Hyperbaric oxygen therapy
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Hyperbaric oxygen therapy (HBOT) is the medical use of oxygen at a higher than atmospheric pressure.
Image:Father and Son in Chamber.jpg
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[edit] Uses
Several therapeutic principles are made use of in HBOT:
- The increased overall pressure is of therapeutic value when HBOT is used in the treatment of decompression sickness.
- For many other conditions, the therapeutic principle of HBOT lies in a drastically increased partial pressure of oxygen in the tissues of the body. The oxygen partial pressures achievable under HBOT are much higher than those under breathing pure oxygen at normobaric conditions (i.e. at normal atmospheric pressure).
- A related effect is the increased oxygen transport capacity of the blood. Under atmospheric pressure, oxygen transport is limited by the oxygen binding capacity of hemoglobin in red blood cells and very little oxygen is transported by blood plasma. Because the hemoglobin of the red blood cells is almost saturated with oxygen under atmospheric pressure, this route of transport can not be exploited any further. Oxygen transport by plasma however is significantly increased under HBOT.
The main indications for HBOT are:
- Certain non-healing wounds (post-surgical or diabetic)
- Radiation soft tissue necrosis and radiation osteonecrosis
- Necrotizing fasciitis (flesh eating bacteria)
- Carbon monoxide poisoning
- Decompression sickness
- Severe infection by anaerobic bacteria (such as gas gangrene)
- Air or gas embolism
- Severe uncorrected anemia
- Chronic refractory Osteomyelitis
- Enhancement of healing in problem wounds
- Sports injuries
HBOT is recognized by Medicare in the United States as an appropriate treatment for 14 conditions. European medicine recognizes it as an appropriate treatment for many more [1] Alternative healing advocates of many stripes believe it is useful for additional conditions. Among the uses of HBOT are therapy for brain healing (as in stroke, dementia, cerebral palsy and absence seizure), and for some infectious conditions, such as Lyme disease and Post-polio syndrome.
HBOT is expensive, with a session costing anywhere from $100 to $1200 in the United States.
In the United Kingdom most chambers are financed by the National Health Service but there are non-profit HBOT chambers, such as those run by Multiple Sclerosis Therapy Centres.
[edit] The traditional chamber
Image:Decompression chamber.jpg
The traditional type of HBOT chamber is a hard shelled pressure vessel. Such chambers can be run at absolute pressures up to 600 kilopascals or 85 PSI (lbf/in²), nearly six atmospheres.
Navies, diving organizations and hospitals typically operate these. They range in size from those that are portable and capable of transporting just one patient to those that are fixed, very heavy and capable of treating eight or more patients.
The chamber may consist of:
- a pressure vessel that is generally made of steel and aluminium with the view ports (windows) or hull made of acrylic.
- one or more human entry hatches—these could be small and circular or wheel-in type hatches for patients on trolleys
- an airlock allowing human entry—a separate chamber with two hatches, one to the outside world and one to the main chamber, which can be independently pressurized to allow patients to enter or exit the main chamber while it is still pressurized
- an airlock allowing medicines, instruments and food to enter the main chamber
- glass ports or closed-circuit television allowing the technicians and medical staff outside the chamber to monitor the inside of the chamber
- an intercom allowing two-way communications inside and outside the chamber
- a carbon dioxide scrubber—consisting of a fan that passes the gas inside the chamber through a soda lime canister
- a control panel outside the chamber is used to open and close valves allowing air to enter or leave the chamber and oxygen to be supplied to masks
In larger "multiplace" chambers, both patients and medical staff inside the chamber breathe from individual oxygen masks, which supply pure oxygen and remove the exhaled gas from the chamber. During treatment patients breathe oxygen most of the time but have periodic air breaks to minimize the risk of oxygen toxicity. The exhaled gas must be removed from the chamber to prevent the build up of oxygen, which could provoke a fire. Medical staff may also breathe oxygen to reduce the risk of decompression sickness. The oxygen masks that are used may simply cover the mouth and nose or they may be a type of flexible, transparent helmet with a seal around the neck. The pressure inside the chamber is increased by opening valves allowing high-pressure air to enter from storage cylinders, similar to diving cylinders. A gas compressor is used to fill these cylinders.
Smaller "monoplace" chambers can only accommodate the patient. No medical staff can enter. The chamber is flooded with pure oxygen and the patient does not wear an oxygen mask or helmet.
