Hyperbaric medicine is medical treatment in which an increase in barometric pressure of typically air or oxygen is used. The immediate effects include reducing the size of
gas emboli and raising the partial pressures of the gases present. Initial uses were in
decompression sickness
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
, and it also effective in certain cases of
gas gangrene
Gas gangrene (also known as clostridial myonecrosis) is a bacterial infection that produces tissue gas in gangrene. This deadly form of gangrene usually is caused by '' Clostridium perfringens'' bacteria. About 1,000 cases of gas gangrene are r ...
and
carbon monoxide poisoning
Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...
. There are potential hazards. Injury can occur at pressures as low as 2
psig (13.8 kPa) if a person is rapidly decompressed. If oxygen is used in the hyperbaric therapy, this can increase the fire hazard.
Hyperbaric oxygen therapy (HBOT), is the medical use of greater than 99%
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
at an ambient pressure higher than
atmospheric pressure
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1,013. ...
, and therapeutic recompression. The equipment required consists of a
pressure vessel for human occupancy (
hyperbaric chamber
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
), which may be of rigid or flexible construction, and a means of a controlled atmosphere supply. Treatment gas may be the ambient chamber gas, or delivered via a
built-in breathing system
A built-in breathing system is a source of breathing gas installed in a confined space where an alternative to the ambient gas may be required for medical treatment, emergency use, or to minimise a hazard. They are found in diving chambers, hype ...
. Operation is performed to a predetermined schedule by personnel who may adjust the schedule as required.
Hyperbaric air (HBA), consists of compressed atmospheric air (79% nitrogen, 21% oxygen, and minor gases) and is used for acute mountain sickness. This is created by placing the person in a
portable hyperbaric air chamber and inflating that chamber up to 7.35 psi gauge (1.5
atmospheres absolute) using a foot-operated or electric air pump.
Chambers used in the US made for hyperbaric medicine fall under the jurisdiction of the federal Food and Drug Administration (FDA). The FDA requires hyperbaric chambers to comply with the
American Society of Mechanical Engineers
The American Society of Mechanical Engineers (ASME) is an American professional association that, in its own words, "promotes the art, science, and practice of multidisciplinary engineering and allied sciences around the globe" via "continuing edu ...
PVHO Codes
and the National Fire Protection Association Standard 99, Health Care Facilities Code. Similar conditions apply in most other countries.
Other uses include
arterial gas embolism
An air embolism, also known as a gas embolism, is a blood vessel blockage caused by one or more bubbles of air or other gas in the circulatory system. Air can be introduced into the circulation during surgical procedures, lung over-expansi ...
caused by
pulmonary barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in ...
of ascent. In emergencies
divers may sometimes be treated by
in-water recompression
In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by returning the diver underwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a ...
(when a chamber is not available) if suitable
diving equipment (to reasonably secure the airway) is available.
Scope
Hyperbaric medicine includes hyperbaric oxygen treatment, which is the medical use of oxygen at greater than atmospheric pressure to increase the availability of oxygen in the body;
and therapeutic recompression, which involves increasing the ambient pressure on a person, usually a diver, to treat
decompression sickness
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
or an
air embolism
An air embolism, also known as a gas embolism, is a blood vessel blockage caused by one or more bubbles of air or other gas
Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure g ...
by reducing the volume and more rapidly eliminating bubbles that have formed within the body.
Medical uses
The
Undersea and Hyperbaric Medical Society
The Undersea and Hyperbaric Medical Society (UHMS) is an organization based in the US which supports research on matters of hyperbaric medicine and physiology, and provides a certificate of added qualification for physicians with an unrestricted li ...
(UHMS) lists 15 supported uses as of 2025:
# Air or
gas embolism;
#
Carbon monoxide poisoning
Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as " flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large ...
including that complicated by
cyanide poisoning
Cyanide poisoning is poisoning that results from exposure to any of a number of forms of cyanide. Early symptoms include headache, dizziness, fast heart rate, shortness of breath, and vomiting. This phase may then be followed by seizures, slo ...
;
# Clostridal myositis and
myonecrosis
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...
(
gas gangrene
Gas gangrene (also known as clostridial myonecrosis) is a bacterial infection that produces tissue gas in gangrene. This deadly form of gangrene usually is caused by '' Clostridium perfringens'' bacteria. About 1,000 cases of gas gangrene are r ...
);
# Crush injury,
compartment syndrome
Compartment syndrome is a serious medical condition in which increased pressure within a Fascial compartment, body compartment compromises blood flow and tissue function, potentially leading to permanent damage if not promptly treated. There are ...
