CO2 build-up at depth - what to do?

[kathydee]

I experienced something new and frightening @ 100ft about a month ago and am now convinced that it was CO2 build up w/mild narcosis.

It truly felt like I was rebreathing old air and getting no oxygen which resulted in a sense of panic and a seriously nagging desire to bolt for the surface.

Because air was coming into my lungs and bubbling out, I was able to logically tell myself that the tank was full -and felt comfort from the company of my partner and access to his octopus. But still, I felt I was receiving no oxygen and started feeling faint. We ascended a little, rested, felt better and continued the dive.

What is the best thing to do in a situation such as this?

If CO2 buildup occurs, does the body still receive oxygen if you continue to breathe from the reg?

Is the sense of suffocating just psychological, or is it also physical?

If you are in current can you continue swimming, sucking on the reg and functioning properly through the sensations?

Any advice would be greatly appreciated!

Thanks!

 

[Colliam7]

I experienced something new and frightening @ 100ft about a month ago and am now convinced that it was CO2 build up w/mild narcosis. It truly felt like I was rebreathing old air and getting no oxygen which resulted in a sense of panic and a seriously nagging desire to bolt for the surface.

Diagnosis from afar is always challenging. I suspect you are probably as accurate in your assessment as anyone could be. The circumstances were favorable for both narcosis and hypercapnia - depth (100ft) and exertion (current).

But still, I felt I was receiving no oxygen and started feeling faint. We ascended a little, rested, felt better and continued the dive. What is the best thing to do in a situation such as this?

You did the best thing. Ascended, and rested. Moreover, from your description, you maintained awareness, and control, of your situation, and were able to take appropriate action. Two other thoughts to consider. Breathing deeply is important. Although the normal volume of air inhaled with each breath is substantially greater than the 'dead space' of your airways, some people in such a situation actually exhibit a breathing pattern that is both more rapid and more shallow. That may inhibit efficient gas exchange, which is not what you need. Deeper breathing, at as close to a normal rate as possible, is a better approach. In addition, you mention 'sucking on the reg' which inevitably raises a question about the adjustment of your reg. Most regs are capable of delivering far more air than a human needs, but some are also associated with greater work of breathing than others, and that may have contributed to at least the psychological sensation you experienced.

If CO2 buildup occurs, does the body still receive oxygen if you continue to breathe from the reg?

Yes. You are still able to oxygenate, and expire CO2. A primary change is that you are producing CO2 at a more rapid rate (associated with exertion), and you need to increase your respiratory activity (deeper breaths) to compensate.

Is the sense of suffocating just psychological, or is it also physical?

Both. The 'sense' of suffocating is probably both a psychological entity, and manifestation of the physical response to an increased respiratory stimulus, caused by increased CO2. The physiology is a bit more complex but, fundamentally, increased CO2 production causes changes in blood chemistry (e.g. pH) that stimulate respiration.

If you are in current can you continue swimming, sucking on the reg and functioning properly through the sensations?

Yes. But, the best thing to do is reduce exertion to the extent that you can.

 

[knotical]

Deeper exhalations reduce the risk of CO2 buildup. They also improve air consumption and have a calming effect.

 

[Teamcasa]

Sometimes a poorly performing regulator will increase the breathing effort and a sense of suffocation and CO2 build up will ensue. Have your regulator serviced and inspected before your next dive.
If it happens on a dive, consciously make an effort to draw in a long, slow, deep breath followed by long, slow exhale. The sense of dread should subside.

I also agree with Colliam7, good answers.

 

[Bismark]

Colliam7 hit the nail on the head. Pretty crappy feeling isn't it? Your experiences are for me two of the arguments for using trimix in deeper dives that I find most compelling. Sadly, narcosis and C02 build up work hand in hand and one amplifies the other, which in turn amplifies the other......etc..........

 

[kathydee]

Thanks for the info!

The reg was balanced. I mentioned "sucking" because at a certain point, when vision and hearing started fading, awareness of air (that felt toxic) moving in and out of my body was all I had to hang on to.

Even though my body felt there was no oxygen in the air, the sound and sensation of air coming in and out of the reg was like a single pointed meditation mantra - a focus to keep me sane in a very insane feeling moment. Yes it was a "very crappy feeling" to have @ 100ft.

Because of current we dropped down really quickly that day. I have heard that a very rapid descent rate can amplify narcosis. Is this true?

 

[Walter]

If CO2 buildup occurs, does the body still receive oxygen if you continue to breathe from the reg?

