In-Water Treatment of DCS

By Dr. Sawatzky

Disadvantages of In-Water Treatment of DCS
If an in-water treatment is attempted with air, the diver is absorbing more nitrogen the longer he stays in the water. The cause of DCS is excess nitrogen. Therefore, at first glance, it makes absolutely no sense to put a diver back into the water on air if he is bent. However, the problem is not really the nitrogen, it is the bubbles that have formed because the diver surfaced too rapidly. Therefore, the increased pressure of going back into the water will reduce the volume of the bubbles and could eliminate the signs and symptoms of DCS very rapidly. A very slow ascent might allow the diver to off gas the excess nitrogen, including the extra nitrogen absorbed during the treatment, and surface without signs or symptoms. The largest problem with in-water treatment with air is that the treatment times have to be extremely long (up to 72 hours) and this is a practical impossibility for most divers. Therefore, I do not believe that there are any circumstances where in-water treatment with air should be attempted.

The second disadvantage of in-water treatment of DCS is hypothermia. The diver is resting in the water and after several hours, could be very hypothermic. Hypothermia reduces the blood flow to the arms and legs and thereby reduces the elimination of nitrogen, counteracting the effect of the treatment. This is especially true of in-water treatment with air as the treatments can be extremely long and therefore, in-water treatment with air (if appropriate anywhere) is restricted to warm water. However, if the in -water treatment is conducted on oxygen, the treatment times can be quite short (two to four hours). In addition, if the dive was conducted in cold water, it is reasonable to assume that the divers will have appropriate thermal protection. There is a large difference between the active diver during a dive and the resting patient during a treatment. The diver would have to be warm at the end of a two hour dive to consider a three hour treatment. Any less thermal insulation and the patient would be too cold for the treatment to be effective or safe.

If the treatment is conducted with oxygen, we also have to face the problem of oxygen toxicity. If the diver has a seizure while in the water, they have a high chance of dying. The probability of this happening can be reduced by having the diver wear a full face mask, having a tender continuously with the patient, limiting the maximum partial pressure of oxygen, and interrupting the oxygen with air breaks. These manoeuvres will reduce but not eliminate the risk. A second problem with conducting oxygen treatments is that the appropriate equipment must be oxygen clean and there must be a sufficient supply of oxygen to complete the treatment. Conversely, if the treatment has to be cut short because of a lack of oxygen, the diver and tender will be able to safely surface. In-water treatment tables using air often result in the patient and tender accumulating significant decompression obliga tions so that if they had to unexpectedly surface, they could be much worse off than when they went into the water. To summarize, the advantages of using oxygen for in-water treatment are that it increases nitrogen elimination, avoids extra nitrogen uptake, increases delivery of oxygen to hypoxic tissues, reduces the depths required for the treatment, and reduces the length of the treatment.

Another problem with in-water treatment of DCS is the difficulty the patient might have evaluating their signs and symptoms. The patient is in a weightless environment and it is very difficult to assess muscle power. The patient will be in a wet or dry suit and it will be quite difficult to assess any sensory changes. In addition, it will be quite difficult for the tender to monitor the patient. Communications will be problematic. However, good use of underwater slates will help and underwater communications are easy to fit into full face masks.

The underwater environment has its own unique dangers. There is always the possibility of the patient drowning (impossible in an air filled chamber). There may be dangerous marine life or strong currents. The surface environment must also be taken into consideration. Night will fall, waves and currents might increase, a storm might move in, the surface support staff might get seasick, etc.

Finally, to consider in-water treatment of DCS, you also will require someone on site who is competent to assess and treat DCS.

Advantages of In-Water Treatment of DCS
The primary advantage of in-water treatment of DCS is immediacy. There is no question that the shorter the time delay between the onset of signs or symptoms of DCS and recompression, the better the results. In fact, a good argument can be made that early DCS is a quite different disease process than late DCS. When symptoms of DCS first appear, it is commonly believed that bubbles have just formed and that the bubbles are directly causing the signs and symptoms. There is minimal tissue damage and there has not been time for many of the complex biochemical changes seen later in DCS to occur. In addition, experience has shown that when a diver is treated shortly after the onset of DCS, the signs and symptoms usually resolve during the press to 60 fsw (18 msw) or very shortly after arrival at depth. This supports the vital effect of pressure in treating DCS shortly after onset.

