Hyperbaric medicine

Hyperbaric medicine
Intervention
A Sechrist Monoplace hyperbaric chamber at the Moose Jaw Union Hospital, Saskatchewan, Canada
ICD-9-CM	93.95
MeSH	D006931
OPS-301 code:	8-721

Hyperbaric medicine, also known as hyperbaric oxygen therapy (HBOT), is the medical use of oxygen at a level higher than atmospheric pressure. The equipment required consists of a pressure chamber, which may be of rigid or flexible construction, and a means of delivering 100% oxygen. Operation is performed to a predetermined schedule by trained personnel who monitor the patient and may adjust the schedule as required. HBOT found early use in the treatment of decompression sickness, but has shown great effectiveness in treating conditions such as gas gangrene and carbon monoxide poisoning. More recent research has examined the possibility that it may also have value for other conditions such as cerebral palsy and multiple sclerosis, but no significant evidence has been found.

Contents 1 Therapeutic principles 2 Indications 3 Hyperbaric chambers 3.1 Construction 3.2 Oxygen supply 4 Treatments 4.1 Protocol 4.2 Home and out-patient clinic treatment 4.3 Possible complications and concerns 4.4 Effects of Pressure 4.5 Contraindications 4.6 Neuro-rehabilitation 5 See also 6 References 7 Further reading 8 External links

Therapeutic principles

Several therapeutic principles are made use of in HBOT:^[1]

• The increased overall pressure is of therapeutic value when HBOT is used in the treatment of decompression sickness and air embolism;^[2]
• For many other conditions, the therapeutic principle of HBOT lies in its ability to drastically increase partial pressure of oxygen in the tissues of the body. The oxygen partial pressures achievable using HBOT are much higher than those achievable while 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 normal 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 using HBOT as the stimulus.
• Recent evidence notes that exposure to hyperbaric oxygen (HBOT) mobilizes stem/progenitor cells from the bone marrow by a nitric oxide (·NO) -dependent mechanism.^[3] This mechanism may account for the patient cases that suggest recovery of damaged organs and tissues with HBOT.

Indications

In the United States the Undersea and Hyperbaric Medical Society, known as UHMS, lists approvals for reimbursement for certain diagnoses in hospitals and clinics. The following indications are approved (for reimbursement) uses of hyperbaric oxygen therapy as defined by the UHMS Hyperbaric Oxygen Therapy Committee:^[1][4] However, these are reimbursement decisions based on cost of medical treatments vs HBOT at the average U.S. hospital charge of $1,800.00 per 90 minute HBOT treatment. China and Russia treat more than 80 maladies, conditions and trauma with HBOT, since dollar costs are insignificant in those countries.^[5]

• Air or gas embolism;^[6]
• Carbon monoxide poisoning;^[7][8]
  • Carbon monoxide poisoning complicated by cyanide poisoning;^[9][10][11]
• Clostridal myositis and myonecrosis (gas gangrene);^[12][13][14]
• Crush injury, compartment syndrome, and other acute traumatic ischemias;^[15][16]
• Decompression sickness;^[17][18][19]
• Enhancement of healing in selected problem wounds;^[20][21][22]
  • Diabetically derived illness, such as diabetic foot,^[23][24] diabetic retinopathy,^[25][26] diabetic nephropathy;^[27]
• Exceptional blood loss (anemia);^[28][29]
• Intracranial abscess;^[30][31]
• Necrotizing soft tissue infections (necrotizing fasciitis);^[32][33]
• Osteomyelitis (refractory);^[34][35][36]
• Delayed radiation injury (soft tissue and bony necrosis);^[37][38][39]
• Skin grafts and flaps (compromised);^[40][41]
• Thermal burns.^[42][43]

HBOT is recognized by Medicare in the United States as a reimbursable treatment for 14 UHMS "approved" conditions. A 1-hour HBOT session may cost between $108 and $250 in private clinics, and over $1,000 in hospitals. U.S. physicians (either M.D. or D.O.) may lawfully prescribe HBOT for "off-label" conditions such as Lyme Disease,^[44] stroke,^[45][46][47] and migraines.^[48][49][50] 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:

