Bent over a BC

[cornfed]

clootie once bubbled...
Interesting articles.

I can see the point of at least considering IWR, particularly where the depth was quite shallow to start, and where the diver is calm enough to be willing & able to do it - not necessarily the case.

(On my quick skim read of it this weekend (doing the course in a few weeks) the PADI rescue course says IWR is generally only of benefit with O2, only to do it with 02, not air, with support teams etc,

This will not only significantly increase you risk of toxing but you will be limited to 20 ft. Most IWR (and dry recompression) strategies involve working your way up from depth.

But like you said,

as a last resort if far away from a chamber

Another option would have been to put your brother on 100% O2 ASAP on the surface (demand mask type, preferably holding it to get as good a seal as possible),

A normal non-rebreather mask should work fine. You don't even need to hold it on.

as the high O2 concentration also changes the partial pressures and shrinks the bubbles forming.

I don't think O2 will cause the bubbles to shrink. My (limited) understanding is that it allows you to transfer more N2 out of you tissues per unit time. You can still bubble and still get bent.

(Much the way Gkwaldee says, but without the risk of drowning, or added stress to a probably already freaked :scared: diver).

If you take someone back underwater you had better be damn sure you know what you're doing. At the risk of repeating myself... IWR is a viable option in some situations, but I would not have take the diver in question back down. If I was seriously concerned about him I would have done like you suggested clootie and put him on O2 on dry land.

I'm glad he's ok , and it had a good ending. Hope he can get back in the water soon. Me, I'm really looking forward to doing both the Rescue course, and the DAN O2 provider courses in the coming weeks (been reading over that one too, as you may guess).

See if you can get your instructors to talk about IWR.

Cornfed

 

[clootie]

Cornfed

If an ordinary mask was what was to hand, yes you should use it. But my coursebook recommends the demand mask for a conscious diver, and getting as good a seal as possible, because you can get effectively 90%+ O2 that way. A continuous flow mask, particularly if below 15lpm, will give a lower percentage of O2 entering the system (about 65% I think?). Not entirely sure why you get a lower % into your system - will be one of the questions I'll be asking. But the reason given for maximising the O2 you breathe as opposed to flowing out the mask was (as far as I recall from first reading) that the higher percentage of O2 can shrink the bubbles.

For the same reason, for an unconscious diver, you should use a continous flow rebreather mask with a flow rate of at least 15 litres per minute. If you have limited oxygen available you should still use the higer rate, thus using up your oxygen faster, rather than be tempted to switch to a lower rate to conserve some O2 for longer. Again, this is because the higher O2 percentage is considered more effective at preventing/reducing DCI.

I think we're both right here. High O2 does allow the Nitrogen to move out more quickly, but in doing so also shrinks any nitrogen bubbles forming. As you say, you can still bubble and get bent - I guess if there are too many bubbles, the O2 needs to be at above atmospheric pressure to get rid of them all, and you win a trip to the chamber.

http://www.mtsinai.org/pulmonary/books/scuba/sectionh.htm

http://www.mindspring.com/~divegeek/why100.htm

(did some googling, in case I was confused).

I will ask about IWR - though I hope never to have to use it. Given the choice between hanging around in the water wondering if every twinge is a symptom, or being in a chamber, give me the ride! (Though I don't fancy either, really)

Clootie

cornfed once bubbled...



A normal non-rebreather mask should work fine. You don't even need to hold it on.



I don't think O2 will cause the bubbles to shrink. My (limited) understanding is that it allows you to transfer more N2 out of you tissues per unit time. You can still bubble and still get bent.


Cornfed

 

[Grajan]

The way I read it the diver did a rapid ascent from a no-decompression dive. He came up too fast and missed a safety stop but he was ASYMPTOMATIC on the surface. If there is no indication of DCS why are we talking about in-water treatment of DCS or IWR?

The way I see it this is not IWR at all, but corrective action for an overly rapid ascent by getting back to depth ASAP. The purpose of this is not to treat DCS but to prevent it happening at all by removing the conditions that allow bubbles to form as quickly as possible.

If there is something wrong with this picture please let me know because my current plan in the event of a rapid surfacing is still to get back down ASAP if at all possible.

 

[cornfed]

clootie once bubbled...
Cornfed

If an ordinary mask was what was to hand, yes you should use it. But my coursebook recommends the demand mask for a conscious diver, and getting as good a seal as possible, because you can get effectively 90%+ O2 that way. A continuous flow mask, particularly if below 15lpm, will give a lower percentage of O2 entering the system (about 65% I think?).

In the US a nonrebreather mask is pretty standard in emergency use. I attached (or at least I think I did) a picture below. Everyone I've talked to says that it delivers "nearly" 100% at 15 L/min. In print I've seen 80-100% at 10-15L/min. I always assumed the lower percentage was at the lower flow rate because it couldn't clear your exhaled breath out of the mask. This is pure conjecture. The little elastic cord does a good job holding the mask on.

