstand the pressure changes. The patient may be surrounded by oxygen filling the chamber; or else, they may wear a mask or a hood through which the oxygen is supplied separately from the chamber: the chamber is then filled with air.

This means that the equipment used for HBO is complex; and it needs to be designed specially for this task. It also needs to operated and maintained by people who have been properly trained for the job. A patient who sees the chamber for the first time may find it so unusual that they may be worried about going inside. The correct use of masks or hoods also needs advice from staff, so that as much oxygen as possible gets to the patient. This means that staff both inside and outside the chamber must be properly trained to look after people in this high-technology environment.In fact, most patients get used to being in the chamber quite quickly: it is less frightening than it looks at first. There should always be a member of staff to talk with before, during and after treatments, so that any problems can be sorted out immediately. Safety procedures also need to be illustrated for all patients and staff, just like in an aircraft.

In many HBO chambers, more than one patient is being treated at the same time; and often patients get to know each other well. So, as well as the serious side of the treatments, they can be enjoyable and even relaxing.



The simplest HBO chamber is big enough to fit only one patient inside. This is called a 'monoplace' chamber. Usually, the patient is surrounded with oxygen, and there is no mask or hood to wear. Sometimes, the patient can sit up, but often they can only lie down. It is always possible to talk with members of staff outside the chamber; and there is usually an intercom system, so that staff can talk with the patient when required. The communication system may also allow the radio to be played inside the chamber; and television can sometimes also be seen through the transparent walls of the chamber. But because there is pure oxygen inside the chamber, no electrical equipment is allowed inside, and nothing can be taken inside which might in any way risk a fire. 

Larger HBO chambers are big enough to walk into and move around inside. These are called 'multiplace' chambers. There is usually an attendant inside the chamber. Each patient has their own oxygen supply, usually from the ceiling of the chamber; so, during the treatments, patients need to stay in roughly one part of the chamber. Even so, there is less chance of being claustrophobic in this larger space. Where necessary, electronic equipment can be used inside the chamber, because the main space is filled with air, which is far less inflammable than pure oxygen. This means also that patients who are critically ill can also be treated in this chamber, which would not generally be so easy in a monoplace chamber.   

In all HBO facilities, there is a control panel outside the chamber, which is operated by a trained member of staff. This means that the pressure in the chamber can be increased and decreased very carefully, and under complete control. These control panels also include safety systems, which prevent the atmosphere in the chamber from changing too quickly or too much.    In a monoplace HBO facility, there is at least a doctor and a nurse/chamber operator. In a multiplace HBO facility, there is a doctor, an attendant in the chamber and also a chamber operator. All these staff must be properly trained and/or supervised.



The first thing most people feel is 'popping' of the ears, like when being in an aircraft which is ascending or descending. This is necessary, because the air behind the ear-drums shrinks as the pressure is increasing and expands again when the pressure is decreasing. Air has to move in and out of the space behind the ear-drum to allow this change to happen; and it gets into the ear from the nose, through the Eustachian tube, a very narrow opening. Sometimes, the patient has to help to make this happen, by swallowing or moving the jaw open and closed, just like in an aircraft.

As the pressure is increasing at the start of treatment, the atmosphere inside the chamber may feel warm. Likewise, at the end of the treatment, when the pressure is decreasing, it may feel cool. In the middle of the treatment, when the treatment pressure is applied, the it may feel no different from normal room temperature.

When the atmosphere in the chamber is at the high pressure, it may feel 'thick' to move around in: this is because it is more dense than the air outside. But the patient does not feel compressed, or that a weight is on top of them. 

The mask or hood (if used) may feel strange at first; but most people get used to this quite quickly.



The most common side-effects are not serious:-

  1. Claustrophobia. Most patients have no problem in the confined space. Some patients need a little time to get used to it. Sometimes, patients need to have a trial run, before staring a real treatment. Very few patients find it impossible to be in the chamber at all.

  2. Ear problems. Some people have problems getting the air to move in and out of the ears during the changes in pressure. Training by staff is usually successful. If this does not work, the ears can hurt, and it is possible to burst an eardrum. Although this sounds serious, the damage is not permanent, as the eardrum usually heals up after a few days. To prevent this from happening, patients are usually not treated when they have a cold, because the lining of the air-passages between the nose and the ears may be swollen and blocked. Nose drops can also be used to open up the air-passages, before the treatment starts.

  3. The lungs. If too much oxygen is given in one treatment, the lungs can become irritated by the oxygen, which can lead to scarring. This would lead to breathlessness and a dry irritating cough. If this happens, treatments are stopped; and the damage is quickly repaired. However, this problem very rarely happens, because the length and intensity of each treatment is strictly limited. As a result of this, courses of HBO can be quite prolonged, to avoid giving too much oxygen on any one day.

  4. The brain. In a very small number of treatments (about 3 in every 10,000) treatments, the patient may suffer a convulsion due to the effects of the oxygen. This sounds very serious; however, the main danger of a convulsion is that the patient stops breathing for a while. In the HBO chamber, the patient has more oxygen inside them than can possibly happen anywhere else. So, even if they stop breathing, there is very little risk of brain damage from too little oxygen. The convulsion stops on its own, soon after the oxygen mask or hood is removed, or soon after the atmosphere in the chamber is changed to air instead of oxygen. If a convulsion happens, this does not mean that the patient is then epileptic, because there are no after-effects of this kind of convulsion. In fact, it is perfectly safe for the patient to go back into the chamber again for further treatments. Treating a convulsion in the chamber is part of the emergency procedures of any HBO facility.