• Autism. A small 2009 double-blind study of autistic children found that 40 hourly treatments of 24% oxygen at 1.3 atm provided significant improvement in the children's behavior immediately after treatment sessions.^[51] The study's effect has not been independently confirmed. Research conducted by the Center for Autism and Related Disorders (CARD) found that hyperbaric oxygen therapy does not have a significant effect on symptoms of autism.^[52]
• Cerebral Palsy;^[53]
• Epidural abscesses;^[54]
• Certain kind of hearing loss;^[55]
• multiple sclerosis^[56]
• Radiation-induced hemorrhagic cystitis;^[57]
• Inflammatory bowel disease.^[58][59]
• Psoriasis.^[60]

The toxicology of the treatment has recently been reviewed by Ustundag et al.^[61] and its risk management is discussed by Christian R. Mortensen.^[62]

Hyperbaric chambers

Construction

The traditional type of hyperbaric chamber used for HBOT is a hard shelled pressure vessel. Such chambers can be run at absolute pressures as much as 6 bars (87 psi), 600,000 Pa. Navies, diving organizations, hospitals, and dedicated recompression facilities typically operate these. They range in size from semi-portable, one-patient units to room-sized units that can treat eight or more patients. Recent advances in materials technology have resulted in the manufacture of portable, "soft" chambers that can operate at between 0.3 and 0.5 bar (4.4 and 7.3 psi) above atmospheric pressure.^[63] Hard chambers and soft chambers should not be considered equivalent in regards to efficacy and safety as they are different in many aspects.

A hard chamber may consist of

• a pressure vessel that is generally made of steel, aluminium with the view ports (windows) made of acrylic;
• one or more human entry hatches—small and circular or wheel-in type hatches for patients on gurneys;
• the airlock that allows human entry—a separate chamber with two hatches, one to the outside 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 and a small airlock for medicines, instruments, and food;
• glass ports or closed-circuit television that allows technicians and medical staff outside the chamber to monitor the patient inside the chamber;
• an intercom or walkie-talkie allowing two-way communication;
• 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 to open and close valves that control air flow to and from the chamber, and regulate oxygen to helmets or masks.

A soft chamber may consist of

• a urethane-coated, nylon-bonded flexible acrylic pressure vessel with steel-weld technology;
• a full-length dual zipper-sealed opening;
• an over-pressure valve, if oxygen is fed into a small mask and expired gas has to be circulated toward the end of the chamber and out through the pressure regulators.

Oxygen supply

In today's larger multiplace chambers, both patients and medical staff inside the chamber breathe from either "oxygen hoods" – flexible, transparent soft plastic hoods with a seal around the neck similar to a space suit helmet – or tightly fitting oxygen masks, which supply pure oxygen and may be designed to directly exhaust the exhaled gas from the chamber. During treatment patients breathe 100% oxygen most of the time to maximise the effectiveness of their treatment, but have periodic "air breaks" during which they breathe room air (21% oxygen) 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 present a fire risk. Attendants may also breathe oxygen to reduce their risk of decompression sickness. The pressure inside a hard chamber is increased by opening valves allowing high-pressure air to enter from storage cylinders, which are filled by an air compressor. A soft chamber may be pressurised directly from a compressor.

Smaller "monoplace" chambers can only accommodate the patient, and no medical staff can enter. The chamber may be pressurised with pure oxygen or compressed air. If pure oxygen is used, no oxygen breathing mask or helmet is needed, but the cost of using pure oxygen is much higher than that of using compressed air. If compressed air is used then an oxygen mask or hood is needed as in a multiplace, hard 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 (21% oxygen), in order to reduce the risk of hyperoxic seizures. In soft chambers, using compressed air and a mask supplying 96% oxygen, no air breaks are necessary as there is negligible risk of oxygen toxicity because of relatively low oxygen partial pressures and the short duration of treatment.

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 re-absorbed into the body. After elimination of bubbles, the pressure is gradually reduced back to atmospheric levels.

Protocol

The slang term, at some facilities, 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, or compressions. Again, these dives last for about an hour and can be administered via a hard, high-pressure chamber or a soft, low-pressure chamber - the major difference being per-dive "dose" of oxygen. Many conditions do quite well with the lower dose, lower cost-per-hour, soft chambers.

