A Scoping Review of the Equivalent Air Depth Concept New!

ABSTRACT

Surface-orientated diving with nitrogen-oxygen breathing gases (nitrox) other than air will commonly be planned according to the Equivalent Air Depth (EAD) principle. EAD is the depth at which a diver breathing air will inhale the same pN2 as the nitrox-breathing diver. Using conventional air decompression tables based on the EAD depth will allow longer bottom times or shorter decompression times compared to air breathing at the same water depth. This scoping reviewed aimed to investigate the validity of the EAD principle. A literature review identified thirteen eligible studies reporting DCS incidence or vascular bubbles following air and nitrox exposures in human and experimental animals. Four experimental (N=1597mandives) and two epidemiological (N=249109 mandives) studies on humans did not disclose a higher DCS incidence or bubble scores following nitrox dives compared to air dives of similar EAD. Seven experimental animal studies consistently showed that a high pO2 (>2 atm) increased DCS susceptibility in goats and rats. This can likely be explained by the reduction of the “oxygen window” due to the high tissue and venous pO2. There is insufficient data from animal studies to conclude whether this can be reproduced within a pO2 range applicable for human operational diving (<1.6 atm). There is presently no reason to modify the EAD principle for manned diving. Still, we would advise improving monitoring of operational nitrox dives to confirm that nitrox dives have a DCS incidence similar to EAD- and bottom time-matched air dives.

Keywords: decompression; decompression illness; decompression sickness; decompression tables; diving tables; enriched air – nitrox; hyperoxia; oxygen; review article; systematic review