, and other acute traumatic ischemias;
#
Decompression sickness
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
;
#
Central retinal artery occlusion
Central retinal artery occlusion (CRAO) is a disease of the eye where the flow of blood through the central retinal artery is blocked (occluded). There are several different causes of this occlusion; the most common is carotid artery atheroscle ...
and enhancement of healing in selected
problem wounds due to insufficient arterial blood flow, including the
diabetic foot
A diabetic foot disease is any condition that results directly from peripheral artery disease (PAD) or sensory neuropathy affecting the feet of people living with diabetes. Diabetic foot conditions can be acute or chronic complications of diab ...
;
# Exceptional blood loss (
anemia
Anemia (also spelt anaemia in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin availabl ...
);
#
Intracranial abscess;
#
Necrotizing
Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who is ...
soft tissue infections (
necrotizing fasciitis
Necrotizing fasciitis (NF), also known as flesh-eating disease, is an infection that kills the body's soft tissue. It is a serious disease that begins and spreads quickly. Symptoms include red or purple or black skin, swelling, severe pain, fever ...
);
#
Osteomyelitis
Osteomyelitis (OM) is the infectious inflammation of bone marrow. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The feet, spine, and hips are the most commonly involved bones in adults.
The cause is ...
(refractory);
#Delayed
radiation injury (soft tissue and
bony necrosis);
#
Skin grafts and flaps (compromised);
#Thermal
burns
Burns may refer to:
Astronomy
* 2708 Burns, an asteroid
* Burns (crater), on Mercury
People
* Burns (surname), list of people and characters named Burns
** Burns (musician), Scottish record producer
Places in the United States
* Burns, ...
(early);
#
Idiopathic sudden sensorineural hearing loss;
#
Avascular necrosis
Avascular necrosis (AVN), also called osteonecrosis or bone infarction, is death of bone tissue due to interruption of the blood supply. Early on, there may be no symptoms. Gradually joint pain may develop, which may limit the person's abilit ...
These uses are similar to those approved by the US FDA as of 2021.
Mucormycosis
Mucormycosis, also known as black fungus, is a severe fungal infection that comes under fulminant fungal sinusitis, usually in people who are immunocompromised. It is curable only when diagnosed early. Symptoms depend on where in the body the ...
, especially rhinocerebral disease in the setting of diabetes mellitus may be supported.
There is insufficient evidence for use in
autism
Autism, also known as autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by differences or difficulties in social communication and interaction, a preference for predictability and routine, sensory processing d ...
,
cancer
Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...
,
diabetes
Diabetes mellitus, commonly known as diabetes, is a group of common endocrine diseases characterized by sustained high blood sugar levels. Diabetes is due to either the pancreas not producing enough of the hormone insulin, or the cells of th ...
,
HIV/AIDS
The HIV, human immunodeficiency virus (HIV) is a retrovirus that attacks the immune system. Without treatment, it can lead to a spectrum of conditions including acquired immunodeficiency syndrome (AIDS). It is a Preventive healthcare, pr ...
,
Alzheimer's
Alzheimer's disease (AD) is a neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...
,
asthma
Asthma is a common long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wh ...
,
Bell's palsy
Bell's palsy is a type of facial paralysis that results in a temporary inability to control the facial muscles on the affected side of the face. In most cases, the weakness is temporary and significantly improves over weeks. Symptoms can vary f ...
,
cerebral palsy
Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, spasticity, stiff muscles, Paresis, weak muscles, and tremors. There may b ...
, depression, heart disease, migraines,
multiple sclerosis
Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...
,
Parkinson's
Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become more prevalen ...
,
spinal cord injury
A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions.
Symptoms of ...
, sports injuries, or
stroke
Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...
.
Furthermore, potential side effects pose an unjustified risk in such cases. A
Cochrane review
Cochrane is a British international charitable organisation formed to synthesize medical research findings to facilitate evidence-based choices about health interventions involving health professionals, patients and policy makers. It includes ...
in 2016 of
autism spectrum
Autism, also known as autism spectrum disorder (ASD), is a neurodevelopmental disorder characterized by differences or difficulties in social communication and interaction, a preference for predictability and routine, sensory processing d ...
found no links to improvements in social abilities or cognitive function. There are also ethical issues with further trials, as the
eardrum
In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit changes in pres ...
can be damaged during hyperbaric therapy. Despite the lack of evidence, in 2015, the number of people utilizing this therapy has continued to rise.
There is also insufficient evidence to support its use in acute traumatic or surgical wounds.
Hearing
There is limited evidence for
sudden sensorineural hearing loss within two weeks of onset. It might improve
tinnitus
Tinnitus is a condition when a person hears a ringing sound or a different variety of sound when no corresponding external sound is present and other people cannot hear it. Nearly everyone experiences faint "normal tinnitus" in a completely ...
presenting in the same time frame.