Emergency HBOT for decompression illness follows treatment schedules laid out in treatment tables. Most cases employ a recompression to 2.8 bars (41 psi) absolute, the equivalent of 18 metres (60 ft) of water, for 4.5 to 5.5 hours with the casualty breathing pure oxygen, but taking air breaks every 20 minutes to reduce oxygen toxicity. For extremely serious cases resulting from very deep dives, the treatment may require a chamber capable of a maximum pressure of 8 bars (120 psi), the equivalent of 70 metres (230 ft) of water, and the ability to supply heliox as a breathing gas.^[64]

U.S. Navy treatment charts are used in Canada and the United States 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 (UHMS) publishes a report that compiles the latest research findings and contains information regarding the recommended duration and pressure of the longer-term conditions.^[65]

Home and out-patient clinic treatment

There are several sizes of portable chambers, which are used for home treatment. These are usually referred to as "mild personal hyperbaric chambers", which is a reference to the lower pressure (compared to hard chambers) of soft-sided chambers. Food and Drug Administration (FDA) approved chambers for use with room air are available in the USA and may go up to 4.4 pounds per square inch (psi) above atmospheric pressure, which equals 1.3 atmospheres absolute (ATA), equivalent to a depth of 10 feet of sea water. In the US, these "mild personal hyperbaric chambers" are categorized by the FDA as CLASS II medical devices and requires a prescription in order to purchase one or take treatments.^[66] Personal hyperbaric chambers are only FDA approved to reach 1.3 ATA. While hyperbaric chamber distributors and manufacturers cannot supply a chamber in the US with any form of elevated oxygen delivery system, a physician can write a prescription to combine the two modalities, as long as there is a prescription for both hyperbarics and oxygen. The most common option (but not approved by FDA) some patients choose is to acquire an oxygen concentrator which typically delivers 85–96% oxygen as the breathing gas. Due to the high circulation of air through the chamber, the total concentration of oxygen in the chamber never exceeds 25% as this can increase the risk of fire. Oxygen is never fed directly into soft chambers but is rather introduced via a line and mask directly to the patient. FDA approved oxygen concentrators for human consumption in confined areas used for HBOT are regularly monitored for purity (+/- 1%) and flow (10 to 15 liters per minute outflow pressure). An audible alarm will sound if the purity ever drops below 80%. Personal hyperbaric chambers use 120 volt or 220 volt outlets. Ranging in size from 21 inches up to 40 inches in diameter these chambers measure between 84 in (7 ft) to 120 in (10 ft) in length. The soft chambers are approved by the FDA for the treatment of altitude sickness, but are commonly used for other "off-label" purposes.

Possible complications and concerns

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,^[67] behind the eardrum,^[68][69] inside paranasal sinuses,^[68] or trapped underneath dental fillings.^[70] Breathing high-pressure oxygen may cause oxygen toxicity.^[71] Temporarily blurred vision can be caused by swelling of the lens, which usually resolves in two to four weeks.^[72][73]

There are reports that cataract may progress following HBOT.^[74] Also a rare side effect has been blindness secondary to optic neuritis (inflammation of the optic nerve).

Effects of Pressure

Patients inside the chamber may notice discomfort inside their ears as a pressure difference develops between their middle ear and the chamber atmosphere.^[75] 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. Increased pressure may also cause ear drums to rupture, resulting in severe pain.

To reduce the pressure, a valve is opened to allow air 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. The speed of pressurization and de-pressurization can be adjusted to each patient's needs.

Contraindications

The only absolute contraindication to hyperbaric oxygen therapy is untreated pneumothorax.^[67] Also, the treatment may raise the issue of Occupational health and safety (OHS), which has been encountered by the therapist.^[76]

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

• Doxorubicin (Adriamycin) – A chemotherapeutic drug.
• Cisplatin – Also a chemotherapeutic drug.
• Disulfiram (Antabuse) – Used in the treatment of alcoholism.
• Mafenide acetate (Sulfamylon) – Suppresses bacterial infections in burn wounds

The following are relative contraindications -- meaning that special consideration must be made by specialist physicians before HBO treatments begin:

