Young and not bent

[Dr Deco]

Dear Scuba and Readers:

Will oxygen reduce the severity of the hit if taken a certain amount of time before treatment can begin and severe symptoms appear ?

Yes, oxygen would probably reduce the severity of a DCS “hit” as would any procedure that kept “silent bubbles” from growing into problem-producing ones. This is true of in-water oxygen on deco stops, surface oxygen, long deco stops in the water, or “safety stops” at fifteen feet.

When a nitrogen “hit” occurs, does the "damage" occur suddenly such that possible damage by the remaining nitrogen is negligible? Alternatively, is the converse true that the problem gradually increases in severity? Does DCS progress in some type of fashion dependant on the level of nitrogen remaining in the system?

If it is a “pain-only" form of DCS (“the bends”), there should not be any residual tissue damage. The pain would continue and increase as the bubbles grew in the tissue and then begin to subside after a period of time (hours). Oxygen would help to shorten the time to recovery.

If the problem involves nerve cells , then the situation is very different. Here, the problem is more akin to a “stroke,” and there might not be complete recovery if the nerves actually are starved for oxygen for so long that they die. Prompt recompression treatment for neurological DCS is always recommended to prevent permanent neurological residuals.

Generally, problems of DCS will appear depending on the dose (tissue loads) of nitrogen and the presence of micronuclei. After the problems appear, they will progress depending on the dose or amount of nitrogen remaining in the tissues around those bubbles.

How long does it take for oxygen breathing to start eliminating nitrogen? Is this from the moment its consumption begins? How long before a significant reduction in nitrogen occurs? Is the rate of nitrogen elimination known?

In principle, an increased rate of nitrogen loss occurs from the moment that oxygen breathing begins. In practice, this will depend on the regional blood flow that could be blocked by gas bubbles . This blockage factor is always a problem in delivery of any medicine to an area of the body; an intact blood supply must be present. If gas bubbles hinder the flow of blood, there will be little nitrogen elimination, even if oxygen is breathed. For this reason, recompression therapy is necessary to reduce the size of the blocking gas bubbles. Because bubbles in the smaller blood channels are cylindrical, a doubling of pressure will reduce their length by one half. This can be very important in the reinstitution of blood flow. (This shrinkage is different from that for spherical bubbles where eight-fold pressure increases are needed to reduce the radius by a half.)

The amount of nitrogen lost will depend on the REGIONAL blood supply to the affected area. Bockage by bubbles will play a crucial role and this is quite variable in a microvolume of tissue.

Even though oxygen does not "mask" symptoms of DCS, does it present some potential problems with diagnostics and treatment of DCS?

None of which I am aware. The major difficulty is that treatment may not be sought because the diver believes the situation is now under control. It is possible that another DCS problem could arise. One should really start moving towards a recompression facility while breathing oxygen if the admistration was performed to remit a sign or symptom that has already appeared. True masking agents are aspirin and beverage alcohol - - bad dive buddies.

Genesis mentions emptying the bottle of oxygen (what size?) for a blown deco obligation or rapid ascent. Dr. Paul Thomas mentions breathing from the oxygen bottle for one or two minutes after climbing a ladder or after certain dives. How long should one breath oxygen if one has blown a deco obligation or had a rapid ascent after a deep dive, and shows no symptoms of DCS?

I would suspect that breathing of oxygen on the surface (after climbing a ladder) would need more like ten minutes rather than one or two for a positive effect. I doubt that a hard and fast rule can be easily made for this situation as it is dependent on the dive profile.

If one were to really miss the decompression obligation badly, I would breathe all that I had while returning to a recompression chamber. The chamber might not even save you if the situation were bad enough. Such a terrible situation was described in The Last Dive.

As one can tell, this is a question with many ramifications. If there are further questions, please continue to submit them, and I will endeavor to sort this out. Please remember that there can be some disagreement with my answers, although I believe that the major aspects are correct.

Dr Deco :doctor:

 

[The Iceni]

What you say makes considerable sense, Dr Deco.

Dr Deco once bubbled...
Dear Scuba and Readers:
. . . Dr. Paul Thomas mentions breathing from the oxygen bottle for one or two minutes after climbing a ladder or after certain dives. How long should one breath oxygen if one has blown a deco obligation or had a rapid ascent after a deep dive, and shows no symptoms of DCS? Dr Deco :doctor:

For clarification can I make it absolutely clear that I was trying to emphasise the point that I often use surface oxygen as an added safety factor during the "hidden stop" and it cannot be considered a medication if used in the way I described by any wildest stretch of the imagination.

For clarity can I elaborate?

The circumstances in which I "breath it on the ladder and for a few minutes after the dive" are generally as follows;-

A dive in which I have incurred decompression penalties and properly completed the deco schedule without problem and will have used 100% oxygen for accelerated deco in the shallower stops. I arrive on the boat with a cylinder of oxygen which will, in general, be at least half full (the rule of halves).

