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Preparation for Board Examination Decompression Illness: Pathophysiology II
Gas bubbles have a causal relationship
to DCS
A.) Embolic intravascular
B.) Autochthonous tissue bubbles
Signs and Symptoms
I.) Musculoskeletal
a.) Usually
within 36 hours of a dive
b.) Found in
upper limbs in bounce dives
c.) Lower limbs
in airmen, saturation dives and caisson workers
d.) 'Trial of
pressure' gives rapid relief
e.) Mechanism
1) No pathologic lesions, man or animals
2) Intravascular bubbles
Ischemia
Complement activation (extrinsic) -> aggregation of platelets, WBC's
3) Autochthonous bubbles
-X-ray shows periarticular, perivascular bubbles
-Freeze-drying shows bubbles in the myelin sheaths of peripheral nerves
(Gersh 1944-45)
-Simulate the same pain with saline injection into tendons
II. CNS DCS
A.) Spinal Cord
1.) Usually has rapid onset - frequent pain in the abdomen, pelvis
2.) Multilevel, bilateral, asymetrical with skip areas.
3.) Comes and goes but usually worsens progressively
4.) Diagnostic techniques - little use - a 'four-minute neurological'
is probably best.
5.) Spontaneous improvement, but rarely complete.
B.) Cerebral
( This is better perfused and more likely due to bubbling than to due to
gas
loading)
1.) rapid onset - 75% within 10 minutes of surfacing
2.) More complete spontaneous recovery
3.) Silent lesions are seen on HMPAO SPET scanning
4.) Secondary deterioration can occur within minutes to hours
C.) Mechanisms
- Spinal Cord
1.) Punctate hemorrhages in white matter in areas with smaller vessels.
(with embolism
gray matter is involved).
2.) Venous bubbles become arterial via PFO, pulmonary shunts can occur
with large
venous bubble load.
3.) Why do arterial bubbles go to low flow areas?
a. Microcirculation blockage in gas loaded tissues
b. Bypass surgery- bubbles to the brain
c. Not the same pathology of arterial embolism
4.) Venous occlusion of epidural venous plexus (EVVP) Not acceptable.
a. Gray and white matter
b. Thromboses seen rarely
c. Time course too fast for venous etiology
d. Difficult to reconcile rapid improvement with recompression
(since clotting is a factor)
5.) Autochthonous gas formation in myelin sheaths of spinal cord axons
a. The gas washout window for this to occur is 3.6 ata (dogs)
b. This correlates well with pathologic findings
c. Pressure can cause spinal cord axons to not conduct (without ischemia)
D.) Mechanisms - Cerebral
1.) Arterial
gas emboli
2.) Low
probability of autochthonous bubbles due to high perfusion
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Manifestations of Decompression Sickness
Causes
Failure to adhere to established
tables
At altitude
Flying after diving
Underestimated depth
Inadequate tables
Deep prolonged air
diving
Daily repetitive diving
after a long lay off
Modify tables to get
more time ('one down and one along' a common practice)
Individual idiosyncrasy
Lack of adaptation
or work up to a level of diving
There is an inevitable
percent of DCS on all tables
Contributory factors,
such as hard physical work, age
Latency of Onset of DCS
Air Diving
50% in 30 minutes
90% in three hours
99 % in 12 hours
100% in 36 hours
Manifestations
Divers report symptoms depending
on the circumstances and their needs. If there will
be loss of earnings or ability
to dive, then mild symptoms might be suppressed.
Subdividing DCS into Types can be
hazardous; a diver with joint pain which can be
severe, often classified as mild
or Type I bends, may not report a simultaneous
symptom that might be more serious
but insidious. It is also impossible to determine
which 'Type I' case will soon develop
a serious symptom and become 'Type II'. The
presentation in 90% is with a limb
symptom, but 30% of these will develop a more
serious manifestation.
The clinical picture also varies
with the cause of the illness, such as, airmen, or air
diving, or saturation diving or
caisson work.
Early Manifestations
Warnings: Unusual and disproportionate fatigue
Malaise, usually unrecognized
Loss of appetite
Skin:
-Itching of the trunk area; called 'formication' or ants crawling. This
is seen
in chamber divers and is associated with the areas exposed to compressed
air.
- Rashes: Marbling, cyanotic vasostasis surrounded by red vasodilation,
particularly on the trunk. This is called 'cutis marmorata' by some and
blanches on local pressure. This lasts for several days and responds to
recompression.
- lymphatic edema; uncommon but can be extensive. Also can be localized
over an involved joint.
Musculoskeletal "Limb bends"
- Associated with joints with synovia. The shoulder is most commonly
affected in compressed air divers.
- May be preceded by polyarthritic sensations in multiple joints before
settling in one joint. Less commonly affected are the hands, feet,
sterno-clavicular and tempero-mandibular joints.
- A 'niggle' is a mild pain in a single joint that improves in 10 minutes
of
onset and then disappear completely.
- The pain of limb bends is described as 'tearing' or deep and 'boring'.
There is
splinting of the limb, local loss of sensation, redness and occasionally
swelling.
-Compression of the joint as with a blood pressure cuff will usually improve
the
pain.
-Most often there are no abnormal physical findings.
Cardiopulmonary, "Chokes"
-This varies from a chest tightness to severe respiratory difficulty followed
by
circulatory collapse and sometimes death.
- In some there is pain behind the sternum, restricted respirations, dry
cough.
- This is followed by pallor, sweating, shallow, rapid respirations, raised
venous
pressure.
Neurological Manifestations
-This is virtually limited to air diving. Seems to be becoming more frequently
seen, but this is probably due to better reporting. 60-70 % of DCS cases
are now
neurological.
- Any neurological deficit may occur: there are more than three tmes as
many
spinal cases as cerebral (Rivera- 935 cases)
numbness and paresthesias 21%
weakness
21%
dizziness and vertigo
8%
visual symptoms
7%
chokes
2%
1.) Cerebral
-Mental disturbances, altered behavior, headaches (migrainous), visual
disturbances (blurring, diplopia, scotomata), difficulties with speech.
Eighth
cranial nerve 'Staggers'.
-'Staggers' is due to DCS of the end organ of the VIII cranial nerve and
is
associated more with rapid ascent on oxy-helium. It varies from dizziness
to true vertigo with nystagmus. Can be associated with nausea and vomiting
and occasionally tinnitus.
2.) Spinal Cord
- Virtually confined to compressed air diving. Has been reported also from
helium diving more than 6 hours after surfacing.
- Described as a cottony feeling of the feet, followed by 'pins and needles'
and progresses within an hour to a true paraplegia or less commonly a
quadriplegia with respiration by phrenic nerve only.
- Milder cases show only decreased sensation. Scrotal sensation and anal
sphincter activity may be reduced.
- Bladder paralysis is common. Impotence is a common residua after
treatment.
Hypovolemia
This is a complication of serious decompression sickness. The PCV is high
(65%) and
there is decreased urinary output.
Diagnosis
Early Diagnosis
Any condition arising within 36 hours of surfacing should be regarded as
DCS until
proved otherwise. The diagnosis
should be made by history alone without extensive,
time-consuming x-rays and 'studies'.
A quick neurological exam can be just as revealing as CT, MRI or HMPAO
scans. There may be no abnormal physical signs.
Blaming other things for DCS is common. An unnecessary recompression is usually harmless whereas delayed treatment leads to worsening of DCS and decreased effectiveness of treatment. A hematocrit and a chest x-ray can be helpful if there is a lengthy delay reaching a chamber.