tx. for hypercapnea

[Ben_Ayers]

Few questions:

It is often suggested on the forums to breath deep and slow to treat high CO2 levels. Wouldn't it be more prudent to suggest a short period of deep breathing, with an increased rate, to correct the resp. acidosis? I understand that slow deep breaths should prevent CO2 build-up and encourage better gas exchange.

On another note: Someone mentioned in the Accidents Forum, that a diving accident was most likely due to a CO2 hit. I have never heard of this on open-circuit scuba! At the time I felt the most likely cause was ox tox. How likely is a CO2 "hit" (leading to drowning) on open-circuit scuba? I was under the impression that divers would experience symptoms such as SOB/anxiety long before it got to the point where one became toxic enough to cause unconsciousness and drowning.

Thanks,
Ben

 

[TSandM]

The critical thing in correcting hypercapnea is to increase the alveolar minute ventilation -- in other words, the volume of gas being moved through the gas exchanging portion of the lungs in a given period of time. Often, the way divers have BECOME hypercapneic is through an inefficient breathing pattern, with rapid, shallow breaths. With that pattern, dead space becomes a significant issue, and despite the rapid respiratory rate, CO2 levels can elevate. Switching to a slower, but much deeper breathing pattern increases the effective alveolar ventilation enormously. Trying to maintain a rapid AND deep breathing pattern is difficult -- Try it while you read this! If you tell someone to breathe quickly, they're going to breathe faster with a smaller tidal volume.

With respect to your other question, on land, elevated CO2 levels produce a rapid and intense anxiety and drive to breathe in normal people. However, people with lung disease can adapt to extremely abnormal CO2s over time. Apparently, there are some individuals who exhibit significant CO2 tolerance underwater, and elevated CO2 levels have been documented in these people. People who are utilizing techniques like skip breathing to try to conserve gas must adapt to elevated CO2s. However, the carbon dioxide is there, even if it isn't causing apprehension, and it is narcotic and lowers the threshold for oxygen toxicity seizures. The combination of elevated CO2 and nitrogen narcosis often results in the "dark narc", or an unpleasant sensation of dread or anxiety. Very high CO2 levels can result in unconsciousness -- I believe this is thought to be part of the cause of Dave Shaw's death at 800+ feet, when he overexerted while trying to recovery a body.