Decompression sickness has special military significance because it can affect divers and pilots, particularly those flying at high altitude. Over the course of 12 years, approximately 50 pilot trainees at an Air Force training site in Colorado required HOT when ground-level O2 failed to resolve their DCS symptoms.10
Symptoms of DCS range from musculoskeletal pain to severe neurologic and pulmonary complications. First-line therapy for DCS is 100% O2 at ground level. When symptoms are severe or persistent, HOT is the treatment of choice. It works by decreasing the volume of air bubbles (as predicted by Boyle’s Law), providing oxygenation to hypoxic tissue and mitigating inflammatory responses implicated in tissue injury9; HOT can be considered salvage treatment for rare, severe, or unresponsive complications of DCS during common activities such as diving and flying.
The emergent nature of DCS often necessitates an on-call, on-site HOT facility or contracted community services. Although DCS is a rare complication, it can be devastating, as was the case for a military pilot flying an ultrahigh altitude reconnaissance aircraft.11 He developed a near fatal case of neurologic DCS during a military mission and required treatment with emergent HOT. Although his symptoms were reduced with therapy, he has persistent cognitive deficits.11
Dermatologic Flaps and Grafts
Although less commonly discussed in dermatologic literature, the use of HOT in compromised grafts and flaps has been addressed in the plastic surgery literature. In a large multicenter study, researchers evaluated 20,821 Mohs micrographic surgery procedures and reported 149 adverse events, of which 20.1% were dehiscence and partial or full necrosis.12 These complications, though rare, are potentially devastating, particularly in cosmetically sensitive locations such as the face. Traditional care for compromised grafts and flaps includes local wound care, surgical debridement, and additional reconstructive procedures. These interventions can be expensive and uncomfortable for patients and carry risk for further morbidity.13
Grafts become compromised when their metabolic demand outpaces the ability of the recipient bed due to characteristics of the graft or the recipient bed or both. Flaps carry their own blood supply, which can be compromised if the flap is too long or too large for the pedicle, there is notable tension on the wound, or blood flow is mechanically obstructed by kinking or twisting. Under these conditions, HOT can be beneficial, as O2 dissolves in plasma, thus improving the O2 tissue cellular diffusion gradient.7 An increased level of systemic O2 promotes wound healing and graft or flap survival by improving fibroblast function, blood flow, and vascularity, and by mitigating ischemia-reperfusion injury.13
In a study, 105 patients with an ischemic flap or graft were treated with HOT; most (89% of threatened flaps and 91% of threatened grafts) were salvaged. In this series, the duration of latency from the creation of the flap to initiation of HOT was directly proportional to the failure rate of this treatment modality.14
Radionecrosis, a complication of radiotherapy, is caused by progressive obliterating endarteritis with resultant vascular stenosis and fibroatrophy, which eventually cause stromal fibrosis.15 In a study that looked at 1267 nonmelanoma skin cancers that had been treated with radiotherapy, the ulceration rate was 6.3%. Most of the ulcerated lesions were treatable conservatively, but some were more treatment resistant.16 Hampson et al17 reported on 58 patients with cutaneous wounds due to soft-tissue radionecrosis who were treated with HOT as part of a larger observational case series in which investigators looked at multiple types of radionecrosis. They found that 76% of these patients improved: 26% showed complete resolution and the remaining 50% had 50% to 90% improvement.17
Vasculitis or Autoimmune Ulceration
Vasculitis and vasculopathy can occur independent of, or in association with, connective tissue disease and can result in chronic ulceration. At our institution, a patient with antimelanoma differentiation-associated protein 5 dermatomyositis who had refractory digital ulcerations despite intensive systemic therapy had an excellent response to HOT; ulcerations resolved after 37 treatments.18
Efrati et al19 reported on 35 patients who had chronic nonhealing vasculitic ulcerations despite immunosuppression medication who were treated with HOT. Twenty-eight patients completely healed, 4 had partial healing, and 3 had no improvement.
Mirasoglu et al20 reported on a case series of 6 systemic sclerosis patients who had ulcerations that persisted despite other treatments. After initiation of HOT, 4 patients experienced complete response and 2 experienced partial response, which is notable because such ulcerations are often extremely difficult to treat and have usually failed multiple therapies before being addressed with HOT.