Dive Medicine
Carbon Dioxide A Silent Killer (par t 1)
BY DR. DAVID SAWATZKY C
arbon dioxide (CO2) can be a silent killer for both open circuit and rebreather divers. CO2 is an excellent example of how a
thorough understanding of diving physiology can have a major impact on how we dive and our dive safety. There are two possible sources of CO2 in diving. First, as we ‘burn’ food inside our bodies, we produce CO2 in addition to energy, water, and other waste products. We produce a basic amount of CO2 all the time, but we produce a lot more CO2 when we are working hard. The amount of CO2 we produce is also directly related to how much oxygen (O2) our bodies are using. We produce approximately 0.8 liters of CO2 for every 1.0 liter of O2 we consume (the ratio depends on the type of food that is being burned).
The other possible source of CO2 in diving is in the gas we inhale. This CO2 can originate in the gas that is compressed into our dive tanks, or it can be CO2 that originated in our bodies and that we exhaled, but then breathed back in. Carbon dioxide can be pumped into dive tanks if the intake of the compressor is too close to a fire or an internal combustion engine; when anything is burned (wood, paper, oil, gas, propane, etc.), O2 is used up and CO2 is produced. In this situation, the gas we inhale may be contaminated with excess CO2, but an even greater hazard is that it could also be contaminated with carbon monoxide (CO). Carbon monoxide is deadly in far smaller concentrations than CO2. There are many ways in which CO2 that originated in our bodies can be exhaled, and then inhaled again, returning the CO2 to our bodies. For this to make sense, we need to discuss the physiology of CO2.
Physiology of CO2 Carbon dioxide is produced continuously by the mitochondria inside each cell in our bodies. From
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there it diffuses into the cell and then into the blood in the capillaries. In blood, CO2 is transported in three forms: a small amount is dissolved in the plasma, a small amount is attached to hemoglobin and other proteins, but the majority of CO2 is combined with water to form bicarbonate. Bicarbonate dissolves very easily in plasma, so blood can carry large quantities of CO2 in the form of bicarbonate.
The formation of bicarbonate releases hydrogen ions, which results in a small rise in the acidity of the blood. The level of acidity of the blood is directly related to the partial
Nuvair’s DE-OX CO2 carbon
dioxide analyzer connects
to a high or
low pressure compressor for in-line
continuous
monitoring of gas quality
pressure of CO2 (pCO2) in the blood, which is related to the total amount of CO2 in the blood. The acidity of the blood is measured by special receptors in the brain and the results are used to control breathing. In our lungs, CO2 diffuses out of the blood and into a gas in the alveolar spaces until the pCO2 in the gas is equal to the pCO2 in the blood. The pCO2 in the blood is in equilibrium with the bicarbonate and if the pCO2 declines it is rapidly replaced by bicarbonate, turning back in to CO2 and water. When we exhale the gas in our alveoli, CO2 is removed from our bodies.
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