Why O2 for DCS?

[giovyledzep]

Hello,

I have a technical question regarding the mechanism through which Oxygen helps with DCS symptoms. I am aware that it is an effective treatment, but I'm not clear on what actually happens inside the body as the Oxygen is breathed to help dissolve gas bubbles in the tissues. What are the reactions that take place?

Thank you for any elucidations.

 

[rsingler]

Apart from any direct effect of oxygen in supplying ischemic tissue downstream of an arterial bubble, the key reason a tight-fitting non-rebreathing oxygen mask is used is to eliminate nitrogen from the breathed gas.
With zero inspired N2, the nitrogen gradient between the DCS bubbles and the capillary gas content is maximized, theoretically helping to decrease the size of bubbles causing symptoms, by diffusion out of the bubble.
That is why oxygen administration for DCS is mostly a wasted effort, because it is the rare diver who knows to never take the mask off to talk, which then promptly adds 79% N2 back into the bloodstream. And a loosely fitting airline style mask or nasal cannula oxygen is just a waste of limited gas you might really need if the diver deteriorates during transport.

Of course, in the event of life threatening symptoms such as unconsciousness or airway obstruction, oxygen administration has its own benefit as a necessary life-sustaining gas during resuscitation.

Diving Doc

 

[giovyledzep]

Apart from any direct effect of oxygen in supplying ischemic tissue downstream of an arterial bubble, the key reason a tight-fitting non-rebreathing oxygen mask is used is to eliminate nitrogen from the breathed gas.
With zero inspired N2, the nitrogen gradient between the DCS bubbles and the capillary gas content is maximized, theoretically helping to decrease the size of bubbles causing symptoms, by diffusion out of the bubble.
That is why oxygen administration for DCS is mostly a wasted effort, because it is the rare diver who knows to never take the mask off to talk, which then promptly adds 79% N2 back into the bloodstream. And a loosely fitting airline style mask or nasal cannula oxygen is just a waste of limited gas you might really need if the diver deteriorates during transport.

Of course, in the event of life threatening symptoms such as unconsciousness or airway obstruction, oxygen administration has its own benefit as a necessary life-sustaining gas during resuscitation.

Diving Doc

Thanks for the info, now I understand.
What about how long? If someone is experiencing mild DCS symptoms is there a min/max duration for administration or is it just until symptoms resolve?

 

[dewdropsonrosa]

The lower boundary would be until resolution of symptoms.

The upper boundary would be defined by an individual's susceptibility to oxygen toxicity as a result of hyberbaric treatment (see abstract)(scientific article, may have paywall), or a reasonable prudent approximation by some other measure (CNS clock, OTU exposure, etc.).

 

[rsingler]

@Duke Dive Medicine reminds me that I've engaged in a bit of hyperbole in my comments. Anything that increases your inspired oxygen fraction will decrease your inspired nitrogen concentration, further increasing the gradient between what's in the bubble and what you breathe. Even air has a gradient compared with the partial pressure of nitrogen in the DCS bubble.
But the point remains, higher oxygen means lower nitrogen, and time is of the essence. And if you're going to use that single small cylinder in the green DAN box on your boat, racing for home, why not do it properly? It's going to be empty in less than an hour, at the rate you use it with a demand valve. You'll get longer with nasal cannula or a mask on low flow, but the benefit is debatable.

 

[Duke Dive Medicine]

Thanks for the info, now I understand.
What about how long? If someone is experiencing mild DCS symptoms is there a min/max duration for administration or is it just until symptoms resolve?

Surface O2 is considered first aid for decompression sickness. The definitive treatment is hyperbaric oxygen therapy. If symptoms resolve on surface O2 and that O2 is discontinued, the symptoms can return and even worsen. If the diver is very far removed from help and mild DCS symptoms resolve on surface O2, hyperbaric treatment may not be necessary, but that's an individual decision and best discussed with a diving medical specialist at the time.

Best regards,
DDM

 

[Jayfarmlaw]

Ok docs, I have the standard non rebreather masks in my 02 kit. I didn't buy the Dan kit because an 02 kit can be pieced together for less than $100....with a bigger bottle. Is there a better mask for a conscious victim than the $4 or $5 generic masks with the bags on the bottom? Like these:

Amazon.com: Adult Non-Rebreather Oxygen Mask: Health & Personal Care

Thanks in advance for your response, Merry Christmas!

Jay

 

[Duke Dive Medicine]

Hi Jay, Merry Christmas to you as well! A non-rebreather is fine as long as you pre-inflate the bag (not like the emergency O2 masks on a plane) and flow it at the proper rate, usually 10-15 liters per minute.

Best regards,
DDM

 

[GJC]

Ok docs, I have the standard non rebreather masks in my 02 kit. I didn't buy the Dan kit because an 02 kit can be pieced together for less than $100....with a bigger bottle. Is there a better mask for a conscious victim than the $4 or $5 generic masks with the bags on the bottom? Like these:

Amazon.com: Adult Non-Rebreather Oxygen Mask: Health & Personal Care

Thanks in advance for your response, Merry Christmas!

Jay

Your nonrebreather masks will deliver 90 to 95% oxygen to your patient. A small amount of room air is inhaled because the mask is not sealed.

A demand valve will deliver 100% with a good seal against the face. It's a lot more expensive than a nonrebreather, but is reusable after cleaning between use.

The advantages are that it delivers 100% and only uses about 6 to 10 liters per minute from your oxygen tank.

The disadvantages are initial cost and it is uncomfortable when properly sealed against the face over long periods of time

Demand Valves | Bound Tree

 

[Dr Simon Mitchell]

A demand valve will deliver 100% with a good seal against the face. It's a lot more expensive than a nonrebreather, but is reusable after cleaning between use.

The advantages are that it delivers 100% and only uses about 6 to 10 liters per minute from your oxygen tank.

The disadvantages are initial cost and it is uncomfortable when properly sealed against the face over long periods of time

Hello GJC,

In theory, a demand valve will "deliver 100% with a good seal against the face" but in practice that is unlikely to happen. The problem is that divers do not maintain a very good seal. Denise Blake (an emergency physician and PhD student supervised by Neal Pollock and myself) compared tissue oxygenation and (among other things) nasopharyngeal oxygen levels during use of a demand valve coupled with several types of oronasal mask and an intraoral mask (effectively a mouthpiece) with or without a noseclip. The most effective configuration was a intraoral mask with noseclip, and the worst was the oronasal mask traditionally supplied with the DAN oxygen kit. Nasopharyngeal oxygen with the latter was barely above 50% and tissue oxygenation was correspondingly much lower. I advise divers to adapt a mouthpiece onto their DAN oxygen regulator.

I have attached the relevant paper. It is also available at:

Comparison of tissue oxygenation achieved breathing oxygen from a demand valve with four different mask configurations

The reference is:

Blake DF, Crowe M, Lindsay D, Brouff A, Mitchell SJ, Pollock NW. Comparison of tissue oxygenation achieved breathing oxygen from a demand valve with four different mask configurations. Diving Hyperbaric Med. 2018;48(4):209-217.

Simon M