Chronic ulcers
HBOT in diabetic foot ulcers increased the rate of early ulcer healing but does not appear to provide any benefit in wound healing at long-term follow-up. In particular, there was no difference in major amputation rate. For venous, arterial and pressure ulcers, no evidence was apparent that HBOT provides a long-term improvement over standard treatment.
Radiation injury
There is some evidence that HBOT is effective for late radiation tissue injury of bone and soft tissues of the head and neck. Some people with radiation injuries of the head, neck or bowel show an improvement in quality of life. Importantly, no such effect has been found in neurological tissues. The use of HBOT may be justified to selected patients and tissues, but further research is required to establish the best people to treat and timing of any HBO therapy.
Neuro-rehabilitation
As of 2012, there was insufficient evidence to support use in
traumatic brain injuries.
In
acute stroke
Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...
, HBOT does not show benefit.
HBOT in
multiple sclerosis
Multiple sclerosis (MS) is an autoimmune disease resulting in damage to myelinthe insulating covers of nerve cellsin the brain and spinal cord. As a demyelinating disease, MS disrupts the nervous system's ability to Action potential, transmit ...
has not shown benefit and routine use is not recommended.
A 2007 review in
cerebral palsy
Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, spasticity, stiff muscles, Paresis, weak muscles, and tremors. There may b ...
found no difference compared to the control group.
Neuropsychological
Neuropsychology is a branch of psychology concerned with how a person's cognition and behavior are related to the brain and the rest of the nervous system. Professionals in this branch of psychology focus on how injuries or illnesses of the brai ...
tests also showed no difference between HBOT and room air and based on caregiver report, those who received room air had significantly better mobility and social functioning.[ Children experienced seizures and the need for ]tympanostomy tube
Tympanostomy tube, also known as a grommet, myringotomy tube, or pressure equalizing tube, is a small tube inserted into the eardrum via a surgical procedure called myringotomy to keep the middle ear aerated for a prolonged period of time, typic ...
s to equalize ear pressure, though the rates was not clear.
Cancer
In alternative medicine
Alternative medicine refers to practices that aim to achieve the healing effects of conventional medicine, but that typically lack biological plausibility, testability, repeatability, or supporting evidence of effectiveness. Such practices are ...
, hyperbaric medicine has been promoted for cancer. However, a 2011 study by the American Cancer Society
The American Cancer Society (ACS) is a nationwide non-profit organization dedicated to eliminating cancer. The ACS publishes the journals ''Cancer'', '' CA: A Cancer Journal for Clinicians'' and '' Cancer Cytopathology''.
History
The society w ...
reported no evidence it is effective for this purpose. A 2012 review article found "there is no evidence indicating that HBO neither acts as a stimulator of tumor growth nor as an enhancer of recurrence. On the other hand, there is evidence that implies that HBO might have tumor-inhibitory effects in certain cancer subtypes, and we thus strongly believe that we need to expand our knowledge on the effect and the mechanisms behind tumor oxygenation."
Migraines
Low-quality evidence suggests it may reduce pain in an ongoing migraine headache. It is not known which people would benefit from this treatment, and there is no evidence that it prevents future migraines.
Side effects
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lung ...
is a limitation on both maximum partial pressure of oxygen, and on length of each treatment.
HBOT can accelerate the development of cataracts
A cataract is a cloudy area in the lens of the eye that leads to a decrease in vision of the eye. Cataracts often develop slowly and can affect one or both eyes. Symptoms may include faded colours, blurry or double vision, halos around ligh ...
over multiple repetitive treatments, and can cause temporary relative myopia over the shorter term.
A 2023 review found that negative outcomes (predominantly mild barotrauma (air pressure effect on ear or lung) that could be resolved spontaneously) were experienced by 24% of patients, but they were not prevented from completing the treatment regimen, and no serious side effects, complications or deaths were reported.
Complications
There are risks associated with HBOT, similar to some diving disorders. Pressure changes can cause a "squeeze" or barotrauma
Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with, the body and the surrounding gas or liquid. The initial damage is usually due to over-stretching the tissues in ...
in the tissues surrounding trapped air inside the body, such as the lung
The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
s, behind the eardrum
In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear from the middle ear. Its function is to transmit changes in pres ...
, inside paranasal sinus
Paranasal sinuses are a group of four paired skeletal pneumaticity, air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the Ethmoid sinus, ethmoidal sinuses a ...
es,[ or trapped underneath dental fillings. Breathing high-pressure oxygen may cause ]oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lung ...
