Decompression sickness

Caisson disease is decompression sickness (A caisson is a large metal vessel filled with compressed air, within which people are able to work in tunnelling or bridge-building projects).

Caisson disease is an important cause of disability in deep-sea divers and compressed-air workers building tunnels or underwater structures.

As a result of the increased air pressure the blood and other tissues, especially fat, become supersaturated with nitrogen. If the air pressure is decompressed too quickly then the nitrogen is released as bubbles, which cause local tissue damage and generalized embolic phenomena.

• when the diver ascends the gas that has dissolved in the tissues will come out of solution to form bubbles of gas in the tissues and in the blood vessels
  • these bubbles are then transported to the lungs where, in most cases, they are filtered out - this is the process of decompression
    • if the bubbles cause medical problems for the diver, then the diver is said to be suffering from decompression illness (DCI) which used to be known as caisson disease
      • gases that are chemically unreactive as far as the body is concerned (e.g. nitrogen, helium and neon) are sparingly soluble in blood - also oxygen, when breathed at high partial pressures, can cause problems on ascent.
• there are three types of DCI recognised - "the chokes", "the staggers" and "the bends"
  • "the chokes" - this was seen in caisson workers - if the decompression procedure was inadequate, then the blood of the workers literally frothed - this was called "the chokes" and proved to be rapidly fatal unless rapid recompression took place
  • "the staggers" - in this situation the decompression was not so provocative so as to provoke "the chokes" - "the staggers" might lead to severe impairment of the nervous system or death
  • "the bends" - commonest form of DCI and less severe than "the chokes" or "the staggers" - characterised by moderate or severe limb pain

The lungs are important in filtering out bubbles in venous blood and preventing cerebrovascular events. In sports divers it has been shown that a patent foramen ovale is a risk factor for developing multiple brain lesions on MRI, presumably caused by paradoxical bubble emboli.

Multiple factors are involved in the pathogenesis of the Decompression Illness

• divers with bronchial asthma, atrial septal defect, patent foramen ovale, or obesity are more prone to develop
• depth of the dive below the sea surface, the temperature of the water, and the speed of ascent are considered as the main contributory factors for development of Decompression Illness. When divers ascend at a speed of 9-10 meters/min, they have minimal risk of developing Decompression Illness. If the ascent is faster (>19 meters/min), the risk of Decompression Illness is significantly higher (3)

Reference:

• 1) Edge CJ. Recreational diving medicine.Current Anaesthesia Critical Care 2008; 19 (4): 235-246.
• 2) Knauth, M. et al. Cohort study of multiple brain lesions in sport divers: role of a patent foramen ovale. BMJ 1997; 314: 701-5.
• 3) Phatak UA et al. Decompression syndrome (Caisson disease) in an Indian diver.Ann Indian Acad Neurol. 2010 Jul-Sep; 13(3): 202-203.