Inert gas washout FAQ

My students asked what happens to the nitrogen bubbles in untreated decompression sickness (DCS). I guessed that they eventually get reabsorbed or off-gassed via the lungs. What is the best answer?

Divers accumulate nitrogen (and/or other inert gases in their breathing mix) while diving. The deeper and longer the dive, the more gas accumulates. In cases of DCS, the inert gas load exceeds the tissues’ capacity, so bubbles form.

Gas enters the body through the lungs, moves into the circulatory system and then into other tissues. Offgassing occurs by the same mechanism in reverse: Inert gas moves from the body’s tissues into the bloodstream and then into the lungs, where it is exhaled. A diver off-gasses when in shallow water after having been in deeper water (during ascent and while performing a decompression stop or safety stop, for example). Offgassing continues after the diver exits the water. The human body has no means by which to indefinitely retain gas or bubbles.

The vast majority of the inert gas is off-gassed within a few hours, and almost all of it leaves recreational divers’ bodies within about 24 hours. Because the bulk of excess inert gas is eliminated within a day, the first onset of DCS symptoms is unlikely after 24-hours following a dive (except in special circumstances such as saturation diving or subsequent altitude exposure, for example).

Bubbles cause inflammation and local tissue injuries. The larger the bubble load, the more severe the injury and the faster the onset. Hyperbaric chamber treatment within the first 24 hours can eliminate gas and bubbles while the injury is still occurring. After about 24 hours, the injury has already occurred. Bubbles are no longer present, but the injury persists. Hyperbaric treatment after the first day can still be very helpful by promoting healing and recovery.

Although leaving DCS untreated is not recommended, its general progression is improvement over time. Some divers who do not get treated recover completely, but others have persistent problems that range from mild to severe.
For more information about inert gas, DCS and hyperbaric chamber treatment, visit DAN.org or call the DAN Medical Information Line at +1 (919) 684-2948.  OR in Southern Africa: +27 828 10 60 10
— Frances Smith, MS, EMT-P, DMT