 

[clootie]

Checked my coursebook - good practice, I may do ok on the test. For the mask pictured it said with 15lpm, good fit and technique, you can achieve 90+%, "but 65-75% is common". Using a demand mask you can get nearly 100%. (NB Think when I said continuous flow rebreather earlier, I meant non-rebreather. D'oh.)

 

[Charlie99]

Grajan once bubbled...
The way I read it the diver did a rapid ascent from a no-decompression dive. He came up too fast and missed a safety stop but he was ASYMPTOMATIC on the surface. If there is no indication of DCS why are we talking about in-water treatment of DCS or IWR?

The way I see it this is not IWR at all, but corrective action for an overly rapid ascent by getting back to depth ASAP. The purpose of this is not to treat DCS but to prevent it happening at all by removing the conditions that allow bubbles to form as quickly as possible.

If there is something wrong with this picture please let me know because my current plan in the event of a rapid surfacing is still to get back down ASAP if at all possible.

I agree with every word in your post. I would redescend provided:
1) no DCS symptoms
2) no more than 5 or at the very most 10 minutes have elapsed
3) I have enough gas to properly recompress and offgas.

 

[clootie]

Grajan

I also see your point, and like I said, might have considered jumping in if it were me (not my novice brother), with Charlie 99's conditions. But I think it is technically still recompression in the water, as the point is still to shrink any bubbles that may have started to form, and to offgas normally to prevent others forming via time at depth and slooow ascent. Is it Dr Deco who says "every dive is a decompression dive" - I know I've read that on Scubaboard somewhere. Just that risk factor for the bubbles is the speed of the ascent, rather than the nitrogen loading.

One thing that would worry me, and I'd really like to know more about it before I would definitely jump back in, is whether an AGE would show up before I was getting back in, because that's what I'd be most scared of with an uncontrolled ascent, and I wouldn't like it to hit me on the way back down, only to find that recompressing didn't fix it.

 

[Grajan]

No getting away from it - there is a definite risk either way. I just would rather take that probably small risk than stay on the surface fizzing like a dropped Coke....

I did a LOT of emergency ascent training and that involved a very similar profile to no (apparent) long term effect. Mind you - it could explain a lot....

Charlie 99
I think your criteria are spot on. I will put them in my emergency plan.

 

[gkwaldee]

I completely agree with the liability issues. Id say that most of the OW students have no clue what M-value, tension, and bubble equalibrium even are. But that doesnt mean that theyre not considerations in the process as a whole. I, personally, hope I never have to decide whether or not to hit (say) 60ft or go to a chamber a long way away.

If I remember correctly, the ENTIRE reasoning discussed in MY OW class as to why a diver doesnt attempt IWR is because of the danger of OOA...........and that is very true, but lets look at it alittle deeper and decide whether or not that is entirely true.......say you have enough air with you to (last resort) attempt a IWR, you go down and relieve fast tissues, all the time loading slow tissues because of lack in understanding of the concept..............youre still bent, plenty of air, but bent.

Like I said, Im no expert........just trying to learn from conversation in a subject I hope never to have to contend with.

That was the point I ineffectively was trying to make.

I certanly dont condone IWR's for craps and giggles........thats just stupid. Im merely discussing the turns and twists of this unfortunate subject.


tiny bubbles

 

[cornfed]

gkwaldee once bubbled...
I completely agree with the liability issues. Id say that most of the OW students have no clue what M-value, tension, and bubble equalibrium even are. But that doesnt mean that theyre not considerations in the process as a whole.

I didn't say they weren't. I said that they aren't taught so you can't teach IWR.

I, personally, hope I never have to decide whether or not to hit (say) 60ft or go to a chamber a long way away.

I doubt you'll every have to make this choice. If you're in the US there will most likely be a chamber near by. (I'm sure people will want to argue with this assertation, so go ahead). If you're diving with some operation outside the US and there is no chamber nearby they might not let you go back down.

If I remember correctly, the ENTIRE reasoning discussed in MY OW class as to why a diver doesnt attempt IWR is because of the danger of OOA........... and that is very true,

That's just silly. The amount of gas you have on hand factors directly into your decision. If you don't have enough gas it doesn't matter how bad you want to get in the water.

but lets look at it alittle deeper and decide whether or not that is entirely true.......say you have enough air with you to (last resort) attempt a IWR, you go down and relieve fast tissues, all the time loading slow tissues because of lack in understanding of the concept..............youre still bent, plenty of air, but bent.

Like I said, they don't provide enough information for you (the basic OW or any rec diver) to understand what you're doing so it would be irresponsible to tell you to do it.

Cornfed