Blinding the blinded - assessing the effectiveness of a sham treatment in a multiplace hyperbaric chamber trial

Hyperbaric oxygen therapy (HBOT) is used for a variety of problem wounds as an adjunctive treatment. The therapeutic impact of adding HBOT to a wound-healing regimen in many cases remains unclear and an ongoing need exists for additional randomised controlled trials. Many of these clinical studies require a sham group of study participants. To date, there has not been any published research on the concealment of sham treatments in multiplace hyperbaric chambers. The aim of this pilot project was to validate the existing blinding procedures used at one hyperbaric facility. Sixty-six volunteer recreational scuba divers, who had not previously been exposed to compression in a hyperbaric chamber, were recruited through local dive shops. One group was pressurised to 203 kPa and the other was minimally pressurised to 121 kPa, the minimum pressure required to cause middle ear pressure changes. Both protocols implemented continuous, though subtle, pressure variations toward the attainment of the final target pressure. A nearly identical number of subjects in both the 203 kPa (n = 32) and 121 kPa (n = 34) groups believed they had undergone a treatment pressure to 203 kPa (72% versus 71%) indicating a similarity of perception between the two groups.