Decompression illness: a comprehensive overview

Decompression illness (DCI) is a collective term for two diving disorders, decompression sickness (DCS) and arterial gas embolism (AGE). These disorders are related in having bubbles as the presumed primary vector of injury, potentially some symptoms in common and similar treatment protocols, but the origins of the bubbles are different and many aspects of pathophysiology and presentation are distinct. Subsequent widespread PFO testing using bubble contrast, which opacifies the right heart with small venous bubbles of similar size to venous bubbles formed from dissolved nitrogen after decompression,2,11 only rarely results in cerebral symptoms even when the test is strongly positive and large showers of small bubbles enter the arterial circulation.12 Any related symptoms are typically evanescent or mild, with only very rare exceptions where serious focal signs have occurred. One argument for using the collective / descriptive (‘DCI’) terminology is that the management of DCS and AGE is the same (see later) and so the distinction may be clinically unimportant. This is the rationale for recommendations that the collective term be used in clinical commentary, with reversion to the original DCS and AGE terminology for pathophysiological discussions.

• 1
  DCS is caused by bubble formation from dissolved inert gas during or after a reduction in ambient pressure (‘decompression’). Relevant decompressions may occur on ascent from an underwater dive, exiting a pressurised workspace, ascent to high altitude in an unpressurised aircraft, and during extravehicular activity in space.
• 2
  The presence of a right-to-left shunt is a well-established risk factor whose pathophysiological relevance was discussed in detail above. Such shunts are most commonly a PFO.
• 3
  The increased risk of DCS associated with becoming cold during decompression after being warm during time at depth was described in the pathophysiology section. The obvious implication for reducing risk of DCS is to avoid becoming progressively colder during a dive.