HBOT AND DECOMPRESSION SICKNESS

Decompression sickness (DCS) has many synonyms. These include Caisson’s
disease, the “bends,” compressed air sickness, or diver’s paralysis. DCS is a direct
result of bubble formation within bodily tissues and the subsequent pathophysiologic
changes induced by these bubbles. Although DCS may follow exposure to increased
pressures, as in compressed gas or scuba diving, it can also follow rapid climbs in
altitude or switches in breathing gas or the ambient (i.e. surrounding) gas medium
during a hyperbaric exposure.. Because of its implications in operating jet aircraft
and the space shuttle, DCS is a subject of research even in aerospace medicine
. DCS has been reported to occur in auxiliary medical personnel who accompany
and treat patients within multi-place chambers. After breathing compressed
inert gases over a period of time, the partial pressures of the different gases reach
new equilibriums within a person’s tissues (in accordance with Henry’s Law). In the
case of nitrogen, for example, it is five times as soluble in fat as in air and becomes
concentrated within fatty tissues, including the brain. Unless adequate time is
allowed during decompression for their elimination, the gases previously dissolved in
solution or in tissues may form bubbles. Since oxygen is rapidly consumed and
nitrogen is basically inert, these bubbles are mainly composed of nitrogen. Because
of the relatively poor circulation in fatty and cartilaginous tissues, a longer time is
required for the elimination of gases from these tissues.
Although reductions in ambient pressure in a ratio of 2:1 were tolerated in Haldane’s
experiments with goats to a maximum of 606 kPa, this ratio was later found to be
optimistic. The true ratio is probably closer to 1.5:1 . That is, DCS is unlikely
when ascending from example a pressure of 303 kPa to 202 kPa but DCS may be
expected if one ascends from 303 kPa to 101 kPa. Therefore, DCS is rare in dives of
less than 202 kPa or climbs of less than 5,550 meters in unpressurised aircraft. It is
possible to dive safely to depths greater than 202 kPa or to ascend to altitudes
higher than 5,555 ft. To do so, however, requires a combination of ascent rates and
pauses at certain depths or altitudes during ascent to allow excess inert gas to be
eliminated before continuing decompression to the next level. In the case of
compressed gas diving, this is called stage decompression. Decompression
sickness can be prevented by adequate decompression times and performing
decompression stops at appropriate depths for sufficient times, following different
diving tables. It is important to realize that these diving tables (guidelines) are not
completely safe and still have an associated decompression sickness incidence of
between 1 and 5 percent,
Hyperbaric oxygen (“recompression therapy”) is recommended and approved for the
treatment of DCS, based on the principle that it reduces the size of the bubbles
which then move to smaller, more distal vessels. Recompression also hastens the
dissolution and absorption of bubbles and eliminates inert gas more effectively by
reducing the inspired inert gas partial pressure through the choice of therapeutic
breathing gas – usually oxygen. Increased oxygen tensions help minimize ischemic
damage in the distal, hypoxic areas. In addition, by using 100% oxygen, nitrogen is
removed from the bubbles and tissues at a faster rate (through counter diffusion).