Cited Passage
3-44 U.S. Navy Diving Manual — Volume 1
limits. Allowable oxygen exposure limits for each system are discussed in later
chapters.
3‑9.2.2.2 Symptoms of CNS Oxygen Toxicity. The most serious direct consequence of
oxygen toxicity is convulsions. Some times recognition of early symptoms may
provide sufficient warning to permit reduction in oxygen partial pressure and
prevent the onset of more serious symp toms. The warning symptoms most often
encountered also may be remembered by the mnemonic VENTIDC:
V: Visual symptoms. Tunnel vision, a decrease in diver’s peripheral vision, and
other symptoms, such as blurred vision, may occur.
E: Ear symptoms. Tinnitus, any sound perceived by the ears but not resulting
from an external stimulus, may resemble bells ringing, roaring, or a
machinery like pulsing sound.
N: Nausea or spasmodic vomiting. These symptoms may be intermittent.
T: Twitching and tingling symptoms. Any of the small facial muscles, lips, or
muscles of the extremities may be affected. These are the most frequent and
clearest symptoms.
I: Irritability. Any change in the diver ’s mental status including confusion,
agitation, and anxiety.
D: Dizziness. Symptoms include clumsiness, incoordination, and unusual
fatigue.
C: Convulsions. The first sign of CNS oxygen toxicity may be convulsions that
occur with little or no warning.
Warning symptoms may not always appear and most are not exclusively symp toms
of oxygen toxicity. Muscle twitching is perhaps the clearest warning, but it may
occur late, if at all. If any of these warning symptoms occur, the diver should take
immediate action to lower the oxygen partial pressure.
A convulsion, the most serious direct consequence of CNS oxygen toxicity, may
occur suddenly without being preceded by any other symptom. During a convul
sion, the individual loses consciousness and his brain sends out uncontrolled nerve
impulses to his muscles. At the height of the seizure, all of the muscles are stimu
lated at once and lock the body into a state of rigidity. This is referred to as the
tonic phase of the convulsion. The brain soon fatigues and the number of impulses
slows. This is the clonic phase and the random impulses to various muscles may
cause violent thrashing and jerking for a minute or so.
After the convulsive phase, brain activity is depressed and a postconvulsive
(postictal) depression follows. During this phase, the patient is usually uncon
scious and quiet for a while, then semiconscious and very restless. He will then
usually sleep on and off, waking up occasionally though still not fully rational. The
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