Hyperbaric medicine

There is limited evidence for sudden sensorineural hearing loss within two weeks of onset. It might improve tinnitus presenting in the same time frame.^[17]

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.^[18] For venous, arterial and pressure ulcers, no evidence was apparent that HBOT provides a long-term improvement over standard treatment.^[19]

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.^[20]

2012年時点では、外傷性脳損傷への使用を支持する十分な証拠はなかった。^{[ 21 ]}急性脳卒中では、HBOTは効果を示さない。^{[ 22 ] [ 13 ]}

多発性硬化症に対する高圧酸素療法は効果が示されておらず、日常的な使用は推奨されていない。^{[ 12 ] [ 23 ]}

2007年の脳性麻痺に関するレビューでは、対照群と比較して差は見られなかった。^{[ 24 ] [ 25 ]}神経心理学的検査でも、高圧酸素療法と室内空気の間に差は見られず、介護者の報告によると、室内空気を受けた患者の方が運動能力と社会機能が有意に優れていた。^{[ 24 ] [ 25 ]}小児は発作を起こし、耳圧を均等にするために鼓膜チューブが必要になったが、その発生率は明らかではなかった。^{[ 24 ]}

代替医療では、高気圧酸素療法が癌治療に推奨されてきました。しかし、2011年に米国癌協会が行った研究では、この目的に有効であるという証拠は報告されていません。^{[ 26 ]} 2012年のレビュー記事では、「HBOが腫瘍の増殖を刺激したり、再発を促進したりするという証拠はない。一方で、HBOが特定の癌のサブタイプにおいて腫瘍抑制効果を持つ可能性があることを示唆する証拠があり、したがって、腫瘍酸素化の効果とメカニズムに関する知識を拡大する必要があると強く信じている」と結論付けています。^{[ 27 ]}

質の低い証拠によると、進行中の片頭痛の痛みを軽減する可能性がある。^{[ 28 ]}この治療から恩恵を受ける人は誰なのかは不明であり、将来の片頭痛を予防するという証拠もない。^{[ 28 ]}

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,^[31] behind the eardrum,^[32][33] inside paranasal sinuses,^[32] or trapped underneath dental fillings.^[34] Breathing high-pressure oxygen may cause oxygen toxicity.^[35] Temporarily blurred vision can be caused by swelling of the lens, which usually resolves in two to four weeks.^[36][37]

There are reports that cataracts may progress following HBOT,^[38] 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.

People have ear discomfort as a pressure difference develops between their middle ear and the chamber atmosphere.^[39] This can be relieved by ear clearing using the Valsalva maneuver 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.

The toxicology of the treatment has been reviewed by Ustundag et al.^[40] 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.^[41]

高圧酸素療法の絶対的禁忌は、未治療の気胸である。^{[ 42 ]}その理由は、特に治療の減圧期に緊張性気胸に進行する可能性があるという懸念があるが、酸素ベースのテーブルでの治療はその進行を回避できる可能性がある。^{[ 31 ]}大きなブレブのある COPD 患者は、同様の理由で相対的禁忌となる。^{[ 43 ]}また、この治療は、チャンバー内の介助者にとって労働安全衛生(OHS)の問題を引き起こす可能性があり、介助者は耳と副鼻腔の圧平衡ができない場合は圧迫してはならない。^{[ 44 ]}

