Instructors: Microbubble alarm after CESAs

[rsingler]

Okay, folks. We CESA repeatedly at every open water class. 4 times? 8 times? I didn't give it much thought; after all, only 20-30 ft.

Last weekend, I happened to be diving with my personal Galileo Luna. It was set at Microbubble level 0; i.e., generic Uwatec dive computer ZHL-8 ADT MB PMG algorithm.
I finish my dive and see a "NO DIVE 2h30m" alarm on my screen. Drilling down yielded Exertion, Ascent Rate and Microbubble Warnings. Looking at the profile on my screen showed the obvious sawtooth pattern of the CESAs.
It's not a hard lockout, but an advisory. Since my CESA's were at 23ft, I ignored it and did the OW#4 dive with my group (guys, see if you can resist flaming me for stupidity - it was a conscious choice based upon a modicum of medical knowledge). As I was diving during #4, the no-dive time continued to decrease, and I finished the day with an hour left on the no-dive clock.

So here's the question: why SHOULDN'T I be worried?

Yeah, we do CESAs all the time. But instructors are a more bent group statistically. Is this just a function of briefly violating 60 fpm plus breathing extra plus sawtooth (which we already know increases sensitivity in dive computers)? I.e., is this just a modeling flaw, or is it telling me that every time I do multiple CESA's, I'm setting myself up for trouble should I happen to do a deeper dive later that day, because I've got microbubbles waiting to expand?

I say this as a former Hyperbaric Air Force flight surgeon, so I hope we can avoid some of the random speculation that this post might otherwise provoke. I'll PM the DAN guys and see if they'll weigh in.

Your thoughts? Is this real? Microbubbles after five 60 fpm ascents from 23ft? I'm actually a little worried.

 

[Diver0001]

Your thoughts? Is this real? Microbubbles after five 60 fpm ascents from 23ft? I'm actually a little worried.

It's a legitimate concern. These days I do OW with a maximum of 4 students and when I have more than 2 students to do a CESA I'll often stagger them over 2 days, particularly if I have a number of repetitions. There's very little (to no) chance that I'll ever teach an OW course again with 6 or 8 students but I think instructors who have groups of that size are indeed at elevated risk.

R..

 

[Duke Dive Medicine]

Bob, in theory dives that shallow should not produce clinically significant venous gas emboli. In practice that may not be the case. I consulted with a fellow hyperbaric RN some years ago about a commercial group who were doing repeated ascents and descents to less than 20 feet over a period of hours and were presenting with symptoms of DCS.

It may also be helpful to reiterate for those reading that that microbubble alarm is strictly theoretical and there is enormous individual variability in quantity and size of post-dive VGE. Also, I'm assuming that your 60 fpm ascents are limited to CESA practice and not part of your everyday diving procedure.

Best regards,
DDM

 

[rsingler]

I'm assuming that your 60 fpm ascents are limited to CESA practice and not part of your everyday diving procedure.

Best regards,
DDM

Believe strongly after the NEDU study and other work that <15fpm for the last 20-30 feet is an important contributor to my safety, especially after deeper/longer dives.
Roger, @Diver0001, I HATE teaching CESA! It just goes against the grain, lol. But students gotta learn. And my CESA 30 years ago was from deeper than that, as I recall.

 

[RainPilot]

I refuse to do a vertical CESA. Luckily RAID agrees and it's an optional skill.

Telling students to follow example and then showing them multiple high speed ascents with no adverse effects (that they can see) makes it hard to hammer ascent rate control into them.

 

[rsingler]

Well, I hear you, but they get that "save your life" exercise only once in their career.
They get buoyancy and ascent technique drilled into them repeatedly, whether it's AOW, or Peak Performance Buoyancy or Deep, or many other classes.
I think they deserve that (brief) memory that teaches them firsthand the physics of Boyle's Law, if only to get some of our anxious students over the psychological hump of diving deeper than they might snorkel. It's good to actually feel what you don't really believe - that you can make it, courtesy of Boyle.

 

[guruboy]

I refuse to do a vertical CESA. Luckily RAID agrees and it's an optional skill.

Telling students to follow example and then showing them multiple high speed ascents with no adverse effects (that they can see) makes it hard to hammer ascent rate control into them.

A CESA should not be a "high speed ascent"

 

[Doby45]

A CESA should not be a "high speed ascent"

It is more high speed that a regular ascent. But yes, it should be Controlled.. That is what the C is for. If it was not controlled in some fashion it would be the PESA - Polaris Emergency Swimming Ascent.

 

[rsingler]

I'll cut @RainPilot some slack for that remark. I'm sure he knows the correct CESA ascent rate.
From a student's viewpoint it might look "high speed", IF they were really looking.
But in my experience, students are so worried about "surviving" their own CESA, I very much doubt that they're processing what they're seeing, i.e., "Wait a sec! They teach me these slow ascents, and there goes my Instructor, over and over, surviving a high-speed ascent. I think I'll ignore that BS about ascent rate (and the alarm from my computer)."

Nah. They don't even put those pieces together. I'm not worried about negative reinforcement from a CESA exercise. But theoretically, a good point. I just don't quite agree on the relative merits of skipping it.

 

[Diver0001]

Actually, I think the reality is that if one ever REAAAALLY needs to make a CESA that it's going to be a "non-standard" speed. Fortunately in 33 years of diving I've never personally had to do one but I've witnessed it in the real world and I can assure you that the ascent rate was not the diver's primary concern, nor did it even occur to him to think about it until after he was safe.

R..