| Diving
accidents requiring recompression in a Recompression
Chamber, namely Decompression Sickness (DCS)
and Gas Embolism (GE) are put together under
the term Decompression Illness (DCI).
The
goal of recompression therapy is to prevent
both further and permanent injuries caused
by DCI.
Fundamentals of therapy for a DCI case are:
1- Raised atmospheric pressure to
shrink the gas-phase (bubble) volume.
2- Raised inspired PO2 to washout the inert
gas, promote tissue oxygenation and reduce
oedema.
3- Adequate treatment time.
4- Adequate fluid management.
5- Appropriate drug therapy.
Proper
application of recompression therapy can abort
the mechanisms by which this illness can cause
permanent tissue deformation and in many cases
complete resolution of symptoms can be achieved.
It
is often very difficult to diagnose accurately
the exact nature or seriousness of a diving
accident; so if any manifestations of DCS
or GE are observed, it is of much greater
importance to evacuate the victim to initiate
treatment immediately than to delay treatment
for a more accurate diagnosis. When differentiation
between a serious case of DCS and GE cannot
be made, the treatment for AGE should be conducted.
An
initial evaluation, which helps to identify
the urgency of a DCI case, is determined by
the following:
1- Onset of symptoms. The longer the surface
interval prior to symptoms appearing, the
less likely they are to worsen.
2- Severity of symptoms. Describing the extent
and intensity of DCI symptoms as: degree and
type of pain, inability to move or coordinate,
walking difficulty, balance or urination problems,
and dyspnoea (level of consciousness deterioration).
Grade the symptoms with the following terms;
mild, moderate, massive and severe.
3- The organ systems affected. (Musculoskeletal
- CNS - inner ear - circulatory - respiratory
systems).
4- The change of symptoms with time. (Evolution).
There
are three degrees (catagories) of urgency
based on onset and severity of symptoms, organ
systems involved and time course. They are
defined as:
-Category A (Emergent) in which all available
resources should be mobilized to ensure that
recompression treatment will be obtained as
fast as possible (do not waste time for examination
or proper diagnosis).
-Category B (Urgent) in which the patient
will need treatment (recompression) as soon
as it can be arranged, (not an extreme emergency).
-Category C (Timely) in which symptoms are
not obvious without detailed examination and
the hyperbaric physician can make the decision
to delay or abort the treatment of a patient
in this category.
In
water recompression should never be attempted
(even if the victim is fully conscious and
equipped with an oxygen rebreather having
a full face mask) because of the following
reasons:
1. The signs and symptoms of DCI are unpredictable
as usually bubbles take time to develop and
other serious manifestations can happen under
water that can lead to serious complications.
2. Lack of proper medical attendance under
water.
3. Recompression tables require a huge stock
of different breathing gases and take long
periods of time which can never be satisfactorily
and safely achieved under water.
The
approach to a diving casualty that needs chamber
recompression has 3 views:
1. Recompress to a pressure (depth) similar
to the depth of the original dive and decompress
according to the time of exposure of that
dive (old French technique).
2. Recompress to a depth that produces a clinically
acceptable improvement (Australian technique),
or recompress to the depth of relief +1 atmosphere
and then decompress according to special tables.
The above 2 methods are not satisfactory because
the choice of treatment tables will depend
upon a lot of variables, which makes it confusing
even for a skilful supervisor since a different
table for each individual case should be worked
out.
3. Recompress to a predetermined fixed depth,
i.e. according to standard recompression treatment
tables.
These
tables are scientifically developed taking
in consideration bubble physics as well as
the effect of gases under pressure, and are
now most accepted by different organizations
worldwide.
A
lot of gases were utilized in the development
of such tables including Air, Oxygen, Heliox
(Helium + Oxygen), Nitrox (Air + Oxygen) and
Trimix (Helium + Nitrogen + Oxygen) or (Helium
+ Hydrogen + Oxygen). The advantages of using
these tables are:
1. They have a relatively high cure rate (up
to 90% when the elapsed time before recompression
is relatively short).
2. They enable the average operator to easily
decide which tables to use according to the
severity of symptoms, prognosis and recurrence
during the different stages of treatment,
(by following given Flow Charts).
3. They require a chamber of a maximum working
pressure of 6 ATA, which is relatively low,
compared to other tables needed to carry out
other higher pressure treatment.
Which
tables to choose?
This will depend entirely on:
*The diagnosis. (Is it Type I DCS, Type II
DCS, Type III DCS or AGE?)
*The initial evaluation. (Severity and Urgency)
*How much time has already elapsed before
getting into the chamber?
*Any change of clinical picture on normobaric
oxygen breathing.
*Response of the patient to chamber treatment
stages, (Recompression, Oxygen breathing and
Decompression). Symptoms can improve, remain
stable, progress or even deteriorate during
the course of the treatment.
Once the treatment table has been chosen,
treatment is conducted by carrying out recompression
and decompression procedures specified in
this chosen table including times and rates
of ascent and descent.
A
flow chart is given to provide a systematic
method for selection, activation and extension
of each individual table, and procedures to
take in case of complications or relapses
during or after the treatment. |
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