以下のような方は、特に注意が必要な場合があります。

• 心血管疾患
• 空気捕捉を伴うCOPDは、治療中に気胸を引き起こす可能性がある。
• 上気道感染症 – これらの症状により、患者は耳や副鼻腔の気圧を調整することが難しくなり、耳や副鼻腔の圧迫感と呼ばれる状態になることがあります。^{[ 42 ]}
• 高熱 – ほとんどの場合、HBO治療を開始する前に熱を下げる必要があります。発熱は痙攣を引き起こす可能性があります。^{[ 42 ]}
• _CO2貯留を伴う肺気腫– この状態は、減圧中に肺気腫性嚢胞が破裂することにより、HBO治療中に気胸を引き起こす可能性があります。このリスクは、X線検査で評価できます。^{[ 42 ]}
• 胸部手術の既往歴 – これはまれに問題となり、通常は禁忌とはみなされません。ただし、手術痕によって生じた病変に空気が閉じ込められる可能性があるという懸念があります。これらの状態は、HBO療法を検討する前に評価する必要があります。^{[ 42 ]}
• 悪性疾患：がんは血液が豊富な環境で増殖しますが、高酸素濃度によって抑制される可能性があります。がん患者に対する高圧酸素療法は、高圧酸素療法が血管新生を介して血流を増加させ、酸素濃度も上昇させるため、問題となります。抗血管新生サプリメントを摂取することで解決できる可能性があります。^{[ 45 ] [ 46 ]} Feldemierらによる研究と、NIHが資金提供したThomらによる幹細胞に関する研究では、高圧酸素療法は実際には幹細胞/前駆細胞の生成に有益であり、悪性化プロセスは加速されないことが示されています。^{[ 47 ]}
• 中耳気圧外傷は、耳の気圧を均等にする必要性から、高圧環境下では子供や大人に発生する可能性がある。

Pregnancy is not a relative contraindication to hyperbaric oxygen treatments,^[43] although it may be for underwater diving. 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.)^[48][49] 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.^[43]

The increased overall pressure is of therapeutic value in the treatment of decompression sickness and air embolism as it provides a physical means of reducing the volume of inert gas bubbles within the body;^[52] 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.^[51]

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.^[53][54]

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 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 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 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.^[51]

The traditional type of hyperbaric chamber used for therapeutic recompression and HBOT is a rigid shelled pressure vessel. Such chambers can be run at absolute pressures typically about 6 bars (87 psi), 600,000 Pa or more in special cases.^[55] 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
• 医療従事者が搭乗者を視覚的に監視できるようにするためのビューポートがあり、補助的な緊急通信方法として手信号にも使用できます。主な構成要素は、窓（透明アクリル）、窓台（アクリル窓を保持）、および保持リングです。ビューポートの外側にライトを取り付けることで、内部照明を提供できます。ビューポートは、内部の人を見て健康状態を評価する必要があるため、PVHOに特有の機能です。他の材料も試みられましたが、一貫して密閉性を維持できなかったり、急速に壊滅的な故障に発展する亀裂が発生したりしました。アクリルは、オペレーターが目視できる小さな亀裂が発生しやすく、壊滅的な故障が発生する前に緩和措置を講じる時間があります。^{[ 56 ]}偽造チャンバーでは、アクリル窓が使用されていないことがよくあります。
• 1 つ以上の人間用入口ハッチ–ストレッチャーに乗った患者用の小型で円形または車輪付きの入口ハッチ; ^{[ 55 ]} 
• 人間の入室を可能にする入口ロック- 2 つのハッチを備えた独立したチャンバー。1 つは外部へ、もう 1 つはメイン チャンバーへつながっており、患者がメイン チャンバーに出入りできるように独立して加圧することができる。^{[ 55 ]} 
• 医薬品、器具、食品用の低容量の医療用またはサービス用エアロック。^{[ 55 ]}
• 透明なポートまたは閉回路テレビにより、チャンバー外の技術者や医療スタッフがチャンバー内の患者を監視できる。
• 双方向通信を可能にするインターホンシステム。 ^{[ 55 ]}
• オプションの二酸化炭素除去装置–チャンバー内のガスをソーダ石灰キャニスターに通すファンで構成されています。^{[ 55 ]} 
• チャンバーの外側にある制御パネルで、チャンバーへの空気の流れとチャンバーからの空気の流れを制御するバルブを開閉し、フードやマスクへの酸素を調整します。 ^{[ 55 ]}
• 過圧リリーフバルブ；^{[ 55 ]}
• 処理ガスを供給および排気するための内蔵呼吸システム（BIBS）^{[ 55 ]}
• 消火システム。^{[ 55 ]}

