Diving after DCS

[Duke Dive Medicine]

I think you meant maybe "setting on air" not O2? This is not a best practice; don't lie to your computer. Just be more conservative than what it allows. A LOT more conservative, as you are already doing.

I disagree. We often recommend that divers in the OP's husband's situation dive nitrox on the air setting on the computer.

It's important to find out why these things happen if you will continue to dive and that means paying for the PFO test even if insurance doesn't cover it. This is not a time to be frugal.

The OP reported that her husband already had a PFO test.

We're trying to figure out how to approach diving after an 'undeserved' DCS hit in Cozumel a few months ago. My husband spent 9 hours in the chamber (one 5hr ride + two 2-hr rides) after experiencing severe vertigo several hours after diving. Much of the vertigo was gone after oxygen. He was 95% recovered after the hyperbaric treatments. He was 100% within a couple weeks of returning home.

Both the hyperbaric doc in Coz and the one he saw when we got home said he could continue diving but should be more conservative. We now think he had one or two episodes of skin bends on previous dive trips. He also has a lifelong history of migraines, with occasional aura, which is often associated with PFOs. So I'm pretty convinced he has a small PFO. But the simple test for a PFO didn't show a problem. He did not get the definitive PFO test as that is more invasive. He's 73 YO, so even if he had a PFO, he wouldn't have it repaired as the surgery has some risk. My question to others who have been down this path at this age-- what are your limits? Do you still dive in remote locations like Raja Ampat? Do you still go do dive boat trips? Or should we avoid going too far afield?

We were already conservative divers and have always followed all the rules to a T. Based on the doctor's recommendations, we are now doing longer safety stops (5+ minutes), shorter dives (50 minutes), shallower dives (max 60'), super slow ascents, diving Nitrox (but setting our computers to O2), only doing 2 dives per day, taking a day off every few days, being extra careful about hydration, not doing any exercise post-dive (not even climbing the ladder with gear on), & no warm showers, etc. We will hire private guides to make sure we can dive the profile we need. My husband is in good physical shape, is normal weight, swims or exercises 5-7x per week and doesn't drink. He has logged 300 dives, with most of those in the past 5 years. We'd like to continue diving a few more years but want to figure out the safest way to do it.

We just got back from a dive trip in Loreto/ Baja. They didn't have Nitrox so we just did super shallow dives-- 30-50'. We did 2 dives per day/ 4 days in a row. No problems. We have an upcoming trip to the Maldives. We are hiring private guides to insure that we can tailor the dives to our needs.

I would love to hear others' experiences after DCS and how they choose where they dive and what boundaries they have adopted. We would love to go back to Fiji, Raja Ampat, French Polynesia, western Australia, but don't want to be too far from a chamber. Any advice would be appreciated.

What you described sounds like inner ear decompression sickness. We would typically recommend a PFO test in your husband's case just to have some data on which to base a diving recommendation, as was done here. Can you say exactly what test he had? Was it a transthoracic echo? If so, was bubble contrast used, and did they have him perform a Valsalva (bear down as if having a BM) maneuver during the test? Also, what did the skin bends look like? Did it have more of a marbled appearance, or was it red and blotchy like hives?

IF he has a PFO, we would generally recommend that he stop diving after an incident of severe DCS. That's not acceptable to some divers, so our recommendation in those cases is usually to do exactly what you all are doing, which is dive more conservatively, use nitrox on the air setting of your computer, take a day off in the middle of the dive trip, limit your dives to two per day, not push the computer to the edge of the no-stop limits regardless of setting, and avoid provocative dives (generally those deeper than 60 feet). You'll have to gauge the risk of taking dive trips in remote locations and mitiage it as best you can. My other recommendation would be to get evaluated by a physician trained and experienced in assessing divers, which you've already done.

Best regards,
DDM

 

[tursiops]

I disagree. We often recommend that divers in the OP's husband's situation use nitrox on the air setting on the computer.

The OP reported that her husband already had a PFO test.

What you described sounds like inner ear decompression sickness. We would typically recommend a PFO test in your husband's case just to have some data on which to base a diving recommendation, as was done here. Can you say exactly what test he had? Was it a transthoracic echo? If so, was bubble contrast used, and did they have him perform a Valsalva (bear down as if having a BM) maneuver during the test? Also, what did the skin bends look like? Did it have more of a marbled appearance, or was it red and blotchy like hives?

