Can we infer DCI before symptoms develop?

[Bubbletrubble]

@DevonDiver: The excerpt from PADI TecRec Instructor Manual addresses a missed deco stop...not a "too fast" ascent or a missed safety stop.

I hear what you're saying with regard to being proactive versus reactive. I'd argue that your "proactive" measure is adding unnecessary risk with questionable benefit. With a too-fast ascent and/or missed safety stop, the diver is already committed to a suboptimal decompression, so at that point all actions are "reactive."

FWIW, the vast majority of recreational dives throughout the world are conducted without access to a "drop tank" at safety stop depth. I don't think you can assume access to one when making "general rules of thumb" regarding missed safety stops for recreational divers.

I'm sorry, but I don't find your other arguments (with respect to re-descending to complete a missed safety stop) very persuasive.

Who cares about clean?...it's an emergency procedure... if it happens, it has happened.... you can sit and bubble, or you can attempt to save yourself. As we've already agreed; it is situationally dependent though (as it is for a recreational diver).

To be clear, you are considering a missed safety stop an emergency, right?
Honestly, I don't know if many people would agree with you.

 

[DevonDiver]

@DevonDiver: The excerpt from PADI TecRec Instructor Manual addresses a missed deco stop...not a "too fast" ascent or a missed safety stop....

I was addressing your comment: "I'm not a tech diver, but I'm aware that tech divers are concerned with the quality of off-gassing on every dive. How "clean" does your deco look if you surface and then re-descend to do a missed safety stop?" It was to explain how technical divers might address that situation and demonstrates the veracity of re-descent in some instances.

If such procedures are adopted by technical divers, who are heavily saturated, then why wouldn't it be applicable to recreational divers who are far less saturated?

To be clear, you are considering a missed safety stop an emergency, right?

Apologies - talking at cross-purposes. The degree of 'urgency' (emergency) applied to any missed stop is going to be dictated by the relative factors involved with the dive. Obviously, for tech divers, missing stops is a pretty sizable problem. Generally, it isn't a problem for recreational divers - unless they can attribute certain other risk factors into the equation - a fast ascent, a particular deep dive, a multi-day repetitive dive schedule, cold water etc etc.

If there's low risk of DCS, then there is low risk of complications from re-descent.

If there's high risk of DCS, then there is high risk in not re-descending (within finite time-scale)

 

[Bubbletrubble]

If such procedures are adopted by technical divers, who are heavily saturated, then why wouldn't it be applicable to recreational divers who are far less saturated?

That's a good question.
Is it the prevailing opinion of the tech diving community that a missed safety stop warrants re-descent?
If so, that's interesting. I would think that with greater nitrogen loading (or being "heavily saturated" as you mentioned) comes greater risk of DCS. Combined with the possibility of bubble-pumping and other issues with re-descending to do a missed safety stop, I'm somewhat surprised that the marginal benefit of re-descent is worth it.

If there's low risk of DCS, then there is low risk of complications from re-descent.

If there's high risk of DCS, then there is high risk in not re-descending (within finite time-scale)

I'm really not interested in the absolute level of risk -- it's more about the comparative risk. More specifically, it's certainly possible that even a "low risk of complications" associated with re-descent is still greater than remaining on the surface.
I don't think I'm going too far out on a limb by saying that a missed safety stop, in and of itself, presents very little additive risk of DCS.

 

[PfcAJ]

What you're calling type 1 DCS is what the PADI courses call DCS. What you're calling type 2 DCS is what the PADI courses call a lung overexpansion injury. The two taken together are called DCI.

DCS according to PADI's definition is nitrogen bubbles coming out of solution, caused by ascending too quickly. A lung overexpansion injury has nothing to do with nitrogen coming out of solution; rather, it's due to ascending while breath holding. One or more of the alveoli burst, allowing the air in the lungs to escape the lungs and go into the surrounding tissue. If the surrounding tissue that the air goes into is an artery, and the air travels along the artery, it's an arterial gas embolism.

Regarding the practice of re-descending in order to recompress, PADI teaches that this is not effective because, once you've been bent, the time it takes to recompress to undo the damage is hours, and in a diving situation you don't typically have that many full cylinders available, and that much time underwater would result in hypothermia. This is only done in extremely remote locations where a hyperbaric chamber is unavailable, and according to PADI should only be done with special training.

This principle is nicely illustrated in a recent post by an experienced diver who was bent. His recompression is done in the hospital over hours and hours of hyperbaric time over a several-day period.