. Temporarily blurred vision can be caused by swelling of the lens
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'') ...
, which usually resolves in two to four weeks.
There are reports that cataracts may progress following HBOT, and rarely, may develop ''de novo'', but this may be unrecognized and under reported. The cause is not fully explained, but evidence suggests that lifetime exposure of the lens to high partial pressure oxygen may be a major factor. Oxidative damage to lens proteins is thought to be responsible. This may be an end-stage of the relatively well documented myopic shift detected in most hyperbaric patients after a course of multiple treatments.
Ears
People have ear discomfort as a pressure difference develops between their middle ear and the chamber atmosphere. This can be relieved by ear clearing using the Valsalva maneuver
The Valsalva maneuver is performed by a forceful attempt of exhalation against a closed airway, usually done by closing one's mouth and pinching one's nose shut while expelling air, as if blowing up a balloon. Variations of the maneuver can be ...
or other techniques. Continued increase of pressure without equalizing may cause ear drums to rupture, resulting in severe pain. As the pressure in the chamber increases further, the air may become warm.
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 toxicology of the treatment has been reviewed by Ustundag ''et al.'' and its risk management is discussed by Christian R. Mortensen, in light of the fact that most hyperbaric facilities are managed by departments of anaesthesiology and some of their patients are critically ill.
An absolute contraindication
In medicine, a contraindication is a condition (a situation or factor) that serves as a reason not to take a certain medical treatment due to the harm that it would cause the patient. Contraindication is the opposite of indication, which is a rea ...
to hyperbaric oxygen therapy is untreated pneumothorax
A pneumothorax is collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and dyspnea, shortness of breath. In a minority of cases, a one-way valve is ...
. The reason is concern that it can progress to tension pneumothorax, especially during the decompression phase of therapy, although treatment on oxygen-based tables may avoid that progression. The COPD patient with a large bleb represents a relative contraindication for similar reasons. Also, the treatment may raise the issue of occupational health and safety (OHS), for chamber inside attendants, who should not be compressed if they are unable to equalise ears and sinuses
Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the sphenoi ...
.
Extra care may be required in people with:
* Cardiovascular disease
Cardiovascular disease (CVD) is any disease involving the heart or blood vessels. CVDs constitute a class of diseases that includes: coronary artery diseases (e.g. angina, heart attack), heart failure, hypertensive heart disease, rheumati ...
* COPD
Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory s ...
with air trapping – can lead to pneumothorax during treatment.
* 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. Fevers may predispose to convulsions.
* Emphysema with CO2 retention – This condition can lead to pneumothorax during HBO treatment due to rupture of an emphysematous bulla during decompression. This risk can be evaluated by x-ray.
* 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
Angiogenesis is the physiological process through which new blood vessels form from pre-existing vessels, formed in the earlier stage of vasculogenesis. Angiogenesis continues the growth of the vasculature mainly by processes of sprouting and ...
and also raises oxygen levels. Taking an anti-angiogenic supplement may provide a solution. A study by Feldemier, et al. and 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.
* Middle ear barotrauma may occur in children and adults in a hyperbaric environment because of the necessity to equalise pressure in the ears.
Pregnancy is not a relative contraindication to hyperbaric oxygen treatments, although it may be for underwater diving
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving (disambiguation), diving, an ambiguous term with several possible meani ...
. 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.) In pregnant patients, HBO therapy has been shown to be safe for the fetus when given at appropriate levels and "doses" (durations). In fact, pregnancy lowers the threshold for HBO treatment of carbon monoxide-exposed patients. This is due to the high affinity of fetal hemoglobin for CO.
Mechanism of action
The therapeutic consequences of HBOT and recompression result from multiple effects.
Pressure
The increased overall pressure is of therapeutic value in the treatment of decompression sickness
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
and air embolism
An air embolism, also known as a gas embolism, is a blood vessel blockage caused by one or more bubbles of air or other gas
Gas is a state of matter that has neither a fixed volume nor a fixed shape and is a compressible fluid. A ''pure g ...
as it provides a physical means of reducing the volume of inert gas bubbles within the body; Exposure to this increased pressure is maintained for a period long enough to ensure that most of the bubble gas is dissolved back into the tissues, removed by perfusion and eliminated in the lungs.
The improved concentration gradient for inert gas elimination ( oxygen window) by using a high partial pressure of oxygen increases the rate of inert gas elimination in the treatment of decompression sickness.
For many other conditions, the therapeutic principle of HBOT lies in its ability to drastically increase partial pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...
