DCS--Playing the Odds

[Bob DBF]

Today we could screen for PFO but do not.

Considering that PFO's occur in somewhere between a quarter to a third of the population, and I assume the same amount of the diving population, it seems a bit of overkill to diagnose and treat an issue which, in most cases, will never cause a problem. It is a factor that may may make the diver more suceptable to DCS, but there is a litinay of other factors we know and others we don't, so it pays to be carefull regardless.

PFO's and Diving - The Diver Clinic
Of those divers who have PFO’s, not all of them will be at increased risk of decompression illness at all and as a population there seems to be little evidence that screening is cost-effective or necessary. Even commercial divers are not routinely scanned for the presence of a PFO as the risk factor is relatively low.

Bob

 

[rossh]

Considering that PFO's occur in somewhere between a quarter to a third of the population, and I assume the same amount of the diving population, it seems a bit of overkill to diagnose and treat an issue which, in most cases, will never cause a problem. It is a factor that may may make the diver more suceptable to DCS, but there is a litinay of other factors we know and others we don't, so it pays to be carefull regardless.

Bob

For the general population of divers, there is far too many of them and the risk is too small to be looking for specific higher risk issues like PFO. But what about the smaller subset of divers engaging is deliberate decompression diving?? These are the people most at risk of the ill-effects of a PFO, and suffering the consequences.

Screening does not require a full TTE/TEE exam. There is a simple indicator test that is reliable enough to sort out and find the PFO people. DAN Europe did this as part of a medical trial some 10+ years ago. If someone with a PFO is forewarned they are at 5x higher risk of getting DCS, then they can positively plan or dive accordingly.

But the status quo, seems to be to nudge everyone a bit slower, in the hope it covers up for those who really need the extra time. Those PFO people don't know of their elevated risk status, because the current system says they can only learn about it, after they get injured.

Cheers

 

[clownfishsydney]

I have not read all of this, but I think that if you do enough dives it is very possible that you may get DCS no matter how safe you dive. I have (as of today), completed 4,001 dives without any (known) cases of DCS. This is not to say that I do no accept that sometime in the future I may get a hit, no matter how conservative I am. My wife got bent after 1,600 dives during a very conservative dive trip. Why? She had a PFO. Even without a PFO, this can still happen to any of us, even if we do 5 or 10 or 20 minutes of safety stops.

 

[Bob DBF]

Screening does not require a full TTE/TEE exam. There is a simple indicator test that is reliable enough to sort out and find the PFO people. DAN Europe did this as part of a medical trial some 10+ years ago. If someone with a PFO is forewarned they are at 5x higher risk of getting DCS, then they can positively plan or dive accordingly.

Now is this a test I can get from my doctor and know for sure I have a PFO and whether it would affect my diving, or is this a study that has never followed up, proved, and provided a test?

I would most likely get checked now, if I was going tech, however the state of the art back in the 70's probably would not have helped me.


Bob

 

[rossh]

I'm trying to locate the article, but its hiding from me somewhere. Its listed in the PFO discussion / paper summary meeting conference, and it was part of one of the trials. That conference paper has been on here before. Some one remember please?

 

[tursiops]

I'm trying to locate the article, but its hiding from me somewhere. Its listed in the PFO discussion / paper summary meeting conference, and it was part of one of the trials. That conference paper has been on here before. Some one remember please?

is this the one?
Transcranial doppler ultrasonography should it be the first choice for persistent foramen ovale screening?

 

[rossh]

is this the one?
Transcranial doppler ultrasonography should it be the first choice for persistent foramen ovale screening?

The paper I was thinking of was 10 years before the above. But hey - same method, same accurate result - this one will do nicely. The TCD screening method seems to be more than good enough for the simple yes/no PFO decision we are asking for. Still it needs a specialized tech to perform the screening.

 

[KenGordon]

Ok, say you spontaneously get screened for a PFO without being previously bent.

Outcome A: very likely have a PFO
Outcome B: very likely not.

How do you proceed?

Should diver A add more deco? Can diver B skip some? Should all As have it fixed?

