A pilot study comparing oxygen delivery from 4 different delivery devices under hyperbaric conditions on healthy volunteers.

The devices used were: • “Hans Rudolph” Rudolph Nasal & Mouth Breathing Mask Face mask with head straps (model number 8930, Hans Rudolph, Kansas, U.S.A) • “Scott” Pressur VakTM II Face Mask (model number 803600, Amron Vista, California) • “Hsiner” CPAP/VPAP silicone medium face mask with head straps (Model number 10214, HSINER, Taichung City, Taiwan) • “Oxygen Hood” Amron Oxygen Treatment Hood. (Model number 8891, Amron, Vista, California) 100% oxygen was used. The oxygen used was not warmed or humidified Head straps were used to secure the Hsiner and Hans Rudolph masks onto the subject’s face. The neck seal for the hood was placed around the subject’s neck outside the chamber before pressurization and the hood was secured and inflated by the subject on testing. The Scott mask was held onto the face by the subject and the subject was asked to ensure a tight seal to avoid leakage. The Scott mask was held in place without head straps to replicate the clinical practice at our institution. A high-pressure O2 hose connects the demand valve to the oxygen O2 outlet. A high-efficiency particulate air (HEPA) filter was attached between the demand valve and mask. To measure the intra-mask oxygen levels, a size 6 paediatric nasogastric (NG) tube was placed through a hole drilled into the side of the mask to lie in the mask dead space. For the oxygen hood, an NG tube was positioned underneath the neck seal on the right side of the subject’s face. The NG tube was connected to a sampling line leading outside the chamber. Mask O2 analysis was performed by connecting the sampling line to a Datex Ohmeda D-CU8 with a MiniTPX side stream gas analyser. The devices were placed on the head by the participants. The overall duration of observation was 50 mins All participants were exposed to all the different devices. There was no washout period.