The Hyperbaric oxygen therapy reference article from the English Wikipedia on 24-Apr-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

Hyperbaric oxygen therapy

Hyperbaric oxygen therapy (HBOT) is the medical use of oxygen at a higher than atmospheric pressure.

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 conditions such as osteomyelitis, problem wounds or infection by anaerobic organisms, the therapeutic principle of HBOT lies in a drastically increased partial pressure of oxygen (pO₂) in the tissues of the body. The pO₂ values 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 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 at atmospheric pressure, this route of transport can not be exploited any further. Oxygen transport by plasma however can be significantly increased under HBOT. This effect is relevant in the treatment of anemia.

The main indications for HBOT are:

• Carbon monoxide poisoning
• Decompression sickness
• Severe infection by anaerobic bacteria (such as gas gangrene)
• Air or gas embolism
• Severe uncorrected anemia
• Osteomyelitis
• Enhancement of healing in problem wounds
• Sports injuries

HBOT is recognized by conventional medicine (in the USA) as an appropriate treatment for about 10 conditions. However, alternative healing advocates of many stripes believe it is useful for many additional conditions. Among the "off-label" uses of HBOT are use as a therapy for brain healing (as in stroke, dementia, cerebral palsy), and for some infectious conditions, such as lymes disease and post polio syndrome

HBOT is quite expensive, with a session costing $100 to $200 in the USA.

In the UK most chambers are financed by the National Health Service but there are non-profit HBOT chambers, such as those run by the Multiple Sclerosis Society.

Table of contents

1 The traditional chamber 2 Chambers for home treatment 3 Historical link to diving 4 Treatments 5 Complications 6 External links

The traditional chamber

The rational type of HBOT chamber is a hard shelled pressurized chamber. Such chambers can be run at pressures up to 6 ATA, 6 bar or 85 pounds per square inch (600 kPa).

Navies, diving organisations 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 or aluminium
• one or more human entry hatches - theses could be small and circular or wheel-in type hatches for patients on trolleys
• an air-lock allowing human entry - a separate chamber with two hatches, one to the outside world and one to the main chamber, which can be independently pressurised to allow patients to enter or exit the main chamber while it is still pressurised
• an air-lock 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
• a storage "bank" of high pressure air cylinders, similar to diving cylinders
• a diving air compressor to fill the bank

Both patients and medical staff inside the chamber breathe from individual 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 minimise 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 mask may be one that simply covers the mouth and nose or it may be a type of flexible, transparent helmet with a seal around the neck.

The pressure inside the chamber is raised by allowing air from high pressure air cylinders to enter the chamber. 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 maneouvre or by "jaw wiggling". As the pressure increase further, mist may form in the air in the chamber and the air becomes warm. When the patient speaks the tone of the voice may increase to the level that they sound like cartoon characters.

To reduce the pressure, a valve is opened letting the air out of the chamber. As the pressure falls, the patients’ ears may "squeak" and the air will cool.

Chambers for home treatment

There are also soft sided HBOT chambers, which are often used for home treatment. Some of these are also used in clinics. These are usually referred to as "mild chambers", which is a reference to the lower maximum pressure of soft-sided chambers. Those commercially available in the USA only go up to 1.3 ATA, 1.3 bar or 18 pounds per square inch.

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-adsorbed 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.

In-water recompression is a very risky alternative means of treatment when recompression in a chamber is not possible.

Treatments

The slang term for a cycle of pressurization inside the HBO chamber is "a dive".

Emergency HBOT for diving disorders typically follows one of these two forms:

• for mild cases, a shallow "dive" to a maximum pressure equal to a depth of 18 metres / 60 feet in water, with a gradual "ascent", totally 4.5 hours with the casualty breathing pure oxygen with air breaks every 20 minutes to reduce oxygen toxicity
• for serious cases, a deeper "dive" to a maximum pressure equal to a depth of 37 metres / 122 feet in water, with a gradual "ascent", totally 8.5 hours with the casualty breathing pure oxygen with air breaks every 20 minutes to reduce oxygen toxicity

The HBOT treatment for longer-term conditions is often a series of 40 "dives".

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. In the UK the Royal Navy 62 and 67 tables are used.

Complications

There are risks associated with HBOT:

• Pressure changes can cause a 'squeeze' in any area of trapped air inside the body, such as behind the eardrum, inside sinuses, or even trapped underneath fillings.
• One of the side effects of oxygen toxicity is a seizure.

External links

• Underwater and Hyperbaric Medicine Society
• Diving Diseases Research Centre

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