The recent document from the Undersea and Hyperbaric Medical Society (UHMS) adding “scientific” considerations to their published indications for hyperbaric oxygen treatment in the USA has rightly been criticized by Dr. Paul Harch in the Medical Gas Research. I would like to add to his comments and correct errors often made by members of the UHMS Hyperbaric Oxygen Committee and others in the field that reduce the acceptance of using oxygen as a treatment. For example, using the term “hyperbaric oxygen” with the word hyperbaric as an adjective suggesting that the oxygen supplied in a pressure chamber is different to that we derive from breathing air. It is not: The correct term is “hyperbaric oxygenation.” UHMS documents even refer to “oxygen under pressure” when it is a gas and must always be at a pressure. The importance of barometric pressure is ignored in mainstream medicine and even in the biological sciences. However, engineers are not without blame as the scales used for pressure gauges should start at 1 atmospheres absolute (ATA, 1 ATA = 101.32 kPa) i.e. not zero (when atmospheres are the unit being used) and in the UK, atmospheric pressure ranges from 0.925 to 1.056 ATA at sea level. In other words, more than 10% but atmospheric pressure is even quoted to three decimal places (in kilopascals) by the UHMS.
There is also no scientific basis for the UHMS claim that the beneficial effects of oxygen are only gained in a chamber at an arbitrary pressure greater than 1.4 ATA. They are produced by the oxygen in air at an absolute pressure of only 0.5 ATA because wounds still heal, albeit slowly, in people living at altitude in, for example, Tibet, China and the Andes. Healing can undoubtedly be improved by an increase in air pressure - referred to by the UHMS as “mild” hyperbaric therapy - simply because the partial pressure of oxygen is increased. It is also stated that “medical grade” oxygen is required when diving or aviation grade are equally suitable. A Food and Drug Administration (FDA) document on wound healing claims that medical oxygen may actually “contain bacteria, fungi bacteria, fungi, or other infectious organisms” and should be filtered. This is incorrect. The grading was established for oxygen derived from the distillation of liquefied air and posed a problem in the USA for the FDA when hospitals installed concentrators which cannot achieve even close to 99% purity. The USP has introduced a new standard for the 90–96% oxygen produced by this equipment (not, as stated by the UHMS, 95%) showing the original purity standard was spurious. However, measurements of the arterial oxygen tension in the blood of patients using a full face mask supplied with gas from a liquid oxygen source at 2 ATA ranged from 1.11 ATA to 1.59 ATA, largely due to ventilation/perfusion mismatch in the lung. This means it cannot be claimed that patients in trials receive the same oxygen concentration without arterial sampling. The UHMS also claims, without providing any evidence, that the chambers used for “mild” hyperbaric treatment are not safe when they are tested and accepted by the FDA for the treatment of pulmonary and cerebral edema in mountaineers. The Society actually supports diving to the same pressures in water that risks death from pulmonary barotrauma, embolism and drowning.
However, the greatest problem that is preventing millions from gaining the benefit of more oxygen is the UHMS demand for evidence that the additional oxygen is beneficial (for insurance reimbursement), when hyperbaric equipment is used, despite accepting that hypoxia must be treated with oxygen. The conclusive, indeed, proven evidence, is provided from breathing the same molecular oxygen gained from the pressure of the atmosphere: It is the primary agent responsible for healing. I have argued that controlled trials are not scientific or, indeed ethical, in Chapter 10 - Anecdotes, evidence, and uncontrolled double-blindness - of my book Oxygen and the Brain. The paradigm is obvious: Minor illness and injury is treated by the “mild” level of oxygen breathed in air: At the other end of the spectrum with severe tissue damage, no amount of additional oxygen can reverse the pathology. For states in between, additional oxygen may produce both faster and better healing and prevent chronic illness.
Those involved in FDA decisions are civil servants and often not clinicians and mirror the prevailing attitudes in mainstream medicine, who derive much of their income treating the consequences of hypoxia with drugs. This failure has allowed “short” coronavirus disease 2019 (COVID-19) to become much longer for millions of people. The virus causes an adult respiratory distress syndrome (ARDS) and a recent review in The Lancet does not discuss oxygen treatment or mention hypoxia. The inflammation and hypoxia responsible for long COVID-19 can still be treated by raising the oxygen content of affected tissues.
There are now many reports of long COVID-19 patients benefiting from hyperbaric oxygen treatment and a detailed controlled study has been published.
1. Moon RE. Hyperbaric oxygen therapy indications 201914th North Palm Beach Best Publishing Company
2. Harch PG. New scientific definitions: hyperbaric therapy and hyperbaric oxygen therapy Med Gas Res. 2023;13:91–93
3. Durfor C. Guidance for Industry and FDA Staff Topical Oxygen Chamber. 2011
5. Fischer BH, Marks M, Reich T. Hyperbaric-oxygen treatment of multiple sclerosis. A randomized, placebo-controlled, double-blind study N Engl J Med. 1983;308:181–186
6. James PB. Oxygen and the brain: the journey of our lifetime 2014 Florida Best Publishing Company
7. Bos LDJ, Ware LB. Acute respiratory distress syndrome: causes, pathophysiology, and phenotypes Lancet. 2022;400:1145–1156
8. Eltzschig HK, Carmeliet P. Hypoxia and inflammation N Engl J Med. 2011;364:656–665
9. Cannellotto M, Duarte M, Keller G, et al Hyperbaric oxygen as an adjuvant treatment for patients with COVID-19 severe hypoxaemia: a randomised controlled trial Emerg Med J. 2022;39:88–93