Hyperbaric medicine

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Hyperbaric medicine, also known as hyperbaric oxygen therapy (HBOT), is the medical use of oxygen at a level higher than atmospheric pressure.

Contents 1 Therapeutic principles 2 Uses 3 Structure 3.1 Traditional 3.2 Oxygen breathing 3.3 Effects of Pressure 3.4 Home treatment 4 Treatments 4.1 Protocol 4.2 Possible complications 4.3 Contraindications 4.4 Neuro-rehabilitation 5 See also 6 References 7 Further reading 8 External links

[edit] Therapeutic principles

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 and air embolism ^[1].
• 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 cannot be exploited any further. Oxygen transport by plasma, however is significantly increased under HBOT.

[edit] Uses

The United States, the Undersea and Hyperbaric Medical Society, known as UHMS, approved for reimbursement diagnoses for application of HBOT in hospitals. The following indications are approved uses of hyperbaric oxygen therapy as defined by the UHMS Hyperbaric Oxygen Therapy Committee.^[2]

• Air or gas embolism^[3]
• Carbon monoxide poisoning^[4][5]
  • Carbon Monoxide Poisoning Complicated by Cyanide Poisoning^[6][7][8]
• Clostridal Myositis and Myonecrosis^[9] (Gas gangrene^[10][11])
• Crush Injury, Compartment syndrome, and other Acute Traumatic Ischemias^[12][13]
• Decompression sickness^[14][15][16]
• Enhancement of Healing in Selected Problem Wounds^[17][18][19]
• Exceptional Blood Loss^[20][21] (Anemia)
• Intracranial Abscess^[22][23]
• Necrotizing Soft Tissue Infections^[24] (Necrotizing fasciitis^[25])
• Osteomyelitis^[26][27][28] (Refractory)
• Delayed Radiation Injury^[29] (Soft Tissue and Bony Necrosis^[30][31])
• Skin Grafts & Flaps^[32][33] (Compromised)
• Thermal Burns^[34][35]

In the United States, HBOT is recognized by Medicare as a reimbursable treatment for 14 UHMS "approved" conditions. An HBOT session costs anywhere from $100 to $200 in private clinics, to over $1,000 in hospitals. U.S. physicians may lawfully prescribing HBOT for "off-label" conditions such as Lyme Disease^[36], stroke^[37][38][39] and migraines.^[40][41][42] Such patients are treated in outpatient clinics. In the United Kingdom most chambers are financed by the National Health Service, although some, such as those run by Multiple Sclerosis Therapy Centres, are non-profit.

Other reported applications include:

• Diabeticaly derived illness, such as diabetic foot ^{[43], [44]}, diabetic retinopathy ^{[45], [46]}, diabetic nephropathy ^[47]
• Epidural abscesses ^[48]
• Certain kind of hearing loss ^[49]
• Radiation-induced hemorrhagic cystitis ^[50]
• Inflammatory bowel disease ^{[51], [52]}

HBOT is controversial and health policy regarding its uses is politically charged. Both sides of the controversy on the effectiveness of HBOT is available in the form of Cochrane Library reviews.^[53]

The toxicology of the treatment has recently been reviewed by Ustundag et al. ^[54] and its risk management is discussed by Christian R. Mortensen ^[55].

[edit] Structure

[edit] Traditional

The traditional type of hyperbaric chamber used for HBOT 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 which are portable and capable of treating just one patient to those which 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 oxygen helmets or masks

[edit] Oxygen breathing

In today's larger "multiplace" chambers, both patients and medical staff inside the chamber breathe from "oxygen helmets", flexible, transparent soft plastic helmets with a seal around the neck similar to a space suit helmet, or tightly fitting aviators oxygen masks, which supply pure oxygen and remove the exhaled gas from the chamber. During treatment patients breathe 100% 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. Administration of 100% breathing oxygen maximizes the patient's treatment. 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 or compressed air. The cost of using pure oxygen in a monoplace chamber is much higher than using compressed air. If pure oxygen is used no oxygen breathing mask or helmet is needed. If compressed air is used then an oxygen mask or helmet is needed as in a multiplace chamber. In monoplace chambers that are compressed with pure oxygen a mask is available to provide the patient with "air breaks," periods of breathing normal air, in order to reduce the risk of hyperoxic seizures.

[edit] Effects of Pressure

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] 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 PSI (1.27 ATA 8.92 FSW). International portable chambers can go to 7.35 psi (1.5 ATA 16.38 FSW) or higher. These chambers are operated with oxygen concentrators (typically 95% oxygen) or with 100% oxygen as the breathing gas. Total concentration of oxygen should not exceed 25% as this can increase the risk of fire.

These chambers are often used in a clinical settings, but are also used in homes. Mild hyperbaric chambers use standard 120 volt outlets and can also be configured for 220 volt use. Ranging in size from 21" up to 40" in diameter these chambers measure between 84" to 120" in length. The soft chambers are FDA approved only for the treatment of altitude sickness but are commonly used off label primarily for the treatment of autism and other neural conditions though there is no proof that it is effective and hospitals refuse to allow their chambers to be used for this purpose.^[56] The FDA has a specific warning that supplemental oxygen is not to be used.

