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8 Hyperbaric Oxygenation Therapy KCE Reports 74 2 HYPERBARIC OXYGENATION THERAPY: HISTORY AND TECHNICAL DESCRIPTION 2.1 BRIEF HISTORY Hyperbaric therapy refers to therapeutic conditions with ambient pressures higher than normal atmospheric pressure at sea level. This pressure can be expressed in relation to this sea level pressure as Atmosphere pressure absolute (ATA). Hyperbaric conditions thus correspond to pressures higher than 1 ATA and typically occur during underwater diving. At a depth of 10 meters pressure is approximately 2 ATA, and every additional 10 meters of depth corresponds to about one extra ATA. As early as the 17 th century, strong airtight vessels combined with pumps capable of compressing air could be produced and where sporadically even used as treatments for various conditions. 1-3 Serious hyperbaric therapy, however, only began as a treatment of caisson disease, a disease occurring in engineering workers who had to labour in caissons under conditions of compressed air, mainly during the construction of tunnels and bridges in the late 19 th 2, 4 century. The first reports of decompression sickness described this condition as ‘the bends’, since caisson workers assumed a bent posture to help relieve the pain caused by the nitrogen accrual in their joints. Although the physiology of the disease was only understood much later, recompression therapy at first with normal air, was proposed as early as 1854, 1, 2 and for a long time caisson disease, or decompression sickness (DCS) as it was later called, remained the main therapeutic indication for hyperbaric therapy. As a result of the introduction of a series of improvements of the working environment, including recompression therapy, mortality from this disease that ran as high as 25% originally, was dramatically reduced. 1, 4 Apart from this therapeutic use, however, all kinds of potential beneficial effects were ascribed to modest hyperbaric pressures and hyperbaric chambers were even introduced in health spas. In the nineteen twenties a 5-storey high hyperbaric building was built by O.J. Cunningham, the largest ever. 2, 3 Serious medical interest, however, quickly faded. With World War II interest in hyperbaric physiology and medicine re-emerged due to the increased demands not only on divers but also increasingly on aviators and later also astronauts who had to work in both hyperbaric and hypobaric conditions. By then also, the use of normal air in hyperbaric chambers had been replaced by that of 100% oxygen or by different mixtures of oxygen, air or helium. Early experiments in the 19 th and 20 th century had shown that breathing oxygen while raising the atmospheric pressure could lead to an increased amount of oxygen in the blood and tissues, but mainstream medical interest was only revived when the Dutch cardiac surgeon Ite Boerema reported in 1956 on the use of an operating room with raised atmospheric pressure to allow longer operating time during circulatory arrest in babies and young children with congenital heart defects. 2, 5, 6 His reports marked the beginning of a proliferation of hyperbaric chambers in hospitals around the world, although very soon they would become unnecessary for the original purpose due to the development of new operation methods and of new equipment to perform them. To use and justify the existing hyperbaric chambers new and sometimes bizarre indications were proposed. In 1987, Gabb and Robin published a manuscript entitled ‘Hyperbaric oxygen, a therapy in search of diseases’ in which they list over a hundred indications that had, by then, been suggested. 7 Those indications ranged from CO poisoning to senility, the preservation of youthfulness and the treatment of baldness. Many of the reported indications were based on very little or only anecdotic evidence. In an effort to respond to those shortcomings, medical societies such as the Undersea and Hyperbaric Medical Society (UHMS, www.uhms.org) 8 and the European Committee for Hyperbaric Medicine (ECHM, www.echm.org) 9 were established with the explicit aim to examine the indications for HBOT.
KCE Reports 74 Hyperbaric Oxygenation Therapy 9 For a long time, however, scientific evidence about HBOT benefits in humans remained scarce and often based on animal studies or small case series, 1 and mainly based on the personal experience of doctors intensively using this therapeutic modality. Recently, some more evidence has appeared and RCTs were performed for specific indications. In recent years several Cochrane reviews were published that carefully examine the available evidence. 2.2 TECHNICAL DESCRIPTION Oxygen is considered as a drug and it can be administered easily under normobaric conditions, but administering oxygen at pressures higher than 1 ATA requires compression. This is usually done by having the patient breathe pure oxygen or mixtures with other gases while being inside a airtight chamber in which the pressure is greater than 1 ATA. Three primary mechanisms are believed to be involved in the potential beneficial effects: bubble size reduction and elimination in case of decompression sickness and gas embolism (commonly called decompression illnesses or DCI), the achievement of hyperoxia in target organs, and the potential enhancement of immune and healing mechanisms through the correction of pre-existing hypoxia in target organs. 1, 8 HBOT is also considered to act beneficially through the pharmaceutical effect of hyperoxia induced inhibition of beta-integrin dependent white cell adherence to endothelium, as a mechanism to inhibit reperfusion injury. 10 There are basically two types of hyperbaric chambers, monoplace and multiplace, and the choice of chamber typically depends on the capacity needs and the conditions being treated. Since oxygen is to be regarded as the active pharmaceutical component, adequate dosing for each of the conditions being treated is necessary. In practice this is done through a combination of dosages, pressures and timing. For DCI, for instance, treatment consists of rapid recompression followed by slow decompression, but for each of the conditions treated by HBOT hyperbaric treatment tables have been devised. In practice, however, the choice of treatment schedules has often been empirical, at least in the past. 1 A number of publications described a therapy delivering topical oxygen at high flow rates locally to the wound surface, sometimes mistakenly calling this ‘hyperbaric oxygen therapy’. However, oxygen delivered with this method is estimated to impact tissues only up to 50 microns deep. 8 This method of delivering oxygen to the tissues will not be discussed in this report as it is neither systemic nor hyperbaric and therefore outside the scope of this assessment. 2.3 ACCEPTED INDICATIONS BY HYPERBARIC MEDICAL SOCIETIES Several medical societies are active in the world of Hyperbaric Oxygenation Therapy. The largest is the North America based ‘Undersea and Hyperbaric Medical Society’ (UHMS), formerly the Undersea Medical Society founded in 1967. Originally, the society supported third party reimbursement for 28 indications but in its 2003 report the number of accepted indications had declined to 13 distinct medical conditions. 8 Table 1 lists those 13 conditions.
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KCE reports 33 Effects and costs of
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