In this section you will find information on:

What do we treat?
How does it work?
The treatment tables

What do We Treat?

 

What we treat is Decompression Illness (DCI) of course but a bit more in details, what are we trying to do? Well, depending on factors such as delay between symptoms onset and treatment, we will not always be facing the same problem. To adapt to the situation, a range of Treatment tables is available (UNSTT6, USNTT5, Comex 30 and more)
The root of the problem is of course an over bubble formation, in turn creating problems. So most divers believe that a recompression chamber is used to crush the bubbles and destroy them. In fact this is not the case. When a diver reports his illness fast enough to be treated in the same day as the symptoms onset, yes we might be working with the bubbles. However, if the inured diver did not come straight to the chamber and preferred to deny the problem for some days, then most likely the bubbles have already been dissolved anyway by the body, which doesn’t mean that the injured diver feels better. In that case, since there are no more bubbles present, we are working on the injuries created by the bubbles instead, which is the biggest problem. This is why the faster a diver gets checked and treated if needed, the less time the bubbles have to create injuries and the faster the recovery. One of my colleagues used to compare this to a gunshot wound, the bubble being the "bullet" and the "wound" the damage done by the bubbles. Now the question is, if you ever get shot and the bullet does not stay in your body, would you just go home and keep on with your day or would you seek first aid?
Well, this is the exact same thing that happens inside your body when you have some symptoms of DCI. The symptoms tell you that you might have been shot by a bubble. It is then your call to let the damage go on or go to seek first aid to the local multi-place chamber facility.

 

How Does it Work?

 

Again, depending on how fast the injured diver makes his/her way to the examination room of the recompression facility after the symptoms onset and the severity of the symptoms, the choice of treatment will vary.
But the general idea is basically the same for all. The treatments will try to get rid of the excess nitrogen as fast as possible. To do so, the injured diver will be given 100% oxygen to breathe through a mask. Now where the chamber comes handy is that if we add pressure, the injured diver’s body will be able to absorb even more oxygen with every breath thus eliminating nitrogen faster (treatment of the "bullet"). In the mean time, oxygen speeds up the metabolism and help the creation of new blood vessels to the oxygen deprived areas of the body (treatment of the "wound").
But oxygen breathed under pressure can be toxic, just like any drugs and need to be monitored. This is done by limiting its inhaled partial pressure, which should not exceed 3 atmospheres when breathed in a recompression chamber (1.4 to 1.6 atm when breathed underwater!).
So no, an injured diver is not recompressed to the depth he/she was diving the day of the injury. The depth of treatment is actually dictated by the oxygen partial pressure in the gas mixture inhaled by the injured diver in the chamber (<3 atm).
This is why treatment protocols for DCI typically recompress the injured diver to 18 meters of sea water (60 Feet) where he can breathe pure oxygen under a partial pressure of 2.8 atmospheres, just under the maximum allowed of 3 atm. Why not treating shallower or deeper? Shallower would not provide as much oxygen to the injured diver’s body, limiting the outcome of treatment and increase the possibilities for long term sequela. On the other hand, treating deeper is possible in specific cases that might benefit from it despite the added risk due to greater depths. But this will necessitate the use of mixed gases as you saw already that while breathing pure oxygen the maximum depth was of 20 meters. In that case, a mixture of oxygen and helium will be used at a concentration of 50/50, allowing deeper treatment profiles.

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The Treatment Tables

There are different organizations who designed treatment. The treatment tables mostly used today in hyperbaric medicine worldwide have been designed by the US Navy over many years of both experience and experimentations. The French company Comex has also developed treatment tables and one of them is still used for deeper treatments up to 30 meters of sea water (100 Feet). The Tables dictate the duration of treatment, treatment pressure (ie depth) the gas to be breathed and the descent/ascent rates.

US Navy Treatment Table Six: The most often used initial treatment protocol is the US Navy Treatment Table Six.The USNTT6 is initiated by pressurizing the chamber to 60fsw or 3 atmospheres and breathing oxygen for intervals of 20 mins oxygen and 5 mins air. Later the ascent begins on pure oxygen until the next static depth (30fsw) - another intermittent gas period takes place before the final ascent to surface on oxygen. The length of the USNTT6 is 4 hours 45 minutes. This table can be extended an additional 50 mins at 60 fsw and 150 mins at 30 fsw if necessary. For this table and the USNTT 5 the ascent rate will not exceed one foot per minute and descent will take place at 20 feet per minute.

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US Navy Treatment Table Five: The USNTT5 is a shorter table, it follows the same trend of pressure, oxygen, oral fluid and air but its length is only 2 hours 15 minutes. It is mainly used as follow up treatment to the USNTT6 to treat any residual symptoms or “Wash Out” the patient’s system along with providing oxygen therapy to damaged areas of the body.

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Comex 30 Treatment Table: The Comex 30 Treatment table is used in more severe cases in the event the injured diver keep deteriorating while already at 18 meters (60ft) after starting with a treatment table six. In that case, there is no choice but to descend deeper to find the point of relief. To do so, the breathing gases introduces into the injured diver’s bask will have to be switched to a Nitrox but preferably Heliox mixture to prevent a central nervous system oxygen toxicity. Additional precautions will have to be taken for the tender accompanying the diver as he/she will be subject to nitrogen narcosis while breathing air at 30 meters (100ft). The second case where this treatment table can be beneficial is when an injured diver is recompressed very soon after symptoms onset (a few hours). At this time, compressing the bubbles still provides better improvement. The graph below shows a modified version of the Comex 30 table where all the oxygen breathing part of the table is based on the US Navy Treatment Table Six, which allows for more flexibility between the tables and eliminate possible mistakes by falling back on a profile operators are used to.