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 under normobaric conditions (i.e. at normal atmospheric pressure). This effect is achieved by an increase in the oxygen transport capacity of the blood. At normal atmospheric pressure, oxygen transport is limited by the oxygen binding capacity of hemoglobin
Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. Hemoglobin ...
in red blood cell
Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...
s and very little oxygen is transported by blood plasma
Blood plasma is a light Amber (color), amber-colored liquid component of blood in which blood cells are absent, but which contains Blood protein, proteins and other constituents of whole blood in Suspension (chemistry), suspension. It makes up ...
. Because the hemoglobin of the red blood cells is almost saturated with oxygen at atmospheric pressure, this route of transport cannot be exploited any further. Oxygen transport by plasma, however, is significantly increased using HBOT because of the higher solubility of oxygen as pressure increases.
Hyperbaric chambers
Construction
The traditional type of hyperbaric chamber
A diving chamber is a vessel for human occupation, which may have an entrance that can be sealed to hold an internal pressure significantly higher than ambient pressure, a pressurised gas system to control the internal pressure, and a supply of ...
used for therapeutic recompression and HBOT is a rigid shelled pressure vessel
A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.
Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...
. Such chambers can be run at absolute pressures typically about , or more in special cases. Navies, professional 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. The larger units may be rated for lower pressures if they are not primarily intended for treatment of diving injuries.
A rigid chamber may consist of:
* a pressure vessel designed to a code such as ASME Boiler and Pressure Vessel Code
* viewports to allow the medical personnel to visually monitor the occupants, and can be used for hand signalling as an auxiliary emergency communications method. The major components are the window (transparent acrylic), the window seat (holds the acrylic window), and retaining ring. Interior lighting can be provided by mounting lights outside the viewports. Viewports are a feature specific to PVHOs due to the need to see the people inside and evaluate their health. Other materials have been attempted, but they consistently fail to maintain their seal or have cracks which would progress rapidly to catastrphophic failure. Acrylic is more likely to have small cracks the operators can see and have time to take mitigation steps instead of failing catastrophically. Counterfeit chambers often do not use acrylic windows.
* one or more human entry hatchessmall and circular or wheel-in type hatches for patients on gurneys;
* the entry lock that allows human entrya 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;
* a low volume medical or service airlock for medicines, instruments, and food;
* transparent ports or closed-circuit television that allows technicians and medical staff outside the chamber to monitor the patient inside the chamber;
* an intercom
An intercom, also called an intercommunication device, intercommunicator, or interphone, is a stand-alone voice communications system for use within a building, small collection of buildings or portably within a small coverage area, which funct ...
system allowing two-way communication;
* an optional carbon dioxide scrubber
A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or ...
consisting of a fan that passes the gas inside the chamber through a soda lime
Soda lime, a mixture of sodium hydroxide (NaOH) and calcium oxide (CaO), is used in granular form within recirculating breathing environments like general anesthesia and its breathing circuit, submarines, rebreathers, and hyperbaric chambers and u ...
canister;
* a control panel outside the chamber to open and close valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...
s that control air
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
flow to and from the chamber, and regulate oxygen to hoods or masks;
* an over-pressure relief valve;
* a built-in breathing system (BIBS) to supply and exhaust treatment gas;
* a fire suppression system.
Flexible monoplace chambers are available ranging from collapsible flexible aramid fiber-reinforced chambers which can be disassembled for transport via truck or SUV, with a maximum working pressure of 2 bar above ambient complete with BIBS allowing full oxygen treatment schedules. to portable, air inflated "soft" chambers that can operate at between above atmospheric pressure with no supplemental oxygen, and longitudinal zipper closure.
Viewports
Acrylic windows with PVHO-1 defined standard geometries and design criteria are generally used. Shapes and sizes vary with chamber application and the requirements for the specific use.
The geometries in general use include:
* Flat circular windows (low pressure)
* Conical edged windows with flat inner and outer faces (high pressure on one side only)
* Circular windows with double beveled edges
* Light pipes
Low pressure, small diameter chambers may use large cylindrical windows fitted inside the metal structure. In some cases the whole cylindrical pressure chamber has been made from an acrylic tube.
The acrylic windows of a hyperbaric chamber have a limited lifespan, which can be expressed as the design life, which is the conservatively estimated life as calculated in the design process, typically about 10 years, and the service life, which is the actual time the window can be safely and legally used when well maintained, properly inspected, and repaired when necessary and possible and which can be as much as twice the design life.
There are three grades of inspection required:
*Operational inspection of the inner and outer surfaces is included in the checks before first pressurisation of the day by a competent chamber operator, and ensures that the surfaces have not been damaged since the last use.
