A recent review by Hadanny and colleagues recommends hyperbaric oxygen therapy (HBOT) for acute moderate to severe traumatic brain injury (TBI) and selected patients with prolonged postconcussive syndrome.
This article piqued my curiosity because I trained in HBOT more than 20 years ago. As a passionate scuba diver, my motivation was to master treatment for air embolism and decompression illness. Thankfully, these diving accidents are rare. However, I used HBOT for nonhealing wounds, and its efficacy was sometimes remarkable.
Paradoxical results with oxygen therapy
Although it may seem self-evident that “more oxygen is better” for medical illness, this is not necessarily true. I recently interviewed Ola Didrik Saugstad, MD, who demonstrated that the traditional practice of resuscitating newborns with 100% oxygen was more toxic than resuscitation with air (which contains 21% oxygen). His counterintuitive discovery led to a lifesaving change in the international newborn resuscitation guidelines.
The Food and Drug Administration has approved HBOT for a wide variety of conditions, but some practitioners enthusiastically promote it for off-label indications. These include antiaging, autism, multiple sclerosis, and the aforementioned TBI.
More than 50 years ago, HBOT was proposed for stroke, another disorder where the brain has been deprived of oxygen. Despite obvious logic, clinical trials have been unconvincing. The FDA has not approved HBOT for stroke.
HBOT in practice
During HBOT, the patient breathes 100% oxygen while the whole body is pressurized within a hyperbaric chamber. The chamber’s construction allows pressures above normal sea level of 1.0 atmosphere absolute (ATA). For example, The U.S. Navy Treatment Table for decompression sickness recommends 100% oxygen at 2.8 ATA. Chambers may hold one or more patients at a time.
The frequency of therapy varies but often consists of 20-60 sessions lasting 90-120 minutes. For off-label use like TBI, patients usually pay out of pocket. Given the multiple treatments, costs can add up.
Inconsistent evidence and sham controls
The unwieldy 33-page evidence review by Hadanny and colleagues cites multiple studies supporting HBOT for TBI. However, many, if not all, suffer from methodological flaws. These include vague inclusion criteria, lack of a control group, small patient numbers, treatment at different times since injury, poorly defined or varying HBOT protocols, varying outcome measures, and superficial results analysis.
A sham or control arm is essential for HBOT research trials, given the potential placebo effect of placing a human being inside a large, high-tech, sealed tube for an hour or more. In some sham-controlled studies, which consisted of low-pressure oxygen (that is, 1.3 ATA as sham vs. 2.4 ATA as treatment), all groups experienced symptom improvement. The review authors argue that the low-dose HBOT sham arms were biologically active and that the improvements seen mean that both high- and low-dose HBOT is therapeutic. The alternative explanation is that the placebo effect accounted for improvement in both groups.
The late Michael Bennett, a world authority on hyperbaric and underwater medicine, doubted that conventional HBOT sham controls could genuinely have a therapeutic effect, and I agree. The upcoming HOT-POCS trial (discussed below) should answer the question more definitively.