柔軟な一人用チャンバーには、トラックやSUVで輸送するために分解できる折りたたみ式の柔軟なアラミド繊維強化チャンバーがあり、周囲圧力より最大2バール高い作動圧力で、完全な酸素処理スケジュールを可能にするBIBSが付属しています。^{[ 57 ] [ 58 ] [ 59 ]}から、補助酸素なしで大気圧より0.3～0.5バール（4.4～7.3psi ）高い圧力で動作し、縦方向のジッパーで閉じられる携帯型の空気膨張式「ソフト」チャンバーまであります。^{[ 60 ]} 

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 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 chamber air (21% oxygen) to reduce the risk of oxygen toxicity. 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 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. Chamber air oxygen content is kept between 19% and 23% to control fire risk (US Navy maximum 25%).^[55] 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.^[55]

A soft chamber may be pressurized directly from a compressor.^[60] or from storage cylinders.^[59]

小型の「モノプレイス」チャンバーは患者1名のみ収容可能で、医療スタッフは入室できません。チャンバー内は純酸素または圧縮空気で加圧できます。純酸素を使用する場合は、酸素呼吸マスクやヘルメットは不要ですが、純酸素の使用コストは圧縮空気の使用コストよりもはるかに高くなります。圧縮空気を使用する場合は、マルチプレイスチャンバーと同様に酸素マスクまたはフードが必要です。ほとんどのモノプレイスチャンバーには、空気休憩のためのデマンド呼吸システムを取り付けることができます。低圧ソフトチャンバーでは、使用する酸素分圧が低い（通常1.3 ATA）ことと治療時間が短いことから、酸素中毒のリスクが低いため、治療スケジュールに空気休憩は必要ない場合があります。

意識がはっきりしていて協力的な患者の場合、マスクによる空気の遮断は、チャンバー内のガスを交換するよりも効果的です。なぜなら、空気の遮断は、より迅速なガス交換と、遮断期間中および治療期間中のより安定したガス組成を提供するからです。

• 潜水医学専門医– 潜水医学の専門家
• チャンバー操作員– 高気圧チャンバーの操作に熟練した者
• 高気圧酸素療法看護師― 患者に高気圧酸素療法を施し、治療期間を通して患者を監督する責任を負う看護師。
• 潜水医療技術者― 高度な応急処置の訓練を受けた潜水チームのメンバー。
• 高気圧酸素療法医– 高気圧酸素療法の専門家
• チャンバーアテンダントとは、基本的な応急処置の訓練を受け、チャンバー内でのダイビングに適した医学的状態にある人物で、通常は治療を受けているダイバーの世話をするために割り当てられたダイビングチームのメンバーである。

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.^[51]

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.^[63]

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 ^[64]

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.^[65] 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.^[66]

A British physician, Nathaniel Henshaw, proposed what would have been the first hyperbaric chamber for medical treatment of humans in 1662. The container was to have been pressurised with air, which at the time was not yet known to contain oxygen, later discovered by Carl Wilhelm Scheele around 1770 and first published by Joseph Priestley in 1775, or carbon dioxide. Although it is widely accepted that the chamber was built and used, there are inconsistencies in the description of the engineering details of construction and use that make it very unlikely that it would have been able to seal or withstand the forces involved, and the procedures described would have been hazardous.^[67]

Victot T. Junod built a chamber in France in 1834 to treat pulmonary conditions at pressures between 2 and 4 atmospheres absolute.^[68]

During the following century "pneumatic centres" were established in Europe and the USA which used hyperbaric air to treat a variety of conditions.^[69]

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.^[69][70]

The English scientist Joseph Priestley 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.^[69]

1955年と1956年に、英国のチャーチル・デイビッドソンは高圧酸素を用いて腫瘍の放射線感受性を高め、アムステルダム大学のイテ・ボエレマは心臓手術でそれを成功裏に使用した。^{[ 69 ]}

