education and awrness
Diving accidents and decompression sickness
Nearly 20+ Dive Accidents Every Year In The Red Sea
What is DCI ?
Decompression illness (DCI) is caused by bubble formation in the blood or tissues after a reduction in ambient pressure. Clinically, DCI may range from a trivial illness to paralysis, loss of consciousness, cardiovascular collapse, and death. Recompression is the universally accepted standard for the treatment of DCI.
Decompression illness (DCI) is the term given to the clinical manifestations of bubble formation in the blood or tissues after a reduction in ambient pressure.1 DCI most frequently occurs in relation to compressed air or mixed gas diving, but it may also arise in aviators after rapid ascent to altitude or cabin decompression, and in astronauts participating in “space walks.” DCI is a collective term covering 2 different problems: arterial gas embolism (AGE) and decompression sickness (DCS). AGE is caused by pulmonary barotrauma, which introduces bubbles into the arterial circulation, and these cause harm through vascular obstruction, ischemia, and stimulation of inflammatory processes that follow damage to endothelium. DCS is caused by evolution of bubbles from dissolved inert gas. These bubbles appear in the veins and vulnerable tissues and may cause harm through mechanical distortion of tissues, pulmonary vascular obstruction, or stimulation of inflammatory processes that lead to tissue edema, hemoconcentration, and hypoxia. Venous bubbles may also enter the arterial circulation via right to left shunts such as a patent foramen ovale. Clinically, DCI has many possible manifestations, ranging from mild constitutional symptoms to sudden loss of consciousness, paralysis, cardiovascular collapse, and death. The widely accepted standard of care is recompression. Recompression involves placing the patient in an airtight chamber, increasing the pressure within that chamber, and administering 100% oxygen. Under these conditions, the partial pressure of any inert gas in bubbles is approximately equal to the ambient pressure in the chamber, whereas the pressure of inert gas in the alveoli is close to 0. Thus, it is possible to greatly enhance the movement of inert gas out of bubbles down a steep diffusion gradient as well as to deliver a greatly increased Po2 to the tissues. At the same time, the volume of those bubbles is directly reduced in accordance with Boyle law (volume of a given mass of gas is inversely proportional to the ambient pressure). Typically, treatments involve pressurization to between 2 and 6 atmospheres absolute (ATA) (203– 608 kPa), for periods ranging from 2 hours to several days. The optimal treatment strategy for differing clinical presentations has not been determined. However, by far, the most frequently used regimen is the United States Navy Treatment Table 6: a 2.8 ATA (284 kPa) maximal pressure, 100% oxygen breathing schedule lasting 4 hours and 45 minutes.4 A review of the effectiveness of the United States Navy oxygen treatment tables suggests complete relief of symptoms in 50% to 98% of individuals, apparently depending on the severity of illness and period of time that has elapsed between development of DCI and recompression. In addition, a number of “first aid” and adjunctive therapies have been applied in the hope of improving rates of complete resolution. The most important target tissues for DCI are the central nervous system and the musculoskeletal system, with musculoskeletal pain being the most common symptom in the early series. More recently, it has been suggested that constitutional symptoms similar to those experienced during viral illness may be a manifestation of DCI.2, Without an objective method of determining whether symptoms are caused by bubble formation, mild symptoms will sometimes result in misdiagnosis. The annual incidence of DCI is not clear but probably varies widely, from low (perhaps 1 in 10,000 dives) among trained recreational divers to high in indigenous underwater harvesters (1 in 245 dives). Severe illness is now uncommon in the developed world, but severe DCI leading to permanent disability or death remains a significant problem for poorly trained indigenous commercial divers in the developing world. In one prospective study, 94.4% of divers reported ever having DCI and 10% had residual signs of spinal injury. Mortality was estimated at 4% of indigenous divers per year in another group.
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Chamber recompression , history and followup
Chamber Recompression Therapy
“No-one who has seen the victim of compressed air illness, gravely ill or unconscious, put back into a chamber and brought back to life by the application of air pressure, will forget the extraordinary efficiency of recompression, or will be backward in applying it to a subsequent case of illness.”
