In-Water Recompression, Revisited

At a gut level, I agree that this is probably true but fortunately haven't personally seen any real-world indication. Please don't take this as a challenge to the statement rather than curiosity.

TT5 IWR... interesting question. This comes to mind:

• After a serious decompression dive (which I wouldn't do without a chamber within an hour). Edit: Omitted decompression perhaps. What is serious decompression? More than half an hour feels about right.
• Severe/undeniable Type 1 symptoms or any hint of Type 2
• A competent support crew, preferably commercial or military diving supers.
• No symptom relief at the 20-33' mark... but I would cheat on conventional IWR by lobbying the dive super for 33'.
• Complete IWR prep
  • 2 or more FFMs or hats with hard-wire comms -- I would treat the buddy prophetically though not at 60' without symptoms
  • Air bailouts and manifolds
  • Umbilicals with pneumos and console
  • Ideally hot water suits or very warm water
  • Shock-isolating downlines (ideally in protected waters)
  • Body bags with weights for burial at sea

 

You can easily find posts on Scubaboard that are only a few years old that claim that any form of IWR is too dangerous to ever consider. The fact is that IWR is dangerous but can be less dangerous with preparation and special equipment.

 

Body bags. You almost made me spit out my non-GMO fig bar.

I would imagine that improvement may be slower at conventional IWR depths than at 60 feet in the chamber, but that would be highly individual.

Pulmonary DCS is probably the most rapidly debilitating and fatal manifestation in a scenario like that. IMO it's a tradeoff because even with recompression in a chamber those patients can still die from pulmonary edema r/t secondary effects of the bubbles. How far down do you (the figurative you) want a diver who may go into respiratory arrest? A big brain hit would be another possibility, in which case the diver could be unstable and would be at much higher risk of seizure at 60 feet than 20, 25, 30 or 33. Benzodiazepines would be tough to give unless you can aerosolize Ativan down the umbilical

Interesting intellectual exercise, hopefully the overall message will not be lost for posterity.

Best regards,
DDM

 

It might be worth reviewing what is going on during DCS treatment. The basics boil down to reducing the size of bubbles in the blood stream and expediting elimination. It comes down to compression and elevated ppO2. There is a tremendous amount data on DCS chamber treatments at 60' and very little at 30'... why would anyone bother stopping at 30' if you have a chamber?

Compressing to 60' is usually enough to reduce bubble size enough to significantly restore blood flow. Therefore, if symptoms are significantly improved at 20-33' there is no motivation to increase the risk of OxTox by going deeper during IWR. Once blood flow is presumably improved, spending more time at half the depth will just take a bit longer to eliminate dissolved gas.

There are rarely used tables that treat to 165' on air and deeper when relief is not achieved in a chamber at 60'. This brings up an interesting discussion for rebreather divers. Would IWR after deep exposure be more effective by maxing out the ppO2 (1.6+) and diving to the depth of relief? Bubble compression resolves the most time-sensitive problem of blocked blood flow and possible nerve impingement. Once that is accomplished, the issue is largely expediting inert gas elimination.

OK, but is pulmonary edema something you are going to worry about at the point where IWR is a consideration? Is the risk of pulmonary edema any greater in the water than in a chamber (again a sincere question)?

 

Too dramatic? I included it to provide perspective.

Meanwhile, I owe you a nutrition bar... or a beer if we ever get a chance to meet.

 

Like you said, bubbles won't be reduced in size as much and the inert gas pressure gradient is less at IWR depths which would increase washout time, but I'd agree that the relatively small gain in that area you would get by going to 60 feet under water is not worth the concomitant risk. Also, O2 has vasoconstrictive effects at partial pressures as low as 0.6 ATA, and it has anti-inflammatory properties at IWR pressures, so the diver is still getting those benefits along with the increased dissolution of O2 and diffusion into the extravascular spaces.

I don't think there's anything to be gained by going to depth of relief on 1.6 ATA and a lot to be lost, so to speak, with the possibility of inert gas bubble growth, increasing tissue inert gas load and having a bent diver farther from help on the surface.

Re pulmonary edema, the fluid redistribution that occurs with immersion could increase pulmonary artery pressure and cause pulmonary edema to worsen in divers with pulmonary DCS.

I'll hold you to that and get the second round!

 

That is the great advantage of pure O2. You don't need a computer or PhD to know that none of the tissues will be taking on diluent instead of giving it off.

I was at Ekofisk in the mid-1970s when a diver passed out (but still breathing) before getting in the chamber for his Sur-D-O2 run. A tender jumped in with him and we drove him straight to 60'. A quick huddle and we took him off the O2 mask and headed to 165'. He started to regain consciousness around 150'. He was fine after the half hour at 165' on air but got a little disoriented at around 80'. Crap, we didn't have any rich treatment mixes or a mix-maker onboard. We held at 75' for a quick huddle and decided to let him take five breaths off the O2 BIBs and five from the chamber. He started to show improvement after about 15 minutes so left him on the mask while moving to the 60' stop. We had no way of calculating if he took on too much Nitrogen so we added a 20 minute cycle to Table 6a at 60' and completed the run without incident.


Note: Green is breathing Oxygen and light blue is breathing air/chamber atmosphere

He was fine, but not a happy camper. Two other divers that week were hit a few hours after Sur-D-O2 on the company's "new deep tables". A few heated minutes on the radio and he was on the next chopper to shore and the new tables were over the side. Yeah, that sucked. However it gave me an appreciation for the value of depth. The problem is that the majority of our treatment data is from hits after relatively short duration dives that are less than 200'. How much treatment data do we really have for the 300'+ jumps that these rebreather warriors are doing?

Related Sidebar:
I was talking to a diver nearing his 30 year retirement from the Navy. He did a tour at EDU and was a guinea pig on some treatment table development dives. I asked him why they stopped at 60' instead of 66'/3 ATA. He said, "Simple, the gauges weren't accurate enough on fleet's chambers -- like +/-10' midscale". Yikes, I was ready for some great physiology insights.