Patients inside the chamber will notice discomfort inside their ears as a pressure difference develops between their middle ear and the chamber atmosphere. This can be relieved by the Valsalva maneuver or by "jaw wiggling". As the pressure increases further, mist may form in the air inside the chamber and the air may become warm. When the patient speaks, the pitch of the voice may increase to the level that they sound like cartoon characters.
To reduce the pressure, a valve is opened to allow gas out of the chamber. As the pressure falls, the patient’s ears may "squeak" as the pressure inside the ear equalizes with the chamber. The temperature in the chamber will fall.
[edit] Chambers for home treatment
There are portable HBOT chambers, which are used for home treatment. These are usually referred to as "mild chambers", which is a reference to the lower pressure of soft-sided chambers. Those commercially available in the USA go up to 4.1 PSI (about 28.268 kPa) which is equivalent to a water depth of 11 ft. These chambers are operated with oxygen concentrators or with 100% oxygen as the breathing gas.
These chambers were originally developed and used for altitude sickness. The benefits of HBOT to a number of other off label conditions such as autism, lyme disease, cancer, stroke, cerebral palsy, multiple sclerosis, cardiac conditions, brain injury, and other immunodeficiency disorders do have research and case studies to substantiate their effectiveness.
Recent studies have also shown that hyperbaric at a lower pressure for a period of 6 months or more is more effective for most conditions as the mild chambers have an immune modulating effect and hyperbaric at a higher pressure has a tendency to be immune suppressive over time.
[edit] Historical link to diving
Initially, HBOT was developed as a treatment for diving disorders involving bubbles of gas in the tissues, such as decompression sickness and gas embolism. The chamber cures decompression sickness and gas embolism in several ways:
- the increase in pressure in the chamber reduces the size of the gas bubbles improving transport of blood to tissues downstream of the bubbles
- the high concentrations of oxygen breathed by the casualty are beneficial in keeping oxygen-starved tissues alive
- the high concentrations of oxygen in the tissues have the effect of removing the nitrogen from the bubble making it smaller until it consists only of oxygen which is re-absorbed into the body
Bubbles are eventually eliminated by long exposure to pressure and high oxygen concentrations, allowing a gradual reduction of pressure back to atmospheric levels.
[edit] Treatments
The slang term for a cycle of pressurization inside the HBOT chamber is "a dive".
Emergency HBOT for diving disorders typically follows one of these two forms:
- for most cases, a shallow "dive" to a pressure the equivalent of 18 meters / 60 feet of water for 3 to 4.5 hours with the casualty breathing pure oxygen with air breaks every 20 minutes to reduce oxygen toxicity
- for extremely serious cases, a deeper "dive" to a pressure the equivalent of 37 meters / 122 feet of water for 4.5 hours with the casualty breathing air.
In Canada and the United States, the U.S. Navy Dive Charts are used to determine the duration, pressure and breathing gas of the therapy. The most frequently used tables are Table 5 and Table 6. In the UK the Royal Navy 62 and 67 tables are used.
An HBOT treatment for longer-term conditions is often a series of 20 to 40 "dives".
The Undersea and Hyperbaric Medical Society (UHMS) publishes a "Committee Report" which compiles the latest research findings and contains information regarding the recommended duration and pressure of the longer-term conditions.
[edit] Complications
There are risks associated with HBOT, similar to some diving disorders:
- Pressure changes can cause a "squeeze" or barotrauma in the tissues surrounding trapped air inside the body, such as the lungs, behind the eardrum, inside paranasal sinuses, or even trapped underneath dental fillings.
- Breathing high-pressure oxygen for long periods can cause oxygen toxicity. One of the side effects of oxygen toxicity is a seizure.
- Vision changes (myopia or nearsightedness) caused by swelling of the lens. This is more a temporary side-effect than a complication and usually resolves in two to four weeks following completion of HBOT.
The only absolute contraindication to hyperbaric oxygen therapy is untreated pneumothorax. Relative complications include grand mal seizure, fever, the inability to clear the ears or sinuses, and the use of certain chemotherapy agents.
[edit] See also
- Recompression chamber, Decompression chamber or hyperbaric chamber (simulates depth)
- Hypobaric chamber (simulates altitude)
- In-water recompression
- Oxygen therapy
