beche de mer
Contributor
Are there standard deco schedules for the treatment of DCI, or is each case assessed individually and a schedule prescribed according to the nature and severity of symptoms present?
deco prescription
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The US Navy developed standard treatment tables many years ago. The most commonly used is known as the "Table 6"- it is a 6 hour treatment table. This can be extended as needed.
Don Burke
Contributor
Here is an explanation that even an old squid like me was able to figure out:
http://www.sssnetwork.com/thai_treatment.htm
http://www.sssnetwork.com/thai_treatment.htm
OP
beche de mer
Contributor
Thanks for the info.
Would there be any circumstances in which you might deviate from these schedules?
e.g. in the book The Last Dive, a buddy pair made a direct ascent to surface from a horrendous depth, totally forgoing a huge deco obligation. They collapsed immediately and were almost fizzing.
In that situation, would you recompress to deeper than 60 fsw?
Were tables 5 and 6 arrived at empirically? Have there been controlled clinical trials comparing them to other schedules?
Would there be any circumstances in which you might deviate from these schedules?
e.g. in the book The Last Dive, a buddy pair made a direct ascent to surface from a horrendous depth, totally forgoing a huge deco obligation. They collapsed immediately and were almost fizzing.
In that situation, would you recompress to deeper than 60 fsw?
Were tables 5 and 6 arrived at empirically? Have there been controlled clinical trials comparing them to other schedules?
Don Burke
Contributor
I've been assigned to several commands with chambers and was given briefs on what a manager needed to know.
The nuts and bolts of it was explained to me as:
1. Press the patient until he gets relief from the symptoms.
2. Figure out where you need to be on decompression and execute that plan.
I don't know how the tables were derived. I do know they have been used quite a bit and I doubt they have gone untested since outfits like Duke and EDU do pressure testing all the time. They are for someone who is at 1ATM and feeling symptoms, not someone freshly bent and in danger of dying.
Saving a diver could involve assuming saturation and using those tables. As a manager, I was told to figure two days for the first 100 feet and a day for each additional 100 feet. The actual time is based on more complex things, but that was good enough for a pencil pusher to work with.
For the Rouse's, I would expect the chamber operator to go until the diver got relief or he ran out of chamber pressure. Many chambers are only rated to 3atm total pressure, so 66 feet is all you get.
When I was on a submarine tender, our chamber was mainly used for carbon monoxide poisoning treatment. The couple of hospital chamber people I have talked to mostly use them for hyperbaric oxygen treatment for wounds. Treating divers doesn't happen as often as I expected.
You're at the ragged edge of what I know about these things. If you wnat to pursue this, I'd start with the U.S. Navy Dive Manual and build up a list of questions for the folks at your nearest treatment facility.
Dr Deco
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Dear beche de mer:
Treatment
The current treatment tables are replacements for the old air treatment tables used until the early 1950s. The air tables frequently (about one half of the time) left the individual will residual DCS and a new treatment was sought. The use of oxygen was the turning point. This allow pressure to be applied, oxygenate hypoxic tissue, while at the same time, it allowed the maximal outward gradient for the release of inert gas in the bubbles.
The treatment pressures were based on the maximum pressure limits to generally prevent oxygen seizures. The treatment durations were based on limits to pulmonary and CNS toxicity . The air breaks were added to further mitigate the problems of oxygen toxicity. Provision was made for the extension of the table (USN 5 extended to USN 6) is the situation warranted it.
Animal experiments indicated that applying greater pressure would help move a trapped free gas phase through the capillaries. The 160-fsw pressure pulse was then added onto the USN schedules. If there were signs of neurological DCS, then this additional pressure (with air) could be applied.
In the recent two decades, it has become customary to repeat the treatments for several days until improvement in the signs and symptoms of DCS reach a plateau.
Testing
To my knowledge, the tables have not been tested to compare one pressure or time duration with another. People have looked at the initial 160 fsw spike with air or helium and there is a bit of a controversy.
Different countries, and commercial groups also have their own treatment schedules. Additionally, there are saturation treatments available for chamber use where the infrastructure exists (mixed gas capability, gas analysis, scrubbing, etc).
What Works?
It is my understanding that if an individual with CNS problems is recompressed within about four to six hours, it matters little what schedule is used, as they all will be found to be efficacious. If one waits longer than about six hours, then it matters little which is used, as none will be found to be particularly effective
The Last Dive
I would suspect that surfacing from that depth (about 200 fsw) having spent that amount of time below would have presented a situation where only immediate recompression would have given them any chance at all - and then only possibly. No repress capabilities existed on the boat.
Dr Deco :doctor:
Treatment
The current treatment tables are replacements for the old air treatment tables used until the early 1950s. The air tables frequently (about one half of the time) left the individual will residual DCS and a new treatment was sought. The use of oxygen was the turning point. This allow pressure to be applied, oxygenate hypoxic tissue, while at the same time, it allowed the maximal outward gradient for the release of inert gas in the bubbles.