*Maintenance inspection is done at specified intervals by a qualified maintenance inspector. This inspection is more thorough and may require removal of the window from the mounting to check for damage that is not visible when installed. This grade of inspection is generally also required for re-commissioning a chamber that has been out of service for longer than a specified period.
*Seat and seal inspection is done whenever a window has been removed for inspection or repair or a new window installed.
The window is examined to detect crazing, cracks, blisters, discolouration, scratches or pits.
Operating pressures
The operating pressure depends on the application. Chambers used for clinical hyperbaric oxygen therapy commonly have a maximum allowable working pressure of with a maximum of about Chambers used for support of commercial or military diving operations and for research may have a maximum allowable working pressure of up to .
Oxygen supply
In the larger multiplace chambers, patients inside the chamber breathe from either "oxygen hoods" – flexible, transparent soft plastic hoods with a seal around the neck similar to a space suit
A space suit (or spacesuit) is an environmental suit used for protection from the harsh environment of outer space, mainly from its vacuum as a highly specialized pressure suit, but also its temperature extremes, as well as radiation and ...
helmet – or tightly fitting oxygen mask
An oxygen mask is a mask that provides a method to transfer breathing gas, breathing oxygen gas from a storage tank to the lungs. Oxygen masks may cover only the nose and mouth (oral nasal mask) or the entire face (full-face mask). They may be ma ...
s, 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 chamber air (21% oxygen) to reduce the risk of oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen () at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lung ...
. The exhaled treatment gas must be removed from the chamber to prevent the buildup of oxygen, which could present a fire risk. Attendants may also breathe oxygen some of the time to reduce their risk of decompression sickness
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from Solution (chemistry), solution as bubbles inside the body tissues during D ...
when they leave the chamber. The pressure inside the chamber is increased by opening valves allowing high-pressure air to enter from storage cylinders, which are filled by an air compressor
An air compressor is a machine that takes ambient air from the surroundings and discharges it at a higher pressure. It is an application of a gas compressor and a Pneumatics, pneumatic device that energy conversion, converts mechanical power (from ...
. Chamber air oxygen content is kept between 19% and 23% to control fire risk (US Navy maximum 25%). If the chamber does not have a scrubber system to remove carbon dioxide from the chamber gas, the chamber must be isobarically ventilated to keep the CO2 within acceptable limits.
A soft chamber may be pressurized directly from a compressor. or from storage cylinders.
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 chamber. Most monoplace chambers can be fitted with a demand breathing system for air breaks. In low pressure soft chambers, treatment schedules may not require air breaks, because the risk of oxygen toxicity is low due to the lower oxygen partial pressures used (usually 1.3 ATA), and short duration of treatment.
For alert, cooperative patients, air breaks provided by mask are more effective than changing the chamber gas because they provide a quicker gas change and a more reliable gas composition both during the break and treatment periods.
Personnel
* Hyperbaric medical practitioner - a specialist in hyperbaric medicine
* Diving medical practitioner – a specialist in diving medicine
* Chamber operator – a person competent to operate a hyperbaric chamber
* Hyperbaric nurse – a nurse responsible for administering hyperbaric oxygen therapy to patients and supervising them throughout the treatment.
* Diving medical technician – member of a dive team who is trained in advanced first aid.
* Chamber attendant – a person trained in basic first aid who is medically fit to dive in a chamber, usually a member of a diving team allocated to looking after the diver being treated.
Treatments
Initially, HBOT was developed as a treatment for diving disorders
Diving disorders, or diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divid ...
involving bubbles of gas in the tissues, such as decompression sickness and gas embolism, It is still considered the definitive treatment for these conditions. The chamber treats decompression sickness and gas embolism by increasing pressure, reducing the size of the gas bubbles and improving the transport of blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.
Blood is com ...
to downstream tissues. After elimination of bubbles, the pressure is gradually reduced back to atmospheric levels. Hyperbaric chambers are also used for animals.
As of September 2023, a number of hyperbaric chambers in the US are turning divers with decompression sickness away, and only treating more profitable scheduled cases. The number of hyperbaric medical facilities in the US is estimated at about 1500, of which 67 are treating diving accidents, according to Divers Alert Network
Divers Alert Network (DAN) is a group of not-for-profit organizations dedicated to improving diving safety for all divers. It was founded in Durham, North Carolina, United States, in 1980 at Duke University providing 24/7 telephonic hot-line div ...
. Many facilities only provide hyperbaric treatment for wound care for economic reasons. Emergency hyperbaric services are more expensive to train and staff, and liability is increased.
Protocol
Emergency HBOT for decompression illness follows treatment schedules laid out in treatment tables. Most cases employ a recompression to absolute, the equivalent of 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 , the equivalent of of water, and the ability to supply heliox as a breathing gas.
