A Scoping Review of the Equivalent Air Depth Concept

Area of Science:

• Diving Medicine
• Hyperbaric Physiology
• Scuba Diving Safety

Background:

• Nitrox (nitrogen-oxygen) mixtures are used in diving instead of air.
• The Equivalent Air Depth (EAD) principle is used to plan nitrox dives.
• EAD ensures equivalent nitrogen exposure compared to air at a shallower depth.

Purpose of the Study:

• To investigate the validity of the Equivalent Air Depth (EAD) principle for nitrox diving.
• To assess the risk of decompression sickness (DCS) and vascular bubbles with nitrox use.
• To review existing human and animal studies on EAD and nitrox diving.

Main Methods:

• Scoping review of 13 eligible studies.
• Analysis of human experimental and epidemiological data (N=1,597 and N=249,109 dives).
• Review of experimental animal studies (goats and rats).

Main Results:

• Human studies showed no increased DCS incidence or bubbles with nitrox dives compared to air dives at similar EAD.
• Animal studies indicated higher DCS susceptibility at high partial pressures of oxygen (pO₂ > 2 atm).
• Insufficient animal data exists for pO₂ ranges relevant to human diving (<1.6 atm).

Conclusions:

• The EAD principle remains valid for planning human nitrox dives.
• No modification to the EAD principle is currently needed for manned diving.
• Improved monitoring of operational nitrox dives is recommended to confirm DCS incidence.