The treatment pressures were based on the maximum pressure limits to generally prevent oxygen seizures. The treatment durations were based on limits to pulmonary and CNS toxicity . The air breaks were added to further mitigate the problems of oxygen toxicity. Provision was made for the extension of the table (USN 5 extended to USN 6) is the situation warranted it.
Animal experiments indicated that applying greater pressure would help move a trapped free gas phase through the capillaries. The 160-fsw pressure pulse was then added onto the USN schedules. If there were signs of neurological DCS, then this additional pressure (with air) could be applied.
In the recent two decades, it has become customary to repeat the treatments for several days until improvement in the signs and symptoms of DCS reach a plateau.
Testing
To my knowledge, the tables have not been tested to compare one pressure or time duration with another. People have looked at the initial 160 fsw spike with air or helium and there is a bit of a controversy.
Different countries, and commercial groups also have their own treatment schedules. Additionally, there are saturation treatments available for chamber use where the infrastructure exists (mixed gas capability, gas analysis, scrubbing, etc).
What Works?
It is my understanding that if an individual with CNS problems is recompressed within about four to six hours, it matters little what schedule is used, as they all will be found to be efficacious. If one waits longer than about six hours, then it matters little which is used, as none will be found to be particularly effective
The Last Dive
I would suspect that surfacing from that depth (about 200 fsw) having spent that amount of time below would have presented a situation where only immediate recompression would have given them any chance at all - and then only possibly. No repress capabilities existed on the boat.
Dr Deco :doctor:
OP
beche de mer
Contributor
Thanks for the information guys. That has really improved my understanding of recompression treatment.
Dr Deco - if I understand you correctly, if there are focal neurological signs, a 160 fsw pulse is applied to squash the bubble.
At what stage of the treatment would that be done? The beginning I would guess. How long is the pulse applied, and how quickly would you then ascend to 60 fsw?
Why only 160 fsw? You could probably get 300+ fsw before oxygen CNS toxicity became an issue. Is it the physical limitations of the chamber, or are there other considerations?
Dr Deco - if I understand you correctly, if there are focal neurological signs, a 160 fsw pulse is applied to squash the bubble.
At what stage of the treatment would that be done? The beginning I would guess. How long is the pulse applied, and how quickly would you then ascend to 60 fsw?
Why only 160 fsw? You could probably get 300+ fsw before oxygen CNS toxicity became an issue. Is it the physical limitations of the chamber, or are there other considerations?
Dr Deco
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Dear B D Mer:
It is my understanding of the story that when researchers t the UN Naval Medical Research Institute studied bubble passage through capillaries, they noted that the bubbles became smaller with increasing pressure. When the applied pressure reached 100 fsw, the bubbles (actually of sausage-like shapes in the blood vessels) then moved from the arterial side, through the capillaries and into the venous system.
Because the US Navy already had a 160-fsw treatment table (from van der Aue, 1945), it was easy to get approval for this pressure. Goodman and Workman simply recommended that an older 160 fsw pressure be added to the new 60 fsw oxygen treatment tables. Thus, the depth was chose for administrative convenience.
This pressure pulse is applied initially and held for 30 minutes and segues to the 60 fsw oxygen table without coming to the surface.
There are some cases where deeper depths might be required, e.g., blowups. Current treatment is aimed at the application of pressure with the addition of oxygen. Sixty feet is generally sufficient for scuba problems. In the case of the Rouses (The Last Dive), the son was taken to the limit of the chamber, but by this time, other problems were developing, probably from the interactions of blood with the bubbles.
Dr Deco :doctor:
It is my understanding of the story that when researchers t the UN Naval Medical Research Institute studied bubble passage through capillaries, they noted that the bubbles became smaller with increasing pressure. When the applied pressure reached 100 fsw, the bubbles (actually of sausage-like shapes in the blood vessels) then moved from the arterial side, through the capillaries and into the venous system.
Because the US Navy already had a 160-fsw treatment table (from van der Aue, 1945), it was easy to get approval for this pressure. Goodman and Workman simply recommended that an older 160 fsw pressure be added to the new 60 fsw oxygen treatment tables. Thus, the depth was chose for administrative convenience.
This pressure pulse is applied initially and held for 30 minutes and segues to the 60 fsw oxygen table without coming to the surface.
There are some cases where deeper depths might be required, e.g., blowups. Current treatment is aimed at the application of pressure with the addition of oxygen. Sixty feet is generally sufficient for scuba problems. In the case of the Rouses (The Last Dive), the son was taken to the limit of the chamber, but by this time, other problems were developing, probably from the interactions of blood with the bubbles.
Dr Deco :doctor:
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