Before I use that cylinder for another dive I will need to refill it and it will cost me exactly the same to fill, whether it is completely empty or nearly full. It therefore costs me nothing to use some,or all of the residual oxygen and it can do me no harm. On the contrary it keeps the nitrogen offgassing gradient the same as it was during my shallower stops, during the period of increased micronuclei formation - when climbing the ladder and immediately after. It delays that sudeen reduction in the off-gassing gradient when air is breathed. If you like it is my own mechanism of adding genuine conservatism into my deco schedule without the need to spend any longer underwater.

This must not be confused with "How long should one breath oxygen if one has blown a deco obligation or had a rapid ascent after a deep dive, and shows no symptoms of DCS?"
I was not suggesting, for a moment that this does not constitute a genuine emergency requiring appropriate evacuation and treatment, and apologise unreservably if gave that impression.

That was not my intention

I was using this as an example of how illogical the current legislation is.

For example, should I wish to use the boat's oxygen on a US charter in the way I described, I could not do so unless someone decides there has been an incident. (There is only one oxygen set for emergency use after all.)

Unexpected incidents of DCI are known to occur particularly after multiple dives over multiple days. Methods to reduce the risks include strategies to reduce micronuclei formation, adherance to deco schedules, adequate hydration, proper mental attitude and an improved level of overall physical fitness.

In view of my age, to this I add the prophylactic use of oxygen on reaching the surface following certain of my dives and most certainly feel that surface oxygen should be more readily available and, perhaps, could even be used more routinely after every dive.

Current legislation and established custom and practice makes this highly unlikely.

I do hope that clarifies the point I was making.

 

[Dr Deco]

Dear Dr Thomas:

Thanks for the comments on your posting. I, too, believe that recreational diving would be better served by having oxygen more readily available on board the boat. I would consider it a part of the offgassing and not a medical useage.

At the very least, it would get the divers to think, “Why am I doing this?” They would then realize that the decompression is not finished when they hit the surface.

Thanks for bringing up the use of surface oxygen.

Dr Deco :doctor:

 

[The Iceni]

MikeFerrara once bubbled...
. . . I just got off the phone with DAN. According to them...If O2 is administered in response to a blown dive plan or other incident that would cause concern it constitutes the beginning of treatment

Interesting discussion. Perhaps you asked DAN the wrong question Mike, because it would seem the one thing Pos-tech did was to avoid setting off that very train of events that logically follows admitting to a blown profile.

The number of near misses I have witnessed in scuba diving is considerable and all divers delude ourselves into thinking "so far so good" - as we pass the fifteenth floor.

Sadly, the violation of deco obligations is not uncommon so it is just as well tables are as conservative as they are.

Genesis once bubbled
. . .In other words, if I can surface, grab a NEW bottle of gas, and go BACK to 10', I have not violated the computer!

. . . .I get on the boat, knowing that I blew the profile.

I grab the O2 bottle and consume it.

Since few, unlike Genesis, have this option this seems to suggest that IWR is officially encouraged in preference to onboard oxygen! Odd indeed.

However, one must never forget that we live in the real world. Being the subject of an "incident" feeds club gossip for months after the event. The basis of my contributions to this discussion is to highlight the considerable danger of denial inherent in the current system.

I dread to think what pos-tech has been making of these posts but IMO he was right (and very brave) to start this thread as it has highlighted a major failing of the current "system". I believe he would have asked to use the oxygen if it did not attract the stigma of being labelled as an incident as it currently does. Using that retrospectoscope again, it would most certainly not have caused him any harm on that occassion.

There were two potential DCI casualties. Perhaps they both should have been given oxygen and contact with the emergency services made, regardless of their wishes.

It would certainly help to know why this was not done

 

[Scuba]

This is been a very enlightening thread for me, thanks to all. Besides providing a better understanding of oxygen use and application, it also serves to show what the repercussions can be when in a highly litigous society legal considerations take precedence over medical considerations in medical matters.

Now its time for more questions.

Does nitrogen load above normal but below where DCS symptoms appear cause any type of damage to the body?

For questions below, assume only dive profiles within existing safety guidelines. No violations of any kind.

Given that withing these parameters the incidence of DCS is quite low, how much of an advantage could be gained by taking oxygen at the surface, in the form of lower risk or possibly reduced minor nitrogen damage?

When I surface and my computer shows a full green nitrogen reading, as opposed to yellow or lesser green. (Green being withing the safe specified parameters.) I assume that my risk of DCS is greater than if the meter was only half full. Is the risk or incidence of DCS known when surfacing with a full green nitrogen meter as opposed to a half full green meter? I realize computers use different algorithms. How about the one for the Sherwood Scuba Logic, Dr. Deco, to which you contributed.

After repetitive dives in one day and over serveral days I assume the risk is also higher, as when climbing a ladder with full gear after the dive, or a long, strenous uphill walk with gear on after a beach dive. Are the benefits provided by oxygen in these scenarios worth the effort? Can they be quantified? I realize that every bit helps and there are so many variable involved.

 

[Dr Deco]

Dear Scuba:

Does a nitrogen load above normal but below where DCS symptoms appear cause any type of damage to the body?