(Robert Davis, 1935)
Diving accidents requiring recompressing divers 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 further or permanent injuries caused by DCI.
Proper application of recompression therapy can abort the mechanisms by which this illness can cause permanent tissue deformation and in many cases the complete resolution of symptoms can be achieved.
An initial evaluation of a diving accident based on onset & severity of symptom, organ systems involved & time course (evolution), will define three degrees (categories) of urgency:
-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 & the hyperbaric physician can make the decision to delay or abort the treatment of a patient in this category.
2
The approach to a diving casualty that needs chamber recompression had 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 result (depth of relief 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.
*These tables are world-wide not used any more though, might be very effective for some cases when prompt recompression takes place.
3. Recompress to a predetermined fixed depth, i.e. according to standard recompression treatment tables.
These tables are now the universally accepted treatment tables as they were scientifically developed taking in consideration bubble physics as well as the effect of different gases under pressure, though a lot of research is still being carried out.
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)
The privileges 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 or recurrence during the different stages of treatment.
3. (With the exception table 8 USN)They require a chamber of a maximum working pressure of 6 ATA, which is relatively low, compared to other chambers required to carry out other suggested treatment tables.
In general, Recompression Treatment has 2 different important mechanisms that will benefit a DCI case:
According to Boyle’s law, the pressure applied per se reduces the size of the bubbles which will increase the partial pressure of the gases involved in bubble formation forcing them into solution in the surrounding tissues and will allow the intravascular bubbles to lodge into smaller capillaries improving symptoms.
The breathing of Hyperbaric oxygen (HBO) will enhance the elimination of the inert gas, promotes oxygenation to hypoxic tissues through dissolving in all body fluids and reduces CNS edema.
3
The tables, which are chosen for recompression treatment in The Red Sea territory, are the U.S. Navy Recompression Treatment Tables (withsome British and German modifications)& Comex Treatment Tables using, oxygen, Nitrox and Heliox as breathing media.
*Tables 1A, 2A, and 3 will not be published here because they are only used in absence of Oxygen and are more or less not recognized any more.
*Table 4 is Air or Air & Oxygen treatment of DCI.
*Table 5 is Oxygen treatment of Pain-only (Type I DCS).
*Table 6 is Oxygen treatment of serious DCI.
*Table 6A is Air & Oxygen treatment of DCI.
*Table 7 is Oxygen treatment of unresolved or life threatening DCI after failure of the initial treatment on table 6A or 4, the table starts upon arrival at 18 meters with a minimum duration of 12 hours on Oxygen at that depth followed by a very prolonged Oxygen decompression schedule.
*Table 8 is a Heliox table used for recompression up to 68 meter for treatment of saturation helium divers DCI.
*Table 9 is a HBO table done at 14 meters for 90 minutes.
*Comex Cx12 table is a shallow oxygen table (12 meters) suitable for treatment of mild and delayed cases.
*Comex Cx30 table is a 30 meters 50 % Heliox table for treatment of serious DCS without the nitrogen load seen in deep air tables.
4
U S Navy Recompression treatment tables 6A, 4 & 7
History and overview:
Table 6A was developed as a very useful treatment table for Arterial Gas Embolism (AGE) in which the case does not contribute any inert gas saturation. The ultimate usage of that table was in the US Navy submarine escape training where candidates went to +/- 60 meters in a simulator and surfaced with the probable lung injury and embolization, they were recompressed directly to 6 ATA (50 meters) and decompressed on that table all way up to the surface successfully and it is the best table to use for such circumstances till today.
But when the Navy suggested the use of that table for serious DCS and AGE super imposed on an element of nitrogen load (happening in the middle or at the end of a dive), the flow chart strictly denoted that you should use the deep air limb ONLY after trial of oxygen at 2.8 ATA (18 meters) which makes some sense as the nitrogen saturation will be a bit less after oxygen breathing at 18 meters even for 20 minutes.