U.S. Navy treatment charts are used in Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
and the United States to determine the duration, pressure, and breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed ...
of the therapy. The most frequently used tables are Table 5 and Table 6. In the UK the Royal Navy
The Royal Navy (RN) is the naval warfare force of the United Kingdom. It is a component of His Majesty's Naval Service, and its officers hold their commissions from the King of the United Kingdom, King. Although warships were used by Kingdom ...
62 and 67 tables are used.
The Undersea and Hyperbaric Medical Society
The Undersea and Hyperbaric Medical Society (UHMS) is an organization based in the US which supports research on matters of hyperbaric medicine and physiology, and provides a certificate of added qualification for physicians with an unrestricted li ...
(UHMS) publishes a report that compiles the latest research findings and contains information regarding the recommended duration and pressure of the longer-term conditions.
Home and out-patient
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. The American Medical Association is opposed to home use or any other use of hyperbaric chambers if it is not "in facilities with appropriately trained staff including physician supervision and prescription and only when the intervention has scientific support or rationale" due demonstrated hazard
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. As with any hyperbaric chamber, the FDA require compliance with ASME and NFPA standards. 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.
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. The FDA warns against the use of oxygen concentrators or oxygen tanks with chambers that does not meet ASME and FDA standards, regardless of if the concentrators are FDA approved.
History
Hyperbaric air
Junod built a chamber in France in 1834 to treat pulmonary conditions at pressures between 2 and 4 atmospheres absolute.
During the following century "pneumatic centres" were established in Europe and the USA which used hyperbaric air to treat a variety of conditions.
Orval J Cunningham, a professor of anesthesia at the University of Kansas in the early 1900s observed that people with circulatory disorders did better at sea level than at altitude and this formed the basis for his use of hyperbaric air. In 1918, he successfully treated patients with the Spanish flu with hyperbaric air. In 1930 the American Medical Association forced him to stop hyperbaric treatment, since he did not provide acceptable evidence that the treatments were effective.
Hyperbaric oxygen
The English scientist Joseph Priestley
Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, Unitarian, Natural philosophy, natural philosopher, English Separatist, separatist theologian, Linguist, grammarian, multi-subject educator and Classical libera ...
discovered oxygen in 1775. Shortly after its discovery, there were reports of toxic effects of hyperbaric oxygen on the central nervous system and lungs, which delayed therapeutic applications until 1937, when Behnke and Shaw first used it in the treatment of decompression sickness.
In 1955 and 1956 Churchill-Davidson, in the UK, used hyperbaric oxygen to enhance the radiosensitivity
Radiosensitivity is the relative susceptibility of cells, tissues, organs or organisms to the harmful effect of ionizing radiation.
Cells types affected
Cells are least sensitive when in the S phase, then the G1 phase, then the G2 phase, and ...
of tumours, while , at the University of Amsterdam
The University of Amsterdam (abbreviated as UvA, ) is a public university, public research university located in Amsterdam, Netherlands. Established in 1632 by municipal authorities, it is the fourth-oldest academic institution in the Netherlan ...
, successfully used it in cardiac surgery.
In 1961 et al. published on the use of hyperbaric oxygen in the treatment of clostridial gas gangrene
Gas gangrene (also known as clostridial myonecrosis) is a bacterial infection that produces tissue gas in gangrene. This deadly form of gangrene usually is caused by '' Clostridium perfringens'' bacteria. About 1,000 cases of gas gangrene are r ...
.
In 1962 Smith and Sharp reported successful treatment of carbon monoxide poisoning with hyperbaric oxygen.
The Undersea Medical Society (now Undersea and Hyperbaric Medical Society) formed a Committee on Hyperbaric Oxygenation which has become recognized as the authority on indications for hyperbaric oxygen treatment.
Incidents
Fires inside a hyperbaric chamber are extremely dangerous. A review article published in 1997 found 77 human fatalities in 35 different hyperbaric chamber fires that occurred from 1923 to 1996. Further studies indicate while the treatment is often considered safe, the use of hyperbaric equipment comes with risks to the operating personnel when improperly used. Proper equipment maintenance and safety procedures for the use of pressure equipment is mandatory.
* 1997: Ten patients and a nurse were killed in Milan, Italy after a fire broke out inside a hyperbaric oxygen chamber.
* 2009: A grandmother and her four year old grandson died after a hyperbaric chamber caught fire and exploded in Florida. The boy was receiving treatment in the chamber for cerebral palsy and had traveled from Italy where the treatment is outlawed to undergo the procedure.
