Hypercapnia Hit and then planning for BO with a delayed Deco Switch?

[Heat Miser]

At last week's local dive club AGM, I was discussing recent events, where training exercises at local dams/quarries had resulted in several Hypercapnia events. I'm doing the gas planning for a similar dam dive this weekend (without the obvious training stress), and I'm uber-sensitive to "what would happen if I had to bail-out from a Hypercapnia" (i.e + 45 Litres per/min SAC) and for how long, Sorry AUKUS cousins I don't know how to put that into imperial for you, but if you give me a sub I'll learn

In my case, I'm diving a hCCR. However, obviously an event can happen on Open Circuit as well. So in terms of planning a deco dive should divers (After bailing out/switching and thumbing the dive) consciously space out their bottom gas, in order to give themselves the maximum amount of PPO2 at shallower deco depths so as to not get bent/run out of gas.

Alternatively is it sensible to switch to the richest mix possible as early as you can.

For example say you have a bailout event at 40 meters (130 feet) but you diving with an Ally 80 Tx 18/45 bottom gas and an Ally 40 deco mix of Nx 50, should you suck the Ally 80 until 9 meters (30 feet) before switching to your 6-3m deco (6-10 ft) Deco for say 20 minutes before looking for the next solution (i.e. Buddy / Back on Breather / Surfacing)

Or should you just do what I'm thinking and dive with 2 Ally 80's (1 bottom - 1 deco)

Obviously its a function of runtime / overhead / remaining deco time / depth but in the 'heat of the moment' are there ANY SIMPLE RULES TO FOLLOW? ... Your thoughts ...

follow up edit see below

Let me ask the question in a simpler way ...

Assuming all other things are equal, depth, resting, not breathing faulty reg etc. Will switching to a richer ppO2 mix reduce tachypnea (rapid breathing) faster? Or is it largely a function of reduced gas density that reduces rapid breathing.

 

[crofrog]

I think there are breathing techinques that are worth learning to help the body exchange gas more effectively.

I think there have been some studies showing that diaphragmatic breathing, and double-inhale prolonged exhale breathing help exchange CO2 and simulate the vagus nerve to lower heart rate?

@Duke Dive Medicine are you aware of any studies that talk about that as it relates to diving, or do you believe the physiology of those breathing techniques might help reduce the gas consumption?

 

[Duke Dive Medicine]

I think there are breathing techinques that are worth learning to help the body exchange gas more effectively.

I think there have been some studies showing that diaphragmatic breathing, and double-inhale prolonged exhale breathing help exchange CO2 and simulate the vagus nerve to lower heart rate?

@Duke Dive Medicine are you aware of any studies that talk about that as it relates to diving, or do you believe the physiology of those breathing techniques might help reduce the gas consumption?

Thanks for the add... I'm not 100% sure I understand the question and apologies if this misses the mark, but I understand correctly, there's been a similar thread recently on how long the tachypnea (rapid breathing) lasts in a hypercapnic event and how much gas would be required. I can't seem to find it otherwise I'd link it.

Anyway, if so, breathing techniques are largely irrelevant in the moment, since the hypercapnic ventilatory response is difficult if not impossible to override. The breathing rate should normalize within a couple of minutes of being on OC and resting (if bailing from a CCR d/t canister breakthrough or sorb exhaustion). Absent equipment malfunction, OC hypercapnia events are generally caused by exertion that leads to overbreathing the regulator. That would be more amenable to resting in place than switching gases.

Best regards,
DDM

 

[jgttrey]

At last week's local dive club AGM, I was discussing recent events, where training exercises at local dams/quarries had resulted in several Hypercapnia events. I'm doing the gas planning for a similar dam dive this weekend (without the obvious training stress), and I'm uber-sensitive to "what would happen if I had to bail-out from a Hypercapnia" (i.e + 45 Litres per/min SAC) and for how long, Sorry AUKUS cousins I don't know how to put that into imperial for you, but if you give me a sub I'll learn

In my case, I'm diving a hCCR. However, obviously an event can happen on Open Circuit as well. So in terms of planning a deco dive should divers (After bailing out/switching and thumbing the dive) consciously space out their bottom gas, in order to give themselves the maximum amount of PPO2 at shallower deco depths so as to not get bent/run out of gas.

Alternatively is it sensible to switch to the richest mix possible as early as you can.

For example say you have a bailout event at 40 meters (130 feet) but you diving with an Ally 80 Tx 18/45 bottom gas and an Ally 40 deco mix of Nx 50, should you suck the Ally 80 until 9 meters (30 feet) before switching to your 6-3m deco (6-10 ft) Deco for say 20 minutes before looking for the next solution (i.e. Buddy / Back on Breather / Surfacing)

Or should you just do what I'm thinking and dive with 2 Ally 80's (1 bottom - 1 deco)

Obviously its a function of runtime / overhead / remaining deco time / depth but in the 'heat of the moment' are there ANY SIMPLE RULES TO FOLLOW? ... Your thoughts ...

I, too, am not sure I understand the question. It seems like you are asking whether there are simple rules for disregarding what your dive planning software/dive computer are calculating for optimal deco. Absent some equipment failure, gas loss or poor dive planning, why would you ever depart from the optimal deco schedule for your BO ascent? That plan, by definition, will have gas switches to the next richer gas as soon as PO2 limits allow (in your case switching to EAN50 at 70'). I get the sense there is some aspect of this hypothetical I must be missing.

Run your worst-case BO scenario(s) in something like multideco using realistic SAC rates and whatever GF you feel is appropriate, see what the volume requirements are, build in your safety factor per training, then stick to the schedule it or your dive computer generates. The simple rule is get shallow as quickly as the schedule allows. I'd never loiter around deeper than I needed to be, breathing a non-optimal gas, and delaying my ascent.