1961年、ウィレム・ヘンドリック・ブルンメルカンプらは、クロストリジウム性ガス壊疽の治療における高圧酸素の使用について発表した。^{[ 71 ]}

1962年、スミスとシャープは高圧酸素による一酸化炭素中毒の治療に成功したと報告した。^{[ 69 ]}

海底医学会（現在は海底・高圧医学会）は高圧酸素療法に関する委員会を設立し、高圧酸素療法の適応に関する権威として認められるようになった。^{[ 69 ]}

高圧酸素治療室での火災は極めて危険です。1997年に発表されたレビュー論文では、1923年から1996年にかけて発生した35件の高圧酸素治療室火災で77人が死亡したことが判明しました。^{[ 72 ]}さらに、この治療法は一般的に安全と考えられていますが、高圧酸素治療装置の使用は、不適切な使用によって操作担当者にリスクをもたらすことが研究で示されています。適切な機器のメンテナンスと加圧装置の使用に関する安全手順は必須です。^{[ 73 ]}

• 1997年：イタリアのミラノで、高圧酸素治療室で火災が発生し、患者10人と看護師1人が死亡した。^{[ 74 ]}
• 2009年：フロリダ州で高圧酸素治療室が火災を起こして爆発し、祖母と4歳の孫が死亡した。少年は脳性麻痺の治療のため高圧酸素治療室で治療を受けており、この治療が違法とされているイタリアからこの治療を受けるために渡航していた。^{[ 75 ]}
• 2012年：フロリダ州で高圧酸素治療室が爆発し、治療を受けていた女性とサラブレッドの馬が死亡した。爆発は、馬が治療室を蹴って火花が出て火災が発生した後に起こった。^{[ 76 ]}
• 2015年：ジョージア州で、治療を受けていた犬が入った部屋が火災を起こして爆発し、犬が死亡した。その犬は関節炎の治療を受けていた。^{[ 77 ]}
• 2016年：インドネシアのジャカルタにあるミントハルジョ海軍病院の高気圧酸素治療室で治療を受けていた4人が火災で死亡した。火災は電気ショートが原因とされている。火災発生後、作業員はスプリンクラーシステムと緊急遮断システムを使用して犠牲者を救出しようとしたが、装置が炎に包まれたため救命活動は不可能となった。^{[ 78 ]}
• 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.^[79]
• March 2025: A hyperbaric chamber exploded in Michigan, killing a five year old boy.^[80][81]
• July 2025: On Wednesday, July 9, 43-year-old physical therapist Walter Foxcroft was found dead inside a hyperbaric oxygen chamber at his health clinic in Lake Havasu City, Arizona, after the device caught on fire.^[82][83]

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,^[84] Canada,^[85] and the United States.^[86] 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.^[87][88]

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.^[89]

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.^[90] In Canada, certain soft-shelled hyperbaric chambers were removed from the market for a potential risk to patients.^[91]

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 $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,^[92][93] and migraine.^[94][95] 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 as a treatment for multiple sclerosis.^[96] China and Russia treat more than 80 maladies, conditions, and trauma with HBOT.^[97]

Tentative evidence shows a possible benefit in cerebrovascular diseases.^[103] Rats subjected to HBOT after some time following the acute phase of experimentally-induced stroke showed reduced inflammation, increased brain-derived neurotrophic factor, and evidence of neurogenesis.^[104] Another rat study showed improved neurofunctional recovery as well as neurogenesis following the late-chronic phase of experimentally-induced stroke.^[105]

The clinical experience and results so far published has promoted the use of HBOT therapy in patients with cerebrovascular injury and focal cerebrovascular injuries.^[106] However, the power of clinical research is limited because of the shortage of randomized controlled trials.^[103]

A 2010 review of wounds from radiation therapy found that, while most studies suggest a benefit, more experimental research is needed to validate its use.^[107]

People who are having extreme difficulty breathing – acute respiratory distress syndrome – are commonly given oxygen and there have been limited trials of hyperbaric equipment in such cases. Examples include treatment of the Spanish flu^[70] and COVID-19.^[108]