 

[Kevrumbo]

PFO's and Diving - The Diver Clinic
Of those divers who have PFO’s, not all of them will be at increased risk of decompression illness at all and as a population there seems to be little evidence that screening is cost-effective or necessary. Even commercial divers are not routinely scanned for the presence of a PFO as the risk factor is relatively low

Professional Commercial and Military Divers also have stand-by multiplace, auxiliary lock Recompression Chambers onsite at dive operations, or readily available 24/7. In contrast, most civilian recreational divers often do not have this emergency hyperbaric oxygen therapy 6ATA support, capable of treating the entire range of DCI pathology from simple type I limb pain only DCS, to worst case full arrest AGE with near drowning.

Ok, say you spontaneously get screened for a PFO without being previously bent.

Outcome A: very likely have a PFO
Outcome B: very likely not.

How do you proceed?

Should diver A add more deco? Can diver B skip some? Should all As have it fixed?

See thread: 2 DCS hits and a PFO closure

---------
Again, it all comes down to a statistical/epidemiological vs clinical dilemma in a personal risk management perspective: a low probability event versus a severe health & welfare outcome if you unluckily suffered such an acute DCI occurrence.

Here are the arguments:

https://www.diversalertnetwork.org/...Proceedings/2015-pfo-workshop-proceedings.pdf (see P.156):

Epidemiological studies have shown an association between PFO and certain types of neurological and cutaneous decompression sickness. . . DCS risk has been reported as 3.6 cases per 10,000 dives, with 0.84 cases of neurological DCS per 10,000 dives, with a 4-fold increase in risk with PFO. . .Thus, if DCS cases were random events, the overall risk of neurological DCS is low, even in the presence of a PFO. . .

Statement 1
Routine screening for patent foramin ovale (PFO) at the time of dive medical fitness (either initial or periodic) is not indicated. . .

Statement 2
Consideration should be given to testing for PFO under the following circumstances:

• A history of more than one episode of decompression sickness (DCS) with cerebral, spinal, vestibulocochlear, or cutaneous manifestations. . .

However IMO and in disagreement with the above Statements, finding out you have a pre-existing PFO by suffering a gross neurological type II DCS episode is neither a clinical best practice nor medically ethical if you could have screened for it beforehand with at least a simple noninvasive contrast TCD.

Dr. Richard Moon, Dept of Anesthesiology, Duke University Medical Center back in 1998 had the best unequivocally stated opinion and advice:

". . .For recreational divers I believe there is no need for a screening examination to look for a Patent Foramen Ovale (PFO). The only relationship we have found between PFO and DCI is for serious neurological bends, a rare disorder, and largely attributable to risk factors which are associated with the dive itself, such as depth, bottom time and rate of ascent. On the other hand, for a person who plans to perform dives that have a high risk of venous gas embolism for long periods of time, for example saturation diving [and especially with regard to present day long runtime open circuit or CCR decompression dives now becoming common to sport recreational advanced technical diving -bracketed underlined italics mine @Kevrumbo ], then I would recommend a PFO Study. . ."

http://archive.rubicon-foundation.o...e/123456789/5949/SPUMS_V28N3_9.pdf?sequence=1

It's not about changing or debating academic viewpoints and position statements of leading hyperbaric scientists/physicians and statistical epidemiologists, but for us laypeople to learn about and insist in making an informed decision regarding our own personal risk management threshold.

(@Dr Simon Mitchell, @Dr. Doug Ebersole and @Duke Dive Medicine are invited to respond)

 

[rossh]

Ok, say you spontaneously get screened for a PFO without being previously bent.
Outcome A: very likely have a PFO
Outcome B: very likely not.
How do you proceed?
Should diver A add more deco? Can diver B skip some? Should all As have it fixed?

"How do you proceed?": Diver A in now informed of his increased risk factor, and he can adjust his diving to suit.

" Should diver A add more deco? ": Yes, he is at a physiological disadvantage for decompression and he must do more deco to compensate. There is no avoiding this fact.

" Can diver B skip some? ": Not really, as he still has the same deco limits as always.


"Should all A's have it fixed?": That's their choice. a/ get it fixed and become a normal decompression diver, or b/ adjust diving style to account for this and avoid all high risk dive profiles, or c/ ignore the knowledge and experience and carry on regardless.


Step back and have a look at public health screening in general. As a society we screen for all manner of diseases and illness, long before they happen. As one example, every person getting older is encouraged to do a set of regular screening tests.

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