Of course, in this thread we're not talking about symptomatic bends, but rather having come up too quickly without decompressing, without having any symptoms. In this case, I just don't know whether re-descending is a good idea. It makes a certain sense. If the gas bubbles have already formed in the tissue, it's too late. But if they haven't yet formed, then perhaps it would help. But this is something that in my opinion can't be determined in a speculative discussion. We're talking about life-threatening issues here, so shouldn't just speculate in my opinion.

Well, no. Type 1 and type 2 are different from lung over expansion injuries. Lung overexpansion CAN (and often does) result in type 2 symptoms. You can get type 2 symptoms without a lung overexpansion injury. I've seen it myself.

As far as in-water recompression goes, the increased risk is significant and makes little to no sense for the recreational diver with a low gas burden. Imagine for a second that you become symptomatic in the water (it happens), and as we'll explored earlier, type 2 (neuro) DCS is more common than type 1. You're got an awful situation on your hands.

Getting back in the water (omitted deco, if you will) for the recreational diver doesn't make much sense either, in regards to body temp, gas supplies, in water support, and other concerns that I won't bore you with. If you aren't symptomatic, then you aren't bent. If you become symptomatic, you're at least on the surface where you CAN get o2, medical support, can BREATH, are dry, etc. There's just not much benefit to going back underwater. There's a reason no one suggests going through the motions if you aren't symptomatic. Do you take cold medicine if you came near someone who had a cold, but you don't have a cold? No, of course not. That would be silly. Pretending to be bent is just as silly, except it costs thousands of dollars.

Then why do they say that you can get the bends hours or even days later?

For example, you get back on the boat, feel no symptoms, then wake during the night with life-threatening bends. And you think, "Well, I read that guy's post, and he said I didn't need to do anything." Then you die, and your family reads this post on Scuba Board...

Well, if you read up on DCS, you'll see that symptoms that present multiple hours after the dive are pretty rare (majority present within 3hrs). Even more rare to be fatal. If I ran to the recompression chamber every time something was slightly off from the tables, DAN would be in the red. This stuff just isn't black and white like that.

I highly recommend a continued study of DCS besides what you got in PADI Open Water. There's much more to it than what you learned.

 

[Jax]

That's a good question.
Is it the prevailing opinion of the tech diving community that a missed safety stop warrants re-descent?
If so, that's interesting. I would think that with greater nitrogen loading (or being "heavily saturated" as you mentioned) comes greater risk of DCS. Combined with the possibility of bubble-pumping and other issues with re-descending to do a missed safety stop, I'm somewhat surprised that the marginal benefit of re-descent is worth it.

BT, if you miss a deco stop for less than a minute, you are to go back down to it and do your deco times at 1.5 x the original plan, for it and all stops above it.

This would allow a diver to bring up a sick buddy and yell for help, for example. Or, if something went really wrong, the diver could go up, request extra gas, and go back down.

At no time are you do do this if you develop any symptoms. It is completely emergency procedures.

 

[DevonDiver]

That's a good question.
Is it the prevailing opinion of the tech diving community that a missed safety stop warrants re-descent?

In terms of gas physics, what's the difference between a safety stop and a deco stop? Gas in - Gas out.

In terms of gas physics, what's the difference between a deco dive and a no-deco dive? Gas in - Gas out.

A diver can get bent from a no-deco, recreational dive. For such dives the conduct of a safety stop remains optional. If that diver opted not to do it, and got bent, then it was obviously the wrong option.

Here's an interesting question: If a recreational diver conducts a fast ascent, from an otherwise 'no-deco' dive... is it still a no-stop dive? If a dive computer is worn, it (if using the latest algorithms) will certainly insist on a stop.... a mandatory stop...for ascent violations. No 'if', 'but' or 'maybe'... fast ascent causes a formal stop to be attributed to the dive. The possibility of bubble evolution has been created, thus the diver has to ensure sufficient off-gassing to mitigate that possibility.

What about dives below 30m, or within 3 pressure groups of an NDL (on tables)... where a 'safety stop' is mandatory?

What about dives in which multiple DCS pre-cursors are applicable, such as; cold water, dehydration, obesity, exertion etc? Surely there is a point where the optional safety stop gains sufficient relevance to be considered, as a prudent decision, to be virtually mandatory?