IF he has a PFO, we would generally recommend that he stop diving after an incident of severe DCS. That's not acceptable to some divers, so our recommendation in those cases is usually to do exactly what you all are doing, which is dive more conservatively, use nitrox on the air setting of your computer, take a day off in the middle of the dive trip, limit your dives to two per day, not push the computer to the edge of the no-stop limits regardless of setting, and avoid provocative dives (generally those deeper than 60 feet). You'll have to gauge the risk of taking dive trips in remote locations and mitiage it as best you can. My other recommendation would be to get evaluated by a physician trained and experienced in assessing divers, which you've already one.

Best regards,
DDM

I'm sorry, but using an air setting while diving nitrox is an OLD solution, no longer a best practice. Today's solution is to use a modern computer and set conservatism on the computer. That way you are not lying to the computer and it is tracking your N2 and O2 exposure, which for repetitive dives is a good idea.

 

[Duke Dive Medicine]

I'm sorry, but using an air setting while diving nitrox is an OLD solution, no longer a best practice. Today's solution is to use a modern computer and set conservatism on the computer. That way you are not lying to the computer and it is tracking your N2 and O2 exposure, which for repetitive dives is a good idea.

I still disagree.

Best regards,
DDM

 

[tursiops]

I still disagree.

Best regards,
DDM

Why not recommend air tables instead of a computer? That has even more conservatism in it.

 

[Duke Dive Medicine]

Why not recommend air tables instead of a computer? That has even more conservatism in it.

True, and we'd probably have to re-teach tables afterwards

 

[davehicks]

I'm sorry, but using an air setting while diving nitrox is an OLD solution, no longer a best practice. Today's solution is to use a modern computer and set conservatism on the computer. That way you are not lying to the computer and it is tracking your N2 and O2 exposure, which for repetitive dives is a good idea.

TLDR; Setting AIR is a simple nudge. The reality when dealing with humans is that as soon as there is even a tiny amount of friction you lose half the audience.

The reason that "lying" to your computer by setting Air on a Nitrox mix works is that it's easy. Practically any diver can do this without additional explanation. Setting conservative options works differently on every single computer and most people don't know how to do it. If you are willing to figure out how to manage conservative options on your computer and stick with them over time, then do that. But don't assume everyone is just like you.

I get your point about wanting "accurate" data, but the O2 exposure for recreational open circuit divers has absolutely ZERO value. O2 exposure is just not relevant to this audience so that level of accuracy is not helpful. And the false N2 reading is the entire point.

 

[inquis]

We often recommend that divers in the OP's husband's situation dive nitrox on the air setting on the computer.

This results in a variable safety margin that is dependent on the mix. I believe it is better to use the conservatism features of the computer with the actual inspired gas.

 

[JMarc]

This results in a variable safety margin that is dependent on the mix. I believe it is better to use the conservatism features of the computer with the actual inspired gas.

I don't think the safety settings are more uniform, even with one setting and one given person, the risk depend on the profile and other factors.

 

[Duke Dive Medicine]

This results in a variable safety margin that is dependent on the mix. I believe it is better to use the conservatism features of the computer with the actual inspired gas.

How does changing conservatism settings induce less variability, and exactly what advice do we give divers on how to change them when (a) as as @davehicks stated above, conservatism settings are not consistent across computer brands and (b) there's very little empiric evidence on how they function in the real world?

Best regards,
DDM

 

[inquis]

How does changing conservatism settings induce less variability

I can't speak to the proprietary algorithms, but anything with gradient factors will have a fairly consistent tissue supersaturation, because that's at the heart of the algorithm. Conceptually, I believe even the proprietary ones will act similarly, as that's the entire point (limiting the tissue loading).

Consider a dive to the air NDL for 60 ft at a medium conservatism of GF x/85 -- 41 mins -- and you do this dive on nitrox. Which nitrox? For the vast majority of divers, that's simply the one the boat crew hands you. Could be 32%, 36%, 37% (because they overshoot the 36% mix) or even 27%. If you lucked out and got the 36% mix, you're effectively 54 mins shy of your actual NDL. On the other hand, if you get the 27% mix, your margin is only 16 mins. As I said, the margin varies with whatever mix you happen to receive.

even with one setting and one given person, the risk depend on the profile and other factors.

No argument there, but reducing the variability where you can seems sensible to me.