  5. The eyes. In a small number of patients having long courses of treatments, (usually more than 20 treatments), the lenses of the eyes may change shape slightly. This can make the patient temporarily short-sighted (myopic). However, when the treatments are stopped, the lenses return to their normal shape after a few days or weeks. Then, there are no permanent effects from this problem.

  6. Fire. Any space filled with oxygen makes it more likely for a fire to happen. To prevent this, patients are not allowed to bring into the chamber anything which might start a fire, such as through static electricity or flame; they are not allowed to have things which could burn easily, like street clothes or books; and there are emergency procedures to deal with a fire should one start. Safety is the priority in this environment; and therefore the prevention of fire is an absolute priority.

Hyperbaric oxygen treatment is essentially very safe, as long as everybody (patients and staff alike) are aware of the proper procedures, and follow them closely.



The normal way of getting HBO for any condition is through a referral to the HBO facility by a doctor. This way, the reason for the treatment is clear; and there is a medical agency with whom the HBO facility can discuss treatment and other medical care which may be necessary. 

This method of arranging HBO may also be necessary if the treatment is to be funded by a public health scheme or an insurance company.   

The HBO may be only a part of the total treatment package; and other specialties may need to be used at the same time, or even just to get the treatment started. It is usual for the HBO facility to be linked to, or be a physical part of, a hospital or clinic.   

In an emergency, there is usually no need for long negotiations. The treatment will be provided first, and discussions about it will continue after it is over. Friends and relatives will usually be kept informed of progress by staff of the HBO facility.   If you arrange treatment yourself directly with the HBO facility, you should find out what arrangements there are for medical and nursing attention there.




In each European country, there are regulations which apply to HBO facilities, usually for technical and safety matters. These have not yet been standardised internationally.

In some countries, there are guidelines on staffing levels, training and education of staff, and operating and emergency procedures. While these may not be regulations, they are essential markers of quality of service. Not every HBO facility therefore complies with quality guidelines; and some are operated on a purely voluntary basis, offering basic treatment for a very small charge. You should find out what the position is in the HBO facility you are using; and the decision on whether to go ahead with the treatment will be up to you, except in an emergency.   

In some countries there is a national association of HBO providers - this usually offers guidance to HBOT providers, so that the quality of service improves all the time.



Every HBO facility should keep records of the patients it has treated, and the outcomes of treatment. This allows the staff to measure how successful the treatment is, and compare their results with others. The information gathered is sometimes pooled with the results from other HBO facilities; this is especially useful where the condition being treated is rare.

This information is confidential, however, and if the HBO facility wishes to send information about you and your treatment to anyone else, it should ask for your permission first. If the information is sent to anyone else, it is usual for your personal details to be removed from the records.




Sometimes, an HBO facility will use the treatment for a medical condition where the success of HBO has not yet been proved scientifically. In this case, it is common for the HBO facility to carry out research to find out whether their treatment is effective or not. 

Sometimes, patients may be given every part of the treatment package except the HBO, so that they can be compared with patients who receive HBO. In all such cases, patients will be fully informed about the research, and asked if they would like to take part. The potential side-effects of the whole treatment package will also be explained in full. If at any time, a patient wants to stop the treatment, this will always be possible.



The scope and goals of the European Committee for Hyperbaric Medicine (ECHM) are defined as follows :

Structure and regulations:

The ECHM is structured around 3 bodies:

ECHM is represented by its President who is elected by the BD. Other specific offices are Vice President in charge of international affairs, General Secretary and Treasurer.

ECHM operates through permanent and ad-hoc sub Committees. Permanent sub Committees are : 

Workshop and Consensus Conference Bureau:

Finance Bureau: 

Research Sub Committee: 

Education and Training sub Committee:

Current achievements of the ECHM



Since 1994, the ECHM has organised major Consensus Conferences, to establish the common ground between specialists if the field, on a number of important subjects. These have been:-

1994 The applications of Hyperbaric Oxygen; standards for education and training, future directions of research; technical requirements.
(1st European Consensus Conference)
1996 The treatment of decompression accidents in recreational diving.
(2nd European Consensus Conference)
1996 The role of Hyperbaric Oxygen in acute musculo-skeletal trauma. 
(3rd European Consensus Conference)
1998 Hyperbaric oxygen in the management of foot lesions in diabetic patients.
(4th European Consensus Conference)
2001 Hyperbaric oxygen in the treatment of radio-induced lesions in normal tissues.
(5th European Consensus Conference)
2003 Prevention of dysbaric injuries in diving and hyperbaric work.
(6th European Consensus Conference)




The European Commission encourages communication and cooperation internationally, in many fields of science and technology. Since 1999, the EC has been organising such a programme for Hyperbaric Oxygen Therapy, under the title Action B14.

The discussions have centred on:

The project will run for five years, until December 2004. It is expected that enough work will have been done by then to keep progress moving after that time.

Current research projects proposed by the COST B14 Action can be found here.

The Working Group "Technical Aspects" prepared the list of hazards in HBO centres.

The Working Group "Safety" prepared the European Code of Good Practice in Hyperbaric Oxygen Therapy (May 2004).

The Working Group "Oncology" prepared the overview of HBO and radiotherapy with the presentation of several randomized clinical studies. The publication from Strahlentherapie und Onkologie (2005; 181: 113-123) can be freely downloaded (here) thanks to publishers: Springer (www.springerlink.com) and Urban & Vogel GmbH (www.urban-vogel.de).