If so, that's interesting. I would think that with greater nitrogen loading (or being "heavily saturated" as you mentioned) comes greater risk of DCS. Combined with the possibility of bubble-pumping and other issues with re-descending to do a missed safety stop, I'm somewhat surprised that the marginal benefit of re-descent is worth it.

Thousands of PADI instructors teach CESAs every day... during repetitive dive profiles and/or at the end of dives. Up-down-up-down-up-down.

Thousands of divers accidentally, or deliberately, ascend to the surface during a dive every day. Buoyancy hiccups. Get lost..need to see the boat. etc

These don't result in DCS. If they did, then teaching practices would be different (PADI released a report on this). There's have to be a lot of ascent-descent-ascent to risk DCS (DAN did a report on this). If there was a real risk in re-descent, then there'd be stringent agency advice about mandatory dive end, if X depth (ceiling) is broken.

SPUMS: A Training Agency Perspective on Emergency Ascent Training

Also, from this report, the link between multiple ascents/descents is suggested... but we're not talking about multiple ascent/descent... we are talking about one re-decsent (I included the quote for general learning value to thread observers about the risks of yo-yo diving):

SPUMS: A RETROSPECTIVE STUDY OF DECOMPRESSION ILLNESS IN RECREATIONAL SCUBA DIVERS AND SCUBA INSTRUCTORS IN QUEENSLAND.

The total number of scuba instructors treated for DCI at the Hyperbaric Medicine Unit of Townsville General Hospital between November 1989 and December 1993 was 38 (20% of the study population). The total number of recreational divers treated for DCI during the same period was 149. Of all scuba divers treated over this time period, 74% (187/251) were recreational divers or diving instructors with a diagnosis of decompression illness, responsive to recompression....

...as demonstrated by the data collected from the Townsville General Hospital records, the proportion [of instructor DCI] is 20%; about 10 times higher than expected. Thus the incidence of DCI in the instructor population diving in the Queensland area is disproportionately high....Their [instructors] propensity towards development of DCI may therefore be related to an excessive frequency of multiple ascents and descents, which, by their very nature, do not fall within the dive tables and are not expected by the limited intelligence of the dive computer....most instructors were afflicted with DCI after a training dive, while this was not found to be true for the recreational divers studied....

...the instructor (assuming a maximum open-water class of eight students without use of an assistant) will make a minimum of 13 ascents and descents on a single dive [to conduct CESA and AAS drills, plus normal ascents], barring any problems that may arise with students bolting for the surface or losing contact with the group....

...It is all the more surprising, since one would not expect sport divers with minimal dissolved nitrogen after a short time atshallow depth to dev elop DCI, even with a rapid ascent. This brings us back to the possibility of multiple ascents and descents being a primary culprit in the aetiology of DCI. Multiple ascents during a so-called single dive, described as “yo-yo”diving, are identified by commercial diving authorities as a predisposing factor in decompression illness.

With regards bubble-pumping...IMHO, this is an issue (if I understand your use of the term correctly) that effects freediving, 'yo-yo' or 'bounce' diving whist otherwise saturated. Quick descent - bubble shrink and pass through into cardio-vascular system - quick ascent bubble re-grow, cannot be effectively off-gassed, start combining to form bigger bubbles. Dangerous. The big difference is that in free/bounce diving, there is a rapid ascent after the descent.

Re-descending to conduct a safety stop doesn't entail a subsequent fast ascent, nor is it very deep (to cause significant bubble compression). Most importantly, it provides significant time to allow any compressed bubbles to begin diffusing, as part of the overall off-gassing process.

I'm really not interested in the absolute level of risk -- it's more about the comparative risk. More specifically, it's certainly possible that even a "low risk of complications" associated with re-descent is still greater than remaining on the surface.

I don't think I'm going too far out on a limb by saying that a missed safety stop, in and of itself, presents very little additive risk of DCS.

Depends on the dive...and the diver.

 

[fdog]

I know this is a "left turn at Albuquerque" kind of response. But....here's the simile.

? Can you infer pregnancy before symptoms develop?



In brief, the answer is no. Either you're pregnant or not. To determine if you ARE pregnant, wait until you're symptomatic- or - test positive. No matter how awesome the weekend was, you can't tell from the weekend, only the outcome.

If being pregnant is something that is a grim prospect before <symptoms or testing positive> appear, take the morning after pill.




So, back to reality: Are you bent?





All the best, James

PS: computers are not the human body. Computers are bent predictably, the human body is not.

 

[Bubbletrubble]

BT, if you miss a deco stop for less than a minute, you are to go back down to it and do your deco times at 1.5 x the original plan, for it and all stops above it.