By trial and error, the US Navy figured out that the failure rate of that air table is relatively high compared to shallow extended oxygen tables, so they started to recommend new issues regarding the use of the 6A table as:
*Compress to the depth of relief (or significant improvement), not to exceed 50 meters!
*Once at depth of relief, begin treatment gas (Nitrox or Heliox) if available!
**refer to US Navy diving manual- Volume 5.
Treatment Table 4 is switched to from table 6A (according to the Navy) when it is determined that the patient will benefit from additional time at the depth of relief (for a maximum of 2 hours). The procedure which (in my opinion) will create the same nitrogen super saturation problem or even worse than table 6A, note that these two deep air tables are used only (according to the navy) in initial recompression and are not used at all in the treatment of residual symptoms of DCI.
Now all recent studies encourage avoiding recompression to 50 meters (6ATA) when Air is the only gas available to breathe unless extremely unavoidable and this is because of the fact that the therapeutic potential of O2 at 2.8 ATA are much higher than those of Air at 6 ATA which is explained as follows:
O2 breathing (HBO) will increase oxygenation of tissues and keep the partial pressure of the inert gas in the lungs as low as possible to enhance its elimination from the body minimizing any further contribution, while absorption of excess nitrogen (N2) during recompression on deep Air tables may aggravate the case.
Studies indicated that the lifetime of a bubble should not vary markedly with pressure in excess of 3 ATA.
Bubble reduction in an O2 breathing patient at 3 ATA is 4 -5 times greater than with Air breathing at the same pressure.
With O2 breathing the gas tension gradient from bubble to tissue is maintained optimal throughout the treatment preventing bubble growth.
Hyperbaric O2 breathing is the ultimate prevention of edema caused by hypoxia of the spinal cord.
It has been proven that O2 breathing at 3 ATA (20 meters) is a specific treatment for cerebral edema.
Research studies showed that intra-vascular bubbles will have a length:diameter ratio varying from 1:1 to 30:1 which makes mechanical reduction of bubble size to 1/6 under 6 ATA only applicable to extra-vascular or spherical bubbles. In other words, recompression on deeper tables is beneficial only in certain incidents.
On the other hand initial recompression on deep air tables (6A & 4) was found to cause aggravation (worsening) of symptoms during ascent which was thought to be due to the massive Nitrogen saturation when using these tables (30 – 120 minutes on air at 6 ATA) where nitrogen was the original cause of the sickness in the first place.
Other difficulties of usage of deep air tables include:
prolonged decompression, nitrogen narcosis, DCS for attendants and respiratory distress due to increased air density under pressure especially in patients already having respiratory affection.
So the US Navy officers came up with a huge compromise, which is Treatment Table 7 that is (according to the US Navy manual) considered a heroic measure for treating non-responding severe AGE or life threatening DCS! Table 7 denotes that you should bring the patient to 18 meters aborting any other treatment table including table 6A and table 4 then giving the patient oxygen at 18 meters for at least 12 hours, then decompress accordingly! Is this not a confession from the US Navy officers that low pressure oxygen tables will succeed where deep air tables fail?
So WHY USING DEEP AIR TABLES AT ALL?
5
The following paragraph is taken from the US Navy diving manual in Volume 3 under “the treatment of DCS”, note that there is no mentioning what so ever of the deep air tables.
3-10.6.4 Treating Decompression Sickness. Treatment of decompression sickness is accomplished
by recompression. This involves putting the victim back under
pressure to reduce the size of the bubbles to cause them to go back into solution
and to supply extra oxygen to the hypoxic tissues. Treatment is done in a recompression
chamber, but can sometimes be accomplished in the water if a chamber
cannot be reached in a reasonable period of time. Recompression in the water is
not recommended, but if undertaken, must be done following specified procedures.
Further discussion of the symptoms of decompression sickness and a
complete discussion of treatment are presented in volume 5.