• Upper respiratory infections – These conditions can make it difficult for the patient to equalise their ears or sinuses, which can result in what is termed ear or 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: Cancers thrive in blood rich environments but may be suppressed by high oxygen levels. HBO treatment of individuals who have cancer presents a problem, since HBO both increases blood flow via angiogenesis and also raises oxygen levels. Taking an anti-angiogenic supplement may provide a solution.^[77][78] A study by Feldemier, et al. and recent NIH funded study on Stem Cells by Thom, et al., indicate that HBO is actually beneficial in producing stem/progenitor cells and the malignant process is not accelerated.^[79]
• Middle ear barotrauma is always a consideration in treating both children and adults in a hyperbaric environment because of the necessity to equalise pressure in the ears.
• Pregnancy is a relative contraindication to both SCUBA diving and hyperbaric oxygen treatments. In cases where a pregnant woman has carbon monoxide poisoning there is evidence that lower pressure (2.0 ATA) HBOT treatments are not harmful to the fetus, and that the risk involved is outweighed by the greater risk of the untreated effects of CO on the fetus (neurologic abnormalities or death.)^[80][81]

Neuro-rehabilitation

A 2004 systematic review of HBOT in traumatic brain injury identified 2 randomized controlled trials and 5 observational studies that met evaluated functional health outcomes. The studies ranged from fair to poor in quality. None adequately reported adverse events, the most serious reported being seizures, pulmonary symptoms, and neurologic deterioration. The review concluded that was insufficient evidence to prove the effectiveness or ineffectiveness, including risks and benefits of HBOT for TBI. In one RCT, the HBOT group had reduced mortality compared to the control group but much higher levels of disability. Another, smaller, study found no difference in mortality. The observational studies were weak in quality and did not provide enough evidence of clinical improvement following HBOT treatment.^[82]

Evidence in a 2005 systematic review of the evidence for HBOT in the treatment of stroke showed no benefit to the treatment, though the generalizability of the finding was limited due to the wide variety in stage and type of stroke, and the treatment given. Good quality studies were recommended to determine if HBOT provides any benefit in stroke.^[83] Another review that examined the effectiveness of HBOT in acute stroke. It found no evidence that HBOT improved clinical outcomes at 6 months, but further study was recommended.^[45]

A systematic review of HBOT for cerebral palsy was published in 2007. Two randomized controlled trials and four observational studies were identified.^[84] The best evidence from a randomized controlled trial (the Collet study) found that HBOT and slightly pressurized room air resulted in similar improvements in motor function of about 5–6% compared to baseline.^[84][85] Neuropsychological tests also showed no difference between HBOT and room air. Based on caregiver report, those who received room air had significantly better mobility and social functioning.^[84][85] Several methodological concerns about the study were raised. Another trial found no difference between a HBOT and a no treatment group.^[84] Some low quality observational studies of HBOT reported similar improvements in motor function. Children receiving HBOT were reported to experience seizures and the need for tympanostomy tubes to equalize ear pressure, though the incidence was not clear. Future research was recommended to determine the efficacy of pressurized room air and non-pressurized oxygen compared with standard treatments.^[84]

A review of 12 randomized studies using HBOT with multiple sclerosis suggested that there is no clinically significant benefit from the administration of HBOT. The review proposed that more trials for selected subgroups of MS and for prolonged treatments may be worthwhile, but that routine use of HBOT in the treatment of MS was not recommended.^[86] The 2004 Cochrane review concluded that further "trials are not, in our view, justified".^[56]

See also

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

References

Further reading

• Kindwall, Eric P; Whelan, Harry T (2008). Hyperbaric Medicine Practice, 3rd Edition. Flagstaff, AZ: Best Publishing Company. ISBN 978-1-930536-49-4. 
• Mathieu, Daniel (2006). Handbook on Hyperbaric Medicine. Berlin: Springer. ISBN 1-4020-4376-7. 
• Neubauer, Richard A; Walker, Morton (1998). Hyperbaric Oxygen Therapy. Garden City Park, NY: Avery Publishing Group. ISBN 0-89529-759. 
• Jain, KK; Baydin, SA (2004). Textbook of hyperbaric medicine. Cambridge, MA: Hogrefe & Huber. ISBN 0-88937-277-2. 
• Harch, Paul G; McCullough, Virginia (2010). The Oxygen Revolution. Long Island City, NY: Hatherleigh Press. ISBN 1578263263. 

External links

• Hyperbaric Oxygen Therapy from eMedicine

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