This would allow a diver to bring up a sick buddy and yell for help, for example. Or, if something went really wrong, the diver could go up, request extra gas, and go back down.

At no time are you do do this if you develop any symptoms. It is completely emergency procedures.

@Jax: Re-read my post. I'm talking about an omitted safety stop, which is characterized by all scuba instructional agencies as recommended/optional.
The procedure you describe is for an omitted deco stop, which most people would characterize as mandatory.
With greater nitrogen loading comes a greater possibility of being afflicted with DCS. Deco dives feature greater nitrogen loading than no-deco recreational dives.

A missed safety stop is no big deal.
I suppose that those who do deco dives have some empirical evidence to indicate that, should a diver miss a deco stop, the diver has a better chance at a good outcome if he re-descends to conduct the procedures for the missed deco stop(s).

 

[DevonDiver]

If you aren't symptomatic, then you aren't bent. If you become symptomatic,

James' post described it well, through the analogy of pregnancy. In that respect, re-descending to do a preventative safety stop is the 'morning after pill'.

No symptoms, just justified concerns based upon what happened.

you're at least on the surface where you CAN get o2, medical support, can BREATH, are dry, etc.

Explain how being at 3-5m for a few minutes are a precautionary measure deprives you of that? The diver isn't trapped there...no ceilings...if they did start to feel unwell, they could ascend, board the boat and access the same. DCS won't hit a recreational diver with sufficient speed or ferocity to prevent that.

If a diver has no concerns about their dive, then the safety stop is a purely conservative safe-guard. Take it or leave it.

If a divers does have concerns about their dive, then the safety stop is a measure that could potentially prevent a DCS occurrence.

Optional... that means you have a choice. It doesn't mean that there isn't a right choice and a wrong &#8203;choice.

I'm talking about an omitted safety stop, which is characterized by all scuba instructional agencies as recommended/optional. The procedure you describe is for an omitted deco stop, which most people would characterize as mandatory.

Such thinking supports the fictitious notion that there is a 'magical dividing line' between rec and tec... between deco and safety stop. There isn't.

With greater nitrogen loading comes a greater possibility of being afflicted with DCS. Deco dives feature greater nitrogen loading than no-deco recreational dives.

Such thinking supports the fictitious notion that you can only get bent by exceeding an NDL... or at least, that DCS risk is determined only by saturation level. It isn't.

A missed safety stop is no big deal.

Unless you subsequently get bent. Then it becomes one of the biggest mistakes you made in your life.

A safety stop has a very tangible benefit for reduction of fast-tissue compartment saturation.
Most recreational divers are controlled by faster-tissue compartments.
Most recreational divers get bent by faster-tissue compartments.

I suppose that those who do deco dives have some empirical evidence to indicate that, should a diver miss a deco stop, the diver has a better chance at a good outcome if he re-descends to conduct the procedures for the missed deco stop(s).

I'm sure they do, but I don't. However, the theory bares out that concept. Bubbles have to form. That takes some time - dependent on saturation level and the speed that pressure has been reduced. It doesn't matter how many 'micro-bubbles' or 'bubble seeds' you have... if you stay at pressure long enough for them to dissolve. What matters is that you don't reduce pressure enough for them to form into symptomatic bubbles. Shallow stops... safety...deco... whatever serve to accomplish just that. Hey presto... a trip to the chamber avoided

 

[Bubbletrubble]

@DevonDiver: You seem to be advocating that all stops (deco, mandatory safety, and optional safety) are mandatory. Correct me if I'm wrong.

I've never been a fan of the term "mandatory safety stop." I believe PADI invented that term so that it wouldn't be making reference to deco stops on the PADI/DSAT RDP. Suunto also uses the term in its dive computer manuals. Personally, I think it would be clearer if the "mandatory safety stop" were simply called a deco stop. Then, it would be unambiguous that the stop was obligatory (safety stops always optional, deco stops always obligatory).

I started writing a point-by-point reply to your posts, but then I vaguely recalled that these identical arguments were brought up in previous threads.
There's really no point in us repeating this well-worn debate. Honestly, both of us have better things to do.

I'm going to refer you and any other interested parties to the following ScubaBoard threads:
So why is it a bad idea to go back to do a missed safety stop if you blow it?
Safety stop immediately after surfacing
Blow a Safety Stop? Redescend?
Disturbing 'advice' from DAN in Alert Diver