You'll get as much oxygen from your regulator as you will breathing at the surface with no regulator. Colliam7 gave a very accurate answer. Follow his advice. The most important item in keeping calm is to take slow deep breaths. When we are over worked or nervous, we tend to take fast shallow breaths, the worst possible reaction.

 

[merxlin]

Thanks for the info!

The reg was balanced. I mentioned "sucking" because at a certain point, when vision and hearing started fading, awareness of air (that felt toxic) moving in and out of my body was all I had to hang on to.

Even though my body felt there was no oxygen in the air, the sound and sensation of air coming in and out of the reg was like a single pointed meditation mantra - a focus to keep me sane in a very insane feeling moment. Yes it was a "very crappy feeling" to have @ 100ft.

Because of current we dropped down really quickly that day. I have heard that a very rapid descent rate can amplify narcosis. Is this true?

It is possible although unlikely to overbreath a reg, balanced or not, at that depth. Not all regs breath well at 100ft if they are not adjusted properly. If yours is a newer model, it should be OK as most modern regs now have some way of compensating for depth.

Could you have been hyperventilating? And were you anxious about the dive (uncomfortable because of the current, rapid descent)? Your feelings:

I mentioned "sucking" because at a certain point, when vision and hearing started fading

Sounds to me (in a purely unprofessional and anecdotal way) like someone who's blood pressure has dropped. The good news is that your awareness of the situation was spot on, and avoided a much more troubling problem had you bolted to the surface. Since you seem to know about meditation and perhaps breathing techniques, make sure you are breathing into your diaphragm and lower chest (belly breathing), and pay particular attention to your exhalations. Make sure you expend all the air in a slow and controlled manner. Long inhales and exhales.

 

[spt29970]

You'll get as much oxygen from your regulator as you will breathing at the surface with no regulator. Colliam7 gave a very accurate answer. Follow his advice. The most important item in keeping calm is to take slow deep breaths. When we are over worked or nervous, we tend to take fast shallow breaths, the worst possible reaction.

I am a little confused by this statement. You will get substantially MORE oxygen through the regulator at depth than you get breathing on the surface due to the increased partial pressure. I am not a physician, but the breathlessness and feeling of "air starvation" has nothing to do with the amount of oxygen you are getting. The previous explanation is almost certainly correct. It was a combination of narcosis and hypercapnia (CO2 buildup due to exertion and shallow breathing).

I agree with the prescription of resting and ascending, but I would break it down into a few steps. First, stop moving. If you are kicking into a current let the current take you. You want to stop all exertion to reduce the production of CO2. Next, concentrate on slowing your breathing. At the same time concentrate on taking deep breaths to maximize gas exchange deep in your lungs. Finally work on your depth. If there is a wall or a rope nearby swim to it and steady yourself. Once you have the breathing and exertion under control, then work on adjusting your buoyancy (if necessary) and then ascending.

Maybe it is just me, but I find I do better if I break things apart into a series of sequential tasks rather than trying to do them all at once. I recently had a similar episode which was quite scary, especially since I have been diving for quite a while and have never had anything like it happen before.

It is described at http://www.scubaboard.com/forums/un...-into-deep-danger-getting-overly-focused.htmlhttp://scubaboard.com/forums/underw...-into-deep-danger-getting-overly-focused.html

 

[pasley]

You have had many replies that I believe are on point. Colliam7 did an excellent job of analysis on possible causes.

I want to add one other possible cause, although I must say I think it unlikely in your scenario, was your valve open completely? If you air was only turned on part way, everything will be fine shallow, but as you go deeper, you will experience more difficulty breathing and eventually may experience a false out of air situation (IE, receive no air with a full tank). Since after resting and calming down you continued the dive (I assume at 100+ feet) without incident, this is unlikely the cause. But I offer it only in case you continued the dive at a shallower depth.

As Colliam7 and Teamcasa said the more most likely cause was, narcosis and/or over breathing the regulator/hyperventilating (shallow rapid breathing causing an increase in CO2). Ascenting and breathing normal to slow deep breaths was the correct RX for the situation. Continuing the dive at your 100+ depth while feeling faint with field of vision narrowing and attempting to swim through the situation was/is not an option. If you had passed out (fainted) you (or your heirs) would not have liked the potential outcome.
In any event, what you experienced is not the norm, and you took appropriate action.

SPT29970 raises a good point as well. Have you had a physical lately? Are there any potential physical conditions that may have caused this? Again, I do not consider this the number 1 suspect but it can not be ruled out with out inspection.