Modern research has shown that the symptoms caused by bubbles depend on their
ultimate location and not their source. Bubbles entering the arterial circulation
from the lung (pulmonary overinflation syndrome) have exactly the same effects
as those arising from body tissues and cells (decompression sickness) that find
their way into the arterial circulation. This means that the treatment of diseases
caused by bubbles is dependent on the ultimate symptoms and symptom severity
and not on the source of the bubbles.
This finding has lead to new treatment protocols in which the initial treatment for
arterial gas embolism and decompression sickness is the same, recompression to
60 fsw. After that, treatment proceeds according to the patient’s condition and
response to therapy. Many agree with the opinion that Direct Bubble Effects are
the cause of symptoms occurring early after surfacing. These cases usually
respond to recompression alone. However, the longer after surfacing that symptoms
appear, the more likely it is that the effect of the bubbles is responsible for
symptoms, rather than the bubbles themselves. In this situation, recompression
alone will be less effective.
6
The following table is the recommended gas mixtures for treatment at different depths taken fro volume 5 US Navy manual:
Table 21-5. High-Oxygen Treatment Gas Mixtures.
Depth (fsw) Mix (HeO2 or N2O2) ppO2
0–60 100% 1.00–2.82
61–100 50/50 1.42–2.02
101–165 60/40 1.62–2.4 (Tables 6A & 4)
166–225 64/36 (HeO2) 2.17–2.8 (Table 8 US Navy)
In both the Royal Navy tables and Comex tables Air treatment tables are absolutely NOT found at all.
6
Which tables to choose for initial recompression?
This will depend entirely on:
*The diagnosis. (Is it TypeI DCS, TypeII DCS, TypeIII DCS or AGE?)
*The initial evaluation. (Severity & urgency)
*The time 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, O2 breathing & decompression) symptoms can improve, remain stable, progress or even deteriorate. You could see a relief or a relapse during any treatment.
*In General, you have to weigh the benefits and draw-backs of the two different benefits of recompression therapy, the pressure per se and the Hyperbaric oxygen and decide what your patient needs more before and during the course of treatment.
The European community of Hyperbaric Medicine (ECHM) during its meeting in 1996 in the 2nd Consensus conference of Hyperbaric Medicine has put the following recommendations:
QUESTION 4 : Which initial recompression modality?
Decompression accidents are true medical emergencies that must benefit from treatment
in specialized centers as soon as possible. A specialized center is considered as a hospital
based facility, having not only a hyperbaric chamber but also a permanent and
adequately trained medical and paramedical staff.
The victims of a decompression accident should be immediately directed from the site of
the diving accident to the closest specialized center (Type 1 recommendation).
Minor decompression accidents (pain only) should be treated with oxygen recompression
tables at 18 meters depth maximum (Type 1 recommendation).
Regarding more serious decompression accidents (neurological and vestibular accidents),
the jury observed that there are presently two acceptable protocols, as neither one has
been proved better by any scientifically valid study to date:
• oxygen recompression tables at 2.8 ATA (with possible extensions)
• hyperoxygenated breathing mixtures at 4.0 ATA.
The choice between the two may depend on personal experience and on local logistics.
However, under no circumstance the un-availability of one of the two accepted modalities
should delay the treatment (type 1 recommendation).
The jury also considered the following optional treatment modalities (type 3
recommendation):
• compression to 6 ATA in case of cerebral arterial gas embolism, with the condition
that this compression is performed using hyperoxygenated mixtures and not
compressed air and that the delay to treatment is not more than a few hours.
• saturation treatment tables in case of persistent symptoms.
Finally the jury recommends that :
• in water recompression should never be undertaken as the initial recompression
modality for a decompression accident (Type 1 recommendation).
• all decompression accidents should be the object of a standardized recording
method aimed at the creation of database for epidemiological studies (type 1
recommendation).