It has been debated over the years, and the answer is not final. Certainly, caisson workers and some professional divers can get aseptic bone necrosis. This is in the absence of “the bends.” So it does appear that some problems can be had from “silent bubbles.” As far as recreational diving goes, I have not heard of any confirmed long-term effects.

There are speculative reports concerning some neurological lesions (injuries) in the brain when brain scans are made. It is not certain however that these lesions are from diving. While divers have more “spots” in the MRI or CAT scans, non-divers also have them. Therefore the question arise, are they really from diving. Possible they are age related, or come from who knows what. If they only appeared in divers, the situation would be clearer. But, at the same time, who really wants something bad to be in only the heads of divers?

Given that within these parameters the incidence of DCS is quite low, how much of an advantage could be gained by taking oxygen at the surface, in the form of lower risk or possibly reduced minor nitrogen damage?

I suspect that a large advantage would not be gained from oxygen breathing, unless the diver had a heavy exercise load on the bottom, or strenuous activities on the surface (swimming or climbing ladders). In general, the incidence of DCS is already very low in recreational diving. If you were making several dives in one day for several days, I would consider “hedging my bets” and breathing oxygen.

When I surface, and my computer shows a “full green” nitrogen reading, as opposed to yellow or lesser green. (Green is within the safe specified parameters.) I assume that my risk of DCS is greater than if the meter was only half “full.” Is the risk or incidence of DCS known when surfacing with a full green nitrogen meter as opposed to a half full green meter? I realize computers use different algorithms. How about the one for the Sherwood Scuba Logic, Dr. Deco, to which you contributed.

The risk would be less if the meter showed a reduced nitrogen load or “dose.” One must bear in mind that the reduction might be from a risk of 0.001% to 0.0005%. While it is a fifty percent reduction in risk, it is really trivial in the real world.

The actual risk of diving is not known because one does not know several factors. Laboratory tests can easily tell the incidence because the DCS problem is known, the profile(s) is known and the number of test subjects is known. One has both the numerator and denominator. In addition, one has Doppler bubble detection data to provide some guide as to what was a real “hit.”

When data comes from the field, you do not know how many divers were involved, nor do you know the real profiles. In addition, you do not know the true number of DCS cases. Many divers will get a “hit” in the field and not know it, because they believe that you will be in agony with the “bends.” This is not so; it is often difficult to tell with certainty. [Lab cases can be diagnosed with a “test of pressure.”] As far as field data goes, the only real trustworthy number is the incidence of neurological DCS cases since they present at a chamber for recompression - usually. This field incidence will generally be lower than in a chamber test series. Incidentally, neurological problems are almost never seen in a laboratory setting. Divers do something else in the field; maybe “Valsalva-like” maneuvers. :bomb:

I am not certain about the Sherwood meters. Many are based on the DSAT trials that were performed for the PADI tables (“The Wheel”). The dives and the results were published in a booklet by PADI/DSAT and some manufactures based their computer algorithms on this data, since it had a pedigree traceable to laboratory tests involving more than 1,200 man dives.

After repetitive dives in one day (and over several days), I assume the risk is also higher, as when climbing a ladder with full gear after the dive, or a long, strenuous uphill walk with gear on after a beach dive. Are the benefits provided by oxygen in these scenarios worth the effort? Can they be quantified? I realize that every bit helps and there are so many variable involved

I would believe that the situation is improved with oxygen as the number of dives per day increases. This is because the nitrogen load (“dose”) increases.

While I believe that the may be value with bigger gas loads, I do not know when it has a good benefit/cost ratio. This ratio is always obvious following a “hit” however. It is difficult to quantify because it involves a large laboratory trials with all of the necessary controls. Some aspects of this have been examined with “maximum likelihood statistical methods. If such information exists, DAN would have it. I really doubt that such has yet been assembled. As they say, all it takes is money and that is not yet out there in big amounts. DAN pays for some studies itself, and PADI supports some studies (I believe) with money from the sale of the PADI tables. Much data is collected from DAN Doppler dive trips and computer downloads such as PROJECT DIVE.

Dr Deco :doctor:

 

[Scuba]

This is such a good thread whose title "young and not bent" does not accurately describe its content, that if pos-tech and the regulator do not mind, I would request that it be changed to a name more descriptive of its content, such as oxygen administration or similar, in order to facilitate an archive search in the future.

 

[The Iceni]

Not all scuba shops have the adapters to be ABLE to fill pin-indexed tank valves from their cascade tanks. If you have the adapter, then its no big deal. But if you don't......

This highlights yet another anomaly!

In my fast-response Jeep I use diving cylinders and DIN fittings on all my oxygen sets so I can carry more and refill them at my LDS (medical grade!) much more cheaply.

IMHO Pin index systems are essential in hospital anesthetistic rooms and hired cylinders for domicillary use but consider these valves have no real place in the field, except when there is a real risk harm of using the same regulator on a bottle of toxic gas.

I very much doubt I would ever connect up a cylinder of argon to the oxygen set, but I suppose it has happened!

My Entonox cylinder and set is most certainly staying pin-indexed. ut: