Cited Passage
Diving Physiology 3-29
• Worsening of the patient’s condition during treat-
ment
• Recurrence of the patient’s original symptoms or
development of new symptoms during treatment
• Recurrence of the patient’s original symptoms or
development of new symptoms after treatment
• Failure of symptoms of decompression sickness or
gas embolism to resolve despite all efforts using stan-
dard treatment procedures
Alternative treatment procedures have been developed
and used successfully when standard treatment procedures
have failed. These special procedures may involve the use
of saturation diving decompression schedules; cases of this
type occur more frequently when a significant period of
time has elapsed between the onset of symptoms and the
initial recompression. Although it is important to know
that alternative procedures are available, it is equally
important to note that they have not been standardized. The use of an oxygen-nitrogen saturation therapy may be
the only course of action when the situation involves a par-
alyzed diver already at depth whose condition is deteriorat-
ing. It is therefore essential that the advice of experts in the
field of hyperbaric medicine, such as Divers Alert Network
(DAN), be obtained early in the treatment process. 3.3.4.5 Counterdiffusion
Divers breathing one gas mixture while surrounded by
another can develop serious skin lesions, nausea, vomiting,
and vestibular problems, even with no change in ambient
pressure. Problems can also occur after switching from breath-
ing nitrogen-oxygen mix to breathing heliox while still under
pressure. Different gases have different diffusion rates. Heli-
um, for example, diffuses faster than nitrogen; in other words,
helium moves into tissues from blood faster than nitrogen
moves out. Total inert gas partial pressure in the body increas-
es even though depth has not changed. This increased inert
gas partial pressure can result in bubble formation. The inner
ear seems particularly susceptible, resulting in vestibular
symptoms. Because two different gases can go in opposite
directions in the body at the same ambient pressure, it is
termed isobaric counterdiffusion or isobaric counterexchange. Interestingly, cases of inner-ear DCS have occurred
after diving heliox, then switching to air. Although it would
be expected that helium in tissues moves into blood faster
than nitrogen in breathing air moves into tissues, which
would reduce gas load and risk of DCS, it’s possible that
the middle ear (and other structures) fill with heliox during
the dive. During the switch to air during decompression,
partial pressure of helium in blood falls quickly, but the
middle ear and other structures remain full of heliox, and
the total inner ear inert-gas partial pressure rises. 3.3.4.6 Aseptic Bone Necrosis (Dysbaric Osteonecrosis)
Months to years after prolonged pressure exposure,
joint surfaces of the long-bone ends can die. The hip and
shoulder are most often affected, resulting in pain, spasm
around the joint, and finally, disabling arthritis. This con-
dition is called avascular necrosis of bone, caisson disease
of bone, aseptic bone necrosis, or dysbaric bone necrosis. The word “necrosis” means death of cells in an area. Bone
necrosis, and its crippling effects, was first noted in 1888 in
caisson workers (Kindwall 1972).