Separately and with the caveat that there are no details about the exact dive plan, that sounds like a non-optimal BO setup. I don't know how deep you're going, but if 40m is your bottom depth, 18/45 is leaner than it needs to be and gives you an unnecessary helium penalty both on deco and the wallet. And the quantities seem reversed for an open water dive where you are making a direct ascent. If your rich mix is EAN50, you're switching off your deep mix at 70', which means you're not going to be on the deep mix very long at all. Run some dive BO dive plans and see what you need, then dive the plan.

Again, apologies if I'm misunderstanding.

 

[Alaskan Scuba Dude]

Alternatively is it sensible to switch to the richest mix possible as early as you can.

Why?

Or should you just do what I'm thinking and dive with 2 Ally 80's (1 bottom - 1 deco)

Yes.

 

[KenGordon]

At last week's local dive club AGM, I was discussing recent events, where training exercises at local dams/quarries had resulted in several Hypercapnia events. I'm doing the gas planning for a similar dam dive this weekend (without the obvious training stress), and I'm uber-sensitive to "what would happen if I had to bail-out from a Hypercapnia" (i.e + 45 Litres per/min SAC) and for how long, Sorry AUKUS cousins I don't know how to put that into imperial for you, but if you give me a sub I'll learn

In my case, I'm diving a hCCR. However, obviously an event can happen on Open Circuit as well. So in terms of planning a deco dive should divers (After bailing out/switching and thumbing the dive) consciously space out their bottom gas, in order to give themselves the maximum amount of PPO2 at shallower deco depths so as to not get bent/run out of gas.

Alternatively is it sensible to switch to the richest mix possible as early as you can.

For example say you have a bailout event at 40 meters (130 feet) but you diving with an Ally 80 Tx 18/45 bottom gas and an Ally 40 deco mix of Nx 50, should you suck the Ally 80 until 9 meters (30 feet) before switching to your 6-3m deco (6-10 ft) Deco for say 20 minutes before looking for the next solution (i.e. Buddy / Back on Breather / Surfacing)

Or should you just do what I'm thinking and dive with 2 Ally 80's (1 bottom - 1 deco)

Obviously its a function of runtime / overhead / remaining deco time / depth but in the 'heat of the moment' are there ANY SIMPLE RULES TO FOLLOW? ... Your thoughts ...

I think you are asking whether to use all your bottom bailout to save on shallow bailout while breathing like a train?

My reply is to plan for this exact scenario as it is the worst case. If you can make it to 6m while breathing at 45l/minute off the deep bailout then have an appropriate gas for that depth as your second bailout. Then play the usual ascent compromise game of slightly weaker and so on it deeper game to optimise for whichever gas becomes the limiting factor.

Multi deco has a max time option in bailout that makes doing this easy.

On the actual dive stick to the plan, this is why you made a plan. What would be the benefit of staying bottom gas longer if your plan says you have enough shallow bailout for this exact circumstance?

 

[Searcaigh]

For example say you have a bailout event at 40 meters (130 feet) but you diving with an Ally 80 Tx 18/45 bottom gas and an Ally 40 deco mix of Nx 50, should you suck the Ally 80 until 9 meters (30 feet) before switching to your 6-3m deco (6-10 ft) Deco for say 20 minutes before looking for the next solution (i.e. Buddy / Back on Breather / Surfacing)

I am also a bit confused by this scenario.

Why not switch to the Nx50 at 21m?

 

[Heat Miser]

Thanks for the add... I'm not 100% sure I understand the question and apologies if this misses the mark, but I understand correctly, there's been a similar thread recently on how long the tachypnea (rapid breathing) lasts in a hypercapnic event and how much gas would be required. I can't seem to find it otherwise I'd link it.

Anyway, if so, breathing techniques are largely irrelevant in the moment, since the hypercapnic ventilatory response is difficult if not impossible to override. The breathing rate should normalize within a couple of minutes of being on OC and resting (if bailing from a CCR d/t canister breakthrough or sorb exhaustion). Absent equipment malfunction, OC hypercapnia events are generally caused by exertion that leads to overbreathing the regulator. That would be more amenable to resting in place than switching gases.

Thanks, yes I realise this a very open ended question, which could be solved by knowing how long the tachypnea (rapid breathing) is going to last.

And I intentionally posted the scenario with a sub optimal (not the best mix) bailout gas for the depth.

Let me ask the question in a simpler way ...

Assuming all other things are equal, depth, resting, not breathing faulty reg etc. Will switching to a richer ppO2 mix reduce tachypnea (rapid breathing) faster? Or is it largely a function of reduced gas density that reduces rapid breathing.

 

[Heat Miser]

Let me ask the question in a simpler way ...

Assuming all other things are equal, depth, resting, not breathing faulty reg etc. Will switching to a richer ppO2 mix reduce tachypnea (rapid breathing) faster? Or is it largely a function of reduced gas density that reduces rapid breathing.

yes even simpler:

I think you are asking whether to use all your bottom bailout to save on shallow bailout while breathing like a train?

 

[Alaskan Scuba Dude]

For those who have been trained in all extremities of despair, I would not go into a hypercapnia situation. You may not survive unless you can rectify your breathing difficulties. I myself would try to finish off the decompression obligation as quick as possible and continue to purge the regulator to flush your lungs, provided you do not panic and resist the urge to surface.

What is the best treatment to resolve hypercapnia?

Breathing Machines

If you are struggling with moderate or severe hypercapnia, your doctor may recommend a device to help you breathe. Often, the first type of device they will try is a continuous positive airway pressure (CPAP) or bi-level positive airway pressure (BiPAP) device.