CPAP in dcs

[huzenhagen]

This thread is mostly me just thinking aloud but I've been ruminating it on a bit so I thought I'd open it up to the floor.

The treatment for DCS is oxygen to help off gas nitrogen as quickly as possible +/- recompression as necessary. We know that a reservoir mask at 15l/minute of 02 is going to give us an fi02 of .8 at best. CPAP would increase that to as close to 100% as realistically possible and open up alveoli to maximise gas exchange and get rid of as much nitrogen as possible.

That said there are some big problems with this. Namely the issue of providing positive pressure to a lung that may have suffered barotrauma although we are only talking about 5-10cm of h20 which isn't very much in the grand scheme of things. There's also the issue that CPAP is horrible and not tolerated well and the issue of equipment but this is my hypothetical scenario so we will ignore the latter point.

I guess it comes down to a risk benefit analysis and does the benefit (if any) of a slightly increased diffusion gradient in the lungs and better gas exchange outweigh the risks of giving a casualty additional barotrauma. So my question is, does it?

 

[miketsp]

..snip..
The treatment for DCS is oxygen to help off gas nitrogen as quickly as possible +/- recompression as necessary. We know that a reservoir mask at 15l/minute of 02 is going to give us an fi02 of .8 at best.

I thought that reservoir masks are more efficient reaching 90% and the extra complexity needed to deliver the additional 10% (power supply for the CPAP machine) will be a complication in most diving situations and bring minimal extra benefit.

Oxygen Delivery Methods

Nonrebreathing face mask with reservoir and one-way valve
The nonrebreathing face mask is indicated when an FI,O₂ >40% is required. It may deliver FI,O₂ up to 90% at high flow settings. Oxygen flows into the reservoir at 8-10 L·min^-1, washing the patient with a high concentration of oxygen. Its major drawback is that the mask must be tightly sealed on the face, which is uncomfortable. There is also a risk of CO₂ retention [2]

CPAP would increase that to as close to 100% as realistically possible and open up alveoli to maximise gas exchange and get rid of as much nitrogen as possible.

That said there are some big problems with this. Namely the issue of providing positive pressure to a lung that may have suffered barotrauma although we are only talking about 5-10cm of h20 which isn't very much in the grand scheme of things. There's also the issue that CPAP is horrible and not tolerated well and the issue of equipment but this is my hypothetical scenario so we will ignore the latter point.

I guess it comes down to a risk benefit analysis and does the benefit (if any) of a slightly increased diffusion gradient in the lungs and better gas exchange outweigh the risks of giving a casualty additional barotrauma. So my question is, does it?

If the patient is breathing spontaneously then in a diving environment a demand regulator would seem to be preferable to deliver 100% with least complexity.

In any case I assume you're talking about the transport phase and not as a definitive treatment which will still need a recompression chamber. There is debate about O2 alone being an effective treatment for DCS.

Alert Diver | Oxygen as Definitive Treatment

 

[Duke Dive Medicine]

The treatment for DCS is oxygen to help off gas nitrogen as quickly as possible +/- recompression as necessary. We know that a reservoir mask at 15l/minute of 02 is going to give us an fi02 of .8 at best. CPAP would increase that to as close to 100% as realistically possible and open up alveoli to maximise gas exchange and get rid of as much nitrogen as possible.

That said there are some big problems with this. Namely the issue of providing positive pressure to a lung that may have suffered barotrauma although we are only talking about 5-10cm of h20 which isn't very much in the grand scheme of things. There's also the issue that CPAP is horrible and not tolerated well and the issue of equipment but this is my hypothetical scenario so we will ignore the latter point.

I guess it comes down to a risk benefit analysis and does the benefit (if any) of a slightly increased diffusion gradient in the lungs and better gas exchange outweigh the risks of giving a casualty additional barotrauma. So my question is, does it?

Good thoughts. To expand on the "+/- recompression as necessary" part: Surface O2 alone may be considered for uncomplicated type I skin bends (as opposed to cutis marmorata, or skin marbling) but divers with any additional DCS symptoms should be evaluated by a diving physician and treated in a hyperbaric chamber. There are a number of cases (we've treated several ourselves) where DCS symptoms resolved on surface O2 but reoccurred after the O2 was discontinued.

CPAP probably wouldn't hurt a diver with DCS. I'd be hesitant to use it for suspected AGE for the reason you specified, though if an AGE patient is intubated the minimum ventilator pressure settings would be right around that.

Best regards,
DDM

 

[DocVikingo]

That said there are some big problems with this. Namely the issue of providing positive pressure to a lung that may have suffered barotrauma although we are only talking about 5-10cm of h20 which isn't very much in the grand scheme of things.

Hi huzenhagen,

While lung tissue is quite delicate matter, pressures in the range of 5-10 cm of H20 are well below the threshold that might be expected to cause damage, even to a lung already compromised by barotrauma.

Regards,

DocVikingo

This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual and should not be construed as such.

 

[TONY CHANEY]

Good answers all around.

 

[TSandM]

If there is any question of pneumothorax from barotrauma, I would NOT administer any positive pressure ventilation. Same with pneumomediastinum or subcutaneous emphysema, although there, you are not really running a lethal risk, as you are with pneumothorax.

In the more typical case of DCS, where lung trauma is not usually at issue, CPAP wouldn't hurt the patient, but as already said, is probably not worth the additional complexity, given that it would only be used during transport. It is often tolerated poorly and may require sedation, which might be contraindicated in someone in whom you really want to follow the neurologic exam. (Is the patient dizzy because they have vestibular symptoms, or because of the Ativan they got?)

 

[huzenhagen]

Sorry for the delay in replying, I was on holiday diving! Thanks for all the great replies. So it seems its exactly what I thought where it is potentially useful but with practical limitations but a tool in the box nonetheless. When it comes to medicine I'm an aggregation of marginals gains type of guy, to borrow the gb cycling teams terminology, and enjoy searching for little improvements everywhere.