Fingertip Pulse ox meter and DCS

[doctormike]

And, those logistics raise an interesting question. Is the patient better off with the maximum gradient for as long as possible, or a reduced gradient for a longer period of time? I can see arguments both ways.

You mean from a decompression point of view? That's what decompression algorithms and recompression tables do - optimize offgassing. DDM can give you the real answer, but if you are talking about a patient with DCS, then the standard treatment (e.g. Navy table 6) involves O2 and air segments at standard pressures. It's not just a question of 100% O2 for as long as possible...

 

[TrimixToo]

You mean from a decompression point of view? That's what decompression algorithms and recompression tables do - optimize offgassing. DDM can give you the real answer, but if you are talking about a patient with DCS, then the standard treatment (e.g. Navy table 6) involves O2 and air segments at standard pressures. It's not just a question of 100% O2 for as long as possible...

View attachment 477595

The context was pre-chamber surface treatment, I thought. So let me rephrase: If the available O2 supply is limited, perhaps you can have 100% O2 for, say 30 minutes, or say, 50% for an hour. Which option offers the best choice for survival or minimizing injury? Without any more information, I'd opt for 100% for as long as it lasted to lower the PPinert to the extent possible as quickly as possible, but on the few occasions in which I've had to offer anyone O2 we had plenty on hand and supply was not at issue. What should we choose to do if the supply is short?

 

[doctormike]

The context was pre-chamber surface treatment, I thought. So let me rephrase: If the available O2 supply is limited, perhaps you can have 100% O2 for, say 30 minutes, or say, 50% for an hour. Which option offers the best choice for survival or minimizing injury? Without any more information, I'd opt for 100% for as long as it lasted to lower the PPinert to the extent possible as quickly as possible, but on the few occasions in which I've had to offer anyone O2 we had plenty on hand and supply was not at issue. What should we choose to do if the supply is short?

Aha... sorry, I misunderstood.

Last year, there was a worskhop on exactly this topic. The full content of the workshop is in preparation for publication, but a summary with guideline statements was just published in Undersea and Hyperbaric Medicine:

Consensus guideline: Pre-hospital management of decompression illness: expert review of key principles and controversies.

Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P.

This is the guideline on that question in the first aid section. I'm looking forward to reading the whole thing when it's available:

A. Normobaric oxygen (surface oxygen administered as close to 100% as possible) is beneficial in the treatment of DCI. Normobaric oxygen should be administered as soon as possible after onset of symptoms.

B. Training of divers in oxygen administration is highly recommended.

C. A system capable of administering a high percentage of inspired oxygen (close to 100%) and an oxygen supply sufficient to cover the duration of the most plausible evacuation scenario is highly recommended for all diving activities.

In situations where oxygen supplies are limited, and where patient oxygenation may be compromised (such as when drowning and DCI coexist) consideration should be given to planning use of available oxygen to ensure that some oxygen supplementation can be maintained until further supplies can be obtained.

 

[TrimixToo]

Aha... sorry, I misunderstood.

Last year, there was a worskhop on exactly this topic. The full content of the workshop is in preparation for publication, but a summary with guideline statements was just published in Undersea and Hyperbaric Medicine:

Consensus guideline: Pre-hospital management of decompression illness: expert review of key principles and controversies.

Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P.

This is the guideline on that question in the first aid section. I'm looking forward to reading the whole thing when it's available:

A. Normobaric oxygen (surface oxygen administered as close to 100% as possible) is beneficial in the treatment of DCI. Normobaric oxygen should be administered as soon as possible after onset of symptoms.

B. Training of divers in oxygen administration is highly recommended.

C. A system capable of administering a high percentage of inspired oxygen (close to 100%) and an oxygen supply sufficient to cover the duration of the most plausible evacuation scenario is highly recommended for all diving activities.

In situations where oxygen supplies are limited, and where patient oxygenation may be compromised (such as when drowning and DCI coexist) consideration should be given to planning use of available oxygen to ensure that some oxygen supplementation can be maintained until further supplies can be obtained.

Maybe this is explained in what you linked to, but my question remains. What if there is NOT enough O2 to cover the evac? What's best? 100% for as long as possible or less than 100% for a longer period? I realize you might not have a definitive answer, and that nobody might actually have it. I'll settle for well-informed guesses from medical professionals if that's the case, because they are more likely to be better than my own.