Conversely, when the signs and symptoms of DCS have been present for several hours or even days, the press to 60 fsw (18 msw) often has little effect. In these cases, resolution of the signs and symptoms tends to occur slowly during the treatment table. In resistant cases and cases with long delays before treatment, TT7 (minimum 36 hours in a chamber) has sometimes been shown to be successful. It is believed that these cases have suffered tissue damage, blood flow is often compromised, and many bio chemical changes have undoubtedly taken place. These observations suggest that treatment of delayed DCS requires long expo sures to increased partial pressures of oxygen and that the pressure per se has less effect. Therefore, it makes sense that immediate recompression might result in rapid resolution of the signs and symptoms of DCS.

International Experience with In-Water Treatment of DCS
There are two large groups of divers who have extensive experience with DCS and in-water treatment. They are the black coral divers of Hawaii and the pearl shell divers of Australia. These groups are very poorly trained, often do several dives a day to depths as deep as 350 fsw (105 msw, on air) and are diving in fairly remote locations. Not surprisingly, they have many cases of DCS and they have developed in-water treatment by trial and error. One study of 527 cases of DCS resulted in 88% cure and 9% such minor symptoms that further treatment at a chamber was not sought (the signs and symptoms completely resolved in two days). Only three percent of cases ended up being treated in a chamber. The secret to their success seems to be getting back into the water and under pressure in less than five minutes. They are usually diving in very warm water (by Canadian standards).

In-Water Treatment Tables
The initial in-water treatment of DCS was to grab two tanks of air and go down until the pain was gone. The diver then stayed at depth for a while and came up slowly. If the pain returned, they went back down. The initial depth was usually more than 60 fsw (18 msw) and surprisingly, the treatments where often successful. However, some of these treatments were as long as 72 hrs!

The first formal in-water treatment table was developed in Australia in 1970. The patient would go to 30 fsw on 100% O 2 for 30, 60, or 90 minutes depending on the seriousness of the symptoms and the response to treatment. They would then ascend at a rate of four minutes per foot (one meter every 12 minutes) to the surface. Once on the surface, the patient would breath oxygen for one hour, then air for the next hour, back and forth for 12 hours (there was a high rate of recurrence if the surface oxygen was skipped). If symptoms recurred during the ascent, a 30 minute stop was inserted and then the ascent continued. This method has been widely used with good results, including very serious cases while arranging transport. The symptoms usually continue to improve during ascent. This table requires about 200 cubic feet of oxygen for the patient and 200 cubic feet of air for the tender.

The Hawaiian Method is derived from the Australian table. The patient is taken to the depth of relief plus 30 fsw to a maximum of 165 fsw, on air. They stop at that depth for 10 minutes and then ascend, stopping every minute to assess the patient and taking at least 10 minutes to get up to 30 fsw. If the patient has return of symptoms during ascent, they go 10 fsw deeper for 5 minutes and then resume ascent. Upon reaching 30 fsw the patient goes on oxygen for 60 minutes (Type I) or 90 to 120 minutes (Type II). The patient is then brought slowly to the surface and breathes oxygen until a diving medical officer can be consulted. The table can be interrupted to allow evacuation to a chamber. The biggest problem with this table is the deep air spike. It requires deep and therefore, usually exposed water.

The US Navy developed an in-water treatment table for use with rebreathers. The patient was taken to 30 fsw for 60 or 90 minutes (100% O2, 60 minutes for Type I, 90 minutes for Type II DCS). They then ascended to 20 fsw for 60 minutes and 10 fsw for 60 minutes. On the surface, the patient continued on oxygen for a further three hours. There is some concern with the rapid depth changes and little experience with this table.

Conclusion
In-water treatment of DCS with oxygen is a viable option in well prepared teams diving in remote locations. However, I do not believe recreational divers should ever attempt in-water treatment and the vast majority of technical divers are equally unpre pared. There are several factors that have to be taken into consideration before in-water treatment should be undertaken. The seriousness of the symptoms, the likelihood of LOC, the risk of hypothermia, and the environment. In addition, all the required equipment must be available and the personnel on site must have the appropriate training and knowledge. Otherwise, in-water attempts at treatment will result in worse outcomes.