I want to second the distinction between In Water Recompression (IWR) and completing an omitted decompression stop and clarify the difference.
The US Navy tables include provisions for omitted decompression as did PADI when I certified in 1985 (the PADI tables at that time were 140' versions of the US Navy tables with provision for decompression not requiring a stop greater than 10 ft as well as provisions for omitted decompression.)
The US Navy Ommitted Deco Procedure for ommitted or interupted stops shallower than 20 ft was:
1. If the diver can be returned to the ommitted stop within 1 minute, he could complete the normal decompression stops with a 1 minute extension of the omiited stop. (That basically meant ascending, getting a tank or surface supplied reg handed to them in the water and immediately descending, then adding a minute to the interupted stop to make up for the missed minute.)
2. If the diver required more than 1 minute to return to the stop, he had to continue to be symptom free and then repeat the 20 ft and 10 ft stops with the times multiplied by 1.5.
For omitted or interrupted stops greater than 20 ft:
1. The diver must be symptom free and return to the stop in less than 5 minutes, then must:
A. Repeat all stops below 40 ft,
B. Stop at 40 ft for 1/4 the omitted 10 ft stop time
C. Stop at 30 ft for 1/3 the omitted 10 ft stop time
D. Stop at 20 ft for 1/2 the omitted 10 ft stop time
E. Stop at 10 ft for 1 and 1/2 times the omitted 10 ft stop time
If the diver showed any signs or symptoms of DCS, chamber recompression was required. In practice, the US Navy did not allow decompression dives unless an on board recompression chamber was available. So in practice, this procedure would only be used in the rare event that a decompression dive was required for some exceptional cuircumstance.
The PADI omitted deco procedure was limited to missed deco stops of 10 ft (their table did not allow for stops deeper than 10 ft), was generally more conservative (as it used a modified "greater than 20 ft" US Navy protocol), and consisted of the following:
1. Be symptom free
2. Return to the water in less than 5 minutes
3. Stop at 40 ft for 1/4 the omitted 10 ft stop time
4. Stop at 30 ft for 1/3 the omitted 10 ft stop time
5. Stop at 20 ft for 1/2 the omitted 10 ft stop time
6. Stop at 10 ft for 1 and 1/2 times the omitted 10 ft stop time
So essentially, if you have DCS symptoms it is no longer ommitted decompression but rather in water recompression which is an entirely different thing.
If you are using air for IWR, the depth needed for effective treatment is 165 ft and the time required will be 5 hours. This makes the whole enterprise very difficult to do in anything other than warm water with good visibility, little or no current, etc. It will also require an attendent and the 165 ft initial depth makes narcosis for both the patient and the attendent a significant risk factor.
If this is not bad enough already, the procedure carries the risk of making the DCS hit worse and there is no way to abort the procedure half way through, which could get interesting if a storm blows in an hour or two into the 5 hour procedure. It is basically not a workable proposition to do it on air.
An alternative IWR treatment was develped in the 1970's using oxygen. This requires 100% O2 starting at 30 ft and a total time of 3 hours in water. There is an obvious risk here of oxygen toxicity and a full face mask is required for the patient. An attendant is required as is an O2 supply fort he patient adequate for 3 hours and the same potential for hypothermia and the resulting limitation to warm water remains.
Also, given the precise and very gradual ascent rates required, it is recommended that the patient have a bar or trapeze arrangement to sit on that can be precisely raised at the required times by the surface support staff.
The good news is that the procedure is not likely to make the divers condition worse and it can be aborted at any time. However the requirements of IWR with 100% O2 make it a procedure that definitely has to be precontemplated with the neccesary O2, equipment, planning, schedules and staff assembled and trained in advance. So it is possibly an option if you are doing expedition diving in the south pacific somewhere a long way from a chamber and have planned for this contingency. It is not a viable option for a recreational diver who is within several hours of a chamber.
In short, an ommitted deco procedure is a valid option IF AND ONLY IF:
1 The diver is REALLY symptom free (as opposed to just being in denial)
2. The surface interval is LESS THAN 5 MINUTES
3. The diver knows what he or she is doing
4. The diver has adequate surface support and
5. The diver has a BUDDY IN THE WATER to get him to the surface in case something goes wrong.
IWR is not, in my opinion, a valid option for a recreational diver.
The only generally accepted procedure for a recreational diver who has symptoms of DCS is to put the diver on 100% O2 as quickly as possible and transport the diver to a hospital as soon as possible. In some mild DCS cases, the symptoms may resolve on their own with administration of 100% O2, but the diver still needs to seek medical treatment.
