Topical oxygen therapy is not hyperbaric therapy and the two treatments should not be confused.

Dear Editors, The recent article describing the use of the Delphi method to provide clinical guidance on the use of topical oxygen for chronic wounds (1) does not do justice to the Journal or enhance the science of wound care. The Delphi method relies on a panel of experts to answer questionnaires in rounds, revising their answers in light of the replies of other panel members with the goal of converging towards the best approach. It presupposes that the information provided to the group is accurate and that the group has sufficient expertise with which to interpret the information. Unfortunately, neither condition appears to be satisfied. It is not factual to state that ‘topical oxygen therapy is also considered hyperbaric therapy’ (see page 273). In hyperbaric oxygen therapy (HBOT), the patient’s entire body is placed into a pressure vessel and the ambient pressure is increased within the vessel to pressures between 1·5 and 3·0 atmospheres absolute (ATA) while the patient breathes 100% oxygen. At 2 ATA, a patient will have an arterial oxygen tension of 1000 mmHg and a muscle oxygen tension over 200 mmHg (2). At 3 ATA, the amount of oxygen dissolved in the blood plasma is enough to sustain life in the absence of circulating haemoglobin, hence its use in acute blood loss anaemia. This oxygen is available to all tissues (e.g. brain, bone, muscle). In topical oxygen treatment, the pressures achieved are approximately 1·0004 ATA and, assuming no barrier to diffusion, (e.g. a wound free from any necrotic debris), a small amount of oxygen can diffuse, at most, 2 mm from the surface of the wound. While 1·004 ATA is technically above atmospheric pressure, it does not fall within the definition of hyperbaric therapy (>1·5 ATA). In the USA, the Center for Medicare Services states unequivocally that, ‘topical oxygen does not meet the definition of HBOT’ (http://www.cms.gov/Regulations-and-Guid ance/Guidance/Transmittals/downloads/R129CIM.pdf). Furthermore, the US Food and Drug Administration (FDA) does not consider topical oxygen to be a form of HBOT. In describing a HBOT chamber, the FDA states, ‘This device does not include topical oxygen chambers for extremities’. Contrary to what is stated in the paper, the FDA does not ‘approve’ these class II medical devices, but it does clear them for use as part of its responsibility to regulate the way in which these devices are promoted and advertised. In 21 CFR 878.5650, the FDA identifies a topical oxygen chamber for extremities as, ‘a device . . . to aid healing of chronic skin ulcers such as bedsores’. There is an entirely separate FDA clearance document for hyperbaric oxygen chambers. Since 1978, the FDA has yielded to the Undersea and Hyperbaric Medical Society (UHMS) Committee report in determining the indications for which a hyperbaric oxygen chamber can be promoted and advertised. The FDA does not use the UHMS list of approved indications for HBOT when determining the way in which topical oxygen devices are promoted since the FDA does not consider them to be hyperbaric chambers. However, marketers of topical oxygen may seek to link their devices to HBOT in an effort to extrapolate to topical oxygen the favorable data and/or recommendations pertaining to HBOT. In the USA, Medicare reimburses for HBOT but not for topical oxygen, arguing that, ‘its (topical oxygen’s) clinical efficacy has not been established’. Therefore, no Medicare reimbursement may be made for the topical application of oxygen (http://www.cms.gov/Regulations-andGuidance/Guidance/Transmittals/down loads/R129CIM.pdf). The mechanism of action of HBOT is not limited to the reversal of hypoxia and includes the mitigation of ischaemia reperfusion injury and the induction of cytokines. A recent review article by Thom provides insight into the protean and well elucidated effects of HBOT as a result of exhaustive in vitro and in vivo research (3). The evidence base for topical oxygen, reviewed by the Delphi group, included only case studies, committee reports and opinions. The limited data available pertaining to topical oxygen are insufficient to suggest that its as yet undefined mechanisms of action are the same as that of HBOT. Orsted and Poulson reviewed the limited, low level scientific data available on topical oxygen, and the authors could and should have limited their comments to this modality. The group lacked expertise in HBOT and should not have asserted that topical oxygen has the same benefits but without the risks. For example, contrary to what is stated in the article, retinopathy has never been reported as a consequence of HBOT, although transient myopia has been observed in some patients undergoing prolonged periods of daily HBOT. Manufacturers of topical oxygen devices should not confuse clinicians by referencing actual HBOT standards, research, mechanisms or regulations when discussing topical oxygen therapy. Topical oxygen may have a role in wound treatment and deserves further study. We applaud the Orsted paper as a rational approach to its clinical use. However, the scientific data which the UHMS (and the FDA) uses to establish the effectiveness of HBOT and regulate its promotion cannot be extrapolated to that of topical oxygen therapy. Detailed information regarding the differences between HBOT and topical oxygen are discussed in the UHMS position statement on topical oxygen, available free of charge at: http://archive. rubicon-foundation.org/xmlui/bitstream/handle/123456789/ 5009/16119307.pdf?sequence=1.