[edit] Treatments

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 by increasing pressure, reducing the size of the gas bubbles and improving the transport of blood to downstream tissues. The high concentrations of oxygen in the tissues are beneficial in keeping oxygen-starved tissues alive, and have the effect of removing the nitrogen from the bubble, making it smaller until it consists only of oxygen which is then re-absorbed into the body. After elimination of bubbles, the pressure is gradually reduced back to atmospheric levels.

[edit] Protocol

The slang term for a cycle of pressurization inside the HBOT chamber is "a dive". An HBOT treatment for longer-term conditions is often a series of 20 to 40 dives.

Emergency HBOT for diving disorders typically follows one of 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.

The Undersea and Hyperbaric Medical Society^[57] (UHMS) publishes a report which compiles the latest research findings and contains information regarding the recommended duration and pressure of the longer-term conditions.

[edit] Possible 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^[58], behind the eardrum^[59][60], inside paranasal sinuses^[59], or trapped underneath dental fillings^[61]. Breathing high-pressure oxygen for long periods can cause oxygen toxicity. Temporarily blurred vision can be caused by swelling of the lens, which usually resolves in two to four weeks.^[62][63]

There are reports that cataract may progress following HBOT.^[64] Also a rare side effect has been blindness secondary to optic neuritis (inflammation of the optic nerve).^{[citation needed]}

[edit] Contraindications

The only absolute contraindication to hyperbaric oxygen therapy is untreated pneumothorax.^[65] Also, the treatment may raise the issue of Occupational safety and health (OHS), which has been encountered by the therapist.^{[66][clarification needed]}

Patients should not undergo HBO therapy if they are taking or have recently taken the following drugs:

• Doxorubicin (Adriamycin) - A chemotherapeutic drug.
• Disulfiram (Antabuse) - Used in the treatment of alcoholism.
• Cis-platinum - A cancer drug.
• Mafenide acetate (Sulfamylon) - Suppresses bacterial infections in burn wounds

The following are relative contraindications:

• Upper respiratory infections - These conditions can make it difficult for the patient to clear their ears, which can result in what is termed sinus squeeze.
• High fevers - In most cases the fever should be lowered before HBO treatment begins.
• Emphysema with CO2 retention - This condition can lead to pneumothorax during HBO treatment.
• History of thoracic (chest) surgery - This is rarely a problem and usually not considered a contraindication. However, there is concern that air may be trapped in lesions that were created by surgical scarring. These conditions need to be evaluated prior to considering HBO therapy.
• Malignant disease: Since cancers both thrive in blood rich environments and may be suppressed in high oxygen environments, cancer and HBO poses a dilemma since HBO both increases blood flow via angiogenesis and also raises oxygen levels. Taking an anti-angiogenic supplement may provide a solution to this problem.^[67][68]
• Middle ear barotrauma (MEBT) is always a consideration in treating both children and adults in a hyperbaric environment, but most children currently being treated with HBOT are being pressurized to 1.3 ATA which reduces the risks of potential side effects.^{[citation needed]}

[edit] Neuro-rehabilitation

The Collet (Quebec) trial^[69] that was published in the Lancet in 2001 was the largest randomized trial of Hyperbaric Oxygen Therapy (HBOT) for children with cerebral palsy (CP); it followed the McGill pilot study on the same subject.^[70]

The evidence showed both groups of children treated with two very different hyperbaric treatment dosages improved significantly. The motor improvements that were seen and measured with the gross motor function measure^[71] were greater, more generalized, and were obtained in a shorter period of time than most of the changes found in any other studies of recognized conventional therapies in the treatment of children with cerebral palsy.^[72][73] The children in both groups improved an average of ten times more during the two months of HBOT (whilst all other therapies and medication were stopped) than during the three months follow-up (when medication and all the ancillary treatments were restarted). This impressive change in the rate of improvements clearly indicates the probable effectiveness of hyperbaric treatment. Both the Lancet commentary^[74] and the tech report by the Agency for Healthcare Research and Quality (AHRQ)^[75] concluded that the hypothesis of both treatments being equally effective should be retained.

Since the Quebec study of HBOT for children with CP, many reports^[76][77] have been made on the possible efficacy of a low pressure hyperbaric treatment and all the trials^{[78][79][80][81]} conducted with HBOT in CP have demonstrated positive results.

An editorial on CP published by the Undersea and Hyperbaric Medical Society in 2007 called for further research that will include "basic science research to determine a reasonable mechanism of action" for hyperbaric oxygenation as well as "clinical studies of the highest possible methodological rigor".^[82]

Some medical practitioners recommend the use of HBOT for the treatment of acute tinnitus but this treatment has not been verified by independent evidence and the treatment was withdrawn from support by the German health insurance.^[83] There is evidence that the therapeutic effects could be greatly due to psychological mechanisms triggered by the patients attitude towards therapy prior to the treatment.^[84]

The earliest randomized, placebo-controlled, double-blind study on multiple sclerosis patients treated with HBOT suggested the therapy could improve balance and bladder function.^[85] However, by 2004 a Cochrane review assessing ten trials and 21 analyses "found no consistent evidence to confirm a beneficial effect of hyperbaric oxygen therapy for the treatment of multiple sclerosis and do not believe routine use is justified".^[86]

[edit] See also

• Undersea and Hyperbaric Medical Society
• South Pacific Underwater Medicine Society

[edit] References

[edit] Further reading

[edit] External links

• Hyperbaric Oxygen Therapy from eMedicine