 

[doctormike]

Maybe this is explained in what you linked to, but my question remains. What if there is NOT enough O2 to cover the evac? What's best? 100% for as long as possible or less than 100% for a longer period?

The way I read that last paragraph is that they are suggesting the second option - some O2 until you can get more. That to me would mean it’s better to supplement o2 for the whole ride than to do 100% and then switch to room air.

But it will be interesting to read the actual workshop proceedings.

 

[TrimixToo]

The way I read that last paragraph is that they are suggesting the second option - some O2 until you can get more. That to me would mean it’s better to supplement o2 for the whole ride than to do 100% and then switch to room air.

But it will be interesting to read the actual workshop proceedings.

I will await them as well. I was thinking of pure DCS, though. So that paragraph seems, to my lay eyes, to leave my question open with, "where patient oxygenation may be compromised (such as when drowning and DCI coexist)." Severe DCS can compromise oxygenation to blocked vessels as well, right? So think what we have seen so far is "you have to guess at whether the DCS is so bad that when the O2 runs out oxygenation will still be compromised enough to increase the risk of survival or permanent injury, or whether decreasing the inert gas load as quickly as possible offers a better chance."

I hope I never have to make that choice, and I try hard to have plenty of extra O2 on hand (more than enough to satisfy the needs of a buddy who loses access to O2 deco gas, to start), but if I do, I'd sure like to know which is better if I have any option at all. Anything that helps me make the right decision might someday save someone's life (like my own!).

 

[doctormike]

And this may bring us back to the original question - the utility of a pulse oximeter. Most of these first aid guidelines are written to minimize the need for non medical personnel to make accurate diagnoses. In most cases it doesn’t matter - it’s not going to change what you do. But if you are transporting a really sick diver, knowing if his A-a gradient (a measure of lung function) was normal or not could help you decide whether or not to try to make the O2 last. If sat is 100% on room air then the lungs are working and it’s just DCS. If the patient is desaturated, then maybe better to keep some O2 going as long as possible. Don’t know if this is feasible.

 

[uncfnp]

Maybe this is explained in what you linked to, but my question remains. What if there is NOT enough O2 to cover the evac? What's best? 100% for as long as possible or less than 100% for a longer period? I realize you might not have a definitive answer, and that nobody might actually have it. I'll settle for well-informed guesses from medical professionals if that's the case, because they are more likely to be better than my own.

Interesting conundrum. So not a dive medical profession here but I wonder if the answer might in part depend on your O2 delivery system. If you are able to provide true 100% oxygen this would seem to be the best option since part of the benefit, as I understand it, is no nitrogen in the inspired air. But many rescuer first air delivery systems supply much less, including the nonrebreather which in reality may deliver around 80%. If this is the case I wonder if it might be best to find the “sweet spot” in flow rate that will maximum oxygen percentage delivery while minimizing O2 use.

 

[TrimixToo]

And this may bring us back to the original question - the utility of a pulse oximeter. Most of these first aid guidelines are written to minimize the need for non medical personnel to make accurate diagnoses. In most cases it doesn’t matter - it’s not going to change what you do. But if you are transporting a really sick diver, knowing if his A-a gradient (a measure of lung function) was normal or not could help you decide whether or not to try to make the O2 last. If sat is 100% on room air then the lungs are working and it’s just DCS. If the patient is desaturated, then maybe better to keep some O2 going as long as possible. Don’t know if this is feasible.

Good question. Blood oximeters are surprisingly cheap on Amazon. (Like $23 with free shipping if you have Prime.) Will it help a lay person make a decision, or would that be wandering into "practicing medicine without a license)" territory--eespecially if it's not me about whom the decision should be made, but someone else?

 

[doctormike]

Good question. Blood oximeters are surprisingly cheap on Amazon. (Like $23 with free shipping if you have Prime.) Will it help a lay person make a decision, or would that be wandering into "practicing medicine without a license)" territory--eespecially if it's not me about whom the decision should be made, but someone else?

Well, you are already providing first aid in that scenario (administering oxygen). This would just be a device to help you effectively do that procedure and decide if you should try to stretch our your O2 supply to help with underlying lung disease or just keep them on 100% as long as possible in hopes of treating isolated DCS.

To quote the first thing I said when I joined this thread, "I'm not a hyperbaric doc"...