* 2012: A hyperbaric oxygen chamber exploded in Florida, killing a woman and a thoroughbred horse who was receiving treatment. The explosion occurred after the horse kicked out at the chamber, creating sparks which ignited a fire.
* 2015: A dog was killed in Georgia when the chamber it was receiving treatment in caught fire and exploded. The dog was being treated for arthritis.
* 2016: A fire killed four people who were receiving treatment inside a hyperbaric chamber at Mintohardjo Navy Hospital in Jakarta, Indonesia. The fire was reportedly caused by an electrical short circuit. After the fire broke out, operators used a sprinkler system and an emergency shut off system to rescue the victims, but live-saving efforts were prevented as the machine became engulfed in flames.
* 2016: A man in Victoria, Australia died in a hyperbaric chamber of undisclosed causes while receiving treatment. The practitioners overseeing his care were found responsible for failing to ensure the patient's safety leading to his death. They were later fined AU$716,750.
* 2025: A hyperbaric chamber exploded in Michigan, killing a five year old boy.
Society and culture
Regulation
The use of hyperbaric chambers for medical and therapeutic procedures is generally regulated. Authorities have warned of potential risks to patients receiving treatment in unlicensed facilities, notably in Israel, Canada, and the United States. In Italy, the use of hyperbaric chambers for therapy was severely restricted to limited medical settings after a serious fire which killed ten patients in 1997.
In some jurisdictions, the use and availability of HBOT is further restricted at the subnational level. In the U.S. state of North Carolina, several cities including Durham, Raleigh and Charlotte have ordered operators of mild hyperbaric oxygen therapy to close to protect public safety due to a risk of fire.
Unlicensed and fraudulent operators have been subject to prosecution. In Australia, Oxymed Australia Pty Ltd and director Malcolm Hooper were ordered to pay AUS $3 million in fines after advertising hyperbaric therapy against the country's Therapeutic Goods Act. In Canada, certain soft-shelled hyperbaric chambers were removed from the market for a potential risk to patients.
Costs
HBOT is recognized by Medicare in the United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
as a reimbursable treatment for 14 UHMS "approved" conditions. A 1-hour HBOT session may cost between $300 and higher in private clinics, and over $2,000 in hospitals. U.S. physicians (M.D. or D.O.) may lawfully prescribe HBOT for "off-label" conditions such as stroke
Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...
, and migraine
Migraine (, ) is a complex neurological disorder characterized by episodes of moderate-to-severe headache, most often unilateral and generally associated with nausea, and light and sound sensitivity. Other characterizing symptoms may includ ...
. 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. In Australia, HBOT is not covered by Medicare (Australia), Medicare as a treatment for multiple sclerosis. China and Russia treat more than 80 maladies, conditions, and trauma with HBOT.
Research
Aspects under research include radiation-induced hemorrhagic cystitis; and inflammatory bowel disease, rejuvenation.
Some research found evidence that HBOT improves local tumor control, mortality, and local tumor recurrence for cancers of the head and neck.
Some research also found evidence of an increase in stem progenitor cells and a decrease in inflammation.
Neurological
Tentative evidence shows a possible benefit in cerebrovascular diseases. Rats subjected to HBOT after some time following the acute phase of experimentally-induced stroke
Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...
showed reduced inflammation, increased brain-derived neurotrophic factor, and evidence of neurogenesis. Another rat study showed improved neurofunctional recovery as well as neurogenesis following the late-chronic phase of experimentally-induced stroke.
The clinical experience and results so far published has promoted the use of HBOT therapy in patients with cerebrovascular injury and focal cerebrovascular injuries. However, the power of clinical research is limited because of the shortage of randomized controlled trials.
Radiation wounds
A 2010 review of wounds from radiation therapy found that, while most studies suggest a benefit, more experimental and research is needed to validate its use.
Respiratory distress
People who are having extreme difficulty breathing – acute respiratory distress syndrome – are commonly given oxygen therapy, oxygen and there have been limited trials of hyperbaric equipment in such cases. Examples include treatment of the Spanish flu[Sellers, L. M. (1964). "The Fallibility of the Forrestian Principle. "Semper Primus Pervenio Maxima Cum Vi". (Orval James Cunningham)." Trans Am Laryngol Rhinol Otol Soc 23: 385–405] and COVID-19.
See also
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References
Further reading
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* (6th edition from Springer in press 2016)
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External links
Hyperbaric Oxygen Therapy
from eMedicine
Duke University Medical Center Archives
contains collections of multiple individuals who worked with hyperbaric medicine
{{Authority control
Critical emergency medicine
Underwater diving medicine
Hyperbaric medicine
Medical treatments
Respiratory therapy