The 7th consensus conference of the same community in 2004 came up with the following recommendation:
** The use of USN 6A table should be limited to cases of CAGE caused by emergency ascent procedure without any previous compressed gas exposure leading to gas tissue supersaturation.
*Only O2 or Heliox mixtures should be used in the treatment of DCS developing after diving with Trimix or Heliox as Air tables are believed to Aggravate the condition on the other hand, Heliox recompression sometimes succeeds when air tables fail in treating serious DCS cases following air or Trimix dives (for further research).
7
Follow-up HBO treatment
Many cases of serious DCI will still show residual symptoms and signs after the initial recompression treatment and will require further treatment in the chamber in the form of Hyperbaric Oxygen (HBO) sessions.
Many tables are used for HBO session after the initial treatment and the choice will depend on:
*Intensity of the residual symptoms.
*Lung status regarding the long exposure of oxygen as in long initial tables.
*The patient’s tolerance to oxygen (CNS sensitivity).
The duration of the treatment (number of sessions) will depend entirely on the estimation of the treating doctor, the prognosis of the symptoms and signs and the lung status vs the benefits of the treatment.
Most popular tables for post recompression HBO are: tables 5, 6 and 9 US Navy tables and Comex Cx12.
Deep air tables are not recommended for HBO by any organization including the US Navy, but anyway these tables are believed not to be as harmful in HBO as they are in initial recompression because after the initial recompression the patient will have no or minimal amount of inert gas in his body, and the efficiency of these tables in HBO is falsely attributed to the deep air limb while they are entirely due to the extended period of oxygen breathing at shallower depths.
The next paragraph is taken from the US Navy manual Volume 5
21-6.5 Treatment of Residual Symptoms. After completion of the initial recompression
treatment and after a surface interval sufficient to allow complete medical evaluation,
additional recompression treatments may be instituted. For persistent Type II
symptoms, daily treatment on Table 6 may be used, but twice-daily treatments on
Treatment Tables 5 or 9 may also be used. The treatment table chosen for re-treatments
must be based upon the patient’s medical condition and the potential for
pulmonary oxygen toxicity. Patients surfacing from Treatment Table 6A with
extensions, 4, 7, or 8 may have severe pulmonary oxygen toxicity and may find
breathing 100 percent oxygen at 45 or 60 feet to be uncomfortable. In these cases,
daily treatments at 33 feet may also be used. As many oxygen breathing periods
(30 minutes on oxygen followed by 5 minutes on air) should be administered as
can be tolerated by the patient. Ascent to the surface is at 20 feet per minute. A
minimum oxygen breathing time is 90 minutes. A practical maximum bottom time
is 3 to 4 hours at 33 feet. Treatments should not be administered on a daily basis
for more than 5 days without a break of at least 1 day. These guidelines may have
to be modified by the Diving Medical Officer to suit individual patient circumstances
and tolerance to oxygen as measured by decrements in the patient’s vital
capacity.
The following paragraph is the last recommendation of the European jury in the second Consensus of the ECHM in 1996.
QUESTION 6: Which treatment protocol for persistent symptoms
after the initial recompression ?
The Jury concluded that there are no scientifically valid data to allow for a recommended
approach to this issue.
More studies are necessary as well as the adoption of standardized evaluation methods.
Concerning spinal cord injuries, a specific scoring system (such as the ASIA
scale) is
recommended for pre and post treatment evaluation and during the two-year follow up.
Randomized prospective studies are needed to better evaluate the efficacy of hyperbaric
oxygen therapy and of rehabilitation before any protocol can be proposed or
recommended. However, in analogy with any other neurological injury, rehabilitation
should be started as soon as possible (Type 1 recommendation).
Hyperbaric oxygen treatment is recommended to a maximum of 10 treatment sessions
after the initial recompression, in combination and during rehabilitation therapy. The
continuation of HBO therapy can be accepted if objective improvement is observed under
pressure during the hyperbaric treatment sessions (Type 3 recommendation).
Prepared by Dr. Hossam M. Nasef
Hyperbaric Consultant Red Sea